1) How much does the size of the wheel and weight make when dynoing.
2) Does weight reduction help in anyway.
3) What should I expect out of an LS which runs 15.5 at 89mph, IHE,

 

1) Wheel size will not change your HP ... It may affect your TQ a little ... but in the end speed is the only difference, when it comes to tire size.
2) NO, weight reduction make no difference when dyno'ing
3) I have no idea

 

1) yes, a bigger/heavier wheel will rob you hp/tq. not sure if theres a formula but i've seen 5hp on 17's. dont know if the actual bigger overall wheel/tire diameter affect the gear reduction calculations or if its just extra weight.

2) none other than maybe lighter front wheels

3) what was your 60ft

 

1) Yes in real life tire size will affect everything with the car ... but on a dyno its a little different. I dont think youll see any HP gain by going to a bigger or smaller wheel. Like I said you may see a little TQ change .. but nothing much to worry about, or to go buying rims and tires about.

You saw 5hp on 17's how .. explain a little more .. went from what rim and size to what rim and size?

2) I dont see lighter wheel gaining any power on a dyno, in the real world yeah .. but on a Dyno Im not sure any gain will be seen.

Both of my OPINIONS are hypithetical, based on my experience with a dyno and gains. What I post are with I think should be the case. Someone with REAL dyno experience in these two areas please post your findings to help us out. Im real curious as what would really happen in both cases i the real world.

 

horsepower is calculated directly from torque (tq*rpm/5252=hp) so if wheel size affects tq then it must also affect hp. a "little TQ change" close to redline means could mean 5hp.

my 1st guess was that the bigger overal diameter changed the final ratio at which the drum spins and the dynamometer didnt know to compensate for it. for example lets say the car made 120ft. lbs of torque at 5000rpm on 3rd gear pull. 120(tq)x1.269(ls 3rd gear ratio)x4.266(ls fd)=649.6tq at the axles, later reduced by wheel diameter. if the wheel diameter changes and the reduction formula stays the same, the fina hp/tq measurment is not accurate. now im not 100% sure on this so if anyone has more experience with dynos feel free to correct me.

another guess is that the wheels weight puts more load on the engine. this is probably the true reason but if this was true, would a bigger, lighter wheel (such as velox's 12.5lb pg- 5 forged 17x7) yield better #'s on a dyno?

 

So there is no real need to change from my 17s then.
For the person who asked my 60ft are around 2.4 I think can't remember exactly.

 

im pretty sure that the dyno uses the ignition signal to figure out the gear ratio each time you run. using the engine speed and the size of the drum the dyno will calculate your gear ratio to figure out how much power your actually producing..

 

Thanks for the explination, though mine is an LS, and everybody knows the LS NA third gear is terrible, so would it be any different to make the run in a different gear, or it just simply how much the engine can put out, with out depending on the gearing.
Its just that I have a dyno session coming up and don't want to look like a fool, just some background knowledge so I know what they are talking about.

 

Yes, wheel diameter really doesn't matter, it's how heavy the actual wheel is.

Also, if you are looking for a 1 hp point or more, make sure the air in your tires are the same PSI. That will throw the dyno off too.

Dyno's also have to be ran in the grear with the closest 1:1 ratio. So if the guy just did a 3rd gear pull in your car. The read out is off.
4th gear is the correct gear for 5spd cars.


This is also is why dynos such as the Dynapack are said to be more accurate. The eliminate the guess work with wheel play and get a direct readout right off the hub.

 

Do you have to take the front bumper off or not?