What carb do I use?

[blacknight80]

Hi Guys,

I know this is going to start a pissing match between Holley and quadrajet guys but I have to ask.......which do I use.

I have a Pontiac 301 carb I can modify to be boost referenced and this was the original plan but here's the kicker. I picked up a 770 Holley street avenger for 50 bucks....it's virtually new from one oft dads buddy's.

I've never used a Holley before but for 50 bucks I couldn't say no....that's Canadian dollars to lol....that is pretty well free in American. I realize I will need an adapter to bolt it down and fuel lines but what else is required to make it fit. Does our linkage line up decently?

The Rochester will be a direct fit and it has a relatively fresh rebuild on it so I'm working with a good carb either way. I just wanted to know what will give me the most power.

I'm not worried about learning to fiddle with the Holley either so I'm kinda split down the middle.

 

[charlief1]

Try one and if you don't like it, try the other. Since the Q-jet will bolt directly on I'd start with that one first.

 

[ek02]

A 770 CFM Holly may just be a little too big for a 3.8. It will most likely have no low end response. A 600-650 CFM Holley would probably work OK. The Q-jet will work on a small engine due to the small primaries and the adjustable secondary air valve. I would use the Q-Jet.

 

[blacknight80]

I started to mod my q jet last night and I ran into a snag. I was drilling my pilot hole and my bit broke off in the hole and Is jammed, so I'm hoping a cobalt bit will cut through it.

I didn't really think you could over carb a motor. I was always under the impression that the motor will only use as much air as it can whether you run a 650 or a 950. I may have to jet it down a bit to lower the amount of fuel in the mixture.....correct me if I'm incorrect. Isn't the stock q jet rated anywhere between 350-950 depending on jetting, rods, hangars, etc?
At any rate I will most likely stick with the rochester as I am more familiar with it. Now I need to find something to put this fancy Holley on lol

 

[charlief1]

You can over carb and engine. If the engine can't suck enough air fuel mix in you have the chance of a cloud of it hovering above the carb. If you broke a drill bit off in the base then there's not much you can do. Hardened steel doesn't drill well at all if you can get it to work.

 

[blacknight80]

Thank god for cobalt steel bits!!!!! I had to drill it oversized but a little epoxy will fix that.

 

[mikemcvaney]

Have a 670 holley on mine like it a lot better than than the quadrajet

 

[blacknight80]

I figured if I jetted my 770 down to what a 670 is jetted at it would basically convert it down? The motor can only use as much air as it needs and if it is jetted smaller it would allow the mixture to be equivilent to the smaller carb. IT would be the same as having a qjet off a big block and changing the rods and hangers from a smaller carb to suit a smaller motors requirements would it? I'm sure I'm missing something so feel free to school me.

 

[charlief1]

You do realize the stock carb is rated at 730, right? The primaries are smaller so for normal driving you get low flow, but when you stomp it, you get the full 730 CFM.

 

[blacknight80]

Yup. That's what I'm getting at. So my over fueling issue will happen while cruising at partial throttle and wot will be almost fine. Wouldn't smaller primary jets resolve this or would that create a lean mixture at wot. It's has vacuum secondaries so that should help minimize bog. I donno just spitballing definately not arguing with anyone. I'm the furthest thing from a Holley master

 

[charlief1]

Don't mess with the jets until you install it and try it. The jets control the fuel but you have a carb with 4 holes the same size, The stock carb has smaller primaries so you can control the fuel with a small flow. The 77 means that you have 192.5 cfm per hole and the stock one might flow 125 cfm per front holes or less. You don't want it to go lean or you're going to have a blown engine, It's always better to run slightly rich on these cars.

 

[blacknight80]

Ya good point. I'll get this qjet bolted on and see what it does and go from there. I wouldn't have ever thought of buying a Holley but I couldn't pass on a deal and its sitting on my bench looking all shiny and staring at me hahaha.