# Tecumseh Engine question



## micah68kj (Oct 8, 2011)

On my 921001 824 the engine is an LH318SA rated at 8.0 HP. On the 921004 mdl the LH318SA engine is rated at 9.25 HP. How does Tecumseh do this? I'm guessing difference in carburetion? How do they do it or am I missing something? Valves? Head configuration?


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## ST1100A (Feb 7, 2015)

Carburetion, RPM's or Gross to Net H.P. ratings. Sometimes that is done for insurance reasons.


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## notabiker (Dec 14, 2018)

https://www.smallenginesuppliers.com/html/engine-specs/Horse-Power-Ratings-on-Small-Engines.html


Not sure that one's age but back in the day the engine only had to be 85% of the rated output. Worked great for advertising...


Otherwise, to change hp it is as simple as a different thickness of head gasket to change compression ratio. Or a different cam with different timing or amounts of valve lift. Or carburetion as now you can't adjust anything on a carb, whereas before you could adjust low and high circuits easily.


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## sscotsman (Dec 8, 2010)

micah68kj said:


> How do they do it or am I missing something? Valves? Head configuration?


There is likely no actual differences in the engines. the HP ratings are different, but the engines are not different.

These models are from 2008..there was a lawsuit over this, not just Tecumseh, I think Briggs and other engine manufacturers were doing it too..finessing the numbers, using creative math and tweaking the definition and calculation of HP to arrive at different ratings for the exact same engine model.

The result of the lawsuit was: no more engine ratings in HP. We now get cc's of displacement (cubic centimeters) and torque ratings, but no more HP. This began in 2010.

Scot


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## dman2 (Sep 22, 2019)

micah68kj said:


> On my 921001 824 the engine is an LH318SA rated at 8.0 HP. On the 921004 mdl the LH318SA engine is rated at 9.25 HP. How does Tecumseh do this? I'm guessing difference in carburetion? How do they do it or am I missing something? Valves? Head configuration?


I did a lot of research on that and I couldn't find a good answer. Some people compared the parts on both engines and they were pretty much the same (same carb and everything). Maybe a little tweak here and there, but you can't really tell. Ariens techs don't even know either. Some of them said this, while others said something else.

I think it has mostly to do with engine rpm and company BS stuff. They want you to pay more for the same engine.

My tecumseh LH318SA was set to 3500 rpm. Horse power was rated at 3600 rpm, so I don't even know how many HP my engine has at 3500 rpm. Some companies lied about HP, so now, they stopped HP rating all together.

I heard flat head engines have high low end torque (big displacements), but they have trouble breathing at high rpm. Also Tecumseh engines can't rev above 3600 rpm. Not only that, but they have non-adjustable carbs that were designed to run lean (to meet government regulations). For those reasons, I haven't increased my engine rpm and messed with it, yet. I thought about re-jet, but afraid it would not run well and give good result. I wish there are examples out there, then I would follow.

I have toro R-Tek engine and that thing was rated 5HP, 6HP and 7HP on different snowblowers, so what the heck.


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## ST1100A (Feb 7, 2015)

Sscot is right about that.
Everybody was buying off of the higher numbers that they were putting on the engines, like horsepower numbers.
The same thing can be said of portable generators with their wattage numbers. Honda put the rated numbers on theirs which were lower, and everyone else was putting the Peak numbers on theirs, which were higher.
The Honda generator still out performed all the other higher numbered generators.


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## badbmwbrad (Jul 30, 2019)

Horsepower is a function of engine speed (RPM). The same engine will develop a different horsepower rating dependent upon the RPM at which the torque is measured. For a snowblower engine, it is more informative to know what the maximum engine torque is. Horsepower = (Torque x RPMs) / 5252

_Torque is simply a force acting on something from a distance (i.e. a piston pushing down on a crankshaft, using that leverage to rotate it), while horsepower is torque multiplied by RPM, or a measurement of how quickly an engine can accomplish a certain amount of work - _ Road & Track


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## SimplicitySolid22 (Nov 18, 2018)

That is so weird you posted this question...I saw a photo of a manual on top of a free craftsman on Facebook marketplace today in great shape. Well the manual said LH318sa/LH358SA and then in parentheses it said HMSK80.

Meaning all of the above...will try to find the photo.


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## SimplicitySolid22 (Nov 18, 2018)

Here it is:


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## ELaw (Feb 4, 2015)

I've done some research on this too, and I think at least some of it has to do with torque curves, which probably relate to valve timing and/or lift.

I had an HMSK110 and an OH318 Tecumseh engine... both rated 11 HP but the HMSK was 358cc displacement and the OH was 318cc.

