compression tester

[fxnteeth]

Probably a dumb question, but what is an accurate tester and where can I get one? at a decent price of course

[booblinker]

ATD, KDT, Snap-on, Craftsman etc. All should be good enough. What are you testing? Most testers don't come with the adapter to test the 4 stroke Hondas.

[fxnteeth]

I need to test it on my 85 ATC 250R.

[fxnteeth]

What kind of adapter do i need for that

[booblinker]

I'm pretty sure it should be 18 mm I think, and should come with any comp tester you buy.

[willreed03]

I got a decent comp tester from AutoZone for 30 bucks and it had a few different adapters and seems to be holding up well after 2 years.

[fxnteeth]

thank you. Going to autozone tonight

[fxnteeth]

AT what compression does a higher octane need to be run?

[El Camexican]

AT what compression does a higher octane need to be run?

What is it you have? Regardless, there is no exact answer for your question. As a wise man once said "You need just enough octane to avoid detonation, anything more and you're wasting power and money" A lot of people think high octane means more power, but the opposite is true as the additives used to surpress detonation displace burnable energy producing fuel.

Look at a modern sport bike that boasts 13:1 compression and a 14,000 redline and runs on pump gas, yet at 11:1 and a 10,000rmp redline an old 1100cc Suzuki will blow out head gaskets on pump gas if run hard. Running temp, combustion chamber shape, spark plug heat range, altitude, cam timing (on 4 strokes), ignition timing, etc. all play a role. Unless you have already loped off .200" from your head and bought a 14:1 domed piston it may be worth your while to run the motor on 92 and see if it will ping. Get it hot and lug it up a hill, that will answer your question.

I'll add I once made a bet with a guy who was running race gas in his essentualy stock street bike that it would be faster in the 1/4 mile on pump gas. We drained his tank and put some cheap pump gas in it and knocked 2/100ths of his best time of the day and added a couple mph as well. Race gas does not make anything faster unless it has an oxigen additive, or the vehical in question was detonating on a lesser fuel.

[willreed03]

You also have to factor in the ethanol in new gas which negatively affects older motors. My 84 250R would get hot and pre-detonate on 93 octane after running for a few hours on the trails or hard circle tracking. Compression was around 200 psi. Switched to a 50/50 mix of 93 and 110 to get 103 and the bike runs better and cooler for a looooooooong time now. It's important to realize that 'premium' gas in the 70's and 80's was a higher octane rating than 'premium' gas today. So the premium gas that is recommended for your 80's machine may need a higher octane than the premium of today can supply. As far as the additives being used to suppress detonation that is only found in octane booster products, like the little orange bottle at the gas station. Here is a good article by Klemm about octane and the effect of new gas on motors...

http://www.groupk.com/tec-gas96.htm
http://www.groupk.com/tec-gas97.htm

And a nice writeup on compression.

http://www.groupk.com/tec-comp.htm