Exhaust manifold porting

[Danno]

I know there's a lot of meat in the stock manifolds that can be taken out, and there's quite the lip on the manifold's flange compared to the stock turbine inlet.

So who's done this? What kind of turbos and cams do you have? Any head work done? What kind of differences did you notice?

Ultimately I want quicker spooling/response. In theory chewing out the meat in the manifold would create more lag since it's now got more volume and less velocity - unless the stock manifolds are quite restrictive...

I'm not planning on doing serious port matching with the head yet (will do that with the other head I have after the work on it is done). I've still got stock cams and turbos in my car now, but I've got a spare set of manifolds sitting here that I was thinking of playing with.

Thoughts and experiences?

[mwracing]

it is true. stock manifolds are thick and meaty but they rarely crack of break.

if you do port them it will cause minor lag, but will help top end slightly.

on stock turbos it isnt worth it, but when you get nismos or other higher flow turbos then only at higher rpm would you get any benefits...


p.s. i am very very happy i had my passport SR7 with shifter's radar jammer on the cruise home. it sure saved us a few times hey?

[donk_316]

Just did this last week. Well, Greg did it while i wrenched on the engine.
Turbos are HKS GT2530s,
Cams are Greddy 264s,
Head is mildly ported (stud boss lumps and casting flash removed, etc etc)

Obvioulsly no idea on what it will actually end up doing to the engine but it seems to be the thing to do. lol!

The exit port looks like its pretty close to half the size it should be.

[Daryl @ RightDrive]

Here's a good picture of r stock R34 RB26 manifold and a Tomei manifold, the difference is huge. The Tomei looks nearly a third bigger.



10% off Tomei manifolds, 2 days left shameless promotion!

[Danno]

Not looking at the Tomei's or other aftermarket tubular manifolds. This is for a street car and the stockers are less prone to cracking.

Donk, with mods like that all at once, it'll be hard to tell what difference there was, but keep us posted. Or you could be a real nice guy and throw on some virgin manifolds and test, then swap your ported ones in.

Martin, have you done this on your manifolds? If not, where did you get your info from?
We were a jammin'! Awesome drive, I may have to look into getting one myself.

I'm looking for somewhat quantifying information. Two dyno charts is worth two thousand words. I may have to do some testing myself.

[GTR-Dad]

Testing would be nice, but it's a fair bit of work to change out the exhaust mani!

Paul at TSS told me they opened my exhaust ports up by an estimated 15%. I did a bunch of mods at the same time, so can't offer direct comparison, but I can tell you lag with my new setup is much less than my OEM setup, which wasn't bad.

In short, with Apexi Power intake, JUN 264 x 9.7 mm lift cams, GT2860R-5 turbos, 8.5:1 CR, HKS dumps, and wide open exhaust I'm making 1 bar of boost at 3300 rpm. (This is with the wastegate shut tight.) With less than ideal boost control of course spool is a bit later.

Dan

[mcfly]

if you are going to the trouble of porting the stock manifolds i would at the same time take the lump out of each exhaust port on the head.

[donk_316]

if you are going to the trouble of porting the stock manifolds i would at the same time take the lump out of each exhaust port on the head.

Done!

[Wingnut]

if you are going to the trouble of porting the stock manifolds i would at the same time take the lump out of each exhaust port on the head.

I take it this is not a big deal, as in a 'low risk' mod. Has it been known to cause premature failure, or cracking of heads? I was thinking about doing it, but was/am a little worried about how it affected the strength.

[GTR-Dad]

I take it this is not a big deal, as in a 'low risk' mod. Has it been known to cause premature failure, or cracking of heads? I was thinking about doing it, but was/am a little worried about how it affected the strength.

The lump is removed from mine, but I'll quote Sean Morris on this one....
----------------------
Sean:
Port the stock exhaust manifolds where they meet the turbos. If you look at the gaskets you will see.

Dan
Mild port and polish are in the plans. I don 't want to open flow passages up so much that I lose bottom end responsiveness.

