Topic: Street Stroker?

[Tracksnblades1]

George,

I believe we have read some of the same pages and contemplated on such as well.

(although I have great respect for old Smokey😉)  RC Engineering’s method was to do a 6mm over weld up stroker crank using dark ages techniques, then combining that with 3mm shorter than stock Golden rods.  It surely made a less than ideal situation. 

I agree with you and in reference to RC's combination as well as Bear's application. RC's combination mirrors the popular SBC 383/w5.565 rods. Bear has found his solution to his application which follows Ole Smokey discipline.

Modern auto engineering appear to be following Ole Smokey also. A quick check of current stock Chevy Ford rod lengths are more high performance optional lengths of yesteryear.

I too am interested in the current opinions of short vs long rod discussion. I've had a 25 year vacation from the SPEED addiction.

What are your current thoughts on the long vs short rods in applications: Where cylinder head port design and flow are limited?  Idle to midrange power is paramount?  Midrange to top is paramount?

Disregarding for now supercharging, camshaft advantages, side thrust loads, inertial deaccel/accel loadings , crank pin/cylinder pressure geometry, and etc.

Thanks

[gschuld]

To be fair, my opinions are almost entirely based on the information that I try to consume whenever possible.  I especially pay attention to those with thousands of hours dyno testing and racing of their engines.  Such as Smokey Yunick and especially David Vizard in the auto engine world anyway.

Personally, I think Bear’s approach has the most sensible hard fought through experience answer.  He did it the hard way converting(way more complicated that it seems at first) a HiVo chains DOHC factory 69mm crank and Honda cb1100f rods(stronger versions of the Sohc factory rod design with better rod bolts and 1.5mm longer, 17mm pin).  Brian also adapted modern pistons with a shorter compression height(don’t know exactly how much).  It’s been proven under very challenging high hp, hot weather road racing circumstances(methanol fuel help with the heat issues anyway)

Is a modern welded Sohc CB750 based stroker crank with standard length rods and very lightweight pistons sufficient for a far less powerful STREET engine, maybe...😏  Using longer rods IS the safe bet though.

George

[Tracksnblades1]

George,

I always liked and tried to follow "as long as you can get in it"  Smokey rod quote.
I'll accept the increased valve to piston clearance (cams keeps turning and opening that intake @ piston dwell).
Purchase better rods, bolts, lighter pistons for the increased accel/decell forces.
Have Professional, like (MRieck) prepare the ports to benefit the increased piston accel/deceleration rates.

Have you seen anyone running a piston like this in the SOHC 750 ? That light weight JE is getting there.

[gschuld]

OK, did some basic number crunching.

CB750 

Stroke:                        Rod length:     Rod/stroke ratio

63mm(std).                 116(std).          1.84

68mm(stroked 5mm).  113(RC short).  1.66
                                  116(std).          1.70
                                  117.15)1100f).  1.72

69mm(DOHC 6mm).    113(RC short).  1.64
                                  116std).          1.68
                                  117.15(1100f).  1.70

70mm(stroked 7mm).  113(RC short).  1.61
                                  116(std).          1.66
                                  117.15(1100f).  1.67

FWIW, the cb550 is 50.6 stroke/107mm rod length for a 2.11 ratio.

Not a lot of ratio difference between standard length rods and slightly longer 1100f rods🤔

Tracksnblades1,

Check with Brian (Bear) he adapts modern Honda pistons (RC 45?) for his stroker motors.  But generally, no, I haven’t seen super low height pistons being used personally.  Perhaps some are and aren’t talking about it.

George

Edit: I corrected my numbers as I originally had mistaken the standard and 1100f rod lengths (thanks Kieth😉)

[gschuld]

For those up for some light reading in reference to auto based rod/stoke ratio articles:

http://www.enginebuildermag.com/2016/08/understanding-rod-ratios/

http://www.superstreetonline.com/how-to/engine/0506-ht-rod-stroke-ratio/

https://www.rodauthority.com/tech-stories/engine/stroker-engines-long-short-connecting-rod-length/

http://www.mustangandfords.com/how-to/engine/mmfp-0711-ford-small-block-stroker-engine-build/
FWIW, this last one is written by David Vizard)

George

[kmb69]

OK, did some basic number crunching.

