Engine to Chassis Dyno HP lose

[Stan Weiss]

Not wanting take an old thread to far off, so I started this thread.

While must of this does not apply to this subject, there are a couple of examples where people say that they have seen much greater power lose between engine and chassis dynos than talked about here.

http://www.yellowbullet.com/forum/showthread.php?s...

Stan

[stevieturbo]

Stan Weiss said:

Not wanting take an old thread to far off, so I started this thread.

While must of this does not apply to this subject, there are a couple of examples where people say that they have seen much greater power lose between engine and chassis dynos than talked about here.

http://www.yellowbullet.com/forum/showthread.php?s...

Stan

That thread seems to be more about one builder/sellers claims, as opposed to discrepancy between dynos ?

I know little of autos, but they really do seem to be a massive variable as to what comes out the back end on a dyno.

[Stan Weiss]

Stevie,
Yes, that is what the thread is mostly about.

Extracted from some of the posts. Most post were about how the Mustang Dyno's numbers are lower than other chassis dynos.

---

That Mustang Dyno is a Heart Breaker our 620 RWHP 975 HP went 9.18 in a 3500 lbs car

620/975=.635 or 63.5% Something seems strange there.

Ive witnessed similar percentage of loss on a mustang many times. Reinforces the fact that the dyno is a tuning tool as opposed to a comparative marker.

Mustang Dyno, issue they don't give up the number like the others do. You want a bigger HP number take it to a different dyno. I dont care what the number is I just try to move it up.

=================================

We've seen from a real honest dyno

18/22% manual trans
29/32% auto trans

Loss to power at wheels

---

Stan

Edited by Stan Weiss on Thursday 9th July 18:26

[PeterBurgess]

Hi Stan

Olde Worlde auto transmission seems to sap power like no bodies business. Modern auto transmission seem much better. Having said that I have seen lock up autos show 10 more on 150 at the wheels than in straight 4th gear auto. I think, to be honest you are looking too hard to get a percentage loss. Modern gearboxes seem to be 97-99% efficient, already a discrepancy in percentages. Tyres and tyre speed makes a big difference too, nothing to do with percentages. Why not just work the maths on what you have at the wheels instead of second guessing what the flywheel power may be?

Peter

[Pumaracing]

Stan, when you type "lose" I presume you mean "loss" as lose makes no sense. Not that you make sense much of the time. This is a strange aberration though, to so frequently misspell a simple four letter word. Do you think dementia is setting in already or is it just an American thing?

[Stan Weiss]

Pumaracing said:

Stan, when you type "lose" I presume you mean "loss" as lose makes no sense. Not that you make sense much of the time. This is a strange aberration though, to so frequently misspell a simple four letter word. Do you think dementia is setting in already or is it just an American thing?

Dave,
Not yet. I am not sure when I will be following you on that journey.

Stan

[Pumaracing]

Ha! You couldn't follow me even with your guide dog and a small team of Indian trackers.

[Stan Weiss]

Dave,
You are right or is that write? While I may someday go on that same journey, there no way that I would ever want to take the same path as you.

Stan

[Stan Weiss]

I have been off doing some other things, and just got back to this and found this article. For me it was a very interesting read.

http://www.superstreetonline.com/how-to/engine/mod...

Stan

[PeterBurgess]

As I keep saying Stan, why not work out your maths using wheel power? I can never understand the back guessing to engine flywheel power, seems irrelevant to me. Too many assumptions such as no binding or problems in the transmission.

We are wiring the SF901 dyno in to the 'liberace' console tomorrow, may get to see if the WinDyn programme does anything. Still way off getting it going though! Shame you aren't over this side of the pond you would be most welcome to come and have a look.

Peter

[Stan Weiss]

Peter,
If all I was doing was looking to run a simulation then the chassis dyno numbers would be great, and I would have no problem using them. But lets say that a car you had on your chassis does a standing mile run and goes 201 MPH and a few cars later someone goes 207 MPH. The two owners talk to each other and the engine that went 207 MPH was on an engine dyno. It would be nice to see know if the car that went 207 MPH did it because of more HP or because of some other reason.

