The other night I was reading a thread where a posted response gave a relationship of listed Brake HP to Rear Wheel horsepower. Something like stock S5 160 HP actually resulted in something like 104 hp at the wheels.

Does anybody have a chart (or care to take a shot at estimating one) along the following:

S4 NA Stock BHP 146:

RWHP Stock flywheel= ???
RWHP Lightened Steel Flywheel= ???
RWHP Aluminum Flywheel= ???

Same for a S5 NA, S4 Turbo, S5 Turbo

Heck, I'd be happy with answers (or even partial answers of any kind) with a stock flywheel just to get an idea what hp is loss between the flywheel and the rear tires.

Come on, I know somewhere in the Wankle brain trust there is an answer to this with some level of detail.

 

Im no mathematician but the general rule of thumb is ~15-20% loss through the drivetrain so whatever it makes at the wheels add ~20% and thats what it makes at the flywheel. Hope this helps u out.

 

for older VW there is generally about 25% loss on drivetrain, my friends Ford S200 or something like that does show same 25% drivetrain loss.....

so i assume 20-25% is what u could count on with most cars out there.....

 

IMHO, if you want to know flywheel horsepower, put the engine on a flywheel dyno. That's the ONLY way to know. The only number that really matters otherwise is rear wheel horsepower.

To give you a ballpark -

A stock NA will make around 110-120 to the ground. A stock TII will make around 150-160 to the ground. A modded NA with intake and full exhaust will make around 140-160 to the ground. A modded TII with full exhaust and intake can easily make 200-220 to the ground.

Flywheel horsepower numbers that are estimated from rear wheel numbers are fish stories. It's just a way to make the numbers seem bigger. Stick with and compare rear wheel numbers, and you'll always be good.

Considering most if not all of the 2nd gens out there aren't performing at stock levels any more, most of them aren't putting out stock power. Tired motors, clogged cats, stuck 6-port actuators, tired turbos...this all adds up. That's another reason why you can't figure backwards from what your car was making stock to what it's making at the rear wheels - the only way to know is to put it on the dyno. Heck, I've seen NA's that didn't break 100hp, mostly due to worn engines, plugs, stuck 6-ports, you name it.

Dale

 

A stock NA will make around 110-120 to the ground. A stock TII will make around 150-160 to the ground.

Is this in reference to a S4 or S5, given that S5 stock are factory rated about 20 hp higher?

 

Really, those numbers are what I've personally seen and experienced. Those are safe numbers to expect on a stock car, regardless of year.

There isn't as big of a difference, stock, between the earlier and later cars. Probably on the order of 10hp. With mods, that all starts to change .

Dale

 

I know this isn't stock but this is someone's dyno of a 1990 NA with Headers and K& N Intake:

 

wow....143 with headers and filter....thats 17hp less than the specs...

http://2ndgenrx7.freeservers.com/specsmaster.html

sometimes i wonder if headers actually make a difference in + hp or just make them go lower.

 

I'd be pissed If my na came off the dyno to not even reach 100rwhp.

 

160 stock is bhp, not RWHP.

 

a all stock s4 n/a will dyno right around 120 rwhp.

 

Yeah, Like Felix said, this is RWHP not bhp. Stock RWHP may be somewhere around 130 for a stock S5 (128 if you use 20% loss in drivetrain).

Using that 20%, 143 to the groud is ~180bhp.

 

How do you define Brake Horse Power, exactly?

 

Brake horsepower is measured with an engine removed from the car and put on an engine dyno. The engine is then run against a brake until it can no longer accelerate (increase RPM) and the amount of brake force is used to calculate horsepower. Please correct me if I am wrong.

All the numbers quoted in the US by auto manufacturers are SAE (Society of Automotive Engineers) NET horsepower numbers. This means that the engine is test on the dyno with the full exhaust system, alternator, power steering, air pump, waterpump, air conditioning, etc on the engine.

In the 60s, horsepower numbers were SAE Gross, so the engine was test with no accessories on it and full open exhaust. So, to compare 60s horsepower numbers to modern numbers, you need to subtract at least 30-40 horsepower from the 60s number and you might get a ROUGH estimate.

From what I have seen, a healthy stock S5 non turbo should put at least 13o hp to the wheel with a net rating of 160 at the fly wheel. A healthy stock S5 TII should put 170-175 hp to the wheels with a net flywheel rating of 200 hp. A S4 TII about 160 to the wheels with a net flywheel rating of 182 and a S4 non turbo about 115-120 with a net flywheel rating of 146.

 

Rx-7s seem to have some of the lowest drivetrain loss

NA - 15%
TII - 18%

 

damn that 1990 dyno is amazing for headers and a k&n filter... i dynoed my car... and i have apexi intake/racingbeat headers back..... and i was rated at 140hp/115 torque..... there must be something wrong there?!?!?!? plus the dyno guy had no idea how to set up an rx7 for a dyno...or is it cause im just in canada lol j/k

 

With the Brake Horse Power determained, Isin't the Dyno called a "donkey Dyno" or something like that to find BHP?