Perdi

There is one thing I don't get about that formula.... Shouldn't the loss be a constant number? What I'm saying is that for example if you had 100 HP you would be at 85 RwHP, but that number should be the same regardless of the total HP cause it's still moving the same amount of mass. I realize that there has got to be a slight difference but that much.... as the overall HP goes up? Is it some kinda law of Physics and inertia?

mills281e

Think of the drivetrain as an equal opportunity employer....it takes a constant percent off the top no matter what. More powercoming fom the motor causes proportionate losses through the drivetrain.

cheftjpeck

actually S197 : standard parasitic loss is avg 15% and automatic is 18% but does increase when blown due to the torque converter slipping and not locking correctly with torques in excess of the rated 360
so 18-20% is the parasitic loss on a blown s197 auto

mills281e

Pardon the oversight.....superchargian is my primary language now

Mikes_BLK_GT

I'll have one eventually wether it's 18 or 20, but I'm begining to think it's gonna cost me jewelry on top of the 5-7k price tag[&:]lol

If you upgrade or change your trans you can reduce those numbers. I would think some kind f upgrade would be advisable over the stock auto when going with FI anyways. I have seen alot of posts lately with peopleloosing 3rd gear in the auto's which is a weak point.

SCCAGT

I gotta Kinda side with Perdi on this deal about % lost through drivetrain. Automatics, ok, I can see the loss being the same % to an extent. But manual transmissions, it seems to me, would not have the same formula apply. There is no slipping unless clutch doesnt hold. Gears are gears. To me, it doesnt seem logical that a manual transmission is going to take away more horsepower just because an engine is modified to produce more.
Lets say a 200hp rated engine puts down the standard 85% of 170hp. A 30hp loss.
The same engine bumped to 300 would put down its 85% of 255hp using this method.Or would it be 270hp? 30 hp loss. I know we have a variance in dynos, cars and test conditions. But dont both those numbers (300hp) pretty much fallon the end rangesof what a stock GT dynos at?

Just to throw something else in the mix. Lets say we have a 850rwhp car, does it make 1000hp at the crank? The trans and drivetrain would naturally have to be beefed up to handle that much. Heavier gears, stronger clutch, etc. So with those changes to the trans, the 15% formula would still seem like a logical approach. But, again when you increase or decrease the power from same engine, through the same driveline. Is it still going to be 15%? I honestly dont think so. Its just become a close way to "guesstimate" flywheel hp from dyno numbers.
My car dynoed at 450rwhp with no other modifications after Procharged . It wasnt dynoed before, so no way for me to compare. 85% formula says 517hp at crank. Did I lose 67hp through the drivetrain or the 50hp it loses in stock form, assuming it would have dynoed at about 250rwhp? ProCharger is who dynoed and tuned my car the first time around, just to eliminate any hater responses.
The last issue of 5.0 had a S197 5 spd with Procharger and Corsa axle-backs hit 466rwhp. Before and after dyno runs showed an increase of 191 hp. Baseline was 275rwhp. A 25 hp loss assuming engine itself hit 300. So whats final engine power now, 535hp or 491hp?

This whole idea is probably just too much nit-pickin, but jeez, the way some people react to horsepower claims (Like the idiot Brit TV car show host, his name escapes me), it seems as though this discrepency would have beenrooted out a long time ago.

So who has the ability to figure this one out. Dyno an engine/trans combo in a car, remove it and use an engine dyno. Then hop it up, engine dyno it, stick it back in the same car and dyno it again.
I know, letsALL write in to one of the Stang mags and see if they will do it.

slySTANGguy

Power is equal to pounds times velocity. Take the angular velocity of the shaft times how many pounds of force is there and you get Force and Velocity. Or Lb*ft/seconds. 550lb*ft/s is equal to 1 horse power. The transmission will suck up some of that force, say about 15 percent of it. There for 15 percent parasitic loss. Correct me if i am wrong.

jrm1900

Must of us take the 450rwhp limit as a universal truth, I'd like to know where this number came from.

Stkjock

I'm with Perdi.. its gotta be some what of a constant....the fact that more power is at the crank should not affect the amount of force needed to rotate the clutch/tranny/DS/axels/wheels & tires.

the hard(impossible) thing to know is what is the S/C taking away in HP to drive it on top of the drivetrain loss. My guess (total guess) would be a total of 65-70 HP from that combo of S/C and DT.

Thought????

jrm1900

I also agree with the fact that drivetrainHP lossshould not be proportional to crank HP, as friction, rotational inertia etc remains the same for a particular car, I think the .85 factor relates to a stock GT.
Now the HP the belt driven SC is taking to do its job has nothing to do in the equation because we are talking about BHP vs RWHP, at the crank the engine is making its net power doesnt matter what is on it or how much power the SC and other accessories are using.
As a noteFord advertises the Whipple HP SC @ 500 BHP and Whipple posts 465 RWHP for the very same setup.
I guess the only way to find out would be testing the same engine on a bench dyno and then on a car dyno, any volunteers?