Combustion chamber help
Turbo Mini Forums

Hi guys.

I need a little help RE combustion chamber size increase.
I have a std MG Metro head (12G940?) & want to enlarge the chambers. They are currently 21.5cc (std) & Looking on various posts, I'm seeing people with 28cc chambers.. Is this a different head, or can the chambers really be taken out to this volume? Is there area's in the combustion chambers that I shouldn't go to for fear of striking water? & the beak...I can see this is a contentious issue. What are the current thoughts?

Thanks in advance for any input

Jason

Yes 28cc is possible, but it's always a bit of a compromise when doing large chambers. Make sure the heads not been skimmed any considerable amount though or you'll struggle to get the volume.
If possible it's better to keep some resemblance of the heart shaped chamber as this helps induce swirl. Though at 28cc this isn't really possible.

Here's what you can remove if needed.



Though something like this will be superior, at least at lower rpm anyway.




Phil.

Edited by Turbo Phil on 7th Jun, 2016.

WWW.TURBO-MINI.COM

I reckon that is very generous of you Phil, giving away your trade secrets.

What's a community if not for sharing.

Phil.

WWW.TURBO-MINI.COM

After owning two of phils heads. Looking at pics and trying to copy to Phil's standards, I would suggest would be more than a little difficult IMO.

Edited by gr4h4m on 8th Jun, 2016.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

honestly having done my own head and knowing the work involved and being any amiture id just have the pro do it as you know it will be right it migh be more cash but its worth it for the hours youl be putting in as a first timer vs a pro it can be done on par with the pro but it will take a lot longer a lot

Wow, that's beautiful work.

Edited by motorgnome on 8th Jun, 2016.

Thanks Phil.. That's awesome, just what I needed. I don't need to go the full 28cc, (25cc), but knowing where I can safely go is a big help. These heads are not thick on the ground over here, (Australia), so I'd be really pissed off if I ruined one.

Edited by motorgnome on 8th Jun, 2016.

No worries.

Phil.

WWW.TURBO-MINI.COM

Be very careful to stay well within the gasket! I think that is the part that is easiest to mess up.

A back cut on the valve (even a miniscule one works) is the easiest flow gain on an a series. the rest is pretty much all hard work :)

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

Yes, it all about the seat!

yep between the seat and guide is the worst section for flow so work on that first if you are going to go in there and play around

a good tip to help stay in the gasket line / protect the face is to bolt an old gasket to the heat woth a cupple of bolts and big washersjust to show where it will be and stay an 1/8 or 16th back from it just to be safe as the gasket can shimmy around on the studs a little so may not end up where you scribed it or where you held it at the time

Edited by Turbo This.. on 10th Jun, 2016.

Ive got a 33cc head done by gavin fox who works out of stuart gurrs site. Did a really nice job and could get an even higher cc, but as said it does depend on the individual head.