re-working a new engine? - Snowblower Forum : Snow Blower Forums
 
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post #1 of 10 Old 04-08-2015, 09:26 PM Thread Starter
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re-working a new engine?

anyone ever pull a new engine ( or a rebuild) apart and " clean up" the intake and exhaust ports just for fun..to see if there is ANY type of performance gain ? I have done it to twosmoker snowmobile engines with very noticable results .
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post #2 of 10 Old 04-09-2015, 10:45 AM
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I've done it on older engines. It's a good idea, and I'm sure it does have some gain.

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post #3 of 10 Old 04-10-2015, 02:51 AM
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I belong to the if it's not broke don't fix it club. I say run some Seafoam in it and it will to remove any carbon that is on the valves. Only do a tear down on an engine if it needs it ie running badly or not at all.
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post #4 of 10 Old 04-10-2015, 05:57 AM
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I thought about doing it to my Honda, polishing, porting, gasket matching. All the fun stuff, but after the winter we are still having, I'm not talking to my machine right now. Maybe in the fall.

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post #5 of 10 Old 04-10-2015, 08:44 AM
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It just doesn't seem the reward would be worth the effort. Would be interested in seeing someone do a before and after dyno run.

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post #6 of 10 Old 04-10-2015, 09:35 AM
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Along the same lines... and I know this is going to sound crazy, but I saw it with my own two eyes. Unfortunately it was a number of years ago and it seems the website has changed since but...

I was surfing the web and stumbled on a page on Briggs & Stratton's website about their 5 HP horizontal-shaft engines. Those engines are (were) used extensively in go-kart racing, and the page was discussing ways to improve the performance of those engines.

So here's the shocker: one thing they discussed was exhaust upgrades - in the sense of better or no muffler, not port work or anything like that. They said that just by removing the (apparently awful) stock muffler and replacing it with a straight pipe, you could get an 80% increase in power! That's not a typo: making that one change would turn your 5HP engine into an 8HP engine. Since engines used in that application are not governed, I suspect the 8HP comes at a higher RPM than the 5HP but I wouldn't consider that a "modification".

Not that I'm recommending straight pipes on snowblowers, but I did find that info pretty surprising.

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post #7 of 10 Old 04-10-2015, 10:16 AM
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And if you add nitrous and a supercharger ....

The thing is a go cart has other modifications. You said they aren't governed so that's one, they need a different connecting rod and flywheel as the stock ones won't hold together at higher RPMs, two and three. That's where I do believe a properly designed exhaust that scavenges the spent mixture would give you a noticeable increase like a tuned motorcycle or snowmobile exhaust does.

It's long been know in the chainsaw world if you open up the muffler and readjust the carb you do gain power. Mufflers are supposed to quiet the machine and do have limitations but that's on something that has massive RPMs and flow is everything. I've done it to a new chain saw last year and it works.

If it's just a stock 3700 rpm max snow blower engine you aren't going to get much of a boost from any modification because the potential just isn't there.

With stronger connecting rod, better head, better exhaust and running higher RPM making modifications that increase volumetric efficiency bring rewards because there is room for improvement. You can un shroud a valve and enough air is moving it helps. Polishing starts to supply a gain because the engine is trying to draw in more air and draw it in faster.

The chance of screwing something up compared to the gain of taking a brand new engine apart to get a marginal increase in power just doesn't seem to make sense.
Your question was about a new engine.

On an older engine tinker away as you likely can't really hurt performance unless you manage to grind through something and you might get something.

My math says 80% of 5 is 4 so that would be a 9 horse engine just by taking the muffler off. If that really worked don't you think almost all of us would be tossing our mufflers out ??

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post #8 of 10 Old 04-10-2015, 10:19 AM Thread Starter
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Quote:
Originally Posted by ELaw View Post
Along the same lines... and I know this is going to sound crazy, but I saw it with my own two eyes. Unfortunately it was a number of years ago and it seems the website has changed since but...

I was surfing the web and stumbled on a page on Briggs & Stratton's website about their 5 HP horizontal-shaft engines. Those engines are (were) used extensively in go-kart racing, and the page was discussing ways to improve the performance of those engines.

So here's the shocker: one thing they discussed was exhaust upgrades - in the sense of better or no muffler, not port work or anything like that. They said that just by removing the (apparently awful) stock muffler and replacing it with a straight pipe, you could get an 80% increase in power! That's not a typo: making that one change would turn your 5HP engine into an 8HP engine. Since engines used in that application are not governed, I suspect the 8HP comes at a higher RPM than the 5HP but I wouldn't consider that a "modification".

Not that I'm recommending straight pipes on snowblowers, but I did find that info pretty surprising.
Quote:
Originally Posted by tinter View Post
I thought about doing it to my Honda, polishing, porting, gasket matching. All the fun stuff, but after the winter we are still having, I'm not talking to my machine right now. Maybe in the fall.
those are the things i was thinking about, other than straight pipe exhaust. all those little things that could be done to a small engine that MIGHT result in more power, smoother idle etc.
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post #9 of 10 Old 04-10-2015, 11:36 AM
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Quote:
Originally Posted by Kiss4aFrog View Post
My math says 80% of 5 is 4 so that would be a 9 horse engine just by taking the muffler off. If that really worked don't you think almost all of us would be tossing our mufflers out ??
Yeah I realized after I wrote that the math is wrong... my memory is lousy. I'm pretty sure the "5 becomes 8" is correct, so the percentage is probably 60 (1.6 * 5 = 8).

I'm sure most folks racing go-karts have upgraded conrods and such, but the page I read did state the only mod was removing the muffler. I think it would depend on how much higher the engine could rev with the stock rod. If you could reach 5K RPM, with torque staying the same, just the RPM increase would take your horsepower to just under 7 (since HP = RPM times torque times a constant, and assuming the 5HP rating is at 3600 RPM). Increasing VE (= increasing torque) by taking away a very restrictive muffler could get you the rest.

That obviously begs the question of whether you'd get an increase just by raising the RPM, but it could be the stock muffler is so restrictive the HP drops above 3600 RPM, so with that muffler on the engine there would be no gain.

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Last edited by ELaw; 04-10-2015 at 11:51 AM.
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post #10 of 10 Old 04-10-2015, 07:34 PM
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Originally Posted by ELaw View Post
That obviously begs the question of whether you'd get an increase just by raising the RPM, but it could be the stock muffler is so restrictive the HP drops above 3600 RPM, so with that muffler on the engine there would be no gain.
To get HP on a small motor, you need RPM.
I modified a 5 HP Briggs go-cart engine about 20 years ago. It wasn't a race engine, just my personal off-road go-cart. It had a higher compression head, a better cam, better carb and a header. I tweaked the governor to raise the rev limit and that little sucker hauled!

I've thought about milling the head down on my blower. I'm sure more compression would make for a nice boost in torque! I'd of course have to run higher octane gas, but that's a small expense.

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