LUVTruck.com

well, i have been debating this topic with some of my elders, and i am trying to convince them of something. i am pretty sure that a two bolt main block is stronger than a four blolt main block. why? because from what i have heard (from a few friends and jhon lingenfelter) is that four blot mains sheer the block in half, and take away metal from the block. i have heard that fords cross bolted mains on the fe blcks were the shit. id like to get some replys on this one, id really like some information.

4 bolt mains are stronger due to the larger surface area of the main caps vs 2 bolt. They will break more violently than a 2 bolt, but seem to hold up to more abuse and power than a 2 bolt. I have built a few engines, and have scattered a few. 4 bolts are definately stronger and better for more horse power.


Flame suit on.

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Hammer to fit, paint to match.
If it aint broke, don't fix it.
There's always room for duct tape and bailing wire.

WATCH YOUR PIEHOLE!!!!!!

i got a friend that has a 750 horse small block 406 in a 69 chevelle ss that swears by the 2 bolts. i also work for a guy who has been around the engine building buissiness for over 35 years and he agrees, i am not relly sure.

well both arguments are valid. The 2bolt main gives more untampered steel mass to the block and the caps. The 4bolt may well have more bolts but there is less steel there. I think they do hold up better in the long run (why eles would GM engineers decide 4bolt mains are the best motor for trucks (yes all GM truck motors a 4bolts). Me i dont like going realy fast of running lots of HP so i dont have any experience in this. But just looking at things i think more main bolts are better to an extent. Why eles would nissan take the time to engineer a 6bolt main engine

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1980 LUV 4x4, going under re-construction...

Let's put it this way, you can run 2-bolt and I'll run 4-bolt. Whomever grenades first is wrong.

as ben puts it simply...

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1980 LUV 4x4, going under re-construction...

only reason to buy a 2 bolt main is to have it drilled and tapped for splayed main caps! HA!

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03Cobra

As I was reading this post, I was thinking I recalled something about modding 2 bolt main blocks for stronger caps with splayed bolts. End up with the best of both designs plus some to boot.

Are 4 bolt main blocks that much stronger than 2 bolt main blocks?

A: Lets start with what a 2 and 4 bolt main is anyway. What holds your crankshaft in are main caps. These are what the crank bearings sit in and most engines have 5 caps. A 2 bolt cap is fastened to the block by 2 bolts and a 4 bolt cap has 4 bolts (2 on each side). Main caps are the only thing keeping your crank from falling out the bottom of your engine. When you increase the load on the crank, you inherently increase the load on the main caps. Any time you increase horsepower and torque, you increase crankshaft load. It would take quite a bit more stress to rip-out 4 bolts than it would just 2. This is the theory behind it anyway. I have never seen a crank get "blown-out of an engine, be it a 2 bolt or a 4 bolt main engine. I have seen engines "blow-up", leaving pieces of crank and engine block all over the track but it is usually due to metal fatigue and failure somewhere else and not the main caps blowing-off. I have also seen 2 bolt main engines in low budget race cars running 8 and 9 second et's that last season after season. The more compression an engine has, the more the crank is trying to be pushed out the bottom of the engine, especially when a blower or nitrous is used. A way to make a 2 bolt main block even stronger than a 4 bolt block is to use a "main support". This is a brace that bolts across all 5 main caps, thus tying them all together and sort of creating a 10 bolt main engine. The theory behind this is simple, if one main cap tries to come-off, it has to take all of the others with it at the same time. If you are going to be building a street engine that has 11:1 compression or less, then a 2 bolt main block would be just fine. Anything higher than 11:1, or if you are going to run nitrous or a blower, then I would recommend a 4 bolt block or a 2 bolt block with a main support just to be safe.Good answer Ben .... i scored a freebie, Listen to your elders.....they have been around longer than thou!!!!

This is the best way to go if you don't mind spending the cash.

Very enlighting answer John.

2 bolt mains can handle more HP than most people think anyway.

^^^ Yup i agree^^^ Two bolts can handle just as much HP as a 4 bolt. I have seen 800 hp 2 bolt main engines take a lot of abuse and 4 bolts take less. But generally 4 bolt mains are better.

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-1981 Chevy LUV, 283SBC, T350 Trans, White In Colour, Long Box, Never Ending Project!
-2001 F-350 Superduty XLT 7.3L Diesel Auto, Ext. Cab, Long Box, White In Colour
-1998 F-150 XL 4.2L V6 5spd , Reg. Cab, Flareside SB, Red In Colour

my 406 motor is a 2 bolt main. I spin it up to 7500 and push some medium size nitrous shots thru it. The fact that its a 2 bolt has never crossed my mind, I have complete confidence in it. I worry more about my factory "x" rods more than anything.

they may be able to hanlde the same amound of power in the short run but whant about the long run? I find it hard to beilieve that there isnt an upside to more main bolts when Nissan took the time to egineer the 6bolt main Endurance v-8 for the Titian.

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1980 LUV 4x4, going under re-construction...

My thoughts exactly MEPR. Why would they recommend a 4 bolt for truck applications, if a 2 bolt is just as good?

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Hammer to fit, paint to match.
If it aint broke, don't fix it.
There's always room for duct tape and bailing wire.

WATCH YOUR PIEHOLE!!!!!!

I really don't have a preference. I understand what you (MEPR and Grimace) are saying but, on that same track why aren't all ford rears 9". I don't think new and improved from the factory is necessarily better than what was done before. Who knows? I guess we'll have to wait and see what happens with Ben's suggestion.

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Resident lurker

Certain things are engineered a certain way for a certain purpose. The extra bolts must have a purpose to hold it together extra good. And as for the 6 bolt main Nissan's....well they must be extra extra durable! Makes sense to me anyways...

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-1981 Chevy LUV, 283SBC, T350 Trans, White In Colour, Long Box, Never Ending Project!
-2001 F-350 Superduty XLT 7.3L Diesel Auto, Ext. Cab, Long Box, White In Colour
-1998 F-150 XL 4.2L V6 5spd , Reg. Cab, Flareside SB, Red In Colour

the bolts that hod nthe main caps are grade eight, they arent going to snap, and the main caps arent going to either, i took apart a small block, 2 bolt main one day, and it had a broken cam, and broken crank, with the rod seperated from the piston ( tore the bottom off the piston off) and the front of the block was broken and bulging out and stuff, and the main cap wasnt even broke off. how much mor punishent does something need to take?

sorry about all of the errors, i just got a new keyboard, and you have to pund the keys to get them to work.