So my truck is not as fun to drive as I hoped. It's a dog pretty much and drinks gas like no other vehicle I have ever owned. Just finished a bunch of work on it to make it reliable so I am keeping it for sure. But, it definitely needs some changes in the power train to increase the fun factor. There a are a few things I am looking at changing - not necessarily all at once or even at all, just trying to bounce ideas around and see what others may think.

So first off, the granny low NP435 is rough - three usable gears. 'Nuff said. Yeah, this thing was built when trucks were used to do actual work and I'm good with that but not at such a grunt level. Seems like the NP435 was designed for tractors and adapted to trucks. Highway driving is the worst - the gear spread is too wide to keep it in the power band. And after enough miles, rowing that giant stick can get tiring.

Besides the trans, the engine is really inefficient. It's a stock, long block 400 (very low comp.) with an MP .484/284 cam and an Eddy Performer RPM hi-rise intake. (p.o. built it that way) Small tube headers into dual exhaust but it all goes into a single muffler. Currently has a Holley 600 on it. Rear gears are 3.23.

I am looking for better all-around drivability - mainly, crisper throttle response, better highway manners and some increase in mileage. So what changes will yield the best results? I know the cam is big factor - no cylinder pressure, not enough rear gear, gear spread in the trans is too wide. Of course I can change the cam but then I still have a stock lo-po long block with an 'RV' type cam and the same driveline. How much better will that be?

I have a bunch of factory small block stuff including a a 1990 roller cam block. I'm thinking a flat top piston 360 or 408 would be a big improvement over the 400 across the board. The 400 will absolutely need new pistons to make it perform better which means the motor has to come out. I could build the 360 and swap it in when it's done without being down for too long. Fuel injection is on the list of priorities too.

And the trans. I'd like to keep it a stick. What would be the best option here? I have an 833 OD on the shelf that needs a rebuild. I would need a bell housing but they seem somewhat readily available. I have seen a few NV4500s for sale on CL for relatively cheap but given that I don't really like the NP435, I'm not sure if that is a good choice or not. I believe the NV4500 MAY bolt up to an NP435 bell so that could save some coin.

In addition, I also have some empty rear end center sections around that could be built any way I wanted so I'd probably match the gear to the rest of the combo. The current 3.23 does me no good with the way the truck is built. Takes about 30 miles to get up to speed.

So what would be the best bang for the buck? Or, what's the first thing that should be changed that will make the most difference? I think it's trans. Trying hard not to have the whole truck apart and spend huge amounts of money but it may be unavoidable at some point to get what I want.

Not really looking for specific answers about this part or that but rather looking at the whole picture in relation to the stated goals. Honestly, I am almost a little reluctant to post this since it's pretty subjective and kind of vague but I figured I'd give it a shot and see what happens.

So what would you do?

Thanks for any input.

- Greg

Its not the trans holding things back, cam is a big one, that cam is way wrong for your ride. A newer desighn fast lift cam with about 200*@.050 single pattern with as much lift as possible and 108LSA would work waaaay better with the low compression. The 600 holley is too small, 400 inches should have at least 750 CFM, small carbs tend to get real rich on too big of an engine when the RPM climbs so jetting at least probably needs significant adjustment.

I built a stroked SB for a customer with mag heads and small cam in a 4x4 85 with 3.23 gears and it pulls like an animal even with a bob cat on the open trailer behind it going up mountain passes. The cam was just a little bigger but the compression was 9.5 ish. It is an 727 with a low stall converter, about the worst trans for performance.

With 3.23 gears the granny gear could be used to take off, don't know why thats a problem. I had one with a 360 TBI engine and used it from dead stops even with the 4.10 gears.

like Dave said.

You won't find many moparts members who like the 484 Street Hemi cam, me included. That cam is more suited to high compression motors.

Its already been mentioned...

That Cam is killing that engine..

Carb is small too..

a833 would be Ok with a 360. Would bolt to the newer np435 dual pattern bellhousing too. Think late 80s.

nv4500 will NOT bolt to a np435 bellhousing.

Don't know how you guys are using 1st gear to take off unloaded in a np435 since its barely synchroed. I only used mine in my 83 and 88 in the woods or hay fields. 3.23s in the 88 and 3.55s in the 83.

nv4500 in my 92 is awesome. Shifter is closer and ratios are different.

You will thoroughly enjoy a 360 magnum , nv4500 combo with 4.10s

Let's quantify what the problem is. What mileage are you getting? What size tires? Is the speedo and odo accurate?, lifted? Etc.

No go on the 833 if 4wd, the only vehicle that used that combo was some early gm diesels. You're not likely to find one for the tail housing.

Is the dist tuned with a good advance curve? Carb jetted right?

I have a mild 440, 435 trans, 4.10 with 37" tires, 1 ton running gear in a heavy 4x4 trailduster that sees mostly street miles. Sure 1st gear is useless and shifts hard, sure she only gets 10 mpg with a tailwind but shes still lots of fun to drive once you get use to shifting that trans. I can break loose all four tires on pavement. Yours is a two wheel drive, short bed, figure that big block out and she'll get fun.

