67 GMC 305 V6 swap to a SBC 305

[406 Q-ship]

Originally Posted by bigwil86

Yea, I'm in the process of trying to find a 71-72 c10 donor truck now. But as for the 305 v8 I'm building its a 305 with 4 bolt mail splade caps for added durability, speedpro/king bearings, 305 X-beam rods with dome pistions, 200cc ACR aluminum heads with 202/160 valves, 1.6 aluminium roller rockers, screw in head & rocker arm studs with polylocks, Jegs 468/488 lift cam with 110 lobe separation, dual plan weiand highrise intake with 650 cfm holley. I run this exact same set up a 83 S10, I know the GMC is a bit heavier so the gas mileage may fall off a bit but after the motor is tuned the numbers are good.
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That combination will never get 22 MPG, even in a vega. The 2.02 heads will NOT work on the small bore 305 (valves will hit the cylinder bore), 200 port is the size you run on a really healthy 350 and bigger not a 305. That Cam is HUGE in a 305. Do yourself a favor, if you want that kind of a combination do it to a 350. Even a 350 in that combination will be a bit lazy bellow 2800 RPM.

[BIGKEV]

Originally Posted by bigwil86

Yea, I'm in the process of trying to find a 71-72 c10 donor truck now. But as for the 305 v8 I'm building its a 305 with 4 bolt mail splade caps for added durability, speedpro/king bearings, 305 X-beam rods with dome pistions, 200cc ACR aluminum heads with 202/160 valves, 1.6 aluminium roller rockers, screw in head & rocker arm studs with polylocks, Jegs 468/488 lift cam with 110 lobe separation, dual plan weiand highrise intake with 650 cfm holley. I run this exact same set up a 83 S10, I know the GMC is a bit heavier so the gas mileage may fall off a bit but after the motor is tuned the numbers are good.
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Not trying to piss in your cornflakes, but those heads and that cam are both WAY to big for the small bore of the 305 IMO. The 3.736 inch bore makes it hard for a 305 to effectively "pump air" making it easy to over cam or over do it on heads. Don't get me wrong here I'm not one of those all 305's are junk guys. For a truck this big I'd run around a 170-180cc head, and something around ,450 max lift. With 1.6 rockers your going to bring your lift up to .499 int and .521 ex. How much stall are planning on running (your going to want +/- 3500 rpm depending on rear gear)? How often are you going to spin the motor to 7000 rpm in the that big truck? I know 305s make great power on paper, but on the dyno it's usually a different story. At the end of the day do what makes you happy

[70cst]

Originally Posted by bigwil86

I apologize about that. Still kinda new to the thread.
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Not a problem.

Oh yes... and from Ohio. Glad to have you on board.

[5150.4.67]

Wow, 375hp from a 305 might be a little high estimate. Ditto for 22mpg. The problem with the 305 is the small bore that restricts you to small valve heads and therefore less flow, not to mention valve shrouding...... now a big cam is completey out of the equation.
About the only decent head for a 305 (without breaking the bank) is the l98 aluminum head. It still retains the 58cc chamber.
Just speaking from experience: I built a mild 305 with 4 barrel FI and Megasquirt and when I was done I was happy. Then it wore off 2 days later and I said to myself, what the hell did i do that for? I could have spent less money and had 50 more hp with a 350!!!
Its fun to be different, but if thats the case, keep the 305 v6. Think of it as half of a GMC v12! (which it kinda is......)

Good luck and have fun!

And welcome! You will learn much here!

[truckster]

Just for comparison, I built a 350 and put it in an 83 Chevy Caprice Wagon. My next-door neighbor had the same car, except his was an 84 and had the 305. Mine had more power and better mileage.

[bucketObolts]

I dropped a 305 in my 68 I took out of a 91 camaro. it was almost free as I traded some very easy fab work for, and I'm not gonna be done with my 502 for quite some time so I figured why not. plus i was tired of pushing the truck around the driveway. it Was a pretty routine motor swap. Easy enough for a beginner. 375hp is a long shot though. thats all i can help you with in terms of power since she has yet to leave the driveway. I had a PO installed 305 in my old 71 c30 dumpbody and that thing couldnt get out of its own way, but then again it was a one ton with a ton of weight in the bed