QUestion about main girdles

Looking for opinions on main girdles. I have a line on a good Mark IV BBC that is a 2-bolt main. I would normally pass, but the guy is desperate and I can get it cheap.

Here's what I plan on building: 4.25" stroke and 4.350 bore, filled, studded, 12-71 Littlefield on alcohol, 15# of boost and 7500 rpm max.

Would you convert it to 4-bolt or will a girdle be sufficient? A few machine shops around here told me that a girdled 2-bolt is actually stronger and more rigid than a factory 4-bolt with studs.

 

girdle

yes a 2 bolt is stronger, only because the gap in between a 4 bolt weakens the main caps and block. but if you make it a 4 bolt and splay the bolt holes then it stronger than a 2 bolt. splayed means angled holes towards the outside of the block. but me be a 2 bolt might work not sure all depends how much hp you are thinking of running. i think 1200 at the most. but lets hear from the other guys.

 

This is just my personal opinion, but I think it would be wise to spend a little bit of extra money and purchase a 4 bolt splayed setup...especially if your going to run a blown alcohol setup. I know were talking about two different dynamics here, but the Gas guys dont even use 2 bolt setups specifically for the reason that it just brings heartbreak in the end...Cautionary advise: spend the extra money before you have to spend more later.

 

Do yourself a favor and put 4bolt caps on it. The girdle would be fine if you were just gonna drive it to sonic on saturday nite. And i wouldn't worry about 4bolts weakening the block... you gotta keep the cap on and maintain your clearances first. I have a 4bolt ARP-studded BBC alky motor that'll still float the caps a little when the blower is really singing (get a little metal transfer between cap/register). No big deal tho... just dress it a little... dab on a little peanut butter and go again. i just think in a race deal settling for the girdle is a bad recipe... have fun with it


ps... iron chevy's will like you better the closer to stock/smaller you keep the stroke

 

mains

The splayed caps are a mess on a MK4 due to the panrail oil galley. You end up with minimal thread engagement and catastrophe if you thread in too far and block the passage. If you're on a budget run the 2 bolt with studs and keep an eye on it. When it starts making power it will rattle the caps and probably give some warning before it comes unglued and trashes everything. I'd recommend running a block that is at least equal in value to your blower..lol.
Mike

 

What are your experiences with breakage?

To you cast iron Mark IV chevy guys, where have you broke your blocks?


Me;
1-cracks from head stud hole to cylinder walls; 4.500" bore
2-break the thrust cast main cap in 2 pieces, right at the bottom
3-main web cracks
4-main caps walking; steel caps, ARP studs

 

Right now I can't remember the name. But in the late 90's, a machine shop had sent us a main girdle to look at. It was like $1100 and was one piece. It looked similiar to this .jpg (I can't seem to upload a jpg) but it also bolted to the block via the oil pan bolts.
Imagine a 2.5" thick plate of steel as wide and long as the oil pan with rectangular cutouts to allow the rods to swing. Your main caps are not used.
Is this the kind of girdle you are talking about?

 

Probably means the steel girdle that uses the same bolts as the caps, just ties the tops of the stock caps together.


http://cgi.ebay.com/BBC-GM-CHEVY-42...6117953QQihZ023QQcategoryZ33623QQcmdZViewItem

 

Yes. That would be the type of girdle I am referring to. If I did go to a straight 4-bolt conversion, would I also have to replace the rear main too? Seems like most kits give you just the middle three or the first four.

 

if you are gonna stick with a cheap* stock block just put the 'first 4' on it... straight 4-bolts, line bore it (NOT hone) and go on. a billet rear main alone is like $450 (not counting the install)!... wouldn't that defeat the cost savings of running a stock block? hell at that point you'd be putting lip stick on a pig... might as well cough up the money and buy a real block like a dart (as real as it gets for us cheby guys)

ps... most the time the if you install a billet cap on the front you will have to modify (ie, grind) the front/outer corners of the cap to clear the pan

hell i'd just keep it fairly cheap and run the hell out of it

*i can call it cheap cause i have a couple of them... one is on 90% and just has 'first 4' billet caps and concrete added

 

and fwiw... here is where you get the billet rear main

http://www.pro-gram.com/catalog.jsp

and it here is what $429.91 gets ya

 

I had a 2 bolt bbc and ran with no problems in the 800hp range. stepped up the power and the caps started to walk. bought Eagle steel caps (non splayed) for 3 center mains, took a stock front and rear main cap from an old 4 bolt block, had it line bored and bought the best studs from ARP. no problems what so ever.
And like someone else stated, don't get too carried away with stroke.
frank

 

Ya. I'm trying to get by on a relatively small budget which is why I was questioning the girdle. We're not pushing it too hard - 1100 to 1200 hp.

 

I was considering dropping to 3.766" to keep the piston speed down and the cylinder wall happy. Might still go that route.

 

I reread my post and should clarify. I wrote "I had" when I should have said I have and still run that block. its a 4" stroke motor w/ alum rods.

 

yep... you and your motor will be happier

 

smaller stroke

is it just for an bbc iron block or you mean smalller stroke for a 10.200 alum. block and what about a std deck alum. hemi block with a 4.5 stroke crank. thx

 

I have a Mark IV iron 9.800 BBC.

 

well especially in the readily available deck height iron bbc's (9.8 or 10.2) it helps everything to keep the stroke short. it can get a little tricky to put a long rod into a chevy so keeping the stroke short helps keep the geometry happy and makes it not wanna throw the rods out the side so bad.

it's all relative to what you are trying to do with the motor. if you are putting it in a mid to light weight car (dragster/altered/etc) shorten up the stroke... if you are trying to push a 3,200# door car into the 6's... well you may need a longer stroke set up? just going from my experiences

 

how small 4.250 or smaller. is the same for a std alum. block hemi have 4.5 thx