Splayed 4 Bolt mains or 2 Bolt???

My machine work is going to be getting done pretty soon on my 383 and I have to decide whether or not I want to have the main caps splayed and converted to 4 bolt. The money isnt rally a big deal but I plan on running a decent amount of N20 roughly 200 if not a little more. But compared to reliability and longevity the 4 bolt should hold together alot longer right?


thanks,
-john

I checked around and it was not the extra bolts that made me do the converion then it was to have better caps ;)

I had the same delima when I did mine. I went ahead with the splayed caps for added insurance and peace of mind.

A 383 with a 200shot might as well have the caps done. Splayed and standard 4 bolt caps will both work well. They both has plusses and minuses when it comes to installing them and how they work, but either one would do.

Bret

A 383 with a 200shot might as well have the caps done. Splayed and standard 4 bolt caps will both work well. They both has plusses and minuses when it comes to installing them and how they work, but either one would do.

Bret



Thanks bret, which would u reccomend, for the most part, which have the least chance of being messed up when being machined? What are the pros and cons of both?


thanks again,
-john

I do not have recomendation but I WILL say i would NOT buy them from Flatlander racing ;)

My machine work is going to be getting done pretty soon on my 383 and I have to decide whether or not I want to have the main caps splayed and converted to 4 bolt. The money isnt rally a big deal but I plan on running a decent amount of N20 roughly 200 if not a little more. But compared to reliability and longevity the 4 bolt should hold together alot longer right?


thanks,
-john

If you plan on making some power and spraying 200 I would definitely do the splayed caps. The stock 2 bolt caps will only take you so far and then you will spin a main.

I am going with the Pro-Gram 4 bolt billet splayeds. I spoke with them and they gave me a couple of part numbers to choose from. Email me if you want the info.

If you decide to have it converted to the splayed caps, make sure and do it before the bore work. It will load the block slightly different.

So far as the stock 2-bolts, I have done a couple 383's with nothing more than adding main studs. They are spraying 200-300 shots on pump gas with no ill's (one for the past 5 years).

I am one of the guys who likes straight 4-bolt mains on stock blocks due to the ease of machining and the lack of any definite benefit of the splayed caps in that use. A Bowtie or aftermarket block has webs specifically designed for splayed caps. Production blocks are designed for straight caps. Either will be fine. In fact, the stock 2-bolt caps are pretty sturdy if installed with studs. But once the engine is disassembled and needing machining anyway, now is the time to upgrade.

Rich

I am going with the Pro-Gram 4 bolt billet splayeds. I spoke with them and they gave me a couple of part numbers to choose from. Email me if you want the info.

That is what I was told I would get. When they got here they were CAT. All three of the caps were machined differently and in the end It would have been cheaper to spend the extra money and get a quality part. Now I am not saying the Cat caps were not usable...but I spent an Extra $150 to get them into shape. This does not even cover they had NO clue What side bolts I should get. I had to call ARP and have them look into it. ARP was a great help BTW. Good people. The bolts and washers were like and extra $30 shipped

This just my experiance but things like this leave a bad taste in your mouth.

Thanks bret, which would u reccomend, for the most part, which have the least chance of being messed up when being machined? What are the pros and cons of both?


thanks again,
-john

John,

4 Bolt Straight Flat Bottom (http://www.pro-gram.com/images/products/SB350CFS4.gif)
4 Bolt Splayed Stepped Bottom (http://www.pro-gram.com/images/products/SBCSA2.gif)

That's the preffered way to go about both of these caps IMHO. You can do a flat bottom splayed (http://www.pro-gram.com/images/products/sbcfa.gif) and a straight stepped cap (http://www.pro-gram.com/images/products/SB350CSS2.gif) but I don't think those are the right ways to go in production blocks.

The straight flat bottomed caps like Rich said are more production block oriented. The big thing that I see as a benefit of them is that you have a larger area to register the cap and you can cut that area yourself and control the width and make sure it is level side to side.

A 2 bolt setup will sometimes leave the cap register that is cut into the block unequal side to side. I just worked on one recently where the step was .119 on one side and .121 on the other pretty much all the way down the block. If you go to a 4 bolt then you have to widen the cap register in the block (well you should, you can run a straight stepped 4 bolt cap but that's not the best idea IMHO) The problem is that you have to make sure you cut the caps to fit the block, rather than the block to the caps to get a good press fit on the caps. If you mess up you can always weld the caps back up and remachine them, it's just lots of fun.

A splayed setup is based off of a 2 bolt cap register which can have unequal sides like I said above. The problem that gives you is that the step in the cap has to account for the miss matched step in the block. Plus there is a clearance that is needed between the stepped part of the cap and the block so you have to make that equal side to side. This gets fun when you have to line hone the block and one cap is coming out to size faster than the others so you have to chase more things when you do this. A straight cap has a lot of advantages during the line hone. The splayed cap is also fun because the outer bolts will change the clearances and main bearing journal size.

I'm a big fan of Olivers Main caps. The Pro Gram caps are nice but since they lack the flat surface on top of them they are a PITA to work with on a surface grinder. Going and blueprinting the rear cap to make sure the thrust face where the bearing sits is perpendicular to the block face is always a dam good idea if you care about your thrust clearances. I also like to make sure the washer faces of the caps are parallel to the block face so they clamp on the caps equally. I get a little carried away with main caps on motors, but they are just easier to 100% right the first time.

Bret

Bret: very informative post! It illustrates one of the many subtleties involved in engine building.

Have anyone ever seen any data that actually shows a measureable difference in the strength of a splayed v. a straight bolt configuration on a production block? How would that be tested? I am having a hard time visualizing a test procedure.

Rich

Rich I thought you had a rant about that here? ;-)

Got me on how it would be tested too.

Bret

I've ran 2 bolt mains on my 383 for 10,000 hard miles with no problems. Most of the guys I know spin the rod bearing as opposed to the main bearing but that just might be a coincidence.

Nothing wrong with going to 4 bolt splayed mains. I would do it if I did a big nitrous shot or a blower on my 383.

Bret: very informative post! It illustrates one of the many subtleties involved in engine building.

Have anyone ever seen any data that actually shows a measureable difference in the strength of a splayed v. a straight bolt configuration on a production block? How would that be tested? I am having a hard time visualizing a test procedure.

Rich

I have seen more out of round and housing bore problems after teardown on the straight VS the splayed even on production blocks but it's hardly enough of a sample size to qualify as a scientific test! The splayed cap obviously has more resistance to paralellograming since it has a horizontal component of force resisting the caps pulling away from the registers. Also even Chevy's new sportsman blocks in cast iron caps are now splayed. No more straight caps.

Iron Chevy older bowtie straight capped motors are known to break the caps pretty regualrly in mud truck and NOS engines whereas these sportsmans are supposed to handle it with their new caps. Of course these are pupose built blocks with the cap design built into them instead of stock with it added later on.

Buy some quality aftermarket 2-bolt caps and use ARP studs... Then let it eat!

Buy some quality aftermarket 2-bolt caps and use ARP studs... Then let it eat!

You still have to fit the caps for press fit, line bore and line hone the block then? I don't get it, go thru all of that and miss the benefits of a 4 bolt.

Bret

You still have to fit the caps for press fit, line bore and line hone the block then? I don't get it, go thru all of that and miss the benefits of a 4 bolt.

Bret

Yes I agree with Bret! Why do all that when its almost the same to do the 4 bolts?

Then just stud the mains and be done with it.. If you buy the 4-bolt mains then you are gonna have to pay more money for a machine shop to do that as well..