Thanks.
Now I have an idea of what I need to do.
Maybe I should just send the head out to you guys and have it ported
$$$$

during valve overlap exhaust can and does move backwards to contaminate intake flow. leaving the lip helps prevent this back flow. second, flame front starts at plug and moves outward. leaving lip allows a smoother travel over the valves.

That's a good idea HG!! a pair of each, and junk the valves. That's a quick and safe method.

I agree with HG, knock it down to so the top of the valve seat insert is flush with the casting.


That holds true on a 2 valve wedge head, with long duration cam and loads of overlap, Like a domestic V8 NA HP build where the vacuum of the exhaust helps draw in the new air fuel charge.

That will not really apply to a "semi-hemi" 4 valve head of the 4g/evo head, off boost driving it may happen, but on the low overlap of most force inducted engines, boost pressures push past the valve, so there is not the vacuum on the intake stroke.

low overlap does not mean no overlap. boosted cars have more back flow than normally aspirated cars. someone just posted back pressure data for fp green and bbk full. both had ~55 psi (exhaust mani pressure) at ~28psi boost. during overlap that 55psi can and does move backwards through the motor with only 28psi holding it back. heck you dont even need technical data. just take a look at you intake manifold on a turbo car after 100k miles. it will be coated with black exhaust soot from the back flow, caked more like it.

so headgames, how many heads have you ruined removing those valve margins? lol.

None...or maybe I do not understand the question, or you didn't read the post

Sounds like the guy needs to degree his cams if that is the issue, or find the restriction in the exhaust system.

Most Forced engines I have delt with have 4* or less of overlap, some set at -2*

Look at the NA world and they have 30*-40* of overlap

The build up in the intake you speak of, doubtful that if from back flow, It is more from the EGR valve opening into the intake, and the oil vapors the PVC (with out a catch can) suck into the intake, add the other VC vapor line to the inlet track and you get a horrid mess in the intake.


HG, from coupes statement, I would have to guess he thinks you are installing the valves you use to protect the seats in a head to be run....

Werd. Pull the EGR, EVAP, and PCV setup out of the intake manifold and the manifold and intake ports in the head will remain spotless for years.

Just my opinion here, but one of the biggest concerns in a turbo motor is hot spots in the combustion chamber. I smooth the hell out of the combustion chambers for this reason and this reason alone.

Instead of tapering the bowl out to match the cylinder though, I would have deshrouded the hell out of the valves first, and then straightened the walls up. With the 87mm bore, I have to imagine you could effectively eliminate the shrouding around the valves.

on my dad the EGR is plugged at the intake manifold. If I could. I would of welded it shut in the exhaust port but there is no way in getting a tig torch in there. I have 2 -12 lines of the valve cover to my catch can. My new catch can setup will be 2 -12s of the valve cover. Either 2 -12' or 2 -10's of the block.

Stupid question. EVAP is located on the drivers side in the back on an Evo 9?
How do I delete it?
Thanks

you guys are seriously off if you think there is no back flow in a turbocharged 4g63. I have worked on nothing but the 4g63 for about 15 years now. I have seen all sorts of evidence of back flow but the one that stands out the most is when an engine loses a spark electrode. I have seen one broke electrode damage all four cylinders before it makes it way out.

maybe you are familiar with the early 4g63? are you aware the early 4g63 came both N/A and turbo.? take a look at the factory manual. the only changes to cams were the intake on turbo was advanced 5 degrees from N/A model.

I would much rather have contamination then detonation...

^^^
For Example:
On paper, removing the quench pads is a terrible idea.

In application, my buddy did it on his 3S-GTE setup. It needed like 8 degrees more timing advance every where, but it picked up another 60WHP over the same setup with quench pads. Go figure...

Detonation supression is king in the power game.

okay . lets spell it out for you.
valve margins= less back flow= less detonation.

removing valve margins is a bad idea.

I have discussed squish on this board before. I seemed to be the only one who cared that mitsubishi designed the 4g63 for evo 8 /9 with a very low deck height. the factoty 8/9 run like .110 squish which is really no squish at all. normal squish being about .035-.040. after market piston manufactures didnt pay attention to the fact that the 8/9 pistons ran low deck height. they just used same height as previous 4g63, which brings squish very close to gasket thickness.