Series 1 exhaust manifolds. How important is it to port? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 06-18-2007, 10:53 PM   #1
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Default Series 1 exhaust manifolds. How important is it to port?

This past weekends work on the SLE (swapping on last year'* Zilla top end) got me thinking about the SLE lacking ported exhaust manifolds. But my recent cylinder head work, and further detailed inspection of the Zilla'* guts over the winter (and my cumulative experience over the years here as well as time to think) got me thinking about how necessary it really is to port exhaust manifolds on the Series 1'*. Not just is it necessary, but what mods may make it MORE necessary? Rockers? Smaller pulleys? Ported LIM'*? Ported heads? Then I was on the phone with TFC, and he started asking the very same questions.........great (or sick) minds think alike. So I told him about a half hour ago, that I'd pull up my old data, posts, and CAD files.

Let'* dig back in history.........


Quote:
Originally Posted by willwren


I don't think they'll show in a sig pic.

Anyway, here'* the completed pics, all fixed and finished, including porting. By tacking the outside of the flange in the pics above, I was able to port them out quite a bit by removing the inside OEM weld. I didn't take ALL of the OEM weld, but most of it. The port diameters increased from 1.35" to 1.45", an increase of 16.5% in surface (flow) area.

On a side note, my LIM manifold from the other topic about porting netted me a flow increase capability of 9% (by increasing the 1.8"x0.8" ports to the head port size of 1.9"x0.9").


Finished painting. 1500 Ceramic header paint (5 coats on manifolds, 3 coats on heatshields).



Ported out from 1.35" to 1.45". A 16% increase in area. This is the biggest restriction in the exhaust. (was)

1.35" in diameter is 1.4314 sq/inches. (before porting)
1.45" in diameter is 1.6513 sq/inches. (after porting)
Actual flow increase is 15.36%.

Now lets dig further:


Quote:
Originally Posted by willwren
Please note that my exhaust manifolds are already ported......did that a year and a half ago. I did a good measurement today before I left for work and created it to scale for this topic.

The full circle is the inside diameter of my exhaust manifold ports. 1.435". Area of 1.6"
The inside profile is my head port. The head port has a calculated area of about 1.2 square inches.

By matching the head port BUT KEEPING THE PROFILE (flats have a purpose), I can squeak another easy 15-20% in exhaust port flow from the heads. If I made it a full matching round (which I won't), I could gain 33%.

It'* better to take half what you WANT if you don't like creating scrap. The D-shaped exhaust port is designed to cancel out the shockwave that returns back to the cylinder from inside the exhaust manifolds. This actually helps performance.



So I'll be enlarging the rounded sections in WIDTH, but leaving the flats where they are.
It'* not just about AREA. You have to take into account the shape of the cylinder head exhaust port. It may only be 1.2 sq/inches, but that'* because it'* missing about 10% of the top, and 30% of the bottom. But you STILL can't ignore the full width of it.

So the actual WIDTH is........

1.3" from side to side, as if it were a complete circle, ignoring where it'* shorter with the flat at the top and the bottom.
And from my measurements on my own manifolds, the 'restriction' of the factory inner welds on each runner are at 1.35". Keep in mind welds may vary from manifold to manifold, but the initial evaluation shows possibly no benefit, or in better words, NOT NECESSARY (untl you get nuts on mods, and I mean REALLY nuts).


In other words, until you port your cylinder heads like I did, that inner factory weld isn't a restriction to even a pulleyed and rockered Series 1.

Velocity is the key.



In a nutshell, the Series 1 exhaust manifolds are alot better designed and built than we thought. And we all learn through experience and time. Just don't forget how prone these things are to CRACKING. That'* still an issue, and the cracks are either impossible or very difficult to see.
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Old 06-18-2007, 11:16 PM   #2
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Who'* TFC?

Thanks for the research Bill. My main concern for my spare set of EMs is fixing the cracks that are there. I know from what JF told me there is at least one large crack in the rear EM. I figured that while I had a spare set, and therefore a lot of time, I would port them as well.

After reading this I feel like porting isn't really necessary for what MY plans are for this car. My engine runs well with no KR currently on a stock pulley, and if all goes well while I own this car, the most I see myself doing is a 2.5 with some rockers, and maybe a P&P'd SC, and further porting of my LIM.

After doing that, I could actually drop another pulley size assuming KR is still not an issue, and even then I may not even bother porting my EMs.
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Old 06-18-2007, 11:19 PM   #3
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You got it. Until you increase your cylinder head exhaust port size like I did, none of the mods you plan will dictate exhaust manifold porting.

Just take extra care and pay attention to detail when looking for the cracks. Especially where they may be hidden by the front or rear heat shields, and particularly the crossover pipe heat shield.

Easy way to test the crossover without having to cut the heatshield welds? Seall off one end with VERY good duct tape in layers, then fill with water from the other end, all the way to the top. If the level drops, and drools out the collar at the bottom of the heat shield, you have a crossover pipe crack under the shield.
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Old 06-18-2007, 11:25 PM   #4
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Hey, good idea on the duct tape method! lol I will give that a shot as well.

The sad thing is my current EMs sound like they are already in better shape than the spare set I am buying. Without any KR now I would likely guess I have very SMALL cracks right now at most. I can't imagine I'd have very large cracks and run as well as I do, UNLESS I have always been wrong in how much I thought EM cracks affect KR.

At least I will have the time to get the spare set done without having my car hung up in the driveway.
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Old 06-19-2007, 12:36 PM   #5
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I won't be porting the EM'* on my SLE, that'* for sure. At least not for another year.
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Old 06-19-2007, 05:18 PM   #6
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Quote:
Originally Posted by willwren
I won't be porting the EM'* on my SLE, that'* for sure. At least not for another year.
Uh huh...
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Old 06-19-2007, 05:27 PM   #7
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Didn't you tell me a while back I could slap you if you got to modding the SLE?
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Old 06-19-2007, 05:28 PM   #8
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Only in person. Then I'll hand you a beer.

The SLE is quicker than Zilla was last year now. And on Stock EM'*. I've never had them off the car.
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Old 06-19-2007, 06:08 PM   #9
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I heard Bill on the phone yesterday driving what I THOUGHT was Zilla based on the whine.

Bill'* got the Sleeper mod bug.
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Old 06-19-2007, 07:11 PM   #10
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Well, I've got all these parts just laying around here......
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