looking for advice on a carb

  • Sponsors (?)


#23
I would recommend you stay away from mechanical secondaries unless it's a race-only car. You will get a lot better results with a vacuum secondary carb, especially on the street. Vacuum secondary isn't necessarily slower than mechanical on the track, but it will function much better at partial throttle. The nice thing about vacuum secondary carbs is the 4 barrels only open as much as you need. This allows you to buy a slightly larger carb which won't restrict the engine at redline, but will still work great in parking lots.

Don't believe some random guy on the internet? Go to Holleys carb selector program and see what the experts at Holley recommend.

By the way, I have a Holley on my '70 and love it. Works good and I haven't touched it since I set it up. I used to have a QJet in a '76 Cutlass back in the day and that thing never worked well, even after taking it to a pro.
 
#24
Bullitt347 said:
If going with a Holley style carb, I would go with one by Quick Fuel. Out of the box one of the best carbs you can get. And for a 331 cid small block I would go with a 750 cfm carb. A 600 would leave HP on the table. It is all about getting the air/fuel right. I can make that 331 run good on a 250 cfm 1bbl. carb or make it run good on a 1100 cfm Dominator. The HP difference between the two carbs would be huge, but they would work, no bog or anything. If the air bleeds are right and it is jetted right the size does not matter. If this is a fuel economy build (and with those heads and intake it will not be) then a 600 cfm would work just as well.
Click to expand...
When I was still in the game, we had installed over 10 Q carbs. What a difference in tuning. Ran like a Holly, tuned up like an Edlebrock...they ALL worked great out of the box and we were buying them from Advance Autoparts cheaper than anywhere else I priced them! Great carb. Its what will be going on every one of my project cars...
 
#25
Find a used carb shop, I paid $65 for a used Holley 600 that totally blows the edelbrock 600 that i had prior to that. The shop flowbenched the carb before I got it, and he guarenteed I wouldn`t even have to adjust a float, and he was right, this thing is awesome.
 
#27
mustangmike6996 said:
from what everyone was saying, they all recommend mechanical secondaries for a manual trans. and vacuum for auto. i understand what you are saying, it just seems to be "a bit against the grain"

decisions decisions... lol
Click to expand...
That is what the recommendation used to be. Now the recommendation is typically only mechanical secondaries if the car is extremely light, the engine very powerful and very little street use. The problem with mechanical secondaries is your carb will be wrong for every situation except wide open throttle racing. Here's a link to Holley's carb selector program.

http://www.holley.com/applications/CarburetorSelector/CarbSelection.asp

I'm building a 408 Cleveland manual trans Fox Mustang and Holley recommends vacuum secondaries for me.
 
#28
The nice thing about the Quick Fuel vacuum secondary carbs is the adjustability of when the secondaries come in. This is adjustable much like an air/fuel screw. No more having to change secondary diaphragm springs ect. Just turn the screw.
 
#29
Hack said:
That is what the recommendation used to be. Now the recommendation is typically only mechanical secondaries if the car is extremely light, the engine very powerful and very little street use. The problem with mechanical secondaries is your carb will be wrong for every situation except wide open throttle racing. Here's a link to Holley's carb selector program.

http://www.holley.com/applications/CarburetorSelector/CarbSelection.asp

I'm building a 408 Cleveland manual trans Fox Mustang and Holley recommends vacuum secondaries for me.
Click to expand...


now hearing it explained that way, it makes more sense. also as mentioned the quick fuel has adjustable secondaries which is pretty appealing.
 
#33
Cast my vote for QFT!

http://www.summitracing.com/parts/QFT-HR-580-VS/

This is generally an updated/upgraded version of the Holley Street Avenger

http://www.summitracing.com/parts/HLY-0-80570/

Almost identical, except with 4-corner idle mixture adjustments, easily changeable idle and high speed air bleeds, easily changeable idle fuel restrictors AND externally adjustable secondaries and for only a few pennies more. A read of all the items on this page:

http://www.quickfueltechnology.com/technical-info

is extremely informative on carbs in general. I have the HR-580-VS and can't say enough good things about the carb and QFT customer support.
My $.02,
Gene
 
#34
horseballz said:
Cast my vote for QFT!

http://www.summitracing.com/parts/QFT-HR-580-VS/

This is generally an updated/upgraded version of the Holley Street Avenger

http://www.summitracing.com/parts/HLY-0-80570/

Almost identical, except with 4-corner idle mixture adjustments, easily changeable idle and high speed air bleeds, easily changeable idle fuel restrictors AND externally adjustable secondaries and for only a few pennies more. A read of all the items on this page:

http://www.quickfueltechnology.com/technical-info

is extremely informative on carbs in general. I have the HR-580-VS and can't say enough good things about the carb and QFT customer support.
My $.02,
Gene
Click to expand...
thats all some good info. i like those carbs. im researching those in 650-750ish CFM.
 
