What would 325rwhp be in terms of crank hp? Would it be about 20-30 more hp?

 

Varies depending on if the car is and auto or manual. I have always heard 15-20% drivetrain loss for autos, which would put 325 at about 375-390 at the flywheel.

 

The rwhp = rear wheel horse power, as you seemed to be asking.....green28 is almost right in estimation about autos., Ironically you say "325", which most LS1's are noted for at the crank.

 

Sadly there is no simply answer to this and all of the simple solutions will usually give you a very wrong number.

This is because there is a lot involved. There's 3 main area's that cause problems.


1. Drivetrain loss.

This is the amount of power lost via the drivetrain from the flywheel to the rear wheels.

IMO this consists of a static amount (engergy needed to move the physical weight) and a variable such as increased friction.

This also follows nicely with Newton's Laws of Physics "That ever action has an equal and opporsit reaction".

Therefore you can not say that drivetrain loss is either a percentage or a fixed loss it would need to be a fixed amount with a deminishing percentile loss.

However some simple terms can be used such as the 15% rule and the 12% + 10bhp rule.

2. The RWHP numbers.

Chassis dyno's vary a great deal and can produce massivly different rwhp numbers, such factors include SAE and STD correction, graph smoothing and dyno type.

A Dynojet dyno is typcially an inertia dyno this uses a static drag brake as opposed to a Mustang Dyno which is a load bearing dyno (can alter the amount of drag braking). This results in Dynojets producing higher numbers, but these are not very comparable to SAE Net which is the rating and standard manufacturers in the US use.

Example, 400rwhp SAE on a Dynojet is about equal to 374rwhp SAE on a Mustang Dyno.

So depending on your starting out rwhp numbers you can end up with a very wrong estimated flywheel HP.

3. Drivetrains

Automatics and manuals will all lose different amounts of power thru the drivetrain this is due to the difference efficences and workings of the transmissions. The problem is compounded with such things as unlocked or locked converters and also high stalls will easily produce false readings.


All this means there is no certain way of calculating drivetrain loss to derive flywheel HP although there are even setups on rolling road that measure the drag as the car free wheels. This is still only part of the picture.

The easiest way to work it out is to use a combination of all potential factors.

1st off if you want to know flywheel HP then you most probably want SAE Net as this is what most US automakers rate cars in, its also what you see adverised.

In Europe the standard is DIN but can sometimes be metric HP (PS) as opposed to imperial. However the numbers are usually pretty close, example:

Mustang GT 300bhp SAE = 297bhp DIN
Dodge SRT8 425bhp SAE = 419bhp DIN

A standard just corrects for temp, humidty and that sort of thing.


Imperial to metric example:

143bhp DIN (imperial) = 145PS (metric)


So to as Mustang Dyno's more readily compare to SAE Net it's always a good idea to use numbers from a Mustang Dyno and even better if they are SAE corrected.

Take a Corvette C5 manual, GM rate it at 350bhp SAE Net and on a Mustang Dyno you would typcially see 300rwhp+- SAE (a dDynoket could be as high as 321rwhp).

This means simple Maths 350 - 300 = 50bhp drivetrain loss.

So if you increase power you will ALWAYS lose a minium of 50bhp.

This tallys in nice with the 15% rule, 300 / 0.85 = 353bhp.

The 12% + 10bhp rule, (300 / 0.88) + 10 = =351bhp.

If say you mod the Corvette (h/c bolt ons) and get it to 400rwhp SAE Mustang Dyno (or 428rwhp SAE Dynojet) we know it will have lost at least a minium of 50bhp as that's what it loses stock. 400 + 50 = 450bhp.

The 15% rule would equal 400 / 0.85 = 471bhp

The 12% + 10bhp rule, (400 / 0.88) + 10 = 466bhp

So you see we are starting to get some variation of results. Here I would take a MEAN average:

So (450 + 471 + 466) / 3 = 462bhp

This is at least quite a realistic figure, for more accuracy you may want to add a +-10bhp tag to it.

But remember using the wrong rwhp number will give you the wrong flywheel number. Remeber the Dynojet number of 428rwhp, if we simply did the 15% rule 428 / 0.85 = 503bhp. This is a massivly higher number and in all reality completly meaningless unless being compared to other like numbers.

It is for this reason that many so claimed 500bhp (flywheel) C5's still get whoop assed by a stock 505bhp C6 Z06. It's because the modified car really isn't prodcing the numbers being claimed and is probably down 40 ro HP.

Hope this helps

 

these engines were underated in the f body,its more like 350 360ish.
theres really not an answer to this question.if an al60e you can figure 18-20% this will be close but not accurate.
if m6 figure 12-15% this will give you an idea

 

somtimes its just to hard, so just add 60 horses