1101cc vs 1179cc vs 1209cc

[Crazcnuk]

The head itself doesn't matter, only that your changing bore size, and using the SAME head.

The actual end compression ratio will depend on a lot of factors, but the question was whether JUST boring out changes your compression ratio.

As for head changes, the only change I am aware of is that the later heads had larger valves, and a slightly different cam profile.

[trbig]

The heads did change after 79. The bowl that the valve faces are in increased, so the pistons became higher domed with a bigger relief valve to try to offset some of the compression loss I presume. It didn't take care of it altogether though because the '80 and above had lower compression than the 78/79 even though the pistons are higher domed.


Tod

[pggg]

I had an 80'SG big valved cylinder head on a 78E motor with 3rd oversize pistons(stamped .75) I also dremelled each piston valve pocket 1mm wider each side, the motor ran great with no compression drop on the gauge, 80' cams ran better than 78 cams with better midrange grunt, current bike has wiseco 1196 pistons and same bigger valves and 80 cams, 1196 cc is definitely gruntier at low and midrange than 1101cc but it feels like extra strong torque rather than horsepower, top speed difference between 1101cc and 1196cc for me was basically 2/10ths of bugger all...

[trbig]

The 80 cams worked BETTER than the 78's?!? WOW... now I am curios. Gonna have to try 'em both out and see. Low and mid range is what I'm after. Whatever was decided that I went... 130-140mph is going pretty good. Do you realize how fast those 25 year old u-joints and gears were spinning?


I know you've probably all seen this pic of the 78 piston on the right versus the 82 piston... The 82 is considerably higher domed.





But I went out to check bewteen the 82 pistons and the Wiseco ones and I think I was wrong. I think the 82 pistons are domed TALLER! The side of the piston is taller by just a touch and a level put on top shows the 82 to be higher. This isn't very scientific as far as measurements, but a pin through both pistons matched them side by side. the 82 piston is obviously the one on the right...









Tod

[79XS11F]

Originally posted by trbig



Assuming you meant 1179... There is virtually no difference between the domes and valve reliefs of the Wiseco and 80's model pistons.


If you did mean the kit for your 1979... it's the same kit I have. And yes, it is a taller dome and larger relief than the 78-79 pistons.

As far as compressing into the same space, it isn't. The top of the stroke isn't coming to the very top of the cylinder. So that's why I questioned it.


Tod

Yes the kit for my 1979 that went into the 1978 engine lol lol
Rob

[TopCatGr58]

Hey Tod,

You might not remember one of my old posts, but I've got the 1179 kit in my 81SH, I kept the OEM head, cams, just put the pistons in. The Stock Comp. values are supposed to be 142 psi at sea level, but after my breakin, I measured 180-185 psi!!

What's surprising is that atmospheric pressure should be about 14.7 psi at sea level, where I'm at! But 10.5 x 14.7 only yields about 154 psi. I realize that it doesn't work exactly that way, but all I know is that my comp. levels are much higher than STOCK, and I have the OEM heads/valves!

With my 4-1 pipes and Indy filters, I think I don't have as much low end grunt but I don't really know because it's been so long since I had or rode an OEM equipped machine! The cams and pipes do give it a very good mid and top end powerband which is where I like to ride anyways!

So...if you are willing to do the cam swaps, it will be interesting to here your impressions on the differences between them!
T.C.

[trbig]

Man,

I wish I had access to Maximan's dyno folks. I have a stock head with two different cams to try, then this ported head with the two cams to try. I could probably feel the difference between each of the cams in the seat of the pants, but to remember the difference between the 4 tries... not very scientific. Know what I mean Vern?!? Then I have this 78 head I could try which would boost the compression..... lol. As if I'm not tired enough of taking this thing apart and back together.


But since most folks will be running stock stuff, I'll try to figure out which of the two works best for me. See if my results agree with pggg's... even though i don't quite get what this means....

top speed difference between 1101cc and 1196cc for me was basically 2/10ths of bugger all...

We Yanks need MPH man!!!


Tod

[pggg]

Trbig, 2/10ths of bugger all = zilch! comparing cams though, on my setup the longer duration 78's showed up the 'dead' zone below 3000 revs distinctly, my 80' cams 'dig in' sooner and the 3000 to around 4500 range is way better than the 78 cams, carburation has a lot to do with it, the below 3000 range with my much criticised/ maligned modern 36mm carbs is so much improved I'm gonna give the 78 cams another twirl sooner or later, believe it or not, with 80 cams my setup takes off with serious power at 1500 revs in top gear! With 78 cams the power kicked in strong and hard at 5000 revs with a thrilling top end , but the 80 cams suit better with massive kick at low/medium while still pretty much matching the 78's top end power