Help me set up our 1972 Dart supercharged 360!! PLEASE!

Help me set up our 1972 Dart supercharged 360!! PLEASE! - 09/14/09 02:16 PM

We got the Dart running pretty good, but it still has a pretty good hesitation/bog when the throttle is pressed down fast (or on a quick/hard launch). Then the car comes to life and pulls like a freight train.
The car is very basic and just put together for pennies so it is making do without anything fancy.
The engine is a stock 1974 360 4-bbl. out of a 53,000 Dodge Truck.
The Supercharger is a B&M 144 (B&M says it maybe a 162?) which was just gone through including new nylon strips in the rotors for tigheter clearencing/better performance.
The intake manifold is a Holley 'Street Dominator' aluminum single 4-bbl. unit with the carb flange shave level/square so the blower sits on it nice/flat.
The car has standard Hooker 'Competition' headers that dump into dual 3" exhaust with Flowmaster 3" mufflers. The exhaust stops at the rear axle.
It also has an Accel 'Super Coil'and the plug gap is at .040".
Thre Carburetor is a Holley 'Street Aveneger' 770 cfm vac. secondary unit with electronic choke. The primary jets are 75 and the secondary jets are 79. The accel pump is a small one (30cc?).
The timing was set around 8 degrees initial (idle) and around 30 degrees coming in around 3,000 RPMs. The ditributor on has one spring in it (light factory spring).
The car has a .429"(I)/.444"(E) with a blower friendly 114 centerline camshaft/lifters/springs, with a double row true roller timing set.
Transmission is a stock 727 and the rear is an 8-3/4" sure-grip with 3.91:1 gears. The chassis is all stock with Yukon big bolt pattern axles, and 1973+ A-body front disc brakes.
The car uses an aluminum radiator as well an external transmission fluid cooler.

We ran the car last year with a 670 cfm vac secondary Street Avenger carb and I had the 770 sitting on a 440 in my garage still in the plastic so I wanted to try it on the Dart because surely the 670 was too small. The car had the same bog with the 670 cfm carb.

The car definitely runs better with the larger carb, however I hate that stumble it has.

When I had the 670 cfm carb a couple people said I should add bigger squirters.
I knew I was going to swap the carb and I did but was shocked when I found out this 770 has smaller squirters (.025") then even the previous 670 (.035"), according to Holley.

Trying to get the car set-up right as we are going to bring it to the strip on Sept. 25th for the first time. Not too mention it would be nice to have it ready to just pull out next spring and have it "ready to go".
The car just runs on street tires, however I have a set of slicks I'll be trying out at the track this time.

Any ideas what would get that nasty hesitation out of there and any other tips?!?

Posted By: MNobody

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 09/14/09 02:49 PM

The bog is probably not enough fuel right off, is the accelerator pump linkage adjusted so it shoots right when you touch the gas? Also i gotta ask, are you getting any belt slippage at the blower?

Posted By: Mr.Yuck

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 09/14/09 02:51 PM

Sounds like you need some more tuning on your carb. What is your vacuum while driving? Make sure you have the right PV. I'd also bump up your timing some. Maybe 35* at 2400rpm. Unless you are worried about burning up your pistons. You might also want to try a little more rear jet. What is your stall? If you have a stock converter that might be part of your problem.

Posted By: daniel_depetro

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 09/14/09 05:05 PM

Quote:

Also i gotta ask, are you getting any belt slippage at the blower?

I have no idea, but it's doubtful.
How would I even check this?

Quote:

Sounds like you need some more tuning on your carb.

For sure!

Quote:

What is your vacuum while driving? Make sure you have the right PV.

Not sure what my vac is while driving. I'll have to check.
The PV is the stock one that the carb was built with (6.5)
Whats the best way to figure the correct PV?

Quote:

I'd also bump up your timing some. Maybe 35* at 2400rpm. Unless you are worried about burning up your pistons.

Well I want it to last...but I want it too be as powerful as the set-up can be. I'll keep bumping it up unless I hear obvious detonation.

Quote:

You might also want to try a little more rear jet. What is your stall?

I'll have to get some jets. These were the biggest out of both carbs so that's what I used for now.
Any idea where it should be, roughly?

Quote:

If you have a stock converter that might be part of your problem.

Yes I am running a stock converter.
Not ideal, but even that shouldn't cause a hesitation/bog in the engine I don't think.

Posted By: Mr.Yuck

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 09/14/09 05:24 PM

try 81's out back, stock stall will cause it to be sluggest of the line. Much like dropping a clutch at a low rpm. The hight the stall the better your launch. You need to get a Air/Fuel meter, even a cheap one. That will make sure you don't burn things up. Also a boost/vacuum gauge in the car. Helps tune things.

Posted By: daniel_depetro

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 09/14/09 06:00 PM

I just picked up a boost gauge & Innovation Motorsports LM-1 air fuel wideband kit so that will help.
I'm still sure it's carb related though. When I hit it too fast it almost dies (just like when you run out of fuel).
Just not sure what I should try and what will work.
I asked a few people and everyone gives different answers, so I figured you guys would know.
Hopefully this thread goes somewhere, and doesn't die out.
I'll keep it updated with any new results (or failures).

Posted By: daniel_depetro

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 09/14/09 06:04 PM

Quote:

The bog is probably not enough fuel right off, is the accelerator pump linkage adjusted so it shoots right when you touch the gas?

I noticed the springs on both carburetors are pretty weak, even though they were both new. The spring would collapse before it squirted fuel.
I was thinking of making a sleeve for it so it would squirt as soon as the pedal was touched.

