Increasing the Compression Ratio

[Crazcnuk]

Hmmm, copper gaksets are used for most types of racing. They are good as they can be reused over and over.

I have them on my big block headers too.

Aluminum shim gaksets on the collectors.

Oh, and what about RC Eng. 1208cc big bores!

[Dan Hodges]

Compression

Originally posted by Crazcnuk
Hmmm, copper gaksets are used for most types of racing. They are good as they can be reused over and over.

I have them on my big block headers too.

Aluminum shim gaksets on the collectors.

Oh, and what about RC Eng. 1208cc big bores!

All other factors remaining equal,raising the static compression ratio from 9 to 1 to 10 to 1 will produce about 4% more power and this remains true for each point of increase up to 11 to 1 after which the increases begin to diminish percentage wise.The pumping compression will increase when you increase the static compression but it is also effected by the intake valve closing event.The earlier you close the intake valve the more pumping compression you make and subsequently when you advance the intake cam you close the intake valve earlier creating more pumping compression which makes more low and midrange grunt.Nothing is free though and by closing the valve earlier you decrease the amount time the valve is open to fill the cylinder which effects the top end.If you use dead soft copper head gaskets,you have to "O" ring either the head or block and in the case of a motor cycle engine that has sleeves it would have to be the head.This done the cylinder would seal but the chain cavity would leak like a sife. Nowaday's most naturally aspirted race engines use gaskets made by Fel-Pro that are fiber with either stainless rings or copper made in as part of the gasket and are very similiar to the stock XS gaskets or the gaskets in the Wiseco kits.25 years ago I used copper head gaskets in my big block Chevies with O ringed heads but no more.Some top fuel engines still use the copper stuff because of the extreme cylinder pressure they are making.R.C. engineering is out of buisness.The Wiseco kit is a quality piece and I just put a 1179 set up in my jewel over the winter and recommend it highly.This big bore kit will give you 8%-10% more power if done right with a whole lot more grunt,you will love it.I had advanced Sleeves in Ohio bore and hone my block for the new pistons,what a slick piece it is.Just say do it!

[pggg]

1208cc RC engineering pistons, wonder where any are, and how many 1208 pistons did they make, maybe there's shelves full of them somewhere, if RC engineering went bankrupt they should be giving their stuff away free

[Crazcnuk]

I use copper all the time, and I never O-ring the engines. O-ringing is only really necessary if your using a ton of compression, or you want to use big boost off a turbo or blower.

As for compression, your right, the static compression doesn't make as much a difference as people think, or as it used to in the 60's when technology of heads and cams was more primitive. (back when hemi heads were actually good)

The biggest factors are your cam, and your heads. You need big valves to get the air/fuel in, and get the exhaust out, and good clean ports to help. You can play with overlap, lobe centers etc., to move your hp peak up or down.

Fuel economy takes different settings than outright power, but not a lot different.

However, in a bike like the XS, you don't have a lot of options. If you have a cam expert handy, as I do, you can get one of the companies to try and regrind your cams for you, but this is spotty at best, depending on how much material you can remove w/o making the cams brittle. I don't know what is available in the way of aftermarket cams, but most will be for racing.

So your really stuck with raising compression, better exhaust and better carbs.

[pggg]

Good cam shops build the lobes on stock cams with harder surface and better steel stronger than original, and need cam dialing to get exact, I'd go for the underbucket shim mod at the same time, kawasaki valve tappets slide in the XS11 cam bucket holes perfect apparently, and setup for just tiny shims underneath, should get a 9500 rev redline if the pistons don't blow up that is

[Dan Hodges]

