Re profiled 4LO heads

[yamark]

Evening lads.

Does anybody have any details/measurements for re profiling 4LO heads?

Angles, volumes, the more info the better as I've asked my mate Dean if he can re profile some of my "mullered" heads.

Cheers, Mark       

[Tobyjugs]

Hi Mark this is a really big subject with lots of theories and and profiles of combustion chamber
The only guidelines I use are
The squish band must follow the profile of the piston crown
The uncalculated compression ratio must not be too high I am using 13:1 on a 195 cc barrel
Have you asked Mick Abbey
I always ask the tuner I use for advice and guidance
I am modifying a standard 4lo cylinder head to accept combustion domes once I'm happy with the mod The combustion domes will be made by VHM

I had a head O-ringed by Metmachex which I think is great but the compression ratio was 16:1 and the tuner I used did not like the width of the squish band
You can see a before and after pictures on my thread help needed from the tuning guru's
The new profile of the head made the dyno graph profile a lot different

[bare]

Simple curiousity: How are you managing 16:1 or 13:1 !?
Total piston travel ?
Normally... on a 2 stroke... it's from closing of Ex port onwards. Hard to compress anything with large holes in the bore.
An easier measure/basepoint is Compression pressure.. as in 155/160 psi is pretty well the acknowledged max for continued engine use enjoyment.

[ringding]

I'm sure that i read that stan stephens uses a 14 degree angle for the chamber. Think it was in one of the articles he's written for cmm recently.

[Tobyjugs]

Aug 6, 2017 0:43:03 GMT 1 bare said:

Simple curiousity: How are you managing 16:1 or 13:1 !?
Total piston travel ?
Normally... on a 2 stroke... it's from closing of Ex port onwards. Hard to compress anything with large holes in the bore.
An easier measure/basepoint is Compression pressure.. as in 155/160 psi is pretty well the acknowledged max for continued engine use enjoyment.

Hi Bare this is measured with total piston travel and does not include port openings that's why I call it UNCALCULATED compression ratio.

When I build an engine this is one of the things I check to make sure there is nothing fundamentally wrong with the engine build.

In my opinion if you are tuning your engine or changing any parts from standard this should be checked.

It's a bit difficult to do a compression test when the engine is on the bench. If you build the engine into the bike and do a compression test and it's no good it's more hassle to strip the engine and fix the problem.

Mark;     If you are not in a rush I can send you a template from my combustion chambers once i'm happy with the insert domes.

[yamark]

Thanks Tobyjugs, that's a nice offer. However there is a time restriction (as Dean is going to a different machine shop).

I think with all the information given, Dean will be fine.

Thanks to everyone for your advice .

I'll let you know the results.