Four barrel 911

[75eleven]

Hi- Just wondering if anyone has made a four barrel carb set up for a 911. I seem to remember in the late sixties seeing quad set ups for corvair engines that were put into VW dune buggies. Any thoughts pros and con. thanks Joe W

[pjv911]

THERES A PICTURE OF A CUSTOM 4 BARREL MANIFOLD ON THE BOARD SOMEWHERE. IT WAS FOR SALE ON EBAY ABOUT 2 MONTHS AGO.

KURT WILLIAMS

[stormcrow]

I saw that one for sale on E-bay also. It seemed a little high. I often thought about doing a conversion to a 4 barrel quad or something of the like.

Once the fuel injection is out, you can start fabricating the intake manifold. flat stock can be used to make the flanges, steel tubing could be used for the intake and a flat plate could be used to mount the carb.

A tubing bender would be ideal to get the right bends for each side.

I also thought it would be neat to install six single barrel carbs, like the ones used on the old 6 cyinder engines of long ago. They would have to be calibrated, linked together and synchronized, but I'll be willing to be it would work.

Steve

[Zeke]

There was a discussion somewhere recently about this. IIRC, the difficulty involved what type of plentum(sp?) would be used to distribute the air/fuel mixture to the ports evenly.

[jluetjen]

I guess the question would be "Why?" and what are you trying to accomplish?

Given the existing options Solex's 1bbls, Weber and Zenith 3bbls, MFI, CIS and DMI -- what would be the benefits of a 4bbl set-up?

What kind of motor are you anticipating putting this set-up on? What will be the size and tuning level?

[gregk1]

That manifold on ebay looked like a black widdow spider I have to agree with John Why! I use to run tunnel ram manifolds on big and small block chevy's. And the single carb one's didn't run very well you had some Holes runing rich and some running lean. Because the plentum didn't work evenley like Zeke said. Even with two four's it was a WFO! type manifold. I saw a tractor puller with like three VW motors in it and it had a manifold like that. A four barrel running all three motors. It was a real tripp with all the pipes for the manifold and then all the hedder pipes sticking stright up in the air it looked like a Calliope!!!!

[RarlyL8]

The "why" part is easy. Cost.

A Holley 4bbl runs $300. Fabbing an intake is just time and materials.
This would be OK for an older 911 engine with not much money in it. Why spend two grand or more on Webers to put on a $2500 motor?
Interesting project. I started to do this several years ago but had to abandon it for lack of time. You have to do it right, don't want to lean out a cylinder.
Just don't open the engine lid. You know how those purists are.

[StuttgartDavid]

As to why:

An engine sharing a common intake between cylinders (as in a 4 bbl. on a 6 or 8 cyl. does) will never be able to match the power potential of an engine using a dedicated carb throat for each cylinder, because:

1) An engine with a dedicated carb throat per cylinder can run a much more aggressive (read more overlap) cam than one sharing throats. The poor idle and fuel standoff caused by reversion from long overlap are both reduced by dedicated throats, which prevent crosstalk between cylinders. Really radical cams require a taller intake manifold in order to idle and have any low end at all(See the tall intakes on the factory racing Carrera 6 engines).

2) The previously mentioned threat of fuel starving one cylinder means that the others must run over-rich to compensate if you share throats. Too lean is dangerous, but as the old hotrodders say: "You've got to be lean to be mean."

[jluetjen]

I suspected that cost might be a reason, but the dollars that you listed for Webers is a little out of line. If the motor is an unmodified or lightly modified 2.0 or 2.2, Zeniths should work fine and you can get them on Ebay for $200. If you've got a 2.4 through 3.0 then Webers are most likely the way to go, but they're not $2000 (That's almost PMO money!). You can get a set of Webers on Ebay starting at $400 and a REALLY NICE set with filters, watershields, manifolds and linkages for about $900. So the price disparity is not that big.

I admit that a 4bbl can draw more air in total then a weber's 6 barrels on individual runners, but a 2 liter (or even a 3.6!) liter 911 motor just doesn't need as much air at wide open throttle as a 5 or 6 liter V8 at 6000 RPM. But it is just such a compromise of the induction system. Considering what you'll be giving up as far as being able to tune each cylinder as well as the instant throttle response of 1 bbl mated to an individual runner for each cylinder. There is also a huge amount of data about how to set-up webers for just about any concievable 911 configuration, while with a 4bbl you're on your own.

I'm all for exploring "the path less travelled" and trying to find the unfair advantage, but putting a 4bbl on a 911 motor just doesn't seem to be worth it.

If you go ahead and do it, please keep us up to date with the results and what you learn. As a skeptic I always enjoy being proven wrong!

[gregk1]

In NHRA Comp Elimanator and Pro Mod class with sheet metal manifolds. They take a 4500 domanator carb and cut it in half and place it over the top of the intake port. So the fuel is going stright down into the port the manifold still has a plentum but the port draws the fuel right out of the carb so it is more direct. This is not legal in Pro Stock if it was they would be running even better times than they are now

[Porsche_monkey]

Wouldn't a cheap fuel injection (ie Megasquirt) be about the same amount of work, cost the same, but much better?

[RarlyL8]

I can't imagine any FI system being cheaper than a 4bbl carb.
Fuel injectors alone would cost more.

I've not seen a complete, ready to bolt on set of Webers for under a grand. I'd surely buy them if I did.

