I'm back with a topic that I have not seen addressed. I am swapping an '85 slant into a 2004 Mazda RX8. The car weighs 3,000# and I would like a higher reving engine and am willing to sacrifice torque. All of the discusions here that I remember were about how to get more raw power. If I am doing a mild build, how do Insqueeze a few hundred more RPM from the 225? I thimk my engine has the lightest crank.

I want smooth and quiet.

Larger valves, clean up the ports, mild cam.

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No special pistons or rods?

I guess a proper balance job goes without saying.

Unless you are talking about building a motor that will rev to the moon stock pistons and rods are perfectly adequate.

The stock motor is pretty much all done by 4000 RPM. Those basic breathing improvements plus a 2 barrel carb and the right cam will let it rev freely to 5500 and still be a civilized street motor. If you want to regularly rev it past 6500 you will need to do a lot more.

A bump up in compression will help it run better but how much will depend on cam selection.

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--> And the race truck build project <--
--> The Diesel Corvette <--

Long stroke doesn't lend itself well to high revs, without a lotta help

1.70/1.44 valves or similar, bowl porting, and moderately higher comp will get you around 200 HP and RPM to 5000-5500. The 225 likes cam duration, so don't be too shy if you want some oomph. The Oregon "346" cam works well with 9.5:1 static comp. We can refine cam selection based on CR choice and other desires or driving habits.

I would mill block 0.100" and get shorter pushrods by that amt. This will give you around 9.5:1 comp, depending on head cc's. Can you cc the head before you mill the block? Then you can get accurate CR number. I have made a quite reliable 250 HP @ 5500-6000 RPM with stock rods+pistons and 10.5:1 and a well ported head. You don't want that much, I gather, but the rods+pistons and other hard parts will handle quite a lot. I always get my engines' recip/rotating assy balanced. New rod bolts and resized rods good. Maybe run your piston choice by us. Go 0.040-0.060" over with that block.

MP-EFI, right?

Lou

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Thanks Lou! I plan on sending the motor somewhere to have the head ported and engine built. The engine has 150# of compression right now, which I understand may mean that it has already had the head and/or block milled. I have read on the forum that there are a few people around the country who can work the head. I'm right outside of Memphis and there are people here building race engines, but not the slant.

Yes I intend on using port injection, but I am clueless on the computers. There is a local guy here who is a tuner and tunes race cars.

With the 3.93 gear, 18" tires, 100MPH will be 5079 RPM. 75 MPH will be 2074 in .71 OD.

I want the car to cruise nicely at 75. I don't anticpate running it over 100 MPH-maybe.