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Spread Bore vs. Square Bore

Spread Bore or Square Bore Carb?

  • Spread Bore

    Votes: 2 100.0%
  • Square Bore

    Votes: 0 0.0%

  • Total voters
  • Poll closed .


Hey, All. OK, so far I have found out that I should be able to run either a Weiand 8004 or Edelbrock Performer intake with my stock Cowl induction setup. Last question on this is has anybody tried the Power Plus manifold from Ecklers?

Now, on to my carb question. I have rebuilt Q-Jets, Holly's and Carters in the past (6 to one, Half a dozen to another). However, I have never gotten info or seen a discussion on the pro's and con's of spread bore vs square bore. Most of the intakes I have listed will require an adaptor for a square bore, so that may take them out of the running. However, I want to get opinion on this topic. I know that the spread bore primaries are supposed to be better for around town driving. Today I have a tired Q-Jet on the Vette that smells like a gas station when its not running and a Edelbrock Performer on my '72 Cheyenne which makes a great around town carb. Opinions?
Anybody that has ever done any tuning with have an opinion on this one. I like the spread bore for street applications.
Hijinx, just so that you are aware, the Weiand intake can be found at a cheaper price than Eckler's. Eckler's sells many products that they source from other retailers, so shopping around is worth it. For example, they sell Vette Brakes & Products suspension pieces for more than Vette Brakes does, themselves. They also farm out some rebuild work to other companies, too. I'm not against Eckler's or anything, but you want your dollar to "be all that it can be." Or would that be "a dollar of one?" --Bullitt
A) Excellent article!
B) Bullitt is the Ecklers unit a Weiand? I didnt get that from their add. It sounded like they had had it cast from the original steel molds and either chromed or polished. Here is the info from their add;

The Power+Plus Manifold is a direct replacement for the stock manifold on 1957-73 Corvette non-EGR engines. Use the stock Quadra-Jet carburetor or a 500 to 650 cmf vacuum secondary carburetor. Kit includes adapter plate to permit use of popular square bore carburetors. Power+Plus manifolds are cast from steel molds, not from sand molds. Permanent molds provide a tighter grain casting thereby reducing the occurrence of porosity, which can make the polished finish. Additionally east Power+Plus manifold is 100% pressure tested to eliminate any installation problems. This manifold accepts late model choke, water-neck, A/C, alternator and HEI. Has provision to add oil filler tube.

Here is the link to their page with this advertised:
Sorry, but it seems that I was thinking of the Action+ series from Weiand. The Power Plus is made by another manufacturer whose name I cannot remember, right now. There is a company that sells them on Ebay, too. I think that you can do better than $210. For example, Edelbrock part #3701 can be had for $140. It's for spread bore and has EGR provisions. The extra install kit with gaskets, carb studs, sealer and intake bolts goes for $167 (part #3701K). The non-EGR intake is part #2101, manifold only or install/manifold part #2102K for $131. The Weiand spread bore is $96 without EGR (#8004) or $140 with EGR (8000). These prices are from the Jegs catalog, but Summit should have about the same prices, too. The advantage with Edelbrock is that you can also buy a camshaft and lifters (#2102 @ $110) later on, that is meant to compliment those particular intakes. --Bullitt

My 2 cents.

Spread Bore wins for the street hands down. The square bore wins at the drag strip if that all you do with the car. For road racing and auto Xing I would go with the Spread Bore due to its great throttle response.
Yo, you with no nickname ;), that sure is a beautiful ride ya got there. Every time I see it I drool. :upthumbs

_ken :w
Spreadbore vs Squarebore

I prefer the speadbore over the squarebore. My 81 vette use to have a Holley 670 Street Avenger. I tried different jets, powervalve etc. (i'll never buy another Holley again) that was very tempermental. I might of as well took over $300. cash...soaked it in gas and lit it. I went back over to the speedshop and spent over $400. for a 795 cfm Edelbrock Performer Q-Jet and never had a problem yet. Spreadbore carbs to me are more streetable.
Ps...any one who loves Holley carbs. wanna buy one cheap?
Let me know. It's got 50 miles on it. Now sitting on a shelf as a conversation piece.
OK, I'm going to rehash the Carb thread again, please bare with me. Here is my delima; I currently have:

