Drivetrain HP Loss

[stang22]

We were discussing this in an earlier thread, but I wanted to get some expert opinions. Many people say 15-20 % loss, but I disagree as you get up into higher HP ranges.

Is drivetrain HP loss static, or is it a percentage? I.E.- Will a car making 1000 FWHP really lose 150 HP through the drivetrain? Take that same car, and put a 300 FWHP engine in it... Will it be the same amount of HP loss, or will it be 15-20% of total HP?

Tim

Here is the orginal thread. http://forums.stangnet.com/showthread.php?t=448855

A section of an article from Superstangs.com;

Lee Bender of C&L Performance and Paul Svinicki of Paul's High Performance are both well versed in evaluating Mustangs on the dyno, and they both agreed that extrapolating drivertrain horsepower loss via percentages is flawed. Lee believes that the stick Mustangs experience roughly a 35hp loss through the drivetrain, whether they make 200 hp or 400 hp. He did explain that ultra-high-powered vehicles - typically race cars - can be an exception to this rule, but that's a topic for another time. Interestingly, a 35hp loss for stick-shifted drivetrains is strikingly similar to the difference between Ford's horsepower ratings and the rear-wheel numbers we've observed on dynos across the nation. Hmmm...

 

[thumper460]

You know... I have been asking also on the power loss thru the drive train... 10-15% on standard trans and 20-25% with an AOD and I have heard as high as 30-35 % on C4 with loose converter !! I think it is all up to the whim of the dyno tech... or the engine owner!! It really all comes down to putting the car thru the qtr mile... weight to MPH = to the ground HP!! Ets and 60 fts can change but the MPH at the end is always within 1-3 HP!! I agree the HP is a good indicator... but the truth of the matter is.. first one to the end wins!! HP, torque, tires, trans, Power adder... mean nothing but bragging rights and when you finish second in a two car race, what do you say?? " I finished second in the car race??" My self I never really cared on FWHP or RWHP, if I was cutting 12s and wanted faster .. I would try to find more power ( just like all of us , I guess) Lately I have found my self concerned on FWHP/RWHP.. and I decided I'll figure it out once as referance and the then just blow the other guys doors off, and brag about winning ... not how much HP I have and LOST!! Cool?? There are a few formulas out there with gear ratio/mph/tire size and rpm.... but I'll keep trying to find it!! come on Stangnet... how do we figure this out???????

Just me..................................

Thumper

 

[Michael Yount]

It is a thoroughly academic debate. It varies with every driveline. It's virtually impossible to know for sure what your driveline losses are. You would have to dyno the engine complete with accessories and similar motor mount configuration, as well as full exhaust system. Be sure to measure ambient, oil, tranny fluid and coolant temps because they'll have to be duplicated - which will probably mean installing coolers on oil and tranny so that temps can be held the same. And then, with the engine in the car, do a chassis dyno, under indentical conditions, and with a type of dyno whose output could be directly correlated with the engine dyno. Even then, simple things like not tightening the hold-down straps on the chassis dyno tight enough can account for as much 10-15HP difference on a run. Rear tires alone can make for a 20-30HP difference between 2 'identical' cars run on a chassis dyno.

It would take megabucks in gear, time and effort to get a valid comparison in order to subtract the readings and get a true driveline loss. And even then, it's probably slightly different in 1st gear than it is in 4th gear. So given all that, people use percentages to try and obtain one reading from another. But, it's not much better than a guess. The loss itself is probable closer to a static figure than a fixed percentage - but even that's not always true. When the same rear end and tranny is turned harder (more power), or to higher rpms, temps increase and the resistance/friction losses probably increase as well.

 

[Musclecarfan88]

As far as I understand the more hp the engine makes at the flywheel the less % of hp that is lost through the drivetrain. soo for a 300hp car it may be a 15% loss but for a 500hp car it may only be 10%.

 

[Michael Yount]

....and if you actually do the math you've proposed above, while the % drops, the actual driveline loss has increased - 45HP loss for the 300HP engine; 50HP loss for the 500HP engine. But it's all conjecture - none of it is based actual valid data because it's virtually impossible to find anyone that's actually done the accurate testing.

 

[stang22]

It really all comes down to putting the car thru the qtr mile... weight to MPH = to the ground HP!! Ets and 60 fts can change but the MPH at the end is always within 1-3 HP!! I agree the HP is a good indicator... but the truth of the matter is.. first one to the end wins!!
Thumper

Mike,

I totally agree with you, it's how you use the horse power. I have never been concerned with FWHP or RWHP. If it feels slow, it ussually is. I figured this would be a good thread to open up with a bunch of "interesting" theories.

