Stroker questions for new engine management systems

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nuttyn01

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Dec 3, 2007

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Sioux Falls, SD

• May 4, 2014

• #1

We all know the benefits of adding larger bore and turbos to our state of the art engines with little to no effects on the factory ECM, but what about adding a stroker to the combination?

Since fuel and ignition timing are controlled more precisely in the ECM and some seem to be very locked up with no change capable. In the snowmobile world strokers never really caught on. My biggest question is how bad would the stroker engine mess with the ECM ignition pre-set parameters? Since the stroke is now changed wouldn't the ignition timing need to be adjusted too?

Im not talking cost vs gain or anything like that, Im just thinking out loud.

 

eddy

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• May 5, 2014

• #2

Stroker

Theory says there are benefits. Reality the last few years says that a stroke over 75MM leads to crank reliability problems. IMHO if the crank is balanced correctly: the longer stroke, even if it results in a lower RPM, would be a big gain. Correct to say the electronics could help it work.

 

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gus bohne

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Apr 23, 2008

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• May 5, 2014

• #3

I like your idea Nick, say 79 x 84..humm
timing change would be small, like a 1.8 degree key, no worries there..

the machining of the cylinder to correct port time and the rework of the head might be an issue though. Dome reshaping that interferes with the injector tips is my only concern.

havent been inside a torch head yet, soon enough though..:face-icon-small-sho:face-icon-small-sho

The oem cranks that had strokes over 75 also had very large crankwheels, the polar moment of inertia MIGHT have been just a bit over the top contributing to some of the crank issues of the past.
In the RT case it was the 2 center bearings being exposed to high lateral loads that brinneled the deep groove ball bearing. 4 yrs ago I swapped to roller bearings on the center 2 locations and have since seen zero crank issues with the big girl motor.

Man now I want to get a crank to Phil for the work !!!! lol

 

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nuttyn01

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Dec 3, 2007

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• May 5, 2014

• #4

My biggest concern was not being able to manipulate the ignition timing that may be needed due to the change in stroke. If its not enough to worry about then good deal. I need to put a pencil to paper and lay some math down to see how this might work out.

 

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gus bohne

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Apr 23, 2008

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• May 5, 2014

• #5

I got that figure from my old tsr portime program.
Based on my target 79mm.

Wanna build a 935 cc turbo
Oh baby. Go gettem.

 

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nuttyn01

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Dec 3, 2007

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• May 5, 2014

• #6

I was thinking big bore stroker combo. I'd like to "see" around 950cc on a boosted application. 79mm stroke might have to get aggressive and trench the cases?

 

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gus bohne

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• May 5, 2014

• #7

yes, I would send the case and crank to Phil. let him do it all IF he will dooooo it..

Appears a 4 mm increase is fitment friendly..lol Im with ya.

Got to doo some further investigations..muhahahaha..

Now your talking good fun stuff Nick, baby bores or slight overbores are not for me. I want as much real estate per say between the bore and the inner oring as possible, lets face it, if you have even minor light det you will regret having the oring tight to the bore edge..
Thats my reasoning to keep the bore 84 or less..with that in MY mind cc totals look like 890 ish, or 50 cc ish for the stroke change to 79.5. 840 and 50 cc .890 cc.
to get that 950 combo you need a 900 to start with. sucks but stroke cahnges dont add that much swept volume .

 

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nuttyn01

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• May 5, 2014

• #8

I think an increase in 4mm on the crank would be alot. Maybe not. I still haven't put anything to paper yet. Still bouncing around in my head. I wish the center spacing was wider on that engine so it would except larger cylinders to begin with. I'd like to see some large Cat cylinders on there and get rid of the questionable castings from Rotax.

 

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Laundryboy

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• May 5, 2014

• #9

4mm increase on the crank would be an 8mm overall increase wouldn't it?

 

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gus bohne

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• May 5, 2014

• #10

4 total was my thought. A 2 mm pin movement.