Slant Six Forum :: Mild build, would like more RPM

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

Author:	MazdaRX8/6 [ Tue Nov 02, 2021 8:23 pm ]
Post subject:	Mild build, would like more RPM
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.

Author:	ProCycle [ Tue Nov 02, 2021 8:29 pm ]
Post subject:	Re: Mild build, would like more RPM
Larger valves, clean up the ports, mild cam.

Author:	MazdaRX8/6 [ Wed Nov 03, 2021 5:37 am ]
Post subject:	Re: Mild build, would like more RPM
Quote: Larger valves, clean up the ports, mild cam. No special pistons or rods? I guess a proper balance job goes without saying.

Author:	ProCycle [ Wed Nov 03, 2021 7:58 am ]
Post subject:	Re: Mild build, would like more RPM
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.

Author:	volaredon [ Wed Nov 03, 2021 10:28 am ]
Post subject:	Re: Mild build, would like more RPM
Long stroke doesn't lend itself well to high revs, without a lotta help

Slant Six Forum https://www.slantsix.org/forum/

Mild build, would like more RPM https://www.slantsix.org/forum/viewtopic.php?t=66273	Page 1 of 1

Author:	Dart270 [ Wed Nov 03, 2021 12:05 pm ]
Post subject:	Re: Mild build, would like more RPM
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

Author:	MazdaRX8/6 [ Wed Nov 03, 2021 4:57 pm ]
Post subject:	Re: Mild build, would like more RPM
Quote: 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 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.

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