2 bolt and 4 bolt mains???

[Andy Butler]

A silly question I realise but with out stating the blatantly obvious, what is the difference between an engine with 2 and 4 bolt mains? What part of the engine has the four or two bolts in it? Its possibly not been asked before as it is such a blindingly stupid question, but thought I'd ask any way I gather that 4 is prefered over 2 but what for? I'll put my 'D' hat back on now and go and sit in the corner. x(

[kdavies3]

Don't worry about what seems to be a daft question, we can't all be into engines and mechanical things.
Anyway a two bolt fixing engine is basically the same as a four bolt engine but not quite as strong. The bolts referred to are the bolts that retain the crankshaft main bearing caps.
So not surprisingly 4 is stronger than 2. It all depends what level of tune you intend to go to on your engine.
My guess is that in most cases a 2 bolt main will suffice in a weekend posing car. If your into more serious driving and track days etc. 4 bolt is probably the way forward.
Hope that helps. :tu :tu
http://www.woodoouk.eclipse.co.uk/Wales.gif

Kev Davies
Dax, 383ci Chevy Stroker, Tremec TKO
South Wales

[roll control]

As Kev has pointed out, its to do with the number of bolts holding the crankshaft main bearing caps in place. On a '4 bolt block', the centre 3 main bearing caps are held in place with 2 bolts on either side. See below - this is my block after machining, you will see what we are on about.

http://www.cobraclub.com/crcforum/user_files/3981.jpg

Rob :tu

[Andy Butler]

Thanks! :tu

[robert]

Then you have splayed or not 4 bolt caps, just to confuse matters. :9 :9 :9 The splayed end caps spread any stress loads.

[russell_ram]

'Then you have splayed or not 4 bolt caps'

AND cross bolted in a deep skirted block - the best way to spread the loads into the block and support the bearing caps (like on Rovers)

Russ

[robert]

More damn options than you can shake a stick at!!!! :tu :tu :tu :tu

[dave]

The top and bottom of it seems to be that if you are not going to have more than 400BHP then a two bolt block will be fine, over that you are best going for one of the four bolt options etc.
:tu

[Jesus]

Hi,
One more point is that if you will get your block from donors, usually the passenger cars including Corvette and Camaros, have two bolts mains, and the trucks and vans usually have the four bolts mains, even when usually the trucks and vans develop a lot of less power than Corvette and Camaros.

Hope this help.

Jesus
Granada, Spain.

[Andy Butler]

Doh! ohhh! Every time I learn something new it pushes some other crap out of my brain... :tu
Thanks for the help guys... just got to try and decide which way to go now. Initially thinking 350 bhp ..(ish ) AND MAYBE UPING IT AS i GET USED TO IT (IF YOU EVER DO?) AND FUNDS ALLOW...