Topic: Camshaft selection and comparison

[maxheadflow]

Well, I wouldn't call it useless. They calculator does give a reasonable calculation for cranking compression. Cranking compression is good for checking the build and can also give you an idea as to whether the motor will ping at lower RPMs.  There are a ton of variables that need to be taken into account like cooling, timing control, squish etc but for a 2 valve air cooled motor like Evo and Twin cam HDs, it seems to work as a valid build aid. 

Here are the same calculators that you can use. I'm sure there are more.  These sights are setup for HDs and use inches (tho some volumes are in CCs) but you can convert what you got and use the calculator.

https://www.rbracing-rsr.com/comprAdvHD.htm

http://www.bigboyzcycles.com/TwinCamComp.htm

The RB racing also unfortunately calls the calculation dynamic. It's really a static type calc as time (velocity) is not involved.

There is also a spreadsheet floating around that does all the calcs. Originally done by a guy named Moe Riggins and an unnamed engineering student to get corrected CR. I added the pressure component.

[turboguzzi]

Max, agree it could give compression values, but that's not what he is after

if you read Ric's initial post, he is trying to understand what kind of torque curve shape he'll get, and peak torque rpm.... that requires way more data entry than those two calculators do.

when i first built my cb500/4 there was a very good and pretty advnaced calculator that predicted my dyno measured hp to within 3-4 hp. regretfully it has been taken off line long time ago. It took constant trips to the workshop for measuring just to enter the data, stuff like inlet cross sections, length and diameters of primaries and secondary pipes and more....it's really a different class of calculator altogether.

[turboguzzi]

Riccardo, BTW, I have contacted a friend who was involved as a student in a Formula SAE project and they did quite intensive dynamic simulations for the Yamaha R6 motor they used.

Hope to hear from him, maybe he still has access to the SW.

[MRieck]

Well, I wouldn't call it useless. They calculator does give a reasonable calculation for cranking compression. Cranking compression is good for checking the build and can also give you an idea as to whether the motor will ping at lower RPMs.  There are a ton of variables that need to be taken into account like cooling, timing control, squish etc but for a 2 valve air cooled motor like Evo and Twin cam HDs, it seems to work as a valid build aid. 

Here are the same calculators that you can use. I'm sure there are more.  These sights are setup for HDs and use inches (tho some volumes are in CCs) but you can convert what you got and use the calculator.

https://www.rbracing-rsr.com/comprAdvHD.htm

http://www.bigboyzcycles.com/TwinCamComp.htm

The RB racing also unfortunately calls the calculation dynamic. It's really a static type calc as time (velocity) is not involved.

There is also a spreadsheet floating around that does all the calcs. Originally done by a guy named Moe Riggins and an unnamed engineering student to get corrected CR. I added the pressure component.

I always enjoyed the "Eat $hit and Die" section of the RB website......scroll to the bottom of the page and click on it. Good reading.

[gschuld]

https://www.rbracing-rsr.com/eat#$%*.htm

It was worth a re-read😉. A little too close to home Mike?😁

George

[turboguzzi]

can anyone explain what happened there? not really clear...

[maxheadflow]

Max, agree it could give compression values, but that's not what he is after

if you read Ric's initial post, he is trying to understand what kind of torque curve shape he'll get, and peak torque rpm.... that requires way more data entry than those two calculators do.

when i first built my cb500/4 there was a very good and pretty advnaced calculator that predicted my dyno measured hp to within 3-4 hp. regretfully it has been taken off line long time ago. It took constant trips to the workshop for measuring just to enter the data, stuff like inlet cross sections, length and diameters of primaries and secondary pipes and more....it's really a different class of calculator altogether.

Well if you couple it with what I said in replay #2, you can use to to ensure that the cranking pressures are not too great.   One worth looking to is:

https://performancetrends.com/Engine-Simulation.htm

You can get the pro program for 10 days to mess with and use it to make decisions.

[livefast_dieold]

So I tried a quick simulation, only thing I don't remember is the rod lenght of the cb750, is it around 140 mm (5.51")? Does anyone remember?

Anyhow with my current setup I would end up at 8.43:1 which is not bad (ideal for regular fuel is from 7.5 to 8.5).



If I opt for the DP295 which closes earlier I would end up at 8.75, the CX3 instead at 8.90

Seems the DP295 is the right choice, more valve lift (intake) but less duration and overlap

[gschuld]

Cb750 rod length

116mm or 4.56”

George

[Tracksnblades1]

PEWE...

What octane are you running @ 195 psig cranking compression..?  Max timing lead...?

can anyone explain what happened there? not really clear...

TurboG..

Are you still thinking 200-205psig max cranking pressure for Air/cooled 91 octane...?
Or are have you went the way of the Harley crowd....?   

[turboguzzi]

Tracksnblades, my question was about the https://www.rbracing-rsr.com/eat#$%*.htm thing

that Behn guy from RB is certainly an "interesting" character, was not sure why his bitterness with the world... thought somebody on here knows the story behind

[gschuld]

TG,

I think is was a general venting from a guy who has been racing and in the racing business for many years and has dealt with some rather unscrupulous customers.  By writing it he probably both placates his therapist and warns others wishing to do business with him that he has pretty much seen it all and isn’t prepared to suffer any more fools.

That’s my take anyway...

