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50bhp transmission losses?
Posted: Sat Jul 23, 2011 1:55 pm
by scudderfish
I was on the rolling road today (thanks Perry!), and made circa 160bhp. However I appear to be losing about 50bhp to the transmission. I'm running an LT77 and the rear axle from a V6 Capri. What could be causing such a loss? What can I do to fix it?
Regards,
Dave
Posted: Sat Jul 23, 2011 2:18 pm
by sidecar
I have an R380 box and a Ford Cosie diff, I also have a 50 BHP loss. Basically its normal to lose this much power, annoying but normal!
The BHP is converted to heat, vibration and noise.
Posted: Sun Jul 24, 2011 12:01 am
by kiwicar
Look at the sort of loss you get through an auto box, high stall torque converter, a heavy duty axel like a ford 9" and a set of crinkle wall drag slicks. I am allowing for about 130 to 150bhp loss from the transmission set up I am puting in the new project and yes it all goes in noise and heat.
Best regards
Mike
Posted: Mon Jul 25, 2011 8:58 pm
by scudderfish
OK, so I'm really worrying for nothing
Posted: Tue Jul 26, 2011 9:59 am
by kiwicar
Hi
You are a long way from worrying about nothing. Transmission power losses should form a big part of the overall desision making process when you decide which engine to select, weather you go auto with torque converter, manual single clutch or semi auto twin clutch set up. Back axel choice again has a huge influance on overall losses, the ford 9" for instance is relativly inefficient, even compared to similar sized axels, I have chosen one for 2 reasons, 1/ I don't think it will break even if I put as mauch power through it as I can get out of a blown SBC on methanol
2/ It has the selection of ratios I want.
I put the information in because I was trying to illustrate that biggest is not necessarily best in all circumstances.
Best regards
Mike
Posted: Tue Jul 26, 2011 12:05 pm
by CastleMGBV8
Be aware that rolling road operators also tend to overestimate the the power losses through the transmission to flatter flywheel BHP figures to keep their customers happy!
Kevin
Posted: Tue Jul 26, 2011 12:49 pm
by Ian Anderson
What tyres and were they at correct temperature and pressure?
It's actually amazing how much drain they can take just to get them to rotate
Ian
Posted: Tue Jul 26, 2011 9:09 pm
by davemgb
Ian Anderson wrote:What tyres and were they at correct temperature and pressure?
It's actually amazing how much drain they can take just to get them to rotate
Ian
And unlike on the road there are two contact patches on the rollers for each tyre which increases the power loss. If you take it to extreme you could even worry about whether both tyres give the same rolling circumference through out the speed range run on the rollers otherwise your needlessly working the diff internals.
Dave
Posted: Wed Jul 27, 2011 7:42 am
by stevieturbo
Ian Anderson wrote:What tyres and were they at correct temperature and pressure?
It's actually amazing how much drain they can take just to get them to rotate
Ian
estimate being the correct word. I dont see how they can accurately measure transmission losses anyway.
Doing a coastdown as some do will not measure losses, as the entire drivetrain is in a totally different state than when it is loaded up during a power run.
Stick with wheel figures and you may be closer to something useful
Posted: Wed Jul 27, 2011 12:34 pm
by SuperV8
Was the 160 the measured wheel power or guestimated engine power?
If it was the measured wheel power then I would suggest that 50bhp losses is too high.
Using the formula in the link below to 'estimate' engine power from a measured 160 RWD power = 193bhp
http://www.pumaracing.co.uk/trans.htm
Tom.
Posted: Fri Aug 05, 2011 4:46 pm
by kokkolanpoika
My rv8 with LT77 has got only approx 35hp loss. My first 3.5 made 173rwhp and approx 210hp flywheel.
When repuild this box i bought same time 4.6l engine and it mede 243 or 246rwhp and approx 281-283hp flywheel.
5.2litre made firts dyno run when it runs lean 285rwhp and 322flywheel next year 301rwhp and 334hp flywheel.
So 50hp is way to mutch without slipping clutch or ford 9"..
All numbers measured same bosch dyno.
Now i´m running Tremec T5 and hope same loss power.
Posted: Fri Aug 05, 2011 5:23 pm
by scudderfish
What did you do to your 3.5 to get those figures?
Posted: Sat Aug 06, 2011 1:38 am
by unstable load
Dredged up from the dim recesses of my mind is the memory that the Mercedes Benz 450SL in automatic guise lost in the order of 35kW to the drivetrain and ancillaries.
Posted: Sat Aug 06, 2011 7:03 am
by kokkolanpoika
scudderfish wrote:What did you do to your 3.5 to get those figures?
std range rover 3.5engine with 9.35compression ratio, SD1 exchaust manifold,+ 2.45" secondary pipes + 3" main pipe. Vitesse camshaft + ECU + adjustable fuel pressure regulator witch will give last 4hp when i set it up to 2.9bar. Slightly "ported/cleaned" heads, ported and fully polished inlet manifold. -30mm shorter trumbets. + efi range rover dizzy with SD1 advance spring and weight.
Dyno sheet available..