CB750 

Stroke:                        Rod length:     Rod/stroke ratio

63mm(std).                 117(std).          1.86

68mm(stroked 5mm).  114(RC short).  1.67
                                  117(std).          1.72
                                  118.5(1100f).   1.74

69mm(DOHC 6mm).    114(RC short).  1.65
                                  117(std).          1.69
                                  118.5(1100f).   1.71

70mm(stroked 7mm).  114(RC short).  1.62
                                  117(std).          1.67
                                  118.5(1100f).   1.69

FWIW, the cb550 is 50.6 stroke/107mm rod length for a 2.11 ratio.

Not a lot of ratio difference between standard length rods and slightly longer 1100f rods

Tracksnblades1,

Check with Brian (Bear) he adapts modern Honda pistons (RC 45?) for his stroker motors.  But generally, no, I haven’t seen super low height pistons being used personally.  Perhaps some are and aren’t talking about it.

George

Pretty sure 300 Rods (CB750) are 116mm.
Pretty sure MA3 Rods (CB1100) are 117.15mm.

[gschuld]

Thanks Keith, I fixed the numbers:

OK, did some basic number crunching.

CB750 

Stroke:                        Rod length:     Rod/stroke ratio

63mm(std).                 116(std).          1.84

68mm(stroked 5mm).  113(RC short).  1.66
                                  116(std).          1.70
                                  117.15)1100f).  1.72

69mm(DOHC 6mm).    113(RC short).  1.64
                                  116std).          1.68
                                  117.15(1100f).  1.70

70mm(stroked 7mm).  113(RC short).  1.61
                                  116(std).          1.66
                                  117.15(1100f).  1.67

FWIW, the cb550 is 50.6 stroke/107mm rod length for a 2.11 ratio.

Not a lot of ratio difference between standard length rods and slightly longer 1100f rods🤔

Tracksnblades1,

Check with Brian (Bear) he adapts modern Honda pistons (RC 45?) for his stroker motors.  But generally, no, I haven’t seen super low height pistons being used personally.  Perhaps some are and aren’t talking about it.

George

Edit: I corrected my numbers as I originally had mistaken the standard and 1100f rod lengths (thanks Kieth😉)

[gschuld]

If you look at the list below showing the popular 4 cylinder Honda car engines, out of the 9 series represented, only one of the nine has a stroke rod ratio over 1.62, and that one is 1.74, well less than the 1.84 of the factory CB750 ratio.

The other 8 series engines were between 1.52 and 1.62. 

For comparison, a dohc crank (69mm stroke) with a standard length rod is 1.68 and 1.70 with a cb1100f rod.  It doesn’t seem like there is much daylight between 1.68 and 1.70 rod/stroke ratio🤔

George

[Tracksnblades1]

If you look at the list below showing the popular 4 cylinder Honda car engines, out of the 9 series represented, only one of the nine has a stroke rod ratio over 1.62, and that one is 1.74, well less than the 1.84 of the factory CB750 ratio.

The other 8 series engines were between 1.52 and 1.62. 

For comparison, a dohc crank (69mm stroke) with a standard length rod is 1.68 and 1.70 with a cb1100f rod.  It doesn’t seem like there is much daylight between 1.68 and 1.70 rod/stroke ratio🤔

George

It's not quite apples to 🍎s. The newer Honda cbr1000 have 104.45mm rods and 55.1mm stroke @ near 1.9:1, 2018 honda cbr1000 bumped compression ratio to 13:1. Ford's 4.9 sports 6.209 rod c/c. Most new small v8 Chevys have 6inch plus rods.

Your above attached current reads have more in common with ancient articles than they differ.
Well Done.

[gschuld]

If you look at the list below showing the popular 4 cylinder Honda car engines, out of the 9 series represented, only one of the nine has a stroke rod ratio over 1.62, and that one is 1.74, well less than the 1.84 of the factory CB750 ratio.

The other 8 series engines were between 1.52 and 1.62. 

For comparison, a dohc crank (69mm stroke) with a standard length rod is 1.68 and 1.70 with a cb1100f rod.  It doesn’t seem like there is much daylight between 1.68 and 1.70 rod/stroke ratio🤔

George

It's not quite apples to 🍎s. The newer Honda cbr1000 have 104.45mm rods and 55.1mm stroke @ near 1.9:1, 2018 honda cbr1000 bumped compression ratio to 13:1. Ford's 4.9 sports 6.209 rod c/c. Most new small v8 Chevys have 6inch plus rods.

