[steve25]

Higher chassis dyno numbers from auto trans car you say?

[lust4speed]

No, the chassis dyno numbers are lower. The auto equipped car wastes more energy getting the power to the rear wheels. So to make up for this inherent loss the conversion factor needs to take this into consideration. A manual car losses "about" 15% getting the power to the ground. Basically the 1:1 drive only has some bearings taking a little power and the rearend, universal joints and wheel friction losses contribute to the remainder. An auto trans car also has loss through the torque converter, transmission pump, and other parts so it looses more. Someone before us came up with the loss ratios and did so hopefully by trial and error.

Looking at it from the reverse side, an engine that produced 400 horsepower on an engine dyno should be expected to produce about 320 horsepower in front of an automatic and 340 with a manual on a chassis dyno using the 20% and 15% losses.

[1968GTO421]

All great info. For fun I found this computation to get a rough idea of power:

https://www.mk5cortinaestate.co.uk/calculator4.php

[Radman]

OK, let's add another fly in the ointment. What if the dyno guy runs the car in drive with an overdrive transmission. For instance say a 700R4 where 4th gear is a 7/10 overdrive gear.

[grivera]

Originally Posted by lust4speed

Looking at it from the reverse side, an engine that produced 400 horsepower on an engine dyno should be expected to produce about 320 horsepower in front of an automatic and 340 with a manual on a chassis dyno using the 20% and 15% losses.

Paul Carter made a good point about not using percentages - the amount of loss would go up the higher the power output of the engine.

[Formulajones]

Originally Posted by grivera

Paul Carter made a good point about not using percentages - the amount of loss would go up the higher the power output of the engine.

Correct. I've only had a couple of cars that went from an engine dyno, then in the car and on a chassis dyno. The percentage numbers commonly thrown around never even came close to what I actually saw, didn't matter what trans or rearend was behind it, the difference was very large. Always been on a dynojet by the way, which usually reads higher than the Mustang dynos.

On an engine dyno, we almost always run the engine, no accessories, open headers (sometimes they are dyno headers which inflate the numbers), rarely ever has an air cleaner on it, and the engine temp is controlled, usually well below what you'll see in a car.

When installed in the car, the air cleaner is in place, a full exhaust system, all the accessories and belts, the hood is up with a fan blowing on it but it's really up to the car and it's cooling system to control temps, so you get much closer to real world running conditions.

I haven't had one yet that has shown less than 100hp difference from a dyno to the car, and I'm betting I have one here that's even worse.
Planning to put dads car on a chassis dyno, and we already know it made 724hp and 764 tq on an engine dyno running pretty much just as I described above, no accessories, through the chassis headers used on the car.
I'm going to bet it will struggle to push close to 600hp at the tire. More like upper 500's is what I think it will do.

[SD455DJ]

Originally Posted by 1968GTO421

All great info. For fun I found this computation to get a rough idea of power:

https://www.mk5cortinaestate.co.uk/calculator4.php

1968GTO421, That calculator shows 389 hp at the crank which compares very closely to the 15% guesstimate for a manual trans car. I know there are sooo many factors that make the comparisons suspect, but I was just looking for general rules of thumb, and it seems to work for the engine (stock 455HO with a hotter cam)...an interesting topic however. Thanks for everyone's input and insight.

Dennis

[mchell]

Originally Posted by Formulajones

Correct. I've only had a couple of cars that went from an engine dyno, then in the car and on a chassis dyno. The percentage numbers commonly thrown around never even came close to what I actually saw, didn't matter what trans or rearend was behind it, the difference was very large. Always been on a dynojet by the way, which usually reads higher than the Mustang dynos.

On an engine dyno, we almost always run the engine, no accessories, open headers (sometimes they are dyno headers which inflate the numbers), rarely ever has an air cleaner on it, and the engine temp is controlled, usually well below what you'll see in a car.

When installed in the car, the air cleaner is in place, a full exhaust system, all the accessories and belts, the hood is up with a fan blowing on it but it's really up to the car and it's cooling system to control temps, so you get much closer to real world running conditions.

I haven't had one yet that has shown less than 100hp difference from a dyno to the car, and I'm betting I have one here that's even worse.
Planning to put dads car on a chassis dyno, and we already know it made 724hp and 764 tq on an engine dyno running pretty much just as I described above, no accessories, through the chassis headers used on the car.
I'm going to bet it will struggle to push close to 600hp at the tire. More like upper 500's is what I think it will do.

^^^Exactly what I’ve found.......

[Stan Weiss]

I know someone in the UK that owns a rolling road. I don't know who the manufacture is. He told me that after the dyno test he can do a coast down test and then is able to give an approximation of flywheel HP.

Stan

[Lee]

Originally Posted by Radman

OK, let's add another fly in the ointment. What if the dyno guy runs the car in drive with an overdrive transmission. For instance say a 700R4 where 4th gear is a 7/10 overdrive gear.

I addressed testing in different gears in reply #15. Does not make a big difference.

