Modded 150cc Gy6 stats: EGT, A/F Ratio, Max RPM

Posts: 146

Here is some data I've collected on the first few runs after installing the new BuggyDepot EGT, A/F, and RPM gauges. We expect to have these gauges in stock soon. These are all 52mm analog needle gauges with backlighting.

Performance modifications to this buggy are:
- Milled yerf (HOWHIT) head (50thou over)
- UNI kit
- Upgraded CDI
- All CVT modifications 10g/1500rpm, 115mm variator, high-stall clutch

Air/Fuel Ratio
With the Uni kit, stock exhaust, and stock jetting, the A/F mixture fluctuates on the lower end of stoich (bordering rich), hitting pig rich during changes in throttle position.

Exhaust gas temperatures:
* Idle: 500°F
* Cruising 6000rpm: 590°F
* Accelerating: depending on amount of throttle, 600°F ~ 900°F
* Peddling at 10,000rpm: 1050°F
* I haven't gone above 10,000 RPM yet, I will get a top RPM stat soon. I'll have to estimate because the dial readings on the tach max out at 10k.

The design of the GY6 amazes me. This engine is running 87oct with the milled head and there isn't a hint of knock. Even while flooring it at 10k.

Posts: 74

Any idea how much HP the engine produces with the mods?

Posts: 2577

Thanks for the heads-up Travis...

Good Info... Any chance you'll ever get that on a dyno?

Posts: 146

I couldn't tell you the HP/TQ of the engine without largely guessing, but between the engine modifications and the light weight of this one-off chassis, this 150cc is very lively. The entire buggy weighs in at only 295lbs, fully loaded with all Buggy Depot reinforcements.

I've been thinking of getting out to the dyno, but I can only get out from under my rock every so often. Wink

I pushed the engine past 10,000RPM this afternoon. The tach needle pegged out at 10k, while the engine RPM kept steadily climbing. I started peddling at what I think was about 11,000, but there was definitely more room to push it farther. The whine from the cooling fan at 10k+ RPM is... very nice.

The exhaust temperature stayed at around 1050°F until I backed off. A/F ratio was bordering stoich/rich the whole way.

These gauges are going to help a lot in finishing up a couple of loose performance projects I'm working on.

A couple of neighborhood dogs thought they could take a bite out of the buggy today, but I wrapped them off a couple dust sandwiches in short order. I couldn't help but grin at the owner. Very Happy

Posts: 2640

wooooooow!!!!

That buggy is sick...

Looks real cool... Is it at all tipsy?

You can really go .050 on that deck of the howhit head??? Any clearance or interference issues at all??? What head gasket did you use?

I soooo want to deck the head and go full port and polish, or at least stroker crank and port and polish, but I heard you need a different head gasket or spacer of some kind???

Looks amazing though!!! got any vids of that bad boy in action????

john Very Happy

Posts: 1832

I love to see YerfDoggs modded all out like that! Nice work Travis. We've got an old Blue Yerf sitting out in a shed behind my garage,.....................gives me something to think about before I go to sleep tonight Wink

Posts: 146

Thanks Guys!

The 0.050" decked head hasn't been a problem at all. I'm using the stock head gasket, and there weren't any issues installing.

The one thing of note is that there is a slight bit of slack in the cam chain, but doesn't seem to be a problem. Until recently the engine has always started up immediately when pushing the start button.. as if it somehow knew I was going to hit the button beforehand. It's getting a little hard to start now, but I believe this is due to the valves needing adjusting after break-in.

The buggy isn't at all tipsy, it actually surprises me how stable it is at high speed. There are a series of speed bumps (haha) built into the gravel road I've been testing the buggy on, which I've been taking at full speed. It seems to have a very good center of gravity. I haven't been able to get it up on two wheels yet even with all the drifting, doughnuts, and powersliding we've been doing lately.

I will try to get a couple of WOT videos tomorrow, providing I can fool around with the camera enough and figure out a way to mount it to show the tach readings.

About installing the stroker crank... the stroker will need a spacer of of one kind or another (either below the jug, or possibly between the jug and head). Without the spacer, the piston will hit even a stock head. On one of our other performance test engines (60mm stroker, 62mm big bore, 0.050" head, etc), I've installed a triple stack of head gaskets in order to space the stroked piston away from the head. I haven't fired it up yet, but hopefully this will work reliably. Also, you will need to grind a small section of the oil pump housing in order to clear the outer rim of the crankshaft assembly. I'm not sure if this is the case on non-HOWHIT engines, but it isn't a big deal anyway.

Posts: 2577

When you get a chance can you get some close up shots of the single seat stuff (seat mount, pedals, etc..).

My son (ACBlind) made his into a single seat Y'Dog and we still need to move his pedals. Now that we have a welder we should be able to do that fairly soon.

His buggy is stable, however I have had it up on two wheels. He rolled it at the National Bash, but that was going down into a ditch around a tree so that's understandable.

Good Info that we can all use.

Good work Travis... Keep it up.

Posts: 3572

I'm trying to figure out how you can be rich with a Uni on the carb. Stock jet is what--110? It's got to be that the restricted stock pipe (you didn't drill out either end??) isn't letting enough air velocity through the carb to finely atomize the gas. I bet you still have some HP locked away in that Howhit. My first Uni & redneck intake was a little disappointing til I opened up the exhaust. Then it came to life!
Are you planning to continue the mods in stages & see what effect each has?

Excellent reporting so far Travis. Thanks much!!

Posts: 2577

Stock Jets on a Yerf can be a 110, 112 or 114. I haven't seen any other than these.

When we did ACBlind's mods we didn't gut the exhuast for quite some time. His buggy ran okay without the gutted exhaust, but Mark's right, once we opened up the exhaust the ol' Dog came to life.