Head Games

[Dan Hodges]

Has anyone ever welded up the squish bands on the Elevens head to reduce the chamber volumn? I experimented with this by filling in the bands with modeling clay and found that I reduced the chamber volumn by 5 cc's. Considering the fact that every CC equals a quarter point of compression and every quarter point of compression is worth 1% more power this could be something big. Naturally there could be a down side because these squish bands were put there to create a squish effect which creates turbulance which effectively aids in the combustion process however the 2 valve vortec drag race heads marketed by Ward and others do not have the bands. A lot of folks cut the stock heads .030 to increase the compression and in so doing most of the band is removed. A .060 cut will remove practicully all of the band or recess but any cut over .015-.020 is bad because the cam chain gets too long not to mention the decrease in valve clearence. Welding these bands up with a TIG welder would be pretty straight forward after which you would take a .007 cut from the head surface to clean it up and make sure it is straight. All of this has to do with compression as the Wiseco pistons only have a 6.6 cc dome which only yeilds about 9.2-9.4 compression when using the 80-81 big valve head in the 1179cc-1196cc configeration. The 78-79 head has a smaller chamber with smaller valves and will fetch maybe 10.00-10.25 compression with the same pistons. Of course you could use the 78-79 head rather than the 80-81 head however the late head flows about 10% more air than the early one. I thought to myself, surely somebody out there among the 1100 plus XS owners have thought about this besides me and maybe might have already been there and done that. Anybody got an idea I haven't thought about relative to this modification? This picture will give you an idea of what I'm talking about.

[prometheus578]

"You may know more about the technical stuff than I do..."

... but at least the "arrows" in my pictures look better than yours!

[Crazcnuk]

I don't think those cuts are to 'squish' anything, or to aid turbulance.

If you think about it, in order for them to do any of that, the air mass would have to be moving up the cylinder, but since the air is captive, with no place to go, it is in fact compressing, not moving.

Think of a sock in there. As the piston went up, the part of the sock against the piston is moving, but the part against the valves is not. By the time the piston nears that area, none of it is really moving, but compressing (sort of a squish, but different.

I would be willing to bet those cuts were put there in order to set the compression where it is, nothing more. Less cut=more compression, more cut=less compression.

[trbig]

I'm just wondering if that bevel helps on the inflow to disperse the air/fuel into the cylinder, then kind of funnel it out on the exhaust stroke? Would squared shoulders there create too much turbulence??

Last time I checked this, you recommended to have at least a .050 valve to piston clearance, but that a .060 was preferable. Mine checked out to be @ .130. MORE than double recommended... so plenty of room to play. What I saw with shaving the head though, was it started getting into the intake boot screw holes as well as the lower exhaust studs.

It would almost seem easier to me to heat the cylinders, drop the sleeves out, and mill the bottom of the cylinders a bit.. along with maybe doing away with the base gasket and just using Yamalube to get your extra compression there? If this causes a loose cam chain, a member here recently milled the face of his cam chain adjuster so it would get even closer to the engine.

But no... this is the first time I've heard of anyone contemplating the head work you describe, Dan.

Tod

[Ivan]

squish bands are mostly a way to control the flame front during combustion. This is very important in diesels and model airplane engines, where latent heat and compression fire the mixture. Essentially the shape of the combustion chamber controls where the flame starts and how it propigates. If the squish on these engines is not right, they will detonate and tear things up inside.

On spark fired engines, Plug heat and spark timing control detonation. Squish area is much less a factor. If the squish is too aggressive, usually the timing is retarded to prevent ping. This also applies to higher compression, which will probably be much more a factor than squish band.

I would think that water injection may be an easier alternative than welding the head, but welding is much more fun, and so is machining.

[Dan Hodges]

Head Games Part II

My research relative to this question regarding the theory of the so called squish/quench bands/regions led me to the works of Charles Fayette Taylor and volume 1: of his book, "The Internal Combustion Engine In Theory And Practice". I will confine my information and comments to naturally aspirated spark ignition engines burning gasoline or alcohol. In a wedge or ployspherical combustion chamber, the squish/quench area creates turbulance. As the piston approaches TDC, the air/fuel mixture is expelled from this region and swirls around the chamber which aids in the burning efficiency in the chamber. The XS has what is called a polyspherical combustion chamber. When you look at the XS chamber you can readily tell that two spark plugs per chamber would be a big improvement in the combustion process however it only has one plug and machining it for two would be cost prohibitive. The question relative this essentially being, how much quench/squish area can be reduced relative to performance relative to what you would gain in compression. Once these bands were welded up, you would want to roll and blend back slightly the edges to the cylinder wall again as you would not want a perfect ledge. You can look at the picture of the Ward 2 valve race head and get an idea of what I'm talking about. Of course special pistons would negate all of this but special pistons from Wiseco, Venolia, J&E and the rest will cost about $800.00 to one thousand big ones, cost prohibitive when I'm only looking for an honest 10.5 to 1 compression. You can cut the bottom of the block, the top of the block and the head however when you cut the block the top piston ring gets too close to the top of the bore and the cam chain gets too long which causes the cams to retard when the motor is running. Of course you can split the cases and use a shorter chain but splitting the cases ie, field stripping the motor is two beetches and a fool. Water injection serves no purpose other than preventing detonation when you have more compression than the fuel you are using can handle. Water injection was first employed during WWII on supercharged/turbocharged air craft engines and it is still used today in similiar applications. How are you going to put a water injection system on a motorcycle anyway. Piston to valve clearence depends on the cams and pistons you are using in addition to how much you have cut the block and heads. If you use aftermarket cams that have more than 250 degrees of duration @.040 lift and .375 valve lift with stock pistons you need to check your VP clearence very carefully. Lastly, when you weld on one of these heads, you must do it very slowly or you will get it too hot and the valve seats will loosen and the hi-temp "O" rings at the base of the guides will burn requiring the guides to be removed to replace them. Even a good welder using a TIG welder can quickly ruin a good head if he doesn't go very slowly. I'm going to do this as there is no other way that I can get the compression I want in my 1179 without bastardizing my block and head. Considering that every point of compression up to about 12-1 is worth 4% more power, I have to do it because 1 point more compression is about what I can get and still keep some remnants of quench/squish. Thanks for you input. Dan