Good closed chambered heads(63-64 cc) and thin head gaskets will help.
As stated bigger carb and some retuning is needed.

I have to wonder what the truck actually does run like. I've owned more then a couple 400ci with the 435 trans, and they will flat whoop a 360 in the same truck. Maybe your tires are too big, what size tires do you have on your 4x4? Big tires will kill the fun and mpg in a hurry, especially with 3:23 gears. 8-10 mpg is pretty standard in a 4x4 Dodge truck. If you are expecting a race truck, everything is wrong.

The carb is small, the cam is wrong, I suspect the dist curve is out of spec, and I suspect you have very big tires on your truck. I'd start off with smaller tires, a bigger carb (dialed in), and dial in the dist. Then give us some real numbers. Gene

Truck is 2WD. Can't remember what the tires are off the top of my head, maybe like a 235/75/15 or so. Yoko SUV tires.

The truck drives OK I guess but it could be better. The trans drives me nuts. Honestly, first gear is useless, it's not synchronized and is like a 6:1 ratio. I've used it a handful of times it's not practical for regular street driving.

The main issue with the trans (for me) is the gear spread. Lets say you're around 45 mph going up a longish grade in traffic and in third gear. For whatever reason, the car in front brakes. I'm over 3 grand at about half throttle and I have to shift out of gear. Then I am in no mans land - if I go to 4th, the RPM drop is too big to keep momentum. If I go back into 3rd, I'm over the normal RPM for that speed. I don't like that dance.

The 600 cfm carb was a recent addition. I had a 3310 on it and it seemed to be better overall it actually did get a little better mileage and ran smoother than the 600 so maybe I will change it back.

Just think the whole combo is not very well thought out and needs some major changes.

In that scenario a cam swap would help a lot as you would have TQ down low to still pull when you hit 4th, it would not feel soft down low.

I have been through this scenario. I sold my orange shortbox for the same reason. horrible mileage. may have got 7 mpg. tuned well. just a pig on fuel.
my opinion...probably wont be popular. low blocks are not for trucks. especially a 160-ish hp 400. pitch it put a 440 in it or a good magnum motor.

I will never run a stock low block ever again unless its for a resto.

OK if you need to spin 3000 in third to go upa grade with your current tire size, something is wrong. A big block should be able to lug that in fourth easily.

Wow that's bad.

As said by a few the big prob with your motor is the low compression and that cam. first thing to change is that. next is the exhaust. Free it up let it breath, very important. yeah the trans sucks but you need to make the engine run right first. Change the cam and exhaust get the distributer curve right and set up the carb. the 400 is going to use some fuel but it should not run like a pig. unless you want to start with a whole new engine that's what needs to be done to the 400 to make it right.

Ever driven anything with an NP435? They were put in trucks that actually did work. Again, for me at least, they are not practical for regular driving.

Here's the results from the Wallace Racing RPM drop calc.

Click here for the calculator.

Gear Shift Drop Calculator
RPM: 3,000
Rear Gear Ratio: 3.23
Tire Diameter: 28"

Gears in Tranny:
1st Gear Ratio: 6.68:1
2nd Gear Ratio: 3.34:1
3rd Gear Ratio: 1.66:1
4th Gear Ratio: 1.00:1

After 1st Shift: 1,500 RPM. 50.00 % RPM Drop
After 2nd Shift: 1,491 RPM. 50.30 % RPM Drop
After 3rd Shift: 1,807 RPM. 39.76 % RPM Drop
1st Gear is 11.59 MPH at 3000 RPM
2nd Gear is 23.17 MPH at 3000 RPM
3rd Gear is 46.63 MPH at 3000 RPM
4th Gear is 77.40 MPH at 3000 RPM

A few have mentioned timing. Distributor is 'new' (reman) one light spring, one heavy. 18 initial and 38 total. Has vac. advance, did not verify how much the vacuum is adding but the canister is new and works (verified with vac. pump). New Champion #14 plugs, new Taylor wires, new rotor, MSD Blaster 2 coil, new engine harness, ballast resistor. Before I changed the carb to the 600, the plugs were a nice light brown and the firing ring was right in the middle of the bend of the ground strap. It's right or at least as right as it could be with the current combo. Timing is not the issue.

If I stick with the 400, the cam will be changed for sure. I guess I'm just trying to figure out whether a cam change alone is worth the effort without doing anything else?

Full dual exhaust in these trucks can be a little tricky with the gas tank along the driver side. I'm sure it can be done, just another hurdle to contend with.

Could probably use another 2 degrees initial but certainly needs about 4 degrees more total and that should be all in by 2000 or 2500 at the latest.

Dual exhaust is over rated an equal cross section single flows more and retains heat better. Make sure you have good merge points and you should be fine with a single 3 or 3.5 inch pipe.

Go back to the 750 and lean out the jets till it starts stuttering and go back up one jet size.

