Re: 283 heads on 350
 

The best mileage I ever got from a small block (307) had an RV cam,HEI with light springs/heavy weights,1/94 valve 64cc heads,headers,and a 450 cfm spread bore Holley Performer.I got 13-14 mpg on the hiway when the speed limit was 55 and I drove no more than 65.Once you break 65 you start losing mileage.The idea was with more effecient and hotter spark,increased fuel/air flow,and more power at lower rpms it took less throttle to get the same power at cruising speed.I had more bottom end grunt at low rpms and more go fast zip at full throttle.But,cruisin`on those tiny primaries sipped the fuel.This was on a heavy K/20 with 4.57s and 37" tall tires and a 4spd!I corrected my odo/speedo with the mile markers and know it was accurate math.I imagine a mile or two more could be eeked out of a C/10 with the right rear/tire diameter.Too tall a gear ratio isn`t the best.The best fuel saver with any combo is the right foot.

Re: 283 heads on 350
 

Alright well I'll see about my experiment in the summer, and in the mean time try to drive a little slower on the freeway and keep my foot off the gas so much :). It's just fun to gun it on the on-ramp. I'll save it for when I have a guest in the car :P.

Thanks for your wonderful input! I'm still welcome to more comments on this thread.

Re: 283 heads on 350
 

If your engine likes so much initial timing, but pings when you punch it at highway speed, your vacuum advance may be a bit wonky. Check it with a timing light at idle, first with the vacuum line disconnected, and then connected to a source of full manifold vacuum (on some carbs the distributor port doesn't get full vacuum at idle).

Ray

Re: 283 heads on 350
 

i'm hoping for 11's in the qtr mile LOL! my 52 F-1 does real well with a mild 355 sbc 700r4 3.0 gear. as for the 72 stepside prostreet smiles by the miles is all i want! this thread was a real good read!

Re: 283 heads on 350
 

Thank you for the advice. I will try that, but can you describe more on checking and fixing my vacuum advance?

Re: 283 heads on 350
 

The 2004r will be a much easier swap than a 700r4. The 200 is the same length as a short tail 350 and powerglide and uses the same slip yoke as the th350 and PG. You just need to move the tranny crossmember back, GET THE T.V. CABLE RIGHT and decide whether you want a lock-up converter or not.

Re: 283 heads on 350
 

Wait, someone else told me it's the 700r4 that's easier to swap... which one is it?

Re: 283 heads on 350
 

What size are the valves in the 283 heads? If they're smaller than 1.94's you're just shooting yourself in the foot on a 350.

Gary

Re: 283 heads on 350
 

Hook up your timing light and let the engine idle. You want to see how much the timing changes when you connect and disconnect the vacuum hose. If there is no change, check to make sure you are actually getting vacuum. As a test, you can put the end of the hose in your mouth and suck on it - hard.

Ray

Re: 283 heads on 350
 

I drove on the freeway with the vacuum disconnected, and there was no noticeable difference in timing, still pinging while acc. on the freeway.

I will check for vacuum by your sucking method! Is perhaps the vacuum hose connected to the wrong side on my carburetor? It's on the left side of my Edelbrock performer.

Re: 283 heads on 350
 

If the vacuum advance is bad there WILL NOT be any difference in timing with it disconnected. Your pinging could be coming from too much initial. The quickest check on on the carb port would be to disconnect the hose and put your finger over the tube with the engine idling.

Ray