How much Torque would I lose if I go from a 750 to a 670 carb?

ajusaf · 04-06-2007

Not sure if I'm going to buy a 670 street avenger or stick to the 750 I have but I still need a carb b/c I have no choke and it sucks on cold start. I think the street avenger model is 670 and 770. I don't want bad MPG as far as fuel goes but I don't want to lose power on my 383.

gsalisbury · 04-07-2007

I would go with the 670 on a smaller motor. I had a 390 with 10:0 pistons, Crane cam, etc... and on that I started out with the 750 but it was too much and had to jet it down considerably for performance. The smaller carb actually improved my performance and after speaking with the Edelbrock folks it made sense. The smaller engines draws "X" smount of air at a given engine speed. The lerger carb needs "Y" amount of air to perform correctly. The smaller carb uses the "X" amount of air more effeciantly and improves performance. I also opted for the electric choke and mechanical secondaries and loved it.

Soaring · 04-07-2007

It takes a big engine to run with a 750 cfm carb. Here, try this cfm calculator to help determine the carb you need for your application.
http://www.4secondsflat.com/Carb_CFM_Calculator.html

Veronica · 04-07-2007

Hello.

You will almost certainly gain a little bit of torque with the smaller carb, especially at the low rpm range. If you are running the car real hard and shifting at about 6 grand then a 670 is perfect for your car. There is a very simple calculation that one can use to ballpark it on how big a carb is needed. (c.i.d.X max rpm)/3456. Hope that helps.

ajusaf · 04-07-2007

oops didn't go through

ajusaf · 04-07-2007

thanks guys. this is what the calculator came up with. I'll go withthe 670 holley street avenger. electric choke, vacuum secondary
I wasn't sure about the shift max rpm so the number below should be a bit smaller
Calculated Results Required Carburetor Size In CFM CFM Required 100% VE CFM Required User % VE CFM Required (Rounded) 100% VE CFM Required (Rounded) User % VE

ajusaf · 04-08-2007

I'll be calling holley to find out what they think but I'm sure I'll get the 670 avenger and I hope its plug and play. I hate to have to adjust anythign since Carbs is new to me

gsalisbury · 04-09-2007

If you are going to run the Holley get the tuniing book that covers them - they are available everywhere. No sense in re-creating the wheel that has been out there for years. Great info and lots of tuning tricks to make it work extremely well.

ajusaf · 04-11-2007

i'll go to barnes and noble b/c holley rep told me to get the 770 avenger since i have a 383 engine. I htink it might be too much b/c the 750 I have now is awful with fuel but then again it needs tuning

not2brite · 04-11-2007

AJUSAF. Unless your shift point is over 6500 rpm, the 670 should be sufficient. My 408 is making just over 500 hp (380 at the rear wheels with a C4) using the 670. According to the formula, and my 6200 shift point, my 408 needs 663 CFM max. The car has great throttle response and breaks the tires loose big time on the 1/2 shift and chirps the tires on 2/3 shift with the automatic. I am really happy with the 670.

Most people buy too big a cam and too big a carb for the street. IMHO, you are better off going smaller rather than bigger.

ajusaf · 04-12-2007

good you are the example i'll follow. Did you install it yourself? I'm not sure what type of cam I have or my shift point but I have a 3.73 rear and c4 like you. I'll go with the 670 street avenger since you have a bigger stroked engine that I do. here's a copy of what the engine has.

not2brite · 04-12-2007

I think you'll be happy with the 670. I installed it myself and it is not difficult. Your fuel lines will match up perfectly. The throttle linkage is straight forward and there are only 4 nuts that attach the carburetor to the manifold spacer. The carb comes with a new gasket so you'll be all set. I needed to adjust the idle mixture slightly richer and increase the idle speed as my car does not like to run below 800 rpm when in gear. Both adjustments are covered in the instructions and take a screw driver. Keep track of the number of quarter turns you make and you'll always be able to go back to the factory settings.

I also needed to increase the fast idle speed on the choke. That is a real pain because the heater hoses and fuel feed are in the way. You should have a fast idle of between 1200 and 1500 rpm. Mine was around 1000 and required a small wrench to turn the idle adjuster screw about 1/2 turn.