Winter/soft tires seem to suck a few whp on the dyno

[scheides]

I got a fresh set of summer tires put on last night up in MG, and while I was waiting, Shane IM'd me and asked me to stop up for a quick test. I've changed zero in my setup, but the car is magically up about 10whp or so from when I dyno'd in feb. I was on the dyno to get everything dialed in on speed density. I was a little bummed that the car was down power, but we figured the uber-soft snow tires I was running (General Altimax Arctics) might be sucking up some of the power.

Before *on pump gas* the car was wanting to run about 360whp or so, best run was around 365 with the timing from my tune last summer on the car. We made a few pulls that were mostly knock free (but not perfect) and the boost was nearly identical up top. Power was a solid 375whp on both runs.

Before *on alky injection* the car was hovering around 390whp, best of 395whp. I only made one pull last night, it knocked pretty bad(6-counts or so), around 2° of timing was pulled out, and boost was again nearly identical to last time. The car put down 396whp. 2° of timing can be worth 7-20whp according to shane, and I can back that up...last summer we took 2° out of my 432whp tune and brought it down to 420whp, so 12whp.

So, if your dyno numbers are a little on the low side, consider what kind of tires you have on your car when comparing to others.


Side note: yea, my car is down on power....again. Isn't modding fun? It's only about 10-15whp off of where it was last summer, but I've switched to speed density (ditched MAF, slightly different filter), added the SpoolinUp COP setup, and widened the gap on my copper plugs from .023" to .030". Also went from basic buschur ported exhaust mani to the MAP Rev2 ported exhaust mani. Timing is about the same. Misc other items changed: bilstein shocks, shaved/powdercoated valve cover, ACD pump swap (now functional).

For reference:

Winter setup:
General Altimax Arctic 235/45-17 ...25 lbs each (with about 12-13k miles on them)
Stock Evo8 6-spoke Enkei's 17x8 ...22lbs each


Summer setup:
Sumitomo HTR ZIII 245/40-18 ...25lbs each (with 6 miles on them)
Rota P45F 18x8.5 cast ...21.7lbs each

[Kracka]

Be sure to also look at the weights of each wheel/tire combination.

[Spikesoftail]

Wow I never even though about that, Shanes tuning my Talon on thursday, I better get the snows off it finally.

[scheides]

Updated post #1 with weights.

[polishmafia]

So my theory was slightly valid!

[tpunx99GSX]

Another item that i was reading up on are these gas mileage saving tires that have a low rolling resistance. I wonder how these fare on the dyno. Such tires that performed the best in the gas mileage are the Bridgestone Ecopia EP100 and the Michelin Energy Saver A/S. Prolly crappy on the track but may be good on the dyno as they gained about 3 mpg in the tests that tirerack put on over the regular tires.

[Kracka]

They'll probably perform great on the dyno assuming they have enough traction to not slip on the rollers.