Cam timing change, vintage bike engine
Moderator: Team
Re: Cam timing change, vintage bike engine
Or a taller and perhaps skinnier tire?
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
Re: Cam timing change, vintage bike engine
A 29" tire will give you 133 at 6900 more or less. That available and fit?
Re: Cam timing change, vintage bike engine
jacksoni wrote:A 29" tire will give you 133 at 6900 more or less. That available and fit?
I have the tallest 18 inch tire on it now....Class rules allow any type of rear wheel larger 16 inches....I can adapt a wheel from an older Triumph with smaller sprocket sizes or even use a Japanese bike wheel... The tires need to be changed anyway.. The bike has H rated for 130 MPH...Need V rated tires because the record to beat is 132..MadBill wrote:Or a taller and perhaps skinnier tire?
I just changed the intake lobe center to 107.5 have to think if 105 might be better.........................might leave the exhaust at 107.5.....Changing timing is a pain in the ass with the tappets loaded by the valve springs...Can't just back off the rocker adjustment screws, need to remove the rocker boxes, can't do it with the engine in the frame because the bike is built from a pile of unmatched parts.....So I have to guess correctly on the cam timing...
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire
Re: Cam timing change, vintage bike engine
No worries ... I understand lots of things work backwards Down Under.Geoff2 wrote:4sfed,
You are correct, my apology..
Re: Cam timing change, vintage bike engine
Since I'm always looking for shortcuts, how about bolt-in upper frame members and/or or a tool to slightly over-compress the open springs while making the changes?
On an unrelated topic, have you considered trombone-like sliding pipes to optimize the exhaust lengths, possibly even in mid-pull if you use a brake dyno? It would be handy for verifying/re-optimizing same after a cam index change.
On an unrelated topic, have you considered trombone-like sliding pipes to optimize the exhaust lengths, possibly even in mid-pull if you use a brake dyno? It would be handy for verifying/re-optimizing same after a cam index change.
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
Re: Cam timing change, vintage bike engine
Like many projects, this bike has become more evolved than originally intended...Originally it was just a fun project and something to do with a pile of parts ...but the first time the bike was on the track it set a new class record right off the trailer....Then we got hooked..made improvements and set several class records at different tracks.We were hot shit while it lasted ..it took the competition several years to catch up....Now I'm making changes and the past "shortcuts" are biting me in the ass...And we pissed away a lot of money on the new double engine Triumph that has yet to prove itself...Actually my riders pay 90 percent of the cost and I provide all the bike and engine building ...
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire
Re: Cam timing change, vintage bike engine
Truckedup,
Can we learn your current exhaust head pipe exit diameter? (First diameter if stepped) I would like to also confirm you are using the stock exhaust valve diameter. I am getting close to adding some thoughts, but still need to run down some unknowns.
Regards,
Paul
Can we learn your current exhaust head pipe exit diameter? (First diameter if stepped) I would like to also confirm you are using the stock exhaust valve diameter. I am getting close to adding some thoughts, but still need to run down some unknowns.
Regards,
Paul
- Paul
Re: Cam timing change, vintage bike engine
More questions:
Are you required to run a muffler or pass sound testing?
How long is your current intake track (Valve seat to start end of bell radius) A reasonable approximation will do.
Is trimming your flywheel and tappet blocks to run a cam with more lift a direction you are willing to consider.
Are you required to run a muffler or pass sound testing?
How long is your current intake track (Valve seat to start end of bell radius) A reasonable approximation will do.
Is trimming your flywheel and tappet blocks to run a cam with more lift a direction you are willing to consider.
- Paul
Re: Cam timing change, vintage bike engine
. NO mufflers in LSR, stock exhaust valve diameter, intake valve to carb airhorn is 8 inches...I trim the flywheel in my lathe...I do the tappet blocks also if necessary..This engine has about .040 trimmed off the flywheel and uncut tappet blocks...My dual engine bike has pre unit 650 cases .407 lift , had to trim about .060 off the diameter of the flywheels, unit 650 barrels with uncut tappet blocks...pcnsd wrote:More questions:
Are you required to run a muffler or pass sound testing?
