[Rick_L]

The ONLY spreadbore (QJ) manifolds that I'm aware of came on GM products from late 60's thru early 80's?

Edelbrock has had manifolds that will wear both a spread bore carb and a square bore carb for many years, still do.

 

[55 Tony]

I ran a few different Q-jets. I loved them but just couldn't get the dammed things from leaking when sitting. Tried all the tricks. Did a lot of reading online and in books and got them tuned right, but the darned leaking just got old. I have a small pile of them and a lot of extra rods I'll never use.
Got an old Holley 800 spreadbore mechanical secondaries, and although it ran well and was really great for the kick in your pants when opening it up, the primary's are a good deal larger than a Q-Jet so the fuel mileage savings wasn't much if any. Come to think of it, the fuel mileage wasn't great in the Q-jets either. Maybe I didn't tune them as well as I thought? The only new carb I've ever used, a Holley, I sent back due to problems from the factory drilling holes crooked for the secondary's. I keep the old Holley 6811 on the shelf. Maybe put it on again someday? The q-jets I'd like to get rid of.

 

[55 Tony]

Thing is, most hot rodders have their opinion even if not based on a big stack of facts, and that has resulted in low demand for spreadbore carbs.

Yup, unfounded opinions.

Holley still makes the 650 spreadbores. Vacuum and mechanical secondaries.

Holley 0-9895 650 CFM Spreadbore Carburetor

Holley Replacement Carburetors are Engineered to Improve Performance and Keep You Emission Legal. The 0-9895 is a Model 4175™ Spread Bore designed to fit several applications. See application chart below in tech resources for specific details.

www.holley.com

 

[55 Tony]

Edelbrock has had manifolds that will wear both a spread bore carb and a square bore carb for many years, still do.

Yes. Even for a BBC, I have one on my car now.

 

[Robert Haas]

Well how about a one barrel

I present the PREDATOR

I was at one time (circa1984) the biggest advocate to using these, but as they began to age I developed a hate for them that still, to this day cause me migraine headaches and fits of rage.

 

[dream66]

An AMC enthusiast near me has several of those. He swears by them and runs 3 of them on Javelins and AMX's.

 

[1971BB427]

I ran a Holley spreadbore carb on my 427 BBC for many decades without any glitches ever, and it was still on the car after 40+ yrs. when I sold it about 6-7 yrs. ago. I love the spreadbore design and have used both Holley and original Quadrajet versions and liked the throttle response.
Holley still sells the 0-6210 spread bore carbs, so they are not extinct at Holley. They're all 650's, so not any selection of various sizes.

Holley 0-6210 650 CFM Quadrajet™ Style Spreadbore Carburetor

Holley Replacement Carburetors are engineering to improve performance and keep you emission legal. The 0-6210 is a Model 4165™ Spread Bore designed to fit several applications. See application chart below in tech resources for specific details.

www.holley.com

 

[mr55/56]

Most manifolds are for square bore carbs. The ONLY spreadbore (QJ) manifolds that I'm aware of came on GM products from late 60's thru early 80's?

Ford used them on 429CJs and I have some pos Mopar squad car 318s from the 80s with them.

 

[tekctrl]

So the carb market consists almost entirely of square bore carbs because someone in Marketing/Sales said "we can sell more square bores than spread bores, so we'll stop making spread bores"?? Not due to any particular drawback or benefit, just profitability?? Am I hearing correctly that there actually is no significant benefit of one over the other except that manufacturers aren't making one type any more? That smacks of Microsoft's tactics; We know what you need better than you do, so you'll take it and like it!

 

[mr55/56]

40 years ago I knew a guy who had a 67 Camaro SS350 super stock car that stood on the back bumper and ran 6.8/6.9 in the 1/8 with a 4 speed and a Q-jet.

 

[nad427]

So the carb market consists almost entirely of square bore carbs because someone in Marketing/Sales said "we can sell more square bores than spread bores, so we'll stop making spread bores"?? Not due to any particular drawback or benefit, just profitability?? Am I hearing correctly that there actually is no significant benefit of one over the other except that manufacturers aren't making one type any more? That smacks of Microsoft's tactics; We know what you need better than you do, so you'll take it and like it!

The market demand for the spread bore just isn’t as strong (in fact bunches less) than the demand for square bores. I believe there’s your answer.

If someone does show believable fuel savings they just might come back, but the savings probably won’t be much if any. It all depends on drivers habits regardless of carb anyway.