Hey guys, has anyone put a standard wrx on a rolling road? What figure did you get for whp?

Thanks Foz

 

are uk dynos not setup for hp at the flywheel? whp is usually an american thing.

 

you could calculate it by taking into account the 22% transmission losses of the Subaru 4 wheel drive system.

 

all the dynos i have used do wheel hp and flywheel hp, scooby clinic/dyno dynamix and g r performance/dastek

 

Yeah I went and used the new one they have at indigo GT. I got 175.9 whp, dunno if is a little bit under 226bhp. Got a cat back exhaust, would that affect it?

 

@ 22% transmission loss it is 216 hp

 

no it's not. take 22% from 226, not add 22% to 176. (22% is a rough guide)

mine was 188whp and 238bhp, i had green panel filter and 3" cat back

 

huh?

you're assuming his car is 226 standard. i took his actual whp and added 22%. your calculations of 188whp equates to a 27% loss if you hp is 238. depends on the dyno i suppose.

taking 176 and adding 28% losses get 226 approximately. is my logic or maths faulty somewhere?

 

Maths is faulty im afraid
for arguements sake say its 200bhp, and loss is 20%, so 20% of 200 is 40hp, so whp would be 160, with me so far?
Now you cant work it in reverse.
160whp + 20% doesnt equal 200 bhp, but only 192 bhp, why? cause 20% of 160 is only 32
losses only occur in one direction, when working backwards things gain
The actual gain from whp to bhp in this imaginary case is 25%

so going into this real case, if it was a 226 bhp engine he would have a transmission loss of 22.2% giving 175.9, or if transmission loss is 22% exactly the bhp will be 225.5

 

Yeah I kinder get it. The car is standard apart from a cat back exhaust. It's a 2006 hawkeye. So how to you do the equation the other way, whp > bhp?

 

ok easiest way to get bhp from whp is divide whp by 0.78
0.78 is the percentage left after losses expressed as a decimal amount (100%-22%=78%) assuming losses is 22%

So 175.9/0.78=225.51282bhp

Hope that helps!!
John

 

Put it on a dyno as there are too many variables for an accurate figure.
Note that my scoob only loses around 16% so as you can see, difficult to work out correctly

Tony

 

Ouch - my brain is hurting

 

Its not that hard normally and if you do a rolling road run then it will give you (normally) an engine and wheel figure for bhp.

For instance, my old car ran between 312 and 316bhp, put down between 260 and 265 on the road.
So if you have the 2 figures to start with, 316 and 265, you divide the lower against the higher, ends up for these as .8386, which is just over 16% losses

Tony

 

Simples!!! :P

 

quite right. i looked at this again today and did wonder. would you believe most of my degree was in physics and maths total brain melter last night, what was i thinking of.

 

Cheers guys!

 

I had 234bhp with only a green panel filter on my 05 wagon at Enginetuner, before mods; I was quite surprised ! Can't be arsed to work out wph.

 

Had mine done as a completely standard car. Nothing touched!! Its a 51 bugeye wrx. Running on shell v power
231.5 bhp
177.0 whp
I also have print out to prove. Hope this helps

Wonkey