How long is your current intake track (Valve seat to start end of bell radius) A reasonable approximation will do.
Is trimming your flywheel and tappet blocks to run a cam with more lift a direction you are willing to consider.
I wasn't planning on splitting the cases for new cams, but..you have cams?
I have to get more cam timing gears to correct the timing...Despite having 3 keyways, it's never enough and no two gears are cut the same...
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire
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Re: Cam timing change, vintage bike engine
Mmm, an early Myford 7? - - hope you're not taking more than 0.020" cuts at slow feeds with that carbide tipped extended boring bar!
Re: Cam timing change, vintage bike engine
No thread chasing dial . . . that makes it more challenging!
Re: Cam timing change, vintage bike engine
1950 South Bend Model A.... That improvised set up cuts about .005 per cut on the slowest speed..Leftcoaster wrote:Mmm, an early Myford 7? - - hope you're not taking more than 0.020" cuts at slow feeds with that carbide tipped extended boring bar!
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire
Re: Cam timing change, vintage bike engine
Truckedup, I was able to make progress in reviewing your combo, but I am not able to pull a viable model (one that matches the known outputs) from either Engine Pro or Engine Designer. This is due to the way the programs process their models, the reference data sets they use and the somewhat odd by modern standards; bore, stroke and valve sizing of your motor and the resultant flow characteristics. Engine Pro literally refuses to accept the I-valve diameter and substitutes 1.583” as the max valve size. This does not mean that I was not able to gleam some value from modeling and review.
The good news; I think I can offer a few suggestions for improvement.
The bad news; There is not much left on the tree for harvest.
I was able to estimate your head flow characteristics based on you peak HP RPM and knowing your carb size. You need about 110cfm @ 28” to peak at 7100rpm. Your 34mm carb flows about 205 cfm@28”. That means your bare head has to flow at about 122cfm@28” and max valve lift. The lift/flow estimate below should be within a few cfm of actual across its range. Note the crappy CD’s required to flow this little with the comparatively large valve.
Using the flow estimate above, this is the valve threshold/lift velocity plot. Again, this is lazy flow by modern standards.
I used four data sources: Engine Pro, Engine designer, PipeMax and my personal spreadsheets.
Suggestions for possible improvements by subject:
Carb size: Engine Pro suggest there is still easy room to grow, the model doesn't top out until 400cfm for the carb. A 36mm round slide will flow about 240cfm@28" Doing this will raise your combined flow rate slightly from ~111cfm@ max lift to ~114cfm@max lift.
Intake: Your current intake track is ~8” long. Four sources suggest it needs to be ~12.5” to provide ramming effect at your target RPM. Anything you can do to lengthen the I-track will be of benefit.
Valve shrouding: There is no way your 59.2% of bore diameter valve is not shrouded… even in a hemi. It helps to explain the poor flow numbers. You may wish to look at opening slightly the chamber and cylinder wall on the long side entry. This is most likely your two inside positions at about 7 O-clock on the right cylinder and 5 O-clock on the left. Doing so should increase your valve CD and impart increased mixture motion during intake pumping. It would be best to optimize this on a flow bench before cutting metal. You could grind the acrylic to mimic the cylinder layout. This picture is of a similar concept applied to a BBC flow fixture. The same concept and sizing is then applied to the block.
Exhaust: Four of four sources suggest your 1.5” pipe diameter is too big. Three of four suggest a 1.25” diameter. One suggest a 1.375” diameter. I suggest you look at a stepped pipe that opens to 1.5” in either 1 or 2 steps. First step is 11-13” from valve.
You are using a 36” pipe length based on dyno results. I think that trumps what I have. All the sources suggest 30-33” lengths at their recommended diameters.
