will someone explain to me the difference between
09-05-2018, 10:40 PM
#1
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Thread Starter
will someone explain to me the difference between
wheel and crank horsepower on our 991.2 turbo s cars
so what do our cars make STOCK at the wheels, while variation from dyno to dyno and car to car the "known" or accepted # by most?
and then say when GIAC or COBB list gains do they give gains at the wheels or crank? and if "they" say 65hp tq bump is that 65 at the crank or wheels??
thank you
so what do our cars make STOCK at the wheels, while variation from dyno to dyno and car to car the "known" or accepted # by most?
and then say when GIAC or COBB list gains do they give gains at the wheels or crank? and if "they" say 65hp tq bump is that 65 at the crank or wheels??
thank you
09-06-2018, 12:36 AM
#2
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(Rear)wheel horsepower is measure at the wheels and is referred to as 'rwhp'.
Crank horsepower is measured at the end of the crank and is referred to as 'bhp' which is, in non-TLA form, brake horsepower. But, that's as much historical as accurate since a brake-type dyno can be used to measure either. But, in the former case the engine is out of the car and on an engine stand.
The fundamental difference between the two is energy (drive line) loss between the crank and the ground (or hubs, if the dyno is bolted to the wheel hubs in place of the wheels.)
The difference between bhp and rwhp is typically in the range of 12% to 20% depending upon the design and architecture of everything between the crank and the road.
In my opinion (based upon looking at lots of dyno sheets, but not many 991s) is that the drive line loss on 991s would be around 12-13% and would expect 580 bhp to 'dyno-out' at in the 505 to 510 rwhp range.
Another thing to consider is that not every engine is the same. Historically, Porsche's advertised BHP is the guaranteed minimum. Normal variations in manufacturing would lead to the average engine being a few percent above the advertised.
rwhp is the 'accepted language' of after-market performance. Most, if not all, of the typical 'tuning shops' do not go the considerable trouble of removing the engine to measure bhp but instead rely on a dyno that 'connects' at the tires or wheel hubs.
However, I never assume that any particular company's marketing is in the 'proper' language.
Crank horsepower is measured at the end of the crank and is referred to as 'bhp' which is, in non-TLA form, brake horsepower. But, that's as much historical as accurate since a brake-type dyno can be used to measure either. But, in the former case the engine is out of the car and on an engine stand.
The fundamental difference between the two is energy (drive line) loss between the crank and the ground (or hubs, if the dyno is bolted to the wheel hubs in place of the wheels.)
The difference between bhp and rwhp is typically in the range of 12% to 20% depending upon the design and architecture of everything between the crank and the road.
so what do our cars make STOCK at the wheels, while variation from dyno to dyno and car to car the "known" or accepted # by most?
Another thing to consider is that not every engine is the same. Historically, Porsche's advertised BHP is the guaranteed minimum. Normal variations in manufacturing would lead to the average engine being a few percent above the advertised.
and then say when GIAC or COBB list gains do they give gains at the wheels or crank? and if "they" say 65hp tq bump is that 65 at the crank or wheels??
However, I never assume that any particular company's marketing is in the 'proper' language.
09-07-2018, 12:56 AM
#4
Rennlist Member
Hi Jeff,
I know what you are thinking, and it really depends on what you want to achieve with your car
BTW, are you going to the Poker Run on Saturday, it’s for the American Cancer Association?
Manuel
I know what you are thinking, and it really depends on what you want to achieve with your car
BTW, are you going to the Poker Run on Saturday, it’s for the American Cancer Association?
Manuel
