7 rib block strength/support

[adds]

Hi all just after some advice.

im building a spare bottom end. Just wondering if those mrp crank girdles would be worth it? Or would the main cap ladders be enough support

I will be using a 16v head and upgraded valve train. Bottom end will have h beam rods c.p pistons, ACL bearings etc.

the motor won't see very high revs as it will be turbo so I'd say 8000rpm limit. Also will be aiming for about 16-17psi of boost.

Are the 4a blocks prone to flex ? How much power would a 4age block safely be happy with before considering a crank girdle


cheers

[Jimmee1990]

It would be revs more than outright power that would cause the block to flex, but at 8000rpm or so the cap reinforcing straps would be plenty in my opinion. I had a balanced bigport bottom end with Mazda pistons that did 9000rpm with no bracing at all and was fine, but better to be safe than sorry. I'm looking into making two billet main caps to replace number 2 and 4 mains if you're interested, but I'll be doing substantially more revs.

[Ae Eightysix Drivingclub]

Just balance the bottom end and it'll happily go to 9k. You don't need those girdles.

[Bren]

I have a related question. At some stage I will be building a 5A with 83mm pistons. With the block bored out that much would it be worthwhile using something like the MRP girdle, or not really?

[Big T]

Going that far with the block leaves paper thin material between the cylinders. The girdle may help somewhat but you can only strengthen the material already there. 83mm bore doesn't leave much. I know people have done it and used CA pistons and etc etc but why not just go to 82 or even 82.5mm to save potential heartache? Custom rods/piston and crank (if you can afford it) will get your 1.7L+ figure without compromising too much block strength.

[Bren]

I see where you're coming from, and somewhat agree, and have had others mention similar. The thing is though, the stroker crank I am getting also comes with a block already machined to suit the crank as well as 83mm pistons. The previous build used blacktop rods and CA pistons, but I will be using the Brian Crower rods and pistons for a bit of peace of mind. Just interested if the girdle will help at all in this situation or if I would be better off keeping that money in the bank.

Cheers for the reply mate.

[Jimmee1990]

The girdle does a lot more to support the main caps than it does the bores, If you're going to be revving it over 8500rpm I would suggest partially filling the water jacket with grout.

[adds]

I think I have decided just to get those MRP main cap ladders. I think in my application it will hold up just fine.

I also read read into filling half the water jackets with grout IMO this would be a good idea for the high hp/revving engines

[Big T]

Get a new block. They don't need much clearancing. The block needs notching next to the oil squirters just where the rod bolts are. That's pretty much it.

[Bren]

If it breaks I will. The previous build had no problem with the block cracking, and I don't plan to rev it too hard.