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Author Topic: Stroker rev limit  (Read 10624 times)

Offline speedduck

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Stroker rev limit
« on: February 09, 2015, 12:55:30 PM »
What kind of rev limits there has been with big stroker (+8-12mm) motors ? And was it set when power curve started to fall or estimated what the parts can handle ?
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Offline C_Henry

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Re: Stroker rev limit
« Reply #1 on: February 12, 2015, 05:09:28 PM »
 :ppcrn: :ppcrn:
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Offline speedduck

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Re: Stroker rev limit
« Reply #2 on: February 13, 2015, 07:00:47 AM »
Yes, my thoughts excatly  :?

I asked this from well known engine builder but wanted to hear users opinions also. I will tell about my experience, after couple opinions first, if anybody cares.
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Offline RansomT

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Re: Stroker rev limit
« Reply #3 on: February 13, 2015, 09:50:28 AM »
From the experience of the ones I have tuned (Busas), they normally peak well prior to 11k some before 10.5k. Which kind of dictates where the limiter should be.   The piston speed isn't an issue, I think it is more of the rod ratio.
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Offline speedduck

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Re: Stroker rev limit
« Reply #4 on: February 13, 2015, 10:37:08 AM »
Quote from: RansomT on February 13, 2015, 09:50:28 AM
From the experience of the ones I have tuned (Busas), they normally peak well prior to 11k some before 10.5k. Which kind of dictates where the limiter should be.   The piston speed isn't an issue, I think it is more of the rod ratio.
I think you are spot on. Somebodys been talking about 25m/s piston speed, after that the power should drop, but i`ve seen 27m/s+ before it started to fall.
What about the rod ratio, it`s hard to keep it like stock when using bigger strokers. Where comes the limit when it starts to have an effect on the revving ?
Some guys install shorter rods to keep the overall motor height lower, and stock timing chain still usable, when there should be longer rods to keep the rod ratio in reasonable range.
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Offline fvance

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Re: Stroker rev limit
« Reply #5 on: February 13, 2015, 12:37:42 PM »
I have seen two of the 1635 motors with the latest Carpenter head on JCs dyno. They were both still gaining HP at the 11650 rev limit. They were both in the neighborhood of 285 HP. That is a nice neighborhood to live in :hys:
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Offline speedduck

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Re: Stroker rev limit
« Reply #6 on: February 13, 2015, 12:46:49 PM »
Quote from: fvance on February 13, 2015, 12:37:42 PM
I have seen two of the 1635 motors with the latest Carpenter head on JCs dyno. They were both still gaining HP at the 11650 rev limit. They were both in the neighborhood of 285 HP. That is a nice neighborhood to live in :hys:
There must`ve been some serious cams in too. 1635 means +9mm(72mm) crank, yes ?
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Offline fvance

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Re: Stroker rev limit
« Reply #7 on: February 13, 2015, 01:33:49 PM »
Very serious cams!! My 1657 makes about 270 HP. Smaller cams, stock size valves. It peaks Hp at around 10200 and flat lines to 10800. We shift it at 10700 and rev limit is 11200.
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Offline RansomT

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Re: Stroker rev limit
« Reply #8 on: February 13, 2015, 02:28:08 PM »
Quote from: fvance on February 13, 2015, 01:33:49 PM
Very serious cams!! My 1657 makes about 270 HP. Smaller cams, stock size valves. It peaks Hp at around 10200 and flat lines to 10800. We shift it at 10700 and rev limit is 11200.

Fred, that is what have seen with the larger stroker motors.  Now, I haven't have the opportunity to work with one with the new Carpenter Head/Exhaust system.

Which head is on your 1657?  Older or new Bob?
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Offline fvance

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Re: Stroker rev limit
« Reply #9 on: February 13, 2015, 02:44:47 PM »
Mine is the older. Karls two had the new. They are in the hands of Dean S. and RyanO now. Speaking of Dean, are you around?
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Offline RansomT

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Re: Stroker rev limit
« Reply #10 on: February 13, 2015, 02:54:42 PM »
While I don't believe that rod ratio is a means to end all, I do believe that is a piece of a bigger combination.

If you look at the rod ratio of the newest generation sport bikes this is what you will find:

Busa is around 1.83:1
S1000rr is just above 2.0:1
GSXR600 is 2.1:1

It seems that higher the peak HP in terms of RPM, the longer the rod ratio.

When you stroke a bike, normally stock length rods are used causing the rod ratio to decrease..
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Offline speedduck

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Re: Stroker rev limit
« Reply #11 on: February 14, 2015, 03:07:36 AM »
One advice i`ve also heard was to keep the rod ratio over 1.75 Gen1 busa it`s 1.89 ,gen2 1.83 and +9(72mm) with stock rods 1.66 , so it`s easily going down.
Fred, do you have stock length rods ? If so, it`s 1.63 for you.

I had +8.5mm stroker with +4mm rods, ratio 1.72 , it was gaining hp until 11400 and limit was 11600.
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Offline RansomT

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Re: Stroker rev limit
« Reply #12 on: February 14, 2015, 06:49:36 AM »
Quote from: fvance on February 13, 2015, 02:44:47 PM
Mine is the older. Karls two had the new. They are in the hands of Dean S. and RyanO now. Speaking of Dean, are you around?

I've only worked with strokers that had Bob's older head or heads that didn't have that extra something on the exhaust side.

Now if Bob wants to sent me a 1635 with all the new designs, I would take it.    :bike:
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Offline Rocketgeezer

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Re: Stroker rev limit
« Reply #13 on: February 14, 2015, 08:04:24 PM »
Quote from: RansomT on February 13, 2015, 02:54:42 PM
While I don't believe that rod ratio is a means to end all, I do believe that is a piece of a bigger combination.

If you look at the rod ratio of the newest generation sport bikes this is what you will find:

Busa is around 1.83:1
S1000rr is just above 2.0:1
GSXR600 is 2.1:1

It seems that higher the peak HP in terms of RPM, the longer the rod ratio.

When you stroke a bike, normally stock length rods are used causing the rod ratio to decrease..
Its not just with bikes, with my drag car motors from years past I always used longer rods, from what I can see the problem doing that with the bike engines is having to move the pin into the ring land area, don't know if anybodys ever tried it and unless you were a well qualified machinist/engineer, the cost of having to pay someone for that type of work would be prohibitive.
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Offline speedduck

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Re: Stroker rev limit
« Reply #14 on: February 15, 2015, 04:38:56 AM »
Quote from: Rocketgeezer on February 14, 2015, 08:04:24 PM

Its not just with bikes, with my drag car motors from years past I always used longer rods, from what I can see the problem doing that with the bike engines is having to move the pin into the ring land area, don't know if anybodys ever tried it and unless you were a well qualified machinist/engineer, the cost of having to pay someone for that type of work would be prohibitive.
The other way is to install lot`s of spacers and longer timing chain. You just have to drill out every mounting hole, in frame and motor.
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Offline glenn71

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Re: Stroker rev limit
« Reply #15 on: March 06, 2015, 02:02:03 AM »
You sure do and run thinner rear engine mount  bolts and offset the lowest mount hole in the cases,Fun stuff,not.
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