I am still doing my carb homework and research,

I had been guilty in the past of dismissing the holley spreadbore qjet replacment after seeing many posts on the net calling them junk,

But i know how that goes so how about feedback from People who have messed with the holley, what are its pros and cons, a quick look around i see 650 and 800 cfm in double pumper or not,

So lets hear some hands on feedback,


Thanks
Cheers
B

 

I know way back in the 70's I installed one on my 1970 350 Camaro. Other than some minor adjustments the engine ran very well. A lot of folks who bought one from Summit seem to like them:https://www.summitracing.com/search/...e/Spread-bore/

 

i like the idea of small cruise around primaries then when i do get on it the larger secondaries,

If i could afford it i would go tri power but not in my budget,

I could be so dead wrong but i would hope when holley made the spreadbore their tech designers tried to make it better than a Rochester qjet, but who knows, and how would it compare to the holley 3310

Im only seeing the holley spreadbore in 650 and 800 which seems a bit small and a bit big for my mild 454, which i was gonna go 750 on

Ill see where this thread goes,

 

Had one on my 327 that thing was decent, had a summit brand spreadbore also which was good. There was one model that was all alum & blingy guys complained about

Edit; Summit has thermoquads, too wow.

 

I have one on my slightly built 1973 350. Right out of the box i had to play with the accelerator pump circuit be cause with my setup it was way to rich. Later I installed an afr meter and adjusted everything to get better performance/mpg. Like anything, if you want it to work right there is no carb that is going to be correct right out of the box.

 

Nice engine,

I know about out of box, i used to be into acvws so i had to learn solex and weber to tune and even mod the solex carbs,
If it didnt require an open plenum low end killing intake i would run dual side draft webers, one for cruise one for fun,
Im not scared to learn another carb, but really only feel like learning one more, lol

 

I ran a 650 double pumper spreadbore on a mildly modified 402 big block about thirty years ago. After I tuned it in, it ran great, started great, got decent gas mileage.

Mike

 

I have run the Holley 4175 650 CFM vacuum secondary Qjet replacement on my OEM L-82 4 speed since 1985 and still run the same carb on the rebuilt upgraded 355 L-82 with AFR 180 64 CC heads, roller cam, 10.2 compression etc today. Great carb! Easy to tune the primaries (currently running a 68 main jet up from the OEM 59), easy vacuum secondary spring kit for tuning the secondaries, easy to rebuild.....Ran better than the OEM Qjet on my 78 out of the box and continues to do so today. Only downside is the secondary metering plate, not jets.....Gas mileage is slightly less than the overly complicated Qjet...I mean slightly like 1 MPG......Holley are so popular because they are easy to tune, easy to rebuild, easy to adjust.

The problem with the overly complicated Qjet is that GM tried to avoid fuel injection, especially mechanical fuel injection, since they thought that the fuel could be precisely metered through a complicated carb mechanism like a quadrajet. They finally gave up after many years of trying to refine the Qjet to the level of mechanical fuel injection systems like the superb Bosch system used on may foreign cars. GM threw the towel in the early 80's with the crossfire being the final attempt at metering fuel through a carb throttle body...not a great idea or execution....There is a reason no one ever really was interested in cloning the Qjet after GM got out the Qjet business????!!!!!!!!!!

 

I ran a Holley 4165 6210-3 for years. Never could eliminate the fuel slosh problem. It would kill the engine under hard braking. Switched to a Lars rebuilt Q'jet - happy as a clam now.

 

Had several of the double pumper version on different cars over the years, never a problem tuning them and the response was great. Fuel mileage was comparable.
people need to face the fact tha except for the Edelbrock version those quadrajets are decades old and harder to fiND in good condition. There is no reason not to use the holley unless you want to change the intake.

 

I am presently running a 6212 with 6211 bowls on it. Its an 800 cfm model on my 454.

Truth be told, I really like it. Response is crisp, and performs very well.

It originally had a power valve front and rear... I have since removed the rear power valve and jetted up. Im still playing around with it, but I think its a neat carb.

 

I installed a brand new Holley O-8679. I also installed a new smog legal Weiand 8000 Intake Manifold at the same time. Ran wonderfully right out of the box....so well in fact-- that I passed easily with no issues. Ran just super for the 7 (or so) years that I had that combination. Never a problem--not that I drive it much, but it really was quite good.

 

Whew!

Lots of hsb ( holley spreadbore) part numbers,

So which is the one to have,

mechanical secondary double pumper or vac secondary?

Seems the nature of this carb 800 cfm isnt too big for a mild 454,

 

Double pumper for sure!

Mike

 

I much prefer the Holley over any other carb I've had for ease of tuning and rebuilding.

Years ago I read in a car magazine that you should get a vacuum secondary even for a manual trans car and the motor will open the secondaries when it needs them versus a double pumper which can be too much opening at low rpm causing a loss of mixture velocity and the car not running as well off the line. I went with a 750 vacumm secondary on my 70 Torino 351 four speed and it ran really nice and was a real screamer.

 

6211 is q-jet style inlet. That is the one I would look for.
6212 has cathedral bowls as does the 6213.

There are other part numbers that fall into these categories as well, and while I don't know all the differences, I'll bet that the throttle linkage of GM vs Ford or Chrysler is one of the differences, but not sure.

I think also the cathedral bowled variants are more of a "performance" version of the carb, but willing to bet there aren't any real differences.

Ive read that that some use different (clockwise vs counter clockwise) for idle mixture/enrichment.

Even though mine is supposed to be "performance" I think the counterclockwise method is what works on mine.

BTW, get the QuickFuel rebuild kit. Its like $35, vs the Holley "All encompassing every list number" rebuild kit is steep.

Edit: FWIW, my motor isn't the most radical but is a powerhouse. In its past life, produced 546 hp 560ft lbs. With my pancake intake Im sure it makes less. With that said, I had every intention of running this carb on the stock LS4.

 

Also, the 800 only came as a dp. It also hasn't been produced in many years, so eBay is your friend. The 650 is till produced as a dp or vs, but too small for a 454 as Im sure you know.

 

when I was rebuilding carbs and a customer had a spread bore I asked if they still had the original Q jet. I told them let me rebuild the Q jet and if you are not happy I will rebuild the spread bore free. never had to do that because the Q jet was better calibrated to the engine than the spread bore

 

I would expect that outcome since the OEM Qjet was calibrated and made for that particular engine. The Holley 4175 650 CFM vacuum secondary Qjet replacement (everything fits just like the OEM qjet-fuel line, linkage, etc) once adjusted for the engine which is really easy, in my case, the Holley 4175 ran Better than the Qjet with 25,000 miles on it from the factory. The vacuum secondary 4175 Holley once adjusted/calibrated for the secondary diaphragm spring is hard to beat since it meters fuel based on load..................

 

I have one of the 800 dp versions collecting dust that I will hopefully send to Lars one day.Too small for my BB Dodge and maybe too big for my small block (Dodge) truck.


Years ago I had one of the edelbrock rpm quadrajets (850cfm) on my 383 stroker in my 72 Nova.Everyone that rode in it swore it had a bid double dumper on it when the secondaries opened.I do regret selling that carb.

I do have a Holley 950 HP vacuum secondary sitting on my 496 Dodge that needs going through(haven't cranked it this year)that someone could talk me out of.I prefer my 750 HP mechanical secondary which will be going back on.