I looked for anyone using anything but separate pipes in the old flattrack miler photos and found none, not even a cross over pipe, although many are running twin megaphones. I think that means most likely a merged pipe will be a dead end. A 1D modeling package could resolve that answer for certain.
Camshaft: The only camshaft modeling I have is pulled from Engine Pro. It does not come up with the correct durations. I think it is because there is no airflow input so it can’t respond to lower than expected flow rates. That said, it does seem to pull out the LSA and suggested advance number. As you might expect it suggest a 105 LSA set on a 102 intake centerline. So in answer to the threads original camshaft question, I think intake on 102 and exhaust on 108 is about where you will find optimum and also about where you are now. Both could potentially be advanced a bit more due to your lower than expected SCR (10.5:1) vs. the expected 11:1 SCR. (101 and 109 respectively). Also note that the cam equations want the peaks a bit higher in the RPM range.
I have a camshaft suggestion that I think has potential for your application. It is based on the premise that as long as you can control the valve train and have more air to flow, there is no downside to more lift. I suggest you look at the Johnson J-460. It is a reworked version of the Sifton 460. It has slightly less duration and more lift than the Sifton and claims to be easier on the valve train.
I am not associated with Johnson Cams, but I do use one of their products. It has been a good choice for me and a comparative best to the other three camshafts I tried.
See link:
http://www.johnsoncams.com/jc_t_cams.html
The good news; I think I can offer a few suggestions for improvement.
The bad news; There is not much left on the tree for harvest.
I was able to estimate your head flow characteristics based on you peak HP RPM and knowing your carb size. You need about 110cfm @ 28” to peak at 7100rpm. Your 34mm carb flows about 205 cfm@28”. That means your bare head has to flow at about 122cfm@28” and max valve lift. The lift/flow estimate below should be within a few cfm of actual across its range. Note the crappy CD’s required to flow this little with the comparatively large valve.
Using the flow estimate above, this is the valve threshold/lift velocity plot. Again, this is lazy flow by modern standards.
I used four data sources: Engine Pro, Engine designer, PipeMax and my personal spreadsheets.
Suggestions for possible improvements by subject:
Carb size: Engine Pro suggest there is still easy room to grow, the model doesn't top out until 400cfm for the carb. A 36mm round slide will flow about 240cfm@28" Doing this will raise your combined flow rate slightly from ~111cfm@ max lift to ~114cfm@max lift.
Intake: Your current intake track is ~8” long. Four sources suggest it needs to be ~12.5” to provide ramming effect at your target RPM. Anything you can do to lengthen the I-track will be of benefit.
Valve shrouding: There is no way your 59.2% of bore diameter valve is not shrouded… even in a hemi. It helps to explain the poor flow numbers. You may wish to look at opening slightly the chamber and cylinder wall on the long side entry. This is most likely your two inside positions at about 7 O-clock on the right cylinder and 5 O-clock on the left. Doing so should increase your valve CD and impart increased mixture motion during intake pumping. It would be best to optimize this on a flow bench before cutting metal. You could grind the acrylic to mimic the cylinder layout. This picture is of a similar concept applied to a BBC flow fixture. The same concept and sizing is then applied to the block.
Exhaust: Four of four sources suggest your 1.5” pipe diameter is too big. Three of four suggest a 1.25” diameter. One suggest a 1.375” diameter. I suggest you look at a stepped pipe that opens to 1.5” in either 1 or 2 steps. First step is 11-13” from valve.
You are using a 36” pipe length based on dyno results. I think that trumps what I have. All the sources suggest 30-33” lengths at their recommended diameters.
I looked for anyone using anything but separate pipes in the old flattrack miler photos and found none, not even a cross over pipe, although many are running twin megaphones. I think that means most likely a merged pipe will be a dead end. A 1D modeling package could resolve that answer for certain.
