Just curious of the negative impact overcarbing an engine will have. When i purchased my current 70 cutlass last fall the p.o. had a 4160 holley 750 on the 350. Try as I may i could never get that thing to run right.

Fast forward, was able to purchased a holley 4150 570 , which i've had success with in the past with rocket 350's. bolted on , adjusted air/fuel, vacuum secondary spring and she runs GREAT!

maybe the old carb was just worn out? or can running a carb that large on a small block cause performance loss?

 

Yeah it can bog down. I ran a 750 on a stock 350 for a few weeks til i bought a new carb. It ran ok at partial throttle but ran bad a WOT. In the upper RPM's it seemed to catch up.

 

Cool, over all happy about getting right size carb on there and having car run right.

 

Your carb will only work at ats best when put on the right engine combo. This is also true of any other part you put on. A wild cam, ported heads, manifold or headers etc will only work properly if the rest of the engine is set up to make the best of it.
This also brings in the question of is the transmission & rear end suitable as well, A high revving engine won't be effective with a transmission set up for soft early shifting. A rough rule of thumb is to set the car to be at its desired cruising speed at the engines peak torque output for road use.

 

Remember the Q-Jet is a 750. It's all in the jetting and carb design. One of the guys in the Olds club here in San Antonio runs high 12s in the quarter with the same Q-Jet that came from the factory.

Check us out at http://www.southtexasoldsmobileclub.org/Home_Page.html

C.J.
San Antonio, TX

 

You have to also remember the Qjet is a variable cfm carb. That secondary air flap only opens as much as needed. It's pulling no where near 750 cfm on a stock 350. There's a reason it's used on everything from 327ci to 500ci GM engines.

 

Actually, it was used on some 6 cylinder engines, too. The Pontiac OHC 6 used either a one barrel on the low horse version or a qjet on the more powerful version.

 

Correct, from the 230 cu in OHC Sprint motor and the 231 cu in Buick V6 to the 500 CFM Caddy.

 

Hey texasred: Thanks for sharing the pictures!

Jaybird