1. Original Q-Jet on the car running, but dumping tons of fuel (I have rebuilt these plenty, but rarely seen much improvement once they start this trend)
2. Holley 650 CMF single line (4175) - needs rebuild
3. Holley 750 Double Pumper (4150) - needs rebuild
4. Edelbrock Performer 600 CMF - New

I know everyone has their preferances, and my simple out would be to move the Edelbrock over when I move the Edelbrock Performer intake, as they are on my '72 and I know they run. However, you guys know the Corvette setup better than I do. If I move the Edelbrock setup over I will pull all of the smog stuff off (which I want to do anyhow). But, would one of the other carb/intake combo's do me better for now?

Since I just bought this car, I have no idea what is in the bottom end. It pulls harder than a 190 HP stocker should, so I would say that there was a rebuild with some upgraded internal parts. However, the cam would have to be a very mild grind, as nothing of a heavy grind shows up at idle.

So, guys & gals, what's the verdict? Sorry, to rehash this so much, but it seems to be a hot topic of conversation anyhow.
Forgot, one last thing. I took a look at QuickFuel Technology's web site. Someone had posted their site in another Carb thread. $190 sounds pretty good for a street 750 CFM. I plan to call them and see if I could get a break if I sent them my 650 and 750. This way I have a pro-built carb for a good price. Since I dont plan to do this upgrade till Christmas I would have time. Just a thought.
Use the Tech link on the top of the page to find out a good estimate on your needed cfm, using the carb calculator. I don't know your maximum rpm, but I think you should probably be around 550-650cfm carburetors for a 350. Like camshafts, going bigger might hurt power down low with your horsepower somewhere in the 200 range. On the intake thing, that's kind of your call. Since you'll be doing the grunt work, it's really up to you on whether you swap parts now or later. It really depends on how you use your Vette. --Bullitt
Thanks Bullitt. I want fast and clean. The Vette is relatively fast, but it aint clean. The top of the motor looks like a battle zone. Too much crap that needs cleaning off. What I have found in the past is that clean (new/better stuff) normally equates to morebetter fast too. I think in the short term the Edelbrock setup will work fine. When I get the bottom end built (383 Stroker) then I will jump up to the 750 CMF Holley or Demon. Then I will have the internals to merit the change. Thanks fo the help.
Hijinx said:
OK, I'm going to rehash the Carb thread again, please bare with me. Here is my delima; I currently have:

1. Original Q-Jet on the car running, but dumping tons of fuel (I have rebuilt these plenty, but rarely seen much improvement once they start this trend)
2. Holley 650 CMF single line (4175) - needs rebuild
3. Holley 750 Double Pumper (4150) - needs rebuild
4. Edelbrock Performer 600 CMF - New

Your existing QuadraJet probably has leaking secondary well plugs--a common problem with aged or high-mileage QJs.

The best manifold choice, if you want to keep your stock hood, is the Edelbrock Performer.

Best carb choice is to have your existing Quadrajet overhauled/repaired as well as tuned for high-peformance. The next best choice is Edelbrock's Quadrajet clone.

A car like the 72 in question will drive best with a spread-bore type carb. If you want to run a square-bore Holley, stick to about 600-650 cfm. *Do not* use a "double-pumper" mechanical secondary Holley on a stock or near-stock small-block in a Corvette. Use a dual-feed, vacuum secondary Holley.

Avoid AFBs and AFB-clones, such as the original Edelbrock Performer carb. That design doesn't work well on Corvettes because of fuel slosh in the float bowls under braking and cornering.
I'll email you this too, but what are your thoughts on EGR vs Non-EGR on the Performer manifold. The Corvette place here said stick to the EGR to keep it from pinging? I decided to order a new intake as opposed to tearing down my '72 and I will rebuild the Q-jet. The difference in price is $149 for the EGR model and $102 for the non-EGR model. Thoughts?
the 4150 is the best by far. if u use it and have it rebuilt be sure to have new bushings for the shafts

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