The Stovebolt Site Forums The Shop Area The HiPo Shop Carburetor Selection for modified 292

Just to let you all know I have dug through a few extensive posts regarding this subject on this forum but still come away confused. Perhaps that is more on me than anything else. So I have a 292 which is bored over .040 has 1.94 and 1.6 ports, lump ports and a mild cam for a compression ratio of about 9.5. In the previous post a lot of people tend to recommend a Holley 390 or a Qjet and the person that built the engine is saying 600-625 4bbl Holley to get the performance out of it. Now I don't know diddly about carbs so I myself want something that will get the performance out of it but isn't too finicky and is somewhat forgiving or easy in adjustment, if such a thing exist. Im not in the financial position nor do I have the expertise to go EFI at this time. Almost forgot the intake is an Aussiespeed set up for a 4bbl.

Looking forward to reading everyones thoughts/advice on this.

Thank you,
Eric

Not that there isn't a lot of good advice of the forum but Holley has a Carb Selection guide. You need to put your numbers in and some other specifics but it will help you make your decision. I built a fairly "Hot" 292 with most of what you have, I did use a lumpy Howards Cam and Clifford manifold, on that I used a 625 CFM Edelbrock .

https://www.holley.com/products/fuel_systems/carburetors/

Something you may consider is a Weber 38/38. You would need an adapter to run it on the Aussie. Or a Holley 750 with Tom Lowe's three barrel conversion, so it runs on one barrel, but when you get on it, the vacuum secondaries kick in, providing the power. You wouldn't need an adapter to run that on the Aussie.

Craig,
Thanks for the link, I have been playing with it for awhile just wish that had more carburetors with manual chokes. Is there any reason you went with Edelbrock over Holley? At this stage I have absolutely
no preference just as long as it works well and I don't need to buy anything extra to make it work.

Eric

I have always liked the dual Clifford intake designed for the two webers but that was just way to pricey. Kinda wanting to stick with something that doesn't require an adapter for the moment.

I have talked to Tom Lowe about the 3 barrel and definitely considering it. I believe he states it will be a low 600cfm after the modification and as you stated is intended to improve gas mileage for typical driving. I have asked a few people on this forum and other forums using it how they are liking it but only one has responded back. He said it is ok but could tell the difference when getting on it not all barrels were there....makes sense. I guess compromise for mileage which is probably a good thing right now. If I heard from a few more people I might be sold.

Thanks,
Eric

I was meaning a single 38/38. They are designed for modified engines.

I haven't heard from anyone running the 3-barrel kit for the Holley. But that setup does sound like it would work. Since these engines like 1 barrels, but having a hot or warm L6, it could benefit from the secondaries being vacuum operated, and you can get the 750 Holley with manual choke.

I’ll take another look at the Weber’s since I was thinking it was the 1500 dollar setup and not an individual carb.

You are right I can get the manual throttle and they do sell refurb. Carbs as well directly from Holley so that makes it more enticing and less of a cost risk if I don’t like it.

Thanks

Dongray, I had no real influence other than price in using an Edelbrock, I built the 292 for a friend of mine. The carb is rated at 625 CFM and required an adapter to mount to the Clifford manifold, I would have went with a Holley if it had been mine. The ultimate goal for the 292 is a blower and EFI.

The rating is based on an engine that calculates to 1.5" Hg @ WOT.
If your engine is too small to do that, the CFM will be less.
292" X 95% VE X 5,500 RPM = 441 CFM

For simplicity, I would look at a Q-JET or the Edelbrock, both will be easier to tune then a Holley. Holley was intended for racing, still is in my opinion, the Q-jet is a proven carburetor that does well on all sizes of engines, and the Edelbrock is a copy of one of the better Carter made carburetors. Any adaptor will hinder the performance, and as for fuel mileage, that ship has sailed. I would expect 7-9 mpg, the Q-jet will likely give the best mileage due to the small primaries. Ideally, fuel injection would be the best choice, a self tuning one.

Joe

The Holley 4150/50 was introduced as OEM in 1957 Ford, Lincoln, and Mercury V8.

