Different carb setup?

TerryBPP · 10-14-2003, 08:51 AM

I saw this pic and wonder if someone had used a similar setup on a flat six. Maybe using a 2 barrell american carb.

Early_S_Man · 10-14-2003, 09:05 AM

Terry,

There was a 911 engine for sale on eBay a couple of years ago with a single Holley four-barrel carb setup on a fabricated manifold ... triggered quite a lengthy thread/debate as to the suitability and value of such an idea!

Years ago ... Crown Mfg. offered a similar manifold setup for Corvair engines.

TerryBPP · 10-14-2003, 09:11 AM

I think the intake runners would be about as long as the CIS ones. My only concern would be atomization. If you were to set it up where there was a 2 barrell on both sides of the motor (similar to webers or mfi) it might be more efficient. Hmmmmmmmmmm....

Early_S_Man · 10-14-2003, 09:38 AM

Ford offered an inline 4-barrel carb for the Boss 302/351 engines ... it was reputed to be a knock-off of a Weber. I suppose a pair of those could be attacked & modified with a band saw to make a 3-barrel alternative to PMO's!

TerryBPP · 10-14-2003, 11:55 AM

I'm pictureing a setup like weber but with a box plenum and a carb on top. Looking similar to the honda performance intakes but upright. If I was to put a carb on each side how would I figure out what size carb to use. I figure if 40cfm webers are on each cylinder then all I would need would need is a carb that would provide 120cfm on each side. Maybe 150cfm to be safe.

dd74 · 10-14-2003, 12:14 PM

Where would you find a manifold to run something like this?

Would it prevent the "starvation" Webers go through with high cornering?

Could this be a good CIS replacement?

Early_S_Man · 10-14-2003, 12:19 PM

Terry,

You wouldn't want to use a plenum on a 911 engine! You would lose a tremendous amount of torque on the bottom end ... say, below 3500 ropms!!!

If you are seriously considering this as an experiment ... I suggest three Holley 2100's with individual runners to each 'barrel!' Three of the center carbs from a MOPAR 340 'Six-Pack' would give you six adjustable idle circuits. Your cfm estimates are WAY TOO LOW, BTW!!! At about $300 per carb ... it would't be a cheap experiment! Then you still have to fabricate the manifold, linkage, and air cleaner ... but, you just might be able to fit 'Hemi orange' & black crinkle painted 'Six Pack' air filter assembly under a big 'Tea Tray tail!!!!

Mukilteo911 · 10-14-2003, 12:24 PM

modify zeniths, they are cheep and work great. I put them on my 2.4 and they are fantastic. faster revs and smoother than the cis. all you have to do is put in the correct venturi and drill out the jets takes a few hours. I even bored out my venturi myself and saved more. You can get solex venturi for about 9 each from online vw shops, or use weber venturi.

TerryBPP · 10-14-2003, 12:36 PM

dd74, the intake could be made if you ran a carb on each side, unlike the pick.

This thread is ending up like the other ones. "The only way to go is 3 seperate carbs". I look at it like this, if a aluminum 427 side oiler can run on 1 4 barrell than a 2.7 porsche can run off of 2.

The cornering issue is a problem but worst case I'd change it to 2 TBI setups (theoretically). If a circle track car can run a carb a porsche can.

Early s man, you are correct about the plenum. I was just trying to give you the visual concept.

I figure 2 350cfm 2 barrels and some aluminum. I think I give ity a shot.

dd74 · 10-14-2003, 01:23 PM

Terry - this sounds interesting because it's a much different setup - innovative. Please post results.

I'm wondering how something like this could deal with CIS pistons and the inherent overlap issues. Also, how it would work with 20/21 or 964 cams...

Hmmmmm...

emcon5 · emcon5's Garage

This was an older discussion on 4 barrel carbs:
Four barrel 911

And an interesting idea on using carbs from personal watercraft:

Jet-Ski Mikuni Carbs on a 911...