[Dan Hodges]

Re: "You may know more about the technical stuff than I do..."

Originally posted by prometheus578
... but at least the "arrows" in my pictures look better than yours!

My mouse never could run in a straight line and next time I will paste the arrows so they will be straight. I don't get any slack around here at all, that damn mouse of mine should have known better.

[Espiritus]

Gotta get a new Dictionary

Whew. I promise, I will never, ever try to understand a post about this subject again. I printed it, got out the dictionary, got out the book, highlighted every other sentence, all to no avail.

This seems like a terribly time consuming task to get what appears to be a minimum about of additional power. If you do it, can you tell me later if it was worth it?

Cam

[trbig]

when you cut the block the top piston ring gets too close to the top of the bore and the cam chain gets too long which causes the cams to retard when the motor is running.

Well... Just by going by the carbon ring on a set of cylinders I have, there's plenty of room for that so the top ring won't be in danger. The talk of the cam chain makes no sense... as well as splitting the cases or "Field stripping" it to put a new cam chain on??

Not trying to argue with you, but the statements there don't make any sense and just seems to be that you just happen to not WANT to do that. Play with the head by all means, but I think there's definately easier ways to get what you're after.

Tod

[81xsproject]

This seems like a terribly time consuming task to get what appears to be a minimum about of additional power. If you do it, can you tell me later if it was worth it?

It isn't always about least work for most power. While Dan is a million times more knowledgeable than myself, I think that we are a bit alike in that it is the tinkering and experimentation that is the fun payoff.

Tr, unless Dan has something against master linked cam chains or using a chain tool, you are obviously correct that the cases don't need to be split. As far as the cam timing, shaving the head, block, or both decreases the distance between the cam and the crank. While you can take more slack out of the front of the chain with the tensioner, the rear side of the chain is straight. So, the distance on the leading (rear) side is shortened, yielding excess chain, allowing the cams to be retarded.

[psycoreefer]

Degreeing the cams?

correct me if I'm wrong but hasn't there been talk before of degreeing the cams. And shouldn't you always check "after market" cams by degreeing them anyways. So if one were to shave the block then simply degree the cams back to where they should be all would be well yes? I understand that this would mean having the cams slotted so that they could be adjusted but I would think that would be relatively cheap.

The reason I bring all this up is that over the winter I was planing to get my cam's slotted so I could dial in a bit more mid range power, as I almost never use the top end anyways.

Then when money permits I want to get one of the big bore kits and if having the cams already slotted would allow me to set proper timing if I had the block shaved a bit I may do that at the same time I have the cylinders bored.

I understand that all these involve some compromise and I'll likely loose some top end power.

Any thoughts?

[egsols]

Hey psyco,

Haven't dealt with slotted sprokets before but how do ensure that they never slip and thus loose your timing? Wouldn't it be preferable to get them set up to where you want them and then drill new mounting holes?

Just asking in case I ever get to that point.

[xschop]

Difference?

What is the difference between shaving the bottom of the block and shaving the top of block?.......For TrBig.....The machine shop That this Big Bore block came from shaved the top of block (head mating side) by how much?.....I will be shaving the head face of mine during the next 3 day weekend coming up and I don't want to overdo it if this block has been ground down too much.....I would like to know how much was removed before I go further.....chop

[psycoreefer]

egsols -
I don't know, I would guess that you just make sure they are tight and they won't slip. If you do a search You'll find a few threads on the topic. I've never done it before but from my understanding one of the other members had his mechanic do it for him and "back in the day" it was one of the low cost mods everyone did.

It is a trade off though because the more low and mid range power you dial in by decreasing the overlap you loose top end power. The way I look at it is that I almost always use my bike for commuting and longer high way trips so the extra grunt will always be used, where as I run it up to red line maybe once or twice a week, usually on an on ramp and mainly just to keep the mains cleared out.

[oseaghdha]

Perhaps you can find some longer rods, or have something close modified. Bore, sleeve, and rebore a couple of MM longer.

Find some forged aluminum slugs and make your own.

There is no substitute for cubic dollar$$$$.