Cylinder Head Tech (great pics)

[scheides]

Saw this on evolutionM, thought I'd re-post here. Great info, applies to DSMs to if I'm not mistaken.

Its been awhile since I have done a "tech article" and since it seemed the piston and rod ones were good discussions I thought it was about time to do one on cylinder heads.

As some of you may or may not know we have been offering cylinder head porting on a limited basis on our bigger engine builds since we already have the engine apart. Some things we have learned about the Evo head is that they are subject to core shift much as the earlier DSM heads were and the VIII seems to be really the most violently affected.

Here you can see the edge of the bowl where it was plunge cut prior to having the valve seat pressed in at the factory:

http://img.photobucket.com/albums/v505/Hurrikain/Evolution/P1010390.jpg

You see its a fairly uniform machine line showing that #4 on this bowl is about where it should be. By the time we get to #1, the mold has been shifting enough during casting that the bowl is now D shaped and definitely not flowing as much. This is really bad news since its the last port on the intake and has some really restricted ports.

http://img.photobucket.com/albums/v505/Hurrikain/Evolution/P1010392.jpg

The VIII also has for want of a better word mold/casting marks on the intake side of the head that further disturb flow:

http://img.photobucket.com/albums/v505/Hurrikain/Evolution/P1010391.jpg

Oddly enough the IX really doesnt seem to have core shift problems nor does it have those mold/casting marks on the intake side. They have them, but they are on the exhaust side of the head. I think alot has been made of MIVEC making power when it has more likely been substandard bowls and ports on the VIII robbing the horsepower. Here is a pic of the same off center bowl after some initial smoothing:

http://img.photobucket.com/albums/v505/Hurrikain/Evolution/P1010394.jpg

http://img.photobucket.com/albums/v505/Hurrikain/Evolution/P1010393.jpg

Exhaust side pic-

http://img.photobucket.com/albums/v505/Hurrikain/Evolution/P1010395.jpg

Now off to the machine shop to have the guides pressed out, a tanking, and then finish what you cant reach if they are in there. Its interesting to note that this head went on a 3582HTA car that at 23.5psi had made 428whp. After the head port and bottom end build (no other changes in the motor, compression was 9:1 so as close as we can get it) the car redyno'd at 478. It allowed for more timing which is where some of the power came from, but with better flow the car will naturally thrive.

I dont happen to have intake port pics of this particular head, but typically nothing more than bowl work and casting line smoothing is needed. The bowls of these heads have some pretty nasty ledges typically which really hurt balanced airflow. The exhaust is generally also not very good, but since the flow laps the ledges on the way out its not quite as critical. We dont leave them like the factory does though for sure. I have seen some heads that are so smooth stock they almost seem ported in comparison to the Evo heads. BMW for instance does not have flaws in the bowls and ports but since they are trying extract every bit of all motor power it makes perfect sense.

Hopefully this can be as interesting as the last article and get some good tech and pics flowing.

original article here:
http://forums.evolutionm.net/evo-engine-turbo-drivetrain/429551-cylinder-head-tech.html

[rose0529]

Interesting write up, .... will be interested to see what kind of results you get!

[FattyBoomBatty]

So, did you get that type of porting done to yours, and was the head you have on the car now affected like that one in the picture?

[Shane@DBPerformance]

Yep, DSM heads are like that too. That's what you actually get in there and port/clean up when doing a pocket port on the Mitsu heads. There are usually some pretty bad droppoff like that on every valve seat. Making the ports all pretty, gasketing matching, and polishing the exhaust ports might look nice in pictures on the interweb, but it might not do anything for power and those polished exhaust ports will be full of carbon in an hour anyways.

[scheides]

A whole hour? LOL I'd think they'd be black after about 5 mins!

[FattyBoomBatty]

or one minute. Basically what you're saying is that unless you make them larger, there's not much point to doing anything in the ports?

[Shotgun!]

or one minute. Basically what you're saying is that unless you make them larger, there's not much point to doing anything in the ports?

No need. Even more so on a Conquest, where the ports are huge but mounted way too low. You don't need them bigger, you need them much higher.