Blown Olds 425

[2Loose]

Here's a project I've been slowly putting together for some time now, it's a work of love and if I never get to run it, that's ok!
My Dad was an Olds mechanic off and on most of his life. He had a '49 Olds he picked up in '51 and was constantly working on that motor to get more power out of it! Later it was a '57 Olds with a reworked 371 and the J2 (triple two barrels) option.

When my three kids were growing up I had a couple of big old Olds gunboats, they were cheap, dependable, roomy, great beach cars, full of sand, surfboards, fins and masks, towels, ice chests, my kids and half the neighborhood, rolling party wagons heading to the beach, kid style....
I paid $50 for this '67 Delta 88 4 dr with a 425 and th400, got several years of beach cruising use out of it and then parked it in my Olds junkyard:

When I finally parted it out and pulled apart the 425 motor in it, I found a forged (oem) crank and forged 7” rods in it. The motor stock is 4.125” x 3.975” bore and stroke. According to my Dad, this motor was known to easily and consistently do 7,000 rpm with the right valve train parts in it, and that was back in the 60’s….
I bored it to 4.155”, decked it just enough to square and smooth it, had the crank reconditioned and polished, the rods beam polished and shot peened, got some JE 8:1 forged pistons, a reconditioned Don Hampton 6-71 blower set up for Olds, a girdle for the bottom end, and started putting it together.

This block is a 2 bolt main, so the main caps were machined for this girdle, the five pan bolt holes on each side were re-tapped to 3/8”, and the girdle was fitted to tie the mains together and also to the block pan rails.
A pair of Edelbrock RPM Performer heads were conservatively ported for this setup, just to smooth out the flow and eliminate some obstructions:

Some health problems have slowed me down on this project, and a cam has not been selected as yet. My next step is to file fit the rings and get the pistons in there, by then I’ll have decided on a cam. I’ve talked to several cam manufacturers about a mild street blower cam, it seems most are recommending a fairly wide cam lobe separation, like 115 deg.
Just what I will end up putting this motor into had not been decided. I do have a pretty ratty ’55 that it would be fun to make into a gasser, but that has not been decided.
Something like this maybe? In black primer?:

I found a pair of used race demon 625's set up for a blower app (see first pix) on the internet, and an MSD distributor and ignition box, so I have most of what I need to put this together and get it running.
More later….
Aloha,
Willy

 

[grumpyvette]

anytime you get into a super charger on an engine the tendency is to use a wide 112-116 LSA it is there simply to prevent a large overlap, in the cam timing that would result in much of the intake charge swirling in the intake and out the exhaust durring the overlap when both valves were open at some rpm ranges, and at least some of the intake charge is likely to exit thru the exhaust during the intake stroke on performance cams with thier higher duration all the time if the LSA was tighter like a 105-108 LSA

viewtopic.php?f=52&t=480

Ive only built a few olds engines, I build mostly buicks, pontiacs,caddys and lots of mopar engines when IM not working on chevys
personally I prefer 400,421,428,455 pontiacs and early 392 hemis over most of the others

 

[2Loose]

My guess is that it would not be so critical with shorter duration cams, but as the duration goes up and the overlap increases, this "blow-thru" effect gets worse. Probably mapping out the duration and looking at the actual amount of overlap would determine how much lobe separation would be desireable. A daily driver on the street versus a strip only machine would also factor into the decision I would suspect.

When you see a blown race car with lots of flame coming out the pipes, in some cases it's gotta be fuel blowing thru to the exhaust due to the overlap then igniting as it exits. It sure is spectacular in some cases!!!