302 modifications

[XM 2742]

What modifications can be made to the GMC 302 to increase mileage and overall performance. I don't want a hot rod. I just need to have an effecient engine and want to optimize mpg.

 

[wreckerman893]

I would say a tuned exhaust (header), porting the cylinders, valve job (to update for unleaded fuel) and maybe a updated carb system would be a start.
You might check to see if these engines were ever used for some high perfomance applications, if so there may be a source for parts that would help you.
Just my.

 

[XM 2742]

I have "googled" my hiney off and can't find much of anything other than history of the GMC 302. Several older posts have debated the need for hardened valve seats to deal with unleaded fuel but not much definitive on the subject. I just figured that someone on here has crossed the elusive 8mpg line.

 

[southdave]

453 detroit ?

 

[jasonjc]

Try looking up "stove bolt" 302. My understandings is that, the 302 was the 350 of its day.

 

[Westech]

look on you tube.. there is a hot rod with that engine in it

http://www.youtube.com/watch?v=mJOZ...818DF918&playnext=1&playnext_from=PL&index=46

 

[wascomatw74]

try clifford research or clifford preformance . used to do all kinds of 6 cylinder preformance parts years ago.

 

[73m819]

try clifford research or clifford preformance . used to do all kinds of 6 cylinder preformance parts years ago.

WOW, i had forgotten about them, delt with them when i built up a 235 for one of my 56 chev, PUs they KNOW every CHEV..6 trick in the book

 

[butch atkins]

GMC 302 motor tips

short of throwing massive amounts of cash,the 134 hp motor in a 16000 lb truck is not going to work,you should check to see if youi have a vaccum leak at the carb governor,and all the rest of the vaccum lines that go to the tranny,and distributor,and make sure you have a fresh tune on the motor,new plugs ,points and the 2 resistors that are in the distributor,timing is a big issue on this motor so make sure you have it timed to about 8 degrees above TDC,thats about 3 deg above what the facrory setting is,and always check the idle speed. I get 10MPG or better on my M211 on the road. CRITICAL TO PERFORMANCE AND GAS MILEAGE IS ADJUSTING THE TRANNY,THROTTLE VALVE.LINKAGE,TRANNY MANUAL CONTROL VALVE,this must be done in the correct sequence,and exactly as the TM 9-8024 manual states,about all you can do to up the HP on these motors is to mill the head NO MORE than .100 of an inch,that will raise the compression ratio with a slight increase in HP,good luck on your project

 

[badgmc56]

Very good advise Butch. If I were going to up the power a bit in the 302, I would ad a camshaft designed for more ft. lbs of torque, add a free fiow exaust, and meter the carb to flow more fuel. Headwork is a must to complete the package. I think you may be asking a little to much to get mileage and more power out of these old trucks . In my opinion it is one or the other. If the truck is set up right like Butch said and is stock, the power and mileage should be sufficient.

 

[avengeusa]

are you talking a straight six, or a V8 302? I am assuming you are talking a six

if so

Headder
Intake
rv type cam or a tad larger
valve job/sdeats

 

[wreckerman893]

Yep....inline six banger.....that hot rod engine was awesome.....might make an interesting bob deuce with a high performance six holer in it.

 

[Westech]

Tom at Alfa has got 270 HP out of his 302.. he shaves the head and does some other stuff to it. Check with him.

 

[XM 2742]

Thanks guys. Just for the record this thing doesn't run yet.but did when it was parked. As many may deduce from my recent posts I am planning to go thru the whole thing and keep things as original as possible with the exception of the color. I am just tyrying to get all my ducks in a row before I start tearing the thing apart.

I know that a few pictures would be nice but as of now a camera is on the list but Santa was not good to me this year.

I lucked into this thing and a decent supply of spare parts from a parts truck and the price was below scrap prices so if I screw up the thing I can part it out . But that won't happen. I have a few dozen motor rebuilds under my belt and have enough experience at turning a wrench that it will be a knuckle busting enjoyment. The motor only has 8000 miles on it and I am relatively confident that the numbers are correct. I will open it up and look at a few things but want to avoid a total motor rebuild.

The bed is the only part on the truck that I will modify, it is kinda beat but salvageable in a cutting torch kinda way. If someone wants to get a beat up bed and wants to swap for some kind of modified flat bed I might be interested. It looks like I will turn the thing into a flat bed myself if I have to.

Pics will come soon I hope and I won't start pulling major things apartI or cutting anything till I see if someone needs anything.

 

[wreckerman893]

Will this be a bob job?

If you decide you want a M105 bed I have one that has been sand blasted and painted an OD green color.

I did some patching on it but it is a decent bed.
I put a flatbed on my bobber instead of this bed.

 

[MWMULES]

If you weren't 10 hours away I would swap, Fire service cut mine down to a flat bed.

 

[tamangel]

for those of you unaware of Clifford Research along with a few others:

Clifford Performance :: Make 6 = 8

Langdon's Stovebolt

Six Banger Parts High Performance Six Cylinder Engine Parts & Speedshop

and maybe these books:

Amazon.com: How to Hop up Chevrolet & GMC Engines (9781931128070): Roger Huntington: Books

Amazon.com: Chevrolet Inline Six-Cylinder Power Manual (9781931128155): Leo Santucci: Books

any other links?

Mike

 

[XM 2742]

Hey Mule...............that bed looks kinda like somethin I may do but my 211 bed and your 135 bed would involve wheel well issues.

 

[tm america]

great info guys that hot rod motor would be awsome to see in a m135.what would you do for a torque convertor since running that carb setup with a big cam and ported head you will end up needing a higher stall convertor to make it all work .

 

[73m819]

B & M hydro. used to (may still do) make awesome T/Cs with unbelievable stall. they had them for about anything that you could think of to bolt together