Stroker crank and spacer plate

[RiverRat]

How would a 5mm stroker crank perform on a cylinder that is currently set up for a stock crank? I have heard that stroker motors are ported for a stroker crank but I don't know the specifics on that. What is the concensis of spacers plates. I get mix reviews on about them.

Also, what kind of power does a stroker crank produce. Would it compare to adding a b-pipe or what? Is it worth it if you come across a stroker crank at a good deal? Any feedback from guys that went from a stock stroke crank to a stroker would be helpful.

 

[Exile]

Gr8 quesion! Im really interested in this thread.....

Exile.

 

[freestylegeek]

Well, the mechanical advantage alone is 7% for a 5mm stroker and 11% for an 8mm stroker. Now, I'm sure there are some losses, so it's not an exact gain, but EVER SINGLE stroke has that advantage. It also changes how the torque is delivered, depending on the length of the rod.

 

[sjetrider]

Well, the mechanical advantage alone is 7% for a 5mm stroker and 11% for an 8mm stroker. Now, I'm sure there are some losses, so it's not an exact gain, but EVER SINGLE stroke has that advantage. It also changes how the torque is delivered, depending on the length of the rod.

How about running the Kawi flattop pistons w/ 5mil stroke????? Instead of a spacer plate????

 

[RiverRat]

From my understanding you want the lower port timing of a 61x cylinder b/c it is better for low end power. So if you do a spacer plate won't that increase the height and move the power band? Giving you more power in the mid and top but not necessarily the bottom. It is just something I have been wondering about.

 

[RiverRat]

How about running the Kawi flattop pistons w/ 5mil stroke????? Instead of a spacer plate????

I think flat top pistons add anouter 2-3hp maybe. It is not that much.

 

[Mile9c1]

My 6mm stroker uses a 61X cylinder, and domes that are cut to allow the extra stroke to travel into the domes. No spacers or flat tops needed, and bottom end is great, even though the cylinder has an aggressive race port job.

 

[sjetrider]

I have a RIVA Girdle head that has an extra 4-5mm plate for this set up. The head is 31cc for domes. Toby and I are trying the flat top piston route w/ 5 mil crank 82mm Kawi pistons. So far it looks good, still debating on what size ADA domes to use though.

 

[SuperJETT]

I think flat top pistons add anouter 2-3hp maybe. It is not that much.

He's talking about the piston pin location, because it's higher up on a Kawi piston allowing you to run some extra stroke without a spacer plate.

Adding the plate will increase your port timing (even further on your cylinder) so I'd stay away.

If you were to try anything, I'd go with Kawi pistons and get some domes cut . $300-400 or so and you could run it.

 

[sjetrider]

I think flat top pistons add anouter 2-3hp maybe. It is not that much.

They also give you 4 of the 5 mil. clearance you need to run a 5 mil stroke right ?

 

[freestylegeek]

I think flat top pistons add anouter 2-3hp maybe. It is not that much.

Like everyone else said, the Kawasaki flat top pistons move the pivot pin closer to the top of the piston, lessening the 'deck height' needed for the cylinder. It also keeps the timing the same with the port height. I would check with an expeirenced engine builder, but I believe you could do what Darin suggested and be OK.

Oh, and the flat top design adds about 2%, not 2 HP.

 

[RiverRat]

My 6mm stroker uses a 61X cylinder, and domes that are cut to allow the extra stroke to travel into the domes. No spacers or flat tops needed, and bottom end is great, even though the cylinder has an aggressive race port job.

My buddy has a 61x cylinder that has a slightly thicker base gasket and has the head milled out so the piston can travel up into the head a little. I was just curious on how spacer plates effect the overall performance. Interesting stuff..........sounds like flattops and a milled head are the way to go to retain port timing.

 

[SuperJETT]

My buddy has a 61x cylinder that has a slightly thicker base gasket and has the head milled out so the piston can travel up into the head a little. I was just curious on how spacer plates effect the overall performance. Interesting stuff..........sounds like flattops and a milled head are the way to go to retain port timing.

It will actually lower your timing, and increase your compression.

 

[RiverRat]

I am interested to see how it runs............ported 5mm stroked 61x motor w dual 44's

 

[RiverRat]

Does anyone have dech height information for lamey cylinders set up for various stroker crank?.....OEM cylinder height? This may be useful reference info for the tech section.

 

[SUPERTUNE]

In my opinion... if you are building for freestyle horsepower with a stroker crankshaft you need to resleeve your 61x cylinder and/or use an aftermarket race cylinder (Lamey-ADA) and machine the cylinder height to get your target port mapping with the stroker crankshaft. When adding increased stroke you are increasing the port timing quite a bit, so running a stock unported cylinder with a stroker will be like having a ported cylinder with more port duration. All strokers do give more port duration and most of the time is bad for freestyle specific built motors as they will make the powerband come on way too late.

 

[sjetrider]

In my opinion... if you are building for freestyle horsepower with a stroker crankshaft you need to resleeve your 61x cylinder and/or use an aftermarket race cylinder (Lamey-ADA) and machine the cylinder height to get your target port mapping with the stroker crankshaft. When adding increased stroke you are increasing the port timing quite a bit, so running a stock unported cylinder with a stroker will be like having a ported cylinder with more port duration. All strokers do give more port duration and most of the time is bad for freestyle specific built motors as they will make the powerband come on way too late.

Now you are a touch over my head. I have a cylender and cases that have been somewhat radically ported IMO.
This set up was:
5 mill crank ported & epoxied cases
61X radically ported 81mm OEM pistons
Riva girdle (non interchangable dome) 31 cc domes w/ 5 mill plate betrween head and cylender.

We decided to do away with the Riva head and spacer plate. We also lowered the boost port about an inch and chanford the transfer port where ring ends are. We are going to try 82mm flattop KAWI pistons w/ a boost hole drilled in them to line up with the lowered boost port. We plan on running the Girddle ADA head w/ I believe 28cc domes??????? We want to achieve aprox 210 to 220 comp. and not really sure where to start w/ domes. ADA didnt seem to know either so we bought 28cc and were going from there. I belieave the exhaust port is arround 37mm from top currently (if my memory serves me right)
I am not sure if we will need a thick base gasket to make up the extra 1mm where the KAWI pistons gave us 4mm but the stroke is 5mm. I am hoping the squish will be ok w/ out the thick base gasket as we do not want to raise the exhaust port any more. This is all experimental by amature wannabe mechanics so any input would be great from you :hail: Chuck.

 

[RiverRat]

The stroker motor that I have belongs to my buddy. He got it for free!! He worked at a dealership and it was a old race motor that they had just laying around. We disassembled the motor to check the condition of everything and just figure out what exactly he had. The domes have been cut to allow more piston travel, cylinders have been ported, 5mm stroker crank, and slightly thicker base gasket. To our knowledge the motor was used is a racing FX-1 back in the day. The FX-1 race ski was in the shop as well and this was one of its spare motors. He wants to use it for freestyle/rec use so it should work fine depending on how drastic the port job is. Either way it is a free motor so if it runs he did good :biggrin:

 

[Legdragger]

Do you need to have a programable ignition to run a stroked crank?

 

[freestylegeek]

Do you need to have a programable ignition to run a stroked crank?

I only know of one person running a stroker without a programable ignition - Steve802cc. I believe it's possible, but I think you severely limit the power. Both Paul (LPW) and Chuckie (Team Scream) STRONGLY recomend programable ignitions for any motor they build. With a stroker, the port timing and duration at TDC are different, so the benifits of a programable ignition are greater.