Open your plug gap to about .045 with that ign it should produce a hotter spark and light the crappy low speed mix better.

Thats about all you can do without tearing into it.

I am convinced in the cam making a huge difference. Get a custom made cam, the few extra $ will be worth it but even a small summit cam advanced a couple degrees will be better than what you got, I just hate tearing into my junk and sort of fixing the issue. It will reduce overlap, close the intake earlier for more cylinder pressure and open the exhaust later for a little extra push on the crank before releasing cylinder pressure. It will result in more power everywhere you need it and you may no longer beconcerned with the RPM drop. A big RPM drop ain't as bad when there is TQ down low to take over after the shift.

Have I driven np435? Yes quite a few. But if your engine can't maintain 45 uphill in a 2wd ramcharger, something is wrong. My 77 crew with a 360 can do that with much taller tire.

I agree. My 440 74 power wagon pulls like a beast in fourth going up a hill with 33-12.50-16.5's. It's mostly stock. 40 over flat tops, edelbrock performer intake and street avenger 670 carb (what I had at the time that worked).

Fuel mileage is roughly 15mpg. If I drive it like I stole it, I can guarantee it'll get about 8. But I have a heavy double return spring on the throttle. Keeps me out of the pedal.

Good luck with that 400! I hope you get it sorted out. A big block 2wd should be a hoot. No reason a 400 shouldn't perform well. If it were me, I'd throw some Pistons in it. Raise the compression. Without compression, your choices are limited.

Keep us updated!

You get no credibility comparing a 440 with a 400.

I agree that am is waaaaay too big, it's something like 234 at 50 lift. I'd go with a Hughes with in the neighborhood of 208 intake at 50.

You don't need duals but as said above a single 3 or 3.5" will do just fine and not cause as many clearance problems.

For the carburetor I'd use a Holley Street Demon 750. If you're using another squarebore Holley I'd suggest the newest model available. They had better metering than the old standbys like the 3310 or 1850. My Street
Avenger 570 is worth 2-3 mpg over a "tuned" 1850. I think it's the part-throttle stuff that's different.

I know what you're saying about the NP435. My NP420 is about the same. Won't pull a hill in Fourth at altitude but Third is screaming the engine at 40
mph. NP445 or 4530 is a way better gear spread. The NV4500 is nearly the same as the 435 with a Fifth gear so in the scene I'm talking about it's just as worthless. The A833 would be better, just not the OD version. You have to look at the gear splits.

R.

PS: Compression and squish would help a lot. The KB 215s with stock 400 rods and a 3.75 crank would work too, you'd have a lot more torque in the midrange where the 400 is lacking.



'

I had that cam in a stock 440 Ebody.. made it a total dog, took it out and replaced with the .471 MP cam. Much better...

You really need a towing cam to make low end torque. My friend has a 78 club cab 2wd, with stock 400 auto 2 bl.. runs great plenty of power..

replace the cam, tweek the timing.

Thanks for all the input gang. Lots to think about but clearly the cam will be the best bang for the buck if I stay with the 400. I will probably put a small block stroker into it at some point but it seems like a cam change should increase the fun quotient for now.

Also gonna put the 750 carb back on and mess with the timing again, maybe will see some more improvement.

Thanks again! Will update soon.

Have u done a compression check out of curiosity? I say swap in an 833 and see how it is. For the low compression big blocks a lot of guys like the Summit cams (6400 and 6401). The gear spread on an NP435 has no place in a hot rod truck. Even with its low compression (8:1 ish) a 400 in good mechanical shape should burn the tires right off that truck. I had a '77 warlock way back with a .030 over 9:1 440, crane 282/.450" lift cam, headers, stock intake and a tiny Holley carb that would get rubber at a 30 mph roll (auto with 3.23's). The intake u have is probably the best one you can get for your application.
If you're willing to do a stroker SB, for around the same money you could put 4.25 arm in that 400 and have a 512. You're already set up for a BB, I'd stick with that.
An Edelbrock 800 Thunder series is a good carb (I know it's easy for us to spend your money lol!)

The transmission is not your problem. Yes, have driven np435 truck. It's a good off road/work transmission, not really a good choice for a hot rod/race truck. But as stated, that cam is your problem. Who ever put that cam in there made about the worst cam choice he possibly could have. A stock cam would be a leaps and bounds improvement for you. That 284/484 cam is killing your cylinder pressure and your sub 3000rpm power. You should be able to lug that thing at 1000-1500rpm without problem. Also, I suspect your distributor timing is coming in too late. For a smogger BB, you'll want all timing in by the 2000-2500 range.

OK, looked at some cams. Gotta say it's kinda odd looking at cams with such low duration. Last one I bought was a solid FT for the 416 in my Duster that is 251/259 @ .050" with almost .600" lift lol.

#1 Hughes HUG SEH1016BL-12

#2 Hughes HUG SEH1620BL-12

#3 Comp XE256H

#4 Comp 255DEH

#5 Comp 252H Says it requires 9.1 c.r.

Any other suggestions? Anyone use any of these and have any comments on any of these cams?

