The Stovebolt Site Forums The Shop Area Engine Shop Any realistic 2-barrel options for the 216/235/261?

Just for "kicks", I have wondered if there are any of the Rochester or Carter 2bbls that (with an adapter)really add much to the performance of Chevy straight-6 classics.

I have toyed with trying a BBD or even a Rochester AA Turtleback just to see how it might go!

I will use the Rochester B for normal use but just want to try something different (sort of as an experiment) at times. Anyone ever tried this?

I bought the 2 bbl adapter from J.C. Whitney, but never tried it on the 235. I can't see where it could do much better cramming 2 bbls down a one bbl hole....

John

I wish a single 2 bbl intake was made for those motors,the twin single bbl intakes look nice but a single 2 bbl would be nicer for ease of service.

You can use a single 2-barrel adapter to the single carburetor original intake - Whitelightening refers to one.

I have used two such adapters. 4-bolt 2-barrel to 1 barrel; and, 3-bolt 2-barrel to 1-barrel (which I am now using with a Holley AA-1 - same bolt pattern as Holley 94/2100/2110).

I talked with a guy at a show, he had a 53 and he was a machinist. So he had a lot of neat pieces on the truck. He made what he called a transition/ adapter for a small 2bbl roch like on the old 283's. It was slick. Said it ran well. I wish I had the ability to do things like that.

This works with a Rochester 2G/2GC on a later 235 intake.

There are Weber 2 barrel kits out there. Some even have the 1 to 2 barrel adapter.

Which Weber?

If you follow NASCAR, think restrictor plate!

Yes, you can use the adapter, and yes it can be made to work.

Will a two-barrel work better through the adapter than a one-barrel? NO, in fact it cannot not work as well, as the lower velocity in each of the venturii of the two-barrel will lower the efficiency of the two-barrel.

For best results (if you NEED more carburetion):

(A) Use a larger one-barrel
(B) Fabricate a two-barrel manifold for the two-barrel of your choice.
(C) Use a multiple manifold with multiple carburetors

Jon.

That looks like the one I have. Did you still use the insulator between the adapter and manifold?

John

I always thought a progressive 2 bbl would be the way to go....

John

I have not used that with a 2G/2GC.
I did not use insulators with Carter-Weber carbs with that adapter.

Once I get one of my Bridgeport mills up and running, I have plans to modify a stovebolt intake to accept the small Rochester 2 barrel intended for the 265/283 V8. It will necessitate some fabrication and welding/brazing of a new flange onto the carb base area. Since the heat riser passage surrounds the fuel passage under the carb, it won't be a simple project. Lots of opportunities to get some unintended exhaust gas recirculation!
Jerry

Lots of options here and all good quality stuff. I'm running two progressive Holley-Webers on my 261, runs strong.

www.langdonsstovebolt.com/store/online-catalog/#!/~/category/id=361512&offset=0&sort=normal

Sounds like you and I are thinking along the same lines. I think there would be plenty of room for this modification.
John

I did this but never got around to welding it up or trying it. See here.

[size:23pt][/size]NICE!! John

That's exactly what I had in mind- - - -just a lot prettier than I can do. How do you plan to seal the exhaust gas away from the intake vacuum? I've been thinking about a 2-piece setup with an oval intake passage welded or brazed to the intake plenum, then an outer housing with the carb flange shape brazed to the outside.
Jerry

It no doubt would need some serious welding/brazing/filling to isolate the heat box but for me it was primarily a machining excersize at morphing one shape to another and investigate feasability. I think you're on the right track with a 2 pc. design to cut down the welding required. Someone over at the Inliner's board did something similar with a next gen intake and used epoxy/JB weld to fill the heat cavity. No Idea how that worked out.

Jerry,

I should have mentioned I carved that intake for a large base 2G carb as that's what I had laying around. You will have more material left than what my pictures show and may be able to keep most of the wall if you taper it a bit on the way down. Good luck with your project.

