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Re: Unexpected Dyno Results [Re: MarkZ] #2527797
07/27/18 11:27 AM
07/27/18 11:27 AM
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So. Burlington, Vt.
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fast68plymouth Offline
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This thread has taken a bit of a detour....... but.....

572 I built, 918 on the engine dyno, 778 on the dynojet.

8.33@165, @2700lbs

Shows 930 on the moroso chart



68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: Unexpected Dyno Results [Re: MarkZ] #2527806
07/27/18 11:40 AM
07/27/18 11:40 AM
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rb446 Offline
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yep slight detour, thats interesting, more hp than the engine dyno, normally reverse of that, but thats the BIG mph, light car doing that I presume, 165 would normally be 8 teens.....I made it 988.

Last edited by rb446; 07/27/18 11:41 AM.

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1971 340 'Cuda, best 11.01@122.8 in 1987
Re: Unexpected Dyno Results [Re: polyspheric] #2527808
07/27/18 11:45 AM
07/27/18 11:45 AM
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Aurora, Colorado
451Mopar Offline
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Originally Posted By polyspheric
Something is wrong.
Not only are the numbers disappointing, the torque curve should NEVER have a big spike like that.


That looks strange to me too. I would think smoking the tires on the dyno? Were you running street tires or race tires?

Re: Unexpected Dyno Results [Re: fast68plymouth] #2527816
07/27/18 12:00 PM
07/27/18 12:00 PM
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Marion, South Carolina [><]
an8sec70cuda Offline
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Originally Posted By fast68plymouth
This thread has taken a bit of a detour....... but.....


iagree I was posting my results just to say not to get discouraged w/ low numbers from a chassis dyno. Always felt like my car ran a lot better than the chassis dyno numbers would suggest...considering the crap you see blasted all over the internet and magazines.


CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
Re: Unexpected Dyno Results [Re: an8sec70cuda] #2527871
07/27/18 01:43 PM
07/27/18 01:43 PM
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Bend,OR USA
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Originally Posted By an8sec70cuda
Originally Posted By fast68plymouth
This thread has taken a bit of a detour....... but.....


iagree I was posting my results just to say not to get discouraged w/ low numbers from a chassis dyno. Always felt like my car ran a lot better than the chassis dyno numbers would suggest...considering the crap you see blasted all over the internet and magazines.

When it comes to racing and car stories I always try to remember the old adage about believe nothing you hear and only half of what you see work whistling grin


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Unexpected Dyno Results [Re: MarkZ] #2527887
07/27/18 02:32 PM
07/27/18 02:32 PM
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S.E. Michigan
ZIPPY Offline
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Here's an ancient sheet of mine from Jake's for comparison.

It would do me some good to head back there.

I don't really dig the spike in the curve from the original post, I have no idea what is going on with that but maybe someone does. If that was mine, that would be the first thing I'd point at and ask questions about.

That 5th Avenue big block sounds cool as heck, I'd really like to check that out sometime.

gtxresults002 old.jpg

Rich H.

Esse Quam Videri




Re: Unexpected Dyno Results [Re: MarkZ] #2527888
07/27/18 02:36 PM
07/27/18 02:36 PM
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central texas
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zippy, what converter is in your car?

Re: Unexpected Dyno Results [Re: MarkZ] #2527908
07/27/18 03:35 PM
07/27/18 03:35 PM
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S.E. Michigan
ZIPPY Offline
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It's a tighter than normal turbo action "J", 9". Originally it was custom built for a much more radical combination. Around 4400-4600 in this car, feels surprisingly tight on the street and can be easily driven normally without alot of slippage at light throttle, etc.


Rich H.

Esse Quam Videri




Re: Unexpected Dyno Results [Re: MarkZ] #2527916
07/27/18 03:38 PM
07/27/18 03:38 PM
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So. Burlington, Vt.
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fast68plymouth Offline
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I know the dyno sheet can be configured differently than what the OP has shown.

I’d like to see a graph where the x axis is speed(mph), and another where it’s time(seconds).

Those should give a much better illustration of how the converter is behaving.

When the converter is pretty loose, and you’re using time or speed as the x axis....... the torque line will just go pretty much straight up at the hit of the throttle.....then kind of flat line until the driveshaft speed more or less catches up with the motor.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: Unexpected Dyno Results [Re: fast68plymouth] #2527950
07/27/18 04:31 PM
07/27/18 04:31 PM
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Pattison Texas
CSK Offline
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Originally Posted By fast68plymouth
This thread has taken a bit of a detour....... but.....

572 I built, 918 on the engine dyno, 778 on the dynojet.

8.33@165, @2700lbs

Shows 930 on the moroso chart



Thats interesting, that shows about 16% drop from moroso slide to wheel. & about 15% from dyno to wheel, all very close. very cool smile

Last edited by csk; 07/27/18 04:49 PM.