The single carb idea is the least desirable induction method, but it should be the most simple and inexpensive to set up and it should run well. Carbs of all types suffer from fuel slosh when cornering hard so there is no disadvantage in that regard.

Helpful hint: use a set of old SC intake runner ends, fab the equal length center sections using aluminum tubing, and use an aluminum 4bbl carb intake carb adapter to mount the carb on. Real cheap stuff found at any auto store.

[Porsche_monkey]

Check out the old posts on Megasquirt, granted you would have to salvage your throttle and injectors, but this is totally achievable for under $500.

[StuttgartDavid]

Gregk1:

The NHRA split carb idea reminds me of what used to be the hottest factory racing team setup for BMC minis and spridgets:

The Split Weber.

Because the old BMC A series engine (998 to 1275cc) had 2 siamesed intake ports feeding 4 cylinders (and 3 exhaust ports!), and the intake ports were spread farther apart than the bores of the 2 throat weber side draft 40 or 44mm carb that was the hot street setup, they had all kinds of mixture distribution problems because the intake manifold had to bend, filling one cylinder more than the other.
Solution: Cut the weber in half and mount each 1/2 carb on a fabricated manifold that shot straight at the siamesed port. This was twice as expensive, because it required two donor carbs (twin webers share a float bowl, and split webers required two floatbowls for the two separated throats).

Bottom line: there are many ways to skin the cat, but when it came to factory racing R+D, the best engineers in racing worked very hard to get a single throat with a straight shot into the port.

How does this relate to 911s?
The webers used on the 911 were originally designed for a Lancia with intake bores located closer together than the 901 engine. Result: Porsche intakes have a bend outward for the outer two cylinders. Does this hurt power? Theoretically it should. I have always wondered if a similar split weber concept would yield more power in a cutting edge racing 911 engine. Anybody ever heard of such a thing? These days with FI, it may not matter, but in vintage or other carb applications it could be interesting.

[gregk1]

The solexes are a single carb per throat but I can't recall if the manifold is stright down my 66 had solexes on it but I changed to webers and sold the solexes to a guy in the UK. Some people say that if tuned right the solexes can out run the weber. That I could not do my self. I guess the Guy's in the UK that is all they can run when running 1965 model cars In a stock type class. They might be able to answer that one??

[jluetjen]

Rarly;
You might not be checking in the right places. Take a look here...

Recent EBay sales of Weber 40's

Some of these included the manifolds, some did not. The first set (which did not include the manifolds) looked pretty nice. Add on another $100 for a set of manifolds and you've got a touch more then $1000. Spend a couple of hours porting the manifolds (for higher applications which are expecting more then 160 HP) and you're ready to go.

Alternatively; get a set of Zeniths for really cheap (Usully $200 or less) and play with them. Apparently Weber venturi's can be made to work in Zeniths. That only leaves the jetting.

I doubt that the 911 intake manifold is leaving much on the table. Generally it is the venturi in the carb which is more constricted then the manifolds. Admittedly the manifolds are a slightly different length, but I suspect that we're talking a fraction of an inch. People have been used 2 sizes of intake trumpets on various race cars (911's and others) for years. Usually the difference between the 2 sizes is at least 1/2 inch. It is reputed to help spread the torque band a little bit at the expense of peak HP. But the effect is small and most likely ownly meaningful for engines which tuned pretty tight.

[dean]

One problem with the 4 barrel on a 911 would be carb icing. Give me FI any day.
Dean

[RarlyL8]

Hehe....
I'm really shocked that this thread has lasted so long without a real purist flamer lettin' 'er rip.

Everyone knows that FI is THE way to go, but absolutely nothing is gonna be cheaper than a 4bbl carb. Nothing. You can pick them up used all day long for a hundred bucks.

I wanna see somebody do this just to hear how it went. If I had the time................

[emcon5]

How about 6 Mikuni motorcycle carbs? Lots of 500cc motorcycles out there. Be a ***** to do the throttle linkage, but it would be pretty cool.

Tom

[911pcars]

[b/"absolutely nothing is gonna be cheaper than a 4bbl carb. Nothing."[/b]

I bet a 2 barrel Rochester is cheaper. How about someone experimenting with six SU, Stromberg or Dellorto sidedrafts, or four or six Rochester 1-barrels (a la Corvair)? Someone already mentioned Mikunis. Adapting some updraft carbs would be very cool .... and conversational.

It should make for some interesting manifolding and linkage setups and a few months of fabrication/working out the kinks. What the hell, since we're already thinking of feeding six cylinders with a four-barrel, why not use dual quads as they're both even numbers (8 into 6, common number is 2) There shouldn't be any fuel starvation with these puppies. Despite the fact there was a 4-barrel carb setup on a dormant engine for sale on Ebay, I'd suggest something a little more practical; like adapting an odd firing GM V-6 distributor into the Porsche. These distributors are really cheap and easy to come by (just kidding - the idea, not the price). FYI, the four barrel setup never worked on the Corvair - probably won't on a Porsche either (due to the reasons listed before), but anyone is welcome to try it again.

Is the purpose of this thread to devise the cheapest induction system or to improve on what's there now? What are we smoking tonight guys? Can I have some?

Sorry if I seem a little incredulous we're still discussing the possibilities, but I guess someone has to push the envelope.

Sherwood Lee