If you look at the torque curves for both motors, the OHV engine peaks at about 3600 RPM, and as RPM drops it gets lower. The l-head engine torque curve peaked at a much lower RPM - I don't remember the number but I'm thinking it was around 3000 RPM - then actually dropped as RPM increased toward the 3600 RPM normal operating speed.

What that meant was that since HP is a product of torque and RPM, at 3600 RPM they would both make 11 HP. But as RPM dropped, the torque on the l-head engine would go up, whereas on the OHV engine it would drop. The effect of that on my snowblower was that as long as each engine was running at full speed it was fine, but when the load increased, the l-head engine would pull harder whereas the OHV engine would bog down as its torque decreased. For me that made the l-head much better as a snowblower engine.

Then I got a 414cc LCT engine and all my problems disappeared... :grin:


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## dman2 (Sep 22, 2019)

ELaw said:


> I've done some research on this too, and I think at least some of it has to do with torque curves, which probably relate to valve timing and/or lift.
> 
> I had an HMSK110 and an OH318 Tecumseh engine... both rated 11 HP but the HMSK was 358cc displacement and the OH was 318cc.
> 
> ...


Yes, I figured increasing rpm on L head engines wouldn't make a different. They have peak torque at 2900-3000 rpm. Their HP would properly flat out, or drop after 3500-3600 rpm.

8HP is good enough on that machine. There is no need to mess around with it and waste your times.
If you want it to do more, maybe change the pulleys to take advantage of the torque curve. I like 318cc.
I think it is a good engine, as long as you take care of it.

Even at 3500 engine rpm, the impeller speed is 1100 rpm, so performance is as good as newer models.


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## micah68kj (Oct 8, 2011)

*Thank you, everyone, for your replies, explanations and videos. The takeaway from this is that There is no real hard, pat answer. HP vs torque, Torque vs HP, Valve timing, carburetion, RPMs & Etc... Hopefully (I'm sure) this Ariens will perform as needed. *


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## notabiker (Dec 14, 2018)

dman2 said:


> Yes, I figured increasing rpm on L head engines wouldn't make a different. They have peak torque at 2900-3000 rpm. Their HP would properly flat out, or drop after 3500-3600 rpm.
> 
> 8HP is good enough on that machine. There is no need to mess around with it and waste your times.
> If you want it to do more, maybe change the pulleys to take advantage of the torque curve. I like 318cc.
> ...





Partly, but a bigger engine will hold rpm with a bigger load whereas a smaller engine will bog down and you'll have to go slower.


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## 1132le (Feb 23, 2017)

dman2 said:


> Yes, I figured increasing rpm on L head engines wouldn't make a different. They have peak torque at 2900-3000 rpm. Their HP would properly flat out, or drop after 3500-3600 rpm.
> 
> 8HP is good enough on that machine. There is no need to mess around with it and waste your times.
> If you want it to do more, maybe change the pulleys to take advantage of the torque curve. I like 318cc.
> ...



The imp rpm is not even close to 1100 @3500 its more like 1000
the stock 2.75 pulley is 1020 [email protected]
my st824 rust bucket lh318 is at 3825 imp rpm is1080
its blows snow 45 feet plus with the imp kit it turned that blower into a star it was rated 25 to 30 feet new it blows slop farther then that


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## micah68kj (Oct 8, 2011)

1132le said:


> its blows snow 45 feet plus with the imp kit it turned that blower into a star it was rated 25 to 30 feet new it blows slop farther then that



I considered installing an impeller kit on this blower I just got but after removing the chute and checking clearances between impellers and sidewall I'm going to try it this winter just as it is. Our driveway is pretty small, one car wide and not very long. However, I do clean up for some of the neighbors because they're simply too old and broken down to do it themselves. At no no time or place do I need to blow it much further than 15'. It will hopefully save me some time getting it done. Actually, blowing snow is one of my very least favorite things to do but something I dislike worse is having people struggle getting in and out and seeing others trying to walk without falling down due to lack of sidewalk clearing.


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## notabiker (Dec 14, 2018)

micah68kj said:


> I considered installing an impeller kit on this blower I just got but after removing the chute and checking clearances between impellers and sidewall I'm going to try it this winter just as it is. Our driveway is pretty small, one car wide and not very long. However, I do clean up for some of the neighbors because they're simply too old and broken down to do it themselves. At no no time or place do I need to blow it much further than 15'. It will hopefully save me some time getting it done. Actually, blowing snow is one of my very least favorite things to do but something I dislike worse is having people struggle getting in and out and seeing others trying to walk without falling down due to lack of sidewalk clearing.





Good on you! I like blowing snow and find it fun, even when I lived in North Pole and it would warm up to the -20's during the day.. Fingers would get warmed up on the exhaust gasses every few passes!


