gauging rpm

[mike75925]

do you guys just go to the dyno, or are you all using michron setups? what is the easiest tach? in getting more power i threw a 1/4" plate across the vehicles seat in case of fragging. as i don't have access to a dyno could anyone ball park my ponies? stock bottom end, GX160 head, gov yanked, carb tweaked, straight pipe 1", super thin head gasket, flat bottomed valves, longer rockers, dished piston, paper element ripped out of filter, and ram aired (not quite sealed yet but should help to inflate 'er lungs)? thanks in advance ps 50 racing oil, 89 octane

[modelengineer]

You can work it out from your gearing, wheel size and max speed. Why do you need to know while your driving? You should know what it sounds like at max RPM, so you can gauge how much you've got left, I would have thought.

But to answer your question I use an Autometer Adjustable Shift Lite Tacho

[BAMBY]

the tach i have is this one...

http://www.tinytach.com/tinytach/commercial.php

i like it a lot. tells rpms, total run time, run time for a job, two service timers. its awesome.
BAMBY

[freakboy]

how did you attach that tach?

[Kaptain Krunch]

65 bucks and it only lasts 5 years :worried2:

[jr dragster Tyler]

You'l spend more in gas in 5 years then you did for the tach. I do agree it is a bit pricey and thats why I dont have a tach on my kart. You just wrap the lead wire around the sparkplug wire. I'm sure if you REALY wanted to replace the battery you could carefully disect it and replace it.

[mike75925]

thanks, for the info. and to model engineer, i'm used to engines the rev to 14k (crotch rockets) getting used to the smaller output type motors though

[Kenny_McCormic]

You can use a cheapo digital bicycle speedo as a tach, simply mount the pickup on your flywheel shroud(might need to cut a hole, the pickup needs to "see" the magnet) set it to display mph and input 268mm for the wheel size.

http://www.instructables.com/id/S9RSH6XFD80WTNY/

[mike75925]

ok grabbed a schwinn 12 function, had to make a jack of sorts for the mag. about 1/8" away and picks up when hand spinning the wheel. jb'd the jack into my manco wheel. figured since it has no tach function, i could take the speed and input it into the speed calculator. installed on non-drive wheel.

[anderkart]

ps 50 racing oil


From all I've heard, you might be better off using a thinner oil (like 30 or10-30 wt.) in a high reving motors like yours.

[EagleTalons]

Here is a cheapie one. I bought two, one for MPH and the other for RPM.

[oscaryu1]

Here is a cheapie one. I bought two, one for MPH and the other for RPM.

Where is here :)?

[freakboy]

Where is here :)?

its over there.

[EagleTalons]

Oh sorry. :p

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=160305540501

[mike75925]

if my revs are low enough i may change weights. i have yet to remove fan fins or use an offset key.

[brendonv]

but a bike computer only reads to like 100km/h so it wouldnt gauge the rpm.

[freakboy]

if my revs are low enough i may change weights. i have yet to remove fan fins or use an offset key.

do not remove fly wheel fans, bad things happen to lightend flywheels man. just cause they wont go stock at 5k that dont mean if you drill or mess with them they wont go at that speed.

[oscaryu1]

Fins help cool the engine also. Remove them, and not give it enough cooling, you'll fry some parts.

[mike75925]

i have some edf's (electric ducted fans) the faster they spin the less efficient they become. on a six blade setup, remove three and you will see high end gains. granted some of the motors spin to 100k rpm, but if the pitch is not matched to the motors capability, it would be like running a 5hp carb on an 8hp engine

[EagleTalons]

but a bike computer only reads to like 100km/h so it wouldnt gauge the rpm.

It reads in 100 rpms, read the link Kenny gave us.

[mike75925]

freak boy plastic fan on metal fly. ok finally road tested with comp, reads 21mph. yeah, a bit disappointed. if the comp is working right which i don't think it is, i am getting around 3700rpm. .... sad. as far as removing fins, when moving the fins are not necessary, so if you don't take a long time warming up, shouldn't be a problem

[freakboy]

ok sorry i thought you ment cuttin them off of a cast fly wheel.

[mike75925]

no i know better than that. rebalancing, rpm test, no thanks

[mike75925]

ok, reinstalled my stock head. had a bowed pushrod. replaced it. it cranks and dies. last time this happened i yanked the governor. started raining so i will check my lash again soon. in setting after swap, i noticed coil binding on the exhaust, so i loosened it up a bit. cranking on it, sent some fuel out of the carb so that is too tight for sure.

[mike75925]

loosened the intake. ran without breather assembly, 20mph. reinstalled breather, 21.4 avg with 22.5 max. seems to like uphill better than down. speedo anyway. died on me once. restarted no problem. next i will try the oe muffler.

[EagleTalons]

What are your gear and tire sizes..?

[mike75925]

10/62 35.75 or 608

[EagleTalons]

Hmm... I don't know how tire sizes work, but it should be running faster than that, I'd think..

[Kaptain Krunch]

10/62 35.75 or 608

What do you mean by 35.75/608 for tire size? Just tell me in inches, like 12" 14" etc. Either way, you have about 6:1 gearing, unless you have like 12" tires you should be going faster. With my governed engine, 6:1 gearing, and 15" tires i do about 25-28mph.

[mike75925]

35.75" circumference, i forget the height. 608 is the metric. what weight oil are you running?

[EagleTalons]

5 30w synthetic in my clone. It runs good with it, might be a little thin, I'd get 10 30w, but I have alot of this light oil.

[mike75925]

i just grabbed some 5w 30. hopefully that will do the trick!

[Kaptain Krunch]

I got 10w30 in mine. But 35" circumference is like 12" diameter isnt it? That would make sense speed wise if the engine was governed, But ungoverned...i dont know.

[mike75925]

changed the oil about to take her around with mildly ported 6.5 head and straight pipe.

[mike75925]

still 21mph (21.4). what is your main jet size, stock of course?

[EagleTalons]

Yes, stock ungoverned.

[mike75925]

hunh?

[EagleTalons]

My bad! I mean stock governed hehe...

[mike75925]

haha, on the calc, i am running 3950ish rpm

[EagleTalons]

Man...get some bigger tires or a smaller sprocket!

[mike75925]

i'd be happy to get the 5200 thats supposed to be there!

[jr dragster Tyler]

It should be revving alot higher then that. Once you find the probelem it wont take a tachometer to know your revving it out.

[mike75925]

so i swapped back to my stock rockers, i removed the lash cap from the intake, the intake spring felt weaker than the exhaust so i swapped them back to stock. same power, but now if i put the filter assm. back on, i draw way too much gas (black smoke). mix cannot fix it. so i removed the breather. sounds different, and starting to sound a bit weaker. also put stock muffler back on, same, just quieter. starting to wonder if it isn't a sleeper! when i say same, i mean no noticeable differences