Hey all,
Everybody is all about the horsepower at the rear wheels these days.
I had a question about it though. Does your gear ratio affect how much horsepower you are getting to the rear wheels? If you had a car with 3.23, say putting 400hp to the wheels, then change only the gears to 4.11s, does the horsepower go up? If not, does it increase the torque? You are increasing your mechanicial advantage, aren't you? Is that why they don't hear about torque at the rear wheels? If the HP does go up or down... is it really a valid number? On a dyno, everybody (generally) is on the same playing field.
Or is it just to be able to say the coveted "I got XXX horsepower" bragging rights. It's my opinion that ETs are the best judge of your cars overall performance, (speed wise, not corning, etc..) Not the HP numbers, you can "1000HP" on the street, but if you can plant it, what good is it? I guess it's good for two reasons, to be able to say that you have 1000HP and that in some weird way to justify all the money and time spent on your car.

Later.
John

 

I'll try my best at this but the answer is NO. If you have 4.56 gears or 2.23 gears you will still have XXXXX hp. All the gears are going to do is determine the amount of rotation needed by the engine to spin the wheel one time. Your transmission plays a role in this also.

Torque is the same way. But it gets a little bit more complicated here. Gears won't change the amount of torque your system "physically" puts out. It will affect the amount of force applied to the road though.

I remember seeing a post on this a while back so you might want to check there for more indepth information. Hope that gives you "some" help and doesn't completely confuse you.

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'91 Z-28 5.7, SLP 1 3/4 headers, 4 inch Mufflex/Flowmaster cat back, gutted cats, Edelbrock intake, 8.5mm Jacob wires, MSD Blaster coil, S&W subframe setup, Jacob Pro Street Ignition, complete Kenwood system.

 

i missed the thread earlier but, i could think of one condition where it might possibly factor in.

I think dyno jets have rear tire speed limition. It might be associated with the tire type, but often times you will see them cutoff at 110 on some LT1s that don't have Z rubber. Anyway, if the motor is not in the area of the peak powerband, before this speed-limition comes into play, it might actually show as significantly less hp.

Another thing the dynojet is very sensitive to is rotating mass. The slighest reduction in drivetrain rotating mass, will show up as one or two hp. The net effect on the road is not as significant.

[This message has been edited by jcb999 (edited July 26, 2001).]

 

I have to agree with you, who cares how much power your making if your car is slow. I think rear wheel dyno came about because of all the electronic, wires, hoses and crap they put in cars now-a-days - its a pain to pull a engine and dyno it alone. But I have one major problem with a rear wheel dyno - it doesnt tell you how much hp the "engine" puts out. Example, my 67 is making 525 to 550hp - thats a realistic guess and has gone 10.80s@125. But my buddy has a 67 camaro race car, it made 650 on a engine dyno and the car only went 10.30s@129. Thats only .5sec and 4mph faster but his engine has over a 100 hp more then mine. ----> MY POINT is I have a 350TH with a 12-bolt while he has a 400TH (which gives up 1 to 2 tenths), and a dana 60 (which takes alot more power to turn.) Both cars are 3200lbs, and another reason why his is quicker is his 60' is mid 1.40s, my car is mid 1.50s on a good day. SO a rear wheel dyno will not tell you how much power your engine is making and you will not know if you have a good engine combo. You could have a killer engine making 700hp but if your drivetrain, car set-up, exhaust, suspension suck it will not be fast, eventhough you have an awsome engine thats making good power. Just look at a 5.0 mustang - a 400 hp engine will get you around 12.0s but a late model camaro is just not as efficient of a car, it may only go 12.50s with a 400 hp engine. I've seen those things make 650rwhp and go mid 10s - THAT SUCKS, it should go mid 9s. I like knowing that my engine puts out good power for what it is, not having to wonder "why is this thing so slow when its go XXXrwhp". With a rear wheel dyno you just dont know if you have an efficient engine or not. To me their only good for one thing, no not that, for making mods and seeing if they make a difference and thats it


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91 B4C 305 TPI - SOON TO BE 383
TREMEC 5-SP, STOCK 1-BOLT REAREAND w/342 GEARS, K&N, AIRFOIL
EDELBROCK HEADERS, DUAL CAT TO HOMEMADE Y-PIPE & 3.5" SINGLE PIPE W/ FLOWMASTER, CRANK PULLEY, MSD, FUEL PRESS REG, COWL HOOD, WELD WHEELS
14.1@ 98MPH
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OTHER RIDE
67 CAMARO - STREET CAR, BIG BLOCK, PUMP GAS
350TH w/ATI 10", 12-BOLT w/373 GEARS
10.94@124.13 ON MOTOR - ET-STREETs w/MUFFLERS

 

A way to measure driveline drag is to keep the dyno running after a pull and put the car in neutral and see what the negative torque numbers are. That should factor in rolling resistance and gear drag.

 

My '86 IROC has 4.11s.

It is faster than my '87 IROC by a country mile but I can feel the motor struggling with the same problems that my '87 does, just faster because the gears allow the motor to spool up easier..

Example: I raced a new LS1 Vette, we were neck and neck (I was maybe ahead by a few feet) but as soon as I hit 2nd gear he was playing with me..

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