I do the same and usually make two passes down the sidewalk for 100' or so if the neighbors haven't shoveled it yet. If we get more than a few inches of snow then I'm likely to hit the neighbor's driveway across the street as he's an older gent. He seems reluctant to let anyone help him with his driveway so if it's only a couple inches I won't bother him, but if it's a big drift (last year he had a 6+ foot drift in front of his garage) then I'm definitely helping him whether he likes it or not!!


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## micah68kj (Oct 8, 2011)

notabiker said:


> Good on you! I like blowing snow and find it fun, even when I lived in North Pole and it would warm up to the -20's during the day.. Fingers would get warmed up on the exhaust gasses every few passes!
> 
> 
> I do the same and usually make two passes down the sidewalk for 100' or so if the neighbors haven't shoveled it yet. If we get more than a few inches of snow then I'm likely to hit the neighbor's driveway across the street as he's an older gent. He seems reluctant to let anyone help him with his driveway so if it's only a couple inches I won't bother him, but if it's a big drift (last year he had a 6+ foot drift in front of his garage) then I'm definitely helping him whether he likes it or not!!





The old guy(82) next door has a bad hip and refuses surgery, has a very steep driveway. The old gent (92+) across the street is just too dang old and frail to do much of anything so I just do it for them. Never ask them for anything. Maybe one day I'll get to where I can no longer help myself and someone will step up. The one guy, if I remember correctly, gave me either $200 or $400 last year. I really don't remember. He just showed up one spring morning, handed me an envelope and left.


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## dman2 (Sep 22, 2019)

1132le said:


> The imp rpm is not even close to 1100 @3500 its more like 1000
> the stock 2.75 pulley is 1020 [email protected]
> my st824 rust bucket lh318 is at 3825 imp rpm is1080
> its blows snow 45 feet plus with the imp kit it turned that blower into a star it was rated 25 to 30 feet new it blows slop farther then that


That is what they specified in the manual book (up to 1160 impeller rpm). It uses the SHO drive pulley. I even measured the pulleys and calculated the rpm myself. It showed the same thing. When hitting a heavy load, I expect it to slow down a little, so 1080 rpm is a safe bet. Going from 3500 engine rpm to 3600 rpm, You only get like 20-30 more impeller rpm.

It is one of the earliest models in the 921 series, so they were probably still testing things out. They called it ST24E instead of Dexue 24.

I'm not 100% sure, so you could still be right. It is good to know.


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## 2.137269 (Nov 15, 2019)

sscotsman said:


> There is likely no actual differences in the engines. the HP ratings are different, but the engines are not different.
> 
> These models are from 2008..there was a lawsuit over this, not just Tecumseh, I think Briggs and other engine manufacturers were doing it too..finessing the numbers, using creative math and tweaking the definition and calculation of HP to arrive at different ratings for the exact same engine model.
> 
> ...


you are correct scot. it was all of them, tech, briggs,kawasaki,honda, kohler, and a few more, the class action was to me pretty much a main reason for tech going belly up for having to pay out


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## UNDERTAKER (Dec 30, 2013)

* The fly weights on the gov determine the HP Rating. I said this somewhere else here awhile back. when the old engine let loose on "SR". Years ago I did a post Mortem on the old engine and saw the HP Rating stamped on the Gov Itself. *


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## dman2 (Sep 22, 2019)

1132le said:


> The imp rpm is not even close to 1100 @3500 its more like 1000
> the stock 2.75 pulley is 1020 [email protected]
> my st824 rust bucket lh318 is at 3825 imp rpm is1080
> its blows snow 45 feet plus with the imp kit it turned that blower into a star it was rated 25 to 30 feet new it blows slop farther then that


Okay, I think you are right about its impeller rpm. Even though the internet showed that it is using the SHO pulley (supposed to be 2.75" diameter). I only measured mine 2.5" diameter. The auger pulley is the same on other models (8.5 inches). That brings the impeller rpm to right about 1020 rpm when the engine speed is 3500 rpm. Hitting a big load, and it will slow down to 1000 rpm???

Information in the manual book is not accurate. At least it is not the same for all models.


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## dman2 (Sep 22, 2019)

1132le said:


> The imp rpm is not even close to 1100 @3500 its more like 1000
> the stock 2.75 pulley is 1020 [email protected]
> my st824 rust bucket lh318 is at 3825 imp rpm is1080
> its blows snow 45 feet plus with the imp kit it turned that blower into a star it was rated 25 to 30 feet new it blows slop farther then that


I re-calculated it again using more accurate measurements. Your information is correct, but that is with the 2.5" pulley. The impeller speed is affected by the v belt as well, so, the result could be slightly different.

[email protected]
[email protected]

You actually ran the LH318SA engine at 3825 rpm with no problem so far? I wouldn't go that high, but want to know.


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