Taken from the RevSpeed Tsukuba T/A thread:

[QUOTE](GoTuningUnlimited @ Dec 10 2009, 04:00 PM)
Almost all the tuners running radial (street) tires right now are running 265/35-18 x4. It's pretty much the standard street tire size. They tested 17" vs 18" earlier this year and found that the lower profile of the 18" tire has less sidewall deflection so they are more stable and gives the driver more feedback. The tires are also maintaining their contact patch with only 3 degrees of front and rear camber. All the tires that come off the car are wearing perfectly even. The wheel is sized accordingly as a result of the tire choice, not the other way around. The GC-07J was also chosen after testing different wheel models and the driver found it to be the most rigid with the best feedback.

 

Also, there are much more tire choices in a 265/35/18 vs. a 265/40/17

 

///KM you are awesome...thanks man!

 

Wow, excellent information! Does anyone know if they actually dynoed the AP1 cats vs the AP2V2 cat? Can't tell from the dyno plots. Either way it looks like I should consider getting a TP, HF cat or even an AP1 cat.

 

Oh and I agree with Ray, Thanks ///KM!

 

Glad I could help

This reminded me I promised I'd read more into the cat section...will do that later.

There are dyno plots of the AP2V2 OEM cat vs AP1 cat vs Amuse HFC. Think they mentioned that since the AP1 cat was designed for the F20C, there's some power loss on VTEC changeover when the AP1 cat is used on the F22C engine. They mentioned something like a 7ps loss vs Amuse HFC on VTEC changeover. I'll read it again tonight.

 

^hmmm, I wonder what would cause the power loss? Wouldn't the same thing happen with a test pipe or HFC?

 

First, if you take a look at the dyno plots on page 109:

Graph 1 (top left)
Purple = F22C + R1 Sports HFC + High Tech ROM ECU (VTEC changeover @ 4900rpm)
Green = F22C + AP1 cat + High Tech ROM ECU (VTEC changeover @ 4900rpm)
Red = F22C + AP2V2 cat + factory ECU

You'll notice that the AP1 cat does make power over the AP2V2 cat, though all things aren't exactly equal (ECU). The HFC also makes more power than the AP1 cat. According to the article, this is due to the AP1 cat being designed for the 2L engine, and it can't handle the instantaneous load of exhaust gasses on VTEC changeover as well as a HFC can on the 2.2L engine; a deficiency in the cat's capacity. This VTEC changeover point is where the AP1 cat loses out to the HFC by 7ps, and it can't quite make up that difference as you go higher up the powerband, as seen in the graph.

Further, if you add an aftermarket ECU to the F22C + AP1 cat and attempt to lower VTEC changeover under 5400RPM, as you can tell by the green power line on the dyno plot, there's a big torque and power loss until VTEC fully kicks in. This is due to the same reasons above, the AP1 cat doesn't have the capacity to handle the instant exhaust load of the F22. However with a HFC, VTEC changeover can be lowered to 4900rpm while keeping a smooth and linear power curve with no dip.

If you have the AP2V2 cat, they recommend changing to the AP1 cat on a budget, or a better dedicated HFC if you have the funds. Whichever way, if you want more power the AP2V2 cat should be the first thing you change out.

 

Thanks for the info, it's very interesting! In theory, all things equal, the AP2V1s should make more power than the AP2V2s, since the V1s are using the AP1 cats as factory equipment. Either way, it looks like I should consider buying a HFC ('cuz I don't really want to run a TP). Too bad we don't have many choices for a HFC here in NA.

 

[QUOTE=alSpeed2k,Feb 4 2010, 01:36 AM] Thanks for the info, it's very interesting!