blow thru carb questions

[v8ranger]

Ok all you carb gooroos, can an edelbrock carb be made a blow thru carb? Is there anyone else thats make that kind of carb other than barry grant?

[widetireranger]

If I remember right, both Holley and Demon have a blow thru carb. I think I saw it either in a Jegs book or at Ebay(where I tend to camp out looking for deals!)
Hope this helps some.

[v8ranger]

Demon's are the only ones I ever see and they are very pricey. I have a modified holy 750, but I dont think it works right. So I need to get a carb that was made for this setup. Maybe I can find one in Carlisle PA at one of the car shows this year there. I am hoping to go to the truck nationls there in August.

[usmcrp1044]

You dont think your carb works right?

I know of plenty of people that dont use blow thru carb's on a supercharged/blown engine.
I was always under the impression that blow thru carbs are only necessary when they are in between the forced induction and the engine, such as in a turbo setup or a procharger, basically anything plumbing the forced air into the engine.

So anyway, what makes you think it doesnt work right?

[v8ranger]

That is my setup. I have a paxton supercharger. The carb I have now was so called convertated to be a "blow thru" carb. It just doesnt seem to run right under certen loads.

[usmcrp1044]

Wanna go into a little more detail?

$500 would be alot to dump on a carb because yours is over-jetted or has to big of an accelerator pump. Check over at sbftech... those guys will definitely point you in the right direction. Are you sure your maintaining steady fuel pressure by the way? like a gauge on the hood. I know you put a new fuel pump on, but unless your sure it is holding pressure with your setup, that could be the culprit.

[v8ranger]

Wanna go into a little more detail?

$500 would be alot to dump on a carb because yours is over-jetted or has to big of an accelerator pump. Check over at sbftech... those guys will definitely point you in the right direction. Are you sure your maintaining steady fuel pressure by the way? like a gauge on the hood. I know you put a new fuel pump on, but unless your sure it is holding pressure with your setup, that could be the culprit.

First off, you cant pay me enough to go back over to sbftech. They are assholes over there. Ok, enough of that.

I know its not fuel pressure. My new fuel pump works great. Before it was running out of gas at 3/4 throttle.The motor loads up at about half throttle. I think its because the secondaries are NOT vacuum controlled, they are linkage, and when they start to open it just dumps to much fuel. At half throttle, its not enough load to call for that much fuel. That's why I think the carb is to much. I personally don't like the mechanical secondaries. I would much rather have the vacuum secondaries for a daily/street driven vehicle.

[usmcrp1044]

Wanna go into a little more detail?

$500 would be alot to dump on a carb because yours is over-jetted or has to big of an accelerator pump. Check over at sbftech... those guys will definitely point you in the right direction. Are you sure your maintaining steady fuel pressure by the way? like a gauge on the hood. I know you put a new fuel pump on, but unless your sure it is holding pressure with your setup, that could be the culprit.

First off, you cant pay me enough to go back over to sbftech. They are assholes over there. Ok, enough of that.

I know its not fuel pressure. My new fuel pump works great. Before it was running out of gas at 3/4 throttle.The motor loads up at about half throttle. I think its because the secondaries are NOT vacuum controlled, they are linkage, and when they start to open it just dumps to much fuel. At half throttle, its not enough load to call for that much fuel. That's why I think the carb is to much. I personally don't like the mechanical secondaries. I would much rather have the vacuum secondaries for a daily/street driven vehicle.

There is nothing wrong with mechanical secondaries on a daily driven vehicle. If you want them to open, then push the gas pedal past x amount of throttle. I like them better for that reason, you're not relying on something else to open them.

On the side of the carb, opposite the throttle itself, is the linkage for the mechanical secondaries. Theres a little rod in between the primary linkage and the secondary linkage. Move that rod to one of the other holes so the secondaries dont open up as early. Give that a try and see if that fixes it. Also, re-jetting a holley carb is really not that hard, and from the sounds of the it accelerator pump in your secondaries could be giving a little to much when they start to open.

Just because the way it's bolted on there didnt give you perfect results, wouldnt you rather save the money and keep what you have?

[v8ranger]

I agree. if re-jeting it would help, im all for that. Dont you thing the 750cfm is to much tho?

[usmcrp1044]

A 750 on a 300 cubic inch supercharged engine is no where near to big. I dont know what to suggest as far as re-jetting, but you will be much better off finding someone that can give you a baseline rather than buying a new carb.

[v8ranger]

Do they offer a re-jetting kit? I know Edelbrock does as I have one and that carb is so easy to work on. I havent ever worked on Hollys.

[usmcrp1044]

http://www.jegs.com/i/Holley/510/36-181/10002/-1

Buy em once and you have a jet for no matter what the hell you do.

First thing that popped up in Jegs, I'm sure they sell small kits if you look though. You might need a smaller accelerator pump to.... just something to consider.

Holley carbs are known to take better to 'tuning' than edelbrock unless I'm mistaken. So, there should be TONS of information about how to do it and where to start.

Good luck.