[Formulajones]

My duramax has a big spread like that. I've never seen a gas engine do that.

[Stan Weiss]

Originally Posted by steve25

How is the reported torque at the crank (1223 ) over 330 foot pounds higher then at the rear wheels when the rear wheel torque is being multiplied by the rear gears?

I am assuming that this motor is NA

Steve,
You need to understand how that type of dyno works. Rear end gear ratio and rear tire size should make no difference. Normally the test is done in drive 1:1. I talk with someone who did the test in both 2nd and 3rd gear and it made also no difference. In some cases they use a fixed amount for tire to crank and other places do a coast down to try to measure the drive train losses.

Stan

[steve25]

Ok got,and thanks for waking me up this morning Stan, but still something is off with those results.

[steve]

Ok so sorry for the confusion but like I said that is the first dyno sheet I’ve seen. Talked to the mechanic and he explained to me what’s going on. The torque numbers are indeed wrong on that sheet. He told me some of the differences between a mustang dyno and a “dyno jet ?” machine and how they work. He is standing by the HP numbers though. Sorry if that upsets some of you.

[JLBIII]

Do you have the dyno sheet with your 3.55 gears in the car?
Paul Spotts built my engine. His shop is a half hour away from my house. I use 2nd Street Speed in Perkadie for my dyno work.

[steve]

No I just swapped the gears this summer and I am still dialing in the tune. I probably won’t do it again though because of the cost and I don’t think the numbers would change much. I am also not overly concerned with the exact figures. The car has plenty of power for me, but everyone wonders what their car could do at the track.

[Singleton]

printout shows 568.5 crankshaft horsepower with the Correction Factor, which is believable, nothing unusual there. I'm unsure of what the rpm of 2950 is measuring, I would expect the horsepower peak in the 5200-5500 engine rpm range. I would think torque to be in the 600-625 range on this 4.5" stroke engine.
Would need more info on car to estimate track times

[Steve C.]

What's the difference between a Mustang dyno and a dynojet?

Opinions...........

http://forums.mustangworks.com/f12/d...-dynojet-9929/




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[steve]

The car is pretty much an unmodified 81 firebird. I think the original curb weight was almost 3400lbs. I have aluminum heads, intake, and wheels so it’s still over 3000 easy. Th400 trans, Holley efi, dennys driveshaft, moser 3:55 rear. 275/40/18 rear tires. What else do you need ? I do have adjustable shocks but no drag tires. Headers, 2.5” exhaust, and turbo muffs

I was told one of the differences with the mustang dyno is that it puts a load on the engine while testing while the dyno jet does not which could result in as much as a 10% difference in readings.

[steve25]

568 corrected flywheel hp i believe.

[Steve C.]

Chassis dyno. Even from dyno to dyno of the same make/brand differences can vary.
In the end, it's a "tuning tool" more than anything else.

It would be interesting to know at what RPM peak power was made and at what RPM was peak torque.
On our 4.5" stroke engine the RPM difference between peak power and peak torque was around 1600 rpm.
Tested on a engine dyno.

Smackdown: Engine Dyno vs. Chassis Dyno
https://www.motortrend.com/articles/...chassis-dynos/



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[Steve C.]

Here this 488-inch 4.5" stroke Pontiac made peak torque at 4100 RPM and peak power at 5500 RPM. The spread between the two was 1400 RPM.

592 hp and 625 lb-ft of Torque.

https://www.motortrend.com/how-to/48...e1B6OEcjx2OCD4


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[Dragncar]

Originally Posted by steve

Ok so sorry for the confusion but like I said that is the first dyno sheet I’ve seen. Talked to the mechanic and he explained to me what’s going on. The torque numbers are indeed wrong on that sheet. He told me some of the differences between a mustang dyno and a “dyno jet ?” machine and how they work. He is standing by the HP numbers though. Sorry if that upsets some of you.

"Sorry if that upsets some of you" ?
You put it out there like your engine is making so much unbelievable power it upsets people.
Its not a standard dyno sheet so people have questions.
Seems like its a nice solid street engine that makes around 560 HP, nothing wrong with that. But no street Pontiac is putting out 887 lbs torque, much less 1200.
And that thing has got to weigh way more than 3400 lbs in street trim. Those cars are heavy.

[steve]

Originally Posted by Dragncar

"Sorry if that upsets some of you" ?
You put it out there like your engine is making so much unbelievable power it upsets people.
Its not a standard dyno sheet so people have questions.
Seems like its a nice solid street engine that makes around 560 HP, nothing wrong with that. But no street Pontiac is putting out 887 lbs torque, much less 1200.
And that thing has got to weigh way more than 3400 lbs in street trim. Those cars are heavy.

That’s the internet for you. Not at all what I intended. I do understand people get ass hurt over the whole “my rides better than yours thing” though.

[Stan Weiss]

Originally Posted by steve

That’s the internet for you. Not at all what I intended. I do understand people get ass hurt over the whole “my rides better than yours thing” though.

I think you just want to believe and that is fine. I have no idea how much HP your engine is making and really don't care. What I and others are pointing out is all of the problem with the dyno sheet you posted. The dyno sheets says 75% drive train efficiency. I believe that is to low yet when you calculate what was used

► 429.6 / 592.1 = 0.72555 which is even lower.

Stan

PS - Let me add 130.7 MPH with a 3.08:1 rear
and a 26" tire is around 5200 RPM
and a 25" tire is around 5410 RPM
and a 24" tire is around 5640 RPM

[Jay S]

Appears the RPMs shown are the actual roller RPM’s on the wheel dyno, and are not from engine speed. Like Stan mentioned with a 26 inch tall tire and 3.08 gears it figures out to be around 630 ft lbs of tq@3200 RPM (engine speed, there is a conversion factor) and the max HP is @ 5200 (engine speed).. Usually the software will convert the engine RPM numbers for you from the roller speeds. Appears they either may have printed off the wrong info sheet (roller RPM) or info wasn’t given to them to calculate the engine RPMs.

[steve]

Thanks for the input guys.

[Steve C.]

Jay,
With peak torque is at 3200 RPM and peak power at 5200 RPM that suggests a 2000 RPM spread.
I'm certainly no expert here but based on my observations that doesn't look right.

I've already posted a few examples but here are two more....

Another 4.5" stroke
Peak power at 7000 RPM
Peak power at TQ at 5500 RPM
1500 RPM spread.

https://forums.maxperformanceinc.com...=4.5%22+stroke

Here on this 4.5" stroke combination the spread was 1000 RPM and as much as 1400 RPM depending on the intake/carb set up.

https://www.motortrend.com/how-to/cc...-alloy-indian/



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[steve25]

Peak torque always takes place in any NA motor once the limit the camshaft sets on air flow is reached, this of course assumes that the heads , intake and carb are not the cork in terms of minimum port area yet or cfm.

So to me this spread being discussed of being too wide is not so easily carved in stone.

[Steve C.]

A non expert opinion here, I was suggesting what I thought might be a normal rpm spread between peaks.

Here is one comment that relates....

"I'm trying to understand why some engine have a wide power band between hp peak and tq peak and others don't."


https://www.speed-talk.com/forum/viewtopic.php?t=3549


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