Shortly before I bought my SP 350, I bought a 17058241 Qjet that's 800cfm. 70 bucks, couldn't pass it up. Carb is off a '78 Buick 350, the one I had on my old motor ran like fuel injection (thanks in part to everyday performance), so I wanted that again with a new motor. My question is, will I have to jet it up and/or change the rods and hangar to be able to cope with the SP 350? Engine is gonna be mostly stock, with the stock really shallow dish pistons (less dish than the "10:1" pistons), TA 284 cam, exhaust manifolds with downpipes and turndowns. Stock valves, stock heads. I do have the 750cfm that the engine came with, but as both carbs would need rebuilt, and I am missing all the choke linkage and thermostat coil thing, I was thinking of going with the 800. What say you all? PS: I couldn't believe how shallow the dish was compared to the 8:1 hypers I had in my other motor.
That dish IS shallow, but if that piston is at TDC, its pretty far "in the hole" which reduces compression. The 800 CFM Q-Jet will be fine, especially being it came off a 350.
Fine in stock form? And the headgasket is not flat on the deck, it came off partially when I took the head off. If you look closer you can see the edge of the cylinder up top. I'm willing to bet that dish is no more than 7cc. It's shallow.
In this case either carb will work fine on your SP engine, and both would benefit from some recalibration if performance is your goal. In stock form they are quite lean. If the 800cfm carb was a BigBlock carb, which in this case it is not, then the idle air bypass holes in the baseplate would be excessive for your engine. Don't forget Everyday Performance LLC offers an Electric choke conversion for the divorced choke Quadrajets like the 750 on your SP engine http://everyday-performance.com/ele...e-conversion-kit/p/60296021/category=16728003
Do the 800. The Qjet will only give the engine what it needs, and the larger primaries on the 800 will give better partial throttle performance.
That 78 is a good style Quadrajet. You can set up the APT to access from the air horn for part throttle adjustment, and convert to electric choke if needed. It probably is set up pretty close to what you would need, be worth a try. May need to make a few changes in jetting. Looks like it came with 73 Jets and 42 rods. AT secondary rods.
The piston dish is rated 10.4. The 800 should be fine . It should match your car accessories anyway. If it ran fine before then put it on and see if it still does. Yes it could use some jetting up , hangers and rods on secondary with adjustments to the top flap drop. But should still be fairly close to start engine and start tuning.. As far as the 284 cam I would degree it in 4 advanced. It would bring lower torque faster.
The "SP" in the title to the thread is for the CODE on the engine letting him know it is a high compression IIRC 1970 sbb 350, it doesn't stand for "single plane" so the Q-jet should work fine for him. Derek
Got one on of a 400' calibrated by ken... Its a beast, i have a 750 mighty demon sitting herewhich supposed to a better carb ( in usual aftermarket setups) and i dont even care to try the demon at all... Qjets 800 work great on my beefed up 350
Ken's 800cfm Qjet put me in the high 13s with a stock low compression 350. He modified it to work with a 200-4r TV cable too. I wish I held onto it instead of spending all this money on EFI haha.
WELP, the 800 later style qjet won't fit on my intake, so I have no choice but to use the '70 750 that came with the engine. Oh well. Anyone know where to get the choke coil thing for the divorce chock for a Buick 4 barrel?
Use the later intake manifold. . You may have to anyways as your throttle cable mounting may be different and require a different bracket.
