MAXINXS

Ok...... I got my car dynoed today on a dynojet dyno. The exact same one I used before during the summer. With only a Weapon R intake, I made 217 hp and 223 tq. Today with the same Weapon R intake, Cattman Y-pipe, Budget b-pipe, Magnaflow muffler and some different wheels, I am making 211 hp and 214 tq. The wheels are 18's compared to the stock 17's. They only weigh 1 lb more than the stock rims that I had in the summer. I am making more power just about everywhere except peak. The obvious hinderance is the wheels, but 1 lb shouldn't make that big of a difference. Car runs great and feels really strong. I'm stumped. Where is my peak horespower gain, and why did I lose power? The door to the garage was left closed. The dyno was sae corrected to the weather conditions outside though. It's just kind of upsetting when you spend all this money in modifications and the gains are not there. Once again, my car pulls really hard! The numbers just aren't there. I'm considering trying a different dyno, because none of this makes sense to me. Any opinions?

MrEous

iTrader: (11)

Do you have the original Runviewer files?

Are you sure they were using the same correction factor from the summer? (i.e. SAE or STD)

Maybe your car is sick?

Quicksilver

iTrader: (1)

It's not really the weight that will make the difference in your wheels...it's that moment of inertia change (going with bigger diameter wheels means it is harder for your engine to spin them the same speed with the same power, basicly)

MannyNJ2k2max

iTrader: (3)

my dyno was also w/ a closed garage.....I'd like to see the dyno if you could...how many runs?

Nealoc187

iTrader: (23)

That is quite strange. Post the graphs if you can.

vipervadim

iTrader: (10)

maybe you gained power in the midrange and down low and lost/didn't gain any high up?

but that's strange beacuse peak power is toward the higher rpms.

bigdo26

iTrader: (3)

wish I had enough time to figure out the losses you'd encounter due to the increased moment of inertia from the 18's but i doubt it would be 6 hp loss. probly a couple hp. What were the conditions you were doin it in? colder, more humid, and fans, etc. All those can make a difference too

Import Roller

To be honest, i feel I lost power with my CAI than my WAI, so it is possible IMO to loose power when you mod something. But bigger rims, will cause you to lose power. You want the diameter of the rims and tires of the aftermarket wheels to match as close as possible to those of the factory wheels. Or you can go to a smaller rim than factory

ripper

Your mods may be leaning you out so much that the ECU pulls timing. I was a little lean before I added Cattman Y and catback slightly more lean after them

Broaner

iTrader: (10)

Another thread perfectly exemplifying the fact that wheel weight/size has a huge difference of power laydown. So what is the real formula for calculating the moment of inertia because isn't isn't very accurate to just assume and use the wheel radius as radius from center to point of inertia.

bigdo26, here you go. I'm assuming that the stock 17" is 20Ibs because I don't have time to check. So...

(8.5^2)20=1445 Units of Inertia(I don't know the units, sorry)= Stock 17"
(9^2)21=1701 Units of Inertia=Aftermarket Rims

These figures are assuming that the weights are as I used. If not adjust accordingly. You get the picture. It shows you that thats a big @ss difference. If your looking to make more power why would you ever consider getting a bigger and heavier wheel. Look at me, I went 2Ibs lighter and they still made me slower because I also went 2" bigger.

MAXINXS

Ok 5 months later, I finally have a camera so I can post the graphs.

This was with i/e/udp.

This was with i/e/udp AND HOTSHOT HEADERS.


Any ideas? This makes no sense.

03BlkSETE

iTrader: (3)

So you last power again when you went with the headers? Can the shop provide you with an overlay of the best runs from each of you 3 dyno sessions? Also what's your A/F ratio, it's hard to read.