Will do a compression check tomorrow and see what comes up. Maybe I will do a leak down test too, there is a tick in #2.

If I was forced to pick one it would be the 252h but really a custom one is not much more and the difference would be noticable.

If I was picking from a catalouge it would be this hughes cam
http://www.hughesengines.com/Index/produ...mp;partid=30250

The extra lift hughes gives you will help keep it from choking as the RPM climbs before a shift as long as you get their recomended valve springs.

If I was ordering one from scratch I would get the hughes cam I listed, have them change the ex lobe to be the same as the intake one. That will reduce overlap and that will reduce unburned fuel going out the exhaust as well as give a couple more degrees to push on the crank before the ex valve opens.

I looked at that one too. The lobe lift is basically the same as the other ones just less duration obviously. Will talk to Hughes on Monday and see what they say.

Can you tell if Comp is measuring their lobe lift @ .020" because it's lower than the Hughes. .283 vs .315/.320.

So the 750 carb went back on, it definitely runs better. There is 2 more inches of vacuum, smoother idle, better throttle response and room for more timing without having to idle too high so it's going in the right direction. I did not reduce the jets yet, there are 70s in the front now which are stock for this model. May go down to 68s but it runs good so I'm not sure if I am going to mess with it. Has a pink pump cam in the #1 hole and a brown secondary spring, takes off great.

The reason I put the 600 on was to see if the mileage and throttle response would be better with a smaller carb but no dice, just the opposite. Like Dave mentioned in his first reply it actually ran richer, even with 65 jets. It also idled rougher and had less room for timing. Seems to defy logic a little, all the math for CFM requirements said use a 600 or less. Lesson learned.

I've traveled 100's of thousands of miles with the NP435 in a working PU. 1974 D200 with a 360. That transmission out lasted two engines... never opened up. Yes it is functionally a 3 speed in normal driving... 1'st is for creeping or getting started with a heavy trailer. That truck was peppy even fast for its day with 4.10's and ~29" tires. The NP 435needs matched up to an engine with wide torque curve.

Agree with all the comments... low compression, giant cam and tall gears do not work together.

The only thing to add, is have you considered building the 400? Make it a 451 with a 440 stroke crank and you could have a superb engine. You already have almost everything else (headers, accessories, manifold ect.) and BB Ramchargers are pretty special. With a 451 built for torque, the gear spread on the transmission and 3.23 gears would not be an issue at all. Different truck.

You know, I have been kicking around the idea of a 451. I mentioned I am a small block guy but the one big block part I have held on to is a '230' 400 block. Basically just need a rotating assembly. And some better heads... and well, you all know how that goes. I need to finish the 416 for my Duster before I start building another motor though.

Something tells me a a properly built 451 may get better mileage over the current combo.

Can't hurt to start collecting parts for now...

Assuming the basic long block isn't hurt or worn out, you can do better with a lot of tuning. Just bolting on a carb and changine jets wont cut it.

Yes as stated the cam is a poor choice. But it should do better. Is the cam timing off? Like a whole tooth? I just can see any big block not being able to run 45 mph in 4th unless something is way way off or the thing smokes like a barbecue.

A compression test (leakdown is better) verifying cam timing and some distributor and carb tuning can do wonders and is cheap.

I would like to see you put a 750 DP on it and play around with the jets and squirters. Check fuel pressure also. That carb won't make a 6 cyl run good. Too small.

I agree the 600 was too small. It has a 750 vacuum secondary on it now that is pretty much in it's original configuration from Holley - 70 jets, 6.5 PV, 31 squirter. I did change the pump cam to the pink one from the orange, (there is no bog) and changed the secondary spring from the yellow to the brown. (yellow was too light) The floats are set properly (trickle out sight plug), the transfer slot is a square yada yada yada.

Thought about going down on the jets to 68 but it seems OK right now, not sure it's necessary.

Idle vacuum is around 16", idles at 850. I have not driven around with a vacuum gauge but I'm sure the PV is in the ballpark. I definitely do not need a lower one and I don't think I need it coming in quicker.

Have not checked fuel pressure. Guy I bought it from claimed it had a 'hemi' fuel pump on it, whatever that means. Looks like a Carter strip pump. Guess I should find one of those little pressure gauges...

I put my Proform 750 DP on it briefly and it worked well but I didn't think I wanted a double pumper on it for regular/highway driving.

I personally believe vacuum secondary's are for lighter vehicles. If you have one on a truck I believe it will run poor. You need a good DP carb and I'd be going up in jets to start. I believe your truck runs bad because it's starved for fuel. My 10 to 1 360 with a 509 and a 750 DP didn't run very good until I started increasing the jets and squirters. I can't remember what they were but they were far from stock and every time I went bigger it run better and better.

I agree to an extent that some combos need more fuel than they are supplied with if things are matched properly but no way with my junk. In my opinion, a double pumper would just be dumping fuel with no real benefit.

