Mazda Talk Forums

Recent pics, Top Time of Day at first autocross event of the year with significant thanks to new 17x10 6UL wheels!

Next mods, likely a OSGIKEN limited slip and 3.9 FDR.

How is the drying of the dyno coming along? Do you need some guys with mops and buckets to help things along?

It was my hope the dyno would be back in service this week, but now looking to be at least next week.

Waiting on the contractor for the roll up doors on the dyno building, which the flood waters tore out. Once the doors back in the computers can go back in and dyno work can begin again.

Sorry to hear about the flooding, good luck on getting everything back in working order!

I'm shopping for an NC right now to use as a streetable track car and after reading this whole thread over the last couple days and seeing all this 2.5 swap stuff has me reconsidering what kinda condition/mileage car I'm looking for...

How would a 2.5 with a Kraftwerks kit work? Given that the 2.5 is a little taller than the 2.0, would a KW kit even bolt up? If it does bolt up, is it possible to buy it with a C30-94 unit instead of the C30-84? I'm thinking with the 2.5 the 94 is a better fit. And it'll give me more room to grow when I decide ~250whp isn't enough. Speaking of not enough power, how difficult are pulley swaps on the KW setup? I'm a fan of somewhat modest power levels at the track but I like a lot of power on the street. I like the idea of showing up at the track and swapping a low boost pulley, switch the ecu map and run that on track, and when I'm done go back to the high boost pulley. Is something like that feasible or would it take way too long to do that track side?

Are there any differences in the head between the 2.0 and the 2.5? Seeing the prices of shortblocks at local junkyards, I'm entertaining the idea of buying that and getting it rebuilt with better pistons and rods and then just bolting that to the 2.0 head. Then I wouldn't have to worry about the whole centering the intake mani on the head thing I read about. Speaking of the whole centering intake mani thing, any chance you have any pics of the process?

sorry for hijacking the thread a bit, but I'm not the first to do it

You want the 2.5 head on the 2.5 for best flow. The 2.5 is a great candidate for supercharger and many have done it (many dozens of pages to read on this in NC Power section at miata.net forum). Yes, you could swap pulley choices between events but more trouble than it is worth in my mind. I find the MP62 blower much more satisfying to drive because it has instant low range and mid range that the Kraftwerks kit just can't match with either blower. The only upside of the Rotrex kits is high rpms efficiency at the track, but for me not worth the compromised low and mid range that makes it a bit of a dog out of tight turns and from stoplights. In contrast... MP62 has the power EVERYWHERE in the rpms. I have raced both, no contest for me, would only do the Rotrex on dedicated track toy.

Brian wrote:You want the 2.5 head on the 2.5 for best flow. The 2.5 is a great candidate for supercharger and many have done it (many dozens of pages to read on this in NC Power section at miata.net forum). Yes, you could swap pulley choices between events but more trouble than it is worth in my mind. I find the MP62 blower much more satisfying to drive because it has instant low range and mid range that the Kraftwerks kit just can't match with either blower. The only upside of the Rotrex kits is high rpms efficiency at the track, but for me not worth the compromised low and mid range that makes it a bit of a dog out of tight turns and from stoplights. In contrast... MP62 has the power EVERYWHERE in the rpms. I have raced both, no contest for me, would only do the Rotrex on dedicated track toy.

I want to go the Rotrex route since I will be using it on the track quite a bit (1-2 events a month during track season). And with the 2.5 in there, I think I'll be ok on the torque with a ~2500lb car.

Since you worked a lot with these cars, do you have an educated guess on how much I'd be losing out with a 2.0 head vs a 2.5 head?

Do you happen to know about the option to buy the Kraftwerks kit with the C30-94 unit instead of the C30-84?

I would talk direct to Kraftwerks about kit with blower upgrade for 2.5, I am sure they can do it. I have seen the flow numbers 2.0 head vs 2.5 head but don't recall the particulars other than conclusion that 2.5 head was the obvious choice and not a place to save money.

Brian wrote:I would talk direct to Kraftwerks about kit with blower upgrade for 2.5, I am sure they can do it. I have seen the flow numbers 2.0 head vs 2.5 head but don't recall the particulars other than conclusion that 2.5 head was the obvious choice and not a place to save money.

Thanks for the advice!
Looking forward to where you take this project next

Hi Brian,
I'm ready to buy the shorty, what say thee?
R

As covered further up this page, lost at least 2 months when El Nino flooding took out our dyno. Still waiting for it to come back online so we can finish up a number of projects, including that header.