Ideal Camshaft Lobe Centreline Angle

Ideal Camshaft Lobe Centreline Angle

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Discussion

Pumaracing

Original Poster:

2,089 posts

206 months

Friday 24th February 2012
quotequote all
So you're just deliberately trying to hijack the thread now out of pique eh?

Very mature.

carlt5

41 posts

176 months

Friday 24th February 2012
quotequote all
Rwdfords said:
I think it is important to clear some things up at this stage







The following applies to 2v single cam engines

The LSA cannot be changed, the LCA can be changed by advancing or retarding the cam, but he LSA will remain the same

LSA cannot be measured directly off the camshaft it has to be measured installed in an engine with lash, with a dial gauge on top of the spring retainer and a large degree wheel (10”+ ) bolted to the flywheel or front pulley

LCA is simply a description of cam timing position in relation to the crankshaft both for inlet and exhaust, this is usually quoted as the full lift point but much more accurately would be to measure the timing events @.010" and .050" lift and determine what the LCA is for both inlet and exhaust and the LSA at these lift points with lash



Some important question for DV:

With all the graphs you have made were you using different LSA's with each of the cams and the same profiles with the same intake LCA, ending up with the same inlet timing but with a change in LCA for the exhaust lobe?

Or were the cams with different LSA's timed in to give the best power curve with varying inlet closing points and the same static compression ratio?






Getting back to selecting an ideal Lobe Separation Angle to get the best power out of a particular engine


Some of the main factors I can think of that influence the ideal LSA to use for a given engine:

1. Engine application, how wide the power band needs to be and at what rpm’s you want best power/torque, (determined by Duration and LSA)

2. The maximum Static Compression Ratio being used to suit the fuel you are using (slightly wider LSA for increased compression)

3. Suitable inlet closing point to suit the SCR

4. Using enough lobe Duration to make the power curve shape you are after judging by the head flow graph

5. Using enough Overlap Area to make the peak power you are aiming for, too little will reduce cylinder filling by not properly getting rid of all the exhaust gasses in the chambers and filling them with fresh charge/using the exhaust overlap to get the inlet charge to move rapidly with the piston still parked at TDC (then piston motion taking over from there)

Too much overlap will reduce idle and low rpm quality, the engine will also come on cam more abruptly due to flow reversals at low rpm

6. Valve size, this has a direct effect on low lift flow which increases the overlap flow with a given camshaft as compared to the same engine with smaller valves

7. Cylinder capacity vs port flow, DV suggests increased cylinder cc needs a tighter LSA and less cc or greater valve size needs a wider LSA

8. Engines with shared ports for each cylinder will need to use a tighter LSA


As said LSA’s around 104 to 111* appear to work best for most engines 2v & 4v with 107* being a good starting point

I would suggest that very tight LSA’s produce an engine that has poor low rpm response, comes into the power band abruptly, great midrange to upper rpm power, wider LSA’s give better low rpm response, reduced midrange, sometimes higher peak power, power tends to drop off slower after peak hp


If someone does not agree with any of the above please say so, state why you think otherwise and offer your own theories in detail, try and keep the comments respectful, there is no need to tear someone else’s theories apart. No one has ALL the answers

Then we can all make our own minds up as to what LSA “could” work best for a given engine

Regards
Jason
I have just been through this again

Pumaracing , if could give me a civilised answer [ It may appear to be a whittering post , but it does have a valid question-possibly]

You have pointed out to me that it is almost impossible to ascertain the exact point of opening of the inlet valve - I totally agree , which is why I gave my measured points an estimated 3deg error

Now the Guru of late 50's/early 60's tuning of the Small Ford Sidevalve [Bill Cooper] timed All his cams using inlet valve opening point
His book - http://www.ford-aquaplane.co.uk/products/tsvf-tuni... , is the equivalent for the Small Ford Sidevalve as David Vizards yellow bible for the BMC 'A' series , [though Bill Coopers' is more of a pamphlet compared to Vizard's tome]

There is a chapter in his book on camshaft design and selection , he explains in detail how to set up and time a performance cam
he uses the lift figures given for the cam to set each valve to give the correct full lift figure [he says to ignore the actual tappet/follower clearance , as long as it is not less than the manufacturers figure]

He states that the cam should be timed to specified inlet valve lift point [ very innacurate you have pointed out ]

Nowhere in the whole book is Camshaft Lobe Centreline Angle considered [ am I correct that using LCA is the current method of timing in a cam ?]

