Small engine RPM question

1,804 Views | 21 Replies | Last: 5 yr ago by MrJonMan
MrJonMan
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I've posted this on the golf cart message boards but not getting an answer, so figured I'd ask the smart minds over here.

Ultimately I'll be doing an engine swap (Vegas Carts), but figured I would use the stock engine until it dies. Plus my wife will approve easier if it needs an engine rather than I want one haha.

I've got a 2007 EZGO ST350 2+2. Engine is a Robins 350 and stock as far as I know, with the exception of me adjusting the governor. I suspect it isn't working based on the speeds I'm getting. I also added an Equus tach.

Here's the question...

I know that running at a higher RPM wears on the engine faster, and no one can say just how fast, but if at WOT it's hitting 5k RPM, what the best guess on how long it will last? Weeks? Months? Years? I believe EZGO says 4K is the max you should run.

It's hitting 25-27 mph (2-4 mph faster than I expected) according to two different GPS on my phone. That's why I added the tachometer, so I could see how much RPM it's churning.

My main concern is that I won't grenade the engine soon....like in the next 2 weeks, when I'm supposed to haul it down to Port A for a week at the beach with the in laws....be a bad time for it to die.

Appreciate it!

Oh and I'd post a pic if I knew how now that photobucket is gone....fail I know
1agswitchin4lanes
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You need a two speed transmission so you can get 45mph
MrJonMan
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1agswitchin4lanes said:

You need a two speed transmission so you can get 45mph


Ha....big block kit and high speed gears will do quite a bit.

Now focus on the question!
The Lost
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If you don't drive it until you get down there it'll last at least until then! (Telling us how often/what you use it for helps)

So I'm gonna go between 1-1000 trips no problem. If you street race it probably lower than if you just take it golfing (assuming you aren't maxing those rpms while golfing which would be terrifying for all, but please post the YouTube video of it in the lake)

Also why are you concerned about not grenading it?

"My main concern is that I won't grenade the engine soon....like in the next 2 weeks, when I'm supposed to haul it down to Port A for a week at the beach with the in laws....be a bad time for it to die."
TexasRebel
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Is it still able to cool itself? Does the oil have sufficient viscosity?

What radial forces are the rotating components designed to withstand? (Flywheel, crankshaft, etc.)

Can the tires take it?
MrJonMan
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The Lost said:

If you don't drive it until you get down there it'll last at least until then! (Telling us how often/what you use it for helps)

So I'm gonna go between 1-1000 trips no problem. If you street race it probably lower than if you just take it golfing (assuming you aren't maxing those rpms while golfing which would be terrifying for all, but please post the YouTube video of it in the lake)

Also why are you concerned about not grenading it?

"My main concern is that I won't grenade the engine soon....like in the next 2 weeks, when I'm supposed to haul it down to Port A for a week at the beach with the in laws....be a bad time for it to die."
Oops....meant my main concern is the i DON'T grenade the engine soon.

The cart has never seen a golf course and likely never will, i just use it for bombing around the neighborhood or the in laws property
MrJonMan
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TexasRebel said:

Is it still able to cool itself? Does the oil have sufficient viscosity?

Its air cooled so technically yes. Running Mobil 1 10w-30 synthetic

What radial forces are the rotating components designed to withstand? (Flywheel, crankshaft, etc.)

I have no idea

Can the tires take it?

tires should be fine, they're basically new (bought when build started) and 22-10.5-12
MrJonMan
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Worth noting, supposedly the engine has a rev limiter built into it, but i can't imagine it doesn't kick in until 5,000. Maybe though since it hits 5, then doesn't budge
TexasRebel
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MrJonMan said:

TexasRebel said:

Is it still able to cool itself? Does the oil have sufficient viscosity?

Its air cooled so technically yes. Running Mobil 1 10w-30 synthetic

What radial forces are the rotating components designed to withstand? (Flywheel, crankshaft, etc.)

