my young 25year old cousin bought a bf mk1, took it to a tuner in campellfield. wont name tuner due to not being a sponser. now mods done are cai,valve springs,60pound injectors,3-1/2 inch dump,200cpicat,into twin2-1/2system with middle muffler and rear muffler,12psi acutor,walbro,14psi boost,and yes a monza cooler[which the tuner sold to him cheap]. now with those mods and even the monza, I would of thought 300/320 rwks. but only came in at 285rwks, tuned with sct. tuner told him would of made over 300 but he's 20inch wheels will robbed him of power. is it true that 20s will rob that much, I have 20s but was tuned on 17s. now is the tuner right in he's theory on the 20s. or is it the combanation of the monza,exhaust,and 20s. thanks. he lives up that way that's why there.

I understand that they do take a few kw off the figure but not anything like 20+kw

usually its due to higher weight and larger diameter

ive never had a car dynoed back to back though...

when I went from factory 19's to my 20's I noticed no difference at all as my fronts are lighter than the stock 19's and rears just the slightest bit heavier due to being much wider, but as a whole set I think its 2kg lighter than factory 19's on my digi bath scales

it would be great if 20's robbed you of 20+kw cos I made 311rwkw

what did it make before the mods?

well it was stock as a rock, he only has had it 1 month he's had mods now 3 weeks. made 216.5 stock. that's what I dont understand, its only made 70rwk gain with all those mods. I think its cooler and exhaust, he's mate is a metal fabricator and the exhaust looks dodgee as. I think 100cpi cat no middle muffler.

If it got tuned on a hot day its possible to show 15kw less especially through the monza.

Of course big wheels rob power, it's a known fact.

My 22s robbed 35rwkw. My old tuner ran my car up on his dyno to recalibrate the speedo, and couldn't work out where the power had gone. He tried flashing the different tune is I normally had on the lower setting to know avail. Tested for leaks etc, but yea could not work it out. Anyways he wound the boost up to get the power back to where it was, then when it went in for a service on 17s he ran it up and there was 30odd rwkw extra.

Bigger wheels will rob power

Heavier wheels will rob power

Different tyres can rob dyno power

Watch out!!! You guys may be giving *Beep* his next excuse

AS Ratter has stated even different tyres will give you different readings on the dyno I lost around 8-10rwkw just by having semi slicks on the dyno! but at the end of the day its just a number.

I should add,

the heavier or larger wheels will show as a power loss on the dyno because they actually are robbing rwkw even on the road, without trying to show a hub Vs roller debate, a hub dyno will not show this loss.

We went back to back on a BA T manual, it had 20's and if I remember correctly was making approx 335, the owner gave us some 16" steel rims and it went 350, it's the only time I have done a back to back comparison, but there can be some issues if trying to be 100% accurate,

1. the car was taken off the dyno to fit the wheels so the strapping may not have been 100% the same although we did try to keep it the same

2. The 335 runs were after the car had been tuned so the heat in the tyres may have made them a bit squirmy which I believe robs a little power and the new tyres were fresh, so the tyres may have made some of the difference

3. We used the same tune in both cases, and tried to keep the same IAT etc, but small changes may have affected the rwkw

Tyres may give differnt dyno readings but do not affect your power on the road, unless wheel spinning etc

worm LOL