As I am trying to apply modern camshaft design to this antiquated engine , is my questioning what the 'Ideal Camshaft Lobe Centreline Angle' is for this engine completely unrelated to your thread

Is the fact that LCA appears not to have been considered for this engine [ Bill Coopers' book printed 1968 deals with engine development up to 1962 ] completely unrelated to your thread

I believe that the apparent strange 121deg cam timing [ relative to modern thinking ] is possibly due to the fact that LCA was not considered

I will be happy to remove all my posts to another thread given a civilised explanation

Edited by carlt5 on Friday 24th February 12:32

Pumaracing

Original Poster:

2,089 posts

206 months

Friday 24th February 2012
quotequote all
Stan Weiss said:
Dave,
You do know where DV lives?
Yeah but A) NC still isn't really far enough south for proper redneck humour and B) DV isn't a yank so it's a bit hard to aim it at him. Believe me I would if I could smile

DVandrews

1,315 posts

282 months

Saturday 25th February 2012
quotequote all
carlt5 said:
Nowhere in the whole book is Camshaft Lobe Centreline Angle considered [ am I correct that using LCA is the current method of timing in a cam ?]
That certainly isn't the method that I use, it is fraught with possible error, from establishing where the particular LCA is WRT to crank degrees to establishing where the full lift point is (especially with cams that dwell at full lift).

I use the 'lift at TDC' method and have done for a long long time, it is very accurate, repeatable and you only need to establish one crank position (that of TDC) in order to correctly time the cam/cams. Most cam cutters will provide the lift at TDC information with the cam specs. I certainly would not use any other method. Finding a number of different crank positions accurately, especially when the engine is in the vehicle is a task fraught with possible error, just the amount of parallax from a given viewpoint can easily skew results.

Dave

Edited by DVandrews on Saturday 25th February 09:46

carlt5

41 posts

176 months

Saturday 25th February 2012
quotequote all
DVandrews said:
That certainly isn't the method that I use, it is fraught with possible error, from establishing where the particular LCA is WRT to crank degrees to establishing where the full lift point is (especially with cams that dwell at full lift).

I use the 'lift at TDC' method and have done for a long long time, it is very accurate, repeatable and you only need to establish one crank position (that of TDC) in order to correctly time the cam/cams. Most cam cutters will provide the lift at TDC information with the cam specs. I certainly would not use any other method. Finding a number of different crank positions accurately, especially when the engine is in the vehicle is a task fraught with possible error, just the amount of parallax from a given viewpoint can easily skew results.

Dave

Edited by DVandrews on Saturday 25th February 09:46
thanks
until now I have been confined to off the shelf cams ,
the rarefied atmosphere of actually getting one ground for a specific engine spec is fraught with numptyness smile


I remember using this method with our KAD motor back in the early 90's , assumed it was specific to twin cams .
only been pottering about with single cam old schite since I got back into motorsport







Edited by carlt5 on Saturday 25th February 12:39

racerbob

270 posts

179 months

Saturday 25th February 2012
quotequote all
DVandrews said:
That certainly isn't the method that I use, it is fraught with possible error, from establishing where the particular LCA is WRT to crank degrees to establishing where the full lift point is (especially with cams that dwell at full lift).