Compression & Cams

Originally posted by Crazcnuk If copper head gaskets work for you that's the way to go.Static compression is important because it allows you to use more cam duration and still maintain good cylinder pressure.Pggg is dead nut on about after market cams as both Web Cams and Mega-Cycle just to name two, take the stock cams and hardweld them and regrind them into what ever profile one wants.A hardweld cam is better than a stock cam in that the journals are practically indestructible.A pro stock motorcycle engine has 15 to 1 compression and some of the 500 ci pro stock cars have that much or more.In an XS it is easy to get 9.5 to 1 static compression and thats actually enough for an air cooled motor operated on pump gas on the street. I have a pair of Mega- Cycle hard weld cams in the motor of my XS and they are finished perfectly.I have also in the past had stuff did by Web that was very nice too.Both Web and MC have hundreds of profiles available and for about $400 will hardweld and grind you a broomstick if you want it.Wiseco or Venola will also make you a set of pistons with whatever dome,ring package and skirt design you want for $150.00 per piston. Crane Cams in Florida will regrind your stock cams (no welding) but the base circle will be reduced and even though they nitride the wearing surfaces after they are reground the wear surfaces will not be as durable as the ones that have been hard welded.Like the old saying,speed cost money,how fast can you afford to go.
I use copper all the time, and I never O-ring the engines. O-ringing is only really necessary if your using a ton of compression, or you want to use big boost off a turbo or blower.

As for compression, your right, the static compression doesn't make as much a difference as people think, or as it used to in the 60's when technology of heads and cams was more primitive. (back when hemi heads were actually good)

The biggest factors are your cam, and your heads. You need big valves to get the air/fuel in, and get the exhaust out, and good clean ports to help. You can play with overlap, lobe centers etc., to move your hp peak up or down.

Fuel economy takes different settings than outright power, but not a lot different.

However, in a bike like the XS, you don't have a lot of options. If you have a cam expert handy, as I do, you can get one of the companies to try and regrind your cams for you, but this is spotty at best, depending on how much material you can remove w/o making the cams brittle. I don't know what is available in the way of aftermarket cams, but most will be for racing.

So your really stuck with raising compression, better exhaust and better carbs.

[Dan Hodges]

RC Has Left The Building

Originally posted by pggg
1208cc RC engineering pistons, wonder where any are, and how many 1208 pistons did they make, maybe there's shelves full of them somewhere, if RC engineering went bankrupt they should be giving their stuff away free

Actually I have one such RC piston myself that I once used as a repository for used Marlboros but now that I had to quit smoking because Marlboros cost more than pistons, it's simply used for paper clips. A 75 mm bore that the RC pistons required left the stock XS sleeves too thin.Of course the stock sleeves can be removed and larger sleeves installed...........................I want money,lots and lot's of money.........!

[HobbyMan]

How hard is it to get the sleves out? That has crossed my mind. Remember this?

How may forum members does it take to change a light bulb?

This is the first thing I thought of when reading this thread. Back on topic though, can you get sleves still?

[Crazcnuk]

The piston set I have came with a set of barrels, already done, and used. They had been used for a short while, and then something jumped in front of the bike...

[HobbyMan]

I know that an 80+ head with 79- camps is the best performance setup but what year pistons? can you use 78/79 pistons with an 80 head?

[Dan Hodges]

Sleeved

Originally posted by HobbyMan
I know that an 80+ head with 79- camps is the best performance setup but what year pistons? can you use 78/79 pistons with an 80 head?

The stock sleeves in a stock XS block cannot be pressed out but have to be machined(bored) out.Once this operation is done aftermarket sleeves can be pressed in. After market sleeves are available from several sources in a multitude of sizes. Advanced sleeves in Mentor Ohio is one company that does this work and they have a web site.The cylinder bore centers of a motor is the determining factor on how big a bore you can use. Aftermarket siamese type blocks are available for early Kawasaki,Susuki and Honda 1100 F motors but not for the XS.These blocks also have a thicker fin root area for added cooling.The Kawasaki stuff for the 900-1100 two valve motors is available as a raw unmachined casting and could I suppose be machined to fit the XS if money were no object.You can go to 75 mm with the stock XS sleeves but there are no longer off the shelf pistons for this combination and it's shaky anyway as the sleeves are getting thin at this dimension.Wiseco sells 74.5mm pistons for the XS which will fetch 1196 cc's and be reliable.Using 78-79 pistons with an 80 and up head is a no no as the piston dome on the 78-79 piston is smaller than the dome on the 80 and later pistons because the late head had a larger combustion chamber than the 78-79 head due to it's larger intake and exhaust valves.The motor will run with this early piston late head configeration but you will be down on compression.