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I'm looking at carburetors and the owner of the speed shop I'm working with suggested going with Quick Fuel over Holley, even though Holley bought out Quick Fuel , he said the Quick Fuel is better quality.
He told me that Quick Fuel has billet metering blocks with four adjustment screws, billet base plates, stainless butterflies, better machining, and higher quality internal parts.
What are your thoughts?
He is also suggesting that 750 cfm is sufficient for my 496 BB that will be used mainly for street use and some spirited driving.
He did state that I could make more power above 5500 rpm with an 850 cfm, but didn't think I would see that high rpm enough to justify the additional cfm.
When ever you talk about carbs the first questions should be is what type of transmission, does it have a roller cam, and what type of intake manifold
imo the most important things about a 4 barrel carb double pumper is simplicity, ease of adjustment and booster type. You need bowl sight level glasses. 4 corner adjustable. Chockless. Annular boosters are the best and they drop cfm total by 30 on a typical 850.
annular boosters atomization is superior at low signal for instant throttle response
I personally haven't had a carb with a choke in 30 years. They are just a crutch for people that don't understand carbs and another failure point. A dual plane intake can have a higher cfm carb than a single plane I have had the same race Demon on all my hot rodded vette motors. From 355 ci up to today. 830 cfm on a bench flow
before you take any one's advice from any car related products. The first question you should ask them is what kind of motor and car do they drive. It is very stupid to ask some technical support person who drives a 4 cylinder rice racer making $12 bucks an hour advice. No real life experience
I've installed and maintained several high quality carbs and this is nice
what is the name and model of this wonderful intelligent carb. I have never seen or heard of it?
You misunderstand. Meaning, if ballpark tuning is good enough, or if adjustment is not fiddled with after the initial tuning, all that extra adjustment (4 cormer adjust, screw in air bleeds) are features paid for but not being used.
Last edited by Dynra Rockets; 03-08-2018 at 12:08 PM.
FWIW I'm using a Ultra Holley Street Avenger. The one with billet metering plates, 4 corner idle, dual sight glasses, electric choke, vacuum secondaries, etc. Although mine is a smaller carb than what you need (670) my point is that these are fantastic bolt on carburetors. I have used Holleys all of my life. These carbs are the best bang for the buck imo. I'd go at least as big as an 850 cfm
First I need to apologize as I typed in Holley or Quick Silver as the thread name instead of Quick Fuel and do not know how to correct it.
The owner of the shop I am working with has been building race and hot rod motors for almost 50 years, is highly respected and dyno tunes every motor they assemble.
He and I were talking and I asked if Holley is still high quality or if there is something better and he recommended Quick Fuel.
I'll be putting together the motor with 496 cu in, 10.3 to 1 final cr, Edelbrock performer RPM oval port heads, Edelbrock RPM air gap dual plane intake, Crane hyd roller 230/236 @ 50 duration .598/.610 lift, MSD, and headers.
I'll be swapping to a TKO-600 close ratio 5 speed manual.
The owner said for a street car a 750 cfm would be sufficient, give better bottom end mid range performance, however 850 cfm would make more power at the top end.
He also suggested: bowl sight level glasses, 4 corner adjustable, choke-less and annular boosters, which come in the Quick Fuel carbs.
Your horsepower goal is also important in your carb choice. I'm just guessing, but with your heads, cam and intake, I would say 550 HP range, give or take. On a single plane intake a 750 would probably do just fine, but on your dual plane air gap, a 750 is going to be a little small, especially if you go with annular discharge boosters. With your dual plane intake I really don't believe you could over carb this engine with any 4500 style carb.
Annular boosters help single plane intakes perform a little better on the street, but are not really needed with a dual plane intake on a mild build such as yours.
Myself I would get the Street Q 850 or 950 Quick Fuel carb with downleg boosters, if you go with a Quick Fuel carb. In Holley I would go with a Street Aluminum HP 950 which has the same venturi and throttle bore size as the original 850, or I would choose an Ultra XP 850 or 950. All of these with downleg boosters.
As to what mike said about dual plane. Dual planes feed off one side of the carb is why you can use a bigger cfm VS a single plane. Down leg boosters don't impede CFM like annular boosters that would knock down a 850 to ~820 cfm. 496 ci will create a massive carb signal and it is hard to over carb one.
AED carbs are also great........
As to cam choice? my first roller 383 used a 232/238 and was ping prone on our 91 octane. I don't want to get into a static and dynamic C/R discussion because it also has a lot of unknowns like the amount of port velocity ram effect and volumetric efficiency which is not addressed in most online calculators. But I felt like it was lacking lots of jam with a 112 LC. The wider LC makes for a very smooth idle and higher mpg with higher duration. My first roller cam with my 427 sbc was a 242/248 extreme profile and you have 60 more cubes to tame even that down. I ended up caming even that motor up and it could be kinda of a daily driver.