I use the 'lift at TDC' method and have done for a long long time, it is very accurate, repeatable and you only need to establish one crank position (that of TDC) in order to correctly time the cam/cams. Most cam cutters will provide the lift at TDC information with the cam specs. I certainly would not use any other method. Finding a number of different crank positions accurately, especially when the engine is in the vehicle is a task fraught with possible error, just the amount of parallax from a given viewpoint can easily skew results.

Dave

Edited by DVandrews on Saturday 25th February 09:46
Agree, this is by far the most accurate and repeatable method of timing cams, assuming that you have accuratly established TDC. Everything (timing) is happening very quickly at this point.

SWR Performance

69 posts

146 months

Saturday 25th February 2012
quotequote all
racerbob said:
DVandrews said:
That certainly isn't the method that I use, it is fraught with possible error, from establishing where the particular LCA is WRT to crank degrees to establishing where the full lift point is (especially with cams that dwell at full lift).

I use the 'lift at TDC' method and have done for a long long time, it is very accurate, repeatable and you only need to establish one crank position (that of TDC) in order to correctly time the cam/cams. Most cam cutters will provide the lift at TDC information with the cam specs. I certainly would not use any other method. Finding a number of different crank positions accurately, especially when the engine is in the vehicle is a task fraught with possible error, just the amount of parallax from a given viewpoint can easily skew results.

Dave

Edited by DVandrews on Saturday 25th February 09:46
Agree, this is by far the most accurate and repeatable method of timing cams, assuming that you have accuratly established TDC. Everything (timing) is happening very quickly at this point.
The only case this is not giving you correct results is if you deal with hydraulic buckets... a small amount of oil drainage can skew the results considerably. And using cams with considerable dwell is no issue if timing at the full lift figure. All one does is to measure at 0.2mm lift on the up-ramp and same after passing full lift and divide the values by 2 to come more than reasonably close. smile

DVandrews

1,315 posts

282 months

Saturday 25th February 2012
quotequote all
SWR Performance said:
The only case this is not giving you correct results is if you deal with hydraulic buckets... a small amount of oil drainage can skew the results considerably. And using cams with considerable dwell is no issue if timing at the full lift figure. All one does is to measure at 0.2mm lift on the up-ramp and same after passing full lift and divide the values by 2 to come more than reasonably close. smile
Err.. that is incorrect, whether the buckets are full or empty has no bearing on the measurement you take, since it is normally measured from the face of the follower that is in direct contact with the cam lobe. If you were measuring at the valve then I would agree with you that any follower compression due to air could be a factor, however not only is measuring off the valve improbable in an assembled engine it is near impossible to do.

Reasonably close is not really good enough.. dwell at peak lift is only one issue, there is also the issue of finding with accuracy and repaatability a fixed timing point on the cranks rotation.. say 106 degrees. Even observing this on an assembled engine, especially on one installed in a vehicle can be pretty tricky to do.

Lift at TDC can be measured down to an accuracy of 1 thou, even on road cams this is around 1/4 of a degree, on more aggressive cams it is within 1/10 of a degree of accuracy. Getting that close using lobe centre is near impossible.

Dave

carlt5

41 posts

176 months

Saturday 25th February 2012
quotequote all
DVandrews said:
however not only is measuring off the valve improbable in an assembled engine it is near impossible to do.




Dave
Except on a small ford sidevalve [on an assembled engine , impossible to measure TDC , easy to measure the valves - the sparkplug is above the valve faces]
tongue out

Stan Weiss

260 posts

147 months

Saturday 25th February 2012
quotequote all
SWR Performance said:
racerbob said:
DVandrews said:
That certainly isn't the method that I use, it is fraught with possible error, from establishing where the particular LCA is WRT to crank degrees to establishing where the full lift point is (especially with cams that dwell at full lift).