Your above attached current reads have more in common with ancient articles than they differ.
Well Done.

I agree, not apples to apples.  I used the Honda 4 cylinder auto engines as an example because it was a large group of specifically 4 cylinder engines.  The ideal rod ratio seems to increase with the number of cylinders, at least according to the quote below:

Food for thought.

George

[kmb69]

Very dependable, high horsepower, 10,000 RPM, GSXR1300 Hayabusa:

C/R:     12.5:1
Rod:     119.5mm
Stroke: 65mm
Ratio:   1.838

Long rods RULE! 

[gschuld]

Sure, but in the case of a 69mm stroke CB750 engine, is there much functional difference between a 1.68 and a 1.70 rod ratio?  That’s it between a factory length rod an an 1100f rod in that engine.

George

[kmb69]

Sure, but in the case of a 69mm stroke CB750 engine, is there much functional difference between a 1.68 and a 1.70 rod ratio?  That’s it between a factory length rod an an 1100f rod in that engine.

George

Maybe not, but I would prefer to have that extra 1.15mm and the 17mm pin for essentially the same price in aftermarket rods. Much stronger combo, especially for nitrous or turbo IMHO. I guess my real argument would be if you're going to all the effort to make a big stroker motor, why would one be cheesy with the rods? That silly 1.15mm might just make the difference providing a longer life for the crank and pistons. I have always believed the shorter rods used in days mostly past, (except for the RC diehards), were part of the reason for short lived cranks.

Regarding the crank itself, Kenny has pretty much proven the welded stroker, even with the HD roller primary, can't hang with a motor making some real power. Gotta use the DOHC crank with a Hy-Vo minimum IMHO.

[gschuld]

True, though some of us are limiting our power potential with non straight port K heads with rational valve sizes, 10.5:1 compression, and just happen to have a set of perfect factory length Carrillo rods on the shelf waiting to be used.  Quality 15mm pins pose no challenge to a potential 110-120 RWHP.  Now for you guys shooting for WAY more power than that, we’ll sure, I totally get it.

The rod ratio is increased by a whopping 1.1% going from a standard length to a 1100f rod with a 69mm stroke crank. If you are comfortable with the 1.1% better rod ratio for 140+ RWHP, I’m thinking backing down a mere 1.1% will be just fine at 20-25 or more RWHP less.

George

[scottly]

If you look at the list below showing the popular 4 cylinder Honda car engines, out of the 9 series represented, only one of the nine has a stroke rod ratio over 1.62, and that one is 1.74, well less than the 1.84 of the factory CB750 ratio.

The other 8 series engines were between 1.52 and 1.62. 


George

George, what is the "redline" on those Honda car engines? My 2001 Civic has a redline at 6800 RPM. With a short rod, more power may be produced in a lower RPM range, but less power at higher revs due to increased piston/cylinder friction.

[Don R]

 I love a good engine thread, I always learn a lot.
  I wondered, if Russ Collins guys can weld a Gilmer belt pulley snout on a 3 engine nitro 750 crank, why can't someone put cb750 ends on a 900 crank?  The right end may just machine down so only the left would need an add on. Seriously. Then a quality hyvo chain and 750A or gl1000 primary? 
  If that's dumb, it's OK just tell me why.
  Or we could be like Mike, he went all in on his cylinders, maybe we could get a few cranks made. Surely there are other folks that con't care that you can just buy a 1300cc bike. How much could it cost? Maybe we don't want to know. What's better, billet or a twisted forging? 

[gschuld]

If you look at the list below showing the popular 4 cylinder Honda car engines, out of the 9 series represented, only one of the nine has a stroke rod ratio over 1.62, and that one is 1.74, well less than the 1.84 of the factory CB750 ratio.

The other 8 series engines were between 1.52 and 1.62. 


George

George, what is the "redline" on those Honda car engines? My 2001 Civic has a redline at 6800 RPM. With a short rod, more power may be produced in a lower RPM range, but less power at higher revs due to increased piston/cylinder friction.

Scottly,

That’s a good question and a good point.  Performance minded modern Honda auto engines seem to have a decline between 7000-8300 depending on the model.  Those that further modify them report low to mid 9000s is not uncommon on street/street racer based engines.