For my 292 I started with a 4-71 and three 2bbl but then I went to two 650DP on my 6-71, but I'm not normal.

I have no personal experience with the 292.

My shop "truck" for years was a extended wheelbase 1979 van with a 300 CID six.

Original carb was a single barrel Holley.

Replaced the Holley with an Offenhauser 4-barrel intake, and a Carter AFB 9400s (400 CFM) carburetor.

If I had been blessed with only the 7-9 MPG suggested in this thread, I would have driven it into the lake, and left it!

And yes, I did modify the AFB for manual choke, and maybe did a wee bit of recalibration on the carburetor.

I won't post the fuel mileage, but the van (loaded) made it from Eldon, Missouri to the Chickasha, OK swap meet without a fill-up, and driving at the speed limit (65/70 in Missouri, 75 in Oklahoma). The fuel tank was original. If anyone is interested, you can look up the miles, and the fuel tank capacity, and do your own math.

Not familiar with the Aussie intake; as I stated, I used an aftermarket Offenhauser.

Jon.

A beast of an engine!

Jon, Does that Carter have the same bolt pattern as the Holley 4160?

The Carter is set up for the "AFB" flange configuration, with 2 additional holes in the "Holley" configuration. The flange is plenty large to mill 2 additional holes so it will fit the "Holley" configuration. Have seen many of them that have been modified with the extra 2 holes (total of 8).

The issue with the 9400 is that Carter made the last one about 1980; they are very much in demand, and fairly pricey.

Jon.

I'm building it for 1300 but I'll never run it over 1000hp. As Mike Kirby told me "The magic is in the head". It's one head for a Ryan Falconer V-12 engine. It flows 340I and 220E. The rest is just trying to keep the billet crankshaft in the building. Thank you for your time.

I think I have one of these 9400's. I took it off my truck because it lost adjustment nearly weekly, drove me nuts. I was a quick starter, though, even after sitting a few days or even when the weather was cold the engine would fire up immediately with a tap of the key.

Edit: The Carter was on a 305-307-350, I don't think it's a 350 because the engine is a dog, but it did lose adjustment quickly, and I don't know why unless they are prone to losing adjustment like that.

Just thought of something, you mention it having two sets of holes, that means it would most likely bolt right up to the Aussie Intake, as it too has two sets of holes that are Holley 4160 pattern.

Aussie Intake

Is this also on Inliner's forum, I have seen this head before somewhere, may be on here, may be Inliner's, I just know I have seen it before. 1,000 HP is insane!

Curiosity got the better of me. 22 gallons is what I found for a '79 Econoline. And roughly 432 miles for your trip, Jon, which came up to 19.6 mpg's, but that was if you used the entire tank, and if the map gave me the correct beginning and ending points. North of 15 mpg in a loaded van is still excellent for a rolling brick. 24 mpg if you had two gallons left.

Okay, I will stop posting now, I got carried away, my apologies for the parts that were off topic.

Shane - about the time we passed Oklahoma City, and I didn't stop; the friend traveling with me to the swap meet starting unobtrusively glancing at the fuel gauge. After a few miles, he started fidgeting. I pulled over, and got a roll of electricians tape from my toolbox, and placed a piece over the fuel gauge. He looked at me, grinned, and went back to sleep. True story.

Looking at the intake, I think you would have to mill the two extra holes in the Carter for it to fit. Not really a problem.

Jon.

Yes and a couple of other forums.

That is far from normal, LOL. Amazing looking it belongs under a glass case in a museum! how long have you been working on it? I can't imagine the price of all those shine goodies but much better spent than waisted on actual jewelry thats for sure. So I was watching a video of a 250 using a 500 edelbrock and they made the statement that it was limiting the performance. Between that and the Holley calculator were you put in your engines details it was recommending carbs from 470-650cfm so I had assumed anywhere in that area would be ok. I did talk to T. Lowe about blocking off a barrel on the 750cfm with one of his kits and he stated it would get me to the low 500 cams and supposedly better miles at typical driving speeds due to bette air flow in the one barrel. Ive been trying to ping people that used his kit for feed back but had only a couple of responses and they seem to like it. Any thoughts on carb size or the 3 barrel system?

