Dyno Dissappointment

I've had a blast restoring my 70 Challenger Vert. Originally a 318/727 car I cloned it into a 440 RT/ 4 speed. Started with a 440 Truck engine out of a motor home, kept the cast crank, bored 15 thou over. had the heads totally rebuilt and taken down 50 thou, steel head gaskets, edelbrock performer intake, Hedman Headers. MSD dist, single wire Powermaster alt and Blaster coil. Just had it Dynoed at 304 HP at the wheels. Really disappointed ----- Thoughts?????. I know I can spend big bucks from here, but I was expected more at this point

I would say you need to provide more specific information here.Carb, cam timing and specs , actual compression ratio and cylinder head info come to mind. If you haven't tried to dial in the combination yet, maybe you missed on the tune up. What you are seeing there is probably not far from actual rear wheel horsepower of a stocker rebuild. More specifics are needed. It sounds like you are just getting started and need to make some adjustments ,one at time ,to get a direction. You may still have some left on the plate. Work the small stuff first , one at a time. Good luck, keep at it. Bill

Missed a little here....thanks.............Installed a Hughes engine "whiplash" cam and at the time,used a cam timing wheel to check it.....o adjustment beyond the timing marks was required Worked Worked with Hughes Engines to have custom length push rods made also, (due to planing down the heads) Have a Holly 850 Street Avenger Carb on her. Dual 3" TTI exhaust system. Id like to see a little more HP, but unsure whats best

Without knowing the exact cam specs I don't think the results are far off from what the combo should make, it's probably closer to 375 at the flywheel, some fine tuning may net a small handful of HP but not a ton. The next thing I would upgrade would be some bigger valves and decent amount of porting in the heads (or sidewinder or edelbrocks) and at least a performer RPM intake as the regular performer is barely any better than stock. Heads or intake upgrade alone would not net much as the other would still be the choke point, doing both together should wake it up.

What RPM did it make peak HP and peak torque?
What was the weather that day?

I have a similar 451 with 906's, performer, and stock big block a body exhaust manifolds. It makes right at 300hp to the wheels on a chassis dyno as it is driven off the street, heat soaked and all. Uncorking the 2.25" repro exhaust is work 20rwhp.

If you have a smaller cam (xe294h w/ 1.6's here) and headers compare to my manifolds I'd guess you might find 15-25 tops at the wheels. What RPM did you pull it to?

The 451 in my dart made a hair under 500hp/500tq on a realistic engine dyno with a Performer RPM and 1-7/8" dyno headers. I figured the manifolds -50hp, intake -15, full exhaust -25hp, factory magnum air cleaner -10hp and don't forget the accessory drives for a very believable 100hp loss at the flywheel. That leaves us with 400hp going into the clutch.

400x.80=320rwhp on a perfect day. Take a car driven in off the street (heat soaked) on an 85 deg. day and 300ish at the wheels isn't out of the ball park.

Sounds like a fairly stockish rebuild and they were only rated 375HP at the flywheel from factory I think. Figure in the drivetrain loss that's sounds about right for a stockish street car rebuild. Do you want more HP just for the number or do you want more power? For a street cruiser that sounds like a nice cruiser. Never understood building a 500+ HP for a street cruiser.

Did you try any tuning? Adjustments such as ignition timing and carburetor (Fuel/Air Ratio) can make a big difference in power. On my hemi, adjustments to timing and changing jets in the carburetor helped me get 80+ more horsepower on the dyno. Not sure if you could see that much, but if you just have a bunch of parts bolted together, tuning would almost certainty help you find some hidden power.

I like Jeremiah's post. Realistic, although approximate, numbers for various parts & factors.

I totally agree with your sentiment. 500 hp is not nearly enough!

I find 650+ is approaching enough power, but I'm thinking 800hp is just about right. I'm limited due to running a stock 440 block, or I would have added a 150hp shot of N2O for use in second gear on up on my street/highway cruiser.

Cam is a lot larger than the stocker. With a good tune I'd expect it to make more than 400 at the flywheel with headers.

Don't know what the ignition timing is at idle, but it's likely going to want in the 16-20 range minimum. Might need a limiter bushing that MSD doesn't make as well.