Another interesting thought to ponder is the rear wheel dyno. Because the car is not acually moving the weight of itself, or in motion, how accurate can a RW dyno be? Does a lighter car put more HP to the rear, or does it just move the weight more efficiently? Someone give me some opinions...

Tim

 

[Schlodes]

To me a Dyno is useful for tuning. Start the 1st pull as you had the car when you got there... by the end of it all you will have figured out where your combo likes its timing, fuel pressure etc... and to me that is ALL I will ever use a dyno for or want to dyno for. I could care less how big looking the HP numbers is as long as it increased even if only by 3 RWHP by then end of the session. Because to me then I have gotten good use of the Dyno.

Track is where it matters and making my car hook, and running a quick ET is what its all about for me. I mean I used to have a 1987 T Type that in the 2000 season ran a bunch of low 12s.. best pass that year being a 12.26 @ 106 MPH cutting a 1.61 60'. My T would always cut consistent 1.6s. There were several cars there that day running low 13s/high 12s trapping 106 MPH. Lotsa 12.50 cars running 110-112 MPH.

In 2000, my T Type was set up in such a way that the motor, turbo, injectors, intercooler, downpipe etc were all stock parts. Trans was built with a convertor that would stall at 3K under 8 or more PSI, back brakes had larger S-10 wheel cyls, longer brake shoes, and had traction bars that bolted to the rear end housing, and relocated the upper control arms.... I would stage the car, mash the brakes and bring up the boost to 18 PSI [the car would literally start to creak..] then when the last yellow went.. with the brakes still mashed, i'd floor the gas, then let go of the brakes.. boost would spike to 22 PSI and off we went 22 PSI all the way down. It would lift the driverside front an inch and felt like getting rammed by a Peterbuilt when you left the line.

I never ever dynoed the car but I bet the numbers would not have been that impressive anyways. Would have been nice to dyno it just to see if I could find 10-15 more HP. Going to do the same thing with my Mustang... just work on making it hook for now,..

 

[thumper460]

Zackly... old school is take it to the track and run the numbers... timing change a degree here or there, fuel jetting up one or down, blah..blah... and then use the MPH as the tuning tool! with the F/I cars... there is a lot to look at.. unless the man with the tech is at the track to change the parimiters.. your sort of lost ( for the masses anyway) and the Dyno IS a good way to make the changes and read the HP increases..( or loss).. then when the track is there your just making mall changes like timing and maybe f/p. Cool?? Michael is right on, and it has always been my point... there are too many variables... on Bobs dyno, he says 10%, accross town Bills dyno says 12%.. run the same car on both and the numbers can be different!! I thing just using the numbers off the SAME machine as a base line and then tune form there!! cause they are all different!! with power adders..?? yeah I guess it is cool to say I have 450 RWHP !! yep, I'd be afraid of that dude... untill I had to find a 1/2 wrench to let him use to bolt his doors back on, cause he cant HOOK IT!! and Old school... that IS the drag race.. all other racing is just that..Other racing!! LOL Dont know about your place.. but here they have started freeway racing..50 MPH roll and the first to 140 wins!! Cause all these boosted cars cant get moving !! And that type racing is pissing me off!! Hell yeah, I'm topped out just a few feet form the end of the 1320 ft mark!! LOL Oh well... times change I guess!! LOL Cool on the heavy car vs the lite car... both will or can make the same power at the rear wheels...say 300 RWHP on the dyno...cool?? but at the track.... guess who wins all the races..?? yep the Supercharged Mini Cooper S ( had to put that in there...LOL) ...

Just me......................

Thumper

 

[Michael Yount]

There's a good article about the differences between different types of dynos and their characteristics in this month's Hot Rod magazine -- those of you interested in things like how vehicle weight impacts the accuracy figures on an inertia-type (dyno jet) dyno should take a look.

They're very useful as a tuning tool - but even then you have to watch variables very closely. And, even then, comparing numbers between changes is only helpful on the same day, same dyno, same operator, same conditions. I wouldn't even try to compare numbers on the same dyno run on different days. It gets strapped down differently - numbers can be impacted. You changed your rear tires between runs - numbers can be impacted. The alignment on an irs car changed - your numbers can be different.

Dyno's for measuring absolute HP/torque accurately - you're fooling yourself unless you're in one of the major race team's/manufacturer's engine labs and even then, bolting the engine in the car can change things. Dyno's for making relative measurements to assess changes - useful -- but only if you're VERY careful.