Cobra4B

I have Kooks LT's w/ OEM gaskets that I got from the Chevy dealer. I'm assuming they ordered by VIN so they got to right ones. First, do LS1 and LS6 have different gaskets b/c the LS6 head has D shaped exhaust port? 2nd do the OEM gaskets restrict flow in any way w/ headers? I was told this but I don't believe it to be true.

Chrisbequick

I sincerely doubt it. I don't know about LSxs, but on traditional SBCs the D-shaped ports have a higher port floor than a round port, meaning that a round gasket/header combo is larger than the exhaust port. This can actually prevent reversion and help exhaust port flow.

-Chris

SpeedyZ

Yes, GM gaskets are different for the LS1 and LS6. The factory gaskets that came off my 2001 LS6 had smaller oval holes for the ports than the 1999 LS1 gaskets I ordered. The LS1 gaskets have a large round hole for the ports, much bigger than the port in the head so they won't restrict any flow. The LS1 gaskets fits the ports on my LG LT perfectly. It looks like the LS6 gaskets would not seal since they are oval shaped. I just ordered gaskets for a 1999 C5 from GM.

Cobra4B

But if the hole in the gasket isn't blocking any of the exhaust port in the head then how could it restrict flow at all even if the header primary is larger?

don527

as mentioned above, the ls1 and ls6 do have different gaskets due to port shape.

you could probably get away with using the d-shaped gasket with the kooks because the main concern, for me, would be to get as tight a seal as possible to the kooks and the round gaskets would provide maximum coverage to the kooks flange.

i used the round ones with my kooks install and not a single problem with leak or anything. worth the few bucks to get the right gasket then to have to deal with a gasket issue in the future.

don

Tino

Just going by physical viewing of cylinder head exhaust ports after they have come off of cars. The Z06 heads have the D port exhaust and look black and sooty around the bottom of the port. In other words leaves the imprint of an LS1 style exhaust port. The cast iron Z06 headers are used on all 2001 and up C5's, therefore would it not make sense that GM is matching the exhaust header and not the heads? As long as the LS6 heads are not being obstructed, it should not make a difference.

Tino

Mr. Jones

Well so fare the answer are close but not 100% I will probably not be 100% eather but here we go.
the 1999 LS1 manifolds (tube) and gaskets are round port.
the 2000 LS1 and 6 heads are D shaped or oval. The gaskets for the 2000 up cast iron manifold are the same. This is not the gasket you want. The gasket may not obstruct the port/flow but it will not seal correctly.
The headers will have a round shape to their port so you need a round gasket to seal. Get a GM 1999 gasket (stainless steel) for a LS1 and you will have no exhaust issues.

HP_Addict

If you want the round gasket order the one for the Camaro.

Y2Kvert4me

I just had to buy a new header gasket this past weekend, and I used GM part# 12558573. Got this # from the LS1howto site, and just told the dealer I needed that part#. I'm not sure what year they are intended for, but they fit and sealed fine. They are metal with round ports.

SpeedyZ

Neither gasket will restrict flow at all. Even the smaller LS6 oval port gasket is bigger than the ports in the head. What I was saying is the oval shape of the LS6 gasket does NOT match the big round ports in most headers. So you want the LS1 gaskets for best seal of headers. Neither gasket will cause a flow restriction.

Cobra4B

Cool... well mine seal fine, if I have any leaks come up I'll re-do them with the "better" gasket.

vettenuts

That is the gasket I used on my QTP's, which is the f-body gasket.

augydog

I have an '04 Z with Kooks headers, and used new LS6 "D" gaskets.

Have put over 1K miles, no problems.


augydog

Monks

I tried a set of GM Z06 gaskets on my Kooks and
FFHP heads. The gasket blocked the top of the
port at least 3/16". I decided to use the gaskets that
came with the headers.

SpeedyZ

Ok, so your already running the LS6 gasket. They may work fine, these MLS (Multi Layer Steel) gaskets do seal very well. I just installed my LG and only put 3 bolts in each side just to fit up the exhaust. I didn't install all the bolts because I knew I would be pulling the right back off to do heads and cam (heads are off right now). But I did run it enough to move the car around and these gaskets sealed up the LG LT very well with just 3 bolts in each side.

Good luck with the gaskets

Dan_the_C5_Man

I haven't seen anyone say this yet, so I will..

The "real" way to address this issue is to form the inlet shape of the header to match the head.. Probably a few ponies to be gained, and should be expected considering the price the "premiere" C5 header manufacturers charge.. Oh well.