SS snowblower engines tecumseh

[bgsengine]

I guess I was hoping that someone like Tman; trouts2 or borat might have migrated over from PERR and taken an interest ...

TMan lurks here (Different username I believe) now and then but has sorta followed in Bruce's footsteps (who is also here now and then when he gets bored of real life retirement stuff) and kinda retired.
I think Borat signed up here too at some point also with a different ID, but not sure.
As Bobo said - Most of us are either in the ordinary repair shop business, or DIY homeowners - Not too many "Take it to the max" performance, engineering or racing discussions here - again as Bobo said, there's other forums specializing in that

But of course, if there becomes enough people (and demand for it) we may add another "Advanced Performance" forum (for those that don't experience brain death trying to make sense of all the finer technical details being discussed.)

[bobodu]

Huh....whut...did you say something...yeah whatever you're having....

[Deere2me]

oh, and on the original post for con rod length given the responses so far, I'd settle for an 'educated' guess within 1/2" +/- from anyone that has worked on the specific model?

So... let me see if I can understand SOME of yer long winded babble.
After reading the first two posts, (and skimming thru the others) I have come to the conclusion that you have a deeply FLAWED knowledge ( if any) of four cycle engines!
You say you need the rod lengths to calculate the piston acceleration to arrive at the theoretical max rpm before ring flutter occurs.
That's just plain WRONG !!! Rod length has absolutely NOTHING to do with piston acceleration...nothing. ( weight notwithstanding) The piston will accelerate at the same speed whether the rod is 5" or 5' long! Think about it. And what kind of "analytical" engine theorist would THINK of working a calculation based on tolerances " within 1/2" +/-" They build skyscrapers to closer tolerances for chit's sake! ( I just saw it on Discovery channel, between Swamp People and Duck Dynasty)
So have fun with your WOT,BHP,Torque/power/rpm curve calculations!
SHEESH!!!!!!

[StarTech]

Wouldn't you only need to know piston stroke distance * 2 and RPM to calculate piston speed? You can measure stroke distance easily if it is not published somewhere.

[Deere2me]

Wouldn't you only need to know piston stroke distance * 2 and RPM to calculate piston speed? You can measure stroke distance easily if it is not published somewhere.

Not according to some "analytical" minds!

[jgflawn]

Sorry to have bothered you all.

Borat spun this engine to 6000 with a string and you guys said 'hey cool, nice video'

I'm just a DIY with a small business cutting lawns and clearing snow, a small 14 x 22 shop that my wife lets me use for something other than cars, in order to pay the bills and make ends meet. I was hoping that after reading on PERR and seeing that video that I could gain some performance given I have the same engine TH139SA 8337G he was using.

A 15% improvement would save me days - yes days - in a single snow season, and allow me to take on extra work to buy something nice for my wife every once in awhile.

But I can't afford and don't want to 'grenade' an engine as was suggested. TEC engine and accessories has this engine anywhere from 3700 to 4000 rpm based on the 2000 and 2004 sheets. the engine parts are relatively the same (differences discussed previously on PERR). The performance chart on the 2000 brochure only goes to 3600 so no help there. So given it wasn't snowing this week, I thought hey, excel does math easily enough. formulas for BMEP, piston speed, piston acceleration and BHP are easy enough. The only piece missing was con rod length, and I haven't opening up these engines to even guess. So I thought I would ask some experts.

I appreciated the response that said 'we can't really help and here's why'. ok. thank you.
so, i said, estimate with 1/2 +/- would be helpful. responses were negative, and have progressed to downright rude. ok, I can live with that to.

again, i am truly, truly sorry to have bothered you.

[bgsengine]

Sorry to have bothered you all.

Borat spun this engine to 6000 with a string and you guys said 'hey cool, nice video'

I'm just a DIY with a small business cutting lawns and clearing snow, a small 14 x 22 shop that my wife lets me use for something other than cars, in order to pay the bills and make ends meet. I was hoping that after reading on PERR and seeing that video that I could gain some performance given I have the same engine TH139SA 8337G he was using.