Clifford has intakes for 2 or 4 barrel intakes, depending on which adapter plate you use.

I've got a couple of small base Rochesters designed for the Mercruiser 4 cylinder engines that might have to be rejetted a little to work with the 216/235 engines. At least it won't over-carburete like most of the dual carb setups do. I can't imagine any kind of epoxy that would stand up to direct exposure to exhaust gas. Even brass would be pretty close to its melting point.
Jerry

The late production (early '80s) 292 used a progressive 2 bbl, the Rochester 2SE, also known as a the Vari-Jet. Might be a viable option, and is a rather common carb used on GM V6 engines in addition to the 292.

From the perspective of someone who used to try to make those pieces of junk work without sucking the secondary metering needle into the engine and imbedding it in the top of a piston, RUN- - - -do not walk away from the Varajet carburetor. They were notorious for wrecking engines when that stainless steel needle came adrift!
Jerry

That's something I haven't experienced with the Varajet, yet (fingers crossed). I have one on a 2.8 V6 in my Blazer, the only major problems I've had with it mechanically are the electric choke that looses it's spring tension, and a float that went sour. Didn't know about the secondary metering needle issue, thanks for bringing it up, might save me an engine in the future.

I've seen several secondary needles that just disappeared, followed by hammering noises from the engine. Pull the head- - - -there's what's left of the needle stuck in a piston! It usually happens on engines that spend a lot of time at or near full throttle, where the secondary air flap cycles a lot. That carb is sort of like half a Quadrajet, with all the bad features and none of the good ones. Keep an eye on the needle, and if it shows signs of getting wobbly in the air valve, use the carb for a fishing sinker!
Jerry

Will do, Jerry.

It would be nice to hear from anyone who used a Clifford 4 bbl intake with an adapter to a Rochester 2G/GC carb as that seems to be the easiest way to make this happen. Hopefully I demonstrated the stock intake leaves very little to work with.

from what I understand the Clifford intake with a 390 holley is quite a runner. I don't have any personal experience, but I think Pre 68 Dave has.

Ok guys.....first no stone throwing at me! Has anybody messed around with a quadrajet, primarily because of the very efficient primaries that can meter fuel very well at very low vacuum, forget the secondaries as they will probably never open up and would be of no use on a 235. In fact fix them shut. I know there is a love hate relationship with them. Some guys hate them , some love them. I have been working with quardajets, rebuilding, modifying for a long time and if they are really understood they are a great carb, no not for strip use I will concede that. They were a trade off between good power and fuel efficiency so pouring gobs of fuel down an engines throat like a square bore wasn't their purpose.

The Q-Jet is a great carburetor!

HOWEVER: one needs a manifold for the Q-jet to fit.

The 216 was rated for 3400 RPM
The 235 was rated for 4200 RPM (1956 and newer)
The 261 was rated for 4000 RPM
The 230 was rated for 4400 RPM
The 250 was rated for 4200 RPM
The 292 was rated for 4000 RPM

DO THE MATH! Mathematics truly IS your friend!

CFM = CID times RPM times volumetric efficiency all divided by 3456.

These 6 cylinders have a volumetric efficiency of maybe 70 percent (0.7).; BUT WAIT (as the infomercials say). Lets say you port the head, put in a full-race cam, put in domed pistons to get the compression ratio to about 10.0, add racing headers, and some form of super ignition system and get the volumetric efficiency up to 80 percent (0.8)

For the 235 with ALL the mods above:

CFM = 235 times 4200 times 0.8 all divided by 3456

CFM MAXIMUM is 228.

For the 292

CFM = 292 time 4000 times 0.8 all divied by 3456

CFM = 270

Note these maximums are the RPM limit for a highly modified street engine.

Now, if want to balance the crankshaft, machine high strength rods, etc., and turn these engines into race only; you may be able to obtain more RPM.

