[SD455DJ]

This is a chassis dyno (DynoJet) for a '71 455HO engine that made an average best of 332 hp and 436 ftlb torque. How does that translate into flywheel numbers?

Dennis

[steve25]

Your posted 332 hp is not average best as you have said, but it's the true peak hp on the most productive pull!

Is the car auto or manual trans?

If auto the flywheel hp could be as high as 390, if manual trans it could be 415 hp.

What was the motors average water temp during these pulls?

[SD455DJ]

Steve25, M22 manual trans and 3.42 rear gears. The engine was rebuilt back in '05 with .030 forged pistons (CCP's?), stock rods with ARP bolts, 8.6 to 1 compression, factory RA (2 1/8" outlet) exhaust manifolds, HO intake & 7041267 Q-jet, and an early Pypes 2.5" mandrel exhaust system with 'X' pipe and Racepro over-axle muffler.

Dennis

[PAUL K]

IMO the numbers don't translate. From our experience chassis dyno numbers are all over the place, especially with an automatic transmission.

But it looks like a nice build.

[Skip Fix]

I had one chassis dyno guy tell me slicks vs street radials even make a difference.

[Steve C.]

Interesting articles...

https://www.hotrod.com/articles/1106...-engine-dynos/

https://www.onallcylinders.com/2012/...u-should-know/

Related topic here on PY:

https://forums.maxperformanceinc.com...t=chassis+dyno


.

[Lee]

Agree with Paul K.

To further illustrate, I've attached a graph with two different chassis dyno tests on it.

This graph is the SAME car/motor/tune. The ONLY difference was that the torque converter was changed. Flywheel HP was unchanged, so how could any formula account for that much difference? I later tested a 3rd converter, and it provided a graph that was nothing like either of these!


Also, always get print out of the HP/TQ plotted against wheel speed, as well as against RPM - especially if you have a looser converter.

[Stan Weiss]

Originally Posted by SD455DJ

This is a chassis dyno (DynoJet) for a '71 455HO engine that made an average best of 332 hp and 436 ftlb torque. How does that translate into flywheel numbers?

Dennis

Dennis
The first think you need to understand is that most chassis dyno software uses a different dyno (weather) correction factor than a engine dyno uses. Note the SAE 0.98 and 0.99 baseline. That is reducing the measured HP. On an engine dyno that would have been around 1.02 to 1.03 which would have increased the measured HP.

Stan

[SD455DJ]

Thanks everyone for your posts. I see now that it is an 'impossible-to-answer' question, just too many variables to consider to make any direct correlations to flywheel data.

Lee, you chassis dyno'd a low compression 455 as I recall...can you repost those? I'm not trying to compare the two 455's, just curious to see what yours did again. My 455HO was rebuilt back in 2005 when it was in the Chicago area and was then chassis dyno'd in 2010 when it was in the Toronto area before I bought it in 2015. It had a Comps Cams XE 276 (230/236/110) when dyno'd (since changed).

Dennis

[Stan Weiss]

As I said about there different weather dyno correction factors that can be used. You dyno sheet says "SAE" and Lee's says "STP"

Stan

[Skip Fix]

I think Lee's comments are good. I've always wondered since rear end gears multiply torque of the engine to rear wheels how that does not affect chassis dyno numbers also.

[Navy Horn 16]

It's impossible to answer, but the track data is the most fun to get.

I wish that I'd been able to get my motor on an engine dyno so that I had that data to go with my chassis dyno and track data. My ET slips (with some math) show 50-65 more HP than I've ever been able to print on a chassis dyno... It's way more fun going to the track anyway, and Alamo City Motorplex has a taco stand that I really like.

[Stan Weiss]

Originally Posted by Skip Fix

I think Lee's comments are good. I've always wondered since rear end gears multiply torque of the engine to rear wheels how that does not affect chassis dyno numbers also.

Skip,
Without getting in the math. While the rear end gears do multiply torque. They at the same time also change tire / roller RPM.

Stan

[Lee]

Originally Posted by SD455DJ

Thanks everyone for your posts. I see now that it is an 'impossible-to-answer' question, just too many variables to consider to make any direct correlations to flywheel data.

Lee, you chassis dyno'd a low compression 455 as I recall...can you repost those? I'm not trying to compare the two 455's, just curious to see what yours did again. My 455HO was rebuilt back in 2005 when it was in the Chicago area and was then chassis dyno'd in 2010 when it was in the Toronto area before I bought it in 2015. It had a Comps Cams XE 276 (230/236/110) when dyno'd (since changed).

Dennis

Dennis, here are a few for you to compare with.

1. This is my own 455. Stock "66" casting heads, bevel-edged pistons, CR ~7.8, 222/242 HFT cam 116lsa, .443/.435. tri-Y headers, 3" exhaust, Performer intake, Q-jet, automatic with stock stall.

2. 400 with SD Performance ported 6X heads. CR ~ 8.3:1. 2.5" R/A manifolds, Performer intake, Q-jet, 4spd manual tranny. HR cam, 224/236, 115lsa, lift just under .540".

