thoughts on C.R,

jarad · Post by **jarad** » Sat Feb 08, 2003 11:32 pm

what are you guys thoughts on this....
1600 single port. .070 DH
48 cc comb.chamber
CR is too high at 7.8

I would like to drop it to 7.4 or 7.3. Whats the best method? I kinda already have a lot of deck height. How much is safe to open the combustion chamber? what about those head gaskets? Thanks

Post by **Marc** » Sat Feb 08, 2003 11:49 pm

Should be no problem getting the ~4cc you need if the chambers are stock now. Once you've got that much deck another .030" isn't going to make any discernible difference in combustion chamber efficiency, though, so any of the methods you mentioned would be OK IMO.
Head gaskets would make the change easily reversible, which is the only reason I'd go that route.

swampy bob · Post by **swampy bob** » Sun Feb 09, 2003 3:25 am

marc, should he use cyl spacers or head gaskets?

jarad · Post by **jarad** » Sun Feb 09, 2003 7:41 am

marc,
Obviously, if I went went with copper head gaskets, I would have to order them from rimco, but what size gaskets give you ?? cc in the chamber? Did that make sense? I'm thinking it might be easier to open the heads. I f I decide to build it up later, then I will already have a good set for a 1776 SP, yeah? Thanks again!

James2 · Post by **James2** » Sun Feb 09, 2003 7:55 am

What makes you think the CR is too high?

jarad · Post by **jarad** » Sun Feb 09, 2003 10:15 am

because its going into a 66 bus with a tall aftermarket "bubble top" aka Snow top camper. The camper has a lot of drag and I've had problems with all previously 'slapped together' motors running too hot. I don't need to go fast, i just need to survive texas summers!

. I'm shooting for 7.2-7.4(at most). I've gotten a 26mm HD oil pump and converted to a doghouse cooler to improve operating temperatures. I know it's not the end-all be-all, but anything helps.
this is the bus http://www.thesamba.com/vw/gallery/inde ... +54077.jpg

[This message has been edited by jarad (edited 02-09-2003).]

James2 · Post by **James2** » Sun Feb 09, 2003 12:43 pm

cool bus. I still would run the higher CR, just adjust the timing and/or move up a grade in gas.

if you must lower the cr, open up the chamber.

jarad · Post by **jarad** » Sun Feb 09, 2003 2:36 pm

i always run 93 oct in my air cooled cars. Not worth the cheap gas to take detonation chances, 'specially with a motor you didn't build. 7.8 just seems like it's gonna be too high with a bus like that and being in tx's 100 degree summers

Post by **Marc** » Tue Feb 11, 2003 1:39 pm

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by swampy bob:
marc, should he use cyl spacers or head gaskets?<HR></BLOCKQUOTE>

You can't run for too long before a ring ridge starts to develop in the cylinder; while you can always add cylinder shims, removing them could cause problems when the top ring starts running into the ridge - that's why I said use head gaskets if you want to make the change easily reversible.
Opening up the heads a little would be best but if you're reringing anyway there's no extra work involved in adding some barrel spacers. Head gaskets are simple too but offer no advantage over barrel shims except for the easy reversibility; they also cost more and I've never trusted `em much.
I ran a 7.15:1 DP1679 in my `73 bus for years on Regular gas; it ran nice & cool and had ample power - IMO jarad's thinking right.

.060" deck @ 85.5mm bore => 8.75cc, if you want 4cc more just ratio it out (12.75/8.75) x .060" = desired total deck. In this case that means an additional .017". Since it probably doesn't have .070" bare, you'd need to see what shims are there before buying the new ones. If you're leaving the barrels undisturbed, order the .020" head gaskets.

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Tue Feb 11, 2003 2:32 pm

bump it up, and hear it thump!!! Hell I'd tighten the deck up to .060 and let her rip!

A single port loves compression, I have built stock cammed single ports with 8.3:1 and they love it and haul *** !

------------------
Jake Raby
Raby's Aircooled Technology
www.aircooledtechnology.com

jarad · Post by **jarad** » Tue Feb 11, 2003 9:43 pm

Thanks for all the help guys! I finally just compromised and opened the heads a couple cc's and lft the CR at 7.6:1. Running a doghouse, 26mmhd pump I think all should be well.