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DarkLogix
Texan and Proud
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join:2008-10-23
Baytown, TX

DarkLogix

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Lawn mower engine question

I noticed while walking around at sears and lowes that there are multiple Briggs and Stratton lawn mowers with the same size engine but different HP numbers

so what's the diff? is it just a different carb? and if so is it possible to upgrade the carb and make it more powerful?

John97
Over The Hills And Far Away
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join:2000-11-14
Spring Hill, FL

John97

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What exactly do you mean by the "same size engine" - are we talking physical size?

DarkLogix
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join:2008-10-23
Baytown, TX

DarkLogix

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said by John97:

What exactly do you mean by the "same size engine" - are we talking physical size?

They're listed as the same size in CC

shdesigns
Powered By Infinite Improbabilty Drive
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join:2000-12-01
Stone Mountain, GA

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Yes, the carb is one thing.

Other differences are side vs overhead valve, valve diameter and running RPM.

My old pressure washer had a real small engine but they ran it at 3800RPM.

enon
@216.151.180.x

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A couple years ago, there were several class-action lawsuits brought against Briggs + Stratton regarding bullshit horsepower "ratings". As a result, nearly every manufacturer stopped putting HP numbers on their engines and instead uses an SAE standard torque measurement taken at the cutting blade.

To answer your question, the torque measurement for the same displacement engine may vary depending on mower features: for example, if the mower is self-propelled, or perhaps is equipped with a dynamo for charging a starter battery. Not only will these features alter the available output torque themselves, but the toque will very likely be different even when they're not in use because the carb has been tuned to accommodate the additional loads.

DarkLogix
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join:2008-10-23
Baytown, TX

DarkLogix

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Well any idea if its possible to make a 6.75 engine that's not self propelled output more?

I noticed that some of the same size (in CC) varied from 6.50 to 7.75 while not being OHV, though some were self propelled I'm just interested in if its possible to change a few parts and get higher output from what I have (which is a 6.75 push mower that's is not self propelled)

cowboyro
Premium Member
join:2000-10-11
CT

cowboyro

Premium Member

Why in the world would you want that? Self-propelled is so much easier to use and if you really NEED that extra power then you should mow more often to start with. Or get a tractor...

Corehhi
join:2002-01-28
Bluffton, SC

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You could probably change the carb out, run a straight pipe instead of a muffler and get a K+N air filter to up the air flow.

Port and polish. Many things you could do but really???

DarkLogix
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join:2008-10-23
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DarkLogix

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to quote Tim Taylor the fictional character from Home Improvement, "MORE POWER"
iknow_t
join:2012-05-03

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said by DarkLogix:

Well any idea if its possible to make a 6.75 engine that's not self propelled output more?

I noticed that some of the same size (in CC) varied from 6.50 to 7.75 while not being OHV, though some were self propelled I'm just interested in if its possible to change a few parts and get higher output from what I have (which is a 6.75 push mower that's is not self propelled)

lawn mower engines have low compression, increasing it by milling the head is one way to get more HP. another is to put a high performance cam in it. I imagine someone makes them.. that will give you the biggest boost.. of course, you can always put a larger stock engine on it. lets say 12 HP. you want an engine with the same shaft size.

DarkLogix
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Baytown, TX

DarkLogix

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Well I had been mostly wondering what changed Briggs makes between the models
DarkLogix

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Interesting Idea
though I doubt there are aftermarket performance cams and such for a push mower
Tig
join:2006-06-29
Carrying Place, ON

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said by DarkLogix:

I'm just interested in if its possible to change a few parts and get higher output from what I have (which is a 6.75 push mower that's is not self propelled)

In theory, yes. But you will need to make mechanical changes and then retune to take advantage of the changes. For every hoped for change in performance, you will get a very real and inversely proportional change in reliability.
If you start with 6.75 HP, you could hope to get over 7.5 HP, but the rub is you may end up with 6. In any case, you have no way of measuring the change and you'll only notice the difference if you screw it up.
Bottom line, 6.75 HP is plenty of power for a push mower. You should be able to run behind that. If not, get it tuned up.
If you really think you need a 7.5 HP mower, buy an 8.5 HP mower.
iknow_t
join:2012-05-03

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said by DarkLogix:

Interesting Idea
though I doubt there are aftermarket performance cams and such for a push mower

said by DarkLogix:

Interesting Idea
though I doubt there are aftermarket performance cams and such for a push mower

not for a push mower, but those engines can be used for racing carts etc. here's a big list of companies that make racing parts for briggs. »www.google.com/#q=perfor ··· r+briggs

Jack_in_VA
Premium Member
join:2007-11-26
North, VA

Jack_in_VA

Premium Member

said by iknow_t:

.
not for a push mower, but those engines can be used for racing carts etc. here's a big list of companies that make racing parts for briggs. »www.google.com/#q=perfor ··· r+briggs

It's highly unlikely that a vertical shaft B&S lawnmower engine is used for racing carts. It takes a horizontal shaft engine for that.

dennismurphy
Put me on hold? I'll put YOU on hold
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join:2002-11-19
Parsippany, NJ

dennismurphy

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said by Jack_in_VA:

It's highly unlikely that a vertical shaft B&S lawnmower engine is used for racing carts. It takes a horizontal shaft engine for that.

Come on Jack, be creative! Just put a 90-degree elbow on the vertical shaft and wala! you have a horizontal shaft engine.