I use the 'lift at TDC' method and have done for a long long time, it is very accurate, repeatable and you only need to establish one crank position (that of TDC) in order to correctly time the cam/cams. Most cam cutters will provide the lift at TDC information with the cam specs. I certainly would not use any other method. Finding a number of different crank positions accurately, especially when the engine is in the vehicle is a task fraught with possible error, just the amount of parallax from a given viewpoint can easily skew results.

Dave

Edited by DVandrews on Saturday 25th February 09:46
Agree, this is by far the most accurate and repeatable method of timing cams, assuming that you have accuratly established TDC. Everything (timing) is happening very quickly at this point.
The only case this is not giving you correct results is if you deal with hydraulic buckets... a small amount of oil drainage can skew the results considerably. And using cams with considerable dwell is no issue if timing at the full lift figure. All one does is to measure at 0.2mm lift on the up-ramp and same after passing full lift and divide the values by 2 to come more than reasonably close. smile
This is the reason I have a solid lifter (SBC / BBC smile ) seating in my tool box right near my dial indicator.

Stan

SWR Performance

69 posts

146 months

Saturday 25th February 2012
quotequote all
DVandrews said:
Err.. that is incorrect, whether the buckets are full or empty has no bearing on the measurement you take, since it is normally measured from the face of the follower that is in direct contact with the cam lobe. If you were measuring at the valve then I would agree with you that any follower compression due to air could be a factor, however not only is measuring off the valve improbable in an assembled engine it is near impossible to do.
True, I was thinking of rocker arm end pivot setups with an hydraulic lifter/pivot where you measure on the retainer and for some reason I wrote bucket. whistle

DVandrews said:
Reasonably close is not really good enough.. dwell at peak lift is only one issue, there is also the issue of finding with accuracy and repaatability a fixed timing point on the cranks rotation.. say 106 degrees. Even observing this on an assembled engine, especially on one installed in a vehicle can be pretty tricky to do.

Lift at TDC can be measured down to an accuracy of 1 thou, even on road cams this is around 1/4 of a degree, on more aggressive cams it is within 1/10 of a degree of accuracy. Getting that close using lobe centre is near impossible.

Dave
True, but when do you know that 2.336 mm at TDC is exactly the optimum for one engine using exactly that cam? More often than not I have tried timing by checking seat to seat values for opening and closing numbers, lift at TDC and lobe center. Unless the cam is uncannily close to what it is supposed to be that usually tends to leave me with 3 slightly different "optimum timings". So I go by reasonably close until the dyno says it's opinion about what optimum timing really is. smile

DVandrews

1,315 posts

282 months

Saturday 25th February 2012
quotequote all
Yarp, It's one thing to very accurately set the cam timing, it's quite another to know exactly what that timing *should* be smile.

Since I build a number of engines to some well established standards I can be pretty sure that the dyno derived figures for each conversion will be near enough to optimum for it not to matter.

Once these figures are known then it's a cinch to set the cams up, the other big advantage with lift at TDC is the speed at which the timing can be set and the relatively little access to the engine that is reqd.

The VX 'j' series uses finger followers and hydraulic posts, that might be a problem if the engine has been standing idle for a while..

Dave

racerbob

270 posts

179 months

Saturday 25th February 2012
quotequote all
When dealing with engines using hydraulic pedestals / rocker arms, we used to do a 'leak down' test on all the pedestals before assembly, any dodgy ones where always replaced. For timing up purposes with new oil, setting cams at TDC was never a problem, I'm thinking twin cam units, so 2 DTI's to watch. If pedestals are working correctly they do not normally 'leak' very quickly, in my experience of course, can't say I've dealt with every variant.

Stan Weiss

260 posts

147 months

Saturday 25th February 2012
quotequote all
DVandrews said:
Err.. that is incorrect, whether the buckets are full or empty has no bearing on the measurement you take, since it is normally measured from the face of the follower that is in direct contact with the cam lobe. If you were measuring at the valve then I would agree with you that any follower compression due to air could be a factor, however not only is measuring off the valve improbable in an assembled engine it is near impossible to do.

