...when you can just turn up the boost?
Reason I ask is I have a cylinder head on the bench right now - I'm only planning on replacing the valve seals and rounding off the sharp edges and some of the casting marks. But if there is some benefit to doing more extensive porting, I'd like to hear it.
Rough casting marks and bad flow paths will increase friction. Friction generates heat. Just my opinion
Work smarter, not harder!
Yes, the same benefits apply, but don't expect huge gains. If you're wanting the most possible power, then do it. If you've got the headroom to just turn up the boost and don't care about breaking records, then don't bother.
What's the motor in question?
^^^ What he said. Really not worth the time and money on most street driven cars unless you are going all out. It might make 10 more hp, but putting that time and money into the exhaust tubing will easily make more hp
I think it depends on the engine... bigger valves and porting on the 8v SOHC volvo engine seems to help a lot.
if I was comfortable in cutting on a head and had the head already apart and on the bench i'd def cut it up a bit...
A lot of times more harm than good has been done porting a turbo head. However, on 4G63 and other multivalve heads IF you go to oversize valves +1mm or larger you must work the head or the larger valves will actually restrict flow.
I had the head ported on my fake mustang SVO.
Fantastic results. Never had a before and after dyno to brag with, but I can say for sure the driveability did not suffer at all, and there was much less detonation.
Anything you can do to improve flow and remove restrictions in a turbo engine will allow more power/same boost, same power less boost, quicker spool times, better flow up top.
It does depend on what motor you are doing. Like the M20 I'm building, there isn't much point in going past cleaning up casting marks, light polish on the exhaust, a little bowl work and good valve job.
Just going in and indiscriminately hogging out the ports will hurt your air velocity at the valve and lose low-end.
yep, that!
Ugh. Quicker spool times.
That's the LAST thing i need. 
port match the ex. mani, more ex flow will certainly show a benefit, same with intake but not as necessary on a turbo car as the exhaust, imo. still will show benefits. the port matching, though, is easy and can be done with a dremel tool at home. just match the mani to the gasket.
From a fluid mechanics standpoint, with the same pressure differential between the throttle and the cylinder (ie constant amount of boost), you will get higher air flow rates (and thus more power) by reducing pressure drop through the runners and ports. You can do this by increasing the diameter of the runners and ports, and by decreasing the surface roughness. Reducing sharp edges/transitions and increasing the radius of bends will also reduce pressure drop.
However, as some have stated you don't necessarily want to increase the port diameter immediately before the valves as you will loose air velocity and will not get the ram effect which increases power at low rpm.
Also, as several others have mentioned, this reduction in pressure drop is typically a second order effect compared with the driving pressure differential (ie: amount of boost). You'll make more power by turning up the boost, so do this until you reach some limit (detonation, turbo's too small, etc...) then focus on porting.
thankfully you guys are more intelligent than the last forum I tried to defend both Port/polish AND a cold air intake for a Turbo car..
Actually "cold" air intakes dont make much difference, but properly sized intakes sure as hell do. On an EVO a popular intake has been shown on the dyno to actually act as a sonic restrictor and limit the amount of air through the intake to the point that the turbo cannot make any more boost. Swapping out intakes for a "proper" one and everything was back to normal.
CAVEAT- IF for some reaon your IAT sensor (including those in your MAF) is way out in front of your turbo then it is possible for there to be a difference in power between a cold air intake and one sucking warmer air as the ECU will decide to make timing and fuel adjustments it might not make if the IAT was being taken properly AFTER the intercooler etc. and as close to the intake as possible for a more accurate reading.
DWalker460 wrote: Actually "cold" air intakes dont make much difference, but properly sized intakes sure as hell do.
i have to LOL every time i see a "cold air intake" with the filter positioned behind the radiator core.
mad_machine wrote: thankfully you guys are more intelligent than the last forum I tried to defend both Port/polish AND a cold air intake for a Turbo car..
I think you are right about both. Neither I nor anyone else here is saying that port work or a cold air intake will hurt. Assuming that your MAF is scaled correctly (if you even have a MAF of course) a cold air intake can add power. And if you have the head off anyways what does it hurt to clean up the intake and port match. But I still think that dollar for dollar an exhaust is the best bang for your buck on a turbo motor. Just my opinion here but I would follow that with intercooler piping, intercooler, and fuel upgrades like larger injectors and fuel pump. Only after that would I look at a cold air intake and port/polish of the heads.
I stumbled across this post. Just looking around for ideas. I have read hundreds of posts on various topics of ICE modifications for various reasons. Most turn into pissing matches and lose the meaning of the original post. This, I must say, is what a forum is about!
KUDOS to all here!
I did find some very good input and may ask questions for further input. Thank you for allowing me in to this group... very cool
I have no actual experience, just theoretical knowledge. But...:
Yes, you can just increase boost to move more air. But more boost means your intake charge temperature goes up. Compensating with a huge intercooler increases turbo lag.
That's my poor understanding. Your reality may very considerably.
David
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