Pumping Compression

[Dan Hodges]

Hello Folks: This is Dan again and I'm seeking pumping compression numbers on the Elevens of fellow XS members for my data base. I'm looking for comparisons between the early ( 78-79 ) and the late (80-81-82) models and specifically those combinations that have the Wiseco 1179 or 1196 kit installed. It's also important to note which cam the bike has (early or Late), how many miles on the motor and if and how much the head has been cut (shaved). Of course if you have an after market cam that's very important too because the closing of the intake valve dramatically effects the pumping compression of the motor. The test should be done with a good battery, screw in type gage on a cold motor with the throttle wide open and the choke fully engaged (pulled open). The shop manual list 142 psi @ sea level as standard on all models with a plus or minus of 14 psi as acceptable. From what I've garnered from my own test, late Elevens with the short cams and about 30,000 miles on the clock seem to generate the most pumping compression but I don't have much data on the 78-79 models with mileage in the 30,000 mile range. Any information that anybody can throw me would be very much appreciated.

[petejw]

Hey Dan,
For my 81R, all stock except the head had been shaved (dnt know how much was taken off and slightly ported,
with the engine at normal operating temp (not sure why you want to check with a cold engine, best to check when hot and rings have expanded) i was getting 155psi, the engine had 140,000ks.
Hope this helps a little.

[Dan Hodges]

Cold Or Hot

Hey Dan,
For my 81R, all stock except the head had been shaved (dnt know how much was taken off and slightly ported,
with the engine at normal operating temp (not sure why you want to check with a cold engine, best to check when hot and rings have expanded) i was getting 155psi, the engine had 140,000ks.
Hope this helps a little.

Thanks for your reply. It's generally true that it will pump higher numbers when hot/warm but for the sake of consistency a dead cold pump puts everybody on the same plane. Of course you can use one of those trick lazer temp guns to get a dead nut on running temp check but not everybody has one and so if everybody does a dead cold pump we are all on the same playing field. Cutting the head .010 will reduce the chamber volume by 1cc which will raise the static compression ratio by 1/4 of a point which will increase the dynamic pressure (pumping compression) by about 3 psi. Speaking of those trick temp guns, they are killer at determing the temp of the header pipes which will tell you many things. You can also use them to check the temp of the FD housing and all gear oil is not created equal.

[TopCatGr58]

Hey Dan,

It's been several years since I did my rebuild on my 81SH with the 1179 kit. It has stock cams, the engine had ~50k before the rebuild, only did the top end, no bearings. Used OLD cam chain. 4-1 pipes, Indy Filters. Just lapped the valves, new seals, old springs, no shaving of head, I think I just checked for warpage and didn't find any, just cleaned out the old carbon with a cup brush on a drill. Ofc, Cometic graphite head gasket. I remember doing a COMP test shortly after it was SLOWLY GENTLY broken in some 500 miles after rebuild, COLD engine, THROTTLE WOT, and found 180-185-180-175 IIRC!? I'm at sea level here in Va. on the coast!

It now has some 16K miles on the rebuild. I'll try to recheck it this weekend for a comparison set of pressures, I want to see what kind of wear has occured. I use higher octane due to concerns about burning holes thru new pistons, and I do play with it, so I don't think it gets much carbon buildup!
T.C.

[DGXSER]

Hey Dan,

My 81SH which is bone stack to the best of my knowledge, pumps right at 155 PSI +/- 3 across the board. It had 24,000 miles on the clock when I ran those numbers a few months ago. The test was done per your requirements, cold at WOT right after valve adjustments were made.

[Dan Hodges]

Hey Dan,

It's been several years since I did my rebuild on my 81SH with the 1179 kit. It has stock cams, the engine had ~50k before the rebuild, only did the top end, no bearings. Used OLD cam chain. 4-1 pipes, Indy Filters. Just lapped the valves, new seals, old springs, no shaving of head, I think I just checked for warpage and didn't find any, just cleaned out the old carbon with a cup brush on a drill. Ofc, Cometic graphite head gasket. I remember doing a COMP test shortly after it was SLOWLY GENTLY broken in some 500 miles after rebuild, COLD engine, THROTTLE WOT, and found 180-185-180-175 IIRC!? I'm at sea level here in Va. on the coast!

It now has some 16K miles on the rebuild. I'll try to recheck it this weekend for a comparison set of pressures, I want to see what kind of wear has occured. I use higher octane due to concerns about burning holes thru new pistons, and I do play with it, so I don't think it gets much carbon buildup!
T.C.

Thanks for your response T.C. That's a lot of pumping compression as I've never seen an XS that high. I've kept pretty good records on mine over the years and when it was box stock with about 20,000 miles it had 145 pounds cold. Still stock but with the early cams it was the same. Over the winter of 07-08 I did the number on it with the 1179 Wiseco kit and a set of M/C cams which have 17 degrees more duration than the early cams. I didn't cut the head and with the big cams I have 145 psi cold with the cams in at 108 degrees as specified on the cam card. I initially put the intake cam in 5 degrees advanced and got between 155 and 160 psi however it made more hp on the dyno with them in @108 centerline but less torque. I now have 3,000 miles on this combination. Supposedly a water cooled motor with a head of this type can tolerate 190 psi on 93 octane pump gas without detonation however an air cooled deal would be less but how much less I don't know as it would depend on how hot the head and fuel mixture was. For every 1 octane number less than the above you need to reduce the psi by 5 pounds or you can raise it 5 pounds for each number you increase the octane number by. The Wiseco pistons only have a 6.6 cc dome which simply isn't big enough for a 1200 cc XS motor if you are using the late head with big cams. The Wiseco pistons I got in late 07 were the 2nd. design and are plenty trick with anti detonation grooves and a U groove on the 2nd. ring land but it's a darn shame the domes are not 3 cc's bigger. They would be fine with the early head which has smaller chambers but the one size fits all is a compromise at best. In your case though you have more than enough psi and don't need any more piston dome volume with your combination. Thanks again for your info. Dan

[81xsproject]

I will get you some numbers for late w/ early cam when I get a chance.