Comparing your 10:1 small block to my 400 is not apples-to-apples either. My 400 is probably like 8:1 if I'm lucky, probably more like 7.5:1. The lack of compression in this motor is probably the biggest contributor to poor performance here, not the carb. It's why the cam was/is such a poor choice. So if that's the case, (which it is) why then would you think it needs more fuel?

Regarding vacuum secondaries, they work fine if you take the time to tune them. Case in point; under normal driving conditions, the secondaries hardly open, there is not enough signal to pull them open at lower rpms where the truck usually operates.

When I first got it a few months ago, it had a bad hesitation under any sort of load, like when I had to give it some gas going up a hill, the thing would buck like a bronco. It was because the secondaries were being opened too soon by a light secondary spring without enough signal from the motor.

The truck came with a yellow secondary spring in it which was too light. I got one of those Holley secondary spring kits to tune the timing of the opening. I changed the yellow spring out for a heavier brown spring ( 2 steps heavier) to hold off the opening a bit. It worked and made the truck accelerate crisper and much, much smoother - no more hesitation, bog or stumble and pulled to a higher rpm, was like night and day difference.

I actually went down on the jets too from 72 to 70 and my seat of the pants dyno tells me it was the right direction.

AFAIK, your assertion about double pumper carbs working better for heavier vehicles is actually the opposite - DPs generally work better with lighter vehicles. Most of your Street/Truck Avenger type carbs are vacuum secondary.

Some members here are confused as to WHAT the vehicle is. The OP never clearly mentioned it other than the -76 D100 at the bottom of the sig. Is this the truck? Is it a Ramcharger? The OP wants help, right?

Here's the money pit. 76 D100, 2wd, SWB.

These trucks are as aerodynamic as a garage door. The taller they are, the worse mileage they will get.
That is just one issue.
Low compression, wrong cam... Yeah, I agree. I had that cam in a Motor home 440 and while it screamed at WOT, at part throttle it was a slug like yours. I may have averaged 8 mpg freeway (UNloaded) with the 4.10 gear and 32" tires.

If you are trying to keep from swapping engines, milled heads on that 400 can raise the CR by about a point. Add in a stock 440 Magnum cam with better flowing exhaust and it should greatly improve. It will never be a 20 mpg truck even with fuel injection, overdrive and bicycle width tires. What numbers are you looking to get? 12 ? 14?
I agree that your transmission is a POS for a truck not used for low speed grunt work. I have the same trans in my 75 Power Wagon. I'm swapping in a 727 since I'm not a fan of manual transmissions. If mine was a 318 or a 360, I'd seriously look into a 518. There is room there for it and the .70 lock up overdrive helps. When I had a Gear Vendors in my 70 Charger, even their .78 OD made a noticeable difference in cruise rpm.
Do you hammer the truck much or is it a mild daily driver? The 833 OD is not a bad trans behind mild big blocks if you treat it right. I'll bet it has lower rotating mass than your 435 so it saves HP there. The OD is near .70 so you win again. The gear spacing is okay from 2-3-4. The 1-2 is a steep drop off though.

Oh, NICE looking truck!

Thanks for the reply.

Chrysler really saddled us with some poor engine architecture during the '70s, eh? It's like they thought low compression was the answer to everything.

To do what I want here is going to take some bucks. Have been looking at cams, heads, transmissions, gears etc. The current plan on paper is for Stealth heads, a different cam, a Passon 4 speed OD and maybe some steeper rear gears when the OD goes in. Possibly EFI down the road too.

The Passon unit has good gear splits, plus the OD, its exactly what I'm looking for. Stealth heads are just modern versions of the OE heads in aluminum but offer a pretty good option over sinking money into 40 year old boat anchors. I almost have to do it.

Never harbored the idea any of this would be cheap but if I can swing the initial cash hemorrhage it will be pretty awesome.

They were straining to reduce NOX emmisions, that was the really tough one to reduce, that is why compression was so low, also why they had EGR valves and retarded ignition timing, they just did not know any other way to reduce it quickly, cheaply and effectively. Now they have catalytic converters, aluminum heads, high swirl heads, EFI, variable cam timing... lots of tricks to allow more compresison once again. We can apply some of there strategies invented to reduce NOX to our old stuff and improve MPG and TQ.

I will never change my mind about carbs, I can't stand vacuum secondary carbs. Most folks have zero business using one, they just don't understand tuning with them. Where as the double pumpers take much of the tuning out of the equation. I also believe that heavy vehicles generally need a dp carb. My personal experience with carbs is that vacuum secondary carbs are best suited on stock, low performance vehicles.

Well, fair enough.

I think I have a handle on my 3310, seems to run OK. No bogs off idle or at speed, plugs are a brown color, idles at 850... what else do I need it to do? It's probably not razor sharp but close enough for horseshoes and hand grenades.

I agree though, there is a probably a lot of misconception out there about how vacuum secondary carbs work. How many guys are gonna try to tune the secondary opening with the spring kit? And frankly, there's probably more guys that get the kit, convince themselves that the secondaries need to open quicker than necessary and put a light spring in the pod and the car bogs. Then they curse the vacuum secondary because "it don't run right" and toss it. Out comes their 'trusty old double pumper' that went 12.20s with a .509 cam back in 1982.

