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Discussion Starter #1
My new 383 dynoed on the stand at 440 HP. After it was installed, it was dynoed on the chasis dyno and only got 292 RWHP. Is it normal to lose 150 horsepower through the drive train? I have a 700 R4 tranny. They tried to tell me that it lost a few horses because the tires were slipping on the rollers and 292 HP was about right after drive train loss. How is it possible to lose traction once the car is up to speed/RPM on the dyno's rollers???? The tires are 245-60's and should be wide enough to maintain a constant grip. I thought that traction wasn't an issue if the pull is gradual. It was a Dynojet dyno if I am correct. If the normal ratio of power loss is 20-25%, I figure at most I would lose 110 HP through the drive train. That should still give me 330 HP at the rear wheels. I know they didn't open the hood and use a fan to simulate wind at high speed. I am not sure if that would make a significant difference anyway. Please help! Any comments are appreciated. :( Thanks, DeAngelo
 

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I have normally calculated loss with a 700r4 closer to 15% per drive wheel. Posi-trac rear? 30%. However I feel that number is a little low....HMMM
 

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what changes are there between the engine on the engine dyno and chassis dyno? It was dynoed on an engine dyno, not by a computer dyno deal, right? Was the engine dyno with open headers, etc.?

The numbers are low and depending on how you answer the questions I might try another dyno.

Jody
 

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I've done hundreds of dyno pulls on a Dynojet 248 and have never seen tires slip on the dyno. Tire slip would show up as a huge anomaly on the graph. We've dynoed some 440 hp 383's from a local builder and they also run about 290-300 hp to the rear wheels.
Here's some things to ponder:
What is different about your engine as it sits in the car and as it was mounted on the engine dyno? Did you put the dyno headers in your car? Did you put the dyno mufflers on your car? Did you mount any more belt driven accessories? Did you use the same cold air to the carb as the engine dyno did? Did you try locking the converter? Were your tires fully inflated?
 

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Corrected (perfect air/ altitude) #'s from engine dyno, vs real world conditions on chassis dyno maybe?
What is you altitude and air conditions where you did the chassis dyno test? Do you have a DA reading from both dyno tests?
 

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Lets get some more specs on the motor> Also...from what I have seen 290 to 320 to the wheels seems about norm for street bound 383's going through an auto.
 

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Discussion Starter #9
WOW! Thx! Great answers! The original engine dyno was with open 1 3/4" headers and no mufflers. It also had no accessories attached. On the chassis dyno, the car was as it is on the street. I have AC, power steering, non-electric fan, alternator, 1 5/8" Thorley Tri-Y headers etc. And if it did slip, it didn't appear so on the dyno graph. I just thought that it was a HUGE difference in HP. I guess the fuel mixture was right. I am not good with that type of thing. It was between 12 and 14, whatever that means. :) And yes, it has a posi-traction rear end. I would imagine that it would also cause a reduction in HP. I have a pic of the chassis dyno run but don't know how to attach it. I would love to do so if anyone could help me with posting it. I will have the engine dyno pic later this week. I am in Virginia and it was about 60 degrees when they chassis dynoed it. I also noticed no anomolies in the dyno graph. It was very smooth. Makes me think that there was no slipping. And the tranny has a 3,000 non-lockup stall if that helps. Thanks again, DeAngelo
 

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If you dont have a decent air filter, exhaust / fuel / ignition system like on the dyno then youre leaving a ton of power on the table.
 

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I've had my car on two "roller" chassis dynos and it slipped on both, wasting my tires and my time.
Maybe find someone with a Dynapack. No possibility of tire slip on these and sensitive enough to see load on the alternator from switching on headlights (so they claim).
http://www.dynopack.co.nz/

http://www.youtube.com/watch?v=RJtV5shYoAs
http://www.youtube.com/watch?v=_WiS_o007Ew (that's me!)
Steve,

I would say they didn't know how to strap the car on the dyno, and at what position to place the tires on the roller. I've made well over 800 rwhp on a Dynojet with no tire spin and street tires.

Jody
 

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Steve,

I would say they didn't know how to strap the car on the dyno, and at what position to place the tires on the roller. I've made well over 800 rwhp on a Dynojet with no tire spin and street tires.

Jody

What I was thinking too.
 

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I've had my car on two "roller" chassis dynos and it slipped on both, wasting my tires and my time.
Maybe find someone with a Dynapack. No possibility of tire slip on these and sensitive enough to see load on the alternator from switching on headlights (so they claim).
http://www.dynopack.co.nz/

http://www.youtube.com/watch?v=RJtV5shYoAs
http://www.youtube.com/watch?v=_WiS_o007Ew (that's me!)
I watched your dyno video labled "thats me".
Who is the person standing in front of the car at full throttle while running on the dyno loose enough to slip the tires?
Have they never seen a car come loose and fly off the dyno?
Looks like a foolish place to stand.
 

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Discussion Starter #15
My point exactly. How could the tires slip when the power is applied gradually???
 

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Discussion Starter #17
Good point, Jody. Thank you for the response. Overall, I get the impression that 292 at the wheels isn't too bad. I justthought that the difference between the 2 dynos was HUGE! I didn't expect such a big drop going from engine dyno to chassis dyno. I just want to be faster than a rice burner or a new Mustang GT. :)
 

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Discussion Starter #20
The torque numbers were a max of 282 at about 5000 RPM. At 3500 RPM, torque was 200 at the wheels. At 4000, it was 250 at the wheels and went up to a max of 282 at approx 5000. Don't get me wrong, the engine has nice power. I can SCORCH the tires and it pulls HARD. I just want every horse I paid for. :) I expected 330 at the wheels with an engine that produces 440 on an engine dyno. I wonder what it will do in the quarter or 0 to 60. I have a printout of the chassis dyno but can't upload it without a link.

And Tom, my compression is 9.5 to 1. I have a Professional Products Hurricane intake (Edelbrock Air Gap RPM copy), Holley 770 CFM Avenger, Lunati cam with 235 intake and 240 exhaust duration with a 490 intake and exhaust lift at .050 with 112 degree lobe separation. The heads are the Holley aluminum ones. The heads and cam were part of the Holley SytemMAX 2 package. My tranny is a 700R4 with a 3000 stall and a 3.73 Posi rear. My tires are cheap no-name 245/60 14's!!! I can melt those cheap tires! I am going to buy some 275/40 17 inch Nitto 555's soon. Hope that helps, Tom.

DeAngelo
 
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