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Hop Ups & Horsepower VS Heat Load

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There are trade offs... Nothing much in the power world comes without a penalty of some sort...

I know there will be a hard limit at some point...  And I don't like being the one to be the pioneer in finding limits like heat load and valvetrain reliability... Lol

We all know liquid cooling is the undisputed king of keeping thermal runaway in check on high output engines... But it does come with its own set of baggage and frailties... Water pumps and seals... Tubing... Radiators... And all the attendant potentials for failure and pain in the arse.... Love it for what is does, hate it for weight, complexity, achilles tendon frailty...

Oil cooling.... Don't ask me why... I just have always had an affinity for oil cooling....  as in oil cooling assist to either air cooling over fins , or oil cooling assist  I to liquid cooling I...Very much a fan of setups that include an oil nozzle that directs a spray of oil under the piston dome... Cools the piston and lubricates the wrist pin and bore...  I also love the integration of using a front frame downtube as a oil cooler/heat exchanger/storage tank... Some XRs use it... My yz450 uses it... And others I'm sure... The XR400 also piggy backs the frame cooling with a wonderfully robust added oil cooler mounted to the steering head...

And then there is just plain old air cooling... Fins and airflow ... Nothing else...as in the case of our 230s... Reliable.. Retro... But most assuredly the least effective at caloric communication...

So... Back to the topic...

Since the 230 employs the least effective means of cooling and isn't really overly generously finned in the first place ....

How far can you increase the power output and attendant heat load , before reliability suffers and race fuel becomes the rule...??

This is all abstract musing... I know there are so many variables in engine builds, riding style and conditions, and even in jetting inconsistencies...  That there will be no hard line drawn in the sand ...  Just felt like bringing it up for discussion...

 

 

 

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On my 11 to 1 218 motor I use an under plug thermocouple. It seems to run ok up to about 400*, but starts to ping after that with 91 pump gas.

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Well good question. I believe mine is about as far as I can go without detonating on premium pump fuel. I've had it in extreme conditions on very large hills without a melt down. 

Engines only 11.5 to 1  69mm near 250cc, ported head, PWK carb, Web 89a cam and different exhaust. 

 

 

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8 minutes ago, stevethe said:

Well good question. I believe mine is about as far as I can go without detonating on premium pump fuel. I've had it in extreme conditions on very large hills without a melt down. 

Engines only 11.5 to 1  69mm near 250cc, ported head, PWK carb, Web 89a cam and different exhaust. 

 

 

Umm Steve,

I think we are all going to need every single technical detail of your machine... Including pictures of all the internal components of the the engine and carb... ;)

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On a more serious note. Mine is a bore that gets toward 250cc's with the 89a cam it is likely more top end oriented than some of the others with a stroker and smaller cam. What is surprising to me is how much bottom end my bike has. 

As it's been said and proven on normal modern watercooled 4T's such as a yz450 even a big bore doesn't usually produce more hp than a stock bore. Not that most on here are looking for peak hp though. I wonder why all the strokers though looking at the motor basically being a square bore and stroke. It would seem as a bore would be more performance oriented as we know a big bore produces more torque than a stock bore. 

A dyno would tell a lot about bores vs strokers. 

 

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Very interesting ,Steve.... VERY much so....

The deal on big bore vs stroker is a Very misinterpreted subject when it comes to application in our motorsports...

Stroker has become synonymous with people thinking of stump pulling torque as opposed to oversquare being formula one rpm style...

But the reality , within the differences we are able to alter factory specs of our sports engines... In short... It doesn't amount to sh!t...!!! Zero, Zip, Nada.... Nothing... No measurable or detectable difference either by butt Dyno or by actual Dyno.... Aside from the pre formed biases in people's thoughts from what they have heard from history... The 6mm and less differences in bore or stroke don't amount to anything beyond just the plain additional displacement... 

I had done a bunch of testing and posting when I texted 100% identical added displacement setups on my shop Dyno with one of my shop 450s... One was by added bore... One by added stroke... OTHERWISE it was the SAME bike.... Zero difference in the Dyno graphs... Zero... Same power... Same power curve at every point...  I had posted the stuff up on a few forums back then... 

 

I take exception to the added displacement not adding more power.... Perhaps if the builders involved don't have the rest of the porting or componentry able to efficiently feed more displacement at higher rpms, you would see a top end loss of volumetric efficiency ... But in all my testing and.setups, the power was typically from idle to rev limiter... Across the board...

