4 barrel intake!

[911pcars]

If you must pursue this project, I'd suggest trying a Rochester Quadrajet; famous for smaller-than-normal primary throttle bores and larger secondary throttles - progressively open according to air flow needs.

The small primaries should ensure higher air velocity which should help atomize the fuel along the longish corridor to each valve.

Let us know if the resultant throttle response meets your requirements.

Get it out of your system or you'll never be satisfied until you know first hand.

Some QJ info:
Rochester Quadrajet Tech Info - The Carburetor Doctor

Sherwood

[scott.k]

Originally Posted by mholbrook38

600cfm would flow plenty for a 3.0 liter. I don't think there is anything smaller but if so, that would probably be better. That intake manifold is a square bore so a Carter AFB or Edlebrock would fit on it. Also some Holley. I've only used Carter/Edlebrock on Mopars in the past.

thanks for the help,
i just bought a holley 650cfm carb off of ebay for pretty darn cheap. and I will be making an intake manifold for it, so I will probably see what shape the base plate is before i make the top of the manifold where it bolts on.
-scott

[scott.k]

Originally Posted by 911pcars

If you must pursue this project, I'd suggest trying a Rochester Quadrajet; famous for smaller-than-normal primary throttle bores and larger secondary throttles - progressively open according to air flow needs.

The small primaries should ensure higher air velocity which should help atomize the fuel along the longish corridor to each valve.

Let us know if the resultant throttle response meets your requirements.

Get it out of your system or you'll never be satisfied until you know first hand.

Some QJ info:
Rochester Quadrajet Tech Info - The Carburetor Doctor

Sherwood

thakns for the help,
I bought a carb on ebay a little earlier today, but it was only $50 dollars, so I wont feel to bad if I end up having to purchase a different carb, like one of the ones on that page
thanks
-scott

[76912E]

Originally Posted by scott.k

thanks for the help,
i just bought a holley 650cfm carb off of ebay for pretty darn cheap. and I will be making an intake manifold for it, so I will probably see what shape the base plate is before i make the top of the manifold where it bolts on.
-scott

You should probably ditch the 650 cfm in favor of a 300 - 350 cfm for a 3 liter-sized engine. The 650 is way oversized. A 350 CI small block only needs about 550 cfm.

Here's one of the typical carburetor sizing selection sites: THE CARBURETOR SHOP / Carburetor size selection criteria

Fran

[fred cook]

Holley used to make a 350 cfm four bbl carb. I had one on a hotted up 1973 Capri 2.6 ltr V6 engine. Once properly set up (jetted, etc.) it worked quite well. I believe that I had it mounted on an Offenhauser aluminum intake. Of course, it was a water cooled engine so the manifold would heat up pretty quickly. If there was a way to warm the intake manifold as shown for a Porsche engine, it would likely work reasonably well.

[scott.k]

Originally Posted by 76912E

You should probably ditch the 650 cfm in favor of a 300 - 350 cfm for a 3 liter-sized engine. The 650 is way oversized. A 350 CI small block only needs about 550 cfm.

Here's one of the typical carburetor sizing selection sites: THE CARBURETOR SHOP / Carburetor size selection criteria

Fran

I think you are definitely right about that one. I will look around for one.


but just wondering, does that mean what EARLYPORSCHE was saying earlier "500cfm would be about it for a 2.2." is off?


THanks
scott

[tobluforu]

Originally Posted by fred cook

Holley used to make a 350 cfm four bbl carb. I had one on a hotted up 1973 Capri 2.6 ltr V6 engine. Once properly set up (jetted, etc.) it worked quite well. I believe that I had it mounted on an Offenhauser aluminum intake. Of course, it was a water cooled engine so the manifold would heat up pretty quickly. If there was a way to warm the intake manifold as shown for a Porsche engine, it would likely work reasonably well.

OMG, I had the same setup on my 73 capri that had a 76 2.8 in it with an offy med rise manifold, isky cam, the holley carb you mentioned, hooker headers, etc.. That car flew.

[scott.k]

would it work to jet down the 650 carb I bought or should I look for a two barrel holley 350?
like jets in the 50's?

It is a track (and some street) car so i would like something that will give good flow if possible, im going for power over gas milage

THanks
Scott

[Brad394]

Well you could do two things - 1) sell the 650 Holley ( to big for 3.0l ) and go with a Q-Jet as mentioned early in thread. This has small primaries which make cruising better - and fairly quick throttle response - and the large secondary will flow more than enough air for WOT on a long straight. Q-Jets come in a variety of sizes as well, so look for smaller ( for lack of a better term ) one. Once you learn how to tune a Q-Jet they work wonderful. Years of experience in the straight line stuff before exposeure to twisties in Porsche. 2) go with the two barrel Holley - again need to learn tuning tricks ... find local short track - stock class "stockcars" usually run the two barrels -

If I were to do this - and have thought of it more times than not - I would shorten the runners ( which requires fab work ) ie. don't use the 3.0l SC intake runners. Look for pics of a single plane manifold (torker) to see what I mean.

BG

[lupin..the..3rd]

Originally Posted by Don Z.