What CAN make a difference, is being able to lock the clutch on some modern converters. With a looser converter, locking the clutch can make a 40+ hp difference, and make for a much more accurate graph.

[slowbird]

Originally Posted by Lee

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!

Any chance you have track results from all 3?

[Lee]

Originally Posted by slowbird

Any chance you have track results from all 3?

At an 1/8-mile track, I was running 7.0x with the green-line converter.

The red-line converter was MUCH tighter than it should have been, and cost me nearly a tenth just on 60' time. Don't remember exactly, but somewhere in the 7.teens-7.2 range.

The third was an experiment by the guy who made the green-line converter, using a hybrid 8" converter. I'll have to see if I can find the dyno for it. At the track, the car blew through that converter, not useable at all.

[Tom Vaught]

Originally Posted by Stan Weiss

I know someone in the UK that owns a rolling road. I don't know who the manufacture is. He told me that after the dyno test he can do a coast down test and then is able to give an approximation of flywheel HP.

Stan

I did Coastdown Testing for Ford Truck for 7 years (Both on the track and on the Single Roll Dynos at Ford and at the EPA).

We used to run at least 6 vehicles in both types of testing to get an AVERAGE Coast Down Time and calculated Road Load Horsepower to submit to the EPA.
Each vehicle would do a 14 run Track Test each night for several days in Florida or at the Proving Grounds in Michigan or Arizona. And there were 6 or more vehicles in each segment of the Vehicle Line (Mustang, Cougar, T-bird, F-150 Truck, F-250 Truck.

We would also run a test vehicle at the Lockheed Wind Tunnel in Georgia and weigh it at different curb weights to get body height, and Frontal Area effects of each segment in a vehicle class.

So when you take your single vehicle and put it on a rear wheel dyno and make a couple of pulls and then try to compare that with drag strip data, I have to smile as you are way short on the info you need to do the job correctly. When we did Emissions Testing we always ran on the same dyno for the series of tests at the EPA. The track testing, (14 runs 7 in each direction) each night for 10 days = 140 runs on actual track conditions to get a number that was close for EPA Testing. Most enthusiasts get less than 10 runs on a dyno test at a hot rod location.

Great bragging rights but actually, as some have said, does not match actual track data unless you actually run on a track under consistent conditions.

Discussions like this one as I said make me smile. Simulations are ok for discussion too but are not the same as actual Track Data under controlled conditions on the same day and testing is over multiple days with one driver using very expensive monitoring equipment to record the data, VS looking at a screen and writing down a couple of numbers.
Engine and Wheel Dynos can be "tricked".

Tom V.

[Tom Vaught]

Originally Posted by Tom Vaught

I did Coastdown Testing for Ford Truck for 7 years (Both on the track and on the Single Roll Dynos at Ford and at the EPA).

We used to run at least 6 vehicles in both types of testing to get an AVERAGE Coast Down Time and calculated Road Load Horsepower to submit to the EPA.
Each vehicle would do a 14 run Track Test each night for several days in Florida or at the Proving Grounds in Michigan or Arizona. And there were 6 or more vehicles in each segment of the Vehicle Line (Mustang, Cougar, T-bird, F-150 Truck, F-250 Truck.

We would also run a test vehicle at the Lockheed Wind Tunnel in Georgia and weigh it at different curb weights to get body height, and Frontal Area effects of each segment in a vehicle class.

So when you take your single vehicle and put it on a rear wheel dyno and make a couple of pulls and then try to compare that with drag strip data, I have to smile as you are way short on the info you need to do the job correctly. When we did Emissions Testing we always ran on the same dyno for the series of tests at the EPA. The track testing, (14 runs 7 in each direction) each night for 10 days = 140 runs on actual track conditions to get a number that was close for EPA Testing. Most enthusiasts get less than 10 runs on a dyno test at a hot rod location.

Great bragging rights but actually, as some have said, does not match actual track data unless you actually run on a track under consistent conditions.

Discussions like this one as I said make me smile. Simulations are ok for discussion too but are not the same as actual Track Data under controlled conditions on the same day and testing is over multiple days with one driver using very expensive monitoring equipment to record the data, VS looking at a screen and writing down a couple of numbers.
Engine and Wheel Dynos can be "tricked".

Tom V.

Simple Honest Question, but not a simple answer to that question.
A very involved process is required to get close to the right actual answer.
Many $$$,$$$s involved in getting actual close to reality answers.

Tom V.

[1968GTO421]

I think Tom's posts 33-34 provided the actual truth to the problem of determining true horsepower/torque. When I consider the costs of all the dyno tests generally available to most people, I begin to think that when Pontiac Jim in another thread said the "butt dyno" was good enough for him, he was right to some extent. If your engine/trans combo makes you feel good about the power you have then your good. If not carefully research the best ways to increase that power.

[Skip Fix]

I went to a "dyno day" then had a "computer tune on my '04 GTO-stock. Same shop but they had a Mustang and a dynojet. 10 HP difference before any computer tuning. One 280 RWHP one 290. Don't remember which.