Motor Question

Home  \  Domestic Cars  \  Motor Question

Hi guys, I've got a really stupid question. I've been reviewing motor assy info for my camaro and I've camed across a thing that keeps my head spinning.

I'm not that much of a machanic so here is my qestion :

What is the difference between a 2 bolt motor and a 4 bolt motor ?
And wich is best ?

Thanks a lot guys


posted by  cmdr-franck

Are you talking about a 2 bolt or 4 bolt main? If so then the 4 bolt main is better cause its stronger (has more holding it in place) so it can take more of a beating. The 2 bolt and 4 bolt mains means how many bolts are used for each support (cap) holding the crankshaft in place. Not the best explaination but thats the best i can do right now.

The 4 bolt mains have 2 bolts in the top and 1 on either side of the cap. A 2 bolt main only has 2 bolts in the top of the cap.

posted by  car_crazy89

Ok .. next question is longblock or shortblock ? has to do with the space is uses that I guessed .. but what are advantages VS disadvantages between the two's ?

I suppose the short block is less strong and prolly heats up faster since is as less place to dissipate heat ?!?

Thanks again !


posted by  cmdr-franck

a short block refers to an engine without heads, intake, or any accessories, like this:

a long block is a short block, plus heads and valvetrain, and sometimes valve covers--like this:

short and long block don't refer to the physical size of the engine so much as they refer to how much is supplied w/ said engine...

as far as 2 vs. 4 bolt main blocks, unless you're building a very high HP or high rpm engine, i wouldn't worry about it. stock chevy 4 bolts have proven to be only marginally stronger than 2 bolt mains. the best way to integrate 4 bolt mains on a small block chevy (in my opinion) is to have the block machined for 4 bolt splayed mains, where the outside 2 bolts go into the block at an angle. (for a pic, just look it up in summit or something) the only clearance issue you are probably going to have is if you use an HEI distributor--they occasionally require a little bit of "clearancing" on the firewall... also headers or manifolds might be a concern. you might want to search around on the net to find out what works best. you can order motor mount brackets for a 4.3 to small block swap on the internet. just look around, they are pretty affordable (i found out after fabricating my own for a swap into an astro van :doh: )

good luck!

posted by  dodger65

I found a thing on short block and long block that was what you said but i didnt think it was right, i thought it had to do with actually block size. I learned something new. And yes, the 4 bolt main chevy engines (ie. 350) may only be marginally stronger but they are still far more desirable.

posted by  car_crazy89

they are desirable because of misinformation, though. most folks think the stock 4 bolt setup makes it a ton stronger but testing has proved otherwise. kinda like an old wives' tale (old husbands' tale?)... i'll try to find some online documentation to back this up b/c i read about it a long time ago...

here's a quote from this article:

"Ironically, the 400 two-bolt main blocks are preferred since they offer superior strength in the main webbing area compared to four-bolt main 400 blocks."

here's a buildup of a sbc using a 2 bolt main... k/0305em_gmachine/

the list goes on, you just have to look for it...

posted by  dodger65

hey, i'm not saying otherwise, i dont really know myself. I can easily believe it though. I'm going by what i've heard. Apparently a lot of people think wrong about 2 and 4 bolt mains, my dad has been offered good money for his truck just for the engine cause it is 4 bolt main and they think it'd be great for their track cars. I never really heard of them being almost similiar, i guess thats something i should read more on.

posted by  car_crazy89

i probably came off wrong there. i didn't think you were gunning for me there. :wink2: i was just trying to back up my statement w/ some facts, as i'm sure some people might find that post incendiary. a LOT of people have been saying for a LOT of years that 4 bolt mains were bulletproof. i was just trying to eliminate a lot of potential flak w/ some facts... :mrgreen:

posted by  dodger65

Oh sorry, i didnt think you were 'gunning' for me lol. I just never heard of that before, i've always heard what everyone else has heard and believes. What about 6 bolt mains, are they an exception of being stronger or are they in the same boat kinda thing as 2 and 4 bolts?

posted by  car_crazy89

I must admit I subscribe to 4 bolt over 2 bolt. The test data I have seen in the past showed quite significant improvement, as did the use of valley girdles. But then we are talking about engines that are fussy about block deformation from incorrect engine mounts.

posted by  Wally

Get you two 426 hemi blocks (good luck). Build them both the same, and be sure to push their limits 100%. Remove the bolts that run through the skirt on one engine only. (then you'll have a 2 bolt main...) Run them hard and see which one breaks.

:hi: I know the answer.

posted by  DodgeRida67

According to what I've read, the factory 4-bolt mains are marginally better than the factory 2-bolt main blocks. On SBC motors, it seems the best solutions is to get a factory 2-bolt main block and then get aftermarket 4-bolt main splayed caps (where the outer-most bolts are angled with the V of the block), and have them match drilled while your engine is being machined. This way the outer bolts do not extend into the cylinder bores. According to research this yields the strongest solution.

posted by  Bino

there's a significant difference between chevy 4 bolt mains and chrysler CROSS BOLTED mains... besides, chrysler bb's are deep skirted blocks anyway. you have to put a lot of power out to break them... (vs. a non deep skirted block; i.e. a chrysler 340)

posted by  dodger65

Different strokes for different folks (and engine blocks & lower ends). Theres the deal in a nutshell. Depends on the engine block.

posted by  DodgeRida67

I Know383 strokers are done to death but this is my first buildup so gimme a break. Anyway onto the question. OK so I have a SB 350 that I pulled from a C1500 Chevy pickup. Unfortunately once I tore it down I had no idea where to go after that. It has two bolt mains with a one piece rear seal. What I want to do is stroke it out to 383 cubes. Anyone have any idea on what direction I should take this as well as any advice on what to look out for?

posted by  poncemon

Your Message