1968 Charger COLD A/C Hilborn EFI
512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim
2020 T/A 392 Stock 11.79 @ 114.5

Re: Unexpected Dyno Results [Re: MarkZ] #2527956
07/27/18 04:45 PM
07/27/18 04:45 PM
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So. Burlington, Vt.
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fast68plymouth Offline
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Another thing to keep in mind when looking at chassis dyno results, from an inertia dyno, especially when a fairly high stall converter is used...... the data on the sheet starts when the button is pushed, which is often prior the gas pedal hitting the floor.
In that scenario, the numbers on the sheet below stall speed are at less that wot.

This is how you can end up with these oddly shaped graphs.

It’s not the same type of test as if there were a load cell and the throttle could be opened, the load stabilized against the brake, then released....... so that all data on the “run” would be at wot....... and the bottom of the run would start at stall speed(which could easily be at a higher rpm than where the motor makes peak tq).


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: Unexpected Dyno Results [Re: ZIPPY] #2527960
07/27/18 04:56 PM
07/27/18 04:56 PM
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Michigan
MarkZ Offline OP
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Originally Posted By ZIPPY
That 5th Avenue big block sounds cool as heck, I'd really like to check that out sometime.


Absolutely, send me a PM. I'd be game for hanging out sometime.


1987 Fifth Avenue - 512/518/D60
Re: Unexpected Dyno Results [Re: MarkZ] #2527963
07/27/18 05:00 PM
07/27/18 05:00 PM
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Michigan
MarkZ Offline OP
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So the most likely culprit is the converter then. I'm open to opinions on what to run. It's a bit weird since I have a lock-up 46RH transmission in the car. Current gear is 4.10, but I wouldn't mind going back down to a 3.23 providing I can get that torque curve where it should be.

I'm looking at a track day next month also. I'll have time slips before I spend anymore money on parts.

Thanks guys.


1987 Fifth Avenue - 512/518/D60
Re: Unexpected Dyno Results [Re: MarkZ] #2527968
07/27/18 05:05 PM
07/27/18 05:05 PM
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fast68plymouth Offline
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See if Jake can email you another sheet or two where the x axis’ are speed and time.

Do you know if the button to start recording was pushed before or after getting to wot?

My “opinion” on it is...... if the motor were tested on an engine dyno, the numbers......as well as the shape of the curve....... would look very similar to the sheet I posted.



68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: Unexpected Dyno Results [Re: MarkZ] #2527994
07/27/18 05:56 PM
07/27/18 05:56 PM
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A drum-RPM vs Engine-RPM comparison could show if there's any transmission or tire slip on the dyno.

In what gear was the run made?
Haven't seen it mentioned but I presume it's not a manual valve transmission, so maybe the throttle linkage is/was adjusted back a little too much to prevent a downshift during the run?

Re: Unexpected Dyno Results [Re: MarkZ] #2528021
07/27/18 06:42 PM
07/27/18 06:42 PM
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low gears and loose converters can give lower than expected numbers.

Re: Unexpected Dyno Results [Re: MarkZ] #2528041
07/27/18 07:51 PM
07/27/18 07:51 PM
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68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: Unexpected Dyno Results [Re: MarkZ] #2528061
07/27/18 08:43 PM
07/27/18 08:43 PM
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I've had my Dart on a hub-mounted Eddy-dyno about 3 sessions already.
It at least takes out the possible tire-slip (not that the engine in the car would be able to spin the wheels on a regular dyno that is...).



Re: Unexpected Dyno Results [Re: MarkZ] #2528079
07/27/18 09:47 PM
07/27/18 09:47 PM
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polyspheric Offline
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The HP and torque cross at 5,252 - always, they're supposed to (if using std. notation).
What reason is there for violent peak torque at the same place: 5,252?
None I ever heard of - tht's very close to the point of maximum VE.
With that small a cam, torque should be nearly flat from 3,500 up (not 200 @ 3,500) and fade slowly after 5,000 (the curves after 5,252 look possible if disappointing).
I don't know what a bad (mechanically failing) converter will do, but I never heard of a converter that sucked up 50% of the power @ 3,500 RPM (200 vs. 400).


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Re: Unexpected Dyno Results [Re: MarkZ] #2528101
07/27/18 10:51 PM
07/27/18 10:51 PM
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If you look at the runs zippy posted, the curve starts down under 3000rpm, and shows about 200ft/lbs.
Obviously that part of the recorded data is not taken at wot....... since the car has a 4600 converter.

Any data under the stall speed is not an accurate picture of the power at wot....... since you can’t be at wot and under the stall speed at the same time.

A quote from the article in the link:
Quote:
“Although some of the latest dyno software adds sophisticated formulas and assumptions in an attempt to correlate rear-wheel numbers with flywheel numbers, there is really no way to measure, predict, or otherwise determine engine flywheel power from a chassis-dyno test with any repeatable certainty, particularly when using a common acceleration test.”


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
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