splayed 4-bolt mains
We just picked up a good 1964 truck engine and we're thinking of using the block for a race only engine. I've been thinking that billet 4 bolt main caps might be a good idea but I'm wondering if they're really necessary? The engine will likely have a 4" stroke and about 13 to 1 compression. It'll be naturally aspirated and be shifted at less than 7,000rpm.
I notice that Lamar Walden likes to use billet caps, then bore the mains out to Big Block Chevy size. He also leaves the crank snout at BBC size and uses a special front cover with a BBC sized seal. If we did go with the billet caps do you think this might be the way to go?
Also I remember someone saying that Eagle was coming out with a 4" stroke crank for the 409. Does anybody know if they're available yet?
I'd appreciate any opinions or suggestions.
My 482 has splayed 4-bolt mains -- not the straight-bolt 4-bolts. One minor problem I ran into was in the clearances for the 3 center mains (the end mains remain stock), with the custom made STEF's oil-pan I'm running. The scrapper screen had to be very slightly notched up near the passenger-side oil-pan rail.
My compression ratio calculated out to 11.3 (bored the truck-block out .060"), with the crank's main journals also remaining stock 409, with the SBC snout diameter. IMO, staying with the 409-sized journals mandated it sensible to use the 4-bolt mains (straight or splayed). I used ARP BBC main studs for the inner bolts, and ARP bolts for the 3 splayed pairs. My 583 heads are also held by ARP studs, not bolts.
I've previously had and ran a stout 468 c.i. BBC roller-motor with stock 2-bolt mains, without any problems what-so-ever. I was advised that so long as I stayed below 700 h.p, I'd have no problems. Although not ever dynoed that engine-combo was designed to be providing a very concervative 550 h.p. The engine was not babied by me in the slightest way, and when later disassembled, the crank journals and bearing wear remained unmolested, and line bore also remained dead-on. I easily sold the disassembled engine for top dollar.
Given your level of expected compression ratio, and the focus on racing only, IMO, you should at the very least, go with 4-bolt mains with a stock 409 diameter journal, and not a bad idea to go to BBC journal sizing. It can't hurt. However, I'm not sure about how ovrboring would effect the strenght of stock 409 end journals, or even if 4-bolt end journals are even easily available.
Also, if using a billet aluminum timing cover, whether with a SBC, or BBC sized snout seal, a problem can also emerge with the front oil-pan rail groove sealing area -- that is, IF you also go with an aluminum oil-pan (STEF's). I tried going with a billet timing cover mounted to a STEF's oil-pan, and the extent of the needed further modification to the timing cover, combined with the accompanying necessity for dealing with the lacking clearances for mounting the water-pump, forced my decision to go with a stock timing cover.
The significantly thicker billet timing cover would have necessitated shimming out the WP legs 1/4" (3/16' shim, plus two extra gaskets), the crank pulley, 1/4", and on to having to diddle with also shimming/adjusting the alternator, and/or A/C compressor 1/4" forward. One solution could have been to notch my billet cover, and maybe even slightly notch the WP (if I used the Rejeski pump I also have -- but, that would have been the easy part. The real problem was, again, the front STEF's oil-pan & timing cover seal interface. I believe that problem would not have necessarily existed if I were able to use a stock 409 oil-pan though.
I hope this helps with your decisions.
Denis