The two things that stick out to me are:
- no mention of any head porting or oversized valves
- “Performer” manifold. If it’s the std Performer, not the Performer RPM there is some potential power left on the table there........ especially if the heads get reworked.
If the motor has stock heads with no porting and the std Performer, I can see where you’d have an under 400hp(at the crank) combo.

I find chassis dyno results can have an even bigger swing from facility to facility than engine dynos(and different engine dyno results can vary quite a bit).
So, without having something to compare to off that dyno...... your 304rwhp is just an arbitrary number to me.
Maybe the dyno service could give you some numbers from bone stock modern muscle to use as a comparison.

A pretty basic pump gas 440 with say...... 9.5cr, a mid-sized hyd cam, some mild head work to factory heads, headers, intake, carb, etc will be in the 425-450hp range at the crank.

DusterKid makes a very good point. You've got a 70 Challenger CONVERTIBLE 440 4spd R/T. Quite a valuable and fun car. The motor sounds like a stump puller.Don't worry about the numbers. If it's fun to drive , do it! Its too valuable of a vehicle to end up around a tree. Spend some time tuning it and enjoy it. There's probably a bunch of us on here that would love to be cruising around and shifting gears in that car .Enjoy it. It's only numbers.
Bill

generally people have unrealistic expectations from a chassis dyno. remember that a chassis dyno is driving the fan, water pump, alternator, mufflers, transmission, rear axle, wheels tires. for what i take on the build 304hp isn't bad. i think unrealistic chassis numbers stems from unrealistic engine dyno (magazine/internet stuff) numbers. the chassis dyno is the truth meter and people can't deal with it.

All chassis dyno give you the net reading (true HP to the rear wheels), not the gross reading like the factory uses on there adds to the flywheel.
My last pump gas street car had a 517 C.I. 400 block stroker motor that made 612 HP at 5500 RPM and 644 Ft. Lbs. torque at 4500 RPM with a set of ported 906 heads with big valves with 9.25 to 1 compression ratio and big solid lifter roller cam on a DTS brand engine dyno with a low deck six pack set up tune to the max, that motor made right at 500 HP net at 5000 RPM peak with a 10 inch custom converter on a local chassis dyno, that is 19.4 % loss with 4.10 gears in the rear end
On your deal you may have more power in the engine that is not getting to the rear wheels because it is running out of fuel above 5000 RPM, been there done that
If I was you I would make sure that the motor is not going lean above 4500 RPM at wide open throttle in high gear, look at buying and using a good wide ban O2 exhaust system so you can see real time air fuel ration while driving

Late model motor home heads are a real cork with any cam at all. Lots of good suggestions above.

I only have one question; how far down in the hole are the pistons? Of better yet, what is your cranking compression?

Sorta. Gross and net refer to the test conditions when they were originally rated- net is still a flywheel number, but it includes things like the alternator, the water pump, the fan, the full exhaust system with representative backpressure, etc.. The gross ratings were not realistic. Both of them will still be higher than the rear wheel horsepower number. Depending on manual vs. auto, or the type of converter, you could see losses in the vehicle anywhere from 12% to 22+%, below the net rating.

Dynos also have 2 correction factors - SAE and standard. SAE is also more representative of real world conditions. STD corrects to completely dry, 60* air, with a density altitude of near 0, so the STD number will always be higher than the SAE. SAE corrects to 77* air, a little lower barometer, and more reasonable humidity (it's closer to 2000' density altitude). This applies to both engine dynos and chassis dynos.

Missed the motor home part, saw truck engine. DOH!!!!

pair of Edelbrock heads would wake this engine up I bet !

Without knowing your cam specs, I think 300ish RWHP is about right, that's about 380hp. 440's especially with stock heads are just not big HP makers. They don't make good dynamic compression (comparatively to other rod stroke combos) and the factory heads can't breathe.

I had a strong running 440 (.030 over) with flat tops, a Hughes solid flat tappet cam and Edelbrock performer heads with 1 7/8" headers. The engine made 360 RWHP (or 450HP). I also was disappointed but the 3700lb B body ran 11.90s @ 115mph.

Bottom line: 440s make a ton of torque and that's why they were feared on the street, they got things moving in a hurry.

There is still so much missing information about this engine build.

