Thread: 390 xtra HP

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Looking for some more horse. I have a 390 with stock heads performer rpm intake holley 750 doulbe pumper, holley blue fuel pump. Headmen headers, rebuilt c6 w shiftkit. 389 gears. msd box and distributor. running about 13 degrees advance and all in 26 degrees advance at around 2800 rpm. Wanting to know what size jet to go to

what kind of cam do you have

Stock heads, no mention of cam lift and way too much carb. I would suggest going to the Eldelbrock site and looking at the Ford FE RPM package.

Unless it is a serious drag car, a vacuum seconday carb seems to work a lot better then a mechanical linkage secondary. A 650 vacuum secondary would probably be about the right choice for power, driveability, and mpg...JMO

I"m not an expert on carb sizing. I only know what I've run on various cars for the last 40 years or so. A 750 may be a bit large for a 390 with some decent power, but it's not out of the ballpark and I wouldn't throw it away (or sell it) to buy a smaller one. Tuned, it will work fine. I ran a 750 DP, manual secondaries on my GTO (400 CID). The original Quadrajet was 750 CFM, vacuum secondaries. I ran a 3310, 750 CFM, vacuum secondaires. I even tried a Holley 3-bbl, 950 CFM. Anyone remember them? The best performer with the best response was the 750DP. The best mileage/performance combination was the 3310, but the Q-jet was close. The 3-bbl was the biggest PITA to tune, but it ran as good as the 3310 once I got it there.

Shoot, the original 302 Z-28 even ran an 850 CFM Holley clone.

Just saying that I'd really work on tuning the 750DP before I spent a lot of extra cash on something else.

QUOTE=Henry Rifle]I"m not an expert on carb sizing. I only know what I've run on various cars for the last 40 years or so. A 750 may be a bit large for a 390 with some decent power,

I tried an early 3310 (780 CFM) for a while on my long gone '79 F350 years ago, thinking bigger is always better. It ran like crap, especially in the Colorado mountains pulling my 30 foot 5th wheel. At sea level, ran OK, but the original Holley was about a 550CFM, if my recollection is good. The 3310 gave me about 11 mpg, the original about 12.5 empty. Got an idea and took the Edelbrock Performer 600 cfm off my street rod and put it on the truck. Performance vastly improved, and better yet, the gas mileage went to 13.5 all around driving. And I could smoke the 12" wide rear tires again. Mind you, this was on a mildly modified (cam, exhaust and dist) 460 CID, 6200+ pound F350 SCab.

My experiences with a 950 3 bbl were interesting on my 390 '68 Torino. It ran like gangbusters for about 6 months, then just plain wore out. Shafts were sloppy, leaked everywhere, power valves blew out about once a month, etc, etc. Finally sold it for $65 - and regretted it ever since as it was a conversation piece worth more than that. I then ran a 406 Tri Power on the Torino for several years afterwards - and finally sold that setup a couple of years ago, long after the Torino was scrapped, probably to make steel for ricers

I thought I would post this link. It's a calculator for carb. sizing

http://www.usaimports.co.uk/Carb_Calculator.htm