Need help - Low compression ratio engines and drivability

[vqpwrd240]

Well, I need to know how the car will drive if I put in a built ka24de with an 8.6: 1 C.R. but no turbo for now. So will it drive well? I wold like to put the engine in now and then after winter add the turbo system. This way the engine can have time to break in with no boost. I do not want to do any damage to the built engine and I do not want the car to act weird or have anything go wrong. I know the car would have less power because of the compression being lower than stock. Will I have to do anything with the ecu to have it drive as normal as possible over the winter? Any help would be great. Thanks in advance.

Ferhan

[480sx]

Your car will run like a champ, you wont really notice any differance.

You'v got a good plan btw, just make sure you break your engine in right and you will have a good platform for a turbocharger.

[vqpwrd240]

Thanks 480sx. So I really have nothing to worry about. No need for ecu or tuning changes at this time? Will have no intention of screwing arounf with the car over the winter, so I will break it in right.

[DevilMB3017]

The only thing I noticed was after going lower compression with no turbo was regular gas is much better. If you use prem. fuel, you'll spit it all out the tail pipe.

[scheffler]

I did the same thing that you are talking about. It ran great. I didnt do any changes to the ecu. I have 8.5 comp pistons and ran it with stock everything until i put my turbo on.

[vqpwrd240]

Thanks guys. How would head work and cams affect the engine without the turbo? Also are cams even worth it on the KA? I was planning on having / building a custom intake manifold as well later on to get more air into the engine. Ideas?

Ferhan

[WDRacing]

Lowering compression WILL effect driving, but it's hardly noticeable at all. It also effect efficiency and gas mileage as well...for the worse. But again, not really noticeable. I'm just telling you so you're aware. Lowering compression allows to add boost or timing. I suggest, if you're going to run 91 or better, that you bump the stock timing up a tad. You throttle tip in will be crisper and the car should "feel" more responsive.

But no tuning or anything is required simply to run lower compression pistons. Hell I had my compression in the 7's on my RB20. But it was purpose built for drag only and ran 28 psi of boost as a minimum.

WD

[spooled240]

I am thinking he could lean out his engine a tad since his compression is lower. Sort of the reverse logic in adding more fuel for more compression, right? He could save a little more gas if its an issue.btw, great way to start off a turbo build!

[eazye2000]

...sounds logical me thinks. Take some fuel away if that's at all possible. Or if you don't want to do that, crank the dizzy and advance her a bit. And running the 'cheap' gas would be awesome! I wish I could do it.. lolAlthough my car has 8.8 Arias stock bore pistons, I have a .080" head gasket. Which is 2mm I think? I've never calculated the actual compression ratio, but it's pretty low. I can make lots of boost!! yay!!

[vqpwrd240]

Thanks everyone. What about the head work and cams? If I am running stage two or stage three cams. Will the car run fine? Will I need to get a ecu upgrade? Thanks.

Ferhan

[480sx]

You can just drop cams in but if you do you arnt getting your moneys worth. You really need a tune to accommodate the different amount of air being introduced to the combustion chamber by the longer duration cams.

It will run fine though.

[240sxfan6882]

You'll be ok. I been running with lower compression built KA for over a year now. I just took my time piecing stuff out. I noticed my car makes less power...but thats cause of less compression and i have 18x9.5 wheels..compared to stock steelies. Gas mileage is still good...i just get more backfires. thats all.

[Zippy69]

If you are backfiring, then it is a timing issue, not compression. Bump your timing up a few and you will burn your fuel more efficiently, and no more backfire.

[spooled240]

if air gets into the exhaust system or just going catless will create some backfires.my buddies mani cracked and he said he was backfiring cuz the air was getting in his exhaust system through the crack. Sounds tight tho lol