I have a 69 chevrolet custom sport truck and the 396 is being a pain to find a carb to run it right . I have gone form 4mpg to 18 with no power. I have power now but only 8mpg , suggestions would be helpful here
Ok lets start at the beginning . I bought a qjet replacement from Summit for a big block . It was a Holley spreadbore . It turned my headers red at an idle and fell on its face going down the road . I changed jets and cooled it down at an idle as it was too rich . The thing still had no power. It has 3:73 limited slip rear and wouldn't even turn the tires if you held the brake. I later found out the replacement with mechanical secondaries summet offers is a 650 cfm. I was under the impression it was an 850. Holley hasn't made that version In almost twenty years Im told. So I found a qjet off a 500 cid caddy ,its an 850cfm , it wouldn't idle so I drilled 2 small holes in the primary butterflies to get an idle , It idles good and has lightning response , the truck will smoke the tires well into 3rd gear and if the turbo 400 shifts into passing gear at less than 40 its all over the road. The qjet is fickle though , sometimes it boggs and sometimes it loads up , I have cleaned it and readjusted it to the point I feel its just wore out . the linkage is sloppy . The gas went from near 18 with a carb too small to 8 with this qjet . I have one of those old Holley 850 mechanical secondary carbs now I dug up at a swap meet . I want to set it up for max power and gas .I just need help here. The engine is a 66 vette 396 4bolt main with the 67 427 4v heads . It has stock .110 dome replacement hypertechnic pistons , roller tip rockers and a wolverine rv style camshaft . It has the 69 fact high rise cast intake from the original engine in the truck. I have installed a Mallory blue print hei distributor , plasma coated headders , it has a 400 turbo with a b3x fact bigblock 2000 stall . and 3:73 gears ,,, ok now you have some Idea of what Im working with ,, help would be appreciated .
I mentioned I bought a holley q jet replacement from summit , its the 650 double pumper and it turned my headders red , we over jetted it and it didn't run red but it still had no power with it . The engine is a 4 bolt 375 , steel crank .110 dome stock .030 with 67 427 425 hp heads . It has a wolverine cam , I will find the actual spects but it is a Corvette hydrolic replacement , I was told it was the hottest hydrolic you could get from wolverine based on a factory 427 460hp engine . It has a distinct lope and makes enough vacuum to run my power brakes just fine . the 850 caddilac is doing better but the milage has dropped even more . I know my main wells were leaking so I jb welded them , that help-ed some .
I am not real sure why you are real concerned about gas milage. 8 miles to the gallon is not real bad at all on a hopped up big block one tip I can think of is to stay away from the manual sec. look for vacume if it was me I would just spend the money and get a 750 double pumper and a jet kit also if you over jet and let it run rich you will lose power my buddy has a chevelle with a 396 it is bored 30 over has the 375 hors heads a high rise dual plane intake and the 282 magnum cam which is a pretty hefty grind we run a vacume sec 750 and it has a 50cc accelerater pump and has not been rejetted and runs good with a slight bog but only sees a best of 10 miles to the gallon. I think if you are going to try to get any gas milage out of this motor look at an edlebrock they have a new 800 out I think will work perfect and they are much eisier to work on than a hooley of a q-jet good luck