compression ratios

bigbrotherjohn · 01-31-2004, 05:36 PM

Sorry for asking so many questions guys but I want to plan out my engine rebuild the best I can so I can do it right the first time. Any help at all is greatly appreciated.

My question this time is, is a 9.5:1 compression ratio (such as that from shasta parts) to high for good reliablity. If not what kind of power should I expect and what would I have to do to ensure reliability.

Touque · 02-01-2004, 08:39 AM

nope, that compression is not too high at all!

the original specs for our 912 engines were 9.3:1 compression. Given that the shasta pistons are of very-high quality, you should have no loss of reliability. If I had the extra $$ laying around, I'd go for those Shasta's in a second.

I think in Duane's book, he has a setup where an engine with Shasta P&C's, a hotter cam, bursch exhaust should develop around 120-125hp with no loss of reliability. If you don't have his book,I'd highly recommend it.

Troy

bigbrotherjohn · 02-01-2004, 08:49 AM

how about 15:1 compression
just kidding

If I ran the Shasta pistons could i use by stock cylinders, case and valvetrain. Also how much are the Shasta pistons w/o the cylinders, Shasta has Emailed me back with their pricing yet.

Touque · 02-01-2004, 08:58 AM

15:1 would be fun for about a second!

there website is here: http://shastadesign.com/

also, they list 9.25 to 1 as the compression ratio and $695 for the prices without cylinders. Also unless you have a big-bore kit now (which have 86mm bore) you will need the cylinders. Even if you did have the correct cylinders, I'd be inclined to buy the complete set - that's just me though.

As far as case and valvetrain - sure. Just make sure they are in good condition. It is very hard (and expensive) to find non-standard crank bearings. If you think you have to crack the case, be prepared for some issues...

bigbrotherjohn · 02-01-2004, 10:21 AM

My engine is already in peices.
Its not really a REbuild but more like a complete build.
I don't think I could afford those piston but they sure sound nice.
Does any one have any experience with honing their cylinders themselves, I have some air tools and a drill press, couldn't I hone my own cylinders with one of those flexible brush things. If not what is a good shop that could do it for me even if I had to ship them.