port matching the intake manifold?

[daves66valiant]

Sorry if this is a lame question. I searched the site before posting.
I have a set of fully ported 340 J heads. There is a 3mm difference between the cylinder head ports (25mm wide) and the intake manifold ports (22mm). The heads look like they are gasket matched. I'm wondering if I should gasket match the intake manifold to the same width as the cylinder heads? Just wondering if this is typically done with heads that have been fully ported. I would think that there would less turbulent flow of air into the heads. Therefore, better flow and performance?
If so, what's the best tool for the aluminum manifold? Dremel, air tool? I have never done this before

thanks

 

[middleagecrisis]

You probably won't see any HP/torque difference with an intake manifold port that is slighty smaller (3mm) than the intake runner on the head side. Now if it was the other way around, you would have flow turbulence and lose HP/torque. If you do make the ports line-up perfectly, it will only be "eye-wash", unless you enlarge the port runner all the way up to the plenum. I'd leave such a small step alone.

 

[dodge freak]

I recall in the "old days" early 80's when folks ask about using a Holley intake which has small size 318 ports on a 340 motor the tech guys at Hot Rod and Car Craft said its fine. In fact they said its better to have a smaller intake manifold port than the head. Something about being able to run a big cam and the smaller ports would help stop the air from coming out of the cylinder at slow rpm's so you can run a bigger cam. Yes I leave it alone.

 

[dusterdon]

I'd gasket match the intake. When you go from a small, higher velocity port to a larger one you will lose a lot of velocity. you don't need to go more than 3/4" inch in. The sharp edge you have now will cause turbulence. A die grinder or even a dremel could work. A cutter will load up pretty easy. Try a sanding wheel.

don

 

[388dart]

What ever you decide to do - make sure the intake port exit is not larger than the head port inlet - major turbulence if it is.

 

[340mopar]

I'd gasket match the intake. When you go from a small, higher velocity port to a larger one you will lose a lot of velocity. you don't need to go more than 3/4" inch in. The sharp edge you have now will cause turbulence. A die grinder or even a dremel could work. A cutter will load up pretty easy. Try a sanding wheel.

don

This is 100% correct, if your velocity slows to much the fuel droplets will fall from suspension from the air. The velocity needs to stay as constant as it can.
Anyone remember the old Edelbrock SP2P intakes? This was the exact thing. The intake port was small for velocity but it dumped into a large port which had the fuel problem that I described. Because of this problem Edelbrock discontinued production of these intakes.

 

[daves66valiant]

See this totally make sense to me especially in a fluid dynamics sense. I wanted to post the question because I've never done this before and wanted to make sure it was okay to do. Still new to the performance tech stuff.

What ever you decide to do - make sure the intake port exit is not larger than the head port inlet - major turbulence if it is.

Yeah I understand that if there is even a small lip there would be turbulent flow. Same reason I"ve heard that your carb base should match closely to the top of the manifold.

More comments or suggestions are more than welcome. I'll learn whatever I can.

 

[rumblefish360]

The speed of the air and fuel at the heads entrance at the intakes exit is at max speed and isn't slowing down enuff to cause any problems after the air and fuel enter the head. It's more of the turn that will create a problem than the port size difference. Not to mention the valve itself getting in the way from stem to head. Fuel will gather/puddle there a hundered times more than a port size change.

Gasket matching is good. Like said above, not larger than the cylinder heads entrance. That would create a damn. (Double meaning.) As in damn I screwed up and a damn for holding the air and fuel back in a puddle. The damn will create a spot for the fuel to puddle and drip in drops.)

 

[66dartgt]

I go along with gasket matching. No larger than the gasket. I'd actually leave the intake a tiny bit smaller, you can advantage of some anti-reversion by doing so.

 

[D-mailman]

You can use carbide cutters to cut aluminum. just have to turn it slower and dip the cutter in oil every couple of minutes. that will keep the cutter from loading up. Aluminum carbides are best (large flutes), but double cut carbides will work ok if you don't have aluminum cutters specific. The oil also helps to cool the cutter. regular motor oil will work just fine. Yes, port match but keep manifold smaller than heads. Good luck, Terry.

 

[dodge freak]

Anti-reversion yeah thats what the old Hot Rod writers were talking about, I seen it talked about many times and always seen thats its fine for the intake manifold ports to be alittle smaller-they even said its better. Anti-reversion where the piston trys to push the intake charge back in to the manifold when the cam is big and the rpm's are slow.

As for the gas building up that might very well happen and I bet this gas today does not burn as good as 25 years ago when everybody had carbs. Now the F. I. sprays the gas in a fine mist so it still burns good but when its in a carb the gas is not in a fine mist. This may be why I notice a nice improvement when I upgrade my msd 6 box to a msd 7al two years ago. All I know is these new cars have 1 coil firing one or two spark plugs and here we are trying to fire 8 plugs with 1 coil. It can be done but not with the stock Mopar stuff. I also notice Mopar does sell the msd 7al box with the Mopar name on it but they claim its "drag race" only, I say BS.

 

[rumblefish360]

I like the new HEMI coming out with coil ON plug. No wires.

 

[AdamR]

I say match it up. Every little bit helps