Flow stats for exhaust manifolds -SURPRISING!!!! - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-05-2006, 11:15 PM   #1
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Default Flow stats for exhaust manifolds -SURPRISING!!!!

I just got my cores back from getting them flow tested -FINALLY!!!!
How much better does a stock Series I exhaust manifold out flow a Series II exhaust manifold?
How does 40% more flow sound? And that'* on the rear mani'*!!

Brought 3 sets in -My Series I ported/coated mani'*, Gordy'* stock unported (Nate had started welding them externally if that matter any, but hadn't done anything with the ports) 1995 Series I mani'*, and Seth'* stock untouched 99 Series II mani'*.

Here are the results

Series II stock front manifold: 302 CFM

Series II stock rear manifold (H-body): 256 CFM

Series I stock Rear manifold: 356 CFM !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Series I ported and ceramic coated rear manifold: 373 CFM

The Series I front manifolds weren't tested due to something about how the crossover being part of the front manifold wouldn't allow for good attaching to flow tester!?!?!

One thing both me and the shop agreed upon when I first dropped the manifolds off for testing, was how Gordy'* manifolds will hardly benefit from porting as they are practically as wide open at the ports as my ported ones. The one'* I had ported had much larger welds in the ports.

Could this, along with Gordy'* excellent injectors be why his car ran so strong -kept up with Whisky_98'* mildly modded 00 SSEi.
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Old 04-05-2006, 11:38 PM   #2
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Thats pretty suprising about the series 2 rear manifold.
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Old 04-06-2006, 12:04 AM   #3
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Quote:
Originally Posted by 95naSTA
Thats pretty suprising about the series 2 rear manifold.
I was especially surpised at the SII front mani outflowing the rear which is tubular vs the cast front. The only conclusion I could think of is the EGR pipe that runs into Cyl #6 runner is angled back towards the head, which could cause turbulance in that runner, limiting the flow.

We figure on the mani'* that are ported/coated already, from stock to now it gained closer to 25-30 CFM.

Every set of mani'* will flow different, but should have within 3-5% flow difference.
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Old 04-06-2006, 12:06 AM   #4
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Having my S2 manifolds in my hands here...I have trouble believing the flow numbers.

I know the S1 manis are better. It'* visible. However the S2 rear mani is very well ported to begin with, whereas the front is very restrictive. Could your S2 flow numbers be reversed?

Say fronts 256 and rear 302?
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Old 04-06-2006, 12:10 AM   #5
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Originally Posted by BillBoost37
Having my S2 manifolds in my hands here...I have trouble believing the flow numbers.

I know the S1 manis are better. It'* visible. However the S2 rear mani is very well ported to begin with, whereas the front is very restrictive. Could your S2 flow numbers be reversed?

Say fronts 256 and rear 302?
The shop said they tested the SII manifolds 3 times to be sure and they came up with within 5 CFM on each until they were certain.

They themselves were stumped by the #'* too.
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Old 04-06-2006, 09:52 PM   #6
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Kind of a bummer for people spending hundreds of dollars for only porting the front manifolds. I always thought that wasn't such a good idea. Do you have numbers for a ported series II manifold?

You may want to put a year on that "series 1" manifold because that doesn't mean much, since there are several 3800 versions before the series II.

-T
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Old 04-06-2006, 10:02 PM   #7
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AS far as I know, that the only * I'* manifolds that he has right now is the 95 l67'*.
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Old 04-06-2006, 10:02 PM   #8
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Quote:
Originally Posted by T-Keith
Kind of a bummer for people spending hundreds of dollars for only porting the front manifolds. I always thought that wasn't such a good idea. Do you have numbers for a ported series II manifold?

You may want to put a year on that "series 1" manifold because that doesn't mean much, since there are several 3800 versions before the series II.

-T
Series 1 L67 1992-1995
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Old 04-06-2006, 10:09 PM   #9
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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. John Wikoff is trying to figure this out.
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Old 04-06-2006, 10:11 PM   #10
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Quote:
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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