I guess they are happy with covering up poor transitions between the circuits by dumping fuel. Maybe it works OK. I'd rather not line the oil companies pockets though.

I'm gonna put one of my Thermoquads on it anyway.

I had a 73 or 74 W100 PowerWagon 318/727 LB that I purchased brand new....it had plenty of power, gas mileage was no different then any other trucks of that era....was a great truck

Rickster

Made the 110 mile round trip to work today. Mostly highway driving, about 1/3 in heavy traffic, got 9.3 MPG. Filled up on 87 swill in the AM at my local Sunoco, rolled back in on fumes to the same exact pump went a total 115 miles.

My dream right now is to get two round trips out of a tank of gas.

As far as mileage, a well built and tuned BB should get more, somewhere in the low double digits... maybe 11 or 12 which would be 20%+ better.

Still, if you are only getting 115 miles per tank @ 9 MPG usable tank capacity must be pretty small. From memory a 30+ gallon tank was available for those. Sounds like a bigger tank is in order.

Huh. Maybe my gas gauge is way off. Not sure how big my tank is, maybe I am thinking its more empty than it is.

It would be nice to go farther than 115 miles per tank but it still only gets 9 mpg.

I got 14 one time from a big block truck, one time! Most fill ups netted 8-9 mpg.

12.7 gal should have been about a 1/2 of tank. Do you have the big plastic saddle tank on the driver side of the frame, or are you running off a rear tank? The frame under my old 4x4 had dual tanks at one time. Someone before me removed the big saddle tank and left the smaller rear tank. It was only 16 gal. 120 miles was the limit on that one (and it was a small block).

I had one big block Dodge truck with want was called a 55 gal gas tank out of a school bus mounted in the box. That 50 or so usable gal netted between 425 and 450 miles before it ran out and I would switch over the the trucks regular tank. That was a TNT 440, with a 727, and 4:10 rear gear, 3/4 ton camper special, 73 club cab, with a wood topper, pulling an open car trailer. Truck and trailer fully loaded ready to go weighed 7650 lbs. It sucked gas, but man it pulled! Gene

I got the tank on the driver side. I did some reading on truck tanks this evening, I guess it's 20 gallons?

However, if it is in fact a 20 gallon my gauge is way off because it's reading just about empty when I could actually have almost 1/2 tank left. Maybe I'll siphon out the remainder when it gets low to see how much is left.

In addition to a cam change, I have to think an OD trans in this situation will really help my highway mileage situation. A 20% drop in highway rpm over 50 miles has to make a pretty good dent.

I can't justify driving this thing on a semi-regular basis, I'll spend more on gas in 6 months than I paid for the truck. I've driven it about 1,200 miles so far @ 9.3 mpg...

Looking into getting an A/F gauge before I make any major changes. I got one in my Duster, it's a nice tool to have.

FWIW, I've known nobody who's had one of these trucks and claimed the fuel mileage was any good. Most are in the double digits, barely. BB or SB.

But doing some quick math, I'll base it on your claim of 9.3 mpg average, and a 110 mile round trip, with 1/3 of it in heavy traffic. I'll assume that means a mixture of stop and go, and varying speeds, etc. That would be about 37 miles heavier driving, 73 miles straight highway. If we assume 6-8mpg during heavy traffic, typical for any cammed BB car or truck, that translates to 10-13 mpg highway. Not atypical for a BB pickup. Many members with BB cars struggle to beat that mpg.

I think if you were to step down to a stock or near stock cam, you could see a 2mpg increase across the board, likely more noticeable during your heavy traffic portion of your commute. An overdrive transmission may gain you a mpg or two on the highway, nothing during the heavy traffic portion.

IMO even if you changed a SB, efi and overdrive, you won't see much more mpg that what you have. If it helps at all to put things into perspective, we took a 97 ram 1500 5.2 4x4, no lift, stock tires, on a 3000 mile round trip. On flat level ground at near sea level elevation we got 18mpg if we kept it at around 60mph or less. Upping to 75 dropped us to 13. Once the terrain started to get hilly even in the slightest, we couldn't break the 15 mark anymore, regardless of speed. That's with EFI, overdrive and the improved aerodynamics of a 90's ram, perfect weather, we drove straight through so no cold starts or warm-ups.

If you're making that 110 mile round trip either way, this is simple the wrong vehicle for this application. Based on your driving habits I can't see you being able to improve your average by more than 2mpg. Is that enough to make the difference between this vehicle being viable and not? I would imagine either way you will have to get used to buying gas and think about putting in a slip tank to extend your range.

yeah but that 97 weighs twice as much as his truck

Alright, think I got a plan sort of nailed down.