You never stated the measured compression ratio. Tell us about the 0.015 over pistons, who made it and what's the final compression distance. What is the cranking cylinder pressure? Because you you milled the heads a bunch, had them "rebuilt", and put a Whiplash cam in it suggests to me that this was a budget build and you put bandaides on it to make up for the low compression.

Does it have headers? If you are using exhaust manifolds, that is not a good cam choice.

Mustang or Dyno Jet dyno?

If that is 304 RWHP on a Mustang dyno for what I'm guessing this build is, that's not bad. And, IMO, 304 RWHP is a nice performing street car. 304 RWHP you should be able to drive it to the track and pull directly into the staging lane and run a 13.00 at 105 mph with a street tire/stock converter 60 ft of 2.0 sec.

HP numbers from any dyno, chassis or engine is just the first step. I prefer an engine dyno, because you can get more data to decide if it needs tuning, and or what is right or not right with the combo. While nothing stops you from having exhaust gas temps, 02's, fuel flow, BSFC, etc. nobody usually takes the time to set up an engine on a chassis dyno. To tune your combination I would want to know cranking compression, to get a handle on dynamic compression ratio, and exhaust temps, along with 02 readings to see how efficient combustion is. One HP per cubic inch is what I use as a reasonable goal on a mild engine with bolt on's as you describe.

What is the actual compression ratio? Very low I’m betting. A buddy of mine has a couple motorhome 440 blocks and both have huge bevels on the bore/deck.

I dyno'd my 78 Ramcharger, it ran perfectly fine, edelbrock 750 cfm carb, performer intake, dual exhaust, it made a blistering 121 rwhp. At 300 rwhp, that's quite the improvement you've made actually. For reference, my SRT10 ram with no mods made 355-ish rwhp.

Some friends in town have a chassis dyno in their shop.
It’s a dyno jet. They’re on there 2nd one.
The first one was the intertia style that had the heavy large diameter rollers.

Probably around 15 years ago they had a 69 Charger on it.
Flat top 440, SD intake, Demon 850, ootb RPM heads, 1-7/8” headers, MP 509 cam, 10” converter, 3.91’s.
Ran fine, felt pretty hot driving it around.
Made around 285hp to the wheels. The guy was all upset.

Took it to the track and it went 11’s.

I’ve seen a lot of that kind of thing that really make me scratch my head.


The new Dyno Jet they have has smaller rollers and uses an eddy current type of absorber instead of inertia....... so you can actually load the motor prior to making a “pull”, along with being able to set the accel rate.

I haven’t seen that one in action yet.

Friends have tried to get me to put my car on a chassis dyno at one of the events we attend.

I have no interest. To me they are a tuning tool and nothing more.

The only numbers that matter to me are the ones at the dragstrip. Even then, mph is what is relevant to hp. You can have crap for tires and chassis and a lousy e.t. but still get a close idea from weight and mph of what the engine is making.

low rear axle gears and loose converters can have an adverse effect on a chassis dyno outcome.

I'm curious on these .015 over pistons also. SO....custom pistons yet you still need steel shim gaskets to and to shave the heads to get the compression up?

After watching a few videos with cars on hub dynos, making simulated 1/4 runs as they go thru the gears........ I can see where that could be pretty helpful.

https://m.facebook.com/590227367683050/videos/522722568322028/

Oh..... and yeh...... that thing sounds bad a$$!!!

I saw a S/C Corvette on the dyno when I worked at a race shop. 406 small block with a glide. 6500 stall and 5.38 gears. Dyno'd 440 at the wheels. Went 8:50@163 at the track. Dyno's are tuning tools, nothing more.

That sounds a lot nicer what do the dyno sheets say ?
Any measurements made on that dyno are not the same as at the track with the hood on forcing air into the carbs would be
I wouldn't trust those results to be same as they would be at the track
Two things I look at and trust the most for tuning is the spark plug and the time slip

The 224 smaller drum is still inertia, the 224xlc is inertia and eddy current. I have the xlc now , I use to have a 248 , the large drum version. The stack has to be matched to the machines drum weight, if you use someone elses stack(dyno computer module), you'll get whacked readings. The 248 actually had loading via the modulation of the air brakes(locomotive brake shoes), if the brakes were acting up or setup wrong, it caused low readings, mine would flutter the air solenoid, it stopped when I fixed the cable shielding.Dynojets are calibrated on the inertia weight so that no matter where you dyno a car, if the same correction is used the number spit out should be pretty close to the same anywhere on a given car strappped down in a consistent manner on any dynojet. I keep notes on cars I dyno that I know are coming back.
Strapping the car down incorrectly will put a dent in the power. The less angle on the straps the better, but some people put angle in to load the tries up if the knurling is worn on the drums. I opted to build my own deck for the dyno, a longer version so that trucks and longer cars would still have less steep angle from the rear strap points.

