4 bolt main or is 2 bolt suffficient

[Guest Jeff Rimmer]

I'm probably doing my whole project backwords, by buildingmy engine first, however, I have had this 350 2 bolt main for two years. So finally I stripped it down and had hopped to get a stroker kit from Summit for it. It has already been bored .003 over. But the more I read up on conversions, the more I realise many of people have chosen a 4 bolt main over a 2bolt.

 

Should I forget about th block I have and seek out a 4 bolt? What are its adavantages?

 

Thanks again for your input, these forums are great!

[pparaska]

The general advice that I've heard says that unless you are going for much over 400 hp, a 2 bolt setup is fine.

 

The next issue is that there are different "4-bolts". The Chevy 4-bolt block has 4-bolt caps on the center 3 main caps, but the bolts are all parallel to each other. Supposedly, the best way to have 4-bolt main caps is to get a set of aftermarket "splayed" 4-bolt caps and have the 2-bolt block drilled and tapped for the new caps, as the outer bolts go into a beefier area of the block.

 

I don't know if I'd go to that expense on a block that's already bored 0.030" over (is that what you meant?) unless it didn't need any more boring and the clean up hone would not stretch it to the point that new 0.030" pistons would not be a good fit. That may take the bores over the allowed tolerance for the pistons. I don't know if it matters for your application, but some people don't think it's a good idea to bore a 350 block more than 0.030" over if you are trying to get a bunch (450+) hp out of it. The cylinder walls can get thin and start moving around under high hp loads. If you get the block sonic tested, the shop can tell you if it has enough cylinder wall thickness in all areas to be bored to actually be able to handle the overbore without having the walls too thin.

 

Whatever block you get, I'd suggest getting it fully magnafluxed and the cooling jackets pressure tested as well. No sense spending that 2-to-4 bolt conversion money unless you know the block is in very good shape.

 

Hope that helps.

 

What's the consensus here on a overbore greater than 0.040" on the various 350 blocks?

[Sumo]

I've seen a couple 350 of engines including a ford 302 that were bored .040 over that was used for street only application and the biggest problem was overheating. But I've also seen a lot using the same bore for strip only and never had a problem.

The way I look at it 4 bolt : street, strip, towing , nitrous, "bragging rites"( i got a 4 bolt main,...blah!blah!) purposes

2 bolt good for street unless you abuse it then it is only good for a boat anchor.

[pparaska]

Sumo, I agree. For street duty, most old timers I've talked to seem to think 2 bolt is fine. That's what I have, but my engine will probably never see the high side of 375hp.

[Guest Anonymous]

I'm not sure going over .040 on a 350 is all that healthy. The older smaller blocks (i.e. 283's and probably 327's) could handle a little more overbore. I'd seen 283's taken to .060 before, but it was'nt something that was gonna last a long time I can guarantee that. 4 Bolt blocks are plentiful and just for insurance if I was building a 350 and had to get a block, I'd use a 4 bolt.

An interesting side note is another combination I've seen on the net somewhere and one that I was'nt familiar with was a destroked 400 motor. Uses a large journal 327 crank (and needs bearing cap spacers) and 6" rods in the 400 block for 348 C.I. . Why bother you ask, well it supposedly RPM's like crazy and has much more top end than the popular 383 stroker (no knock on those from me either, they put out big block HP for their size). I would think the 4 bolt splayed mains would be in order for that destroked motor if it is possible in a 400 block. Oh well, rambling here, but just wanted to toss that out there..

 

Regards,

 

Lone

[Guest Jeff Rimmer]

I probably should've included more detail of the engine.

 

When stripped it out, it had really bad bearing wear, the rod bearings had been worn down to their, I believe its copper, centers. Main bearings were fine. Apparently it was burning oil. They had bee nrunning an edelbrock performer rpm intake and cam, which I inherited along with the engine, and a 750 cfm edelbrock carb, and a crane cams ignition system. It was the

midas company truck, so it saw some hard driving...

 

The block itself looks good, It had 185 - 190 psi compression in each cylinder, which I gather for a 350 that isn't too shabby. It had been bored and rebuilt a year before I got it, which makes me wonder how well it was rebuilt due to the wear and tear on the bearings.

 

Never the less I think I will get it sonic tested as suggested, that sounds like it would be the best course of action.

 

Getting it drilled and tapped out for a 4 bolt setup sounds like a worth while investment. I had planned on purchasing the 383 stoker kit, but I'm not sure on its effect with a carburated setup.

 

Which brings me to yet another quetion, Have any of you purchased and used the Summit stroker kit with a carburated setup?

 

Thanks

 

Jeff Rimmer

[BLKMGK]

FWIW - my block is 2bolts an dit'll be pushing 450hp. Frankly, I'm NOT worried. It won't see high RPM and unless I really abuse it I don't expect to see it come apart. 4bolt factory blocks are overrated but the 4bolt conversion is better if you can afford to have it done. It'll need line boring and whatnot afterwards, my machine shop didn't think it was needed.

[Guest Drewz]

2 or 4 bolt nothing replaces a proper machine job on all the parts to be used. Do it properly the first time and you will have fewer problems on the horizon.(hopefully) HEY, not all Midas guys bag their vehicles. (I manage one HEH HEH!!!)I do!! My buddies vette ended up having a 2 bolt and he drove it to the nuts with a major cam, heads, and BG carb. 3 hard as hell years and little wear on the bottom end. This block now is in my 260. IMO as always.

 

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The only stupid question is one you wanted to ask but never did!!!

 

Drewz