Stroker motor - 5mm, 6.25mm, or 8mm

[GeorgeC]

I'm about to pull the trigger on a weld-up stroker crank (billet is too much $$$ for my poor ass).

Initially my plan was an 8mm or so, with 2.5mm shorter rods and appropriate spacer.  Now I'm thinking of just doing the more common 5mm to end up with what should be a more reliable 1507.

What are everyone's thoughts?  Is it worth considering the 8mm?  Will it be that much harder on everything?  How significant would the difference in power be between 5mm and 8mm?

I think I'm down to either 5mm, or 8mm...  I'm not keen on the idea of a 6.25mm, since it would require a thicker spacer plate with stock length rods, and I don't want to run a shorter connecting rod if I don't have to. 

[duncan]

wait till 08 and get a 2mm stroker! just kidding. my buddy has a 5mm with 7000 or so miles on it with no trouble. boy this thing has some torque. he changes the oil(synthetic) every 750-1000 miles. this bike is street driven only. GOOD LUCK ON YOUR DECISION

[Gixx1300R]

I'm about to pull the trigger on a weld-up stroker crank (billet is too much $$$ for my poor ass).

Initially my plan was an 8mm or so, with 2.5mm shorter rods and appropriate spacer.  Now I'm thinking of just doing the more common 5mm to end up with what should be a more reliable 1507.

What are everyone's thoughts?  Is it worth considering the 8mm?  Will it be that much harder on everything?  How significant would the difference in power be between 5mm and 8mm?

I think I'm down to either 5mm, or 8mm...  I'm not keen on the idea of a 6.25mm, since it would require a thicker spacer plate with stock length rods, and I don't want to run a shorter connecting rod if I don't have to. 

I have built plenty of stroker motors. My fav is 5mm and stock length Carrillo H beam rods. Shorter rods put too much side load on the piston skirts. Key elements to mod is the starter,oiliing,cooling and fuel system. I used to run S2000 injectors but they were too much with my T-Rex fuel pump. I run stock injectors with my T-Rex now. Right now my motor is a streetable 1525cc. Bearing setup is crucial on stroker motors. Let me know if you need a good crank to get stroked. I have one with straight splines. Use only A.P.E to stroke you crank. DO NOT USE FALICON!!!!

[Ardec2]

interesting post,..  

i recently built a 1610cc 5mm over bore with 6.25 welded falicon  and stock length carrillos with .125 spacer.

pros-cons,...  my experiances with busa's   even with update starter drive gears,. etc and very good battery can be hard start if not well tuned. add any combination of bigger motor higher comp,  its gonna have hard start and especially hot start problems,.. no offense to those who have no problems,.. in my shop i get one or two a week to diagnose and try and repair!

bigger is bigger period! the main difference is how reliable and user friendly it is!

as to reliable,.. that is in fact directly related to RPM/HP  i've heard from reliable sources that stock rods are good to 500 hp,.. in my years of engine building never one!!!  

any stroker/bore will raise the compression ratio and or produce harder starts and better gas requirements!

if you talk to very experianced racers builders they'll all rule against shorter rods,.. then stock as it decreases engine power and efficency, and the increased piston speed and higher rod angle greatly increases wear and tear!

All of the "Reputable experienced builders reccommend stock length rods and spacers,..

problem with even an 1/8 inch spacer is the upper motor mounts dont fit gatta drill out or jury rigg it!, also 6.25 mm stroker is considered the max to use the stock length chain other wise different chaing gear set up,.. which id do anyway!

id not waste my time building a bigger motor with hahaha stock cams and head,.. why bother?

Personally from my own builds id build a stock engine size with GREAT HEADS and CAMS,.. degreed,. with full system exhaust and velocity stacks,...   a few other small things,..   its totally relable,. and mostly easy to build up and works the the best stock bike on the road!

whatever you decide good luck,...  may the HP be with you!  robert

I'm about to pull the trigger on a weld-up stroker crank (billet is too much $$$ for my poor ass).

Initially my plan was an 8mm or so, with 2.5mm shorter rods and appropriate spacer.  Now I'm thinking of just doing the more common 5mm to end up with what should be a more reliable 1507.

What are everyone's thoughts?  Is it worth considering the 8mm?  Will it be that much harder on everything?  How significant would the difference in power be between 5mm and 8mm?

I think I'm down to either 5mm, or 8mm...  I'm not keen on the idea of a 6.25mm, since it would require a thicker spacer plate with stock length rods, and I don't want to run a shorter connecting rod if I don'

[GeorgeC]

APE will be doing the crank (already have a good core crank that they've had for awhile).

The 5mm with stock length rods is what I'm really starting to lean towards (mainly due to the side loading issues Gixx1300R mentioned).

