View Full Version : Why do I lose so much through the transmission?
GeordieSteve
05-06-04, 17:53
Been on the rolling road today and got these results
Click here (http://www.thegeordieconnection.com/stevep/supra/suprabhp.gif)
How am I losing 83bhp through the transmission?!?!?! Flywheel figure looks good for standard but the at-the-wheel figure is terrible surely?!?! :blink:
Because he's just guessing the Flywheel figure?
GeordieSteve
05-06-04, 18:06
Does the flywheel figure look about right for 246bhp at the wheels? :looney:
No mate it doesn't look right at all.
246bhp at the wheels means it's losing over 32% through the drive train (if you believe the 326bhp flywheel figure)
If your car is making 246@wheels, and you assume a 20% drivetrain loss, that would work at to 295bhp@flywheel, which is believeable for an unmodified J-Spec (is that what you have?)
I 'm guessing that the dyno guy has just put down the figure from 'the book' as the flywheel power.
Tannhauser
05-06-04, 18:57
Originally posted by Jake
No mate it doesn't look right at all.
246bhp at the wheels means it's losing over 32% through the drive train (if you believe the 326bhp flywheel figure)
If your car is making 246@wheels, and you assume a 20% drivetrain loss, that would work at to 295bhp@flywheel, which is believeable for an unmodified J-Spec (is that what you have?)
I 'm guessing that the dyno guy has just put down the figure from 'the book' as the flywheel power.
I can't make that a 32% loss. I make it a 24.5% loss. Like this: (326-246)/326 * 100 = 24.5%. A number of rolling roads seem to use a figure of 25% loss to calculate flywheel bhp for autos.
He seems to have used 24.5%, an odd figure to use unless (a) he's got some magic formula or (b) as Jake says, he's looked up the book figure and adjusted accordingly.
My money is on (b), because the 249 and 329 bhp at the bottom of your scan uses a slightly different ratio. What he's done there is just added on three to each figure.
Your figure comes out similar to 'SoopDog's on here, so it looks about right for an unmodded one? I'll attempt to link the thread, but this usually ends in failure for me:
http://www.mkivsupra.net/vbb/showthread.php?s=&threadid=5582&highlight=transmission+loss+auto
Cliff
It also depends on the gearbox, manual or automatic...
When I took my Jspec on a rolling road first time I had about 240Bhp, but that was because of a boostleak. :mad:
GeordieSteve
05-06-04, 19:06
Buggery :( It's an Auto J spec - 2JZ-GTE
Originally posted by Tannhauser
I can't make that a 32% loss. I make it a 24.5% loss. Like this: (326-246)/326 * 100 = 24.5%. A number of rolling roads seem to use a figure of 25% loss to calculate flywheel bhp for autos. Pete at Thor says to add 20% on the hub figure to get a guess at the flywheel figure. I just did 246 x 1.325203 = 326
I see what you're saying though Cliff:
246 + 32.??% = 326 is not the same as a 32% loss because I was putting it on the starting figure rather than taking it off the finally figure.
Maybe my workings out are differnt but I make 246bhp at the wheels 307.5 at the flywheel. My working out is as follows
246 at the wheels is 80% of the flywheel power (20% being approximate transmission losses)
so surely you divide 246 bhp by 80% to work out what 1% of the flywheel power would be then times this by 100% to work out total flywheel power.
i.e 246/80 = 3.075 * 100 = 307.5bhp at the flywheel.
Do you agree?
Originally posted by GeordieSteve
Buggery :( It's an Auto J spec - 2JZ-GTE
I've got a stock 93 J-spec TT. Last time on the rollers, 249 RWHP.
Gaz Walker
06-06-04, 09:36
Steve,
What power does there dyno take, I heard it was only like 400bhp or similar?
Gaz.
what gets out the back wheels is all that matters.
It's been said before, but try not to take much notice of total power figures. Use it as a baseline for any further modifications. The best way to do it is whenever you get any major modifications done and want to see what effect they've had take it bake to pete and then you can say it's running x amount over stock bhp.
Regards
Tony
GeordieSteve
06-06-04, 13:43
I dunno what the RR down there can take. First time I've been down.
I just wanted to know what my standard motor was putting out. From what I hear he gets lots of motors on the rollers. I'm gonna try it somewhere else and get another reading
I lose 57hp through my auto transmission according to the rolling road. That's 26% of my flywheel figure (220hp)
errr scrolling to the top of each and every page on this BBS allows you to see a GREAT BIG ADVERT SAYING IT WILL TAKE 1600 BHP!! :p
Originally posted by TLicense
errr scrolling to the top of each and every page on this BBS allows you to see a GREAT BIG ADVERT SAYING IT WILL TAKE 1600 BHP!! :p
:conf: i dont think he went to thor
Originally posted by TLicense
errr scrolling to the top of each and every page on this BBS allows you to see a GREAT BIG ADVERT SAYING IT WILL TAKE 1600 BHP!! :p
1600bhp on 4wd, 800bhp per axle. The CRD supra almost went over that when it was there :)
JB
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