Corvair guys do it all the time.

Corvair guys also bang their heads against the wall because the fuel won't atomize...

In the air cooled VW world, most of those air cooled flat-4 engines came from the factory with a single center-mounted carb, and very long intake runners to reach each of the heads. Very similar to the design of this ebay item.

To keep the fuel atomized, the VW engineers ran an exhaust tube up and attached it along a section of the intake manifold. The constant stream of 350 F exhaust gasses kept the intake manifold warm enough to keep the fuel atomized.

[aston@ultrasw.c]

Years ago I put a Holley 390 on a Rover 3.5L V8. It had vacuum secondaries and was mounted on an offenhauser dual plane manifold. The dual plane increased the gas velocity at low RPM thereby mitigating the effects of having the carb at the end of a long tube. At WOT the web for the dual plane did reduce total intake area but I never noticed it. The car was crazy fast ;-) MGB-GT!

That carb/manifold was a gem, easy to set up and very flexible.

[djpateman]

a 2.2 L at 7000 RPM is 270 cubic feet per minute
a 3.0 L at 7000 RPM is 370 cubic feet per minute

[Joe Bob]

Idle and WOT can be achieved. It's midrange and driveability in the real world which would be sucko. Hence a big single toilet bowl of a carb would be optimal in straight line race applications. Not good in road races or grocery getting.

[scott.k]

Its probably just me, but I find it challenging to find the quadrajet carbs in a small size, like 350cfm. WOuld i need 350 in my car or could I use bigger if using a quadrajet because the small primary venturis would still take care of the lower rpm range?

THanks
Scott

[Brad394]

Originally Posted by djpateman

a 2.2 L at 7000 RPM is 270 cubic feet per minute
a 3.0 L at 7000 RPM is 370 cubic feet per minute

I used the online calculators as well - I would think that a 350 cfm 2barrel carb would do well - jetted of course. I think the 500 cfm two barrel would still be to big but may work better in the upper RPM

[Brad394]

Originally Posted by scott.k

Its probably just me, but I find it challenging to find the quadrajet carbs in a small size, like 350cfm. WOuld i need 350 in my car of could I use bigger if using a quadrajet because the small primary venturis would still take care of the lower rpm range?

THanks
Scott

The Q-jet if memory serves me is about 750 cfm total - the trick is to get it jetted for your needs. If I remember correct the range is about 500 to 750 . There are a few sizes of primary and secondary butterflies... would have to dig for old HotRod magazines ... smaller primaries for the part throttle stuff and use all the cfm you can when secondaries are open. The progressive linkage for the secondaries can be worked so they are only open full at WOT. Might be to much f'n around to get right combo... try 2 barrel and work from there. Holley has 350 - 370 - and 500 cfm, I think - rochester has a couple as well, 360 and 500 cfm me thinks.

[911pcars]

A similar Corvair conversion would be a good comparison for real-world usability. Suggest you peruse the Corvair forums for owner feedback of this intake system. They've had over 40 years of chances to use a single 4-barrel to feed their 6 cylinders with success. However, it seems like you're on that slippery slope already. Best wishes. Hope it works out for you.

IMHO, your secondaries must open according to engine demand (rather than mechanically) in order to work most efficiently.

Sherwood

[scott.k]

Originally Posted by Brad394

The Q-jet if memory serves me is about 750 cfm total - the trick is to get it jetted for your needs. If I remember correct the range is about 500 to 750 . There are a few sizes of primary and secondary butterflies... would have to dig for old HotRod magazines ... smaller primaries for the part throttle stuff and use all the cfm you can when secondaries are open. The progressive linkage for the secondaries can be worked so they are only open full at WOT. Might be to much f'n around to get right combo... try 2 barrel and work from there. Holley has 350 - 370 - and 500 cfm, I think - rochester has a couple as well, 360 and 500 cfm me thinks.

Thanks for the help. When I was reading up on quadrajets, I was surprised that the large secondaries opened up not by throttle position, but by demand of the engine, I wonder how someone figured out how to get that to work. Because i know they say that if you are revving your engine with quadrajets in a parked position, the secondaries wont open up even if you hit the gas all the way when revving it. THey sound like the combination of power and performance (secondaries) and a smooth idle and low rpm driving (primaries). I think ill have to try to find a good deal on one of them.

[G50-Love]

individual throttle bodies are what you want

if you got the 4 bbl. thing as a gift with a Rochester included then it would be a toss up as to whether to ash can it or not

[sc_rufctr]

Originally Posted by gestalt1

check this out:
http://cgi.ebay.com/ebaymotors/PORSCHE-911-CUSTOMS-4-BARREL-INTAKE_W0QQitemZ160039720862QQihZ006QQcategoryZ336 40QQrdZ1QQcmdZViewItem

i've not seen this before. I have no affiliation to the auction, just thought it interesting.
-matt

I've seen a very similar intake with a 4 barrel central throttle body, after market EFI and coil packs on a 2.7.
The injectors and fuel rails were in a similar location to a 3.2 (down near the ports)... Seemed to work really well but I never drove the car.