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I am getting ready to build a 360 sbc out of a 880 4 bolt block,its been machined lined ,decked bored,and I recently bought some aluminum heads for it ,these heads will fit either vortec style intake manifold or conventional ,my block does have third bypass hole for the water pump and mechanical fuel pump hole.To me it seemed simple to just set it up like old school 350 build but Im wondering if I might be missing something.or over thinking it,and another thing is Ive got my mind set on a air gap manifold,do I have to have it? motors going in a 4x4 jeep.there's other cheaper intake manifolds that do the same. other than the cooling part.I guess I should add that the runners are 200cc 68cc chambers,2.02 -1.64 valves,flat top forged pistons, .500/.510 cam, thank you
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If your engine will be subjected to prolonged low-speed lugging situations which you might get if off-roading is your gig, then the air-gap style manifold will help by keeping the intake charge a little cooler. Also, I would pay more attention to mid-range torque output for off-roading, and ".500/.510 cam" is a little much for that situation. Just sayin' . . . 馃檮
 

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Air gaps perform better where the engine revs are kept high and the weather is warm. The reason being that engines need finely misted fuel as liquid in globs doesn鈥檛 burn well making for a late burn and erratic running to lost power.

There are two solutions to getting around this one mentioned is keeping the revs up around 3000 or higher which creates enough violence in the manifold flow to prevent fuel pooling thus evening out the cylinder to cylinder mixture and presenting a finely divided fuel mist in the mixture flow that is easy to ignite and burns sufficiently fast in the chamber. The other short of fuel injection is to heat the incoming air or the intake manifold itself the latter being the OEM鈥檚 favorite way. This in their hands is sufficient to actually vaporize the fuel. While this burns nice and makes for a stable running engine between start up cold and running hot it does cost power in that vaporized fuel expands a lot (you鈥檙e essentially making it into the equivalent of hydrocarbon steam) so this expansion takes space which reduces the air volume in the flow to the cylinder thus power is lost. The companion problem and the one the hot rod community seems transfixed on is the loss of air density itself but while a valid concern this is not the sole problem.

So the decision on an air gap needs to have some rest upon how the engine gets used and the typical weather you operate it in. The combination of cold and especially if combined with high humidity can be problematic especially at revs under the torque peak. A partial answer here is simply an unheated intake but one that closes the valley with the runners such that the manifold at least sees engine operating temperature. I run this combination with aluminum heads on my daily driver to where much of the year is cool to cold and wet, it is something of a PIA in city traffic till the engine is good and warmed up.

Bogie
 

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My take on air gaps...

Aluminum is highly conductive of heat. It's going to get just as hot as a non air gap, it will just take a few more minutes. If you're drag racing, it might help. On the street you want to get the engine up to temp as fast as possible, both for the health of the engine, and for air/fuel mix... getting off the choke... driveability, etc. Millions of tests have been done and it may account for a couple hp... which you'll never feel in your butt, but if it shaves .002 seconds off your quarter mile, it might be worth it.

My opinion is that air gap intakes are 100% gimmick. I might even go as far as snake oil. Squarely in the "bling" category.

In my builds, I typically keep exhaust crossovers. I want that intake hot. Does it cost me 2.7 hp? Yup. Gladly. I'll never miss it.
 

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Discussion Starter · #8 ·
Howard cams 180245-10,I'm running around but I remember that sorry
My take on air gaps...

Aluminum is highly conductive of heat. It's going to get just as hot as a non air gap, it will just take a few more minutes. If you're drag racing, it might help. On the street you want to get the engine up to temp as fast as possible, both for the health of the engine, and for air/fuel mix... getting off the choke... driveability, etc. Millions of tests have been done and it may account for a couple hp... which you'll never feel in your butt, but if it shaves .002 seconds off your quarter mile, it might be worth it.

My opinion is that air gap intakes are 100% gimmick. I might even go as far as snake oil. Squarely in the "bling" category.

In my builds, I typically keep exhaust crossovers. I want that intake hot. Does it cost me 2.7 hp? Yup. Gladly. I'll never miss it.
I understand,I was kinda feeling that way,for a air gap it $345 and for $285 u can get manifold gaskets bolts for traditional style same rpm.thanks
 

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Run a rpm performer if you plan on floating valves.

For lower rpm(under 5000) run a performer intake.

You don't need or want a air gap for anything that is run below 50F degrees ambient(cold mornings).

When I find them on something I either give them away for free, sell them for $20, or outright scrap them.

The standard edelbrock performer intake will be just fine for 90% of the piles that drive under 5500rpm. $50 used or around $180 new.
 

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Discussion Starter · #10 ·
If your engine will be subjected to prolonged low-speed lugging situations which you might get if off-roading is your gig, then the air-gap style manifold will help by keeping the intake charge a little cooler. Also, I would pay more attention to mid-range torque output for off-roading, and ".500/.510 cam" is a little much for that situation. Just sayin' . . . 馃檮
yea I know, but it wont be offroading all the time,mostly will be on street and it has a 700r4 overdrive so that with the heads I have makes sense,if Im only offroading here and there,not rock crawling.The original engine had only 120 hp 160 tq,and that tfkin sucked!!!!!!!!now I will have 3.5x hp and tq,so idk
 

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I have tried just about every intake made, tunnel ram, airgap, rpm, and performer. For a street driven vehicle (sbc) with a cam under 270 degrees, Wait for it......stock older cast iron tall Quadrajet intake (No EGR) with Early Q-Jet carb. Great driveability and performance and about as simple as you can get. GM spent thousands of hours in research and development on this set up. IT works as long as you limit cam duration to acceptable limits for a street driven vehicle.
Just my opinion. Your mileage may vary.
 

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Discussion Starter · #12 ·
I have tried just about every intake made, tunnel ram, airgap, rpm, and performer. For a street driven vehicle (sbc) with a cam under 270 degrees, Wait for it......stock older cast iron tall Quadrajet intake (No EGR) with Early Q-Jet carb. Great driveability and performance and about as simple as you can get. GM spent thousands of hours in research and development on this set up. IT works as long as you limit cam duration to acceptable limits for a street driven vehicle.
Just my opinion. Your mileage may vary.
Had good friend tell me that too,thanks
 

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Wait for it......stock older cast iron tall Quadrajet intake (No EGR) with Early Q-Jet carb. Great driveability and performance and about as simple as you can get. GM spent thousands of hours in research and development on this set up. IT works as long as you limit cam duration to acceptable limits for a street driven vehicle.
There's a guy named Jon at The Carburetor Shop who specializes in kits and rebuild services for older OEM carbs. He says the GM Q-jet manifolds are perhaps the best manifolds ever made -- for their intended use, of course. Obviously he's also a big fan of Q-jet carbs, but also the original AFB.
 
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