Discussion
Doing the camshaft timing on my car for the upteenth time I thought I would pose the following question.
Is it more important:
1) To have the car setup up exactly as the book but a syncronometer on the inlets shows a good one litre/min dissimilarity between cylinders, making some look good and some look bad.
2) To have the cam timing at least five degrees away from the book value but the syncronometer registers all cylinders about the same reading.
Is it more important:
1) To have the car setup up exactly as the book but a syncronometer on the inlets shows a good one litre/min dissimilarity between cylinders, making some look good and some look bad.
2) To have the cam timing at least five degrees away from the book value but the syncronometer registers all cylinders about the same reading.
You reasoning aside ..
I believe when an engine builder builds an engine - he will
set-up the head with a light valve springs (perhaps an inner spring only)
Put a small amount of putty on piston head and turn engine to find the degrees limits of max lift on inlet and ex.
You now know the outer limits for cam timing with your cam.
You then start at specified timing figure for the cam and work backwards from this point then forward - within the known limits..
A rolling road would be needed to actually see what gave the best results.
Sorry it's a long post.
I believe when an engine builder builds an engine - he will
set-up the head with a light valve springs (perhaps an inner spring only)
Put a small amount of putty on piston head and turn engine to find the degrees limits of max lift on inlet and ex.
You now know the outer limits for cam timing with your cam.
You then start at specified timing figure for the cam and work backwards from this point then forward - within the known limits..
A rolling road would be needed to actually see what gave the best results.
Sorry it's a long post.
rev-erend said:
You reasoning aside ..
I believe when an engine builder builds an engine - he will
set-up the head with a light valve springs (perhaps an inner spring only)
Put a small amount of putty on piston head and turn engine to find the degrees limits of max lift on inlet and ex.
You now know the outer limits for cam timing with your cam.
You then start at specified timing figure for the cam and work backwards from this point then forward - within the known limits..
A rolling road would be needed to actually see what gave the best results.
Sorry it's a long post.
I believe when an engine builder builds an engine - he will
set-up the head with a light valve springs (perhaps an inner spring only)
Put a small amount of putty on piston head and turn engine to find the degrees limits of max lift on inlet and ex.
You now know the outer limits for cam timing with your cam.
You then start at specified timing figure for the cam and work backwards from this point then forward - within the known limits..
A rolling road would be needed to actually see what gave the best results.
Sorry it's a long post.
Not long enough for me to understand how that relates to my question
. If I understand you, you are saying that the gold standard for the cam position would be a rolling road. But given an engines efficiency could be measured as its efficiency at being an air pump, surely a poor mans rolling road is a syncrometer and a simple addition of all the cylinders as an overall indicator of performance?
However, you don't want it to pump air well at idle.
You want it to pump well at the optimum engine speed to achieve peak torque/power or a nice spread between.
Also you need the intake system plumbed up as the volumetric efficiency of the manifolds (read purple pipe) and plenum's will effect this also. Hence you can't check it with a synchro.
You want it to pump well at the optimum engine speed to achieve peak torque/power or a nice spread between.
Also you need the intake system plumbed up as the volumetric efficiency of the manifolds (read purple pipe) and plenum's will effect this also. Hence you can't check it with a synchro.
ridds said:
However, you don't want it to pump air well at idle.
You want it to pump well at the optimum engine speed to achieve peak torque/power or a nice spread between.
Also you need the intake system plumbed up as the volumetric efficiency of the manifolds (read purple pipe) and plenum's will effect this also. Hence you can't check it with a synchro.
You want it to pump well at the optimum engine speed to achieve peak torque/power or a nice spread between.
Also you need the intake system plumbed up as the volumetric efficiency of the manifolds (read purple pipe) and plenum's will effect this also. Hence you can't check it with a synchro.
Surely that depends what you are comparing it with. For a given butterfly opening then the greater airflow the more power from the engine. Obviously you can't compare differing butterfly positions with each other.
but the original question still stands
Until you can simulate actual airflow through an engine, which will include exhaust gas scavenging, Im not sure how valid your test is ??
And ultimately, testing on a dyno is the only way to determine optimum cam timing....
What engine is it ? And are all inlet ports exactly the same ? All exhaust ports on each cylinder exactly the same ?
Inlet tract ? etc etc
And ultimately, testing on a dyno is the only way to determine optimum cam timing....
What engine is it ? And are all inlet ports exactly the same ? All exhaust ports on each cylinder exactly the same ?
Inlet tract ? etc etc
dident the cams come with dialing them in info,after all the cam manafacturer as dyno tested to develop them to get the benefits ,they must have played with different settings(advanceing & retarding the cam timing),i have never had problems with the cam manafactuers recommended settings give or take a couple of degrees,it generally puts the powerband within what they quoted,just maybe ive not read your post correctly,julian.
Cam timing will have been set dependant on how the manufacturer wanted the spread of torque.
It's harder to tweak with a SOC as you can't move the intake/exhaust timing independently.
You can set the cams to give you loads of top end with bugger all low down torque and even cause it to barely run at idle.
