My Chamber Shape- Opinions Please
Turbo Mini Forums

I did some head grinding yesterday, and forgot one key step in the process. However, the shape I ended up with seems to be viable. I'm pretty sure I've seen this basic shape on another person's head, so it's not a ground-breaking effort. Aside from the lowered compression, is this a good shape for an A-series turbo for power and detonation prevention, or is TurboPhil's steep angle, kidney shaped, no-beak design vastly superior (his is more the shape I was trying for!)...?

Here's a pic (I don't know how to get it embedded in the post, as I tried dragging, and that didn't work):
http://www.drjing.com/Mini/Images/HeadWork1/IMG_1970.JPG

Though it looks rounded, the chamber walls are actually flat, but taper from the deck down into the orignal chamber shape. It's not a Hemi design, even though it looks it in pictures...

BTW, this head will be getting insulative/reflective coatings, so it should be interesting to see how it performs! I just wanted to get your guys' takes ahead of time...

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1967 Cooper 's' Turbo build @ www.drjing.com

everyone has there own opinons on here about what works but basically give it a go. The main aim is to ruduce compression ratio after that is to make a good shape chamber to reduce detonation. Some do away with the beak and some keep it.

I'm no expert but i will add some pictures of mine later

Thank you, Mike. I look forward to seeing your results.

Has anyone posted a thread showing different combustion chamber shapes and their dyno results? I know results are very relative to the overall engine package, but there might be some useful info even with comparing apples and oranges...

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1967 Cooper 's' Turbo build @ www.drjing.com

Edited by Tom Fenton on 8th May, 2005.

Thank you, Tom! How do you do that? And is there some way that I can make future pics smaller so I don't chew up too much of TurboMinis' bandwidth?

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1967 Cooper 's' Turbo build @ www.drjing.com

Its quite straightforward, you need to put the letters img in square brackets, then the web address of your picture, and then afterwards put /img again in square brackets. With no spaces between or it won't work.

As for resizing, just reduce the size of the picture in Photoshop or similar before you upload it to your own webspace.

Thank you, Tom! I'll make sure to do that in the future.

As an update, I was reminded that my beaks are way too sharp, and will cause problems by being foci for heat (causing detonation). I'll be grinding them down, but will experiment on a Canada-model head first, to know how much of the beak I can remove without hitting a water jacket... The Canada spec 1275 heads are not that desirable, even though they are identical to the 12g940 with the addition of smog ports...

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1967 Cooper 's' Turbo build @ www.drjing.com

also tape an old or cheap head gasket to the head so if you slip with the grinder you dont damage the head

no longer a series, but still 1.3 turbo.

And leave some old scrap valves in the guides to protect the seat area as well.

Thanks, guys. I saw the scrap valve technique the other day and thought it a good idea, too!

Too late on the deck surface. Good advice, but a little late, I'm afraid. I've already rolled the grinding bit across the surface... -sigh- Guess I'll be skimming off a gnat's arse again...

Thanks, again, guys! This is a great place to come for turbo-specific info! I'll be modding another head soon, and will use the advice you all have given me to make sure I don't bung that one up too badly... :)

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1967 Cooper 's' Turbo build @ www.drjing.com

Just wanted to update you all on my head progress. I've completed the chamber shaping. Here it is:

I've removed the sharp edge of the beak, and left a small amount of rounded beak in its place. I'll get the chambers blocked off soon and figure out my volume. I'll then balance as necessary.

I'll be working on my MG Metro head, soon. That will have the proper shape, and will be the one headed out for coatings. It should be fun to play with these heads, though, and see what the power differences are. Of course, it's kind of apples and oranges, since the MG head has larger intake valves... Other than that, though, they are pretty evenly matched but for chamber shape/volume.

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1967 Cooper 's' Turbo build @ www.drjing.com