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Posted By: ndounias 302 GMC engine - Mon Dec 30 2019 11:52 PM
I have started down the modernization road with my GMC 302, without the 'extreme' part. The engine is rebuilt with a bump in compression, lighter pistons, balanced assembly, mild cam, mild head porting, and full flow oiling conversion.
The modern part is the addition of HEI, and a FiTech EFI system on the factory 2 barrel (military) manifold. This will be backed up by a T5 overdrive manual transmission, and a 3:38 diff, and all of this under a '53 GMC panel truck.
As it is yet to run, I can't say how it will perform, but I expect a world of difference from stock!
The goal was to make this set up be as smooth, reliable, economical, and powerful as possible without the very specialized work you are planning on doing. I plan to drive the heck out of this truck, and reliability is paramount!

I collect vintage motorcycles, and sell insurance for vintage vehicles, so this truck will transport me to shows all over the West Coast, serving as my transportation, as well as a way to haul my bikes and booth to shows. Looking forward to it!
Posted By: Tiny Re: 302 GMC engine - Tue Dec 31 2019 01:14 AM
This was piggybacked on a swap meet thread. Had nothing to do with the thread.
Posted By: Bogart's Truck Re: 302 GMC engine - Tue Dec 31 2019 01:30 AM
Sounds cool! Let us know how she performs!
Posted By: 52Carl Re: 302 GMC engine - Tue Dec 31 2019 01:40 AM
I suspect that you will spend very little time in 5th gear/overdrive with the 3.38 rear gears. What size tires are you going to run? Shorter tires will make overdrive more usable.
If you haven't selected your T-5 yet, I would suggest the .86 to 1 version. This would work better with your 3.38 gears than the .72 to 1 T-5.
Carl
Posted By: TrknGMC Re: 302 GMC engine - Tue Dec 31 2019 02:36 AM
I don’t have experience with the 3:38 gears, I do have experience with the 3:55z

I’m running a 302, with Pertronix, dual Zeniths, and a Truckstell .73 overdrive, with Patrick’s 3:55 gears, and 16 inch tires. It does very well and I use overdrive often. This set up in the 45 Art Deco GMC does very well. I’m confident your 302 can handle the 3:38 in overdrive. Log some miles for yourself and then adjust if necessary.
Posted By: coilover Re: 302 GMC engine - Tue Dec 31 2019 05:46 PM
I am very interested in your FiTech install. We have used the FiTech on a number of V8's including replacing the factory system on LS engines. I've been waiting for a customer to request one and figured we would have to get a 4bbl intake for a 235/261 and then use a four to two barrel adapter. Your 302 is already there. GMC's were often worked hard and were in the 10-12 mpg range and maybe 13 or 14 for an unloaded highway pickup so mileage with the FiTech will be of interest. Keep us posted!
Posted By: 52Carl Re: 302 GMC engine - Wed Jan 01 2020 10:52 PM
I missed the part about the FiTech. If that system has the sensors and a computer which will continuously adjust fuel delivery rate efficiently at all RPM, the 3.38 rear gears may not be much of an issue for performance and efficiency. I would suspect that with the 3.38 gears, you will not be able to pull stumps in 1st gear however, but you can't have everything I guess.
Posted By: coilover Re: 302 GMC engine - Thu Jan 02 2020 03:43 AM
With a spiced up 302 and loaded with a bike you will HAVE to have a World Class T5. We have a pile of broken regular T5's from behind V8's with sticky tires. If shifter position is not a factor the WC ones for Mustangs are easier to find and easy to adapt. Seems you allotted sufficient funds for the build so you might check out the TKO 500, a 5sp that will take everything your 302 can dish out.
Posted By: Tiny Re: 302 GMC engine - Fri Jan 03 2020 12:32 AM
The OP hasn't been on site since the first post. Don't expect a lot from this thread.
Posted By: ndounias Re: 302 GMC engine - Mon Jan 06 2020 07:52 PM
Tiny, I am not too familiar with these threads, so if I did something wrong I apologize.
Thanks!
Posted By: ndounias Re: 302 GMC engine - Mon Jan 06 2020 07:55 PM
The T 5 is already installed and is a .72. We will just have to see how it works out. Tires have not been purchased so I may have some wiggle room.
Posted By: ndounias Re: 302 GMC engine - Mon Jan 06 2020 07:57 PM
Coilover, I have friends that have used the FiTech with good results. I hope for the same, and will let you know what happens.
Posted By: ndounias Re: 302 GMC engine - Mon Jan 06 2020 08:13 PM
52Carl, you are absolutely right, there is always give and take with these builds.
I had a '54 Chevy 3/4 ton some years back that I drove the heck out of. With a speed of 55 mph that engine was spinning way faster than was comfortable. The Granny Gear low on that truck was great for pulling stumps, as you said, but was pretty useless for my daily driver. The hope is that this transmission compromise will allow me the opportunity to use the truck as more of a highway cruiser as opposed to a tractor.If it doesn't work as I hope, I will have to make changes. My fingers are crossed!

Also Coilover suggested that a World Class T5 was the way to go. That is what I installed in the truck. I have the early tail shaft housing on the WC trans to get the shifter in the right location, and can set up the mechanical Speedo down the road.

More questions than answers, but it is still exciting to be getting close to having a runner!

I have attempted to add a photo of my panel. If you can access it, we have a '53 with a '54 front clip on it. It's ugly as sin, but a solid truck.

Attached picture 1953 GMC.JPG
Posted By: TrknGMC Re: 302 GMC engine - Tue Jan 07 2020 01:50 AM
Great looking Jimmy!
Posted By: 52Carl Re: 302 GMC engine - Tue Jan 07 2020 03:01 AM
That is the kind of ugly I prefer! You won't have to worry about belt buckles, kids with ice cream, or greasy finger prints.
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