This is all before starting to play with valve lift and profile.
It's harder to tweak with a SOC as you can't move the intake/exhaust timing independently.
You can set the cams to give you loads of top end with bugger all low down torque and even cause it to barely run at idle.
This is all before starting to play with valve lift and profile.
ridds said:
Cam timing will have been set dependant on how the manufacturer wanted the spread of torque.
It's harder to tweak with a SOC as you can't move the intake/exhaust timing independently.
You can set the cams to give you loads of top end with bugger all low down torque and even cause it to barely run at idle.
This is all before starting to play with valve lift and profile.
It's harder to tweak with a SOC as you can't move the intake/exhaust timing independently.
You can set the cams to give you loads of top end with bugger all low down torque and even cause it to barely run at idle.
This is all before starting to play with valve lift and profile.
Well said.
Not playing with profile just cam timing. The reason this thread got started is that on my engine if you set the cam up perfect by the book, cylinders 5 and 6 run a low CFM compared to the rest. Leakdown testing on all eight is pretty much identical, so I breathed a big sign of relief.
However it is possible to set the cam timing to cause the cylinders all to be slightly less but completely even. But its not to the original spec.
I don't have a rolling road to test, but I do have a comment from jools in a thread sometime back where he said that he doesn't use the original spec of cam timing or some such, and he doesnt use the original spec of shim sizes. Obviously if he changes shim sizes he basically is changing cam timing or at least reprofiling without touching the cam when used in conjunction with cam timing.
I suspect manfacturing original specs have less relevence to the engine in a low volume, lets say individual manufactor like the AJP8. So I lean toward what my brain is telling me that even airflow is more important than original specs. But if I do that will my adaptives be forever at one end of the scale, or is the difference between what I can measure and what I want to do just simply telling me I can't measure TDC accurately?
However it is possible to set the cam timing to cause the cylinders all to be slightly less but completely even. But its not to the original spec.
I don't have a rolling road to test, but I do have a comment from jools in a thread sometime back where he said that he doesn't use the original spec of cam timing or some such, and he doesnt use the original spec of shim sizes. Obviously if he changes shim sizes he basically is changing cam timing or at least reprofiling without touching the cam when used in conjunction with cam timing.
I suspect manfacturing original specs have less relevence to the engine in a low volume, lets say individual manufactor like the AJP8. So I lean toward what my brain is telling me that even airflow is more important than original specs. But if I do that will my adaptives be forever at one end of the scale, or is the difference between what I can measure and what I want to do just simply telling me I can't measure TDC accurately?
Indeed. An inbalance of airflow really should be addressed with cam timing.
It could also be some strange effect of the length of the exhaust runners and gas flow at idle. It really could be anything odd.
Set the cam timing to nominal and adjust the airflow on the throttles.
Only tweak the timing of the cams when you know the limits of their operation and you have a dyno handy.
It could also be some strange effect of the length of the exhaust runners and gas flow at idle. It really could be anything odd.
Set the cam timing to nominal and adjust the airflow on the throttles.
Only tweak the timing of the cams when you know the limits of their operation and you have a dyno handy.
350matt said:
At idle the sealing of the individual butterflies will have the most effect on your synchrometer readings, in fact TVR built the cars with screws that have holes through them to balance up the low cylinders
Matt
Matt
Thats because at idle you have the most manifold vaccuum and therefore small changes to the butterfly positions will have most effect on syncro readings. But at rest using feeler gauges there is no discernable difference, so the difference will likely be comming from the pump not the restricting effect of the butterflies?
Furthermore, my car will actually stop running if I let the butterflies completely close. I like that on a car. I think a nice low idle shows a well sorted car. Fast idling cars usually show a car where someone has been to busy with the drill, or is hiding a bigger problem.
My readings weren't taken at idle but at 2000 rpm. Don't like going much above that with no load on the engine. But would be much happier if they were even at that rpm.
A bit wary I'm talking myself into this. I want my car to be right but don't like dynos. Currently running the car as spec but with uneven airflow. I think I'm gonna scratch my itch and see what happens. I don't like the car running with uneven airflow
I'm no expert on this by a long way, so feel free to say if I've got this completely wrong but if only 2 are out how can it be cam timing, if each cam does 4 pots each. Surley more than likely to be a shimming/valve clearance issue 
.
I would have thought that 2k rpm with no load is only just off the throttle stops anyway, I understand that the butterfly control/slack/play of the 4.5 tb's is worse (not as good) as on the 4.2 tb's so it could just as easily be the tb's.
As to going away from the OEMs cam timing, its something that does go on with all the independants but the exact figure is dependant on each installation and I'm not so sure they will give you a magic figure of say advance it 2 degs, it always gives 20hp more.
Back to basics for me, how far are they actually out, as if I read it right, it's about 1 ltr/min out, is that such a large difference to worry about, I don't know, but it doesn't seem a lot to me to an engine sucking in god knows how much per minute (can't be bothered to do the math 
)
. I would have thought that 2k rpm with no load is only just off the throttle stops anyway, I understand that the butterfly control/slack/play of the 4.5 tb's is worse (not as good) as on the 4.2 tb's so it could just as easily be the tb's
. As to going away from the OEMs cam timing, its something that does go on with all the independants but the exact figure is dependant on each installation and I'm not so sure they will give you a magic figure of say advance it 2 degs, it always gives 20hp more.