Posted By: Mr.Yuck

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 09/14/09 06:13 PM

When I S/C's my coronet I sent my carb to Scott at SDCE and he set it up perfect. Mine was blow thru not draw thru. Try BDS tech line and see what they say.

Posted By: DaytonaTurbo

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 09/14/09 07:23 PM

Sound to me like a lean spike when you nail the throttle. My thermoquad did the same thing, nail it and the motor would basically die for a second or so then spring back to life and pull hard. My problem was my secondary air door was opening too early and too easily. For me a couple adjustments took care of this, for a street avenger you'd need to try a stiffer spring for the secondaries.

If that doesn't help, I'd be looking at accel pump squirters and cams.

Also try tweaking your base timing. 8* at idle seems awfully low, even with a supercharger. Your distributor may need to be recurved to limit the total advance so you could run a normal amount of advance at idle without overadvancing during rpm/boost. Try bumping your base idle to 14 and try launching it again. But get OUT of the throttle right away if it does or does not help. With the extra timing you may not want to get into much boost/rpm but seeing if it helps you out of the hole will tell you if this is an area you need to look at or not.

Posted By: blown340

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 09/14/09 10:07 PM

what fuel pressure are you running?

Posted By: daniel_depetro

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 09/14/09 11:03 PM

The fuel pressure is stock whatever that is (~6 psi?!?).
It's a stock 5/16" fuel pump and 5/16" lines.

Posted By: daniel_depetro

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 07/18/10 12:36 AM

Dad wanted to try drag racing again so we got the new water pump installed and changed the oil. dad robbed the Sun Super Tach II out of the 1964 Ford F-100 and also installed a driveshaft loop.
I mounted the 26.50 x 8.50 - 14 slicks on the rear rallye wheels and the car was as completed as it was getting.
Unfortunately we didn't have time to finish up anything else. It was simply put the car in 'D' and let nature take it's course.
The good news is that the trip went without anything imploding.
The car launched straight and drove smoothly down the track like it was a Sunday cruise.
The bad news is we only got 2 passes and then the event got rained out.
That's too bad because there was only about 50 cars down there and we could have easily got ~10 runs in that night. We got there at 5:00pm and a few people already had 5 runs in by 7:00pm, when they pulled the plug!

Sitting in the staging lanes before the first run:

Launch on the first heads up run against Brad LePine:

The first run seemed to go pretty good, however the serpentine belt was off the pullies by a tooth (or was it two?).
It ran a 14.0288 @ 98.11 mph. Considering the car was shifting ~4,400 RPMs, the carburetor was not dailed in, the transmission is stock (low RPM stall speed & no shift kit), and the blower belt came off on the big end that's not so bad either.

For the second run I decided to put the shorter 'race' belt on (takes about 20 seconds to swap belts on this system we have) which just bypasses the power steering pulley. This way the only thing the serp. belt goes around is the supercharger, crank, and tensioner. This gives the belt more bite on the supercharger pulley and would eliminate any slippage, if in fact there was any. We also bumped the timing up a few degrees.
The water pump belt came off and the blower belt broke. It wrapped itself tightly around the harmonic balancer and made scary noises. It sounded like the bottom end was knocking.

Dad said it was extremely strong through the middle of the track, but really nosed over on the big end with both passes.
We quickly tossed the 'street' belt back on and got back in the staging lanes. We got up to the front and down came the rain.

Unfortunately this was the last test and tune of the 2009 year and our only outing to the track with this car.

Posted By: daniel_depetro

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 07/18/10 01:34 AM

Back at this car for the time being.

We changed from the standard B&M kit tensioner to a tensioner off a modern truck.
The exhaust now exits under the rear bumper like it should.
two weeks ago I picked up a new Holley 750 cfm 'Double Pumper' (4779s) for $250.00 from a guy on Craigslist. It's fresh out of the box and runs awesome!
We have a 3" pulley on supercharger, 6.75" (or 7"?!?) pulley on crank.
Air cleaner is a $115.00 Iola, WI swap meet special that was picked up last Saturday because the B&M unit was somehow misplaced?!?! Looks fantastic, however it has a small cheap filter element and the no center stud/bolt going through the top makes removal/tinkering a real pain in the @$$.
The car is now complete though I have yet to bolt on the front valance panel.

Now it's finally tiem to start getting this car "tuned in" and running up to it's potential.

Posted By: Mopar_Country

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 07/18/10 02:29 AM

Quote:

Sound to me like a lean spike when you nail the throttle. My thermoquad did the same thing, nail it and the motor would basically die for a second or so then spring back to life and pull hard. My problem was my secondary air door was opening too early and too easily. For me a couple adjustments took care of this, for a street avenger you'd need to try a stiffer spring for the secondaries.

If that doesn't help, I'd be looking at accel pump squirters and cams.

Also try tweaking your base timing. 8* at idle seems awfully low, even with a supercharger. Your distributor may need to be recurved to limit the total advance so you could run a normal amount of advance at idle without overadvancing during rpm/boost. Try bumping your base idle to 14 and try launching it again. But get OUT of the throttle right away if it does or does not help. With the extra timing you may not want to get into much boost/rpm but seeing if it helps you out of the hole will tell you if this is an area you need to look at or not.

I second that, mine did exactly the same.

Posted By: TheOtherDodge

Re: Help me set up our 1972 Dart supercharged 360!! PLEASE! - 07/18/10 10:42 PM

I still don't like the belt wrap around the blower pulley....

I have no experience with that type of blower but I know with my centrifigal blower, I need about 60% belt wrap or I would get slippage and sometimes the belt would fling off.