Combustion chamber mods

[Sam_Q]

I am doing some research into modifying my combustion chamber and I would like to know what others have done, if they have any pictures and how they did it: ie what with.

For what i am looking at I think i will have to use a milling machine with the head bolted to an angled mechinism (forgot the name).

[jeffro ra28]

angle milling is typical of 23 degree chev v8's. Its not very relative to over head cam engines like the 4age.

A little more information on the application would be nice. its hard to give an answer, as always, every different application requires a different design.

[Sam_Q]

angle milling? as in milling the head when its bolted to an angle like mine? why isnt it relevant to overhead cam engines

[jeffro ra28]

v8 engine builders have been angle milling since the 60's to gain air flow. A standard chev engine has a 23 degree valve to bore centerline angle, a race engine chev head will have 10-11 degree angle.
Are you seriously considering milling your head so that one side is lower then the other? Then are you going to order yourself a custom short timing belt to fit the new fucked head with a thin deck on one side?

It is not desirable on overhead cam engines.

The main gains are acheived via re-shaping/ unshrouding the valves.

[Sam_Q]

oooh I get you, no I dont want to touch the face of the head i mean just the combustion chamber, angle milling the squish areas to do unshrouding and some other mods

[jeffro ra28]

well, what you want is a regular flat surface grind. You should only radius the edge from the squish to the chamber itself. If you angle the entire squish area you are taking away the whole squish affect. However, this is also relative to application.

If this was a heavily boosted engine, i would probably advise otherwise.
A Larger radius on the squish to chamber to give it a smoother transition, However i would still leave majority of the squish area flat.
The "tighter" the chamber, the less boost and ignition timing you will need aswell as more prone to detonation.

[Sam_Q]

ok I better be more specific which I know I should of done to start with, its a 4afe or 7afe head (atmo application) and I want to not only unshroud it but also take some of the squish area away between the intake and exhaust valves. I would very likely of kept the head flat as you mention but for some parts I might of angled the edge of the squish area down to the bottom of the chamber.

[jeffro ra28]

there is no squish area between the intake and exhaust valves.

Are you running custom pistons? Because you would have lost a shit load of compression by doing what you say.

[Sam_Q]

if I go ahead with this I would likely run 4age pistons, I will see though. As far as I can tell the 4afe head has a smaller chamber than a 4age to start with so I may already be in the right direction. I can assure you I will do some carefull measurements and many calculations before I do anything.

[Sam_Q]

as for that squish area



nicked off Bills wesite

ok it isnt directly between the intake and exhaust but more like just off it but still every peformance head doesnt have much of a squish at all to either side of the flow path. I will of course do even more research before I just assume thats how its meant to be. Anyway sujetions?

[jeffro ra28]

i see what you are getting at. If it were me, id blend this area you are talking about into the chamber shape.

[Sam_Q]

thats exactly what I was thinking, I plan to start a thread on chamber shape soon, i also want to go to a motorbike shop and take some pics there, that has to be a good guide right?

[jeffro ra28]

There is always something to get idea's from. At work i use NASCAR engine parts as regular examples, as we have a few around the shop.

I have also gained a few idea's from late model motorcross engines. As they are factory designed as a performance engine. There are still gains to be made from the production engine, but i have seen things such as "from the factory port job" on a KTM 250sxf i did up. I also did up a RMZ 450. There where area's i could see an improvement and saw considerable increases in performance after modding. But its a good place to start your design idea train. The other thing to bare in mind with motorcross engines in particular is that they are designed as a maximum effort engine, with a broad smooth powercurve. So its sorta like the best of both worlds with these. Ofcourse there can be mods made to make it a higher HP engine, but then it sacrifices ridability.

I highly suggest you do a google search on "mike chapman" of chapman cnc cylinder heads.You should learn alot about the nitty gritty if you find the right article.

[jeffro ra28]

http://www.circletrack.com/techartic..._porting_tech/

[Sam_Q]

I will thanks, anyideas where I can see some 4v combustion chamber shapes?