Okay,
I've been wondering about this for quite some time. Some people say to subtract 15% for drivetrain, and other say 20% for drivetrain.

Which one is more correct, or is it involve an equation?



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1987 Firebird
2.8L Auto
T-Tops
New Paint last Fall
No mods yet...

 

i say 20% for auto, 15% for manual

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1989 Firebird
2.8 v6, t5 swapped in

Ram Hi-po clutch, Cold Air, 1.6 rockers (ready to install), Lakewood LCA's, Lakewood Lift bars, 3" y-pipe, Random Tech Cat, 3" I-pipe, Flowmasters, MSd 6a, MSD Coil (Fireball in future) Accel 8.8 wires, MSD Ignition Module, 4th Gen Seats (not front yet)

" I'd rather run last in a full out race, than to NOT run at all ".

 

I say it would actually also depend on the condition of your transmission.

 

good point
i think stock trannies with 130,000 take about 25%... so 135 hp - 25%=102...so everything should be in good working order

 

After helping build and building several cars there is no way to really generalize the power loss... Though we all cannot go down to the local dyno every time we add something on, a good place to start is like gramesfibird said to look at the condition of the parts being judged...
If they have been beaten up then the loss may not be as bad as you may think. In instances like this it can get the drivetrain "tuned" into a certain positon and help lock it into place. I have seen this happen on cars with as many as 130k miles, the loss was only 12 percent...
While a brand new drivetrain with 7k on it had 32 percent loss... Some thing do get better with age...

 

Thanx guys,
well my Trans and engine has 244,000KM (150,000miles) so I guess I just subtract the 25%, and maybe someday when I get it dyno I will be shocked, rather than pissed...

102hp, not the best, but atleast its a # to work with.



[This message has been edited by Joe_L (edited April 03, 2001).]

 

our cars are already rated at the rearwheels!

 

Is this true???

 

no its not true, they rate our engines at the crank.

 

they quiet rating cars at the crank in the early 70's!!

 

hate to tell u, but ur wrong.

Gross Horsepower: horses an engine makes at the crank before any accesories
Net Horsepower: horses an engine makes at the crank with all load bearing accesories on (compressor, alt, p/s etc)

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1989 Firebird
2.8 v6, t5 swapped in

Ram Hi-po clutch, Cold Air, 1.6 rockers (ready to install), Lakewood LCA's, Lakewood Lift bars, Wonder Bar, 3" y-pipe, Random Tech Cat, 3" I-pipe, Flowmasters, MSd 6a, MSD Coil (Fireball in future) Accel 8.8 wires, MSD Ignition Module, 4th Gen Seats (not front yet)

" I'd rather run last in a full out race, than to NOT run at all ".

 

yeah, from what i've heard, most cars are rated with Net HP and not Gross. So, we have 135hp with all the added accesories. I've heard that 2.8L's made 200ponies at the once, that might have been Gross HP, not sure. But worth finding out, you could brag the truth, saying my car's got 200 GHP !!!

 

yeah grames right..back in the 60's the manufacturers were using different rating systems. 1 would rate at the crank with no accesories and others would give the real use horsepower(all accesories on) then they would publish the higher number. The gov said no go and came up with rating at the crank with all accesories on period. The RWHP was never published because the numbers were rediculously low.
Try a 502 aftermaket block rated at 510 HP and 545Pds trq had only 336 hp at the wheels and 450 lbs trq. and this was in a 69 chevelle with a brand new 700R4 and rear end. Do you think that the GM aftermarket parts would advertise this number hell no! but thats what you have to look at.

 

Well, they also don't publish RWHP because it depends on EVERYTHING behind the motor, and with as many options you have w/ transmissions and gearing, it differs, so they just report it at the flywheel.