Inliners International Forums General Discussion Engines gmc 302

first time posting. but i have watched from a far and have learned a great deal and thanks to all a lot i have learned here. i have used to do a 261.

but now i will be doing some plans on a 302 gmc. but i have some questions what years of block are the best base to start with ?

the next is the head. what is the best head to get a hold of ?? i have heard some talk on inliners of a D head what is that ??

how about cranks i have heard they have a soft crank did they ever use a steal crank ?

i am looking to build a 302 for the street that will leave some v8 things thinking holly cow !

thanks again

All 302 engines are more or less the same.The D head was the original head on all 302's,it has a D shaped combustion chamber similar to V-8's of the same time period.All 302 cranks are forged steel,they were induction hardened for surface strength at time of manafacture.Turning the crank for oversize bearings removes the hardness,but it doesn't seem to matter for the way guys use these engines today.
A moderately tuned 302,hotter cam,more carburation,higher compression,headers,etc,will make around 225 hp,more money spent on some headwork will give 250 hp for a streetable engine.There are all out race 302's making fantastic power,but they aren't streetable.
These engines are expensive to build properly,a liitle more power costs a lot of money.
I have a built 302 in my 37 Chevy pu,the estimated 240 hp moves this 3000 lbs truck quite nicely.It gives fits to the kids in their stock 90's V-8 Mustangs,and the torque will surprise sleepy drivers in 350 hp Camaros.But once they wake up and wind up the engine,they do pull away.
302's are vintage engines and for street use are somewhat RPM limited,but are the best vintage inline engine.
If you wanna get serious,I believe a 292 Chevy can make more power for less money.

The best block "to start with" is the one you can find that is not cracked or otherwise damaged. Use the "Casting #'s" link on this page to see the numbers that identify 302 blocks. "Military" blocks may be somewhat more readily available. They require an electric fuel pump and some grinding on the passenger side of block so a starter can be installed.

Some "late" 302s were produced with a "small-port" head; you will likely want the earlier head with larger (1.75-inch) ports. A large-port 270-H head will bolt to the 302 block, but will require pistons different from those used with the 302 head.

The 302's great strength is low- and mid-range torque. My "streetable" 320 cid 302 ran in at 265 hp at 4390 rpm and 362 ft-lbs of torque at 3065 rpm. i think that the GMC can be made to run with any engine of its time--the 1950s--in a full-bodied automobile. Gearing and weight and other factors will enter into that equation. If you plan to run above 5000 rpm, you should have the best vibration damper you can afford.

As the brother says, these engines are expensive to build. Do not skimp on the machine work or the assembly.

If you seek now to replicate what could have been done in the 1950s, the 302 is an excellent inline choice, and few of its competitors in that time can match it. If you want to make the most power and rpm that you can make with an inline, then the later Chevrolet 292 or the Ford 300 are wiser choices--but they will always be more expensive than a modern "crate motor" and will be hard put to make more power.

God's Peace to you.

d
Inliner #1450

I've been building 302's for over 30 years. A stock one puts out 160 HP. As others stated they are expensive to build. (Try a Ford Flathead)
A good cylinder head is a must. Seats in the head can be changed. Chev V8 valves work great. Any of the cam grinders can come up with the right springs and retainers. Don't kill the cam/lifters with a lot of spring pressure.
You can make it think is a Chevrolet V8 with an adapter from Buffalo Enterprises. Then the starter is no longer a problem with the block. A good cam grinder can put a RV style grind on a stock cast iron cam. You will need a steel core for a bigger one.
The stock rods can take 5000 RPM forever with a little massaging. High compression pistons are bulky and heavy with the stock 7" rods. I think Ross has them on the shelf. An old set of high compression cast pistons would be great for the street and the are much lighter.
You can take up to .100" off the head if you like but I would not do it for the street.
Old intake manifolds come on E-bay every so often and Clifford Research lists a 4-barrel. Any 194-292 manifold can be worked to fit. My LSR roadster has one I did 10 years ago.
Nicson cast iron repop exhaust manifolds are listed in the 12 Port News..

Good Luck-Have Fun and they definately turn heads at a cruise..JD

thanks guys

if it was easy to do it wont be worth doing !

the search for parts, the learning, the being able to say i did something different that no one else has done. and meeting and BS along the journey to the goal to get there.

thanks for the tips !

292 just wont look right in a 48 gmc, so i will pass on that !
plus i searched high and low and long for a three carb harper intake and that wont fit a 292 !

my intake is my starting point.

when i did my 261 i had to watch for different cranks and cams because things changed from year to year which maid somethings very hard to find !

did all things on the gmc 302 interchange threw the years ?? cams, cranks and internal parts ??

i know a place that has about 15 military trucks with 302s in them so at this point that is what i am going to wind up with. which is probable be better less chance of be totally wore out. are the cranks the same in these motors ? because i hear the fly wheels are diffent in these trucks ?

what is a good way to stroke one of this 302s for a little more cubic inches ? i have read they can be taken out to a 341 ! any clues for a starting point would be helpful!!

my goal is a some were between mild and wild ! i have been collecting parts. i have a mini hei. the three carb intake. fenton headers and some other small parts. but the search for a block and head starts now !

thanks guys

Don,No 302's were produced by GMC with any other head than the large port D type.