Intake/Exhaust Port Matching...

Has anyone ever considered port matching the intake and exhaust ports on the 4.2L? I wonder what kind of gains could be realized if any? Or has GM already done an excellent job in this regard :undecided

Thoughts anyone?

would love to know....looking at the head of the L6 on the other post, it looks like a very well done job from the manfucaturer, so i'm just wondering if it would be worth all the hassle....sombeody estimated previously it would yield around a 20whp gain??

I'd start on the exhaust side, as they are small from the factory. Remove an exhaust gasket & you'll see there is a good 3/16" 'step' to the exh manifold runner. You'' scratch you're head & wonder how this engine runs so well with such small ports. Nice thing, though- plenty of meat for expansion all the way down to the bowls.

The intakes do real well with throat blending & guide blending. You can't take much off of the roof (thin), but it doesn't need it. The intake is short & has a nice split from the factory. Unless you want to make BIG numbers, I wouldn't mess with the intakes that much. The is a guy who's done some wleding & port relocation on the 4.2 head, but that was for a BIG power car.

Umm.. I dont know if you guys know this but are intake manafold is plastic and not that thick there would not be enuf plastic to remove to get it to match better..

If you wanted to match the exhaust side that would work well you might even wanna get the stock header extrude honed and ceramic coated while you were at it.:undecided I think doing those two things to the stock header would give you just as great of a gain..

I had a header of mine ceramic coated befor and I could tell a hp diff at higher rpms becuase the ceramic holds the heat in and the extra heat inside the header makes the air expand more and force its self out faster than a cooler header and you gain a few hp from this affect.

Umm.. I dont know if you guys know this but are intake manafold is plastic and not that thick there would not be enuf plastic to remove to get it to match better..

If you wanted to match the exhaust side that would work well you might even wanna get the stock header extrude honed and ceramic coated while you were at it.:undecided I think doing those two things to the stock header would give you just as great of a gain..

I had a header of mine ceramic coated befor and I could tell a hp diff at higher rpms becuase the ceramic holds the heat in and the extra heat inside the header makes the air expand more and force its self out faster than a cooler header and you gain a few hp from this affect.

We dont actually have a header, its more like an exhaust manifold. But for some power gains, you could extrude hone the intake manifold and ceramic coat the exhaust manifold. I know that SVT uses extrude honing on quite a few of their cars.

Extrude honing doesn't work on Zytel (plastic) intakes & doing the stock exh manifold would take a good 4-5 passes with their heaviest media. The stock exhaust ports and manifold are purposely built small, to keep plug (air) velocities high.

I just wish these guys would get off their butts and get a good header done. The funny thing- they could make the design semi-modular as the port architecture is shared with the 4/5 cyl engines.

Turbo4200, is it possible to gasket matchet the exhaust side with the head still on the engine? :)

Yes, but I wouldn't do it. To do it right, you need to work the whole port & bowl. Gasket matching (bellmouthing) would most likely loose power due to reversion (the step from port to manifold helps prevent this a bit).

I'm working with a CNC porting shop to come up with a good street port. It's at least a month away, so don't hold your breath.