Originally Posted by Fiat48 View Post
I want to enter this food for thought.
What do 4 bolts do for the main cap? Do they keep the main cap from walking? No. Maybe they help if splayed but they dont help with straight.
Using main studs does not stop the main caps from walking either.
Since I never saw a bbc main cap actually break....I have to wonder what converting to 4 bolt caps really does for me? Is it possible this is more cosmetic than structural?
I understand the resale value of a 2 bolt engine vs a 4 bolt. And for that reason alone would not consider sinking a bunch of money in a 2 bolt motor.
But if the main caps are walking around....transferring metal from one surface to another and changing the dimensions of my critical line hone....I have to ask myself what am I solving (except for etticut) by going to 4 bolt caps?
Would it not be better to dowel pin the caps? How about a girdle?
These are questions in my mind and have been for many many years. What I have seen is the more hp....the more the caps walk regardless. Perhaps shortly I will have a little more data. My current engine runs high rpm and is splayed cap (but it is a Dart). Now that it has run 3 seasons it will come apart
and be inspected.
Also a 427 was fitted with a girdle and it has been run hard all season and it will come apart also for inspection. Maybe some data there.
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We were doing 4-bolt conversions 25 years ago. To help answer Fiat's questions here is what I have learned, having done hundreds of line-hones on the CK10. Main caps stretch first, then start moving around due to lack of "squeeze" from the lips in the side of the block mating surface. It is readily visible when you grind the caps for line-hone.Just like big end egging on connecting rods.
Some blocks actually get weaker from drilling the outer holes in the web area.
Short of buying after market, quality blocks, I liked using good aftermarket steel caps, splayed outer bolts that were smaller dia. then the inner long ones. That left more material in the block. Then dowel the inner holes. Course I had access to bridgeports and Sunnen machines so labor never factored in. I could take as long as I needed fitting them as close as possible and matching before actually honing it.
Its all to try to reduce cap stretch. That leads to all the walking and moving.
I also would not consider doing it and using straight Chevy caps. Not worth in IMHO.
The biggest improvement doing this is on 400 small blocks. The 4-bolt 400 has almost no material in the saddle area. A 2-bolt 400 block w/ splayed steel 4-bolt cap conversion was always in better shape after races.
If your assembly isn't correctly balanced by some one who knows right from almost right, none of it matters anyway. That is where to spend the money.
I have no proof other than my own experiences and certainly don't claim to be the guru on this. Just my .02
If someone's entertaining the conversion (worth it or not) make sure the machine shop knows what they are doing. I had it done by REX Racing Engines in Sacramento and they ended up raiseing my crank .020 closer to the cam. Chains dont come in .020 so you need a gear drive with smaller idlers. It was a big surprise when my new motor blew in short order, I tore it down and found a sloppy IWIS chain...
Good god, what a nightmare.
Fiat,
Have you found out anything interesting about the Dart and the 427 w/the girdle once you cracked them open??
Just wondered.
DaveA
Finally able to inspect my own motor. Here's the Dart:
http://www.***boat.com/image_center/...0/SUC50213.JPG
http://www.***boat.com/image_center/...0/SUC50211.JPG
http://www.***boat.com/image_center/...0/SUC50212.JPG
I can't tell you how many times this thing has seen 8500 + rpm. So I am pleased at how it looks.
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