Reasonably close is not really good enough.. dwell at peak lift is only one issue, there is also the issue of finding with accuracy and repaatability a fixed timing point on the cranks rotation.. say 106 degrees. Even observing this on an assembled engine, especially on one installed in a vehicle can be pretty tricky to do.

Lift at TDC can be measured down to an accuracy of 1 thou, even on road cams this is around 1/4 of a degree, on more aggressive cams it is within 1/10 of a degree of accuracy. Getting that close using lobe centre is near impossible.

Dave
Maybe it is on which side of the pond one is on. That seems much more accurate than I have measured from cylinder to cylinder on the same core. This was with off the shelve cams.

Stan

carlt5

41 posts

176 months

Saturday 25th February 2012
quotequote all
"Pumaracing"

"At the end of the day you can posit any arguments you like but when Bill Jenkins went through all this on the dyno and race track in the 70s with the Chevy engine he found empirically that long rods wanted narrow LSAs and vice versa. I believe my argument explains this from simple first principles."

Interesting , that having found different LSA's were required for different rod lengths Bill Jenkins then :

"The famous Chevy tuner Bill Jenkins used to use 109 degrees in every engine he built, big, small, track or drag race. He stuck to it like it was some sort of magic number and I think I was too much influenced by this many years ago."

even though

"Jenkins was trying to get the most power out of every engine in every situation."

scratchchin

carlt5

41 posts

176 months

Saturday 25th February 2012
quotequote all
Pumaracing said:
Right, let's get into this in detail now. Margaret Thatcher once said that to get a message across you have to say it three times. First tell the people what you are about to tell them, then tell them, then tell them what you just told them.


1) 2V versus 4V engines...................

That alone increases potential power up to about 21% on an average engine with the same valve area as a 2v one. However the 4v engine has further benefits to offer. With its better swirl,]
From reading various of David Vizards articles , didn't he conclude that 2valve heads had far more swirl than 4valve , hence giving a far better intake mix for better combustion ?
This was why he came up with the polyquad head

DVandrews

1,315 posts

282 months

Sunday 26th February 2012
quotequote all
The swirl on 4 valves is not particularly good, but tumble is.

It is not unknown on some engines to phase the inlet valve openings slightly diferently on the cylinder to promote swirl, or use differently sized inlet valves.

Dave

carlt5

41 posts

176 months

Sunday 26th February 2012
quotequote all
DVandrews said:
The swirl on 4 valves is not particularly good, but tumble is.



Dave
My point exactly , Pumaracing stated 4 valves had better swirl than 2 valves therefore better combustion , Vizard maintains the opposite to be true .
Are we going to get another 'pistols at dawn' thread on swirl and tumble in 4 and 2 valve heads ? biggrin

carlt5

41 posts

176 months

Sunday 26th February 2012
quotequote all
While we wait for David Vizard to get back with the results of his Cam master program on Pumaracings Peugeot figures

The results of the 100e 1172cc Ford Sidevalve testing so far would back Pumaracings assertion that the graph shown on his first post does not work for small capacity engines .

The std cam has an LSA of 112deg , we have tried 109deg LSA and 106deg LSA

106 LSA is far superior for power throughout the rev range , it gives a wider power band and increases the upper power band by at least 1000 rpm [ I'm sure it would happily go further and explode itself smile]

This engine started out with max overbore , well worked ports , larger inlet valves , high compression .

the only change [other than the cams] has been a better exhaust manifold to utilise the potential of the last cam in the mid range - [ I believe the increased overlap caused intake reversion and large intake stand off , which was not present with the std cam and barely noticeable with the second]

Lift figures were different on the cams so this will have obviously influenced things
I dont know anything about the specifics of each of the cams' lobe profiles

Whether this is at all useful I have no idea

forgot to add the figures

CID/inch = 14.579 [ very much near the bottom of the graph]
Rod/Stroke ratio = 1.68

