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Old 12-06-2003, 12:01 PM
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port matching the intake.

Well, i'm finally ready to bold on my intake on my 350. Some time back I posted about port matching my 882 heads to my intake gaskets. Learned alot and had fun doing it. I have an Edelbrock Performer Qjet intake going on and put one intake gasket on the intake to see how it looked. What I noticed is the intake runners are a little smaller than the gasket and head ports. Is it necessary to match the intake to the gaskets and heads if they are a little smaller? I understand the need not to have smaller head ports against the manifold due to the flow impacting the head surfaces, but is it bad to have the intake a tad smaller than the heads since the flow is going from the smaller intake to the larger head runners?


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Old 12-06-2003, 12:08 PM
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If the intake runner is slightly smaller, that is not a real problem, vice-versa is a problem.
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Old 12-06-2003, 12:15 PM
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Nice clean looking engines. Porting in most cases is over-rated. A good polishing and cleaning of the runners should be a 1st choice. Also like the fact that you are using the Q-Jet carb.
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Old 12-06-2003, 12:15 PM
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A little overhang coming from the intake isn't bad. Like you said the other way around isn't good.
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Old 12-06-2003, 12:21 PM
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Actually, there will potentially be a slight performance drop with the discontinuity. Intake manifolds are designed using 'organ pipe' theory - taking advantage of sound pressure waves traveling up and down the runners to 'supercharge' the cylinder just as the intake valve closes at certain design speeds. If there is any change in diameter in the runner that the engineers didn't anticipate, there will be pressure and vacuum reflections that will affect performance. It isn't just a matter of pressure drop. For a cruiser or street engine I wouldn't give it a second thought. However, if you are planning on drawing an occasional time slip at the Friday night drags, I would go to the trouble of port matching.
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Old 12-06-2003, 01:33 PM
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Thanks for all the input. The left engine is going in my truck. Its a dialy driver/boat puller. Guess I'll go put it on and bag it up. the right engine is going in my sons 4X4 crawler.

Mark
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Old 12-06-2003, 06:16 PM
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nairb hit the nail right on the head
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Old 12-07-2003, 05:47 AM
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Willy is right. if your already doing it, go all the way and match them all.

Porting is the main thing, and the most important. Polishing is a waste of time.

Troy

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Old 12-07-2003, 07:08 PM
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i put my rpm on my gasket matched heads without gasket matching the intake and i cant see any problems. i agree with everyone else as well.
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Old 12-08-2003, 10:13 AM
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267 heads on 305; port matching

305 heads and presumably 267 heads (haven't pulled the 267 heads off yet) have intake ports quite a bit smaller than 350 ports. Does anyone know if gasket matching these heads to match a 350 manifold (either a 79 350 truck manifold or an edelbrock performer) will break into the water jackets?

My 305 uses flat-tops and a pair of 416 heads (10:1 compression I believe, 212 psi cranking pressure) to push a 79 3/4 ton on propane. Since I do a lot of driving between 70 and 100 mph (I have a 9 hour once/month commute), I want all the power I can get. The cam is a crane energiser with a designed operating range of 1600-4600rpm selected to maximize economy.

When I get the 267 heads off, I will have hardened seats installed, intakes cut for 1.84 valves, pocket porting, and perhaps gasket matching. The 416 heads I am presently using do not allow proper intake line-up, so i want rid of them -I think the dowel holes are machined in the wrong spot.

Also, will a 30 degree back-cut on the valves help flow noticeably?
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