New To Forum: 72' GMC Jimmy with a 302 'Jimmy' GMC Inline 6?

[Phil_Suppi]

Hello,
I am new to your forum and must say i appreciate the vast wealth of knowledge i've absorbed here. I am in search of some information myself...I appreciate any and all help with my inquiries.

I have a 1972 GMC Jimmy sporting factory 2wd suspension. There were very few of these trucks made, and it is near and dear to my heart. I'm 22 years old in the middle of a body off resto and plan to keep this truck for life.

I recently learned about the infamous GMC 302 'Jimmy' Inline 6 motor. I INSTANTLY began pondering this engine instead of a modern 6.0 LS engine. Here are my questions:

1) Obviously, the motor will have to be converted to an alternator setup for my purposes. Possible?

2) Does the 302 provide enough power/torque to move this truck (production weight supposedly 3375 pounds) effectively?

3) What transmissions originally bolted up to this engine? I'm thinking a TKO or T56 (with custom adapter kit obviously...)but if there is some kind of super cool weird transmission akin to these motors i could definitely appreciate its significance. I'm into different...

4) Does the 302 produce enough vacuum for power brakes, steering, etc? Use an electric vacuum booster?

5) Who hot rods 302's? Who can beef one up and HOPEFULLY fuel inject it?

6) What is a good price on a 302?

7) Where can i find a good 302?

8) Can a 302 be a reliable daily driver?

9) Fuel economy?

10) What needs to be done to bring a 302 into this century? (i'm not seeking a perfect motor,i know this engine isn't going to be similar to a newer type engine) I just want to make it drivable daily/reliably.

i'll have to contract one of the many fantastic fabricators on here to build a custom crossmember for the engine.

I know these are "noob" type questions, but i'm fascinated with keeping my GMC as "GMC" as possible. Everyone converts their Jimmy's to a Chevy Blazer.... I appreciate any and all help. I think a Jimmy with a Jimmy in it would be a cool, different, refreshing build.

Thanks in advance!
-Suppi

[Zeke's Garage]

Are you talking about the GMC 302 V6 engine? I'm not aware of a larger displacement inline, 292 was the biggest I've heard of.

I know I've seen a couple of sites around that discuss this engine, but they were mostly used for monster torque applications, such as big trucks and as pump engines for oil well rigs.

I'm sure someone will chime in soon and set us straight.

[cdowns]

GMC inline 302 was produced rom 52-60 they are in great demand by nostalga hotrodders and racers. can b made with obscene amounts of horsepower with a great deal of money invested. probally the most legendary is the crossflow WAYNE engineering conversions

i've heard of core engines going for $1000-$1500 the speed parts are just as pricy so expect to spend ALOT per horsepower built

check on www.inliners.org for info or just google the 302gmc inline 6 theres plenty of info on the web

[RichardJ]

The guys that really know those old GMC 6 cylinders are on http://www.oldgmctrucks.com/. Click on the "Discussion Boards". You have to log in.
There are some guys there that have hopped up the 302.

Obscene horsepower by '50s standards, maybe. High performance parts are only going to be found on forum message boards, ebay or custom machined.

If you want a high performance inline six, you can get a lot more power for a lot less money with a 292. There are many more sources of information and parts. The 67-72 trucks came with the 292 so you have a lot more to start with.

If you were building an older truck from the early '50s, '40s or '30s then the 302 would be a worthy addition and even period correct.

[RichardJ]

That may not have really answered your questions. Let me answer it this way. From the time the 302 is sitting on the ground next to your truck, every single part you touch will have to be hand fabricated.
An LSx installation would be easier and cheaper.

[glimmertwin01]

I say hop up a 250 like Kyull did...

[Big Port Jimmy 6]

I have a Hot 302 with a .125 over bore, lightweight venolia pop ups .500 lift cam with long duration, 3 two barrels on a high rise, cast header, and a cylinder head with over 40 hours of port work, .100 longer small block Chevy valves. It has been converted to a full flow oil filter set up etc. etc . Its a full on hi po jimmy. A small block with as much effort would easily make 400+hp, I will eat my hat if the 302 makes more than 250hp. A box stock 4.8 would give it a fair run, so imagine what a 6.0 would do to it. Its a Flat Head Killer, (100 hp stock on a flattie)it makes all the right noises, it gets all the looks wherever I go. I have a great time with it, but I wouldn't put it in your Jimmy.
If you want a six, build a 292, they came stock in it, they use a V8 bell housing so the trans issue is solved. Get the Santucci books. Join inliners.org You can make plenty of power and not go to effort and expense( I have approx $17-1900 in mine) that the early motor would require.
I have a spare 302 If you would like to come look at one or buy one. You can come and see the hot one and take a ride, If I can get the crochety old bastard to run. It dropped a cylinder before Christmas, either a rocker backed off or it ate a plug. PM me if you have any questions. Jay

[Big Port Jimmy 6]

One other thing, The 302s are a big bore (4") long stroke (4" stroke 7" rod) heavy engine, Fuel economy is not one of the virtues of these engines. They were made for torque to move loads in 2 ton and up trucks. You will only find them in big trucks or busses from 52-59. The quick rule of thumb is that the truck should have 20" wheels to be big enough. The first three digits on the pad beside the distributor on a GMC six is the displacement. Jay

[Phil_Suppi]

you guys have been a GREAT DEAL of help. I see the cons of this motor now. I'm still considering it, as i'm fascinated by the idea of a Jimmy with a Jimmy in it. I've never witnessed one with my own eyes. I understand the LS swap would make more power, but it seems somewhat of "generic" fix. Perhaps a 302 would be better suited to my 86' GMC S15 instead of the Jimmy.

Jay, I may take you up on your offer of a ride in the truck, if i decide to use a 302, i can tell you will be a great resource! Thanks for the info.

This forum and the people here are top notch!

[averagejimmie]

Stay away from the 302 for your application. The term you are looking for is "Stovebolt." It's an old school engine. That engine has the old draft tube over the modern (and less polluting) pcv valve GMC/Chevrolet 250 & 292 family of motors. You will get more from these latter two motors in the terms of real-world useability and cheaper horsepower. They are easier to maintain, modern parts swap capability, daily driving, etc.

The direct benefits for the more modern 250/292 are: Lighter weight engine; modern internals, pistons, cam, rockers, etc.; HEI ignition is an easy and clean swap; no swapping from generator to alternator; modern spin-on oil filter and it is period correct for your truck. Check out Stovebolt.com and stoveboltengineco.com.