The Stovebolt Site Forums The Shop Area Engine Shop Edelbrock 500 CFM carb?

I spoke a repair shop today and explained that I would like them to change out my older stlye intake for the 2 BBL intale model and put on the new Holley carb. He went on to explain that I should have gotten the Edlebrock 2bbl model because the holley's tend to leak.

I contacted the carb shop and was told that edlebrock does not make a 2 bbl unit?

Any thoughts?

i have the edelbrock 500 4 barrel on my 292 inline six. i don't have mine tuned purfect yet i need to take the time to do it. i haven't drove it since i installed it on the engine. i researched the holley 390 verses the edelbrock 500 and both had pros and cons for my application. the holley 2 barrels are pricey for what you get. good luck on finding what you want. hr

What a crock! Any properly rebuilt Holley will work trouble free for many, many years. There is a world of sales people who get an idea, and no matter how wrong it is will stick with it till they die. If what he is saying is even remotely true, why did they come out as the factory carb on inboard boats for almost 30 years? I have one on my boat that dates back to 1975, and it is still working perfectly.
Holley have been making 1,2 and 4 barrel carbs with the same basic design since I started playing with cars in 1957, and I think that the design would have been changed if a problem, so potentially dangerous, was that serious.
I am not against the Rochester or the Carter ( Edelbrock ) designs at all, and am running Rochesters on a couple of my vehicles. I would be just as happy to have Carters ( Edelbrock ) carbs, if they were on the vehicle I wouldn't change them.
Bob

I agree BBC, I just wanted to get a consenus of thoughts. some of our 6066 GMC members have made the switch, I was just concerned something might be up.

I agree with BBC. Go for the Holley. They're not as expensive as one would think, and they're dirt simple to work on. I have 2 of them on my 235, both off of IHC 1 1/2 ton Black Diamond 6 cyliders. Actually, the base of one of them is from a GMC V6 school bus, the original had a crack in the mounting tab. Rebuilt them myself, real cheap, swapped the jets fom #57 to #54 (jets interchange w/4 bbl. They outperform the Carters that I had on it.

I built a mild 283 4 bbl some years back. After fiddling around with several different carbs on it (Rochester 4GC, Quadrajet, Holley Econimizer, and a small Edelbrock, I finally bit the bullet and bought a new Holley 390 for it. Great carb for a smallish engine like that 283.

"I contacted the carb shop and was told that edlebrock does not make a 2 bbl unit?

Any thoughts?"

I don't think it was our shop who told you this, but I also am unaware if edelbrock ever sold a two-barrel under their name.

As to the 500 CFM Holley two-barrel: several years ago, we thought these would be an excellent inexpensive replacement for the 2 barrel WWC Stromberg on the larger GMC trucks. We had some special adapters machined (the WWC has a trapezoidal flange, not rectangular), and acquired a bunch of the Holleys. Memory says we sold about 15 of them, and every single one FAILED IN SERVICE within a three month period. Several with major leaks, the others with broken choke mechanisms (this was about the time Holley went to the plastic choke brackets). We had to eat the cost of every one, so guess I am not too fond of these units. These were all NEW, not rebuilt units.

Now we suggest repairing the original Strombergs.

Holley did make some EXCELLENT 2 barrel carbs for trucks (852 series and 885 series); but these are governored and quite expensive.

Jon.

Joe - the first 2 or 3 failures guys called with broken chokes. We contacted Holley, and at that time, they had no metal choke brackets, and were replacing with plastic. Our customers didn't want to hear that, so we pulled some metal ones off old cores; then the leaks started, and we gave up. These were all sold for working trucks. When the truck needs to be working and is down with a defective NEW carburetor, one has a VERY unhappy customer!

Others may have different experiences. This was ours.

Oh, and I REALLY LIKE YOUR SIGNATURE! Wish everyone would pay heed to it!

Jon.

A 235 engine at 3,000 RPM only flows 204 CFM, and that's if it is getting 100% volumetric efficiency. At 90%, which is a much more realistic figure, it's flowing 184 CFM. What is it supposed to do with more than twice that CFM capacity, when a 500CFM carburetor is installed?

A small block 350 at 5,000 RPM flows 506 CFM at 100% efficiency. At 90%, it's only 456, so the 500 CFM 2-barrel is plenty for normal street use on a 350!

