exhausting matters
Discussion
OK got new exhaust built a bit back + new gaskets supplied for LS7.
In an earlier thread I mentioned the manifold was blowing and asked if dry-fit was right as advised by the exhaust maker.
Now I think I know why:
The supplied gasket is D shaped as per head exhaust port, yet the manifild is cirular - there is not enough meat on the gasket D to make a true seal. Surely this is wrong?
Yes I could use sealer, but I would expect there is a better shaped gasket somewhere to do a proper job? But what and where from?
The original exhaust was trhe same round profile, and I had to seal that one.
Ideas please?
In an earlier thread I mentioned the manifold was blowing and asked if dry-fit was right as advised by the exhaust maker.
Now I think I know why:
The supplied gasket is D shaped as per head exhaust port, yet the manifild is cirular - there is not enough meat on the gasket D to make a true seal. Surely this is wrong?
Yes I could use sealer, but I would expect there is a better shaped gasket somewhere to do a proper job? But what and where from?
The original exhaust was trhe same round profile, and I had to seal that one.
Ideas please?
I am sure there are according solutions already available somewhere.
But if you end up doing an own design, maybe they could make them for you:
http://www.stephensgaskets.co.uk/Gaskets.html
But if you end up doing an own design, maybe they could make them for you:
http://www.stephensgaskets.co.uk/Gaskets.html
Edited by AndreasW on Wednesday 22 August 21:35
Might be worth checking/resolving the port face to header bore diameter too Keith... many just bolt up and go without resolving the first likely restriction in their system....... Hotspots there, heat transfered back to the chamber, upsets design burn, ecu compensates etc etc. Well worth sorting that for a few HP, MPG and valve gear life.
Edited.... if you cannot open up the header flange large enough to match the port (because you will grind away the header tube on the other side of it) then at least form a flowed chamfer from the mating face through the flange material, into the tubes.
Its one reason for choosing a slighty larger header tube.. matching and the ability to leave anti-reversion on the inside !! ( no need to go all EG velocity on me for those in the know... we can stand a little low-mid loss velocity on these torque monsters)
G luck.
Edited.... if you cannot open up the header flange large enough to match the port (because you will grind away the header tube on the other side of it) then at least form a flowed chamfer from the mating face through the flange material, into the tubes.
Its one reason for choosing a slighty larger header tube.. matching and the ability to leave anti-reversion on the inside !! ( no need to go all EG velocity on me for those in the know... we can stand a little low-mid loss velocity on these torque monsters)
G luck.
Edited by 738 driver on Thursday 23 August 11:22
Thanks for all your comment guys. I have emailed the supplier/builder of the exhaust for his comments. Generally the job was exellent apart from this little hiccup.
I still would like to find the right sort of gasket for this myself, just in case - but google doesn't come up with much at all!
cheers
I still would like to find the right sort of gasket for this myself, just in case - but google doesn't come up with much at all!
cheers
Look carefully ... the anti-reversion needs to take place against the direction flow ... the bore of his flange appears overlapping/ smaller than the head port on the photos (a flow restriction)... carbon burn ring evident (may just be gasket mis match)... the flange and port should be at least matched in size but if his header tube is smaller than matching will allow he can only taper match. Most common on SBC stuff where after market heads have exhaust ports in slightly different places/ sizes to stock flange patterns.
The LS1 and LS7 too have different exhaust faces... most flange kits are produced circular and avaialble in differing dimensions to suit chosen header tube size.
Not sure why Gm went to a larger diameter flat bottomed exhaust face shape on the 3 and 7 ... GM headers are quite tight so maybe to improve short side flow or maybe theres a physical restriction on continuing the larger radius.
To put it simply Keith, the header flange diameter (at the gasket face) should be equal to or bigger than the cylinder head ex port diameter (measure across it and disregard the flat bottom) .. If not you have a proper restriction which needs to be sorted... the LS engine management will compensate for the restriction but will rob performance. The top edge and sides of the exhaust port profile flow the most so shouldnt have restrictions
The LS1 and LS7 too have different exhaust faces... most flange kits are produced circular and avaialble in differing dimensions to suit chosen header tube size.
Not sure why Gm went to a larger diameter flat bottomed exhaust face shape on the 3 and 7 ... GM headers are quite tight so maybe to improve short side flow or maybe theres a physical restriction on continuing the larger radius.