Camshaft: The only camshaft modeling I have is pulled from Engine Pro. It does not come up with the correct durations. I think it is because there is no airflow input so it can’t respond to lower than expected flow rates. That said, it does seem to pull out the LSA and suggested advance number. As you might expect it suggest a 105 LSA set on a 102 intake centerline. So in answer to the threads original camshaft question, I think intake on 102 and exhaust on 108 is about where you will find optimum and also about where you are now. Both could potentially be advanced a bit more due to your lower than expected SCR (10.5:1) vs. the expected 11:1 SCR. (101 and 109 respectively). Also note that the cam equations want the peaks a bit higher in the RPM range.
I have a camshaft suggestion that I think has potential for your application. It is based on the premise that as long as you can control the valve train and have more air to flow, there is no downside to more lift. I suggest you look at the Johnson J-460. It is a reworked version of the Sifton 460. It has slightly less duration and more lift than the Sifton and claims to be easier on the valve train.
I am not associated with Johnson Cams, but I do use one of their products. It has been a good choice for me and a comparative best to the other three camshafts I tried.
See link:
http://www.johnsoncams.com/jc_t_cams.html
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- Paul
Re: Cam timing change, vintage bike engine
Wow, pcnsd has really dug into this! No calculations from me (unless I get around to scaling the airflow from a similar layout 438 cc/cylinder Alfa Romeo), but a few comments:
0 British bikes of the era all seemed to have very large pipes. My 1,000 cc Vincent twin's (~40 HP/cyl.) factory race pipes were 2" x ~ 53", whereas the calculated and widely used diameter for my 1020 cc/100 HP/cyl. BBC is also 2"...
o I have a Chevrolet Engineering HP/TQ graph from the sixties comparing several header systems on a ~ 575 HP BBC. The individual stack system at its best tune (~4800 RPM for a length including port of 48" x 2" dia.) has ~ 4% better torque at its peak than a standard collector system, but has a 'tune band' of ~ 500 RPM vs. >1500 for the latter. Ergo, with a straight pipe you can't afford to be too far off on the length.
o A number of sources I've consulted, e.g. the attached, concur with pcnsd's intake runner length numbers (valve seat to air bell) Re carb size however, I'd sound a note of caution. For an IR system with no plenum and very intermittent flow (active for less than 40% of the 720° cycle), CFM is not the relevant metric. (perhaps the 0.85 multiplier constant covers this off) Ideally, the minimum port cross section area is first selected, then the desired runner taper. Next the carb location along its length is chosen and finally a matching bore carb is selected (with perhaps a small correction for throttle shaft area, but not for any venturi). Any remaining required runner length is incorporated in the air bell and stack.
o I've got some useful airbox sizing data around, will try to unearth it.
0 British bikes of the era all seemed to have very large pipes. My 1,000 cc Vincent twin's (~40 HP/cyl.) factory race pipes were 2" x ~ 53", whereas the calculated and widely used diameter for my 1020 cc/100 HP/cyl. BBC is also 2"...
o I have a Chevrolet Engineering HP/TQ graph from the sixties comparing several header systems on a ~ 575 HP BBC. The individual stack system at its best tune (~4800 RPM for a length including port of 48" x 2" dia.) has ~ 4% better torque at its peak than a standard collector system, but has a 'tune band' of ~ 500 RPM vs. >1500 for the latter. Ergo, with a straight pipe you can't afford to be too far off on the length.
o A number of sources I've consulted, e.g. the attached, concur with pcnsd's intake runner length numbers (valve seat to air bell) Re carb size however, I'd sound a note of caution. For an IR system with no plenum and very intermittent flow (active for less than 40% of the 720° cycle), CFM is not the relevant metric. (perhaps the 0.85 multiplier constant covers this off) Ideally, the minimum port cross section area is first selected, then the desired runner taper. Next the carb location along its length is chosen and finally a matching bore carb is selected (with perhaps a small correction for throttle shaft area, but not for any venturi). Any remaining required runner length is incorporated in the air bell and stack.
o I've got some useful airbox sizing data around, will try to unearth it.
You do not have the required permissions to view the files attached to this post.
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.