When porting the exhaust manifold, on vfaq its more than a port match and it causes lag for a 14b. Is porting that much better for a bigger turbo? Or did the people of vfaq over do it, because thats more than a match. Would a port match of the exhaust manifold and head be better then porting the exhaust manifold too far?

porting should make it have less lag no matter the size, due to you are opening up the runnners on the manifold letting more air flow through it. more air going to a turbo would spool it faster. so small turbo mid turbo or big turbo im pretty sure porting would = less lag

hmm yea porting should help with flow, my ported 16G and ported 2g mani have full boost at 3400

ApexVIII said:

hmm yea porting should help with flow, my ported 16G and ported 2g mani have full boost at 3400

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exactly. 3400, with it port matched or stock it will hit full boost at 2500 rpms.

pj91gsx said:

exactly. 3400, with it port matched or stock it will hit full boost at 2500 rpms.

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hmm what is your boost level? i hit 20psi at 3400

and 14lbs at 3200. i dont think that the porting should have slow'd it down that much, do you have any pictures?

and are you talking about the manifold? or you ported the turbo? ### i ported a 14b for a friend and he said it spooled faster then it did befor it was ported

ApexVIII said:

hmm what is your boost level? i hit 20psi at 3400

and 14lbs at 3200. i dont think that the porting should have slow'd it down that much, do you have any pictures?

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It is just stock boost, I dont have any pictures. I didnt consider the higher boost level. I just remember after rebuilding my friends motor completely stock no port at all. once I hit the gas in all the way it was at full boost. It was instant. Ill just trust your word on it. Im just wondering about porting the exhaust manifold so much because its going from port matched gasket to huge ports if you port the way from vfaq. Wouldnt it be best to port match both head and manifold to the smaller oem gasket vs. the bigger oem gasket? It would eliminate turbulance. Or would it be best to port out the head ever more as well.

Yes, as per the vfaq it is better to port to match the smaller gasket. The larger one will give you 1/4 inch larger ports than the head which is probably a waste of time.

It is better to have the manifold ports a bit larger than the head exhaust ports because things don't always line up perfectly.

yup... IMO you should always machine the manifold larger than the head

if you overmachine the port (more extreme cases) you will lose air velocity and hurt spool time... this is why the ports are different sizes straight from Mitsu. The longer ones are smaller.

so. use the vfaq way (larger gasket) or port match the smaller gasket?

I believe the vfaq suggests to match the smaller composite gasket, not the 2 layer stainless or 4 layer copper. Port it a small amount over the size of the gasket

ok. thanks for the help.

Yes I second that

Freerevving said:

yup... IMO you should always machine the manifold larger than the head

if you overmachine the port (more extreme cases) you will lose air velocity and hurt spool time... this is why the ports are different sizes straight from Mitsu. The longer ones are smaller.

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Amen! Wider ports don't help spool. Just overall flow. Some of the above is wrong.

The stock 1g manifold ports are the same area as 2g ports and both are the same area as evo3 ports. Port matching the outlet of the manifold to the turbine housing is what helps.

dsm-onster said:

Amen! Wider ports don't help spool. Just overall flow. Some of the above is wrong.

The stock 1g manifold ports are the same area as 2g ports and both are the same area as evo3 ports. Port matching the outlet of the manifold to the turbine housing is what helps.

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afaik there's nothing wrong... I was talking about the port volume of the head... the exhaust ports that connect to longer runners have less volume. Wasn't talking about the manifold port volume... Although the manifold does have different hole sizes that correspond to the different sizes on both head and gasket

And you can gasket match the manifold... but there are benefits to keeping the head's exhaust ports smaller than the exhaust manifold ports.

It should be mentioned I guess, if it is a 2g/evo manifold then that obstruction in the #3 runner should be removed as much as possible. It is located at the end of the runner where it meets the collector. It blocks about 1/4 of the overall area if not more. You 'll see it if you look down the runner. It is done from the collector side though. I 've seen it more than once when people hog out the collector, even try to open up the runners (which I wouldn't recommend) but leave that thing in there.

^^^Are you talking about the divider between number 2 and number 3 at the collector? Hacking it would make the number 3 runner suddenly wide at the collector end. The ends of all the runners are of equal area on the ev3 manifold. The number 3 runner suddenly turns toward number 4 at the end. Otherwise it will be extremely short, even shorter than it is now.

Number 2 is on left and number 3 is on right. Number 4 & 1 are at the bottem.