i am looking for advise on a carb for my L72 until i can find a good date coded 3247 holley. i have a modified open plenum 69 manifold of which i will replace as well at that time. i suspect the open plenum will want more CFM. i am stuck between a 750 and 850 cfm and double pumper with mech secondaries or single pumper with vacuum. summer is coming and i just want to drive my car. i find the double pumpers interfere with the air cleaner port to the right valve cover, so unless it is a decent gain i am leaning away from them. any input on this would be apreciated. bill
-
-
Re: carb advise for a 66 427
Bill,
I am no authority on this subject but I believe if you take stroke (427) x RPM (6000) divide by 3456 = carb size. I think 750 CFM with vacuum secondary's will work fine for street driving and you can tune from there. The open plenum will be a low RPM torque killer and the carb may have to be made richer. Check out the Holley web site for good info and tuning help with your carb.
Others here will know better then me but I would seriously consider the dual plane manifold for street use and don't pick a large carburetor. -
Danger, danger Will Robinson!!!
The open plenum manifold has SERIOUS fuel mixture distribution issues. You need to stagger jet the carb to get proper mixture distribution in the engine. That said, the BEST carb to get would be a service dated 3418 1967 L88 carb - pick it up on e-bay for about $100. Although it is a true 850 CFM carb, it has vacuum secondaries (so it's a great street carb) and it has the proper mixture distribution tabs on the booster venturis to fix the mixture distribution with the plenum divider cut out. The stock 3418 jetting is usually about 2 jets too rich on the primaries and 4 jet sizes too rich on the secondaries. In addition, it will work perfectly with your air cleaner.
The 3418 does NOT have a PCV provision, that was added to the 1968 4054 L88 carb (don't bother to look for one of those, there are NO service dated ones and they cost $$$$). You can easily drill the 3418 base plate for the PCV if you must as the boss is cast in, just not drilled, but I wouldn't bother.
MarkComment
-
Re: go back to original 3005069?
is it best to just put on a unmolested 3005069? i can get a 3418 but feel i am just adding on problem to another and sraying too far from my goal. does a divded perform the same as the earlier 3 hole design? my current intake is very nice but not worth the trouble.billComment
-
Re: go back to original 3005069?
Divided plenum loses some low speed torque, but gains higher (over 3000) RPM power. It's all about the $$$. How soon were you going to get the new intake and carb anyway? If soon, just get the right stuff and be done - you could even get the right intake and just buy a used 3310 LIST 750 CFM vac secondary carb (for about $50) and have a good running combination. On the other hand, if you were planning to wait a year or more before getting the intake, get the 3418 and drive the car! I have been running L88 type intakes with the plenum cut out for over 20 years, and as long as you stagger jet the carb like the stock L88 did, the mixture distribution is PERFECT - I used the mid 70's chevy Power manual to get the jetting sizes.
Always run a vacuum secondary carb on the street.
MarkComment
-
Re: go back to original 3005069?
thank you for your advise, it is very helpfull. billComment
-
Re: carb advise for a 66 427
bill-----
Want a good running carburetor? Do as follows:
1) Buy a NEW Holley 3310 ("classic" finish) for about $300. This is a model 4160 carburetor (i.e. uses secondary metering plate rather than block), so your original fuel line to the carburetor will not fit. The 750 CFM rating will be perfect for your application;
2)This is a manual choke carburetor. However, you can convert it to electric choke with Holley kit #45-223 for about $50. You cannot convert it to remote choke like your original carb;
3) If you wish, you can convert it to a secondary metering block (i.e. effectively convert it to 4150 configuration) by installing Holley secondary metering block #34-13. This will make your original fuel line fit perfectly and will give you closer-to-original configuration, but is not otherwise necessary.
One thing that you will need to check on here, though, is the air horn diameter of the 3310. I am not 100% sure that the current 3310 has the same air horn diameter as your original carb. IF it doesn't, then your original air cleaner will not fit.In Appreciation of John HinckleyComment
-
Re:question for joe
it all goes back to not running right(the rebuilt L72) i ruled out everything but the carb. then post suggested it would lose bottom end with the open plenum. i put on a 850 cfm dbbl pumper at the builders sugestion. proved it was my 3247 carb. have not ruled out it was the intake. air cleaner hits the seconary pump. research since leads mt to the carb you sugested and holley recommended the 770 avenger. i can exchange the 850 for any one i want because i "can't hook up my emmisions" thought it sounded good. my goa from the start was to find out what a L72 in 66 was like and i am now wandering. i eventually will go back to the 3247 after i have it gone through so i should probablt replace the intake. billComment
-
Re:question for joe
bill-----
Regardless of what you do about the carb, I really think that you need to do something about the intake manifold situation. I should have mentioned that my aforementioned suggestion was contingent upon a stock configuration plenum.
I would not use a "double pumper" or mechanical secondary carb for the street.In Appreciation of John HinckleyComment
-
Re:question for joe
i agree, i bought one today on ebay for $200 (a 3885069) what do you think of the avenger 77 holley. i want to pick one i can sell easy when i put my 3247 on after having it gone through. at least it runs smooth now, just doesn't scare me yet. billComment
-
Re:question for joe
Bill-----
I don't know very much about the Avenger.In Appreciation of John HinckleyComment
Comment