Does 10,5:1 JE Pistons will work w/single plug

[RS-GT]

I plan to do a cheap upgrade of my 2,4T : going with JE pistons, S cams and Weber 40. I don't really know if it's better to choose the 9.5 or the 10.5:1 compression ratio ?? any experiences ?

Thanks
JD

[DanS911]

I have just completed a rebuild of a 3.o with 10.5/1 J&E pistons and 46mm Webers and single plug heads. The motor was in a friends car before and it ran like stink. I hope the end result is the same for me!

[JohnJL]

You're on the edge there. My 10.5:1 JE's measured out to 11.2:1!

[DanS911]

Wow how the heck does that happen?

[Bobboloo]

It'll work but only if you use race gas. If you want to use pump gas then you need to go with the 9.5:1 set.

[juicersr]

Sure, IF you are able to fill you tank with 100+ octane gas everytime you fill up, or don't mind worrying constantly that your newly rebuilt motor is going to detonate if dont. I researched this a lot before starting on my rebuild. Gas quality is prolly going to get worse, so if you are not going to go twin plug, or use race gas every expert on this board that i read in threads and corresponded with said keep the compression lower than 10.5:1. I actually decided to go with 9.8:1 JE's with custom domes due to the fact that i have an EFI system with Wideband o2 that will allow me to make sure the AFR stay right where i want. Good luck with your build.

[alniki]

I wonder if a 3.4 with low compression ratio needs twin plugging?

Heard from a friend that a Japanese specialist offers rebuilt engines with displacement up to 3.6 without twin plugs that do not detonate. Dunno about the C/R but is there any other ways to prevent high C/R engine from detonating besides twin-plugging and high octane gas?

[Bobboloo]

Originally Posted by alniki

I wonder if a 3.4 with low compression ratio needs twin plugging?

Heard from a friend that a Japanese specialist offers rebuilt engines with displacement up to 3.6 without twin plugs that do not detonate. Dunno about the C/R but is there any other ways to prevent high C/R engine from detonating besides twin-plugging and high octane gas?

1. Flat top pistons with the spark plug placed in the center = shorter flame front = less advance needed = less chance of detonation.

2. You could always just retard the ignition but then that kind of goes against what you were trying to achieve in the first place with a higher C/R.

[Bobboloo]

Originally Posted by RS-GT

I plan to do a cheap upgrade of my 2,4T : going with JE pistons, S cams and Weber 40. I don't really know if it's better to choose the 9.5 or the 10.5:1 compression ratio ?? any experiences ?

Thanks
JD

In all truthfulness. The cheapest upgrade for your 2.4T is to replace it with a bigger motor. Unless your motor was recently rebuilt and everything is in spec this cheap upgrade will end up costing you $10k large. Many owners of these mag case motors go in for a cheap $500 reseal to fix some oil leaks only to end up 10 to 12k lighter in the wallet. If your motor is running well you might just want to leave it alone.

[RWebb]

Originally Posted by alniki

I wonder if a 3.4 with low compression ratio needs twin plugging?

Heard from a friend that a Japanese specialist offers rebuilt engines with displacement up to 3.6 without twin plugs that do not detonate. Dunno about the C/R but is there any other ways to prevent high C/R engine from detonating besides twin-plugging and high octane gas?

yeh - put the spark plug in the middle!

[onboost]

Originally Posted by RWebb

yeh - put the spark plug in the middle!

Yeah, I caught that one too...

[JeremyD]

Originally Posted by alniki

I wonder if a 3.4 with low compression ratio needs twin plugging?

Heard from a friend that a Japanese specialist offers rebuilt engines with displacement up to 3.6 without twin plugs that do not detonate. Dunno about the C/R but is there any other ways to prevent high C/R engine from detonating besides twin-plugging and high octane gas?

I have a 3.4 with single plug - I have decent gas in Florida too though