Thread: Air gap manifold question

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Has anyone had driveability problems with an air gap manifold?

I'm thinking about running dual quads on my T and the manifold is available in both air gap and non air gap. I've never run an air gap.

I know that the air gap manifold helps build horsepower by allowing the A/F mixture to stay cooler(and denser). All the dyno data I've looked at bears this out, but dyno pulls don't always tell the whole story.

My question is about low speed driveability. Most of the stock engines I've seen that had manifolds raised above the block had some means of heating the runners(water or exhaust). I know that engines I've had with blocked off heat risers were very cold natured.

Originally Posted by Hotrod46

Has anyone had driveability problems with an air gap manifold?

I'm thinking about running dual quads on my T and the manifold is available in both air gap and non air gap. I've never run an air gap.

I know that the air gap manifold helps build horsepower by allowing the A/F mixture to stay cooler(and denser). All the dyno data I've looked at bears this out, but dyno pulls don't always tell the whole story.

My question is about low speed driveability. Most of the stock engines I've seen that had manifolds raised above the block had some means of heating the runners(water or exhaust). I know that engines I've had with blocked off heat risers were very cold natured.

With dual carbs. the manifold will be the least of your worries.

Eric

Yeah, I know they're not the easiest things to sort out, but I'm hoping I can tune them where they will run.

Sometimes I'm too stuborn for my own good, though!

Mike

go with the smallest cfm 4bbl carbs you can get. maybe holley 300cfm or 350cfm? they were made for puttin a 4bbl on inline 6's. this guy i knew had 2 450cfm holleys with a weind duel tunnel ram an a points ignition with a stock coil its always ran rich an like crap an on top of it the dummy had a monster circle track cam in it with a 3000 - 7000 rpm range. but i had ran a victor jr with a single 600cfm edelbrock carb on a stock motor an it worked great no heat problems ran a 160 t-stat also

Originally Posted by speedy55779

go with the smallest cfm 4bbl carbs you can get. maybe holley 300cfm or 350cfm? they were made for puttin a 4bbl on inline 6's. this guy i knew had 2 450cfm holleys with a weind duel tunnel ram an a points ignition with a stock coil its always ran rich an like crap an on top of it the dummy had a monster circle track cam in it with a 3000 - 7000 rpm range. but i had ran a victor jr with a single 600cfm edelbrock carb on a stock motor an it worked great no heat problems ran a 160 t-stat also

Things could run a little different, he lives in LA. and you live in MN.

Go with the non air gap..........

Before the Air Gap intakes were around . We would just block off the heat ports . And run a Lifter valley tray . By do so the intake would stay much cooler . But when driving the car on below 50deg days . It would be like a car with no choke . And after say 50 min of driving with the under hood temp higher . Then the car was more drivable . The Air Gap will do the same thing in below 50deg days . If you take out your rod on the more warmer days then it will work great . Because on the hot days with are old set up . Or with the new Air Gap . Your manifold will be at a much cooler temp . The chance of Vapor Locking is next to none . Or you can run the non-Air Gap intake with the heat ports open . And just the valley tray that keeps the hot oil off the bottom of the intake . I do it this way on a car that is more street then strip .

Run the air gap. Run Holley 600's; 1850 vacuum secondaries. You should be able to get them cheap on eBay if you know how to rebuild them with a Holley, repeat HOLLEY kit. Run the vacuum balance kit on the vacuum secondaries. Don't forget the power valves, especially if you run an automatic. Holley 'tuners' change jets all the time but ignore the power valve. Use a vacuum guage for tuning if you don't know already. Have fun with those quads. It takes alot of nerve to run them.

If your running a small block, they usually just run off of the rear carb till half throttle. Big block, on the other hand, need to run one to one linkage, otherwise the front cylinders run hot. Edelbrock uses 500 carbs for small blocks and 600 carbs for big blocks.

I run 600 carbs on my 454 with one to one linkage.

Originally Posted by gassersgarage

If your running a small block, they usually just run off of the rear carb till half throttle. Big block, on the other hand, need to run one to one linkage, otherwise the front cylinders run hot. Edelbrock uses 500 carbs for small blocks and 600 carbs for big blocks.

I run 600 carbs on my 454 with one to one linkage.

I don't think he needs a 1,000 cfm for a 5,000 rpm engine.

A street driven car needs heat and small carbs. Two 600 cfm carbs even with a progressive type linkage is way too much. A single 500 CFM on a 350 is just about right for 90% of driving, with a 600 as a nice choice when you want to kick it in the butt:

Size = (Engine CI x RPM) /3456 X Volumetric efficiancy

= (350 x 6000) / 3456 x .85

= 516 CFM TOTAL !!!!

Most engines without major mods wont have a VE (Volumetric Efficiency) much greater then 85 - 90%. Seldom will you be running at 6000 RPM. Choose your carbs accordingly - but a FI setup would be a better choice.

He definatly does not need 1200 cfm either........

I know I will get flac over this suggestion ,but its a good one ,just not as impressive.......I would use the adapters and run 2 big 2 barrels on that manifold ,under the aircleaner they will be mostly hidden anyway.A couple of 350 cfm 2 barrels or in that range ,maybe a pair of 300s.........Then use non progressive linkage,both open and close at the same time.
Some thing like this......Holley 0-807871 High Performance Race 350 CFM 2-Barrel Carburetor.
Amazon.com: Holley 0-807871 High Performance Race 350 CFM 2-Barrel Carburetor: Automotive

This is a list from the Holley web site:

Holley Performance Street Performance – Traditional Products

Look at p/n 0-8007. It's a 390 CFM !!!!
* Vacuum Secondaries
* Power Valve Blow-out Protection
* 100% Wet-Flow Tested
* Model 4160 W/Side Hung Floats
* Calibrated for Small V8 or 6-cyl Engines
* 2x4 Street Tunnel Ram Carb
* Ford A/T Kickdown
* Electric Choke
* Includes Single Inlet Banjo Fitting

WOW,I never knew you could get a 4 barrel that small......
You could run those non progressive too!!!!!!!!
I think those are perfect for your engine...........
With the non tunnel ram intake and those carbs ,it should be a walk in the park.....

Originally Posted by shawnlee28

WOW,I never knew you could get a 4 barrel that small......
You could run those non progressive too!!!!!!!!
I think those are perfect for your engine...........
With the non tunnel ram intake and those carbs ,it should be a walk in the park.....

At $347 EACH from Summit .

Oh well it's only money. I used to run 750CFM 3310's and they are $270 ea and the good ol' 600 cfm 0-1850s are $250 ea