The engine makes the HP or TQ the gears only transmit it to the wheels. Granted changing your gears can help you accelerate quicker, make you run faster in the 1/4 or whatnot. Not to be rude but HP and TQ are 100% functions of the engine. Here could be an example a car with say 3.88 gears and weights 3500 pounds can run the quarter in 14 seconds and has 350 hp and 350 TQ. Take the same motor and put it in a RV with 3.88 gears that weighs 10,000 pounds it runs the 1/4 in 30 seconds. You still have the same HP and TQ just different applications.

 

I read that as RWHP numbers?

In which case, higher numerical = lower HP at the ground.

 

by higher number you mean lower gear ratio?

 

Well gald you mentioned that, because in pure theory (math) lower gears reduce rwhp or rwtq because there is a parasitical loose due to friction of more teeth in the ring and pinion set. This may be a very small amount but with pure theory applied it is reduced. Think of this, if you did a dyno run on a car with say 2.73 gears that had 350/350 at the wheels at say 6000 rpm and you swaped them out for 3.88 gears and did the same run. The hp and tq would still be the same at 6000 rpm. Actually by pure math it would be about 349.5 / 349.5 as you are spinning more gears. More teeth on the gears = more friction more friction = less transmitted HP / TQ.

 

Yes, say 342s to 410s, you will lose a few hp transmitted to the pavement.

 

you will have more torque to the rear wheels at 6000rpm with higher gears. However, the wheels will be moving slower, so the horspower will remain about the same (a tad less because of increased frictional losses).

 

In the real world lower gear ratios, higher number, usually make a quicker car not a faster one. (we will skip the math lesson)
In my case i have 3.88 and want to move to a 3.42 to have more top end speed. I want faster not quicker. Clear as mud i am sure now 167 @ redline is top now with a gear change 189 @ redline. But you can tell by my tag line i am a very sick unit

 

I guess that would explain why the world speed record was set with 2.73's...

 

If you want to read a very good discussion of hp vs torque, read this...
http://www.crystalridge.net/cars/hptorque.htm

 

The rear end gear doesnt make as much a difference as the final ratio (rear X tranny).

Gears will translate higher RWTQ numbers (not dyno numbers). The higher numerical gears will multiply the TQ by more than lower ones will. So in theory, if you shift your powerband up 20% and get 20% higher gears, then you will get 20% more usable power (not that its 20% faster than stock gears, but 20% more power than stock powerband with stock gears) and not lose much low end, because your low end is also multiplied by 20% as well.

It is kind of complicated, but as a rule of thumb... i wouldnt get new gears until i raise the peak HP up in the powerband (unless you have 273s).

But dont fall into the theory that lower gears accelerate better at higher speeds, because they dont. Typically most lower geared cars win because they are racing high geared A4s with bad top end gears with "dead spots". A Higher geared M6 will outrun a low geared as long as it isnt shifting into an OD gear. The goal is to avoid "dead spots" where you arent near peak HP.

The land speed record was on a low geared car probably because it would top out the 5th gear and didnt want to shift into a .5 OD gear (im assuming it was a t56 tranny) with anything higher.

Talk to someone that REALLY knows their stuff about TQ/HP and they can explain it to you. I can gaurantee you this, 99% of the people on this board dont know EXACTLY how it works.

-Stu

 

good reply Disco but as the entire message of the thread suggests it is both a bit subjective and application specific. I guess my impression of the start of the thread was does changing gears give you more hp / tq? My basic thought is no, but it may make your car behave with more OR less acceleration. I guess i was applying my thoughs to my specific application only. I want higher top speed. Hell if changing gears could give you more horsepower i would go change the final drive in my Yugo to say 50.88 to 1 I would then have 15 hp triple what i have now Of course just trying to keep it light!! Didnt want someone to think that by buying a 4.11 rear end they gain 100 horsepower. Nuf said on my part!

 

it feels like it but no it does not add torqe nor hp. bottom line end of story. its been dyno proven. and i found it in a thread on this board. where someone dynoed before and after, and i think they gain .2 torqe.

but topic all depends on if you are a dyno racer or a track racer. and track will see a very good gain. and a dyno racer will not see anything but a hole in his check book.

 

engine torque remains the same but rear wheel torque increases.

Every time you shift a gear, you get a change in rearwheel torque. This is why we start in 1st gear (most rearwheel torque) and not in 6th gear (least rear wheel torque).

Torque on the rear wheels = transmission gear ratio TIMES rear gear ratio. If you increase the transmission gear ratio (downshift), you increase rearwheel torque. Same applies to the rear end gear, except that changing that gear cannot be done while driving.

"I guess my impression of the start of the thread was does changing gears give you more hp / tq? My basic thought is no, but it may make your car behave with more OR less acceleration."

Acceleration is directly proportional to rear wheel torque. Think about it it, the more force the tire applies, the faster the car will accelerate. I hope this clears things a bit.

 

im a dyno ***** vince...