early 875.1

markv8 · Post by **markv8** » Mon Dec 22, 2008 7:38 am

i have a early 875.1 cr block and heads ready for rebuild, if i use comopsite gaskets would this lower cr enough for a 471 charger not to blow by and play havoc pressurizing the sump thanks, any other info on the build greatly apprieciated thanks rover v8

Post by **Rossco** » Mon Dec 22, 2008 8:20 am

Hi

You probably know already that it's the pistons that set the compression on the Rover not the heads.

Composites will drop your compression to around 7.75: which will allow for quite a wadge of boost.

Be carefull though because those earlier pistons are a bit marginal once you get over 6psi.

Allan

ChrisJC · Post by **ChrisJC** » Mon Dec 22, 2008 9:26 am

I'm not sure that blow-by is related to compression ratio. I thought it was more related to the state of the bores and rings.
Compression ratio will limit max boost before detonation becomes a problem.
Chris.

markv8 · Post by **markv8** » Mon Dec 22, 2008 2:59 pm

thanks for info guys , i was just using composites to lower cr ,also milling 1.5 mm off tpo of pistons allows for greater boost but, new rings will be used

Post by **Rossco** » Mon Dec 22, 2008 6:08 pm

Hi

I'd really avoid machining the pistons.

With high boost you want as much meat in the top land as you can get.

topcatcustom · Post by **topcatcustom** » Mon Dec 22, 2008 6:22 pm

Is milling standard pistons a good idea?! Anyway you'll already be at about 7.75:1 which should be plenty low enough for most applications- dont forget there's no point trying for ridiculous power when it is an old block with (maybe) thin ribs and 2 bolt mains...

markv8 · Post by **markv8** » Tue Dec 23, 2008 3:20 pm

ok here,s the plan, old block, which i thought had extra webbing, new rings, bottom end shells and mains, 3.9 heads blower cam with longer exhaust duration rhoads lifters keeping hydraulics, composite gaskets, roller timing chain and cogs , hp oil pump spring new gears, 471 blower 390 holley should be good for 250 bhp in my 110 , but any one have any idea how to plumb in the lpg all built by me with arp bolts

Post by **Rossco** » Tue Dec 23, 2008 5:17 pm

Early blocks have less webing than the later 'stiff' blocks.

For 250 you dont need to run that much boost.

topcatcustom · Post by **topcatcustom** » Tue Dec 23, 2008 6:51 pm

Personally I'd find a later stiff block with more meat- just to be sure! Easy to get hold of too!

Never seen a 110 with a big blower out the bonnet- should be interesting!