how do you calculate flywheel hp?

[burninator]

Dyno power numbers should really only be used as a reference against themselves on the same dyno for that exact reason. It's a piece of cake to make the numbers say what you want it to say. A dyno operator with integrity will at least keep his numbers consistent for each run on his machine, allowing you to compare every pull on that machine with a reasonable degree of accuracy.

 

Exactly.

[johnc]

Real racers downplay how much horsepower their car makes. Internet racers exaggerate how much horsepower their car makes.

[Daeron]

Real racers downplay how much horsepower their car makes. Internet racers exaggerate how much horsepower their car makes.

 

:mrgreen: "around five hundred"

[Ruiz Racing]

:mrgreen: "around five hundred"

 

 

maybe more:flamedevi

[RIPSNZ]

Real racers downplay how much horsepower their car makes. Internet racers exaggerate how much horsepower their car makes.

 

Phew, lucky I said only 1400 then

[Tony D]

He also stated that even with a modified engine. There is no way a l28 could ever, in any posible way, make 300hp, or even 300rwhp with only 10 psi.

 

Quit arguing with idiots on Myspace! I have seen on a dynapack, an L28 make 280ft-lbs at 8.39psi. The same engine after further tuning (identical mechanicals) made 300+ at 10psi.

 

The same externals and head made well over 300hp on a bone-stock L28ET bottom end!

 

Making 300HP at less than 12psi is not hard at all, and anybody saying it was impossible isn't worth arguing with in the first place as he is expressing his ignorance of the L-Engine's capabilities.

 

475 HP on a stock L28ET Bottom End? Sure, why not. More boost.

 

And those are all RWHP from Dynapacks, Dyno Jets, Mustangs, and one Clayton in-ground unit. I won't get into which read the most 'optimistic' but I will say the Mustang was the 'heartbreaker' of the bunch. When using 1/4 mile and trap speeds as a predictor, the Mustang was the closest predictor of performance on the road. Mustang and Dynapack needed the least (if any) compensation to the fueling maps when driven off the dyno onto the real road.

 

But back to the topic, I'm with Drax on this one: Claim you made 180RWHP. That is what the dyno said, that is what you made.

 

Unless you use an SAE traceable Dyno (er...like the Mustang in some configurations) you will not be able to reliably calculate flywheel HP numbers.

 

Stick with the numbers given to you. If you want an engine number, put it on an engine dyno.

I tend to take any dyno number with a grain of salt, as it's a 'grabbed number' that could be higher or lower on any given day. The differential between your last run, and the present run on the same dyno is probably the only useful number you will get from most of the dynos out there. It's a tuning tool, nothing more. If you want bragging numbers, read the operations manual from the Dyno and figure out how to play with the smoothing and other operator entered variables...you can make them read almost any number you want if that is what your inclination is...

 

Two Lane Blacktop Quote of the Day:

 

"How fast she go?"

"Depends on who's around!"

[Drax240z]

Well said Tony, one thing to add:

 

Even quoting a PEAK hp number is kindof pointless, as it tells very little of the story. I've seen lots of "200hp" examples of car A that would be absolutely obliterated by another 180hp car A in any kind of race. Peak numbers are really best used to sell cars to those that are uninformed.

 

In the end, none of the numbers tell you how fast a car is except for the slip from the drag strip, or the lap time.

[Sideways]

I wouldnt go as far as to say comparing dyno numbers is pointless unless youre doing it on the same dyno. Depending on what type of dyno youre using and unless the operator is being an idiot to get bigger numbers (Not unheard of but not as common as a lot of people seem to think, at least not in my experiences), the numbers will be, while slightly different, pretty damn similar, within a small % of each other (given same conditions, humidity, ambient temps, altitude, etc). If youre fighting about 10 hp then ya its popintless- But its not like youll dyno a car and have it do 150 whp on one dyno then have it go lay down 200 elsewhere.

[Nizm0Zed]

comparing dyno numbers between two different cars on the same dyno IS pointless, as it still achieves nothing, If it was two very similar cars (eg, two L28 turbo zeds running similar boost pressures) then yes, some comparisons can be made, with reference to the differences in the particular setups.

But ultimately, its the torque output, and more importantly, where in the powerband AND FOR HOW LONG that maximum torque can be applied to the driven wheels.

that is what will determine a quick car or not.

 

a little while ago, i built a home job twin turbo RB30 skyline (R31 sedan)

I was asked pretty much all the time "what did it make on the dyno" to which everytime i would reply,

"dont know, doesnt really matter, i allready know it'll roast most things off the line, thats what it was built for"

If i had dynoed it, the power output would have been pretty woeful, maybe 150-170kw at the rears. (90 or so rwKw standard NA)

but the fact that it'd be on 8 psi by 2200rpm, and full 12 psi by a shade over 3000rpm with a very meaty torque curve made it a lot of fun to drive.

That and it was a true sleeper.

It was only ever built to be a traffic light racer, top (legal) speed round here is 110kph, so no need to try to prove anything going faster.

and most of the lights i raced off from were on 80kph roads anyway, so i'd rev it out, hit redline and max out the turbos, then cruise at the speed limit.

 

One bloke was pretty confident that his 600kw supra could beat it, shame he didnt get useable boost till over 4k rpm, by then, i was allready at 80kph, and didnt need to go any faster.

[johnc]

Lots of people forget that dynos (both engine and chassis) are TUNING tools. The numbers generated should be used as variables to further the TUNING process. The numbers generated are meaningless outside of the tuning process.

 

A dyno sheet that says your engine makes x horsepower doesn't mean squat until you run the car in some kind of objective test - drag race, road race, autocross, etc. and we all know that.

 

How many people, when looking at a car to buy, would believe a dyno chart handed to them by the seller?

[Tony D]

But its not like youll dyno a car and have it do 150 whp on one dyno then have it go lay down 200 elsewhere.

 

I have done just that! One dyno said 147HP. Same day, across town another brand of dyno said it made 202HP.

 

I have seen dyno operators who host 'club days' on a sunday or saturday when business is slow 'tweak' for higher numbers than they normally would get. Keeps 'em coming back.

 

I know people who 'shop' dynos---the braggers JC is talking about. They avoid places that show 'low' numbers.

 

The numbers are really pointless. It's the variation between pulls from the adjustments made that are worth their weight in gold. Two hours playing with cam timing (advancing and retarding) are probably the best $200 you will spend on the car. Our Bonneville engine went from undriveable (wouldn't pull the next highest gear) to a record setter after two hours of judicious tweaking, making a run, tweaking, making a run...until as Drax mentioned, the 'power under the curve' was maximized. It didn't return the same PEAK HP number as previously, but the car would pull between the gears like a banshee afterwards.

 

When it's all said and done, no matter what your dyno sheet says...if you can't hook it, and translate it to a track result, it's nothing more than a number on a piece of paper that you will use for bragging and not a whole lot more.

[Drax240z]

Despite all this talk, I think dyno tuning is extremely valuable, and among the best bangs for your buck as far as making power goes. Key point, TUNING. As johnc said, it's a tuning and troubleshooting tool, and it can do both VERY well. (assuming its a decent dyno and has the ability to hold a steady load)