93 head port & polish progress pics (56k a little slow) - Page 7 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


Performance, Brainstorming & Tuning Talk about modifications, or anything else associated with performance enhancements. Have a new idea for performance/reliability? Post it here. No idea is stupid! (please use Detailing and Appearance for cosmetic ideas)

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Old 10-01-2005, 01:26 PM   #61
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My one thought on all that:

Since air only flows to one cylinder at a time, how much does it matter if flow isn't evenly distributed when all the runners are open? The air only has one place to go at a time, so it will go there, right? It may not be exactly perfect distribution, but can't be that far off, I would think.
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Old 10-01-2005, 01:47 PM   #62
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I would think slight differences in port filling would be a big factor. You'll have all the ports running different percentages of lean/rich, since you only have one maf sensor and one O2.

The whole point of flow-matching your injectors goes out the window with improper porting. What I did to my LIM should have no effect on this because I left my heads alone, and simply portmatched my LIM to them.
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Old 10-01-2005, 01:54 PM   #63
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My point (rather, question) was: can they be different enough to matter since the intake is pressurized and air only goes to one place at a time...

Have you (ssei1995) checked flow one runner at a time with the others blocked? If so, disregard what I said.
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Old 10-01-2005, 02:08 PM   #64
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Quote:
Since air only flows to one cylinder at a time, how much does it matter if flow isn't evenly distributed when all the runners are open? The air only has one place to go at a time, so it will go there, right? It may not be exactly perfect distribution, but can't be that far off, I would think.
Air does flow to each cylinder at a time; however, how many intake/exhaust events and pulses do you have per each RPM???

It does matter. Evenly distributed airflow in the intake reduces reversion duirng the exhaust pulse. This is a problem with blown engines and worst when the camshaft has a lot of overlap. That is the reason why when you remove the SC and look at the bottom of the intake, you will notice a lot of soot, or what you guys call carbon deposits. The intake is pressurised most of the times underboost, therefore, all you are doing is improving the filling of the cylinders and atomization. I can write a whole thesis on the subject based on findings and other people'* results and observattions. If you take a close look, the SC opening does not cover the whole length of the intake opening. Also, the intake opening does not expose all the runners either.

You can easily get lost on the subject if you also add the issue of engine builders changing the firing order of the cam to dampen the pulses in the intake tract.

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I would think slight differences in port filling would be a big factor. You'll have all the ports running different percentages of lean/rich, since you only have one maf sensor and one O2.
Yes, you are correct. What I doing is improving the efficiency of the LIM.
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Old 10-01-2005, 02:11 PM   #65
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Quote:
Have you (ssei1995) checked flow one runner at a time with the others blocked? If so, disregard what I said.
Each runner has been testetd separately, with and without the intake attached. WOuld love to attach the SC and TB, however, it would need a fixture with a motor to drive the SC.
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Old 10-01-2005, 02:15 PM   #66
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Whoa, stuff I hadn't even considered... It is coming appearent that you know what you're doing.

Makes me even more anxious to get your porting results. Rock on!!
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Old 10-02-2005, 11:54 PM   #67
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ssei1995, you certainly have my undivided attention, and apparently that of many others as well. Please keep us posted. Also, I am sure if you need any type of assistance, all you need to do is ask. Many of us are eagerly awaiting the results of your research.
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Old 10-03-2005, 12:37 AM   #68
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Related followup on mine:

I'm glad I didn't touch my heads for the time being. I believe in the long-term the port-matched lower intake should help, and I know the ported EM'* are a benefit. However, it appears the ported TB is too much with even the modified curves in my Jet PCM. I'll have to take data, then switch back to a stock TB and see how it acts. Even without the ported TB, I should be at least 30hp stronger in the top end of the motor alone.

More testing and scanning to come.
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