The biggest problem confronting massive low end TQ in a C-3 is wheel hop. 5 speeds can become a pounding wheel hop if going to WOT at low rpm. Hence why I went to bigger cam on my first 427 amongst other things and fixes
What I was really trying to say is that big CI is much more tolerant to duration without effecting drivability and octane requirements. It beats someone as dumb as me and having to go through the cam upgrades later.
For the Diff cross member. take it out and eliminate the old crusty rubber bushings. Grind the top ends flat and install aluminum disks "washers" and grade 8 bolts. There are discussions about raising the diff and welding it all up to lower the car. But the real idea is to solid mount the rear end. I have a machined aluminum disk in place of the front diff snubber to get the ~2 degree down angle of the drive shaft input from my TKO600. So it is basically solid. You can put lot's of power like me through a stockish diameter drive shaft even with big slicks if you use 1320 12 point U-joints. The rear end gear ratio is a TQ multiplier. Posi unit, yokes, half shafts, outer axles take the major beating determined by tire size and compound. Every time I broke something over the years I bought the better stuff. Safety is the major concern The whole idea of SFI rated stuff and hoops is because of failures over the years on many peoples stuff. So buy the best first and not worry later
FWIW I run a Quick Fuel 1050 Annular booster on my 496. 4 corner idle, no choke etc.
4 Spd Muncie, 3.08 gears and an LS-6 dual plane pancake intake to retain my stock BB hood.
Reworked Edelbrock performer rectangle heads, 10.2:1 compression with a healthy roller cam. .242 .248 duration @.050. .540 and .560 lift on 110 LSA (probably a bit much for what I am doing with this car).
The carb is an excellent addition to my 72. The throttle response is amazing with power all the way up through the rpm. Surprisingly "decent" mileage if I can keep my foot out of it.
What you may look at are the parts costs for the internals if you want to tweak anything. QF part numbers are A LOT less than Holley OEM part numbers (Look at Power valves). Granted they are pretty small in comparison if you look at the big picture but it does make a difference.
The cool thing about this carb is that you can tweak almost anything to suit your environment, driving style, car etc. if you wanted to really fine fine tune stuff.
Now, I'm old school and wasn't aware of this newer carb tech. When I was doing this there were two idle mixture screws, 4 jets, a couple PVs and if you wanted to get into IFR you brought a drill index out. Then there are idle air bleeds, high speed bleeds etc. I guess my point is that if you went with an annular booster QF of decent size CFM you won't have any issues. Problem being is that the annular vs. down leg booster is a considerable dollar amount.
Pictured is my down leg Holley 850 and my QF 1050 Annular. When V2 and Gkull are talking about reduced CFM with an annular CFM rating, you can see why by looking at the boosters.
Good luck!
Last edited by Ryan Menzies; 03-08-2018 at 10:54 PM.
It sounds like I will go with the 850 cfm quick fuel carb as suggested.
I will be going thru the rear end as part of this project. Even though I'll be using it for mountain, foothill and coastal roads with some spirited driving, I plan to use the good parts and overbuild to keep things together so I don't have to redo it.
As always, thanks for all the advice.
I personally haven't had a carb with a choke in 30 years. They are just a crutch for people that don't understand carbs and another failure point. /
I love it. Totally off topic, but as a flight instructor one of the harder things to teach is starting carburetor engines to people who never dealt with a carburetor. In the winter it is really fun. The engines do have manual priming capability typically injecting fuel directly into the cylinders. But ensuring it isn't overdone, to avoid flooding, getting them to adjust initial throttle position based on temperature (like, hey, it's 10 F out there, don't open it all initially), listen to the engine when cranking and knowing is it too rich or lean as it tries to start, etc. If this is all understood, then chokes are not needed.
In fact, on a '76 Century I drove back in the '80's the choke was such a pain I just tied a piece of rawhide around it to keep it open. I drove it like that in both summer and winter.
All that said, properly set up I still like a choke, but properly set up can be time consuming as I've learned with the Q-jet.
Last edited by vince vette 2; 03-09-2018 at 11:55 AM.
The 850 cfm it is, quick fuel for the better quality.
The speed shop told me they have dyno'd several motors with the annular boosters and they aren't seeing much difference in the performance of the motors to justify the cost difference over the down leg boosters. They said the technology makes since but their real world testing says for a street motor it isn't worth the costs, but he will leave it up to me as either way it won't hurt the performance.
Even with the cost of the upgraded quick fuel with annular boosters it's still less than a sniper set up, I'm still on the fence going EFI.
I bought this car for a classic hot rod and I'm fighting putting anything on it that is computer controlled.
Dyno runs are not a good booster type tester. Dyno runs are made from the point a motor can take on WOT under a load. typically that is over 2500 rpm to even 3000 rpm on up to so peak rpm.
Annular boosters are made to atomize fuel even at low rpm and air flow which is not measurable on a dyno . So for the street they work just off idle speed with instant throttle response.
Just look at the above carb pictures and the QF carb is just beautiful. The air flow to all 4 barrels is even. where a choke tower impedes the secondary smooth air flow
03-08-2018, 01:01 AM
Holley or Quick Silver
