A buddy just had a 95" kit put in along with new SE heads. He has a compression release on the top of each head that he says is used due to the higher compression. He pushes these buttons in when starting on a very cold or hot day. Never seen it before. Is this build as reliable as the other 95" builds that have lower compression and no compression release. What is the good bad and indifferent ?

 

With a higher compression motor it simply makes it easier for the starter to turn it over, There is no reason to assume his build is notreliable because of this, you could have borderline cranking pressure that would never be a problem until you get a 100 degree day and you stop for gas and get a heat soak issue, this is where the comp releases would be worth their weight in gold. As for the bad, you kind of lose that stealth thing, someone sees comp releases and knows you have a modded motor.

 

Anytime you start pulling more hp/torque out of a system than it was originally desighned for (and using that increase) reliability decreases. You can take a bone stock Twim cam and beat it every time you hit the starter and b4 long something is going to give up. Build a 110 hp/torque motor and leave all the other bike components stock and treat the bike like your new born babby girl and it will last 4ever. Common sense. The starter is no differant. It was desighned to turn over a motor with compression of 8.8:1 (88 inch). When you increase the compression to say in my case 10:1 you have added a little over 10% load to its work load. Will it do this extra work as is? Sure, Just like if you are moving 50lb feed sacks from one store to the other and some one adds a 5lb sack of Cat Chow on top of your bag. You can still move it but you will wear out a little sooner. The releases just take SOME of the innitial compression off the cylinders to reduce the load on the starter. The hotter it is the harder it is for the starter to turn it over. I just get in a habbit of using mine every time.

 

My 95 inch motor on my 03 ,

Bill Bishop Heads
Andrews TW 60G cams gear drive
KB pistons 10.5:1
V Thunder Pro Magnum lifters
Rivera Pro Clutch
SE 44 mm carb
Kerker(supertrapp) exhaust, 12,000 miles runs great.

No compression release's but if I did over I would have installed them
you can tell when my bike cranks over there is plenty of compression
bottom line is compression makes power, along with right
Components , as Phil would say.....

 

The higher the engines compression, the more work a starter must do to get each piston up and through its compression stroke. Combine that with ignition advance and the plug firing BTDC and you have a hard starting engine and more wear and tear on the starter. With compresion releases, the first time through the compression stroke, some of the cylinders compressed air/fuel mixture is expelled through the releases in effect lowering the engines compression, allowing the starter to get things spinnning before coming up against a full compression stroke. One through the first stroke, the releases automatically close and the engine will start on the next revoltion

Think of using a manual bicycle tire pump, the less air in the tire, the easier it is to use the pump, the fuller the tire gets (more compression) the harder it is to put a full stroke on the pump handle. There are other possibilities also if using certain ignition systems. I am running the DTT TCFI II and have it programmed not to fire the plugs on the first revolution of the engine, again letting it get a good free spin before trying to start.

If everything is good with an engine build, and you dont flog it every time you leave a red light, a properly built engine will last a long time. Compression releases are just one way to make everything last longer and work better, I use mine for every start, hot or cold.

 

After seeing some testing at R&R CycleI believe they are always a good idea. R&R tested hydrocarbon levels on their research dyno and found that when the battery was recharging the levels were higher which means that the amperage drop to the ignition makes a differance. They say the battery can have as much as 30% of its amperage depleted from a start.

 

Thanks for the reply's everyone. Very informative