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

 

Is it the softness of the sidewall or the actual weight of the tires thats making the difference? I also noticed that your summer tires are 18's whereas the winters are 17's. What wheels are these tires mounted on? Ive always known that its beneficial to drop rotational mass however I never knew how much of a difference it would make. In theory the car should handle a lot sharper also not just because of the stiffer sidewall and change in compound but because of the drop in weight.

 

Winter tires are HARD. Summer Tires are SOFT

 

It's a cushy ride, with soft flexible sidewalls. That's what I think he meant!

-Jalal

 

Winter tires are not hard, they use a different compound and have more rolling resistance because of all the sipping in the tread.

Summer tires are going to have less rolling resistance as long as they're not super sticky tires.

I'd be willing to bet low rolling resistance Michelin MXV4 or Goodyear Assurance tires will dyno a little more power.

 

Weights/rims added to post number one!



This. Winters are very skooshy, no doubt about it.

 

AH correct. I thought we were talking compound/threadwear.

 

so youve lost power from those new mods? weird.. is this on a low reading mustang? sure u posted up a vdr that was 470whp or sumthin?

 

those definitely look like Mustang Dyno numbers, when he did the VDR it was on Dynojet settings and it was like -2 degrees outside as per his post...im willing to bet that its quite a bit hotter when he made these pulls with the tires.

 

Winter compounds are only hard in the winter. In the summer they are like pencil erasures.

I think it is more about weight, my winter tires are silly heavy, they also have a higher diameter with the same measurements. That may also be a factor.

 

Dyno dynamics numbers, so a smidge lower than the low mustangs. Figure about 15% difference to get to dynojet numbers. This was at about 60-70F so ya the numbers work out. I made 432whp on this dyno last summer, and we took out 2* to keep it safe, that brought it down to 420.

 

You're totally right about the eraser thing, but check the data I posted about wheel/tire weight; it's very close!

 

yeah i just looked up the weights and my winters are actually lighter than my soon to be received summers.