345 18hp vs. 20hp

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345 18hp vs. 20hp

Greg345 I own a 1997 345 with an 18hp Kawasaki LC, what is the difference between this engine and a 1998 and up 20hp Kawi? A co-worker of mine turned his LX176 (15hp) into an LX178 (17hp) by simply turning the engine up 200rpm. I'd like to eek out a couple of more ponies before I put a snowblower on the machine for next winter.
Justin Gray Your Co-worked is wrong.You can't go from 15 hp motor to a 17hp motor by increasing the engine rpm by 200. You especially can't change the motor from a LX176 to a LX178. Its simply impossible. The Internal design of the motor could be slightly different for the increase HP.

When the engine is spinning faster the amount of work the is needed to slow the engine down increases. which means, spinning up attachments qill be a bit easier or quicker, but the MAX amount of HP the engine produces will judge how easy the engine has to work at keeping the attachment spinning.

All engines run on the same basic principles. The need Air, Fuel and Spark. The hotter the spark, the easier the Air:fuel mixture will ignite since its HEAT that ignites the A:F mixture and not what you see.

Increasing the amount of air the enters the cylinder will increase the amount of HP the engine puts out IF you are adding the right amount of fuel for a given RPM.

At the same time, the exhaust has to be able to flow out of the engine as quickly and as easily as possible to so there is very little exhaust left in the cylinder, which will allow for more air to be injested at a given time, which will increase the HP.

Increasing the MAX RPM could put the engine at an RPM with a LOWER HP rating. Say the engines max RPM is 2500rpm and it makes 15HP at 2500. You increase the rpms to 2700, you are now at a mark where the HP could be around 10 HP. Have you ever looked at a dyno sheet from a cars engine? Its exactly the same.

The only way to really increase the engines HP is to create less restriction in the intake and exhaust. Since on some motors, the amount you can do, to reduce the restriction of both areas is minimal, TUNING the air:fuel mixture would yeild more power then simply increasing the RPM or removing the filter or some how modifing the exhaust on the small engine.

I don't know what type of carb is on your motor but there should be atleast one A:F mixture screw. Some of two, one for idle, and one for high rpm. You want to turn the screw to a point in between where the engine runs rough due to, to little fuel and to much fuel. Also looking at the spark plug(s) to make sure they are a light tan instead of black or pure white will also let you know if the engine is injesting to much fuel or not enough.

Greg345 I know how an engine works, I've been building FE Ford engines for 18 years now. Let me rephrase my statement about changing a 15hp to a 17 hp. Let say you HP rating is taken at 4800 rpm, that also happens to be the top of the power curve (engine still making power), any increase in RPM produces a increase in RATED hp until one of the factors (camshaft, carburator) hits it's limit. A 15hp engine limited to 4800rpm makes 17hp at 5000rpm, same carb, cam, head, block pistons etc etc. It's all semantics.
Cummins did this with their 6BT 12valve motors. The engines put into Dodge trucks could have huge HP numbers added to them by simply turning up the fuel flow. Same exact parts, different state of tune. And an intentional on at that.
It's all semantics and numbers. Why would anyone buy a 15hp mower that cost exactly the same as a 17hp? John Deere gets to charge a premium for the extra 2hp and it costs them zero.

ross The only difference in an LX176 and LX178 is that the LX178 is liquid cooled. I have a 170 lawn mower and it has the same engine as the LX176. I just adjusted the high idle and with the increase in engine rpm's it helps cutting and transport speed. But if you only increase the rpm's by 200 I don't think your going to get two more horsepower.
Greg345 His LX176 has the same LC Kawi as the LX178. You're probably thinking of the LX173.
Let's try this another way.....by raising the rpm 200, it doesn't gain 2hp, it allows more hp.
An engine that has it's rpms governed also has it's hp restricted.

Justin Gray Im glad you know how engines work, and you are right about raising the rpm untill you hit the limits of the intake, exhaust and intake/exhaust timing. Just because the engines rpm raises, doesn't mean its making more power.

On a side note, I read Ross's post saying there is no difference between the 2 engines, only one is liquid cooled. If there is no difference between an 18hp and 20hp, mechanically, then try the same.

Either way, raising the high idle does help.

Justin In my 318. I have actually had the idea of just throwing a Mazda 13B rotary Engine in it :) Widing it out at 8000rpm making 160hp. Wearing the best hearing protection available. :)

I have a couple on my work bench.

Greg345 Justin:"If there is no difference between an 18hp and 20hp, mechanically, then try the same."

This is exactly what I'm trying to find out. I don't know if the carb/cam/heads etc etc etc are the same or not. And I have a very unhelpful Deere dealer in my area. I might as well ask my dog.

Greg345 From what I've heard, the 318 is one of the best tractors JD ever made. I'd put the rotary in something else, probably with a stick trans, I don't think the hydro would like 160hp. I have a neigbor who has a bunch of racing mowers, a while back I was thinking of one-upping him by building a mower with a spare 2.3 turbo 4 Ford that I had for my SVO Mustang. I don't think the Craftsman chassis would have liked 200hp too much.

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