Tom

Mukilteo911 · 10-14-2003, 03:54 PM

I had actually started a thread on this about a year ago. Several freinds and I discussed it at length and thought it would be cool to play with. We came up with the idea that we find a car in a junk yard with a simular displacement and then build a manifold. We never had the time to do it and I ended up doing the Zenith thing. If someone proved it which would only take time and a few hundred bucks it could prove to be a nice option. Early Isuzu troopers had, i am pretty sure 2.6 liter engines, with carbs. It would probably be a cheep unit to try from the local yard.
For the manifold you could use a 2.4 CIS manifold, cut off all the stuff on top and clean up the air box to bolt the carb to.

dd74 · 10-14-2003, 04:32 PM

Zenith question: why are Webers so highly touted over Zeniths or Solexes?

Steve Marshall · 10-14-2003, 07:13 PM

Covair Corsa's used this type of set up. Might want to check out some Corvair sites.

911pcars · 10-14-2003, 08:15 PM

Corvair Spyders used a suck-through turbo. The intake manifold was a single Y-pipe that fed each bank.

The aftermarket 4 barrel adapter for the normally-aspirated Corvairs always had a problem with throttle response due to the long intake tract (and the fact that 2 intake passages (per bank) don't really divide evenly into 3 cylinders). Hot rod versions of the Corvair six use an adapter plate welded in place to run, guess what? ..... two 40 IDA/IDT Weber 3-barrel carbs.

It's easier to move just air rather than air AND fuel.
Let's see. Instead of the central 4-barrel carb feeding air/fuel, let's have it control only air with the throttle valve on the central air intake. Attach a TPS (throttle position sensor) onto the throttle valve. Next, install electronic injectors at each intake port, wire this up to a control box and voila .... you've got yourself a semi-modern EFI system.

GM outfitted some engines using an experimental Rochester MFI system (a la Corvette). Probably produced decent power, but that proved too expensive. Too bad. Typical GM, they bottom-lined it again.

Sherwood Lee
http://members.rennlist.org/911pcars

Early_S_Man · 10-14-2003, 08:24 PM

Steve,

The Corvair 140 hp engine used 4 ea Carter 1 bbl carbs on short manifolds on the four corners of the engine! The single four-bbl setup was aftermarket, as I already mentioned ... used a 390 cfm Holley 4160 from an International Harvester V-8 application!

Mukilteo911 · 10-16-2003, 09:48 AM

DD74, I think people like the webers because you can get parts and people are used to modifying them. When I modified Zeniths I had to stick with the original emulsion tubes for the lack of bigger sizes.
I hear in Germany that Zeniths are the rage and they look down on webers, go figure.

TerryBPP · 10-16-2003, 11:39 AM

I have decided to try this experiment this weekend. I'm going to use a 350 cfm 2 barrel on each side of the motor. Im going to fabricate the intake mainfolds. They will consist of 1.5" tubing. The 2 outer intake tubes will be at a 45deg angle and the center will be 90deg. These will lead straight to a plate that the carb will sit on.

My only worry is that the equal length of the tubes will effect hp. I guess we will see what happens.

911pcars · 10-16-2003, 12:08 PM

I think you might find the throttle response to be less than desired due to the distance between the accelerator pump jets and the combustion chambers, but let us know how it goes. I'm not one to discourage innovation.

Have you calculated the optimum throttle area to feed the six cylinders? There are published formulas (also in B. Anderson's book). Perhaps a Quadrajet might be better suited to maintain gas velocity (small primaries, larger secondaries) and still have max. CFM?

Or why not try something with Mikunis or Dellorto carbs........ or Webers?

Sherwood

TerryBPP · 10-16-2003, 12:16 PM

The formlua I got off of the Holley website was:

Cubic inches X max rpm/ 3456 = necessary CFM

I don't really like the max rpm part of the equation.