Spoke at length with Tim @ Hughes today to discuss cams. I told him I didn't really want a Whiplash and said I was looking at some of the low duration hydraulic cams. This is the one he suggested:

HUG SEH1620BL-12

BB HYD FLAT TAPPET CAM 216/220 -112ºLSA

LOBE LIFT .330"/.335"

It gets installed @ 108. Smooth idle, high vacuum, up to 3.55 gear. He didn't think the ones under this would be worthwhile and I tend to agree. I don't want a milquetoast truck.

I asked about making it a single pattern, he didn't think it was worth the minimal expense with my combo. He said the little extra exhaust duration would help with clearing the cylinder.

We talked about heads at a few points, I told him I was considering a set of Stealth heads. He did not seem to think they would add much save for having them in place for future upgrades. Of course the smaller chambers will help but I will likely still be under 9.0 C.R. with the stock pistons.

My reasons for changing them out are more related to not wanting to deal with 40 year old, lo-po iron heads. I would need to replace the springs with the new cam, which I suppose I could do with the heads on but why? I still have a valve tick - no idea what it is but I will assume the worst which means to fix the problem the head will most likely have to come off. If I am taking them off, they are not going back on, especially if I have to spend money on them. So assuming they need some amount of work, it's kind of a no-brainer to go with the Stealths. The springs on the 440 Source heads are compatible with the cam I am looking at so I even 'save' a few bucks not having to buy springs with the cam.

We also talked a little about the intake. I would like to change out the Performer RPM for a regular Performer. He concurred that theoretically the shorter runner will help with velocity to fill the cylinder quicker but I wouldn't really notice any difference over the RPM. If I can find one relatively cheap I will grab it. I actually want it more for the spread bore opening and the choke well so I can run one of my Thermoquads.

I think I am going to go through with the plan as is and wait on the trans for now. IMO it would be prudent to wait on it and see what the other changes do. Swapping in a whole top end is a decent job, should satisfy the need to tinker for a while. Plus, there's always the potential for something to go wrong. Taking the trans out multiplies that tenfold.

Besides, a trans swap is really expensive no matter how you slice it. It is something I want to do though but perhaps just not at this very instant.

Will update when things start coming together.

Just a quick update for those following along at home;

Ordered my cam that I mentioned above from Hughes. Not in stock, should be soon though. Grabbed a Performer intake off Ebay. probably paid too much for it. Whadyagonnado.

Also got an A/F gauge to see where that all is at. I will put that in before any changes to get a good baseline. I'm betting it's pretty close but it will be fun to mess with it.

Decided against buying heads, saved me a bunch of coin! Sometimes you gotta control yourself.

Pretty warm here this winter, might get to this before long.

The a/f gauge is a fun tuning tool. You will learn a lot! Hope you got a wideband not a narrowband.....

The Air/Fuel ratio gauge will be a big help finding out where you are.

Since you desire better fuel economy
you should shoot for a high air/ fuel,
at least 18 at highway cruise part throttle.

If you switch to new iridium tip spark plugs and renew the ignition parts you might be able to successfully ignite 20 to 24 air to fuel.

You should consider swapping to a modern low rolling resistance street tire like the Bridgestone Dueller HL or similar in a tall thin profile. Run the highest air pressure as it improves emergency braking, reduces hydro planing, even though it will wear out the center most tread bar slightly earlier.
This tire change could improve your fuel economy by as much as 2 MPG.

The picture of your truck shows no front air dam below the front bumper.
A large air dam,
coming within 4 inches of the pavement
could improve 70 mph steady MPG by 1.0.
An air dam can be made cheaply from black plastic "lawn edging" with the round pipe like moulding down near pavement.

For further aero improvement consider covering the back part of your cargo box top from the tailgate forward about 4 foot, leaving the 2.5 feet just behind the rear window open to the air.
I know that sounds a bit odd,
but that gives the best aero improvement,
slightly more than a full length tonneau cover.

If the original EGR valve is still on the 400 V8
take it off if you try adjusting the air/ratio up to a high number like 18 to 24.
EGR and lean burn do similar things by reducing engine pumping losses on the intake side but you do not want to do both at the same time.

In an earlier post you mention a vacuum gauge.
If you try high air/fuel ratios
a vacuum gauge is valuable.
At highway cruise in top gear you want low vacuum: 8 to as little as 4 inches Hg
If the vacuum is higher than this,
lean out the A/F more
until the leanest cylinder begins to misfire.

My guess is that your truck with the
leaned out 400 V8,
3.23 diff,
low RR tires,
aero improvements
should be able to get 16 MPG at a steady 70 mph
when the wind is below 5 mph
and the air temperature is 50 to 70 degrees F.

Good luck.

I have an an LM1 with an A/F gauge in my Duster so I am familiar with them. I got a wide band, not sure if anyone even makes a narrow band these days? It's an Auto Meter Cobalt, a digital stepper motor type.

When I was looking, I found that Summit sells a clamp/band thing that you wrap around your exhaust pipe which has a bung built into it. You just drill a hole and put the band on where the hole is. No more muffler shop!

Going to make a mount panel for the gauge in my dash where the radio was.

Great info and tips, thanks!

