Ok, heres my problem. I had a 600 cfm vac holley on my 302 and it ran ok. I put a 750 vac holley on for testing purposes and it ran MUCH, MUCH better. You can feel the difference through out the rpm range! When the secondaries on the 750 open up the wheels started smoking again in 3rd gear (street tires). ....doesnt do this with the 600. There is no bog with the 750 off the line either. Is the 600 just in bad shape (rebuilt it just before running it) or does this motor just like the 750 better? I have always heard that the 750 was overkill for a 302 but I am leaning towards using it instead of the 600. So, my question is, do I figure out if the 600 has something wrong with it or run a 750. Who else is running a 750 and how do you like it. the motor is .30 over 77 302. cam = comp cams E268H (.509 in, .512 exh) 4 spd toploader MSD 6AL ignition Hooker headers (6901, I think) dual plane intake ported/polished 1970 351W heads w/roller rockers (1:6) and a few other goodies. Picture of the porting/polish job. I figure the compression is around 9:1 Advice please......
i've got a 302 with edelbrock heads, comp cam, .544 lift. hooker headers, c-4, 4500 stall, msd6al. had a 650 double pumper, mechanical secondaries on it. switched to a holley 750hp and reallly woke the motor up. using 76 jets in front and 77 in the rear. gained .4 immediately in the 1/4
Hey, theory on paper is all good, but if the damn thing runs better with the 750, don't look a gift horse in the mouth!!!
I went to QuickFuel, gave them all my engine specs and they built me a 750 that flows 870cfm. Took it right out of the box. The only thing I had to do was change the idle bleeds on it cause it was a little rich at idle.
Do you know what secondary spring the 600 was running. From Holley they install like the second worst spring(tightest) and it never total opens up the back 2 of the four barrel. I am running 1 up from the lightest spring possible to get my secondaries to open up but I have also done other mods to the carb too. I almost bought a demon carb this spring and they insisted nothing bigger than a 575 ?? So I guess I would experiment and go with what works.
Yeah, Demon suggested some really small carb for my 347 stroker...I went the next size up which is a 775 cfm. I've got the removeable sleeve carburetor so you can basically have any size you want/need.... I recently changed it to an 825cfm and have yet to run it but I think it will help......gonna try the 950 size next.....
Jim I just changed from an edelbrock 600 to a Holley double pumper 670 with vacuum secondaries and man what a difference...no bog off the line..really peppy and when those secondaries open up you really know it. Havn't got it to the track yet though but I'm not looking back...I wouldn't look a gift horse in the mouth
I went from a Holley 650 to a Demon 750, like you it REALLY woke the car up. Like John I only had to mess with the idle mixture....and I like the looks of the Demon...lol
I'm running a 750 proform main body with the billet metering blocks on my 302/351windsor head combination . No power valves , 84 jets all around and it runs beautifull with lots of torque off the line 10.25 compression ! Flow is way up there ! If it ain't broke , don't fix it !! Richard Miller
