head button shape

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C

carlo cardinale

Member
Joined
Sep 1, 2009
Messages
13
Who can help me to design a high performance head button for .21 engines for low nitro fuel (25%)

Spherical, troncoconical or toroidal ????

tks

Carlo
 
Here's my Tip, Search "Head button" or "Combustion chamber" you'll end up with more opinions than you can poke a stick at.
 
There are many things that will come into play. What eng ,timing #. with that said most stock button are designed for low nitro to start with. you will not gain much if any with a different design with 25% nitro. most design changes are done to make it possible to burn high nitro.

More nitro will give much more HP than a different button design for 25% nitro.

Most testing has bin done for high nitro or none at all.

David
 
I think you will find that alky heads are pretty much flat across their chamber with a small bubble. Very little squish band angle if any. This is what I have learned studying Webra engines which are built for low (10%) to no nitro.

210952.jpg

DSCF1770 modified 2.jpg

083235.jpg

049w.jpg
 
Last edited by a moderator:
Application plays a big part in it. What might work in a tunnel might detonate like crazy in a mono for example.

Generally on lower nitro you can get away with less bowl volume for higher TCR before the onset of deto.

Hemi is a good start for bowl shape, but a flatter "roof" with a tighter radius has been netting some good results also.
 
Yes the flat top and strait sided chambers are working very good. tested on on my .91RS this weekend and the RPM's where noticeably better with no other changes to setup.

The flow meter numbers where 5 point lower. This setup dose burn nitro much better.

the top pic is the button for my.91RS and the bottom is a test set for a MAC .21 with different plug depths.
 

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