To put it simply Keith, the header flange diameter (at the gasket face) should be equal to or bigger than the cylinder head ex port diameter (measure across it and disregard the flat bottom) .. If not you have a proper restriction which needs to be sorted... the LS engine management will compensate for the restriction but will rob performance. The top edge and sides of the exhaust port profile flow the most so shouldnt have restrictions
Edited by 738 driver on Thursday 23 August 14:36
OK, I measured both the inner pipe in the manifold and the outlet on the head and there is a 1mm diameter difference according to my gauge, so the match is not bad. I can easily chamfer the tube a tad to make it exact.
The overriding issue is then the gasket, and I have failed to find anything that migh fit the LS7 with a circular port profile!
What engines have the same port spacing?
Does any one know?
The overriding issue is then the gasket, and I have failed to find anything that migh fit the LS7 with a circular port profile!
What engines have the same port spacing?
Does any one know?
LS 1 .... ^ .... the bolt pattern is the same central layout/spacing... just the diameter and flat lower that edge that differs (the 1's are circular) . There should be enough meat on the LS1 gasket to match to the LS7's increased radius if needed.
http://www.speedwaymotors.com/Dynatech-LS1-Stainle...
http://www.speedwaymotors.com/Dynatech-LS1-Stainle...
For those who are interested, after much googling and calls to GM builders and partsworld where I frankly got nowhere, and was getting rather frustrated as no-one would either comment or were able to advise...
so after much I got a cunning
I went to the most obvious source - the factory themselves - well you would wouldn't you!
Problem solved - easily -
It appears that the Factory use a round profile gasket for their engines and exhausts!!!!!!!
...so I bought a set!
Easy when you know how!
so after much I got a cunning
I went to the most obvious source - the factory themselves - well you would wouldn't you!
Problem solved - easily -
It appears that the Factory use a round profile gasket for their engines and exhausts!!!!!!!
...so I bought a set!
Easy when you know how!
For those that use the GM exhaust gasket (and probably other similar one's) they are not designed to be used more than once. When they are compressed between the head and manifold as the bolts are tightened they fill any gaps as they compress (which is why they are not completely flat). They do not spring back when you take them off so if you use them again they are unable to fill an gaps again (by gap I mean tiny surface variations).
If you trial fit your exhaust then leave the gasket out and only fit it during the final fit.
Could this be the cause of your problem Keith?
Paul
If you trial fit your exhaust then leave the gasket out and only fit it during the final fit.
Could this be the cause of your problem Keith?
Paul
No Paul,
These are brand new ones supplied by the exhaust builder as I said. If you look closely in the pics you will see where the O of the Ex flange plate meets the D of the gasket, and it is very clear that the bottom of the raised D in the Gasket is not getting compressed at all unlike the surrounding area. This leads to a weak spot at the bottom of the D, and so it blows as evidenced by the carbon deposits. Bit like fitting a square peg etc...
I know that many have been given D type gaskets, and most have got away with it, however with the very slightest variation in dimensions you would get a 'blow' unless youy are using copious amounts of sealant.
For me, once I realised the differences in the profiles, it was pretty clear that there would be a potential weakness.
Obviously the factory twigged this early on, and have moved to the correct Gasket profile for the flange - totally logical really, especially as the D profile on the head is totally inside the 'O' so-to-speak, thus a good seal!
These are brand new ones supplied by the exhaust builder as I said. If you look closely in the pics you will see where the O of the Ex flange plate meets the D of the gasket, and it is very clear that the bottom of the raised D in the Gasket is not getting compressed at all unlike the surrounding area. This leads to a weak spot at the bottom of the D, and so it blows as evidenced by the carbon deposits. Bit like fitting a square peg etc...
I know that many have been given D type gaskets, and most have got away with it, however with the very slightest variation in dimensions you would get a 'blow' unless youy are using copious amounts of sealant.
For me, once I realised the differences in the profiles, it was pretty clear that there would be a potential weakness.
Obviously the factory twigged this early on, and have moved to the correct Gasket profile for the flange - totally logical really, especially as the D profile on the head is totally inside the 'O' so-to-speak, thus a good seal!
GTRMikie said:
My first thought on reading this was: why didn't you use factory supplied exhaust manifolds and gaskets in the first place?
+1Keith - you LOVE giving yourself completely unnecessary stress, don't you....
Out of interest, how much cheaper were the manifolds you had made, compared to the factory ones ?
Regards
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