As far as good head/cams, the setup I'm running already is better suited to a 1500+cc motor than the 1397 it's on now (Ward CNC ported head, .445/.415 cams).

Starter shouldn't need any work, as it's the better '05 setup already, with 24v starting.  As far as oiling, what's recommended besides ensuring bearing clearances are good, and a high-volume oil pump gear?  Cooling isn't a concern since I won't really be street riding.  The stock system should be good for getting me down the track. 

Gixx1300R, feel free to PM me if you have any other tips that may help.    Don't forget, I want one of your upper cam chain guides. 

[GeorgeC]

...as far as rods go, I was considering going with the Crower I-beams.  Any thoughts?

[Gixx1300R]

...as far as rods go, I was considering going with the Crower I-beams.  Any thoughts?

I have never used Crower rods but I have heard good things about them. Also get the oil pressure regulator. You will have to either use S2000 injectors with the stock fuel pump or and aftermarket fuel pump with stock injectors. If you are planning on spraying it I would suggest having the Piston domes ceramic coated and the skirts dry film coated. It cost around $125.00 for a set of pistons and it is cheap insurance. May want to check on a oil pan baffle instead of a swivel oil pump pickup. The swivel oil pump pickup have been known to fail. Do you have any transmission work done yet?

[Chet]

...as far as rods go, I was considering going with the Crower I-beams.  Any thoughts?

I have never used Crower rods but I have heard good things about them. Also get the oil pressure regulator. You will have to either use S2000 injectors with the stock fuel pump or and aftermarket fuel pump with stock injectors. If you are planning on spraying it I would suggest having the Piston domes ceramic coated and the skirts dry film coated. It cost around $125.00 for a set of pistons and it is cheap insurance. May want to check on a oil pan baffle instead of a swivel oil pump pickup. The swivel oil pump pickup have been known to fail. Do you have any transmission work done yet?

Do you have any actual experience of the swivel oil pickup failing on a real Koenig oil pan?

The Koenig pan also provides more ground clearance over a stock oil pan. We have definitely seen problems with a cut down stock oil pan due to the resulting shape. 

Chet

[Gixx1300R]

No I havent. The swivel was with another company that suppied a  billet oil pan along with the swivel pick up.

[Chet]

No I havent. The swivel was with another company that suppied a  billet oil pan along with the swivel pick up.

Thanks for the quick answer.

We have had good success using the Koenig oil pans and sometimes the knockoffs really are not as good as the original.

Chet

[GeorgeC]

I've already got an aftermarket fuel pump, regulator, and fuel rail, so I'm covered there.  Good suggestions about the piston coating. 

I also already have a baffle/windage tray, billet pan/swivel pickup. 

[Gixx1300R]

Are you going with a set of Nitrous Pistons?

[GeorgeC]

No, I wasn't going to change pistons...  I know the extra 5mm of crankshaft stroke will increase the static compression up .8-.9 or so, but I run nothing but race fuel through the bike as it is.  I see no reason the JE 84mm pistons in there now wouldn't be fine.

I do have a small dry nitrous system on the bike, but I doubt I would ever spray more than 40hp or so.

[Gixx1300R]

sounds like you are all set. If there is anything else I can think of I will let you know.

[GeorgeC]

sounds like you are all set. If there is anything else I can think of I will let you know.

Thanks!

I just got off the phone with APE, and things are in motion. 

[GeorgeC]

Well fuck me...    I just found out that the crank I was going to use as a core has a bad rod journal AND a bad main journal...  I kind of "inherited" it, so I'd never actually seen it myself.  The rod journal is no problem, as it would be welded up and re-grinded anyway, but the main journal repair kind of renders it "not worth messing with."

I guess now I'm back to square one, and will try to find a decent deal on an outright crank, or just save up and do a billet.

[Rocket Rider]

George,
I have a crank that I spun a bearing on the #3 rod...I don't know if its something that you may be interested in, if so let me know...if not I'm going to send it off and have it fixed as a spare?
Keith

[DarkFalcon]

George, many solid points have been made including fueling, fitment, rod angularity, side wall loading, piston speed and compression ratio changes. I would only add that the piston speeds of an 8 mm stoker are getting really, really high........around 5067 ft/min. This, obviously, will tax all of the major components and make reliability all the more difficult. And with increasing cylinder pressure, the bearings will be subject to higher compressive forces........making adequate oiling and routine bearing inspections mandatory. For these reasons, along with the fact that your current head and cams will probably work better with a shorter stroke and less displacement than what the 8mm would create, I would go with the 5 mm..........maybe the 6.25 mm ......and use stock injectors with an aftermarket fuel system set at 67psi to 72psi. Some time ago Dave O posted a link to an article discussing case modifications done by Rick Stetson. I have cut and pasted what I believe is applicable to your requirements. Look at the skirt coatings as well.