Both Stromberg and Zenith offered one-barrels that will bolt directly to the 235/261 manifold that are rated 215 CFM, and, while not readily available, Zenith offered a larger 1-barrel that was rated at 252 CFM.

Note that the maximum CFM in the illustration above are for wide-open-throttle requirements at the maximum RPM.

With no offense meant to anyone by my next statement:

If a two-barrel or a four-barrel equals "cool", then by all means go for it; just don't expect any great performance increase, and you might just LOSE performance at normal city or cruise RPM.

Oh, and bztguy, the Q-Jet on an engine which can handle it, works great on the strip. They even can be made, although with some difficulty, to go around corners for that form of racing.

Jon.

Having said all of the above, if you ARE looking for a slight increase in performance, and don't like the looks of a single one-barrel:

Multiple carb setups (WITH PROPERLY SELECTED AND TUNED CARBS) will give a modest increase in engine efficiency (power and fuel economy), even over a properly sized single carb. The multiple setup decreases the distance and the variance in distance from the A/F source (carburetor) to the cylinder. This promotes better cylinder fill ratios, and more constant A/F ratios among cylinders.

And, as I stated in the previous post, do the math. Mathematics really is your friend.

Jon.

Some QJ installations were adjusted to conform to the "1 hp per 10 lbs. of chassis weight" GM dictum of the day.
The GTO and Firebird had the same big block motor options, but the weight differed by a few hundred lbs. The GTO got the "normal" QJ for 335 hp, while the Firebird's secondary air valve was set to only open to 80° (more or less) which trimmed off enough peak power to officially conform at 325 hp.

What about the 250" Sprint? 230 hp (special standard shift option) @ 5,400 rpm & 90% VE only needs 352 CFM, but the QJ supplies up to 750 (if the air valve opens fully)?

The quardajet is a very misunderstood carb. My father who is now 85 and spent his life as a professional mechanic working in GM dealerships for years as well as farming all of his life taught me the ins and outs of QJets 30 years ago. They are one of the best carb designs ever made when you learn them in detail. They survived decades with minor design changes all the way into the mid 80's with the addition of a few electrical components such as TPS for the computers until the government emissions controls exceeded what could be done with them. How many carb designs can say that and the later Qjets were a 850 CFM carb. I recently dropped a mild performance cam in my 75' Hurst Olds 350, ported the heads and manifolds, dualed the exhaust and modified a stock QJet to handle the air/fuel/vacuum requirements of the new configuration. Had a guy tell me what I really needed to do to finish it off right was drop on new Edelbrock 650 CFM in there to really open her up. When I pointed out I would be going from an 850 to a 650 CFM carb and lose the stock appearance of the engine - I got the deer in the headlight look.

The Q-Jet DID have a good run: 1965 - 1985 (21 years).

Other models that come to mind:

Carter BB 1932 - 1964 (33 years)
Carter BBS 1954 - 1983 (40 years)
Carter BBD 1952 - 1989 (48 years)
Carter YF 1951 - 1982 (32 years)
Carter AFB 1957 - 1984 (28 years) (I don't count the AFB-clones still being made today)!

Stromberg WW 1952 - 1974 (23 years)
Stromberg SF 1932 - 1968 (37 years)

There are others.

Jon.

Bztguy, I'm going to have to send you a PM, you just might have the knowledge to answer my question on adjustments for a Quadrajet 4 bbl.

John

I built a tractor pull engine for a SuperStock truck from a bored-out MOPAR 440 (459 cubic inches) and got 714 HP at 6500 RPM from a single Q Jet from a 455 Buick and Cam 2 racing gasoline. That's temperature and humidity corrected dynamometer figures, not some pipe dream from too much to smoke!
Jerry

Wouldn't you basically be doing the same thing with a DualJet?

Here's what a fellow "Bolter",(Jeff Bradshaw), installed on his '78 C-60/292...https://www.youtube.com/watch?v=obzULioHc64

Where's the link Willy?

Mike B