BAD-HABIT

I have a 86 Quadrajet off of my 86 5.7l. I have upgraded to a 1989 roller block with roller cam and L31 Vortec heads. My Quadrajet does not have an electric choke and I will need one since the L31 heads do not have a provision for a heat activated one. Does anyone make a conversion for this? I have been told no. My mechanic says he has some quads with electric chokes that we can swing a deal on...What's the difference between the quads for the small blocks and the bigblocks? Do they have different CFM ratings? Also any suggestions on what jets to use or rods? Where can I get sets? I was figuring on using the 350 mags sizes as a base-line to start. HP should be about 360. Max RPM's will be around 52-5500. Cams rpm range is 13-5200. I am running a performer manifold with the vortec heads. Stainless marine thru-transom 4" exhaust. Compression ratio is 9:3-1. Cam has a duration of 218 and 224 and lift of 503 and 510. All on a 112 centerline. I am using a Alpha one with 1:32 gears and a Mirage 3 blade. Boat weighs 4000lbs loaded.
ANY Tips or info on Quadrajets will be helpfull Sorry about the long post......

"Bad-Habit"
86 F3LS

Blueman

They do make different sizes. Try one for older BB I think you can get about 750 cfm. Hope this helps

Mbam

Unless you do a lot of snow boating (you know, when it is so cold everyone thinks you'r nuts) the chokes should not be an issue. You gain a few CFM if you pull the shaft and butterfly.

Cord

The secondary air door is based off vacuum. Many people have run into a tuning nightmare by putting a quad that is setup for a big block onto a small block. I'm not saying that the carb can't be tuned, but you'll have some work to do.

Try contacting Jones Carburation or the Carb Shop. Both of these guys specialize in quadrajets.

jafo

Get Dennis Moores's book `Small Block Chevy Marine Performance'
HP Books 2000 (Amazon.com) if you don't already have a copy.
Dennis likes the Q-Jet for SBC's, and will give you all the tricks to set one up, the jet and rod numbers, etc.
350 Mag is a good place to start-I have similar engines in the Formula and had to more aggressive with the secondaries. Jets and rods are available from Edelbrock. Lots of performance gains here! Get plenty of sizes and experiment!
Your Performer should have provisions for a divorced choke- I'm using Performer RPM Q-Jets and have a divorced choke set-ups just like stock, except I had to get a different rods (Edelbrock again) because of the high-rise profiles. I think electric can be had from GM, but the divorced seems to work fine, other than a little longer warm-up time with aluminum manifold vs. cast -iron.
A standard marine Q-Jet for SBC is more than adequate for a 350-355. Strokers may require a little more CFM, but it is rare a SBC needs more than 750.
Jim

BAD-HABIT

What do you mean divorced choke set up? I have the Vortec heads and performer intake. The heads don't have any provison for a standard choke.....

excaleagle42

i had quadrajets on my engines. can't say i'm a big fan though. i liked holleys and edelbrock better. although, i would suggest a new edelbrock 650 or 750 marine carb from summit racing for $261. they already have an electric choke. you just hook up a hot wire to it and a ground to the manifold. i would say the 750cfm because of the mods. to your engine and the stock carb would be close. the 650 would work too but you may need it a little fatter. you will need an adapter plate too around $20. a new holley is twice as expensive.
i'm sure people are reading this and are going to spew the minimum carb sizing formula and say 750 is too much but if you ever need more air because or the mods you may make in the future, you won't have to buy another carb.

Vinny P

On my last boat, I ran into the same problem as you with the choke. My solution was to wire tie it open. It worked fine that way. As far as jetting goes, as other posts have mentioned, Edelbrock makes several different size metering rods for that carb. I got mine from Summit. Do yourself a favor, just order all the sizes they have for the secondary rods, they are cheap enough. You will need them to play with to get the motor to run right. I was able to get away with leaving the primary side stock, saves fuel that way. REMEMBER, when jetting quadrajets, the smaller the diameter of the metering rods, the more fuel it will deliver.

enticer

F3LS.......
I have a new Quad in the box..this is a copy of the ad I have on another site.

Mercury Quick Silver PT# 1347-9863A-3 Quadrajet Carburetor Assembly "Marine Use Only" was purchased to replace a carb on a 454 Mag engine..the boat was sold and we still have the carb in the box.

jafo

A lot of it comes down to what RPM you spend the bulk of your time at while boating- the Q-Jet is more fuel efficient if you tend to cruise. I have seen guys with built SBC's get zero benefit from going up in CFM size to 750 unless they have stroker SBC. There are enough choices availablein jets and metering rods to get it right with the stock carb, which will flow more than enough air- you just need to get the fuel metering right.
I have modified/ported Sportsman II heads and EFI Thunder exhaust, and have the Q-Jets working just fine (after some patience with a bunch of different rods). If you choose to go with a choke, the divorce set-up as supplied by Merc has nothing to do with head design or model- it mounts to a pad on the intake. The Edelbrock carb is a good design as well- very similar and actually improved in some areas over the original Q-jet, as well as the simplicity of the electric choke. Just have to cough up the cash for it.