Jason,I may have overstated using "bogus",lol.Here's what I found,like I mentioned,the actual rocker arm ratio is 1.4 not 1.5,so keep that in mind when choosing a cam cause all the cam grinders think it's 1.5.I measured the lift at the lobe and at the valve with corrected rocker arm geometry.So I had a cam ground with more lobe lift to make up for it.
I also noticed the stock oil pick up tube is a smaller diameter than the pressure feed tube of the pump.Just about every other engine design has a larger pick up tube than the feed side of the oil pump.I modified a small block Chevy pick up tube,it's larger than the stock GMC item.The 90 degree fitting on the feed side of the pump is restrictive,I bored out the diameter as much as I dared, better yet would be to throw away the sharp 90 degree fitting,and use a larger radius fitting.Same goes for oil lines on a full flow filter,avoid any fittings with sharp turns.Each sharp angle fitting reduces oil pressure by a few PSI, add em all up and you loose 10 psi.You can jack up the pump relief valve spring,but that just takes more power,and may overload the drive gear and heat up the oil.
Quality bearings were another problem,I searched quite a while to find genuine Clevite 77 main sets.The only readily available bearings are Federal Mogul CP's made in Mexico.The are supposed to be a good bearing, but I wasn't satisfied with the bearing crush,the Clevites were much better.
The factory machining on this standard bore block was horrible,the bores weren't straight,the block deck wasn't parallel to the crank,but the crank bores were right on.The machinist had to mill the block at a angle to get it straight,The bore problem was solved by properly boring the cylinders on true centers.
The Crankshaft was standard and smooth,but the throws were off and the factory had cut the crank slightly undersize.I didn't want to cut the crank at all cause you loose the hardening,but I compromised with a .010 cut, and trued up the crank throw indexing as much as possible.The connecting rod bores were off as much as .010.Took care of that by rebushing the small ends for .990 Chevy big block V-8 wrist pins,offsetting the bushing bores to get all the rods the same length.
I'm not vendor bashing here, but both Arias and Ross didn't seem interested in making me pistons.Venolia was interested and asked for a head combustion chamber mold so they could build a piston to fit my specs.And they were cheaper by 100 bucks.
All these little items do add up ,makes no sense to throw money at a performance engine unless you check every item and correct any problems.I mocked up the block,crank,rods and pistons several times at the machine shop to check clearances along the way.My machinist is careful,but it's my engine,I do my own assembly,it pays to be involved during the machining process.
I did these steps on the 261 I built for the truck 7 years ago and it had excellent power and was smooth,hopefully the GMC will run as well and the 3500 bucks I spent for machining and parts will be worth it.
And the long motor myth,in my case,the GMC 302 was the same lenght from the bellhousing mounts to the front of the fan as the Chevy 261 engine that was in the truck.The motor mount holes in the front crossmember will be moved forawd only 3/4 of an inch with a slight trimming of the corssmenber for oil pan clearance.
