Exhaust port dilemma!!

**Stav** · 16-04-2006, 10:52 AM

Guys if anyone can make a suggestion here Id really appreciate it. It relates to the exhaust port.Many experts say to not match the exhaust port to the headers so as to create a reversal trap and keep the gasess moving outwards. The other lot of experts suggest to match port perfectly to the exhaust headers. Now I am leanning towards openning the port to match the exhaust for less restriction.What do you guys think?

xr8ute · 16-04-2006, 11:08 AM

Dont do it, keep the exhaust port (cross section) the same size. Changing the shape and volume of the port in that way could really hurt flow...

Is it really a restriction anyway? Just how big a cam, and how much compression are you planning on running? :P

You've done good work where it really counts (bowl), dont mess it up now by getting distracted by "BIGGER is better" ;)

stiddy · 16-04-2006, 01:16 PM

Id say just clean it up a little...

**Stav** · 16-04-2006, 03:23 PM

I have done most of the ports and deburred them .Also I opened up the exit to the port a tad.I have still left around 2mm of metal to maintain the anti reversal properties. However the smaller port may be choking the cylinder head.I might flip a coin on this one.

The AU exhaust ports are very close to standard size as I dont want a head which has max efficiency at 9000rpm,especially on a daily driver. I have shaped these ports only enough to remove rough castings . Efficiency of the ports is maxed out by the smallest diameter from the port to valve seats. By keeping the exhaust port very close to standard and eliminating internal obstacles I am hoping to lift the power from 3000 to 6000 rpm.

**Stav** · 16-04-2006, 03:56 PM

Sorry mate I forgot to say that the dev 4 cam is staying.I dont think it will work in every six but I think this cam needs some more compression and porting to come alive. Installing it into an AU is a 50/50 proposition of it working.My guess is that it has around 278 to 290 duration and hence is most likely togo well with headwork.

NeishaXR8_347 · 16-04-2006, 08:34 PM

The general rule of thumb with exhaust ports is to match it or very close to the size of the exhaust valve any more is pointless, which i think the AU ones are pretty good from factory. when we reco all the Ford heads at work (they keep us in business those i6's) i backcut the valves aswell with a 30deg about 40thou wide(1mm) helps it flow out smooth, when you were porting try not to loose the 70deg angle below the valve seat this is critical for good flow. just some more ideas too confuss you

**Stav** · 16-04-2006, 08:46 PM

The sharp edge under the seat left over from casting has been smoothed.Out of much material I have read it all said to do this.There is much contradicting advice.The head tonight has one set of ports left to do.

I will be taking it somewhere next week to flow test the stock ports and the completed ports to see if I have done the right thing.A 30degree back cut is definately on the cards if it flows well with some kline guides and 3 angle valve job.It will also cop some more compression due to some chamber work that I have completed. But first only after a crack test in temperatures of 300 degrees.

NeishaXR8_347 · 16-04-2006, 09:00 PM

personally from what ive seen at work with the bronze guides is that they dont last as long as the original cast guide, they are a quick fix and are a good invention, in my own jobs that i have done for myself i put the std ones back in the cast ones they do last longer and are around the same price, the only good thing that the bronze ones have over the cast ones is that the bronze is a better bearing surface meaning less friction, and bronze ones have spirals inside too retain oil to lube valve, but you wouldn't notice the diff between the 2, but my opinion is go for cast after working in the auto engineering trade for 6 yrs and recoing god know how many heads i think the bronze guides aren't what they are cracked up to be.

**Stav** · 17-04-2006, 09:27 AM

Quote:

Originally Posted by neishaxr8

personally from what ive seen at work with the bronze guides is that they dont last as long as the original cast guide, they are a quick fix and are a good invention, in my own jobs that i have done for myself i put the std ones back in the cast ones they do last longer and are around the same price, the only good thing that the bronze ones have over the cast ones is that the bronze is a better bearing surface meaning less friction, and bronze ones have spirals inside too retain oil to lube valve, but you wouldn't notice the diff between the 2, but my opinion is go for cast after working in the auto engineering trade for 6 yrs and recoing god know how many heads i think the bronze guides aren't what they are cracked up to be.

I had a suspicion of this.But everyone else had sung its praises.I had bronze guides in a head 16 years ago.The engine was nice and quiet for a month.Maybe this was it.

NeishaXR8_347 · 17-04-2006, 03:16 PM

Im not saying they aren't any good because installing a set of bronze liners is far better then leaving the guides worn and sloppy, the only guides that are good besides the orig cast ones are the ones that bmw, merc and most after market heads come with they look like a cast guide but are made from bronze/brass and last much longer but are a bit dearer. but at the end of the day you wont gain much from doing this just knock em all out and put std cast back in, the inlet ones should be fine just change ex if need be.