gday,

this is a picture of the combustion chamber on my jim mock 'race' spec ported head. I've read a few things about enlarging the combustion chamber to drop compression n so forth, just wondering if this head would be suitable for a turbo project, as when my mate picked this head up from jims work shop, jim said that this was a 'turbo' head.



if needed i can take a few photos of the intake and exhaust ports, they have also been ported, the head has stainless exhaust valves and performance valve springs, with rebuild rocker gear.

How about a better picture, even a pic of the ports with the valves removed would be good.

That head would be fine for turbo, just cc the chamber to work out what compression your aiming for.

i cant really get a clearer picture, thats the best the camera will take, and im not real keen on pulling the valves out. Its just that jim mock said it was some sort of turbo head, and there are scribed lines around the combustion chambers, sought of like an outline for the die grinder.

How close to the scribe lines did he get on the opposite side to where the spark plug is. Alot has been taken out there which is good. The compression with stock pistons and that head should be good.

If you could line up a head gasket on the head and take a photo it would help in seeing how close he got to the combustion ring. See you can get close, say 5mm but you dont want to get too close to get rid of the squish area. Just interested to see how close JMM went here.

heres some better pictures, and you can see the scribe lines around the combustion chambers.

With turbo and sohc heads they don't need too much to make a difference..The main thing imo is correct compression for your power level and what suites best to turbo flow map..You want it in the higher island around its peak torque to gain the most out of turbo and engine..
What I'm saying is IF a GT3540 flows at its peak between 15 to 25 Lb then you are leaving some power on the table!!! So if your runing 9.5 compression as most engines after E.D are you'll need to drop compression..Yes you'll make power with high compression and boost BUT only up to a point..Like most things with engines its the total package...One thing to keep in mind the engine manu made this engine to go fairly well N/A so ports etc are not too bad when it comes to forced induction... Having said that though a head ported maybe too far on port size where it is actually loosing low end power with forced induction this comes back. Check and try to read turbo flow maps as its now the heart of engine power and how efficiant it will be...
This is a GT42 flow map..

Last edited by EBXR8380 on Tue Jan 17, 2006 12:26 pm, edited 1 time in total.

righteo, thanks for that mate

The way they have modified the combustion chamber for turbo is extremely important. They have left some squish area there at the same time removing the material around the exhaust valve which helps heaps IMO, probably more than porting work. It seems a good head to use.

Thanks for the photos

nice that one is a keeper then, worked out well actually. I bought the dev5 package when i was gonna do my next car N/A but have decided to build it up as a turbo now, i can still use all of it bar the cam! nice