Lower Compression

[rigger]

I was thinking of lowering my compression. I know I can install a thicker head gasket to do so but wanted to know what is the best way to do it. What gaskets to use.

I am currently sitting at 195 psi. Running straight race gas and the motor seems to run pretty good. What gaskets would I need to get her down to pump gas?

Only reason I am really thinking of doing this is because there is only one station in my area that sells race gas and they are not always open when I need the gas. And it is about $9 a gallon here.

If I drop compression, what kind of a performance drop am I going to see? And will I need to re-jet or will it be fine where it is now?

Thanks for the info.

[86250rrider]

what kind of head do you run? cut stock or aftermarket ? thats pretty high so im sure you have something going on there.

[rigger]

It is a stock head. I assume the head was milled to get the compression up. It has also had a good bit of port work done too.

I was thinking of trying it with a little lower compression so that I could run pump gas since it is so much easier to get. And if I knew what gaskets to use to try it, then I may give it a shot just to see if I like it.

If I loose to much performance, then I will put it back like it is now.

All I do is trail and play ride so getting every last pony out her is really not needed. But I want the motor to be fun to ride at the same time so if lower compression makes her a bore to ride, then I will leave it like it is now.

[1promodfan]

$9 a gallon!! Man that is high. I'm only paying $6 per gallon. I don't blame you for wanting to lower your compression.

[86250rrider]

what kind of head gasket you running ? my portwork actually lowered my kicking compression on mine,it bleeds off at kicking speed.when running the cylinder pressure is higher due to the volume increase. using a stock trx gasket will lower the compression assuming yours is either a atc or split trx or atc gasket. the trx is the thickest one that fits stock. let me know what you have now.

[rigger]

The gasket kit that I used was one for a 250R. I toor the motor down when I got it just to go through it and check everything out. Since it was a 250R kit, then I would think it is the thicker head gasket. I don't think that kick starting compression is all that bad at all. I can start her with flip flops on if I am feeling brave.

I am guessing that if what I have now is about as thick as you can go for a gasket then I either need to stay with what I have now or find another head that has not been milled down.

My only concern is how much performance will I loose by droping down the compression levels to somthing closer to stock numbers.

Thanks for any info.

[86250rrider]

stock compression is around 160-170 range. it will be weaker but not slow.it will lose some of the bottom end snap and some pull too. i have a few stock heads here if your interested in one. i think 2 are uncut or shaved. i ran 180-185 lbs. on pump gas on mine.

[rigger]

I sent you a pm on a head.

Mine does not have a lot of bottem end now. I would not really want to loose much more than what I have. But it does have a pretty strong but smooth mid range hit. It has a little bog if you chop the throttle to it hard off of dead idle but other than that it runs well.

Guess all I can do it try it and see what happens.

[86250rrider]

my jug is ported by neil at c-leigh racing. i also use the paul turner type 6 pipe with the compression stated earlier.race gas needed it will ping on 50/50 even. with that combo it hits hard and almost immediately and it can even lug real well. its weird!!



what pipe you using ? reed cage ? carb? i have 2 other pipes too. they have dents down by bend but work nice. sparks mx and paul turner race. they actually feel like the same pipe to me. the type 6 is a woods,gncc type pipe.....i love it. not much top end,but short shift it and it rips.great for short drags and trails.

give e-mail for pics of head

[86250rrider]

pics of head. was shaved lightly,but not much as compared to a stocker. i got 170 psi with it and stock gasket

[86250rrider]

top view. .075 was my squish on my motor.

[rigger]

I am running an older FMF pipe. 36mm carb. Just regular Boyseen reeds.

This motor has had a good bit of port work done to it but I could not tell you what it was ported for. It does not have a lot of bottom end but it still seems to pull pretty well. Then it comes on with a good strong mid range hit but it is not a harsh hit. Top end pulls well but is a little flat. So I am assuming it is ported for a low to mid.

From what I have read in the past, the FMF pipe retains the stock R's power curve but with just a few more ponnies than stock. I would not mind having a little more low end but it really seems to work well like it is. I can't go to fast with it in the woods any way cause she is at 50" wide.

Only real reason I was thinking of lowering compression was to run pump gas since race gas is alittle harder for me to get but as long as I plan ahead, it is not to big of a deal.

I think what I would really like would be somebodies 310 kit ported for low to mid and set up for lower compression.

If you want, shoot me an e-mail on your head. I sent you a pm the other day on it.
mkball3@comcast.net

Thanks