All that putting a too-big carburetor (or two of them) on a stovebolt accomplishes is that it creates a terribly throttle-sensitive situation that causes stumbles, flat spots, and backfires. Driving an over-carbureted engine is a major pain in the butt, one I can definitely do without!
Jerry

I used to just love taking on those people who would boast about how large the carb was on their dream machine, because they were always easy meat. It is just like Hotrod Lincoln says, you have to do the math. There are several excellent sources that publish graphs which will allow a person to install the carb that will meet their driving needs. One source is Basic Carburetion and Fuel Systems By Hot Rod Technical Library. Another of many sources, is Rochester Carburetors, by Doug Roe and Bill Fisher, publisher HP Books.
There are a lot of people who can give you excellent information on carbuetion, the trick is to do some homework first so you can tell if the person is watering down your boots at the same time he is talking to you.
Bob

Fell down that too large a carb trap years ago.

Being young and dumb, I replaced a very leaky 4GC with a Holley 600 double pumper. I'd mash it flat and eventually the engine would catch up to the carb.

It didn't take long for me to get a fresh rebuilt 4GC

On the topic of CFM, just how much deos the old Rotchester B flow anyway? And maybe the Carter YF and Holley 1904?
Also, I don't know if y'all checked, but V-6 Modelmans truck isn't a 235, it's a 305 V6 GMC, one BIG V6! I know the early ones had either a Stomberg or Holley single, later ones had the 2 bbl. I think that's what he's really looking for, a good replacement for the OE carb.

"There are a lot of people who can give you excellent information on carbuetion, the trick is to do some homework first so you can tell if the person is watering down your boots at the same time he is talking to you.
Bob"

Really good advice! Doing the homework, however, can also be difficult, as there is a lot of "less than desirable" information both posted on the internet, and in more than one book.

Bob - I think you would appreciate a true story from many years ago, when I was attending a local car club meeting and we had some visitors. One local youngster's daddy had just bought him a 396 Chevelle. We asked him about the engine, and I will never forget his answer - "yeah, its the big engine... got 3 4-barrels and fuel injection!!!" When the club had finished laughing, and the kid had finished blushing, we explained to him he didn't have to impress us, he really did have a nice car. He turned out to be a really decent kid after that.

The Roe book is very good. If one has sufficient math background, another REALLY good book is "Weber Carburetter Theory" by John Passini. You really need a background in calculus and differential equations for this last one. A new book on the market which is REALLY keyed to the lay person is "Modifying Rochester Q-Jets" by Cliff Ruggles. Explanation in this book is outstanding.

But understanding circumstances is also important. I had a factory equiped 121 CID 4 cylinder with two 500 CFM carburetors, and it ran STRONG.

Longbox - the subject of CFM gets rather tricky. I think the Rochester B is covered in the Roe book. I know Carter did not publish CFM figures on the myriad of YF carbs, and I don't recall seeing information on the Holley 1904's. Zenith published CFM charts on 1 and 2 barrel carburetors as early as the mid 1930's (possibly earlier); but CFM changes due to the desires of the publisher

The Zenith charts may be used with a reasonable degree of accuracy for any of the 1 barrel or 2 barrel carburetors. The main issue would be main venturi size, with a secondary issue being throttle bore.

Jon.

I looked through the Roe book for the B carb, and it has every piece of information you would need except the CFM. The book does list numerous tips to improve the B, and it also states that it was a very good carb except for 1949, the first production year, when there was a problem with the air horn flange warping.
I liked the story, Jon, I also have the Weber book and agree that it is the best for the theory.
The carbs that I would think would be the most fun to put on the Chevy six, would be three variable venturi Strombergs or SUs. That would make people look twice and would probably make a nice driving machine.
Bob

I wasn't sure if the info was available easily or not, just more out of curiosity.
I liked that story about the Chevelle. My dad had one with the 360 horse 396. His had a 3 bbl Holley on it.

The engine that is presently in my Cameo is the 1967 350 HP 396 that I installed in 1970, Now I wish I had kept the rest of the car, they are getting a little pricey. I have kept it bone stock and am replacing it with a 454 that I am building up. I will keep the 396 on a stand in my shop. It is a great engine but the compression ratio is too high for this new gas.
Bob