chamber shaping
Turbo Mini Forums

I am going from 8.6 CR to bit lower.
I am wondering what the best shape of combustion chamber is?

gregor

now there's a question with a million answers.

Sorry I can't be more specific

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

yep, lots of answers...

Waht works for nat asp, will also work on a turbo for sure, but it's often a question of compormise!

everyone has a theory , i use the striaght scoop out and it seemed to work

Everyone knows that instructions only have to be read if the thing doesn't work....

Here's what Vmax were doing back in 1995 if it helps.


Karl.

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

sorry guys, I was not precise enough with my question. My English is not well and and I put my question as short as possible. But let me try again.

I saw so many different shapes of chamber and I was wondering if there is any differnce in power if chamber has a beak or not? Is a beak so important? Afer some comments from people I was a little afraid of round shaped chamber. I believe that round shape makes good job under high boost, but my turbo is used as a daily car offen in a big traffic.
Maybe the question is not smart and my opinion is wrong but I would like to hear your comments.

The chamber shape , need the beak to promote the vent of the combustion chamber ( so not jail some exhaust wich will stop the front flame ( bad combustion, ie more fuell more ignition needed for the same job) , the round chambers are the worst for the front flame propagation, ie : you'll need more retard and more and will be prone to more detonation for the same amount of boost (we are lowering the c/r to avoid this).
In fact the main question is, how many boost will you use?, as 8.5 c/r is ok for high boost application.you can simply deshroud your valves, clear out the chamber as described in many books (Vizard, Dee Hamils, Cars and car conversions, pics from the net), and it will low your cr enough for 12/15 psi on good fuell and intercooler, my next tweak to lower the cr after this would be to dish the pistons a little more , and would go further than this only for track ( I prefer using my car everyday with 10 psi's of boost , and use high octane with octane improver (or race fuell ) for track days and more boost)
regards
fab

hope the pic will work:

http://fr.f252.mail.yahoo.com/ym/ShowLetter/Photo_0050.jpg?[/img]

Fab, here is your pic, cheers Jim

Edited by Jimster on 11th Mar, 2004.

Edited by AlexF2003 on 11th Mar, 2004.

Edited by AlexF2003 on 11th Mar, 2004.

http://us.f1.yahoofs.com/users/79262c9c/bc.../__sr_/71d0.jpg?[/img]

[img]http://us.f1.yahoofs.com/users/79262c9c/bc/Dossier+des+pi%e8ces+jointes/__sr_/71d0.jpg?

HELP!!!!!

well I dont know what you hve done there FAB.

Alex

AlexF

Thanks Fab,
That is what I wanted to hear.

p.s. I have never got so many replays from one person at once.

Edited by gregor on 11th Mar, 2004.

not being too tech minded , i can not argue ( or spell) about what shapes best/worst all i know is my shape works for me , and other turbo people who have driven my car , say its as quick as most others, that have ?500+ heads on them.

Everyone knows that instructions only have to be read if the thing doesn't work....

[what I have done, it 's an impossibility to post a pic on the board...had to ask the help of Jim in emailing him the pic] ( , thanks Jim)

this pic show a head that I have done for my first turbo, it have 28cc chambers , 36/30 valves , and lightly cleaned ports with the exhaust port rounded in the upper exterior corner ( the exhaust manifold was matched too.
the chamber cleaning, started with the Vizard manner, deshrouding the valves to the gasket line and then grinding also the other faces to join the deshouded area , finished the job by cleaning the roof . was glad to see that it ended at 28ccs .
I used it with 10 psi's to start and then upgraded the boost at 12 psi's, with the std ignition setted at 5? an intercooler and std bdd needle ( couldn' t access to a dyno and I'm not recommend his use; I was also presurising the float chamber from the plenum to the vent pipe and the idle was set rich, the leaning thing was blocked , it worked as it)
fab