The next important item on the list, Rick installs Heavy Duty Studs to keep the cases from moving under those High HP loads, there is nothing more important than keeping your cases from shifting once assembled.

Rick then closes some oil passages, and re-jets the piston oil spray jets. Without giving up all his secrets for his magic, suffice it to say, if you don’t start with a set of cases capable of lubricating and holding over 400HP on Nitrous, then this whole project is doomed before we even get started. Let me repeat myself, if you’re going to build a custom big bore, high HP motor, then you must have a set of motor cases capable of properly lubricating and holding that kind of HP! Need I say more?

Rick’s main concern is to lubricate the rod journals more efficiently which is why he says that you must have at least .002” of an inch clearance in the Rod Bearings and .001” of an inch clearance in the Main Bearings. You have to keep the oil in the crank bearings and move the oil in the rod bearings. He shuts off the oil passage to the balancer shaft (which we will not be using) and removes the oil flow restrictor. Oil flow is the most important aspect of a race motor and can not be compromised. If your motor builder is not doing these important things to your Big Bore, Big Nitrous or Big Turbo motor, then you could be taking chances on your motors survival when running the Big HP.

[gazza414]

Why is it that guys that build and run 400 or 500hp Busa turbo motors dont run these mods?...after all we are normally only talking about 220 to 240hp here NA

[GeorgeC]

DarkFalcon, thanks for your input...  I've considered having those oiling mods done.  I know it wouldn't be a bad idea by any means, but I think I can get by without doing so in my application.  I'm looking at a MAX of probably 270hp or so, and that's on the rare occasion when I would be using N2O.  It may be one of those things I come to regret, but I believe I will forgo the case mods (for now anyway).  Routine teardown and inspection aren't an issue with me, since I like to try to stay on top of things anyway (it's just that sometimes I try to take shortcuts that come back and bite me in the ass  ).

Jay says the crank I have there is useable, but just isn't in the best shape...  The splines are a little buggered up, and one of the mains is a little scarred.  I still think I'm going to pass on having that one done.  The good news is that I believe I may have found a nice 6.25mm crank fresh from APE just how I was going to have this one done.    If so, I'm back in the game, and will continue piecing everything together to make my motor a 1534.

Due to the need for routine disassembly, etc., I think I've decided to go with Carrillo H-beam rods with the upgraded Carr multiphase bolts, since they can be cycled many many times over with no worries of overstressing them.

[Gixx1300R]

When I built my first stroker motor back in 2000 I made this

It is a Cam Chain tensioner spacer. When you use a A.P.E spacer plate under the block it also tightenes up the Cam chain so tight that the tensioner did not ratchet. It acted like a manual tensioner (solid) which put alot of stress on the cam chain. By backing out the tensioner it gave it room to ratchet. It worked fine. This was used on Busas that had no milling done to teh surface of the head.

[DarkFalcon]

Why is it that guys that build and run 400 or 500hp Busa turbo motors dont run these mods?...after all we are normally only talking about 220 to 240hp here NA

Gazza, you raise an interesting question.........and were it a contest it would beat my humble answer. Some of the turbo bikes run oiling mods......but others, including mine, do not. The same is true for strokers........some do and some don't. FWIW, though, I think high compression, high cylinder pressure NA motors are harder on bearings than turbo's only becasue the latter typically have low CR's spend more time off boost than on boost. And during one of the more critical oiling periods.......start-up.........the boost is off. 

[gazza414]

The question was put forward on the board DF as over the years there has never been a definative answer or a group of facts which might hold water .
We all know that the so called high compression as seen by the motor is only there when the camshaft profiles / durations make this possible...we put high compression pistons in to compensate for "wild" cams to an extent.

also when you look at BMEP's on a NA Vs a turbo motor you'll see increases as expected on the turbo motor...they are only air compressors after all and shoving an xtra 1bar or 2 or 3bar into that chamber doesnt go unseen on the compression stroke and less so on the power stroke.

DF, point taken about the boosted bikes being off boost more so than on boost

[gazza414]

When I built my first stroker motor back in 2000 I made this

It is a Cam Chain tensioner spacer. When you use a A.P.E spacer plate under the block it also tightenes up the Cam chain so tight that the tensioner did not ratchet. It acted like a manual tensioner (solid) which put alot of stress on the cam chain. By backing out the tensioner it gave it room to ratchet. It worked fine. This was used on Busas that had no milling done to teh surface of the head.

Very good piece of info my friend as some forget about this aspect and attempt to "shove " it in and hope for the best when in actual fact they may well be "stretching " the chain prematurely...some put 2 or 3 gaskets underneath but this is really a jury rig attempt to overcome the issue.

My next stroker motor I'm going with the APE chain conversion. Just waiting on some further info from a board member before I jump.

[busa416]

I've been kicking a stroker around also would a roller chain conversion help out?