[rpgoerlich]

When I got the 79 special I checked compression as well. It had 180 -185# on all 4 cylinders. Dont know if it has a kit in it or not.

[Dan Hodges]

Under Pressure

Thanks all for your numbers and it appears the Top Cat and the man from Katy, Texas get the pressure awards with those 180 something numbers. When I took mine apart this last time the combustion chambers and piston domes had a lot of carbon build up and when I cc'd the chambers I got 38 cc's. I cleaned them up removing all of the carbon residue and cc'd them again and got maybe 38.5 cc's and so I didn't have as much carbon build up as I thought. I have another 81 head that I bought off E-bay and it too had lot's of carbon and it checked out at 38 cc's also. Some folks don't believe in paying much attention to pumping compression and prefer to rely solely on the results of a leak down test to guage how well the motor is sealing up however both are important. I've checked the combustion chambers of several late heads but I've never cc'd a 78 or 79 head which leads me to the next question. Have any of you guy's/Ladies ever cc'd the combustion chambers of a 78-79 head and if so what numbers (cc's) did you get? Thanks again for your help. Dan

[tw1980]

Hey Dan,I also run MC cams w/ a 1196 kit.I did not advance my intake cam.Should I have?I ordered the cam gears they recommended at MC but they would not mount onto the cams.So I used the original cam gears.Thanks Terry

[Dan Hodges]

Cam Sprockets

Hey Dan,I also run MC cams w/ a 1196 kit.I did not advance my intake cam.Should I have?I ordered the cam gears they recommended at MC but they would not mount onto the cams.So I used the original cam gears.Thanks Terry

You can order slotted sprockets from Mega-Cycle and as far as I know they use the stock Yamaha sprockets that they modify to allow the cams to be advanced ot retarded. I bought new sprockets from Yamaha and modified them myself. When you install the M/C cams or any cams for that matter they should be degreed to make sure they are being put in per the specs on the cam card. With the stock cams you simply put them in and align the dots which will work but it isn't dead nut on and without slotted sprockets you can't alter them. If a set of cams will go in at plus or minus 2 degrees from that on the cam card they are good to go otherwise you will need to alter them to get the recommended center line setting. Whether or not you should advance the cams you got from M/C would depend on the grind you got from them and where you want the power curve to be. If they sent you the wrong cam sprockets you should send them back because I'm sure they would be happy to get you the correct ones.

[tw1980]

Thanks Dan I'll give them a call.Terry

[Bigleo]

compression

Hi Dan,
My 1980 with the 1197 kit in it, and 1978 cams, has 160 PSI across the board. The head was cut slightly just to make sure it was flat, but only about .002 or so.
Leo

[Dan Hodges]

Optimum Compression

Hi Dan,
My 1980 with the 1197 kit in it, and 1978 cams, has 160 PSI across the board. The head was cut slightly just to make sure it was flat, but only about .002 or so.
Leo

Hi Leo:

This is a dead nut on number and ideal for an air cooled street combination on 91-93 octane pump gas. When my 81 was bone stock with the 78 cams it had between 145 & 150 lbs. warm with 27,000 miles on the clock. I never got any numbers on mine with the 1179 kit and the 78 cams because I put the MegaCycle cams in when I built the motor and those cams have 17 degrees more intake duration than the 78 intake does and with 3,000 miles on the rebuild I've got 145 psi. When I spin it, the guage flashes to maybe 150 but settles on 142-145 psi. When I first put it together I had the intake in at 103 degrees ICL which is 5 degrees advanced from the recommended numbers on the cam card and it had a tick less than 160 psi and made a lot of torque on the dyno and when I put the cam in at 108 degrees ICL per the cam card it made more horsepower but about 3-5 lbs. less torque and significantly less pumping compression. I have an even bigger intake cam than the the one I'm using however the static compression of the Wisecos isn't suffiecient for it to work properly. I appreciate your assistance and now all I need is a set of good numbers for a 78-79 model with the Wiseco 1179-1196 kit and my data base will be complete. I can only assume they would pump more with the Wiseco kit because they have a smaller combustion chamber and subsequently would have more static compression all other things being equal.
Thanks again.
Dan

[TopCatGr58]

Followup Values.

Hey Dan,

This won't complete your database, but I wanted to provide the followup data that I promised compared to my 'just broke in' data.

It had been a long time since I had checked it, and while I was doing a bunch of stuff on the bike today, changing oil, new plugs, the cam chain tensioner, I did the comp test. The values I got were:
105-115-100-90 I thought, my god, what have I done to it!

Then I had the DOH moment, and realized that I had not had the throttle wide open. I've instructed many others on this, but just forgot! So folks you see it DOES make a big difference in the values you get if you don't use WOT!

The WOT values were:
170-165-155-160. They are within 10% of each other, although #3 is lowest. I didn't try adding any oil.

Again, these are on an 81SH with stock cams, valves, just the 1179 and graphite head gasket, now with some 16K miles on it. Nice to see/read what you said about BigLeo's readings for using 93 Octane, that's what I use in it.
Hope you get the early model values soon!
T.C.