#35
My internet knowledge tells me that a slightly smaller carb, (I.E., 600 or 650 VS 750) will give better overall throttle response. You mentioned stop lights and street fun, I would stay 700 or under. Actually, my recommendation is either a 600 or 650...Preferably a Holley product.
 
#36
woodsnake said:
My internet knowledge tells me that a slightly smaller carb, (I.E., 600 or 650 VS 750) will give better overall throttle response. You mentioned stop lights and street fun, I would stay 700 or under. Actually, my recommendation is either a 600 or 650...Preferably a Holley product.
Click to expand...


this is what i have always known to be true. but ppl have been saying otherwise. i was always told that stock 302s (stock heads mild cam and intake) like 550 cfm.. since i will have pretty big heads and a large cam with a 331 i figured 700 wouldnt be *too* big
 
#37
I think ultimately, driving style will have a lot to do with how happy you are with it. Regular track visits, or mostly around town, economy, the "deal" you get on the carb, will all add in to your ultimate decision...
 
#38
my buddy and i have been trying to tune this cleveland headed stock stroke 351w shortblock. since it is a budget deal we have been trying to keep it simple. we tried 3 holleys. an 830, a 750 hp and a 650 hp. they all had a stumble. finally we got tired of screwing around with junk and pulled an AED HO modified 750 out of the box from summit. with only tuning the idle mixture screws it picked up .3 of a second in the 1/8 mile (from the cars previous best of 7.28). the difference is amazing and we havent even pulled the bowls off it yet. dont worry so much about the cfm, especially on a street type carb. its BS. the only people ive ever heard say a mech secondary carb doesnt work on a street car, havent owned a quality mechanical secondary carb.

http://www.summitracing.com/parts/AED-750HOM/
 
  • Like
Reactions: 1 user
#39
clement said:
the only people ive ever heard say a mech secondary carb doesnt work on a street car, havent owned a quality mechanical secondary carb.
Click to expand...
I think Holley recommends vacuum secondary carbs because they'll run better "out of the box" with less tuning. It helps to keep calls to their support line down. I have 3 different cars with mechanical secondary carbs that run flawlessly. I have a friend who is an ex-GM engineer who worked on designing carburetors and distributors. He is an expert at tuning Holleys and Demons, and dyno tested cars with both vacuum secondaries and mechanical secondaries. His test results showed that you do pickup horsepower with a properly tuned mechanical secondary carburetor.
 
#40
clement said:
my buddy and i have been trying to tune this cleveland headed stock stroke 351w shortblock. since it is a budget deal we have been trying to keep it simple. we tried 3 holleys. an 830, a 750 hp and a 650 hp. they all had a stumble. finally we got tired of screwing around with junk and pulled an AED HO modified 750 out of the box from summit. with only tuning the idle mixture screws it picked up .3 of a second in the 1/8 mile (from the cars previous best of 7.28). the difference is amazing and we havent even pulled the bowls off it yet. dont worry so much about the cfm, especially on a street type carb. its BS. the only people ive ever heard say a mech secondary carb doesnt work on a street car, havent owned a quality mechanical secondary carb.

http://www.summitracing.com/parts/AED-750HOM/
Click to expand...

^That carb is like a more expensive QFT. For the the price of that AED, you can get a (Jeg's 793-SS-680-VSK) 650-680 cfm QF with a braided feed line, filter, and pressure gauge. Your 351w probably only needed larger squirters not another carb. I don't see how you could've gained 3 tenths by tuning your idle mix. Power is gained by adding or taking away fuel or timing or a combination of both. For the cash you guys spent on the carbs you tried, you could've tossed those Cleveland heads for some nice AFRs or ???
Do your homework mustangmike- if you go too small on cfm, you'll be leaving HP on the table. If your cam is anywhere in the .600+ lift range or your engine is built for 5500+ rpm, 750 cfm will fit the bill and can be tuned properly without stumble and instant response.
 
You must log in or register to reply here.

Similar threads

C
347 stroker power estimate? Expected 1/4 mile run?
Replies
0
Views
530
The Welcome Wagon
clayton seiders
C
C
331 build power expectations?
Replies
2
Views
1K
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
FastDriver
FastDriver
D
Carb Spitting
Replies
14
Views
2K
Classic Mustang Specific Tech
7991LXnSHO
7991LXnSHO
nothwoods
Fuel Carb advice
Replies
9
Views
832
Fox 5.0 Mustang Tech
90sickfox
90sickfox
coachrick
72 Q Carb opinion
Replies
0
Views
645
Classic Mustang Specific Tech
coachrick
coachrick
Top Bottom
Back
New
Hot
Menu