I have no idea

Can the tires take it?

tires should be fine, they're basically new (bought when build started) and 22-10.5-12



The surface area on an air cooled engine is only designed to shed so much wasted horsepower. Just because it's air-cooled doesn't mean you can safely run it hotter.

Radial forces increase a lot with centripetal acceleration. Balance is a huge deal. So is material. Ever watch a CD disintegrate by spinning too fast? Don't want that to happen to a mechanical accumulator.

Tires are also only designed for a certain speed. See: Goodyear's current issues with the RV tires lawsuits.
MouthBQ98
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These things are designed with a significant margin of error generally speaking, and also the governor settings were probably by the cart manufacturer for safety liability reasons and not by the engine manufacturer. There may be applications out there where the engine is run at higher RPM like you are doing. If it is kept properly lubricated it should be fine I would imagine.

I have an old 4 stroke Briggs and Stratton edger that is probably 40 years old and it works just fine.
MrJonMan
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MouthBQ98 said:

These things are designed with a significant margin of error generally speaking, and also the governor settings were probably by the cart manufacturer for safety liability reasons and not by the engine manufacturer. There may be applications out there where the engine is run at higher RPM like you are doing. If it is kept properly lubricated it should be fine I would imagine.

I have an old 4 stroke Briggs and Stratton edger that is probably 40 years old and it works just fine.


Yes the governor settings are due to safety restrictions and the speeds golf courses like. Plus not being required to manufacture them with seat belts and what not.

80085
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I think I had this question on the PE
MrJonMan
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The response I got from a member on the golf cart forum....quite comforting

To predict when something, anything, will fail is sheer speculation. So many factors, including Lady Luck and Murphy's Law.

But if you are going to run it to 5,000rpm briefly or sustained I would go ahead and get your complete engine swap shopping list finished.......

And maybe add a 1/4" steel plate under the seat to keep what's yours in the condition it is in now. Or there are those new ballistic proof athletic cups some of the MLB catchers are going to.
CanyonAg77
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I always thought these little gas engines peaked out at 3600.
TexasRebel
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Depends on the intended application. Some will hit 10k.

3,600 just happens to be a very nice number for 50 Hz and 60 Hz generators as well as round number math on many gear sets.

2^4 * 3^2 * 5^2
80085
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CanyonAg77 said:

I always thought these little gas engines peaked out at 3600.
http://www.buggiesgonewild.com/gas-ezgo/957-ezgo-diagrams.html

it looks like a decent design, so after the governor its whatever the valve springs and cam can do. I'm guessing they are light springs to keep the cam healthy under warranty so valve float will probably set in well before anything can let go.



MrJonMan
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When I get a chance, I'm going to back the governor off this week and see what happens with the RPM. At least then I'll know if it's working or not.

Like I said, if the engine dies it dies, just hoping it lasts another month or so. I'd say I will try and stay away from WOT all the time but I'd just be lying.
dubi
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Quote:

I'd say I will try and stay away from WOT all the time but I'd just be lying.
#truth
JSKolache
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Is this why so many chachis in my neighborhood are cruising around in golf carts every night - it's the new mini brodozer?
EMY92
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MrJonMan said:


And maybe add a 1/4" steel plate under the seat to keep what's yours in the condition it is in now. Or there are those new ballistic proof athletic cups some of the MLB catchers are going to.
I've got a nice seat sized plate of 1/4" steel in my garage. You're welcome to it.
Silvy
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Tim Weaver
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Small engines are supposed to be run WFO for hours on end in adverse conditions. I'd be willing to bet you'll be fine. It will be an ignitor, carb, or fuel delivery problem that makes it quit. Just tell her that it blew up when the ignitor goes out. Problem solved.....
MrJonMan
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Golf cart boards say 4500rpm starts to run the risk of floating a valve but can possibly push it to 5000 and still be ok. It's obviously just a guessing game.

Today I backed the governor adjustment off quite a bit and it's now running 3700-3800 RPM flat out (if I leave it where it's at) and ~22 mph

Very likely I'll adjust it to hit that 4,000 EZGO suggested max

EDIT: and oh yea, I got the tach hooked up

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