Sheesh, think outside the box once in a while, would ya?!
iknow_t
join:2012-05-03

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said by Jack_in_VA:

said by iknow_t:

.
not for a push mower, but those engines can be used for racing carts etc. here's a big list of companies that make racing parts for briggs. »www.google.com/#q=perfor ··· r+briggs

It's highly unlikely that a vertical shaft B&S lawnmower engine is used for racing carts. It takes a horizontal shaft engine for that.

actually, there are racing lawn tractors, which use a vertical shaft engine. but, many parts for a horizontal shaft engine will fit a vertical shaft engine. also, some of these companies will make you a camshaft..

Cho Baka
MVM
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there

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Turbo it:

»www.youtube.com/watch?v= ··· XwQp-MWo

DarkLogix
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join:2008-10-23
Baytown, TX

DarkLogix

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said by Cho Baka:

Turbo it:

(youtube clip)

You build it I'll use it to mow the lawn
iknow_t
join:2012-05-03

iknow_t

Member

said by DarkLogix:

said by Cho Baka:

Turbo it:

(youtube clip)

You build it I'll use it to mow the lawn

that's a bit much. but try contacting one of the companies that I linked to in google. they may have, or can make a high compression head for yours. normalyy it's low, like 7:1 compression, if the head is milled down to get 9:1 compression, you'll get more power. the principle is the same as for a car engine, you know the maximum CC when the piston is down, you just have to bring it up into the compression cycle, and add oil from a syringe into the spark plug hole until it fills, then you know the compression ratio. of course, you have to put clay where the valves and piston line up with the head, and measure the thickness, so you can make sure nothing will hit the head after it's milled.. sometimes you have to make reliefs to get enough clearance.. but this is the simplest, and cheapest way to get more power.

DarkLogix
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DarkLogix

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said by iknow_t:

that's a bit much. but try contacting one of the companies that I linked to in google. they may have, or can make a high compression head for yours. normalyy it's low, like 7:1 compression, if the head is milled down to get 9:1 compression, you'll get more power.

If I went that far I think I'd go for 10.5:1 comp ratio though I wonder how hard the pull start might get.

garys_2k
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join:2004-05-07
Farmington, MI

garys_2k

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I'd buy a new, more powerful mower.

DarkLogix
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join:2008-10-23
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DarkLogix

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said by garys_2k:

I'd buy a new, more powerful mower.

Why would I do that it works fine and starts super easy and runs smooth

Corehhi
join:2002-01-28
Bluffton, SC

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said by iknow_t:

said by DarkLogix:

Interesting Idea
though I doubt there are aftermarket performance cams and such for a push mower

said by DarkLogix:

Interesting Idea
though I doubt there are aftermarket performance cams and such for a push mower

not for a push mower, but those engines can be used for racing carts etc. here's a big list of companies that make racing parts for briggs. »www.google.com/#q=perfor ··· r+briggs

LOL I might try with an old mower just because. LOL. Looks like they do sell the parts. I rebuilt trail bike motors before, I would think this isn't any harder.

DarkLogix
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Baytown, TX

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DarkLogix

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BTW as far as mods go so far (and no I don't think I've actually upped the HP/torque yet, I've done the following

1. E3 spark plug
2. added a fuel filter
3. switched to Royal Purple 5w-30 oil (and before you ask no it hasn't lost any oil yet.)
4. had a friend sharpen the blade with a grinder and balance it.

also in the recent tune up added a good bit of seafoam to the gas, after cleaning the carb jets and pretty much all parts of the carb related to fuel flow.

after that tune up it starts super easy and have almost no vibration.

Pacrat
Old and Cranky
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join:2001-03-10
Cortland, OH

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said by DarkLogix:

...it works fine and starts super easy and runs smooth

Why screw around with it at all, if that's the case. Your desire to modify it to get more power/torque mystifies me. If it ain't broke, don't fix it.

alkizmo
join:2007-06-25
Pierrefonds, QC

alkizmo

Member

said by Pacrat:

Why screw around with it at all, if that's the case. Your desire to modify it to get more power/torque mystifies me. If it ain't broke, don't fix it.

More power to compensate for a dull blade? :P

DarkLogix
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said by Pacrat:

Why screw around with it at all, if that's the case. Your desire to modify it to get more power/torque mystifies me. If it ain't broke, don't fix it.

More power = more bragging rights I guess.

Pacrat
Old and Cranky
MVM
join:2001-03-10
Cortland, OH

1 recommendation

Pacrat

MVM

But you'd be bragging about unsubstantiated claims. How're you going to prove any increase in H.P.??? Or torque?? If the thing is working just fine now... not bogging down, or running rough and sputtering, how will you know you've gained anything. Of course, you could strip the engine and send it out to be "bright chromed" and add some "zoomie" header to it and just run a straight pipe. Perhaps, a glass-pack muffler!?! I'd just give the mower a good tune up... change the plug, and gap it properly; change the oil, replace the air cleaner, clean the carb/fuel filter; clean, sharpen and balance the blade, and mow to your heart's content. Or... you could just purchase a new, bigger mower (which has already been suggested). Perhaps a nice, new set of polished alloy wheels , or spinner hubcaps would make your day.

DarkLogix
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DarkLogix

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said by Pacrat:

spinner hubcaps

Oh please those are lame

I'm about function over form