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Ziegelsteinfaust · 02-08-2017, 01:43 AM

My 74 K20 would do 15 highway if I drove 65. City was probably 8-10 but I find it hard to quantify.

I had headers, roller rockers, and a fully tuned Q-jet. Also I bumped my timing to 14* initial. Which worked good with my engine. For rims I used the rotary forged PYO's, and AT tires.

Lastly I had a 14 bolt SF with 3.42 gears. Which is 1/2 the weight of the FF, but also a good 50 or so less rotational weight.

When I first got the truck it was a C20, and had turbine rims. Well they were rotted out, and I swap on 265/75/16's with PYO's. Even with the very heavy 14 bolt FF you could feel the truck had a lot more pick up. I sold the FF, and went to a SF. Even though the FF had 4.56 gears, and the SF had 3.42's. it still felt as lovely as ever. Even with a engine that was dead the mpg went up considerably. When I got it I got about 8mpg. Did a full tune up with bolt one's, and got to 11 mpg. Swapped to lighter rims/tires and it went to 11.5/12. With the 14 bolt SF it would touch 14. The 350 had only about 65-70 cranking psi during this time, but ran like a top otherwise lacking power.

02-08-2017, 01:43 AM	#3
Ziegelsteinfaust Registered User Join Date: Dec 2012 Location: Temple City Posts: 3,561	Re: 78 K20 Gas Milage Suggestions My 74 K20 would do 15 highway if I drove 65. City was probably 8-10 but I find it hard to quantify. I had headers, roller rockers, and a fully tuned Q-jet. Also I bumped my timing to 14* initial. Which worked good with my engine. For rims I used the rotary forged PYO's, and AT tires. Lastly I had a 14 bolt SF with 3.42 gears. Which is 1/2 the weight of the FF, but also a good 50 or so less rotational weight. When I first got the truck it was a C20, and had turbine rims. Well they were rotted out, and I swap on 265/75/16's with PYO's. Even with the very heavy 14 bolt FF you could feel the truck had a lot more pick up. I sold the FF, and went to a SF. Even though the FF had 4.56 gears, and the SF had 3.42's. it still felt as lovely as ever. Even with a engine that was dead the mpg went up considerably. When I got it I got about 8mpg. Did a full tune up with bolt one's, and got to 11 mpg. Swapped to lighter rims/tires and it went to 11.5/12. With the 14 bolt SF it would touch 14. The 350 had only about 65-70 cranking psi during this time, but ran like a top otherwise lacking power.