Max Compression

Team Rose Motorsports · Tue Mar 18, 2008 1:25 am

Does anyone know that the beginning of the danger zone is for the Spree engine as far as compression goes? Also, I'm finding that no one really wants to shave off more than 0.02" but it looks like there is more material that could be spared than just that. Is that about the threshold before the compression maxes out the blocks abilities?

Farfignugin · Post by **Farfignugin** » Tue Mar 18, 2008 12:09 pm

the reason why we say "only shave off 0.02 in." is because otherwise the piston will smack the spark plug, and we all know that that isn't good.

79vwrabbit · Post by **79vwrabbit** » Tue Mar 18, 2008 3:41 pm

The best thing to do would be to measure the compression ratio and decide how much you can safely remove. Measuring the squish with a piece of solder would be another way to make sure the piston isn't coming too close at TDC. But compression ratio would depend on which year piston you're using. When I get around to working on my own engine, I'll post what the stock ratio is for the 1985 engine & piston.

Team Rose Motorsports · Tue Mar 18, 2008 4:38 pm

On an '87 I don't think the plug would hit at TDC, maybe on some of the less concave earlier model heads, but it looks to me like I could get away with shaving down more on an '87. Has anyone gone too far on an 87 that remembers how much they had taken off?

Post by **noiseguy** » Wed Mar 19, 2008 6:39 pm

Best thing to do is measure your clearance with solder, and everything bolted down, and see what your engine can handle.

Your compression is limited by how hot you want to run... you can always switch to premium to lower combustion temps if you need to.

tru72 · Post by **tru72** » Sat Mar 22, 2008 1:55 am

compression is one thing to look at ,but more important is the squish.
again to much compression will make it run slower because of the added pressure in the cylinder, the motor will not be able to rev up to its full potential. Check the squish, then adjust for compression, some where in between you'll find a happy medium that will suite your needs!
aloha

stillspeeding · Post by **stillspeeding** » Mon Mar 24, 2008 2:43 am

I can still get those silly j.c.c. port matched 55cc pistons for the spree, they are in stock, just find a machine shop that can do the cut, wiseguy can't seem to find a shop- sent him 2- yrs ago?

Kenny_McCormic · Post by **Kenny_McCormic** » Mon Mar 24, 2008 3:45 pm

stillspeeding wrote:I can still get those silly j.c.c. port matched 55cc pistons for the spree, they are in stock, just find a machine shop that can do the cut, wiseguy can't seem to find a shop- sent him 2- yrs ago?

If you can get the pistons prove it and show us where to buy one.

Post by **noiseguy** » Mon Mar 24, 2008 8:48 pm

I've got 2 of them on my shelf; I just can't find anyone to bore the cylinders in MI.

gashead · Post by **gashead** » Mon Mar 24, 2008 9:55 pm

is it opening jug for larger dia piston?,

Kenny_McCormic · Post by **Kenny_McCormic** » Mon Mar 24, 2008 9:58 pm

noiseguy wrote:I've got 2 of them on my shelf; I just can't find anyone to bore the cylinders in MI.

There gotta be somebody, have you tried looking for people who bore dirt bike jugs? Sucks balls i dont have any relatives in Hawaii.

gashead · Post by **gashead** » Mon Mar 24, 2008 10:12 pm

Noiseguy not uure where at in Canton you are at, Stony Creek motersports in Bellivelle was going to open up my SB jug for $70.00, untill I found another on E-bay for $4.99. It was guy with hiped piston, recieved pictures of bore and it looks good think he broke the piston skirt geting cylinder off.

Post by **noiseguy** » Tue Mar 25, 2008 3:59 pm

Was it $70 for a standard 0.025 or 0.05" overbore, or will he go larger?

Places I called wanted close to $100 for the 5mm overbore that I'd need. To put that in perspective, guys in HI will do this for $30.

I'm actually headed to HI this summer, but to Kauai, not Honolulu where all the shops are located...

gashead · Post by **gashead** » Tue Mar 25, 2008 4:26 pm

He didn't care how much over I wanted, his consern was that I had piston first, so he could fit cylinder to piston.

Post by **noiseguy** » Wed Mar 26, 2008 8:36 am

I'll give them a call when I get into town; that's fairly close to my place.

He should be concerned about the piston; I'm leary of guys that don't ask for that kind of stuff when they're doing their work.