Exhaust Ports Too Big?

[camorinta]

Hi all.. Well nearly sorted the 5k back together but tonight had a look to see while i had everything apart to maybe port the intake , match bla bla etc..

Its a 5k, 5k head, extractors are 4-2-1 ( dnt know brand) gasket is a Toyota product.. that metal one. (can get code if helps)

 

I put the gasket onto the extractors to see how they line up and was surprised to see that the gasket ports were much smaller then the size of the actual

extractor ports.. As an estimate like 2mm on each side. So not like the intake where I will probably need to take 2mm at the bottom but all round. The

gasket lines up resonably well with the head ports and the intake ports... sooo I'm thinking that this would interrupt flow substantially..

 

Is it like this always or?

 

Cheers Amar

[Taz_Rx]

Google "scavenging effect" ;)

[snot35]

It's more anti reversion, but if the ports are smaller than the extractors this is a good thing. Exhausts are fairly complex for a bunch of tubes and there is a pressure wave that is generated when there is a change in size of the exhaust (i.e. at the collector) which travels toward the head and can help to push burnt mixture back into the cylinder. Having a miss match reduces this effect. I've read that if you can line up the top of the extracts with the top of the port and then have a larger miss match at the bottom that's the way to go.

[camorinta]

 

I found this clip to be useful. snot35 seems like you spot on :P

 

Cheers Taz, good research.

[altezzaclub]

Cut the gasket out to fit the smaller of either ports of manifold, With the exhaust you could spend the time to match port to gasket to manifold if the port is biggest. If the port is smaller then match the gasket to either, as that small part wall stops reversion waves like snot35 said.

 

Make sure they all line up when you fit them together, I marked the positions on all three items carefully before I bolted them on. Because the studs allow play, the real way to do it is get it all lined up then drill 3mm pins through the manifold into the head to hold them in place.

 

My extractors both fouled a bolt with a weld and didn't match the ports correctly to start with.