Sean:
Just knife edge the walls between the cylinders. Be careful of the bump on the exhaust side. You can hit a water jacket if you go too agressive.

[mcfly]

I take it this is not a big deal, as in a 'low risk' mod. Has it been known to cause premature failure, or cracking of heads? I was thinking about doing it, but was/am a little worried about how it affected the strength.

there is supposedly a water jacket placed in a very accurate position somewhere under there. I say supposedly as i have yet to see it and i have removed a lot of material.

there has though been a few rb25 guys who have hit one while porting. If all you are doing is removing the lump and no more then you will not hit anything.


Also the stock exhaust ports flow at about 68% so there is room for major improvement.

[XS Engineering - Greg]

We ALWAYS port the factory exhaust manifolds as well as the turbine inlets whenever we have the turbos and manifolds off. It's basically free HP. The "lag" is non existant, you're talking about reducing the backpressure on the exhaust side. Porting the manifolds is akin to running a 3.5" exhaust. You will not lose power, especially on a turbo car. We don't have any direct A - B comparison for RB26's (since the turbos are usually replaced at the same time), but on a stock EVO8, we made 28hp ( i believe... i know it was around 25-30) by porting the factory exhaust manifold and turbine outlet.

I also would not recommend porting the head exhaust ports with the head on the car. You are just asking for debris to get into your bore. You can take all the precautions in the world (rags, tape, etc.) but it's too risky for me.

[Danno]

We ALWAYS port the factory exhaust manifolds as well as the turbine inlets whenever we have the turbos and manifolds off. It's basically free HP. The "lag" is non existant, you're talking about reducing the backpressure on the exhaust side. Porting the manifolds is akin to running a 3.5" exhaust. You will not lose power, especially on a turbo car. We don't have any direct A - B comparison for RB26's (since the turbos are usually replaced at the same time), but on a stock EVO8, we made 28hp ( i believe... i know it was around 25-30) by porting the factory exhaust manifold and turbine outlet.

I also would not recommend porting the head exhaust ports with the head on the car. You are just asking for debris to get into your bore. You can take all the precautions in the world (rags, tape, etc.) but it's too risky for me.

So Greg, you're saying the "lag" is non existent pre-turbo? I know anything after the turbo doesn't matter, but increasing the volume of the manifold too much would create lag, no? This is assuming all other variables (and parts) stay constant.

I think I'll just port match the runners to the stock head (if they need it - have to check), and to the turbine inlet this weekend. Quick polish, and bolt the stock turbos back on. Then see what kind of difference there is.

Thanks,
Dan

[GTR-Dad]

So Greg, you're saying the "lag" is non existent pre-turbo? I know anything after the turbo doesn't matter, but increasing the volume of the manifold too much would create lag, no? This is assuming all other variables (and parts) stay constant.

I think I'll just port match the runners to the stock head (if they need it - have to check), and to the turbine inlet this weekend. Quick polish, and bolt the stock turbos back on. Then see what kind of difference there is.

The 'lump' is removed from my exhaust side and I'm making 1 bar by 3300 rpm, so spool is great.

When I'm running above 3300 rpm and drop the hammer, delay from throttle input to when vision starts to blur is about half a heartbeat. Lag pretty minimal! I suspect the derestriction that comes with removing the lump more than pays for the slight increase in volume. You're not removing a large volume of material, just opening up a diameter over a short distance.

If you're worried about hitting the coolant jacket, I'd track down an instrumentation rental shop, get an ultrasonic thickness tester, and measure how much material you've got to work with.

Cheers,
Dan

[GTR--J]

I did mine while I was waiting for my engine to arrive.I get 1.1 bar @ 3800 RPM with my TD-05-16g turbo's and Blitz SBC id-3 boost controller and stock cams.I still have the stock dumps which I kick myself for not changing when the engine was out.The rest of my exhaust is a Trust downpipe,no cat or resonator and 3" Fujitsubu exhaust.I'm sure new cams and aftermarket dumps would help for sure though.