Air & fuel that is. would you belive how much of a bitch it is to get an intake to fit a 86 & up 350? its magical how much auto parts stores DONT know. "well it might fit...", is never words i wanna hear. after a call to sumit i now have a working, and non jack legged, intake system. and i found out that when you dont fully assemble a HEI Accel distributor, (previous owner), when you go to start the car all hell breaks loose. So as you can see i frankinstine'd the distributor using a stock Delco ne and what was left of the Accel. it looks better anyhow. once i mount the exaust manifolds properly ill tune it better.
now i cant really get a straight answere on this bit, because no ones really delt with it, would a 750 holly be too big for the SBC?, because thats what's on it now. ran the block front number through Year one and they said its <i>Most likely</i> a late 80's-Early 90's 305 HO, or plain 350, no other parts on the engine or inside have been worked, other then the intake.
I never got a 350 to run right with a 750 but others have. I've found 600-650 cfm for the street ideal. If it's stock I wouldn't go with anything more then a 600. I'm sure there will be induction experts joining in with more info then I have. You need the right combination of cam, carb, headwork and exhaust port working in conduction to get the most performance on a street engine. If you just want a little extra umph, a 600cfm is the way to go. Hell, a good 390 if it's a 305 would be great, or a Holley 500 cfm 2 barrel.
I think he's referring to the 4 center bolt holes on the intake. '87-95 Cast Iron Heads have the 4 center bolt holes for the intake pointing almost straight up. I don't know why the hell they did that, because everything else is the same...but that's the issue with the later motors. I've got an '89 TBI SBC in our '53 Chevy. Swapped Serpentine out for V-belts, Swapped TBI out for Carb. Swapped the Ignition over to a stock HEI setup. Stock motor otherwise. First was a Weiand Single Plane Intake and the 4150 Holley 600cfm 4bbl. I had to ream out the 4 center holes on that intake to fit the heads. Car idled like shit, but would go sideways with the pedal on the floor. Then after hogging a stock Q-jet manifold to fit the 4 center fucking boltholes for about 4 hours one night, I almost gave up ordered the Edelbrock #2104. But I didn't want to spend the money, so I let it sit for a while, then finally a few weeks later, got around to making the Q-jet manifold fit, and I got it on there nice and flush. The Weiand would have been great if the motor had a cam, hotter ignition, and some headers. But this is the lowly 305ci 140hp Caprice motor, so it couldn't handle the Weiand and Holley combo without those upgrades. The Stock GM Spreadbore Q-jet manifold and 80457 Squarebore Holley with a 3/4" adapter bolted up and finally tuned makes this car run like it should, with much more power and throttle response than it did in the donor car, and it idles nice too. I've got a hot 365ci stroker motor that's been in the works for a few years. That will replace the 305 when it gets tired, or I get tired of going slow. It's modeled after John Beck's "Engine Masters Challenge" 307ci stroked to 365ci 10.5:1 556hp motor. The only difference is a log manifold with six Rochesters 2GC's instead of one 1150 Dominator. Here's the engine when it had the Weiand...
if its a stock 350 a 750 holley will kill it power-wise. unless its over 400 horse and has a big cam, you dont need that big carb.
And yes, I agree about the carb. 750 is WAY too big for that motor. Get yourself a 600cfm Holley and you'll be fine. You're just flooding the tiny combustion chambers with fuel that it can't burn. I've had good luck with these 80457 Holley's. Easy to tune, and pretty much trouble free. Sell the 750 on craigslist and it'll pay for a new 600. If fuel efficiency is your concern, a stock Quadra-Jet or 2bbl carburetor would be good for that motor. Or even a 450cfm 4bbl carburetor.
I use to run a 350 bored .030 over with 11:1 popups and closed chamber power pack 327 heads and I had a Mickey Thompson wedge with two 650 vacuum secondaries on it. With what you got, I wouldn't go over a 650. And screw the double pumper crap, if you aint on the drag, keep it vacuum on the secondaries....especially at gas prices right now. I've had my fair share of times with Rochesters Quadra-Bog. Save yourself the pain. They have a great idea, but those secondaries are so frickin huge that by the time they open up, half the time they almost drown you out on a 350. Qjets are better suite for the BB's. Give the 650 VS a go and she'll perform great.
The center 4 bolts I just drill out the threads straight with the intake surface and install helicoils. It works good. On a stock engine the 750 can work, but you will get better throttle responce with a 500 or 600cfm. Think of the 750 as a two barrel, because with the fuel injection heads on that engine the secondaries may hardly ever open. They had swirl ramps in the intake ports that were a bad restriction above 4500rpm
Strange. I had a Carter 750cfm (1407) on my boggo 350 and changed it for a 600Vac secondary Holley. Truck is now slower off the line and in general driving is not as responsive. Does use a hell of a lot less petrol though! P.
A quick formula for carburetors - CFM = 1.68 x Horsepower. For example, a 350 Chevrolet, stock, running 250 horsepower - the CFM would be 1.68 x 250 resulting in 420 CFM. I would bump it up to 500 CFM making the Edelbrock 1403 or an equivelent Holly a good choice. Another formula using different plug-in's would be CFM = Engine Displacement x RPM divided by 3456 - for example a 350 Chevrolet running at 5000 RPM would need a 506 CFM carburetor. Hope this helps
quadra-jet works the best for street holley vaccum sec. with auto.double pumper with a manual and a 750DP will work if your running stiff gears
750 vacuum is just fine for a stock 350. A little on the big side, but not so big that you should be changing it. You got a lot better ways to spend time and money on that car than f-ing with the carburetor. FWIW it's not really 86-up, the newer vortec is totally different. That screwball deal ended around 95 when everything was either vortec or LT1. All you really have to do is egg out the center intake bolt holes to allow the different bolt angle, then make/buy tapered washers so the bolts pull flat. Get on mortec.com and you should be able to positively identify the block's origin. good luck
briggs&strattonChev, what i meant was that no body had the one that fits, the all had the old style for some odd reason. its all buttoned up like in the pictures, i kept trying to get dad to trade me carbs, he has the same one but a 650 Holly on his BBC, its all oxidiezed to shit on the bowls and base, but it would be more fitting on my engine and my carb more fitting on his. still havent had the chance to fire the thing. We will see, as soon as i get it going i found out my camera has sound too. should be fun.
A 600 cfm carb would be plenty on a basically stock motor. I have a holley 80457 on the 350 in my 51 and one on the 401Fe in my 69 F-100. A 750 double pumper is way to much carb for a stock small block
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