Mrtaterman Posted April 23, 2017 Report Share Posted April 23, 2017 thought i would share the drastic difference between a quality compression gauge vs others on the market. the bike: 98 banshee fresh 421 assassin low ports 33mm pwk's vf4 reeds cpi inframe noss head 18cc domes +4 timing the gauges: ac delco from orielly. 24.99 craftsman from sears. 47.99 snap-on eepv500. 234.99 current elevation 6500ft. where i ride 7000ft. all tests were done one after another on an engine that ran for about 5 minutes to pull it out of the trailer to garage, both plugs out, throttle WO, kicked until gauge stopped climbing. estimated compression from driveline 170psi for 110 First test was with the ac delco: about 15 kicks until gauge stopped right on 140 psi second test was with the craftsman: about 15 kicks until gauge stopped at 155 psi third test was with the snap-on: about 15 kicks until gauge stopped at 165 psi the difference concerns me a little due to the fact that if i would have ran fuel appropriate for 140 psi i would have probably had serious detonation and could have hurt motor easily. i am sure this has been posted before but just thought it would help out others. i didnt have a snapon, but i easily found one to borrow for an afternoon. if you are in a similar position to what i was, take a day to find someone to help you out with a good compression gauge. 2 Quote Link to comment Share on other sites More sharing options...
ClaudeMachining Posted April 24, 2017 Report Share Posted April 24, 2017 Maybe it's the snap on tool who is off lol!! Quote Link to comment Share on other sites More sharing options...
spurdy Posted April 24, 2017 Report Share Posted April 24, 2017 Maybe it's the snap on tool who is off lol!! I have a craftsman and a lisle and they both read exactly identical every time I've compared them. Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
ClaudeMachining Posted April 24, 2017 Report Share Posted April 24, 2017 When I did my engine, Billmtold me I should have about 145psi. So when i tested it with my canadian tire gauge, I got 135lbs. So I went to an autopart store I bought a 200$ gauge. It was reading something like 137psi... So I give back the 200$ gauge to the store. if it would have a big gap, I would keep the 200$ gauge, but since it was 2 psi.... But usually quality goes with higher price. Quote Link to comment Share on other sites More sharing options...
special06shee Posted April 24, 2017 Report Share Posted April 24, 2017 Zilla is 100% correct. Were the tips all equal lengths between each comp tester? If not that will change readings quite a bit. Its best to use a tip the same length as the spark plug. 2 Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted April 24, 2017 Report Share Posted April 24, 2017 thought i would share the drastic difference between a quality compression gauge vs others on the market. the bike: 98 banshee fresh 421 assassin low ports 33mm pwk's vf4 reeds cpi inframe noss head 18cc domes +4 timing the gauges: ac delco from orielly. 24.99 craftsman from sears. 47.99 snap-on eepv500. 234.99 current elevation 6500ft. where i ride 7000ft. all tests were done one after another on an engine that ran for about 5 minutes to pull it out of the trailer to garage, both plugs out, throttle WO, kicked until gauge stopped climbing. estimated compression from driveline 170psi for 110 First test was with the ac delco: about 15 kicks until gauge stopped right on 140 psi second test was with the craftsman: about 15 kicks until gauge stopped at 155 psi third test was with the snap-on: about 15 kicks until gauge stopped at 165 psi the difference concerns me a little due to the fact that if i would have ran fuel appropriate for 140 psi i would have probably had serious detonation and could have hurt motor easily. i am sure this has been posted before but just thought it would help out others. i didnt have a snapon, but i easily found one to borrow for an afternoon. if you are in a similar position to what i was, take a day to find someone to help you out with a good compression gauge. Cranking compression isn't the sole factor on picking fuel. Always know the calculated compression and use the cranking compression as an indicator of what the motor is doing inside. You can have a motor built for race fuel, but have an exhaust large enough to let some volume pass. So the number may look lower on a gauge. But kudos to you for checking with multiple gauges. 1 Quote Link to comment Share on other sites More sharing options...
Dunatic619 Posted April 24, 2017 Report Share Posted April 24, 2017 Snap-on and craftsman were the same for me. 180 on the dot each for each tester. Quote Link to comment Share on other sites More sharing options...
guns4children Posted April 24, 2017 Report Share Posted April 24, 2017 Snap on and craftsman both at 210 for me. Quote Link to comment Share on other sites More sharing options...
Ayesully810 Posted April 24, 2017 Report Share Posted April 24, 2017 Zilla is 100% correct. Were the tips all equal lengths between each comp tester? If not that will change readings quite a bit. Its best to use a tip the same length as the spark plug. This. When we were getting funky compression readings at driveline trying to do dome swaps we ran into this. Once we used an adapter that was the same as a spark plug, we got 170 psi on the dot. good write up either way, a quality compression reader will def read better. Quote Link to comment Share on other sites More sharing options...
jbooker82 Posted April 25, 2017 Report Share Posted April 25, 2017 Gauges that use one hose and a bunch of different adaptors are not going to be real accurate. The adaptor is hollow and that extra hollow space is added volume to the combustion chamber. Look at how much of a difference a cc or two makes when shopping for dome sizes. The same is said when doing a compression test. Snap on gauges with the proper hose has the Schrader valve in the very tip of the hose so there is no added volume. Quote Link to comment Share on other sites More sharing options...
jbooker82 Posted April 25, 2017 Report Share Posted April 25, 2017 Snap on hose. Cheap gauge with adaptors. 1 Quote Link to comment Share on other sites More sharing options...
ClaudeMachining Posted April 25, 2017 Report Share Posted April 25, 2017 Dude, multiple dudes here have already said that their craftsman gauge is giving the same read as a 250$ gauge. A pressure gauge is not exactly a space shuttle you know. But yes, I agree, 90% of the time you got what you paid for. Envoyé de mon SM-G935W8 en utilisant Tapatalk 1 Quote Link to comment Share on other sites More sharing options...
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