GS1100 comp

[Anonymous]

why does a stock gsxr have 12 to 1 and street kits for a GS only have 10.25 will a gs with 12 to 1 run ok on pump gas?

[Anonymous]

Well, the GSXR has 20 years of additional port and combustion chamber R&D on it, a bit smaller bore, better ignition system, liquid cooling and revs higher. All of which make it less subsceptible to detonation problems.

I doubt a 12:1 GS would run well even on premium pump gas. Unless your premium is a lot different than the stuff here, anyway. There are things you can do to minimize detonation problems if you get a bit of pinging occasionally, but this would be a continual battle with a 12:1 CR in a street GS.

Mark

[Anonymous]

not all gsxrs are water cooled. but port design and bore size make sense

[Anonymous]

wouldnt a gsxr have a bigger bore when a gs has a 66mm stroke vs 58 or 59mm for a gsxr
Dave

[Anonymous]

not all gsxrs are water cooled. but port design and bore size make sense

wouldnt a gsxr have a bigger bore when a gs has a 66mm stroke vs 58 or 59mm for a gsxr

The air-oil cooled GSXR's never ran anything like a 12:1 compression ratio, though. My 86 750 was around 11.5:1 and I think the 1100 was less than that. It's only in the last few years that big street bikes have crossed into the 12:1 territory.

Bore and stroke dimensions:
82-83 GS1100: B-72mm, S-65.93mm
84+ GS1150: B-74mm, S-65.96mm
02-03 GSXR1000: B-73mm, S-59mm

The fact that the GSXR revs higher also helps a fair bit. Since combustion is happening in a shorter time span, there is less time for detonation or pre-ignition to get started. The major improvements are in the port and combustion chamber design, though. Everything else is a small increment, but the R&D work has been huge. The efficiencies that the Jap bikes are achieving now are amazing.

Mark

[Anonymous]

All of that considered even cam timing can have an effect as well. do you have any idea how much the thickness of the base gasket changes the ratio?
Dave

[Anonymous]

do you have any idea how much the thickness of the base gasket changes the ratio?

Not off hand, but it is fairly easy to calculate if you have the current CR, current base gasket thickness, displacement, bore and stroke and new base gasket thickness.

Mark

[massakins]

I would expect the success with higher compression engines today owes a lot to combustion chamber efficiency (4 valves superior to 2 valves), fuel management (fuel injection superior to carburetors) and improved ignition controls. Some newer bikes even have detonation control devices and throttle position sensors that vary ignition timing, I think. Much different than our beloved old GSs.

[SqDancerLynn1]

Just like the cars of today electronic controls/ efficient combustion chambers have enabled the mfg to raise comp ratios.

[Anonymous]

For a more efficient and reliable motor, stick with 10.25 / 1 compression combined with carbs, cams, header and Dana ignition with a good port and valve job, all in the correct combination will give you tremendous power gains for the street. At the same time loads of fun.

Best of Luck! Archie

[saaz]

GSX1100 had 4 valves, but relatively low (by todays standards) compression ratio. A GSX-R1000 makes 150 rear wheel horses bog standard (emissions etc) that a hotted up GSX1100 would be hard pressed to make (and would not meet emissions). Just remember how much more power the GSX1100 made when it came out compared to 10 years before it....

Power is not all of course..the GSX14000 makes 100 hp standard, but is a torque monster, with relatively mild tuning. It all becomes a bit academic after a certain point....

[cbxchris]

Archie pretty much hit it on the head. Anything with over 180 pounds of cranking compression on a GS is going to have problems with fuel. I recently had a hayabusa that easily ran pump fuel with 220 pounds of cranking compression. Stock on a hayabusa is around 190-195. Gives a person some idea of advances in head/ignition/fuel designs since the GS series. I think it may be possible with cams to use a 11 to 1 piston and maybe just get by on pump fuel. I personally do not like shimming the bore with base gaskets for compression ratio. Without going into great detail I have seen many problems in racing engines doing that especially with turbo`s and NOS.

[Anonymous]

You have been a lot of help.I have picked up a lot of info in a few days this my first time using a forum of any kind.
Dave

[Anonymous]

My GSX1100 (1170cc) runs fine on UK fuel (95) with a 12/1 compression.

[Paul]

Isn't there two ways of expressing compression ratio.
1, Swept volume + combustion chamber volume divided by combustion chamber volume.
2. Swept volume divided by combustion chamber volume.
Take a 1000cc 4 cylinder engine, the swept volume is 1000cc divided by 4 = 250cc
The combustion chamber volume is the volume left in the combustion chamber when the piston is at TDC, lets say 25cc.
So with method 1 the compression ratio is 250 + 25 divided by 25 = 11:1
But with method 2, it is 250 divided by 25 = 10:1
Same engine!
Or lets tune it up a bit!
Bore it out to 1260cc, thats 315cc per cylinder, bigger domes on pistons gives us combust vol of 20 cc
With method 2 we have an engine of 15.75 C.R.
But with method 1 it is 16.75.

Be careful, figures can be misleading. The Japs are past masters at this.