can someone give me a idea how they make the gmc 302 into a 341 ?
is that even poi ssable ?

Bore it 0.125" and offset grind the crank for a 0.250 stroke increase.(engine will then be 4.125
bore and 4.250 stroke)

I'm building a 321 inch Jimmy now.

do you know if there using a stock rod and piston combination or custom built after market rods and pistons ?

what are you doing your self to come up with the 321 cubic inches ?

thanks for the tip ! i want to have a plan in place before i start

321" are .125 over bore from stock 4". Ross has pistons for GMCs. Arias takes a few weeks. If you offset grind the crank for the stroke increase and use the stock rod length of 7" the pin can move up 1.25 to help with piston weight. I have heard others using 300" Ford rods but I don't know their large end diameter or length. If they are smaller you may not need to weld up the crank.
You can call Doug Rodinson at Horsepower Engineering on Fulton St. in Pasadena Ca. I believe he used an off the shelf Oliver rod and off set grind for of his GMC's...Good Luck

Don't find an Horsepower Engineering or HP engineering in Pasadena-anyone have their number? Thanks,

Ed

Doug Robinson, Horsepower Engineering 47 Fulton Ave, Pasadena, Ca. 91107 626-440-0440

341 C.I. is a 4 1/8" x 4 1/4" engine.

Seeing this, I re-read Tom Langdon's article on how he built his 341 in the March/April 1991 issue of 12 Port News (Vol 11. Issue 2).

He used 400 C.I. SBC pistons (TRW#L-2477) with 55-60 Chrysler 6 rods (Fed Mogul #R-22DD) as they are 7.81" long, and used Continental 6 cyl industrial bearings (Vandervell #VPR91846), narrowing the rod and cap to 1.430", and honing the small to accept the Chev pin.

To use these rods, the crank is offset ground, from 2 5/16 (2.3127") to 2 1/16" (2.0625") thereby stroking the engine by 1/4".

Looking st more "contempory" rods, I note that SCAT makes BBC rods that have a 7.1" long, and have a big end size of 2.2" diameter. Not quite the 1/4" stroke that is required, but may well allow for lighter factory-type pistons to be used.

I hope this helps some-one out there.

I'm looking st building a 302" out of a 261 Chev block, using the 3/16" pop-up pistons I have with 292 rods, and stroking it to suit the pistons. I'll probably do this after I've worn out the engine using smaller pistons, making it a 302 on its last rebuild.

Don't you just love the possibilities of bore and stroke combinations when working on old engines???

Is there a single sorce of newer tec for these older sixes(270,302,etc)? A lot has been done and learned sence the books of the early '50s when the 302 was new. There is the Mopar rear seal thing,this rod/piston stuff,andthe offset crank grinding. There must be newer info about valves,springs and rockers. We need a Leo for these engines.

I don't think you will find a single source for everything. Every guy has his own way or does what he needs by using what's available.

Others will buy what they can and have the rest custom made and won't worry about the costs.

There are many piston manufacturers out there who will make exactly what you tell them. Others like Arias, Ross & Venolia (if they are still around) have the designs for all the combustion chambers and only need to know what rod length you will be using. Cunningham and Carillo will make rod you design it's only $$$$.

I've read 10 different ways to do a rear seal on this site and they all must have worked for some one.

Camshaft designs have changed along with springs, retainers and keepers. Most every head guy has his favorites.

For years I've heard "that will never work" and he's leading the pack. Best this is to read it all and gleen what you need for your application..Good Luck

JD, what valve springs would you recommend for a flat tappet reground cam for the GMC that has a lift of .613" and will be turbocharged?

No clue. My flat tappet has about the same lift, is naturally aspirated and I keep them under 100#. They are singles and have a 1.50" diameter. Cranes big chart and their tech line helped me. I will be upping it as I now have some roller tappets and looking to get a cam done. Remember I keep the RPM lower than most guys. Good Luck

What cam grind would be best on a supercharged 302? Use wuold be as a driver in a '53 1/2 ton,t-5,3:55 rear. I have a nos cam and several good cores. The plan is a close to stock build with a McCulloch.