The performances built sohc4 engines are typically peaking under 10,500rpm.  Some are higher of course.  So yes, certainly not and apples to apples comparison.

Don,

Sure, that type of work could probably be done.  Machining down the right side rotor snout would be an easier task than creating and rotor snout on the left side, but sure it’s possible.  Not sure if it’s worth the risk hanging a rotor on a welded snout😬

Either way, there is quite a bit of effort necessary to make a dohc crank work in a Sohc race engine, but the results are proven over the many examples that have raced.  It’s a bit more work to make it work for a street engine that requires electric start and a functional charging system.  All doable, just extra work.

George

[Tracksnblades1]

True, though some of us are limiting our power potential with non straight port K heads with rational valve sizes, 10.5:1 compression, and just happen to have a set of perfect factory length Carrillo rods on the shelf waiting to be used.  Quality 15mm pins pose no challenge to a potential 110-120 RWHP.  Now for you guys shooting for WAY more power than that, we’ll sure, I totally get it.

The rod ratio is increased by a whopping 1.1% going from a standard length to a 1100f rod with a 69mm stroke crank. If you are comfortable with the 1.1% better rod ratio for 140+ RWHP, I’m thinking backing down a mere 1.1% will be just fine at 20-25 or more RWHP less.

George

Are these perfect length Carrillo rods for sale?  condition?
Thanks

[gschuld]

True, though some of us are limiting our power potential with non straight port K heads with rational valve sizes, 10.5:1 compression, and just happen to have a set of perfect factory length Carrillo rods on the shelf waiting to be used.  Quality 15mm pins pose no challenge to a potential 110-120 RWHP.  Now for you guys shooting for WAY more power than that, we’ll sure, I totally get it.

The rod ratio is increased by a whopping 1.1% going from a standard length to a 1100f rod with a 69mm stroke crank. If you are comfortable with the 1.1% better rod ratio for 140+ RWHP, I’m thinking backing down a mere 1.1% will be just fine at 20-25 or more RWHP less.

George

Are these perfect length Carrillo rods for sale?  condition?
Thanks

No, they are not for sale.  Sorry.😏

George

[bear]

Regarding the crank itself, Kenny has pretty much proven the welded stroker, even with the HD roller primary, can't hang with a motor making some real power. Gotta use the DOHC crank with a Hy-Vo minimum IMHO.

I managed to work that one out twenty year's ago.
The hard way of course (I'm not the sharpest tool in the shop)

Brian

[gschuld]

Regarding the crank itself, Kenny has pretty much proven the welded stroker, even with the HD roller primary, can't hang with a motor making some real power. Gotta use the DOHC crank with a Hy-Vo minimum IMHO.

I managed to work that one out twenty year's ago.
The hard way of course (I'm not the sharpest tool in the shop)

Brian

So for reference, can we define “real power” in terms of both HP and rpm?  Both are big factors on judging the suitability of a certain crank.  And where was the crank made?  I suppose these answers require a NDA and knowledge of a secret handshake...😎

George

[bear]

Sure, but in the case of a 69mm stroke CB750 engine, is there much functional difference between a 1.68 and a 1.70 rod ratio?  That’s it between a factory length rod an an 1100f rod in that engine.

George

No there's not George but in my case these where the two options that I had .
And many years ago in the back block's of Australia those two options (factory rods) where the only one's available.
The std 750 rods or the M4 1100 rods that where stronger had 17mm pins and where a little closer to optimal length.

Cheers,
Brian

[bear]

Regarding the crank itself, Kenny has pretty much proven the welded stroker, even with the HD roller primary, can't hang with a motor making some real power. Gotta use the DOHC crank with a Hy-Vo minimum IMHO.

I managed to work that one out twenty year's ago.
The hard way of course (I'm not the sharpest tool in the shop)

Brian

So for reference, can we define “real power” in terms of both HP and rpm?  Both are big factors on judging the suitability of a certain crank.  And where was the crank made?  I suppose these answers require a NDA and knowledge of a secret handshake...😎

George

I don't think it's a matter of suitability. I think the process of welding cranks itself for these applications is flawed.
But having a large hot reciprocating mass disintegrate between my nether regions a couple of times may have clouded my judgment . 

Cheers,
Brian

[gschuld]

I could understand that....😳.  Out of curiosity what timespan were you running and breaking welded cranks?

George

[Medyo Bastos]

how did your nether regions hold up?