Vintageman wrote:
I opened the intake boot and port to match and followed that about 3/4" into intake where it opened up nicely anyway. I run the later (mine is a 1975) ignition timing (24 degree?). I like midrange torque. I run a 0.020" head gasket versus the 0.040". I run 2mm OS pistons (~200 cc)
Fun Stuff
Vintageman.... I'm interested in your experience of reducing head gasket thickness from 0.040" to 0.020." What specifically did you notice in performance, rideability, economy or other issues?
Are you running pure copper head gaskets and did you make them from flat stock or purchase them; if so where?
They put back a little of the midrange I lost with the radical chambers specifically between 5-6k rpm I was trying to fix.
And if you take a little off EX port height you can recover some compression back for just a few dollars. Some examples you see for raising EX port height say to shave head about 1/3 - 1/2 the amount you raised EX port assuming you have a lip. For example if you shave head, just lip off on GT185 (maybe 0.020" to .030" lip?) most machine shops do that at a relatively low cost versus reshaping domes as well. And you get another 0.020" for thin head gasket since Suz used 0.040' on the GT185 and some other models->
For example last year I raised my GT550 Ex port ~ 0.050"-0.060" and switched from stock 0.040" head gasket to 0.020" Aluminum head gaskets from T350 . It made a difference you feel midrange ( I also had a GT550 head which I machine 0.035" off). I think that was too much (ping unless high octane) and I was thinking I was going to take 0.070"-0.080" of EX port but stopped sooner than that.
I just ported a set of GT380 Cyls for my GT380 which where like 33.3mm now 32.0mm Ex height and plan to run 0.020" Al T250 head gaskets instead of the 0.040" stock ones.
There is a Suz bulletin for the changes in the later builds of 1976 GT250 to reduce compression. I think the put back 0.010" on later builds and good for a couple tenths (i.e. 6.8:1 versus 7.0:1) Check the bulletin for sure. That's a could rule of thumb me think when you don't cut into head dome shape.
The gaskets were something I had kicking around. I think I had to work them a little about the head bolt studs to fit. Maybe they were from RD200 or CS3/CS5 Yam. Not sure.
Look around. For example a TM100 may work , but you'll have to make one new hole...