George

[turboguzzi]

yep, i could sense that,

I know it's not a kawasaki site here, but was wondering if anyone knew some more

Im active in KZR forum due to my Gpz and KZ, never seen it mentioned there, neither in any magazine or internet story in umpteen years...

[Tracksnblades1]

Tracksnblades, my question was about the https://www.rbracing-rsr.com/eat#$%*.htm thing

that Behn guy from RB is certainly an "interesting" character, was not sure why his bitterness with the world... thought somebody on here knows the story behind

Yes Turbo,

I got all that,  the plagiarism, copyright/pantent infringing, the theft in general, of equity,ideas , intellectual property,  and credit of such that he as all of us have been a continuing victim of.

But what are your thoughts on the Harley's street max cranking compression....

[turboguzzi]

"TurboG..
Are you still thinking 200-205psig max cranking pressure for Air/cooled 91 octane...?
Or are have you went the way of the Harley crowd....?  "

mmm.. dont remember saying anyhting about cranking pressure, didi I? honestly not even a term im familiar with... dont know what Harley guys do either

my experience is that when i got detonation, it was always at the peak torque of the rpm range, thats in deed when cylinder filling (VE) is best and there's the most amount of mixture. In the 500/4 it would around 8-9K or so... i solved by pulling back from 13.5:1 to 13:1 with a new set of pistons.

I guess that in applications with milder cams than those of a 12,000 rpm engine, like a harley, you get the highest VE very early, so having too much presure already at cranking speeds is an issue.

the only "cranking pressure" issue i experienced, if you can call it like that, was with my supermono 700c.c. single racer. That could be started only with rollers!

[PeWe]

I use Shell V-Power +98 octane as we have in EU.
The pressure measured with a cheap compression tester running on starter and full throttle.

Good enough for compare cylinders and cams.

[PeWe]

I compared cams April 2018 same engine. A few days tests.
RC295 -195 PSI

DP315 - 175 PSI at 0.3mm valve lash as recommended.
Pressure significantly lower with less valve lash that increase duration and overlap.
http://forums.sohc4.net/index.php/topic,171759.msg2000796.html#msg2000796

This will give a feeling about the compression if going from DP315 to DP295 if the DP295 has exactly same data as my cam with RC295 engraved under the washer. The timing numbers felt right.

At least + 15% up from what you have now with DP315

[livefast_dieold]

I compared cams April 2018 same engine. A few days tests.
RC295 -195 PSI

DP315 - 175 PSI at 0.3mm valve lash as recommended.
Pressure significantly lower with less valve lash that increase duration and overlap.
http://forums.sohc4.net/index.php/topic,171759.msg2000796.html#msg2000796

This will give a feeling about the compression if going from DP315 to DP295 if the DP295 has exactly same data as my cam with RC295 engraved under the washer. The timing numbers felt right.

At least + 15% up from what you have now with DP315

Just re-read your post, I'm basically sold on the DP295 :-)

[PeWe]

I compared cams April 2018 same engine. A few days tests.
RC295 -195 PSI

DP315 - 175 PSI at 0.3mm valve lash as recommended.
Pressure significantly lower with less valve lash that increase duration and overlap.
http://forums.sohc4.net/index.php/topic,171759.msg2000796.html#msg2000796

This will give a feeling about the compression if going from DP315 to DP295 if the DP295 has exactly same data as my cam with RC295 engraved under the washer. The timing numbers felt right.

At least + 15% up from what you have now with DP315

Just re-read your post, I'm basically sold on the DP295 :-)

I'm sure you'll get much more torque from lower rpm's

My bike has an even power from low (around 3000rpm) to at least + 9000 rpm. Not much sudden power increase at around  6000 rpm as many other cams. The cam produce already the power

I have had thoughts about what the cam gives when test ride after jetting the carbs, needle area and main jet.

[turboguzzi]

ric, while lookign aroudn for airbox info, i think i found you something serious for free....

Lotus Engine Simulation (LES)

http://www.lesoft.co/

link here is for the free single cylinder sim

http://www.lesoft.co/files/freeware_software.exe

but they also sell full licenses to multiple cyl sim, "For users who require only occasional use of simulation tools, shorter term license options are also available."

[Tintop]

That's very interesting stuff TG.  Really intrigued by the suspension module, thanks for finding & posting the link.

[livefast_dieold]

ric, while lookign aroudn for airbox info, i think i found you something serious for free....

Lotus Engine Simulation (LES)

http://www.lesoft.co/

link here is for the free single cylinder sim

http://www.lesoft.co/files/freeware_software.exe

but they also sell full licenses to multiple cyl sim, "For users who require only occasional use of simulation tools, shorter term license options are also available."

Thanks Yossef!!! I'll take a bit to understand how it works :-)

[PeWe]

Which cam was finally used in this build?
It worked as intended or has Covid-19 blocked the testing?

[turboguzzi]

our federation has essentially dismissed the vintage 70's-80's 500-750-1000 classes, the numbers were really dwindling, COVID must had a role,
Bottom line is that Ricardo will be racing 600 Supersport this year, so will not continue developing the sohc 750, maybe he'll add some details...

Im on the same boat. my 72' 500 racer is now good only for regularity.... sad state of affairs but it is what it is... Vintage racing is moving on towards 90's superbikes and supersports...

[simon#42]

sad indeed