Thanks

To quote Jerry, it would seem to be a solution to a problem that does not exist???

It is my understanding that this is a modified 750 Holley, blocking off one of the primary throttle bores.

So, the 750 Holley should have approximately 375 primary, and 375 secondary. Blocking one primary should give about 187 on the primary side.

The Rochester quadrajet comes in 750, 800, and 850 sizes.

The 750 is 150 on the primary side, the 800 is 200 on the primary side, and the ridiculously expensive 850 is 250 on the primary side.

Does anyone really think that any Holley is going to even be in the same ballpark as a quadrajet for fuel economy?

But no, I have not used one.

And while in the various "other" existing options, Carter made an 800 that is 200 on the primary side.

Both the quadrajet and the Carter are "on-demand" secondary carbs, so the secondary will provide only as much as the engine requests, but 600 is available from the secondary.

Carb size depends on LOTS of variables, but the smaller primary (like the modified Holley or the Rochesters are Carters) is going to provide better primary venturi air velocity on the street. The 400 was plenty for my 300 CID Econoline.

Jon.

You are leaving out a lot of variables. You only mention a mild cam and lump port head, what are the cam specs, was the head reworked any further( blended are shaved). What RPM range are wanting to operate at?

All of these thing work need to be taken into account, the engine should be built with your end result in mind. A good daily driver would not require that much of a carb, after all how often are you going to get into the secondary?
?

The Weber 38/38 is not a good choice for mileage, both barrels open simultaneously (there is no "primary").

I mentioned the 38/38 because Weber recommends the 38/38 for a modified engine. I wonder if the 32/36 would be enough for a modified 292? The lump kit and bigger valves do increase the air flow considerably.

The larger valves may increase volumetric efficiency (VE in Panic's post 9). He estimated 95 percent VE. Really difficult to get above 90 percent in a street normally aspirated stovebolt engine.

Note at 95 % the engine could use 441 CFM at 5500 RPM.

So at 90 % - 418

And 100 % - 464

Where is your absolute redline, and where is your practical (street) redline?

Jon

Jon, remember the hotrodders' mantra- - - - -"My mind is made up- - - -don't confuse me with facts!" (or physics)
Jerry

As the RPM goes up, the VE goes down, 6,000 may be only 85%.
I was generous!

Porting the head only increases air flow if the rpm calls for more air flow. If the heads have really large openings to gain air flow, at low rpm the engine becomes real sluggish and fuel hungry due to the low air velocity. A well ported head will keep the air velocity high at low lift and flow enough air at high lift to allow the engine to run reasonably well. I have killed enough heads porting on them trying to chase air flow on my air flow bench.
I made a crude gauge for my truck that hooked to the throttle pedal, it measured how much throttle I was using just to drive around town and out on the highway. 90% of all my driving was using 25% or less of the total throttle opening. So when you go figuring absolute cfm's needed, don't figure it for top rpm, you won't ever need it!

Eric,

Whenever you get your setup running, if you don't mind, I would like to hear back what your results are. My engine's internals will be setup very similar, if not identical to yours, but is going in to get rebuilt in the next month. Which cam did you go with? I got the one developed by Tom Langdon for improved low end and mid range. Which pistons? Ross?


I am now going to share some information from conversations with my Pop, and information he has reported back (on the same subject matter) after speaking with the machinist we use:

My Pop, a crotchety guy like Jerry, and similarly off the cuff and in age, says these engines get better mileage than the 6-8 mpg's reported on here and other forums. I reiterated to Pop that the consensus is these 292's get less than stellar mileage. After he said a bunch of cuss words I can't write on here, and the guy building the engine also agrees with Pop; they said this engine should see an easy 15 mpg with the right carburetor and tuning. Pop mentioned a 2 barrel carb, not a specific brand, just a 2 barrel. Both he and the machinist stand by their personal experiences in the auto repair trade that the 292 is not as inefficient as some say. Perhaps in a heavy dump truck with a full load in the back, but a regular truck cruising down the highway, they say no.

