Hey there,

I have a mid-80's 351W in my truck, 2bbl carb, it's old and dead and I decided that instead of rebuilding it I would get a shiny new 4bbl while I'm at it. I'm looking at Holley's line. Any thoughts about what series and how many CFM?

 

If you want a Holley the 4160 600 CFM would be good if you are stock, You can go up in CFM depending on engine mods & use.

 

The one I was looking at was the Street Avenger (possibly the aluminum model) with 670CFM or 770CMF. I have the C6 transmission, it will be able to handle the extra power. Recently rebuilt differential also. You think that would work?

 

The Holley 770CFM would work, but you would probably be wasting your $$$ unless you had done other engine mods to increase the required airflow. I would go with either the 4160 or the Street Avenger 670CFM.

 

Ok thanks guys. Through my guy the 770 is only $10 more than the 670, so I think I'll go with that to leave some room for expansion with other parts later. Thanks for the help!

 

You will NOT be happy with a carburetor that big, Chief.

You are driving a TRUCK, not a race car. What modifications have you done to your engine that would make you think you need a carburetor as big as a 770cfm? A carburetor that big will be a dog down low, where you really need it. I agree with going with a 4V carburetor, but the carb you have chosen will not run at its best until it reaches about 5000 RPMs. How often will you be running that tight?

From the factory, Ford used a 600cfm carb. The Holley 570cfm Street Avenger should be all your truck will ever need. If you have done a lot of modifications to your engine, perhaps a 670cfm carburetor, but no bigger than that for a 351 TRUCK engine.

 

As always, rock-solid advice LARIAT. You are the guardian angel over my shoulder, providing the "you're an idiot" comment whenever my youth-driven quest for more power blinds me. Thank you.

But one more question. And this is just because I have had little to no experience with carbs and am learning on my own here. So with a 4V carb, the maximum CFM rating is at all 4 barrels full open, correct? So what will be the amount of air that can move through before the secondaries open? I ask because I am curious what would happen if I put a very stiff spring on the secondaries, so they only open when the engine is close to WOT. Would I then not have what I need "down low" with the smaller airflow, as you mentioned last post, with the ability for a higher airflow once I reach higher RPM's (vacuum secondaries open)?

I ask because I wish to learn. Teach me.

 

Quote:

Originally Posted by Jordan901

Through my guy the 770 is only $10 more than the 670, so I think I'll go with that to leave some room for expansion with other parts later.

The other guys are right, 770CFM is WAY too big for a 351.

Here, read this (direct from Holley's site):

http://www.holley.com/data/Catalogs/...Carburetor.pdf

 

If the 770cfm is a vacuum secondary carb, it will work. The secondaries will only open as much as the engine is able to digest. That being said, the larger carb will be jetted a little richer more than likely, and the smaller carb will be a little more streetable and a little bit better on gas.

So I will have to agree with the other guys and go with the smaller carb. It will handle any modifications to the engine you intend to make, unless you are going racing.

 

I agree 100% with you. I run a 600CFM on my 460 with dual exhaust edlebrock performer manifold & the cam advanced 4 degrees passed TDC, for low end torque. For low & mid end torque a I could get by with a 570 CFM Street Avenger. I never run above 4000 RPM, but 99.9% of my driving is around 2500 RPM.

 

Ok, thanks guys. Next question:

Street avenger vs. Traditional Holley?

The avenger comes in 570 and 670, the traditional comes in 600 and 650. I'm not really sure what the difference between the two is. Thoughts?

 

From what I have seen, Holley has come out with these "named" carbs, that have little modifications to them to make them more suited to the their application. I personally have never run one, since the old regular style holleys always met my needs, and the higher price of the others always turned me off. I like the old #1850 manual choke 600. It's the cheapest carb they make, and it always works good for me.

 

Since the old stock one is a 2bbl, do I need to make more modifications (intake manifold?) to put on a 4bbl?

Also, holley vs. edelbrock?

 

IMHO,

To place a 4V on a 2V intake, well, is almost a total waste due to the choke the intake plenum is placing on the 4V carb.

If you're going to replace the intake I would highly recommend the edelbrock Airgap. While I am not a big edelbrock fan, the Airgap is an excellent design producing power only seen in the original torqer manifolds from the 60's in a very broad RPM band.

For the carb, I completely agree with Franklin2!!!! I would also recommned that if you have a automatic, get the vacume secondaries, if it's a stick, get the mechanical secondaries.

If you are going to stick with the 2V manifold, then I would highly suggest Holley's 500 CFM 2V carb- the carb is basically the front half of the 1850 4V carb and has been used extensively in many forms of high performance applications very successively. The intake match should be very nice as well. Given the restriction of placing the 4V on the 2V manifold, I would bet (especially at the rpm range you are operating in) that this 2V carb would work equal to the 4V on this manifold if you choose to go this route.

 

I notice Beechkid lives in southern California. The airgap may be alright there, but I would have reservations running one where it gets cold in the winter. You need the carb down close to the engine, with the exhaust passage hooked up to heat the intake during the cold weather months, or it will not run very well at all. I would also keep the original aircleaner with the hose going to the exhaust manifold also for winter use. Run a chrome aircleaner if you like in the summer, but put the original one back on for the winter.