Edited by mixxer
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Heat load, yes, I was concerned about this because we sometimes ride in the most unholy places.  Crossing the penninsula from the cool Pacific to the Sea of Cortez at Laguna Diablo, My Xr250L had no oil cooler and suffered massive pinging while we were doing everything wrong.. Lugging the motor on the hiway pulling a long grade in 115F heat.  Even the stock Xr400 with its big oil cooler had some pinging that day.  Adding an oil cooler to my stock 250 made a huge difference.

So far, everyone says no oil cooler necessary on the two valve 230 but we sometimes ride through Diablo's blast furnace.

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4 hours ago, mixxer said:

But the reality , within the differences we are able to alter factory specs of our sports engines... In short... It doesn't amount to sh!t...!!! Zero, Zip, Nada.... Nothing... No measurable or detectable difference either by butt Dyno or by actual Dyno.... Aside from the pre formed biases in people's thoughts from what they have heard from history... The 6mm and less differences in bore or stroke don't amount to anything beyond just the plain additional displacement...

Right on!  Area x Moment Arm is constant for two engines of the same displacement regardless of bore and stroke.  "Desktop Dynos - Using Computers to Build and test Engines" has a lot of data on this very subject.

All things being equal and at most normal engine speeds there is little (if any) difference.  However, as engine speeds increase so do losses from piston speed/friction as well as does inertia of the rotating parts.  For a stroker the piston must cover a longer distance in the same amount of time so piston speed is higher at any given RPM.  Again at most normal engine speeds (like our little engines) the difference is very small, if not negligible (perhaps zero).

I think the connection with stroke and low-speed torque comes from the fact that many long-stroke engines often tend to have smaller ports and valves (due to small bore and chamber) and tend to be tuned for low-speed power (GM LG-4 305 ci).  One the other hand many short-stroke engines often tend to have larger ports and valves (due to large bore and chamber) and tend to be tuned for high-speed power (GM DZ 302 ci).

Terry miller and I had a fun and interesting discussion on this very topic.

"There's no replacement for displacement"

Edited by VortecCPI
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Really enjoying all the input and info .. thank you all...

More please

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Okay...  With standard Wiseco piston, stock head gasket, Web 40mc/402 cam, and Procom CDI I have seen head temperatures at the plug go up to about 360F when riding very slow and lugging the engine.  A quick downshift and short run brings it right back down again.  While I wouldn't mind a little more CR I know I am very safe at ~10:1 with the short/small cam and faster timing.

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Higher compression or over bore aircooled can shed their heat when used in short bursts like a lot off road riding. Long hard drones on the road or in the desert head temps can get crazy. Power can fade till it cools, valves seals get baked and bike can start using oil or smoking, valve seats can move, oil can be destroyed in 1 ride.

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I has been my understanding that an air cooled engine is every bit as efficient at cooling as a liquid cooled engine but is harder to control.  Ultimately we want an engine to maintain the perfect temperature at all times with as little fluctuation as possible.  This is easier with a liquid cooled engine, it maintains temperature better.  An air cooled engine can shed heat faster and easier but actually too well and too fast.  A radiator is air cooled, it is shedding most of the heat the engine had produced the same way an air cooled engine does, transfers the heat to the air.

I think the proper use of oil cooling to maintain the heat and also as another way to shed extra heat when needed is the way to go as well as an under piston squirter.  I'm not sure how to go about designing a complimentary oil cooling system which would maintain the perfect engine temp at all times, probably have to do some testing and adjusting.

Big bore from the factory allows the manufacturer to use larger diameter valves and more of them.  This will support the flow requirements for the larger displacement and higher rpm.  An engine makes torque which can be measured, horsepower is calculated from torque.  For horsepower to increase, either torque must increase or rpm.  HP = (Torque x RPM)/5252 , IIRC.  The right combos work the best, figuring out what the right combos are is the trick!

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When I was flat track racing ATC200x's the class cc limit was 206cc's.

Everyone was going the std stroke and 67mm piston route. 

I went with a 63mm XR185 piston and a 66mm stroker and this thing absolutely used to blitz everything out there. Out of the gate, down the straights, out of the corners, everywhere. It won me two State Titles and one National back in the day. Probably why I blindly believe in the stroker route. With my lay down conversions of late the 70mm stroker in the ATC70 frame is an animal. Within the next month I will have the 74 stroker up and running with a 69 bore then the 74 x 74.

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12 hours ago, mixxer said:

Umm Steve,

I think we are all going to need every single technical detail of your machine... Including pictures of all the internal components of the the engine and carb... ;)

Mixxer Steve will show you picture of a motor someone else owns. I know these people.

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Getting back to over heating the first bike to over heat any 4 stroke KTM. As far as water cooled bikes V my air cooled bikes (slow trail hill climbing) Air cooled are the last to over heat. My 254 stroker runs cold every look at the thickness of the fins?  It never gets hot we all know baja gets hot.

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