307 carb question with my set up ...... have i accomplished anything?

[mbc9ieII]

I know that the 307 is limited to its performance. I also know that there is only so much that can be done with them. Its a '69 C10 307 3 speed. It was my grand fathers truck. I kind of wanted to keep it stock, but make it mine in the same way. I am jsut curious to see if i have actually accomplished anything with my engine modifications. i rebuilt the 307, threw in a 480 lift cam, eldebrock high rise intake with an inch spacer, '91 350 vortec heads (i think there Vortec they came off a 91 350 out of a suburban) longtube headers, 2 1/2 ich exhaust exiting in front of the back tires. The big question is, what carb do i need? i can get my hands on a 750 and de-jet it, but dont want it to run to lean, and a 650 that needs rebuilding.

What carb size do you guys recomend?

I am also curious to see if i have accomplished anything by the modifications. I will probably change motors eventually but for now, i wanted to keep it close to what it was.

does anyone run a set up like mine, what kind of HP does my set up make. Any info let me know.

[hereinmissoula]

650 for sure..... 750 would prob be soggy on mild 307..... much better throttle response with 650.... has to do with booster signal... not enough air moving to keep good signal with 750 on that small of an engine without rpm's... which your not turning...

[hereinmissoula]

and 91 heads should be tbi heads, which are horrible for performance.. better off with the stock 307 heads... am i right here????

[dfosh]

That one inch spacer will takeaway some low end power . The 650 cfm carb will be more than enough .

[WIDESIDE72]

Originally Posted by hereinmissoula

and 91 heads should be tbi heads, which are horrible for performance.. Better off with the stock 307 heads... Am i right here????

yep

[68Stepbed]

Well the TBI heads have some sort of stub that sticks up inside of the intake ports which limits flow, but increases torque. I would be more worried about the larger combustion chambers reducing compression ratio. The actual Vortec heads would've been better, but for a driver, the TBI heads should be fine.

As far as carb, I would either go with a 500 Edelbrock or 500 2-bbl Holley. And NO, the 2-bbl Holley won't limit performance. It's the same thing alot of circle track racers use. Definetly no to the 750. You could get the 650 to work with some tuning, but it may still run rich alot.

[mbc9ieII]

thank you guys. we did do a mild port job on the headsn to open up the passageways, i did forget to mention that. and i do have a holley 600 or 650. not sure.... how do i find out the correct size so i can get a rebuild kit for it.

[stepside454]

307s have more potential that they get credit for, but as far as how much cfm, it sounds like with the heads & intake your using, youll be staying within 5500 RPMs or so.
With that in mind I would recomend you stay more in the 500-525 cfm range.

[airdale94]

The stubs are "swirl ports". I think the CC's are about the same 64CC.

[pissonNOS]

dont let the 307s fool you mine has lots of power for whats been done to it which is quite similar to what youve done and im running a 650 cfm on mine as well it works great

[69GMCLonghorn]

That 307 will be just great with a 600 or 650. If you do the math, it says 500 or 550, but I ran a 307 with a 600 with MANUAL secondaries for years. I got 14 MPG on the hwy and it had plenty of cajones. Enjoy it!!

[mbc9ieII]

Hey 69GMCLonghorn...... what kind of power does your truck make?

and thanks again....

[WIDESIDE72]

307's get a bad rap. They are better than a 305 any day. I think the reason they get tossed is it costs the same $$$ to build a 350, and not much more to build a 383 now a days. If I had a 307 than was running good, I would leave it well enough alone, but I would not spend big $$$ on machine work to get a wasted 307 going again. They are great for cruising around in an empty truck, or with a bed full of stuff, but hook them to a trailer (of almost any kind) and they demonstrate their lack of torque. My dad bought a 72 Custom Deluxe LWB new (when I was 1 yr old!) w/ a 307 (2 bbl of course) and TH350. He later bought a 18' Longhorn bass boat w/ a 150 Envinrude. He traded the 72 for a 74 Silverado with a 454 because the 307 would not pull the boat! (and the Silverado had AC that the 72 did not). The 454 got the same mileage as the 307 when towing, but the 454 got that mileage all the time. The 307 beat it hands down when empty. Later on, dad wished he would have kept the 72 and swapped in an RV cam and 4 bbl or swapped in a 350 4 bbl., but the truck was only 3-4 yrs old. No one thought of doing that to a "new" truck. It would have been cheaper in the end. My older bros. talked him into the 454 (!) Dad got tired of the 454 mileage when empty and after a few yrs, one of my bro. bought a 73 Camaro with a good running 350 (Edelbrock intake, Crane Cam nad Carter AFB carb) and they swapped the 454 into the Camaro, and the 350 into the truck. The 454 got a aftermarket cam, Edelbrock intake and Hooker headers. It ran like a bat, with a TH350 trans and a 10 bolt 3.08 open gears. He never did get around the swapping in a 12 bolt with 4.11 posi like they planned. That car had a WICKED top end!!! It was OK off the line, the 454 had torque to make up for the lack of gears, but once you hit 45-50 mph, hang on! Sorry I got off track. I was reminiscing...