Flow stats for exhaust manifolds -SURPRISING!!!!
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Originally Posted by Hans
Originally Posted by willwren
1992 Series 1 L67 manifolds are different than the 93-95. We don't know what that difference is, or whether the 93-95 manifolds are backwards compatible to the 92.
"we dont know what the difference is" How do we know there is a difference then??????
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Maybe becuase the N/A '92s didn't have an EGR?
Maybe one of the reasons that the front manifold flow better is because it is cast? IIRC cast will be better as long as it is smooth.
I'd like to see ported series 2'* get tested.
Maybe one of the reasons that the front manifold flow better is because it is cast? IIRC cast will be better as long as it is smooth.
I'd like to see ported series 2'* get tested.
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Originally Posted by llBlazin_llLo
Maybe becuase the N/A '92s didn't have an EGR?
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Those are shocking numbers. This shows why actual testing is so important. Our intuition tells us that the front S2 manis would flow worse than the rear, when in fact they flow much better.
Thanks for testing those. Good info!
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Originally Posted by lash
Those are shocking numbers. This shows why actual testing is so important. Our intuition tells us that the front S2 manis would flow worse than the rear, when in fact they flow much better.
Thanks for testing those. Good info!
It seems this latest round of testing confirms that. I'm not going to make the call on the matching idea, but it'* something to think about.
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Originally Posted by willwren
Originally Posted by lash
Those are shocking numbers. This shows why actual testing is so important. Our intuition tells us that the front S2 manis would flow worse than the rear, when in fact they flow much better.
Thanks for testing those. Good info!
It seems this latest round of testing confirms that. I'm not going to make the call on the matching idea, but it'* something to think about.
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Correction, I got it backwards. It seems Hector'* data conflicts with this new data. Maybe it varies by casting?
This however the first time anyone (to my knowledge unless ssei1995 has done it) has flowbenched the S1 manifolds. The S1 mani'* are widely considered (not just in our community) to be the best flowing stock manifolds ever produced by GM.
Here'* a link to some Hector manifold info:
http://www.bonnevilleclub.com/forum/...pic.php?t=3657
And some other info:
We did some flow testing on the manifolds. We found out the Series II cast iron manifold ported outflows the rear tubular manifold (stock and ported versions). This is because it has much smother flow and the tubular just slams the exhaust gases into the walls. The rear exhaust manifold welded on the outside only gains a few cfm per port which is nothing. There ya go.
This however the first time anyone (to my knowledge unless ssei1995 has done it) has flowbenched the S1 manifolds. The S1 mani'* are widely considered (not just in our community) to be the best flowing stock manifolds ever produced by GM.
Here'* a link to some Hector manifold info:
http://www.bonnevilleclub.com/forum/...pic.php?t=3657
And some other info:
Originally Posted by 99BonnevilleSE
We did some flow testing on the manifolds. We found out the Series II cast iron manifold ported outflows the rear tubular manifold (stock and ported versions). This is because it has much smother flow and the tubular just slams the exhaust gases into the walls. The rear exhaust manifold welded on the outside only gains a few cfm per port which is nothing. There ya go.
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I'm going to quote the meat from that link, because I think it adds to this discussion:
This is definitely contradictory to what Gordy found out above, but also not as specific, leaving a few questions to be answered.
Do the S2 exhaust manifold flows vary considerably between vehicles?
What benefit would there be to flow matching front and rear manis? I would think that it would be a good thing.
What extra data could be provided that would help answer these questions?
- flow testing of additional stock front and rear S2 manifolds.
- flow testing of ported front and rear S2 manifolds.
My thoughts are leaning towards the possibility that when someone gets a set of ported front and rear manifolds for a S2 3800, maybe, in addition to the extra total flow, they are getting a more evenly matched flow, front to back. That isn't to say that the rears shouldn't be done, as we already know of the tendency for weld cracking etc. on the rears and the welding-porting process on these helps durability if nothing else (though probably some flow increase per the quote in Bill'* post above from Hector).
What do you think?
Originally Posted by 99BonnevilleSE
We have learned quite a bit. We flow benched the front exhaust manifold stock and ported. Once ported, it flowed 22-25% greater over stock. So for example, rather than the exhaust ports being 20 cfm behind in flow, they are now 30-40cfm more than the stock exhaust ports can flow (a good thing). In our flow testing, we discovered that welding the rear exhaust manifold and grinding it out provides no gains. Even removing many of the casting bumps and large interior welds. It turns out that the ported front exhaust manifold outflows the rear exhaust manifold by around 5%. Funny how air does not act like you expect it to.
Do the S2 exhaust manifold flows vary considerably between vehicles?
What benefit would there be to flow matching front and rear manis? I would think that it would be a good thing.
What extra data could be provided that would help answer these questions?
- flow testing of additional stock front and rear S2 manifolds.
- flow testing of ported front and rear S2 manifolds.
My thoughts are leaning towards the possibility that when someone gets a set of ported front and rear manifolds for a S2 3800, maybe, in addition to the extra total flow, they are getting a more evenly matched flow, front to back. That isn't to say that the rears shouldn't be done, as we already know of the tendency for weld cracking etc. on the rears and the welding-porting process on these helps durability if nothing else (though probably some flow increase per the quote in Bill'* post above from Hector).
What do you think?
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Man this is getting confusing. I been reading alot of old threads and pretty much everybody says to do ported manifolds if can't afford headers. Now this info??? I was planing on ordering some mani'* soon I guess I'll hold off for awhile and see where this goes.