GS1000 Increasing Compression Ratio?

[DonPearsall]

I have a 1979 GS1000E. I want to increase the compression ratio from the stock 9.2 CR to about 11.0 but want to keep the stock 70mm bore. I have looked and looked online and can't find any kits that will do this. I know there are lots of overbore kits, but need to keep the displacement under 1000cc. All overbore kits take the displacement over 1000cc.

Does anyone know of a kit that will do this? Alternatively I can mill the head, but that is the last choice.

Has anyone milled their GS1000 or 1100 head? 

Thanks,

Don

[wraith]

Yoshimura did a hi comp pistions of standard bore for the gs1000. Don't know if they still do.

You could skim head/barrels to help get the comp you want.

Take it's for track use.

[DonPearsall]

Thanks for the reply. Yes, land speed racing in the stock class so can't go over 1000cc.  I will do a search for Yoshimura. 

Don

[cnap504]

Custom pistons, to your specs, could be had from a manufacturer.  The stock pistons, I believe, are cast, light and reliable for normally aspirated engines.  They also have less thermal distortion than a forged piston allowing for a more snug cylinder fit.  Milling the head, fly cutting the piston valve reliefs and degreeing the cams just might work.

[coombehouse]

I'd measure everything to see if it is possible to get the increase by reducing squish to about 0.030" with whatever head gasket you intend to use &  then skim the head to gain the rest assuming you can maintain enough valve clearance. 

 

 

[Gixer1460]

10 hours ago, coombehouse said:

I'd measure everything to see if it is possible to get the increase by reducing squish to about 0.030" with whatever head gasket you intend to use &  then skim the head to gain the rest assuming you can maintain enough valve clearance. 

Probably good advice for a shell bearing'd crank but rollers and needle bearings have a little more 'give' and 0.75mm is pretty tight even for shell bearings! I don't think i'd like less than 1.0mm squish in these 'old' engines, assembled (as that is what matters) - just my opinion!

[Reinhoud]

JE can make pistons on customer specs.

 

[Reinhoud]

On 3/16/2021 at 8:11 AM, DonPearsall said:

Thanks for the reply. Yes, land speed racing in the stock class so can't go over 1000cc.  I will do a search for Yoshimura. 

Don

Are they going to take the head off and measure the bore and stroke?

[coombehouse]

On 3/17/2021 at 9:54 AM, Gixer1460 said:

Probably good advice for a shell bearing'd crank but rollers and needle bearings have a little more 'give' and 0.75mm is pretty tight even for shell bearings! I don't think i'd like less than 1.0mm squish in these 'old' engines, assembled (as that is what matters) - just my opinion!

Yes you are probably right but as this is a race motor & every little bit matters, it's probably worth the risk. I have run that close on my road bike for many years but these days, I have backed off to 1mm as you say. In the past we built some superstock motors that had almost zero clearance when they were cold. They didn't last long but they were fast & were rebuilt after every race.

[slayer61]

55 minutes ago, Reinhoud said:

Are they going to take the head off and measure the bore and stroke?

Been my experience, that's only done in the event of a protest. 

[DonPearsall]

If you go faster than the record speed you must have your bore and stroke measured. On my Hayabusa that was fairly easy because they have a device that can measure both through the spark plug holes. The 'Busa has centered straight plug holes. But the GS1000 has angled holes so that is not possible. You must take off the head and get it measured that way. It is a real hassle. But you can't break a record unless that is done.