Back to basics for me, how far are they actually out, as if I read it right, it's about 1 ltr/min out
, is that such a large difference to worry about, I don't know, but it doesn't seem a lot to me to an engine sucking in god knows how much per minute (can't be bothered to do the math ) HarryW said:
I'm no expert on this by a long way, so feel free to say if I've got this completely wrong but if only 2 are out how can it be cam timing, if each cam does 4 pots each. Surley more than likely to be a shimming/valve clearance issue .
I would have thought that 2k rpm with no load is only just off the throttle stops anyway, I understand that the butterfly control/slack/play of the 4.5 tb's is worse (not as good) as on the 4.2 tb's so it could just as easily be the tb's.
As to going away from the OEMs cam timing, its something that does go on with all the independants but the exact figure is dependant on each installation and I'm not so sure they will give you a magic figure of say advance it 2 degs, it always gives 20hp more.
Back to basics for me, how far are they actually out, as if I read it right, it's about 1 ltr/min out, is that such a large difference to worry about, I don't know, but it doesn't seem a lot to me to an engine sucking in god knows how much per minute (can't be bothered to do the math )
. I would have thought that 2k rpm with no load is only just off the throttle stops anyway, I understand that the butterfly control/slack/play of the 4.5 tb's is worse (not as good) as on the 4.2 tb's so it could just as easily be the tb's
. As to going away from the OEMs cam timing, its something that does go on with all the independants but the exact figure is dependant on each installation and I'm not so sure they will give you a magic figure of say advance it 2 degs, it always gives 20hp more.
Back to basics for me, how far are they actually out, as if I read it right, it's about 1 ltr/min out
, is that such a large difference to worry about, I don't know, but it doesn't seem a lot to me to an engine sucking in god knows how much per minute (can't be bothered to do the math ) You might well be right. But I did manage to make the airflows even with adjustment of the camshaft. I hope this wasn't simply disadvantaging six cylinders for the benefit of two.
I also hope that I'm not simply increasing advance to solve my problem as I will run into the dangerous territory of engine knock on an engine with no knock sensors
. And I'm more than a bit worried that suggesting I run adaptives on one end of the scale despite every indie I've ever heard of tries to get the adaptives to run close to zero.
Still discussing it with you lot helps me make a decision.
Julian64 said:
Doing the camshaft timing on my car for the upteenth time I thought I would pose the following question.
Is it more important:
1) To have the car setup up exactly as the book but a syncronometer on the inlets shows a good one litre/min dissimilarity between cylinders, making some look good and some look bad.
2) To have the cam timing at least five degrees away from the book value but the syncronometer registers all cylinders about the same reading.
Is it more important:
1) To have the car setup up exactly as the book but a syncronometer on the inlets shows a good one litre/min dissimilarity between cylinders, making some look good and some look bad.
2) To have the cam timing at least five degrees away from the book value but the syncronometer registers all cylinders about the same reading.
Did you set cams with DTI and degree wheel? If so, did you rotate the engine after setting a cam and check what the degree says when the DTI shows equal lift? Pressure on the cam lobes can change tension in timing chain and 'settle' the cam in different position after setting. I find I have to set equal lift on odd cam @ 1.5deg advance, and even cam at @ 4.5 deg advance to get actual equal lift at TDC after engine rotated. This could account for the uneven suck your experiencing
. Some other reasons why you may get difefrent synchro readings:
a) Holding my TBs up to the light when they are closed I can see slightly different amounts of light around the edges of each butterfly as if the bore doesn't quite match the plate (surely not!)
b) slightly worn cams can show higher/faster lift on one bank compared to the other or even between lobes on same cam
c) The std exhaust manifold creates different pressures in each cylinder during valve overlap (because of very unequal pipe lengths, which also differ between banks)and this will translate into different depressions in the inlet tracts. It also has high back pressure at low rpm which will make the situation worse.
To your question: IMO the point at which valves open and close should be as per the engine/cam was designed. Given the inherent variability with the AJP8 very low speed running then it is more important that the engine is intake-balanced from 2,000 rpm onwards as that affects its on the road smoothness and power output. If you start off with standard cam timing and equal (measured) butterfly opening at least you will be closer to optimal than if you shift cam timing to get equal idle suction - tail wagging the dog - which will almost certainly rob the engine of power. You need a rolling road unfortunately to get this absolutely right.
Cheers
Julian64 said:
I also hope that I'm not simply increasing advance to solve my problem as I will run into the dangerous territory of engine knock on an engine with no knock sensors
. This confuses me. I've been following this with interest as I'm hoping to start servicing the car myself. I thought that advancing, retarding cam timing was a physical change to the valve events with respect to the crankshaft rotation. The danger here would be a piston smacking a valve. Engine knock is associated with ignition timing and i didn't think that was adjustable.
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