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Re: Any realistic 2-barrel options for the 216/235/261? [Re: stoveboltgator] #1021417 Sun Apr 13 2014 05:52 PM
Joined: Nov 2002
Posts: 1,892
C
carbking Offline
Carburetion specialist
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.


Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify
If you truly believe "one size fits all" try walking a mile in your spouse's shoes!
[image]http://www.thecarburetorshop.com/Avatar.jpg[/image]
Re: Any realistic 2-barrel options for the 216/235/261? [Re: stoveboltgator] #1021422 Sun Apr 13 2014 06:09 PM
Joined: Nov 2002
Posts: 1,892
C
carbking Offline
Carburetion specialist
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.


Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify
If you truly believe "one size fits all" try walking a mile in your spouse's shoes!
[image]http://www.thecarburetorshop.com/Avatar.jpg[/image]
Re: Any realistic 2-barrel options for the 216/235/261? [Re: stoveboltgator] #1021506 Sun Apr 13 2014 11:39 PM
Joined: Dec 2008
Posts: 1,319
P
panic Offline
Shop Shark
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)?

Re: Any realistic 2-barrel options for the 216/235/261? [Re: panic] #1021823 Tue Apr 15 2014 02:48 PM
Joined: Jun 2010
Posts: 248
B
bztguy Offline
Shop Shark
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.


1949 Chevy 3600
1975 W-25 Hurst Olds
1991 Chevy Silverado
1970 GMC 1/2 ton Fleetside

I'm a GM man!
Re: Any realistic 2-barrel options for the 216/235/261? [Re: stoveboltgator] #1021872 Tue Apr 15 2014 05:06 PM
Joined: Nov 2002
Posts: 1,892
C
carbking Offline
Carburetion specialist
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.


Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify
If you truly believe "one size fits all" try walking a mile in your spouse's shoes!
[image]http://www.thecarburetorshop.com/Avatar.jpg[/image]
Re: Any realistic 2-barrel options for the 216/235/261? [Re: bztguy] #1021951 Tue Apr 15 2014 09:30 PM
Joined: Dec 2001
Posts: 1,247
W
Whitelightning Offline
Shop Shark
Originally Posted by bztguy
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.


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

Re: Any realistic 2-barrel options for the 216/235/261? [Re: stoveboltgator] #1021967 Tue Apr 15 2014 11:32 PM
Joined: Feb 2004
Posts: 19,163
H
Hotrod Lincoln Online
Boltergeist
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


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Any realistic 2-barrel options for the 216/235/261? [Re: bztguy] #1086166 Tue Feb 17 2015 06:20 AM
Joined: Oct 2008
Posts: 47
S
stoveboltgator Offline OP
Wrench Fetcher
Originally Posted by bztguy
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.


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

Re: Any realistic 2-barrel options for the 216/235/261? [Re: stoveboltgator] #1086989 Sat Feb 21 2015 07:20 AM
Joined: Nov 2010
Posts: 1,189
W
wetwilly5757 Offline
Shop Shark
Here's what a fellow "Bolter",(Jeff Bradshaw), installed on his '78 C-60/292...https://www.youtube.com/watch?v=obzULioHc64

Last edited by wetwilly5757; Sat Feb 21 2015 07:32 AM.

Just sold: 1955 2nd Series 6500 2-Ton Flatbed Truck
Mo' Tater
In the Stovebolt Gallery
More pics and videos on Photobucket

It takes an awful big dog to weigh a ton.
Re: Any realistic 2-barrel options for the 216/235/261? [Re: stoveboltgator] #1086991 Sat Feb 21 2015 07:29 AM
Joined: Mar 2004
Posts: 3,984
M
Mike B Offline
Shop Shark
Where's the link Willy?

Mike B smile

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