Topic: Carb suggestions?
in Forum: C3 Engines
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Engine finally arrived. So now I'm buying parts, slowly. Still unemployed and now I have two tuitions to pay for now that I'm heading back to school.
Anyway, Looking to the experts for advice on a carb. New crate motor 330hp and 360 tq. Currently, stock tranny, may go to 700r4, stock rear end, 3.07 as I recall. I'm thinking of a 600 cfm from Holley. What about keeping the original q-jet?
When it comes to rebuilding an engine I am a shmutz(sp?). I can change an intake and a carb, thats about it as far as the engine goes. That's why I bought a crate motor.
Also, what headers have worked for your application. What are your feelings on the heat wrap they sell, the stuff actually work? I've placed the heat shield/blankets under the rugs. The driving compartment did get a little toasty as I recall.
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Frederick, MD - USA
Joined: 9/8/2003
Posts: 3398
Vette(s): 1969 convertible L71 427/435 4-speed black interior
You won't find a better street carburetor than a Quadrajet. You'll need to get it rebuilt by someone who knows them and can set it up properly for the 350HO...different cam specs can make for different jetting requirements. If the new engine came with an intake for a spread-bore carb like the Q-jet, you should be fine. If you need an intake, get an Edelbrock Performer or equivalent from Weiand or other quality supplier.
If a Q-jet is not available, my own preference would be an Edelbrock Performer carburetor...they're simple, easy to adjust and maintain their adjustments. Get a Performer 600 or 650 with electric choke and you should be quite happy. Get either an Edelbrock Performer or Performer EPS intake (the EPS is made strictly for a square-bore carb and is optimized for them).
After that I would choose a Demon or Holley carb...preferably the Demon. If you plan on racing the car, they may be better choices, but for the street and street performance, I believe the Q-jet and Edelbrock are better.
For whatever brand headers you buy, don't use wrap on them...that will void the warranties and supposedly promote rust. Get ceramic coated...it costs a bit more but will last longer, maintain its looks better and help with the heat.
As far as what brand headers, I like Sanderson, but there's lots of good brands. You first need to decide what design headers will do what you want. Block hugger headers fit well, don't hang close to the road, but don't give max power. Long tube tuned headers provide more power, but often cause clearance problems. Tri-Y headers increase torque, but again, can create clearance issues. Figure out what characteristics you want and then decide what style headers best suit that...then find the brand that best fulfills that.
These are all my less than objective preferences...someone else may well disagree or have their own preferences, which is fine. As I said...you have to decide what you want out of the car, then determine what mix of parts will accomplish that. Mixed parts that work in unison will do you better than a lot of expensive parts not matched and end up working against one another.
The formula to determine the CFM of a carb for your engine is.....cubic in's X RPM divided by 3456 X VE% = CFM carb needed, the VOLUMETRIC EFFICIENCY PERCENTAGE or VE% is the amount of air your motor can ingest, some motors can ingest 100% some can't and some more than 100% depending on cam , compression, etc, a middle of the road number would be 95% so a ....350 cu.in motor times 6500RPM = 2275000 divided by 3456=658.27546 x 95 VE = 62536.168 or a 625 CFM carb....
anips 2009-09-05 08:40:23

Where can you purchased different jetting kits for a quadrajet? I am going to be in the same situation and i plan on using the oem quadrajet.

Former Member
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Frederick, MD - USA
Joined: 9/8/2003
Posts: 3398
Vette(s): 1969 convertible L71 427/435 4-speed black interior
Edelbrock used to make modern versions of the Quadrajet and still sells rebuild kits and jetting kits. Some GM dealers may still be able to get kits but you need to know what size jets you need. That's why you need a tech who understands Quadrajets. The '78 L82 I used to own had a bigger cam than stock but the previous owner didn't do anything to change the carb calibration and it wouldn't idle worth a darn. I took the car to a carburetor rebuilder and he installed different jets and bingo! No more problem.
Thanks for the input guys, it's really appreciated. I'll start looking for a good carb rebuilder when I get back into town but that won't be until middle of the month. Anyone have any leads on a good carb rebuilder in western NY?
I'll look at those ceramic coated headers. I want to do this right the first time and not have to redo stuff later.
I have a Demon 750 Double...love it..
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Pocatello, ID - USA
Joined: 8/4/2009
Posts: 10
Vette(s): 1969 L-36, 427- 390 hp. coupe. 4spd. air.
I would recommend you contact Sean Murphy Induction, Huntington Beach Ca. The website is www.smicarburetor.com. He's one of the best in the business.
Another suggestion for a very good Q-Jet rebuilder is;
The rebuilder there is named Jim McGowan in Rockford, Ill.
He rebuilt mine and did a great job! What I liked was that he wanted to know about my motor and what I wanted from the rebuild, i.e. type of driving.
Let us know what you decide to go with.
Kevin

Hot Springs, AR - USA
Joined: 4/24/2004
Posts: 3236
Vette(s): 69 Conv #'s match 427, TKO-600/.64, 3.36HD-Posi, HT, T/T, PS, PB, PW, SP, Leather, Comp XE264HR & Roller Rockers & Lifters, Air-Gap RPM intake, Holley St Av 770 VS, MSD 6AL+Dist+Blaster SS, K&N, Jet-Hot Hooker Side-Pipes, Steeroids, Al Rad, Spal Fans
[QUOTE=anips]The formula to determine the CFM of a carb for your engine is.....cubic in's X RPM divided by 3456 X VE% = CFM carb needed, the VOLUMETRIC EFFICIENCY PERCENTAGE or VE% is the amount of air your motor can ingest, some motors can ingest 100% some can't and some more than 100% depending on cam , compression, etc, a middle of the road number would be 95% so a ....350 cu.in motor times 6500RPM = 2275000 divided by 3456=658.27546 x 95 VE = 62536.168 or a 625 CFM carb....
[/QUOTE]

95% is very optimistic...
i usually use 90 as a high figure. with reality on street engine really hovering around 80-85%
in Forum: C3 Engines
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