Demon 720

zugsyn · Dec 19, 2010

So I My friends own a shop "Wanderlustkustoms.com" and I needed a carb for my stock 351w I put in the old fox so I gave them some money and they got me a 720cfm demon jr and its just to much carb for the car They say we can jet it down and it will be fine they just have to find small enough jets my question is should I try and jet it down or just get a 600cfm and call it a day

Shaolin Crane · Dec 19, 2010

I say if you actually give some engine specs we'd be able to help you out more.

85_SS_302_Coupe · Dec 19, 2010

Well...without any details on the engine...and with you sounding a little inexperienced (no offense intended there, just that you're working with a shop to get it jetted instead of doing it yourself) but yet even with being inexperienced you still feel it's too big...that leads me to believe it must be running poorly or giving you some impression that it's too big, which means it likely IS too big.

Now...my own personal belief here, is that most of the time smaller is better as far as carbs go unless you're talking about a large H/C/I street/strip only car. Can they jet it down to "make it work"? That's debatable. IMO, they "can" but, no they can't. It'll never run as good as a smaller carb will. It's gonna sacrifice somewhere....either high or low RPM in order to make the fuel curve acceptable. They can jet it down and make it run, but it'll never have the throttle response and bottom end that a 600-650 will.

sbm713 · Dec 19, 2010

??? a demon 720 too big for a 351? People are running 750cfm holleys on 302's and love them. Id try to see if you can figure out whats wrong with the carb itsself, rejet see if you can master it, if you cant sell it and get a 670 street avenger or a 700 cfm holley

85_SS_302_Coupe · Dec 19, 2010

sbm713 said:
??? a demon 720 too big for a 351? People are running 750cfm holleys on 302's and love them. Id try to see if you can figure out whats wrong with the carb itsself, rejet see if you can master it, if you cant sell it and get a 670 street avenger or a 700 cfm holley

If they are, they're going slower than i was with my 650 on a 302, and it was still too big for it. Unless you have giant heads, a giant cam, and a single plane intake and you're running 6500rpm, you don't need a 750 on a 302.

zugsyn · Dec 22, 2010

No offence taken on the whole no experiance thing, this is the first time I've built up a car so I'm still learning being that I started with a 2.3 probably makes a difference too but yeah the 720 is just to big my engine is a bone stock except for the edlebrock performer intake and the demon, the 351w is out of an old police car it just jumps around alot unless you have your foot to the floor and even then it feels like it should be giving me more if that makes anysence but I drove the the LTD the engine came out of and that monster size of a car would hit 140 the old stang gives up at 100 something has to be wrong right? I picked up a 650 holly today freebie and I'll put the demon on a shelf till I have the motor built to handle it but the last jets that were put in were 58s not sure how jet sizing works but we started with 70s its still to much I bought an 8.8 with 3.73 gears that will go on it in the spring we'll see if that helps a bit too.

85_SS_302_Coupe · Dec 23, 2010

Yeah see 58s are silly small for a 720cfm carb. If you have to jet down that much the carb is way too big. On an engine that's built to use that much carb you'd be in the 70s and maybe even 80s depending on how radical the build is. The 650 is about perfect for a mild 351 IMO. If it were a drag only car you could get away with a bigger carb because it does all its running at WOT but it'll suck on the street. You want snappy throttle response and you lose that with a carb thats too big.

zugsyn · Dec 23, 2010

thank you very much

Demon 720

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