A 15% improvement would save me days - yes days - in a single snow season, and allow me to take on extra work to buy something nice for my wife every once in awhile.

But I can't afford and don't want to 'grenade' an engine as was suggested. TEC engine and accessories has this engine anywhere from 3700 to 4000 rpm based on the 2000 and 2004 sheets. the engine parts are relatively the same (differences discussed previously on PERR). The performance chart on the 2000 brochure only goes to 3600 so no help there. So given it wasn't snowing this week, I thought hey, excel does math easily enough. formulas for BMEP, piston speed, piston acceleration and BHP are easy enough. The only piece missing was con rod length, and I haven't opening up these engines to even guess. So I thought I would ask some experts.

I appreciated the response that said 'we can't really help and here's why'. ok. thank you.
so, i said, estimate with 1/2 +/- would be helpful. responses were negative, and have progressed to downright rude. ok, I can live with that to.

again, i am truly, truly sorry to have bothered you.

Perhaps, if you were to explain *WHY* con rod length is a needed input..

You may be mis-reading it as the STROKE of the engine, which has nothing to do with the con rod length - the stroke is 2x the crank throw.

WEIGHT of the con rod on the other hand can be a factor - a heavier con rod has more mass, and greater durability, and thus reduces performance but a too light con rod can literally explode at excessive RPM , and length of the rod may factor in there - a longer con rod experiences more stress and breaks sooner that a short one, but piston speed, which you indicated is your goal to calculate, is not affected by con rod length, - It's the stroke x rpm that determines piston speed.. and stroke is determined by the crankshaft throw.. However, an OFFSET con rod and piston CAN affect overall piston speed slightly.

[jgflawn]

piston speed = .166 x L x N
L is stroke inches
N is rpm
piston speed in ft/min

Piston Acceleration = ((N^2 x L)/2189) x (1 + 1/(2A))
N is rpm
L is stroke inches
A is ratio connection rod length between centers, to stroke.

BMEP (2 stroke only) = (HP x 6500)/(liter displacement x rpm)

BHP = PLAN
P is BMEP in psi
L is piston stroke (this time in feet)
A is area of one piston (Sq. inches)
N is rpm

[jgflawn]

piston speed absolute upper limit = 4000 ft / min
piston acceleration causes piston ring flutter
based on ring thickness:
.125 = 40,000 ft / sec ^ 2
.094 = 53,000 ft / sec ^2
.063 = 80,000 ft / sec ^ 2
.047 = 106,000 ft / sec ^2
.039 = 138,000 ft / sec ^2

'tuners' will put two .03 rings in a .06 slot to gain performance (not suggesting that...)

Dykes rings were created because they also resist ring flutter

[jgflawn]

practical example - my West Bend 580
at 5500 rpm a 4 HP rated machine
95.06 cc
bore 2.06
stroke 1.75
rod length 3.126 between centers
.06 rings

bmep @ factory specs = 49.7
piston speed = 1598 ft / min
piston acceleration 30953 ft / sec ^2

max. rpm based on 80000 ft / sec ^ 2 piston acceleration limit for 0.06 rings = 8842 rpm
max rpm based on 3500 piston speed = 12048 rpm (not 4000 as that blows the engine apart - truly a 'max' limit

The West Bend 580 is used on Karts everywhere (I got mine for $40 on a jumping jack)
Tuners spin to 11,000+ with weekly (sometimes more) upper end rebuilds (because of the ring flutter) (80000 ft/ sec^2 limit is 8842 ) they are exceeding and causing ring flutter. But they keep below 12000 as that ruins their $1000 engine.

so my math (took 1 hour) given I had the rod length because the engine is sitting beside me right now as I await my rebuild parts) confirms 11000 as the upper limit and is observable in upper forums. But given I don't want to do a top end every snowfall, I can rev to say 8000 (2500 rpm above factory) - although I may need to add a second carb to keep from running lean. But with a 2" drive and 6" load pulley on all SS snowblower I would be at 2.6 x the paddle rpm if I replace my 5.25 torque power B&S turning at only 3060 rpm