A setup similar to what Jon had/has on his 79 econoline seems to be a great option.

These old boys on here know a ton of great information, and it's great when they share it from their many experiences, and wealth of knowledge. I have learned a lot from their sharing on the various threads. That said, I also sometimes run by Pop, what I read on here to get his feedback, as he is no slouch himself. Pop would not be accepted on here because he is Ford guy, but has worked on everything in his many years.

I came up with roughly 400 in my calculations, when I was running my own numbers. I think I used 5000 as redline, but it will never get revved up that high.

There is another factor which affects any engine: how many cylinders draw from the same carburetor at the same time?
For 8 or more, the usual calculation (D × RPM × VE ÷ 3,456 for 4 bbl. carburetors) is accurate enough.
For an L6 with a single carburetor on a common (plenum) manifold it's different.
Without 500 words of explanation (as it appears in my book http://victorylibrary.com/235BK.htm), just take my word for it.
Add 10% to the total.

For fewer cylinder (at the same displacement) the correction is higher.

Panic, thanks for sharing that link. I have always wanted to read the contents of your book. I will be bookmarking it so I can refer back to it.

Panic - at my age, I have no intentions of building another engine (well, maybe a plastic model kit ); however:

I have read enough in your posts to know. If the carburetor and intake manifold sections are finished, please either message or email me with a price for the book as is, and how to acquire it. I am certain these sections alone will be worth the price of the book.

I hope it is wildly successful for you; your posts on intake manifold design have filled in some blanks for me.

Jon.

Jon and Panic, thanks for all the information and sorry for not being able to respond sooner but I don't get much time lately. I do have to say it is a lot digest considering I have never worked on a carb and only limited amount on a couple engine rebuilds with my dad many years ago.
I think a major point that was made and finally sunk in on me was the amount of time just driving normally 95% vs amount of time wanting it to perform. That being said I know this engine won't sip gas and am willing to suffer some for fun every now and then. Although filling up at the pump today for my daily took a chunk out of my wallet!
I think what got me considering larger carbs were first the Holley site where you punch in the size of your engine size and if it is stock, mildly modified or highly modified and it would consisently spit out 470- 650? when I put in mildly modified. Then there were videos of folk doing dyno runs on 250s and 292 saying 500 was insufficient for the 250 (first video) and I think they used a 750 on a 292 that was somewhat modified being built for turbo (second video). I really wish Richard Holdener would have finished his series on a 292. He did compare a two barrel vs a very large 4 barrel at the time and I think the 4 barrel was almost equivalent with the two barrel but the engine and head were stock if I recall correctly. Unfortunately the video series was never completed. I would have been great see how it performed with multiple carbs and intake manifolds.





Richard Holdener 292 Series



I am not going to argue the math or physics and the excellent explanations provided for a smaller carburetor in this forum but you can see where this confusion stems from when watching these builds. I mean based on everyones calculations on this page anything over 450-500 is a waist. I understand that there are a lot of variables but other than the video of the 250 the other two builds had less done my build.

So is there anyone that makes a decent Q jet carb that you might recommend in the size Im looking for? I would prefer one that is easier for the newbie to work with if that is at all possible.

Eric

Quadrajet is a General Motors carburetor that was used as original equipment on all their V8's, a few inline sixes, and a few V6 engines from the late 1960's to the mid 1980's when they went to computer controlled carbs. Nobody that I'm aware of makes an aftermarket QJ- - - -they're just too expensive to manufacture for anyone to make a profitable clone. Holley tried, with a carb called the "spread-bore" but that didn't last long, IIRC.

Try to find a QJ calibrated for any 5-liter (300-something cubic inch) GM engine, Cnevy, Olds, Cadillac, etc. It will give you good gas mileage with the small bore primary barrels, and the air valve controlled secondary barrels will flow all the air the engine will ever need to run as fast as you dare to hold the throttle wide open. It will outperform anything the hotrodders can bolt on, at a fraction of the cost.

If you believe in the saying "There's no substitute for cubic dollars" go for some of the fancy stuff and spend a lot of unnecessary money.
Jerry