billyride

I just got a 71 LT-1 with aluminum heads, headers and a high lift cam. It has a Holley double pumper carb but only 600 CFM. New the carbs were 780 CFM but that carb is no longer made. There's a 750 CFM available 0-4779 CE available. Is that the best way to go? Is there something out in the world that is better?

Thanks

cv67

what heads or cam?assuming a stick?
780 vs are a little overrated modern day carbs are SO much better. add a wideband its carb heaven
Considered EFI but it just doesnt belong on mine lol

jb78L-82

Answering your question, a Holley 750 CFM will work fine in place of the 780 CFM carb. A 780 CFM OEM Holley was way overcarbed for an OEM 71 330 Gross HP LT-1. There are some who will argue that there are better carbs today for your motor which may be. A 600 CFM DP seems a bit small for your motor.

I am using a Holley 4175 650 CFM vacuum secondary Q jet replacement carb on my OEM L-82 up until 2014 and still use it today (rejetted) with my 355 L-82 AFR aluminum Heads, Howards Roller cam (.525/.525 lift, duration 219/225, LSA110) with 10.2 compression and the engine runs great and makes big power....650 CFM carb size is perfect for my engine

VintageMusclecar

The factory 780 carbs are awfully hard to beat, they make fantastic all-around street/performance carbs.

What intake are you using? If you're running the factory intake and wish to retain an OEM style choke setup, you'll need to stick with a factory style carb with a divorced choke. You can not convert a thermal/electric/hand choke style carb over to use with a divorced style choke. Of course you can also use a hand or electric choke with the factory intake, just another point to consider.

If you're running an automatic trans with a stock style converter, I would not advise using a mechanical secondary carb.

Hope this helps.
Eric

F4Gary

I just put a Holley Street Avenger 670 w/electric choke and vacuum secondaries on my stock '72 LT-1. I'm very happy with it. I used the wire that went to the anti-dieseling solenoid for the electric choke. I'm going to block off the exhaust crossover to the intake manifold.
My original date coded 780 is now in a box for the next caretaker of this car.

Duane4238

I've been running the 600cfm double pumper on my '72 for about 10 years and I have no complaints. I had a 650 on before that and there's no measurable difference. If you do the calculations for your engine according to Holley guidelines I think you'll see that a 600 is even more than you'll need. Everyone seems to overcarb so they can say "I'm running a 780" or whatever. I guess it sounds good but doesn't make a difference, of course unless you're running 11 to 1 comp, a hot cam, etc. but then you're probably only good for the strip and not cruising on the street.
Duane

billyride

The car is a 4 speed (I believe all LT-1s are). It has Brodix aluminum heads. The cam is a hydraulic roller, Comp #12-433-8

7t9l82

750 double pumper, don't waste your time on anything else.

cv67

[QUOTEOperating Range: 2500-6000 RPM
Duration Advertised: 288° Intake / 294° Exhaust
Duration @ .050'' Lift: 236° Intake / 242° Exhaust
Valve Lift w/1.5 Rockers: .520'' Intake / .540'' Exhaust
Lobe Separation Angle: 110°


and imo stay the f away from trendy Xtra ?? lobes
r
Dont be a marketing burro.

toylman

shameless plug
https://www.corvetteforum.com/forums...1-and-z28.html

stingr69

My opinion - Not worth the cost and effort to change it. Tune what you have.

A 780 rated carb has the same internal parts/dimensions as the carbs rated as 750. The Holley vacuum secondary "3310" is the closest aftermarket match for the factory 780 carbs. They can work on anything.

Dynra Rockets

IMO, An LT-1 that has the heads and cam changed out is no longer an LT-1. It is just a 'built' SBC now.

What RPM are you taking it to? If you are only taking it to 5000 rpm then the 600 cfm is probably fine and just tune it to what the engine wants. A lot of people buy 750 cfm carbs to get the larger accelerator pump squirt and jets, when all they really needed was the larger accelerator pump and jets in their smaller carb.

Sigforty

What are the vacuum readings in the car at WOT? If you have a restriction because there is still vacuum being drawn, you could benefit from a bigger carb. If there is currently little to no restriction, keep what you have.

billyride

I want to take it to 5400 RPM on occasion. The current carb leaks and needs to be rebuilt. It also has a power drop off above 4200 RPM. The original carb on the LT-1 was a 780 CFM. Looks like the 750 CFM is the way to go.

maj75

No need to waste money on a new carb. The 600 DP you have is plenty. Just get it rebuilt by a competent builder and enjoy the car.

I ran a 600 DP on my ‘68 GTO. The “experts” said the carb was too small. I had great throttle response. So good I blew up the motor at the track...

Tonio

I took my original 780 carb off my stock '72 LT-1 and put it in a plastic wrapper and in a box on the shelf. Replaced it with a Holley 650 electric choke. It's a street car, will never see rpms over 5500 unless I blow a shift. The 650 works fantastically. (My idle vacuum at the manifold is 20").

billyride

Of course it's still an LT-1. It's written right on the hood. And don't forget about the 4 bolt mains. And I have the original heads and exhaust manifolds in a box. I ordered the 750 CFM Holley and will post when it performs in the way I expect. If it doesn't, I'll post that too.

MelWff

you do realize the 4479 is a double pumper while the original carb you have is vaccuum secondary?
why didnt you just rebuilt the original carb?

Dynra Rockets

My '69 300 hp ZQ3 has 4 bolt mains.

Barry's70LT1

I've had a R4779 DP on my LT-1 for about 45 years now. It continues to work great. I have made a few tweaks to improve the original configuration.
There is over 100,000 miles on that carb now, with only a few gasket changes over the years.