Modman Maniac!

Sorry for the long rant - but some may find this informative..........

This argument of excessive Rear Wheel HP arises often - especially on the LX Forums - but there's a simple way to resolve it -

First - parasitic losses. They are all different, but I've discussed this enough with US dyno operators to know that you will lose an absolute MINIMUM of 17% though the drivetrain on an LC/LX car.

Big wheels and sludgy auto make 17% a very generous figure - in reality its more like 20% - but lets stay at 17% to illustrate my point. :)

The "math" - We take the "380" RWHP recorded on these various RW Dynos and add the 17 % parasitic losses of the drivetrain - The formula is 380/ .83 = 457.83 Engine HP.

(IF we had used 20% - it would be 380/.80 = 475 Engine HP!)

So...................

............. the first question that has to be answered is - Do you think these "380" RWHP cars are actually making 457 Fly wheel from the factory?

Answer - those with a tune and cold air MAY be - those with no mods definitely ain't - Why?

Because stock track MPH vs weight posted on various forums shows they are nowhere near it.


Or....

Lets work backwards - take the FACTORY output of 425 Engine HP - take 17%. losses....Hell..lets take 15%..which is unheard of in auto trans cars..... the result is losses of 63 HP...= 362 RWHP..... So how is a factory 6.1 making 380 rwhp???????

The Rear Wheel output figs I have read on LX Forums for a 6.1 vary from 350 to 390!! ..so the argument that the factory rating is "under-rated" just doesn't hold water.


The problem - The issue lies with Rear wheel dynos - pure and simple. They are a tuning tool - unless the results can be calibrated against track performance...(More on that later)


Then - I would also ask your friends Dyno operators if the Dyno intake temp sensor was used..this "convenient" device is supposed to compensate for excessive high or low engine bay temps - trouble is..its usually far to generous and not a realistic compensation -

I always leave it off - after all, no one changes the weather at the track for me ;)

Then I would want to know - What type of chassis dyno, and there are other factors as well - Ambient barometric conditions are also "conditioned" by the dyno to achieve the final output figure. The SAE conversion factor varies from country to country as well.

Also - What tyre pressures? I made 25 RWHP once by pumping my tyres 15 psi more.

And then - Do dyno operators want return business? Its usually in their interest to make sure their livelihood is "protected"..so a "happy" dyno is a "happy" customer.


Here's a story..........My car made 366 rwhp on another chassis dyno with a single carb - But I knew that was bs from what the car ran at the track.

...then another Dyno said 310 rwhp.

At the time my car weighed 3650 and ran 111 mph - most calculators put that at appx 400 engine HP.......Guess which dyno I believe?..Certainly not the one that said 366 rear wheel!!


The simple truth is - you can't race RW dynos. They vary so much...and so much is at the discretion of the operator and the type of dyno.

Unless you reference them against weight and track MPH and add REALISTIC losses (like I have)....they can say anything....usually on the + side.


I don't doubt several of your friends recorded higher numbers than mine - but tell me what MPH they ran at the track - and I'll tell you what the REAL HP output is of their motors....give or take 10 HP.


Finally! - MY HP rating is probably down a little compared with the = EFI motor....but its not losing a huge amount...and I haven't run the AF anywhere near as rich as it should be....so there's more in it.

Anyhow..track time will tell ;)



PS - Here's a prediction - if my car is making a genuine 450 at the crank - it SHOULD run around 114mph for its weight....I'll be sure to post back and go thru the results. :)