Stan

[PeterBurgess]

Strikes me you need measured flywheel and measured wheel power, dynos vary so ne'er the twain shall meet? I still don't see why it needs fly power when it is wheel power which does the job? Looking at this another way, once we get the SF901 up and running do you think I will hear the opposite question from usual.....what is that at the wheels?

Peter

[Stan Weiss]

Peter,
Yes, it is what is at the wheels which gets it done. But on this side on the pond I see more engine dyno numbers than chassis dyno numbers.

Stan

[PeterBurgess]

That's interesting Stan. Do you think that is because there are more engine dynos than chassis dynos Stateside or folk divulge more info from engine dynos?

Peter

[Pumaracing]

PeterBurgess said:

As I keep saying Stan, why not work out your maths using wheel power? I can never understand the back guessing to engine flywheel power, seems irrelevant to me.

That's not much help when what you've got to work from is flywheel bhp or OE manufacturer road car power curves. It's essential to be able to at least approximate transmission and tyre losses.

In fact much of the early work I did circa 20 years ago on establishing what true transmission and tyre losses really were was by computer simulating many cars tested by Autocar and Motor magazine and seeing what level of losses were required from the quoted flywheel bhp to match the tested performance. Now of course there's no guarantee that every car tested had exactly the claimed flywheel bhp but averaged over many simulations I was able to find very consistent patterns of loss which eventually gave rise to the loss equations for manual transmission cars on my website.

https://web.archive.org/web/20110909141356/http://...

In the 15 or so years since writing that I've found nothing to alter my view that these give a very close approximation of real losses for most cars.

[Stan Weiss]

PeterBurgess said:

That's interesting Stan. Do you think that is because there are more engine dynos than chassis dynos Stateside or folk divulge more info from engine dynos?

Peter

Peter,
I believe that different groups will have a different average usage between the 2 types of dynos. When I had my 4.6l Mustang that group used the chassis dyno much more than the drag racing groups I deal with do.

When you get your 901 up and running I do not know what output you are going to give people. But some here in the states give them the SFD files. I have had people send me SFD files and that is the reason I have the SF program to read and display those files on my computer.

Stan

[Stan Weiss]

Pumaracing said:

That's not much help when what you've got to work from is flywheel bhp or OE manufacturer road car power curves. It's essential to be able to at least approximate transmission and tyre losses.

In fact much of the early work I did circa 20 years ago on establishing what true transmission and tyre losses really were was by computer simulating many cars tested by Autocar and Motor magazine and seeing what level of losses were required from the quoted flywheel bhp to match the tested performance. Now of course there's no guarantee that every car tested had exactly the claimed flywheel bhp but averaged over many simulations I was able to find very consistent patterns of loss which eventually gave rise to the loss equations for manual transmission cars on my website.

https://web.archive.org/web/20110909141356/http://...

In the 15 or so years since writing that I've found nothing to alter my view that these give a very close approximation of real losses for most cars.

Dave,
There has been changes in automatic gearboxes over the last twenty year. Have you done any calculations with vehicles using the ZF 8H or 9H gearboxes?

Stan

[Pumaracing]

No Stan. I've confined my work almost exclusively to manual boxes.

[Pumaracing]

I was thinking about changing the cambelt on my Ford Focus after 14 years but it seems like a scutter of a job so I'll probably leave it until it breaks. I found a cracking video on youtube of how to do it though which made me think of you Stan. A good ol' southern boy from Tennessee or Louisiana narrating and honest to god you can hear his hound dog howling away in the background. I bet it lives under his front porch and gets used for chasing furriners off his land or catching possums.

https://www.youtube.com/watch?v=d4IgVvfovhA

[PeterBurgess]

Hi Stan

I am not sure what the files will be from the dyno, I think we will be using the Performance Trends SF901 dyno software. Our dyno has a lot of goodies on it which will only be any good run through a PC. Martin and I spent all day on the dyno installation today. It fired up sweetly and we were checking the barometric pressure. Next step prime it with water and see how it leaks. Lots of work still to do and I could see it being Christmas by the time we get it all running and produce some results. Lots of wiring to do on the unit yet.






Peter