Increasing comp ratio

[Jashdown]

Long story short, my road bike (09 GSXR 1000) has been written off after an accident, which resulted in engine top end seizing.

Externally, and judging by the gentle nature of the failure and lack of metal in the oil, I'm going to hazard a guess there's no head or crank/rod damage, so I'm just looking at replacing the pistons, pins, rings and bearings, plus any associated seals and gaskets.

The bike has been written off and I'm converting it to a race bike, I'll be rebuilding the engine, but I'm just wondering if there's any significant power increase to be had from upping the CR from standard 12.8:1 to a more hefty 13.8:1 (aftermarket wiseco pistons). I'll likely chuck in a marginally thinner head gasket to get it to 14:1 and then adjust valve timings to get the power output closer to other litre bikes on the track.

What I'm really wondering is whether there is going to be any significant decrease in engine longevity and reliability (track bike, so not that much use). Obviously clearances will all need to be checked and what not, but I'm also wondering what other work needs to be done to account for a bumped up compression ratio. Will the head be fine for the increase, the head bolts, the rods.

It will be my first time doing any internal performance modifications, and I can't find much information relating to this stuff, so if anyone has experience doing something similar with other bikes, I'd love to have your input.

[nigelnobody]

IMHO build it back to stock specs.
My 09 has 11k road and 30+ ride days.(no issues)
Geared properly(-1 +2)with a good exit loses prob 15 kph on straight,and launches of corners around the back.
Spend rest on suspension depending on your pace as they start to suffer around .38's with standard rebuilt internals.

[Jashdown]

Stock specs was what I was initially going to do, but the cost difference is less than a couple hundred dollars for stock pistons vs high comp ones. It doesn't make sense to me, to go stock specs if the financial outlay is only about 10% more, unless of course the reliability suffers significantly.

I haven't been on the track in a few years and definitely couldn't utilise the power of the stock engine just yet, but every little bit helps when you're trying to keep up with the new bikes.

[Marshy]

Stevem should chime in here.....
He rebuilt his motor using wiseco pistons (much cheaper than stock ones), and had lots of hp, until it went bang on the main straight.

I'm not a fan of modding motors on track bikes, as they run 100% of their use at 10-tenths. Having a modded car motor, say, and you only floor it for a few seconds once in a while, it's not very highly stressed. Unlike a track bike.

If you've got deep pockets and are willing to rebuild it frequently as a preventive measure, go for it.

Also, have a look inside first. I was sure that a motor that dropped a valve at idle would be relatively fine inside, but the bores were very slightly damaged and it turned out not being worth fixing.


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[Jashdown]

That's definitely the sort of information I'm after.

I've heard various things about wiseco (or all aftermarket piston manufacturers) but the bad reports tend to be few and far between. There are a number of other options for forged high comp pistons, all around the same price +/- $100.

I'd be very interested to know what it was that caused steve's engine to go bang, whether it was actually a piston failure or another engine component overstressed by the use of the high comp pistons. I'd be inclined to go with the latter.

This engine lost oil pressure, and according to my mechanic, the oil jets had reduced effectiveness which caused at least one small end bearing to seize. There was definitely a spun bearing, I heard it moments before the engine died. I'll consider myself very lucky if there's no damage to the crank or cams, but only time will tell. I'm yet to get the bike back from insurance, but should be within the week. After that, it will take the next few weeks to pull it down and inspect it.

[stevem]

Stevem should chime in here.....
He rebuilt his motor using wiseco pistons (much cheaper than stock ones), and had lots of hp, until it went bang on the main straight.

I'm not a fan of modding motors on track bikes, as they run 100% of their use at 10-tenths. Having a modded car motor, say, and you only floor it for a few seconds once in a while, it's not very highly stressed. Unlike a track bike.

If you've got deep pockets and are willing to rebuild it frequently as a preventive measure, go for it.

Also, have a look inside first. I was sure that a motor that dropped a valve at idle would be relatively fine inside, but the bores were very slightly damaged and it turned out not being worth fixing.


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Mine went bang because a std BMW conrod bolt backed its was out. Apparently it was a common problem at one point with the beemer. I replaced it with a stock motor but even then it was pulled down and nicer bolts put in that were installed by measuring the stretch rather than torque. Hi comp pistons will give it more jump of the turns but personally I would leave it stock.

[BoB]

Mine went bang because a std BMW conrod bolt backed its was out. Apparently it was a common problem at one point with the beemer. I replaced it with a stock motor but even then it was pulled down and nicer bolts put in that were installed by measuring the stretch rather than torque. Hi comp pistons will give it more jump of the turns but personally I would leave it stock.

With the 600rr it recommended all new bolts and torque setting for the conrod bolts. How do you measure stretch instead of torque?

[stevem]

Shane Kinderis from Alpine performance in country Victoria was the guy who built it. San Diego BMW fly him to the states to build their engines and run on the salt flats.He built and ran Glen Allertons Next Gen bikes. From memory the bolt holes are open ended and he stretches them 6 thou.http://catalystracingcomposites.com/n-8936-https-www-press-bmwgroup-com-pressclub-p-us-pressdetail-htmlt.html https://youtu.be/s2oRJ9hdCMI