FWIW...my cuda only made around 630 RWHP on the local dynojet. I was surprised (figured it'd be higher, of course), but didn't really care since the car had already run 9.50s at 140+ mph at 3800 lbs.

Use the dyno as a tuning tool and nothing more.

My friends bought both of their dynos new from Dyno Jet...... complete with whatever electronics were needed to go along with them.

Dyno's are just a tuning tool, fact, however here in the uk I don't know what dyno's were used but I know of 2 cars that were tested and both those cars weight/mph@the track showed pretty much spot on dyno numbers. Whether this was just luck I'm not sure.

One of which was the car I crewed on last year. Dyno'd@695fwhp at EDF......weight@the line 3800lbs.+/- a few either way with the slicks, best mph last year was 130.14 on a perfect day with no headwind, plenty of 129+runs......thats 680hp, this is through the same carb/timing as dyno run but with all ancillaries and a full exhaust system with an air cleaner, basically as it drives on the street.

wallace has it with 680fwhp/3800lbs>

60 Foot E.T. : 1.44 Seconds
1/8 Mile E.T. : 6.52 Seconds
1/8 Mile Trap Speed : 104.22 MPH
1/4 Mile E.T. : 10.34 Seconds
1/4 Mile Trap Speed : 130 MPH
its gone a best of 10.35 with a best 60 of 1.431

so not saying dyno's are the be all they are certainly not, weight/mph is your dyno just sometimes at least here they showed pretty accurate numbers twice that I know of.

Dyno results through an automatic can sometimes be misleading, especially with a higher stall converter. Some produce realistic results, some read super low.

That power may be dead on but we need more info because you’ve got a lot missing. Does the car feel strong to you? If you really want to know if it makes the power it should take it to the track and see what the trap speed is.

If you did not buy a higher compression piston for it then the results sound about right.

Still should be checked, you have to send your stack in every once in awhile for a chip that expires, also your software disk is serialized as well with the dyno particulars.
My old and new dyno produced pretty much the same numbers when the same car was run on both.

Why? The dyno is measuring power at the wheels, how it’s transmitted is irrelevant at that point.

Yes Pacnorthcuda but with an accurate weight and a couple of runs to get a trap speed, the horsepower can be calculated and that will be accurate. His 60 foot times and traction are irrelevant. It would either confirm or call into question what the dyno is telling him

I think the difference is, launching the car at the track as normal, you have max converter slip for a short time and it's coupled as close as it will be by the top of low gear.

Now take the same car and launch/make a pass in high gear. Would be a ton more slip/heat (resulting in less power to the tires) and to the same effect, would also show on a chassis dyno.

On cars with multi plate lockup converters, can often be a huge difference between locked and unlocked numbers.

Or, going from a less to more efficient converter with no other changes can result in much higher numbers with no other changes.

“Dyno Disappointment”

Actually......... not at all uncommon.

Sort of similar to...... “first time at the track disappointment”

Torque converters can make so much difference in the car performance that is is hard to believe until you test several different ones or see someone do that at the track.
the last converter swap I did was from a custom built 10 inch street and strip Contintental to a 8 inch SS Hemi Turbo action, that swap made my car pickup .2 ET in the 1/8 mile and gained 2.0 MPH
We've seen .8 ET gain and very little MPH loss going from a stock 11 inch street Hemi converter to a custom built 8 inch Rossi race converter in the 1/4 mile
The bad side of different brands is also possible, GER were junk The first 8 inch race converter we bought and used was a Art Carr 8 inch race converter for Hemi NHRA stocker, it would slow the car down 3.0+ MPH and .3 ET in the 1/4 mile from the stock 11 inch street Hemi converter