Bringing this back up. Finally installed my A/F gauge and as expected, the engine is on the rich side.

I am impressed with myself for getting it in the ballpark just tuning by ear and feel. The truck runs pretty well and has no hesitation. It is not "pig rich" by any means but based on the reply above, I have some work to do.

The main thing I was looking for with the gauge was cruise A/F ratio. Currently, it's under 14. 70 mph seems to be the sweet spot for best A/F ratio at around 14.2 but the RPM required to keep it at 70 likely negates any benefit of a leaner mix.

Most of the time the gauge was between 14-13 with dips into the 11-10 range when accelerating and 16-17 when you mat the gas from a roll. After the initial opening, it recovers and goes back to 13-14 depending on how long the throttle is needed to get up to speed. Closing the throttle creates a momentary rich condition into the 12-11s but then it recovers.

Idle mix was on the rich side just under 14. I may have a linkage/cable issue because there are times when the throttle blades don't seem to close all the way without pulling the throttle back with my toe. My throttle return bracket is from a small block so it might not be entirely correct. Will have to look into that one. That's been there since I got the truck so yes, I need to get on that. It also takes a while to idle down after a stop but it's a stick with a heavy flywheel.

Besides that, I have not played with anything on the carb yet, not even the idle mixture screws. Reading up on tuning techniques, I think I may be getting in deep with air bleeds which unfortunately are not real adjustable on a garden-variety 3310. My quaint hope is that one of my Thermoquads will be more tunable in this regard, meaning no drilling of fixed orifices, changing metering blocks etc. and will potentially do a better job with cruise A/F.

I also need to drive with a vacuum gauge to see if the power valve is coming on at the right time. Not sure yet but based on the gauge, I don't see a big rich spike when accelerating so it must be fairly close. It's a 6.5 now.

So the main goal right now is to get the A/F ratio as good as it can be with this combo of parts. I believe the Holley might be limited in it's tunability but again, I have not gotten too deep into this yet so we will see. When I get to the high point I'll start thinking about swapping the cam and intake.

Sounds like you could lean out the main jets just a hair (perhaps 2 numbers) and get just a little more fuel when you mash it by playing with the accelerator pump, not gonna see a whole bunch of improvement based on those numbers. High swirl and tight quench will run better at leaner numbers but those open chamber heads bite a big one and will not like going really lean.

I had the thought that the rich condition that I am seeing when the throttle is closed is unburned fuel due to the cam and low compression. Might need to open the throttle blades a little more but 2 points on the gauge is a lot of hydrocarbon.

I also spoke too soon on the idle numbers. Once it warmed up outside (mid to low 60s, really nice today) and the motor finally got down to it's normal idle speed, it was under 12!

Guess I might need to go back and look at the timing again too, probably could use more?

When I say 2 numbers I am talking jet sizes not AF ratio numbers, probably going to be more of a dog if you get a that much leaner.

Carbs just run rich on decell, I don't know much you can do about it, perhaps you can get an air valve like a reverse blow off valve to open when vacuum gets high and let some air in. This is why the NASCAR cars (before EFI) would always be dumping fire out the exhaust when they let off to go into a corner. Now they can shut off the fuel completely on decell and help MPG... not something easily accomplished with a carb.

No, I got that thanks. It might need more squirter for sure.




I don't know either. I think if you start from a better point, the swing will be less dramatic.

Well, drove the truck some this last week, getting around 10.25 mpg. Slight improvement over the 9 I was averaging a few months ago.

I kinda 'fixed' the throttle return issue by using a much heavier return spring which seemed to help. It idles down quicker now when you close the throttle and does not seem to get stuck in a high idle position though it takes more foot pressure to accelerate. I believe I need to really dial in the fast idle cam on the electric choke, it might be on the wrong step or some such thing. If I see something there that can be changed and it works maybe I can go back to a lighter spring. The choke works but I am considering ditching it for the warmer months.

Messed with the idle screws a bit, the idle is pretty good right now, generally around stoich. It idles at 1,000 rpm but what can you do, it's got a big cam with a lot of overlap and a good amount of initial timing at 18.

While driving, the A/F swings are not as big as before, it goes to low 12s-high 11s at WOT and about 16 when the secondaries open then it goes back to 12-13. Cruise was about 1/2 point higher all around, mostly above 13.5 depending on road speed/rpm.

Was thinking a jet change would be a good place to see if I could lean out the cruise, has # 70s in it now. I gave my buddy my only pair of 68 jets a while ago which I think would have been good for this situation, thought 67 might be a little too small and 69 wouldn't do anything. Still have yet to hook up a vacuum gauge, maybe I will do that this weekend. Might try a lighter spring in the secondary as well to see if the accel is a little more snappy.

I have to say that the aero thing is relevant here. The couple times I drove the truck it was really windy, like 40+ mph gusts. When driving out on a more open stretch of road with heavy crosswinds I could feel the truck struggling. Really thinking about a front spoiler.

Just chipping away at it a little at a time. Hope to get to the cam and intake swap soon now that it's warming up.