Edited by carlt5 on Monday 27th February 20:35

Rwdfords

34 posts

146 months

Monday 27th February 2012
quotequote all
carlt5 said:
I have just been through this again

Pumaracing , if could give me a civilised answer [ It may appear to be a whittering post , but it does have a valid question-possibly]

You have pointed out to me that it is almost impossible to ascertain the exact point of opening of the inlet valve - I totally agree , which is why I gave my measured points an estimated 3deg error

Now the Guru of late 50's/early 60's tuning of the Small Ford Sidevalve [Bill Cooper] timed All his cams using inlet valve opening point
His book - http://www.ford-aquaplane.co.uk/products/tsvf-tuni... , is the equivalent for the Small Ford Sidevalve as David Vizards yellow bible for the BMC 'A' series , [though Bill Coopers' is more of a pamphlet compared to Vizard's tome]

There is a chapter in his book on camshaft design and selection , he explains in detail how to set up and time a performance cam
he uses the lift figures given for the cam to set each valve to give the correct full lift figure [he says to ignore the actual tappet/follower clearance , as long as it is not less than the manufacturers figure]

He states that the cam should be timed to specified inlet valve lift point [ very innacurate you have pointed out ]

Nowhere in the whole book is Camshaft Lobe Centreline Angle considered [ am I correct that using LCA is the current method of timing in a cam ?]

As I am trying to apply modern camshaft design to this antiquated engine , is my questioning what the 'Ideal Camshaft Lobe Centreline Angle' is for this engine completely unrelated to your thread

Is the fact that LCA appears not to have been considered for this engine [ Bill Coopers' book printed 1968 deals with engine development up to 1962 ] completely unrelated to your thread

I believe that the apparent strange 121deg cam timing [ relative to modern thinking ] is possibly due to the fact that LCA was not considered

I will be happy to remove all my posts to another thread given a civilised explanation

Edited by carlt5 on Friday 24th February 12:32
Hello Carlt5

You quoted one of my posts above but did not comment on it, is there a specific question you have?

About measuring cam timing events the only way to accurately measure timing events is to set he cam up with exactly the same lash setting you will use in the engine, then place a dial gauge right on top of the retainer lined up perfectly with the valve angle, set up a 12" to 18" degree wheel bolted onto the flywheel or crank front pulley, with the timing belt or chain fully tensioned, everything as it would be in the engine, set the pulley to exactly tdc with a dial on top of no 1 piston, then fit the head

Measure the timing events at .001" lift, .010" lift, .050" lift and steps of .050" all the way up, and also .010" each side of full lift, write down all of the timing points on a cam chart, at the exact lift figure (not even a quarter though either side), turn the crank in one direction only, do not turn it both ways as you will have error in the measurements due to play in the timing belt pulleys or timing gears

Pay close attention to the .010" and .050" timing points for inlet and exhaust and use these timing points to properly time the cam given the .010" before intake closing point and the static compression ratio, you can work out he dynamic compression ratio, aim for 9 to 1 DCR for best power

Quoted cam figures are mostly BS, pay attention to the full lift figures, lift at tdc and the power band, if you measure a cam very accurately in an engine as above (with the proper lash setting you will be using in the engine) you will quickly find out quoted seat duration figures are often totally different to what the cam companies quote especially with finger follower valvetrains

Once you have mapped a number of profiles you can easily compare them, knowing the true real world duration figures, LSA, valve lift, lift at TDC etc

You can then map different profiles on an excel spreadsheet and see what is really going on, comparing valve acceleration, if you swap valve lift for the true head flow figures you can then view valve open area and overlap through flow area

I absolutely hate the way cam companies quote bogus seat figures at random lift points, you cannot trust these figures, even the quoted .050" figures are often measured without lash, what is the point of measuring a cam without lash? useless information, it needs to be measured in an engine with the exact same lash you will be using in the engine

Regards
Jason