3. 455 built back in '03, using box-stock Edelbrock heads, pretty sure they were 85cc. Cam is a Crane HFT single pattern, 228/228, 112 lsa, lift was somewhere in the .530-.540" range with the rockers used. Stock intake with a Q-jet. Doug's headers and a good exhaust (don't remember specifics). Transmission was a switch-pitch THM 400, with the testing done with the converter in the tight position. Owner's desires were "run fine on pump gas, and I want it mild enough that my wife can take the kids to get ice cream in it." I talked to him a few years ago, and it was still running fine.

[Lee]

Originally Posted by Stan Weiss

Skip,
Without getting in the math. While the rear end gears do multiply torque. They at the same time also change tire / roller RPM.

Stan

Stan & Skip,

I've done/seen some testing in different gears, and the differences have been less than expected. They are usually a LITTLE different, but a few times no real difference at all. The mild 6.0 LS in my Cutlass put 386 to the wheels in 2nd and 3rd gears.


Oh, in post #7 above, I mentioned testing 3 different torque converters and getting 3 totally different looking dyno curves. I forgot to mention that all 3 of those converters were SUPPOSED to have the same stall speed!

[SD455DJ]

Originally Posted by Stan Weiss

As I said about there different weather dyno correction factors that can be used. You dyno sheet says "SAE" and Lee's says "STP"

Stan

Thanks Stan...I see that is a 5-6% difference between the two correction factors.

Dennis

[SD455DJ]

Originally Posted by Lee

Dennis, here are a few for you to compare with.

1. This is my own 455. Stock "66" casting heads, bevel-edged pistons, CR ~7.8, 222/242 HFT cam 116lsa, .443/.435. tri-Y headers, 3" exhaust, Performer intake, Q-jet, automatic with stock stall.

2. 400 with SD Performance ported 6X heads. CR ~ 8.3:1. 2.5" R/A manifolds, Performer intake, Q-jet, 4spd manual tranny. HR cam, 224/236, 115lsa, lift just under .540".

3. 455 built back in '03, using box-stock Edelbrock heads, pretty sure they were 85cc. Cam is a Crane HFT single pattern, 228/228, 112 lsa, lift was somewhere in the .530-.540" range with the rockers used. Stock intake with a Q-jet. Doug's headers and a good exhaust (don't remember specifics). Transmission was a switch-pitch THM 400, with the testing done with the converter in the tight position. Owner's desires were "run fine on pump gas, and I want it mild enough that my wife can take the kids to get ice cream in it." I talked to him a few years ago, and it was still running fine.

Thanks Lee! Appreciate you posting the dyno sheets again. I have a '71 Bonneville with the "66" headed 455 that is totally stock with the 067 cam. When it's time to rebuild that engine I'll have to talk to you about your cam design.

Dennis

[Steve C.]

Not necessarily related to the OP's topic at hand, but Lee's comment in his post #15 should be be well noted........

"I forgot to mention that all 3 of those converters were SUPPOSED to have the same stall speed!"

This knowing the torque converter is often stated, and should be, a great "bang for the buck" when it comes to performance enhancement. Like a camshaft catalog operating range, don't always rely on what the catalog states about a torque converter, this regarding the stall !

.

[lust4speed]

Originally Posted by steve25

...Is the car auto or manual trans? If auto the flywheel hp could be as high as 390, if manual trans it could be 415 hp.

You and I use the same conversion figures, but you swapped auto and manual numbers. So auto is 415 and manual is 390 at the flywheel.

We always have to make allowances when attempting to convert rear wheel to flywheel horsepower or vice versa. a conversion factor estimates converter slip, and the more converter slip the higher the ratio. Manual trans have no slip and the power train loss is loosely figured at 15% while a "normal" converter with an auto is figured at 20%. As soon as converter slippage changes the ratio changes also. The converter with the lowest rear wheel horsepower has to be the one with the most slippage. I could see a loose converter needing a 25% conversion factor.

So in my "normal" world 332 rear wheel horsepower would be converted using 332/.8=415 for auto, and 332/.85=390 for manual. If the converter was sloppy, then we might have 332/.75=442 flywheel horsepower.

Is this precise? Hell no. Other than ripping out the engine and sticking it on an engine dyno after running on the chassis dyno, it's the best we have -- and at least makes for some light conversation at the end of the dyno session.

[SD455DJ]

"You and I use the same conversion figures, but you swapped auto and manual numbers. So auto is 415 and manual is 390 at the flywheel."

I can agree with this statement from lust4speed as many 455HO's with similar builds to this particular one have engine dyno'd at 400 hp +/- and 510 lbft torque +/-...so the 15% is close. The 455HO we last dyno'd made 430 hp and 535 torque (stock w/8.6 SCR and a Summit 2802 cam, through the factory exhaust manifolds and 2.5" mandrel headpipes).

Dennis