I'll get rigt to it. I'm building up my recently broken LT1 to a 396. I've decided to go old school and convert it to carb (I know, I know )

The goal is to make 500 HP at the flywheel N/A. I'm going with the GM duel plane intake since it appears to be the only intake available for the LT1. What carb should I go with?

This is my first car and will be the first time I've ever rebuilt a motor. I'm doing it all myself and learning as I go along. I never knew there were so many different options when it came to carbs. There's got to be atleast 500 different ones out there Edelbrock's seem to be the best prised while the "Demon" carbs cost an arm and a leg. Money is an issue so I doubt I'll be going with any of the Demon's. This will still be my daily driver so keep that in mind too.

Any info would be great. thanks.

 

I work at a carburetor shop in Burbank CA, www.carbsonly.com, all i can say is edelbrocks are junk, they are using the same old castings that carter used to make the carburetors in the late 50's-70's, if you are looking for best reliability go with a holley or demon, holley's should be a little bit cheaper, and should perform exactly the same, most holley parts are interchrangable with demon carbs, keep in mind there isn't going to be a carburetor that you can jsut bolt right up and go, You're gonna need to do basic tuning I.E. idle mixture screws, jetting, power valve's, and size, I've seen stock 200 hp 350's running 750 double pumpers with no problem, they ran faster with the correct carb, that was jetted properly (i'm talking about sotck rochesters from GM) , you're gonna be in for a lot a work and a lot of money, but you'll learn a lot about carbs that ytou can probbaly use in the future. anyways let me know if you ened anything and feel free to call in and ask for somehelp.

-Mark

 

Today we dyno'd a pump gas 350 that had an old $100 Ebay 650 double pumper Holley converted over to a 750 with the little $99 ProForm main body kit and we were pretty impressed by how well it performed. All we had to do was jet it right and the fuel curve was right on the money for us. BTW, this made 520hp at the flywheel so it should be plenty for your application. Quick Fuel sells a setup like that for about $500

 

A member of another forum I'm on highly reccomended the Holley "Street Avenger" 770cfm carb. It cost's $395 at Jegs. What do you think? Would I be better off with the next level up (the 870) in case of future mods or would the 770 (part #80770) be good enough?

 

They arent great carbs, they dont have very good low end torque unles you have a short runner intake and they're still vaccuum secondaries, I would recomend staying with a double pumper, as long as you have a higher stall torque converter, that would probably be the best bet, btw, I can give you a better price ont he 770 if you do decide to go with it.

 

For a 396 with a dual plane intake, if you want to use a vacuum secondary then I don't have a problem recommending a 870, but a 770 should be adequate. I like the Avenger carbs but don't expect the performance of a double pumper.

 

I was told that if I am to continue using this car as a daily driver (which I am) to STAY AWAY FROM THE DOUBLE PUMPER !! I don't know why (forgive my ignorance but carb's are completely new to me) but is there any truth to that?

As far as being able to get a better price, thanks for the info, I'll get back to you the next paycheck

Holley Street Avenger 870

 

I'm sure Z28poweredLT1 would agree that the only people who don't recommend a double pumper (or any Holley carb) are the people who don't have a clue how to tune them. The only down side to a double pumper is worse gas mileage. But, if you set it up right (especially the power valve selection) you can still do pretty decent. I would HIGHLY suggest going to a bookstore or at least the library and picking up any of the Holley high performance tuning books and read up.

 

I plan on doing that tomorrow.

I have decided though that I'm gonna order up the Holley Street Avenger 870 cfm carb. SEEN HERE

But just so that I'm sure, will the 870 bolt right up to the GM LT1 Duel plane intake SEEN HERE without any problems?

I'd hate to think I'd be spending all that money and wind up with a carb that won't fit on the intake manifold.

 

Yes a Holley will bolt up to that intake. Those intakes are drilled for square or spread bore type carbs to bolt up. The intakes have dual carb mounting holes as most performance intakes do. A Holley WILL fit right on it.
For a stout 396 c.i, a 870cfm is gonna be a good choice for serious performance. Make sure you get a good cam and heads for the total package.

 

Carb. =

You're saying money is an issue, yet you're willing to spend $360 for a carb, $250 for an intake, and another how much for a distributor, a fuel pressure regulator, and all the other little things needed to convert? Doesn't make alot of sense to me since your stock LT1 intake flows enough air to support a 396 to 7000+ RPM. All you really need are some bigger injectors and a little tuning.

 

The main difference between the double pumper holley and a vacuum secondaries of the same carb, is that the carburetors both have primaries and secondary's, on a double pumper carburetor, the primaries open with your foot pedal, and a mechanical arm from the primary side (front) progressivly opens the secondary butterflys (bottom of barrels) half throttle on most progressives would normally be about 50% primary maybe 15-20% secondary, the reason why they call it a "double pumper" is becuase in order for the carburetor to work properly it recieves two different injections of gas (primary/secondary), so the carburetor has to have two accelerator pumps, as the barrels start to open, the motor produces vacuum which eventually will be sucked through the venturi's, in other words if you go from a dead stop and full throttle it, you will have all four barrels open as soon as your foot hits the end of its road, on a vacuum secondary's carburetor, the amount of amount of vacuum that the engine produces actuates how much the secondary's open, for instance, if you were to go full throttle from a dead ***** stop the primary's would open 100%, but the secondary would slowly progressivly open as the engine vacuum raised and actuates a diaphragm which by engine vacuum, (hance the name "vacuum" secondary) opens them.

sorry a little too long but its gonna come across somehow.

-Mark

 

If you're limited to a dual plane then you can run a larger carb like the 850 without a hitch. The new carbs with billet metering blocks are nice. They cost a bit more but they eliminate the chance of chasing problems associated with porous metering blocks. I don't know your budget but defintely take a look at the annular booster models. Much better signal from the annular models.

-Mindgame