Inliners International Forums General Discussion Engines The right carb for a 292

Hey all,
I'm putting an offy 4-barrel intake and stovebolt headers on my'64 C-20 w/a stock 292. Power Manual suggests the Holley 600 w/vac. secondaries is the way to go. The archives here raise more questions than anwers. Clifford seems to think the Weber40 or 44 IDF is just the ticket. Not looking for an RPM machine,just maximum power within the stock config, maybe some modest head-work later. Hope I'm not beating a dead horse here. Thanks.,
Conan

The pros and cons of any suggested carb would help.

The 600 will definitely wake the motor up at higher rpms, but you may like the results better of a slightly smaller carb (450 cfm or so) with the stock cam. A stock engine will likely never or only rarely open up the secondaries on a 600.

If you were upgrading now to a bigger lift cam, I would recommend the 600, otherwise go with a 4-bbl with a smaller diameter pair of primary butterflys for better tip-in throttle response. Once the engine reaches about 1600 to 2000 rpm, you won't be able to tell the differece between those carbs. And the Offy is fine also with either carb.

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David
newbie #4153

I think a Quadrajet would work well here, they will flow 750cfm but act like a small carb until they need to open up. The mixture settings aren't too hard to adjust and the float bowl is in the center so you can mount it sideways with no trouble. You will be able to keep the same carb when you upgrade everything else. I used one on my Buick 225 motor in my Jeep and went through several intake and exhaust upgrades and it only needed minor adjustments.

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1950 Chevy pickup with '62 261, 4 speed.

I tried a quadrajet on my Offy manifold years ago, and the fuel distribution was terrible. It really sputtered under certain throttle conditions, and those conditions changed as the motor warmed up. Problem is, you have to use an adapter to bolt the carb onto the Offy adapter, and there is a big difference in how things are centered. The fuel has to turn too many corners before it gets into the intake runners. Don't get me wrong, I like them for manifolds that have the ports already matched, but the only 6-banger I remember set up like that was the OHC Poncho 250.

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David
newbie #4153

hello..

[This message has been edited by LeeLites (edited 08-07-2003).]

I've had excellent performance from an Edelbrock 600 on my 302, as has "Fast Eddie" Wilson on his 292. Both engines have had some head work and use RV-type cam grinds, he uses an Offy intake and mine is a Clifford, both with heat. The Edelbrock is a
very tunable carb and is real close right out of the box for street use. The tech line guys at Edelbrock actually speak inline six performance, too. One change in step-up springs and metering rods took 5 minutes and about $15 to get my carb running crisp and stumble-free. It's been trouble-free for years, gets decent gas mileage, and you can definitely feel those secondaries open up.

hi,
sorry I dont mean to steal your post (and i hope im not) but this is kinda going towards a question im having. I am in the process of tubocharging my 230 chevy. I have heard from many people that a double pumper mechanical secondary carb work well for blow thru turbo. the thing is the smallest one i can buy is 600 cfm. this seems to large for a 6. is there a smaller holley 4brl with these qualities? or do you guys have a different recomendation? thanks
drew

I had the 390 cfm Holley w/Offy 4BBl intake on a .030-over 292 [296 actual CuIn] for years. I've had Carter AFBs on V8s in other trucks and like the AFB for its robust simplicity. Now I hear FedMogul isn't making Carter carbs anymore. So I may have to go to an Edelbrock clone. For my next build I'm thinking of an AFB @ 500 cfm. They always used to say less is more in carbueration.

hello..

[This message has been edited by LeeLites (edited 08-07-2003).]

Sounds as if the Holley 600 will do the trick quite nicely if set up with properly. Any good starting points for springs/jetting?

64 Custom,

Bolt on the carb and test the exhaust with a CO analyzer. That's about the only way to really nail things down. You can work your way down on jet size until it gets to about 2% to 3% CO under wheels-in-the-air unloaded condition with the motor turning about 2000 rpm. You can start out with the stock 72 jets. I ended up with 70's in one of my early engine combinations using a 600 w/vac secondaries on a 292.

63 Deuce,

Any Holley carb that works well aspirated on a given engine will be great for a blow-through turbo. I've got several buddies here in the Phoenix area that have done that over the years on other make engines (Pintos, Vdubs and Corvairs come to mind). Doesn't matter if it's a vacuum or mechanical secondary unit. The signal to open the butterflys on the vac models is taken from inside the carb, and it's a balance between signals that determines how much and how fast they move. The turbo only makes more air go through, so nothing really changes. Kinda like putting a 600 on a big block. They work great unless the motor needs more air than the carb can supply, and then it just tops out and doesn't go any faster!

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David
newbie #4153

I dont mean to hijack the post but I got a 292 bored .060 over with a mild cam ,an advanced curve on the distributor and an offenhauser intake . Which carb should i use? I have a 450 holley econo willthat be enough? thanks

I've still got a lil Holly one barrel on mine and I'm not running at the momment so here's Car Craft's two cents from the June 2003 issue:

Q: How do I choose the right size carburetor for my engine?

A: Edelbrock responds: A simple formula can assist you with this. Multiply your cubic-inch displacement by the maximum RPM limit and then divide by 3,456 to represent the volumetric efficiency. The result is the amount of CFM the engine requires at the maximum RPM limit.

Example:
350ci x 6,000 rpm = 2,100,000
2,100,000 / 3,456 = 608 cfm
A 600-cfm carb would be sufficient.

Or in my case with my 250 and a 5500 rpm limit.

250ci x 5,500 rpm = 1,375,000
1,375,000 / 3,456 = 398 cfm
So I could get away with a 400-cfm carb...

Or yours:
292ci x 5,500 rpm = 1,606,000
1,606,000 / 3,456 = 465 cfm
So a 450-cfm carb might be all you need and still get good gas mileage...

I hope this helps!



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(O)2(O)5(O)0(O)S(O)I(O)X
PHAT250Six
Git in! Sit Down! Shut Up! Hang On!
And when in doubt... STICK YER FOOT IN IT!
250 L6 in a '69 Camaro


[This message has been edited by PHAT250Six (edited 07-12-2003).]

Jack, what jets, springs and metering rods are you useing in your 600. Also what kinda milage are you pulling.

67chev,

Jets are stock "out of the box". The step-up springs are the "Orange" 5" hg and the metering rods are #1427.

This is what Edelbrock recommended when I described my "off-idle" stumble. It fixed the problem and I haven't done any further tuning. Your results may differ. There is a lot you can change on any carb, it's a trial and error routine.

My best MPG was about 13-14 highway with 3 model B Rochesters on a McGurk log intake. City driving was horrible, about 9 MPG. Changing to the Edelbrock 4-barrel on a CLifford intake increased this to about 12 city, and 18 on the road. Still not great, but a big improvement.

According to the formula above a 500 CFM Edelbrock would probably work as well as the 600 (maybe better) for a 302 that rarely sees 5000 RPM, but the 600 is actually cheaper if you want the electric choke version. BTW, the Edelbrock "Performer" carbs are just Carter AFBs under another name.