Inlet Cam timing??
Discussion
Hey
Here is a comment from a friend of mine concerning the timing on my '83 turbo.
"The stock ignition timing is real retarded for emissions. It's common to
recurve the distributor for a faster mechanical advance (same amount, but
all in by 2500 rpm) and set the static advance to 12° BTDC."
Hope it helps,
louis
Here is a comment from a friend of mine concerning the timing on my '83 turbo.
"The stock ignition timing is real retarded for emissions. It's common to
recurve the distributor for a faster mechanical advance (same amount, but
all in by 2500 rpm) and set the static advance to 12° BTDC."
Hope it helps,
louis
Hi,
Two separate animals. Mark, you are asking about mechanical or valve timing and the reply referred to ignition timing.
Both are correct. The valve timing on the US 910 enignes was retarded for emissions purposes. Switching to a 104 pulley will restore the timing to where Lotus intended.
Also, the ignition timing is also retarded. The 910 engine loves lots of advance up to 30° total advance. Total advance includes the static timing added to the amount of advance from the districutor (centrifugal and vacuum).
Recurving the distributor does not add any adavnce, only where in the RPM range the advance comes in. Centrifugal advance is altered by altering the calibrated springs and weights which live in the distributor.
To see how much advance is in your car as well as when it comes in, hook up a timing light and start the car. Check to see what the static timing is by strobing the light against the flywheel when at idle and read the scale. Then, increase rthe RPM's steadily, the advance will climb, note at what RPM these increases take place. At about 3k RPM, the timing will not advanceany further, read the value on the flywheel, this is your total advance.
If you are at less than 30°, add the difference to the static timing value so that the total advance increases. This is something that you can play around with and is not the same on all engines. My car likes 28° best, 12°static timing and 16° of advance. I know one guy who's car runs best at 32° total, but I think that is too high and certainly is for my engine. Too much advance, and the power begins to trail off. Hope this helps. Happy Motoring!...Jim'85TE
Two separate animals. Mark, you are asking about mechanical or valve timing and the reply referred to ignition timing.
Both are correct. The valve timing on the US 910 enignes was retarded for emissions purposes. Switching to a 104 pulley will restore the timing to where Lotus intended.
Also, the ignition timing is also retarded. The 910 engine loves lots of advance up to 30° total advance. Total advance includes the static timing added to the amount of advance from the districutor (centrifugal and vacuum).
Recurving the distributor does not add any adavnce, only where in the RPM range the advance comes in. Centrifugal advance is altered by altering the calibrated springs and weights which live in the distributor.
To see how much advance is in your car as well as when it comes in, hook up a timing light and start the car. Check to see what the static timing is by strobing the light against the flywheel when at idle and read the scale. Then, increase rthe RPM's steadily, the advance will climb, note at what RPM these increases take place. At about 3k RPM, the timing will not advanceany further, read the value on the flywheel, this is your total advance.
If you are at less than 30°, add the difference to the static timing value so that the total advance increases. This is something that you can play around with and is not the same on all engines. My car likes 28° best, 12°static timing and 16° of advance. I know one guy who's car runs best at 32° total, but I think that is too high and certainly is for my engine. Too much advance, and the power begins to trail off. Hope this helps. Happy Motoring!...Jim'85TE
lotusguy said:
Hi,
Two separate animals. Mark, you are asking about mechanical or valve timing and the reply referred to ignition timing.
Both are correct. The valve timing on the US 910 enignes was retarded for emissions purposes. Switching to a 104 pulley will restore the timing to where Lotus intended.
Also, the ignition timing is also retarded. The 910 engine loves lots of advance up to 30° total advance. Total advance includes the static timing added to the amount of advance from the districutor (centrifugal and vacuum).
Recurving the distributor does not add any adavnce, only where in the RPM range the advance comes in. Centrifugal advance is altered by altering the calibrated springs and weights which live in the distributor.
To see how much advance is in your car as well as when it comes in, hook up a timing light and start the car. Check to see what the static timing is by strobing the light against the flywheel when at idle and read the scale. Then, increase rthe RPM's steadily, the advance will climb, note at what RPM these increases take place. At about 3k RPM, the timing will not advanceany further, read the value on the flywheel, this is your total advance.
If you are at less than 30°, add the difference to the static timing value so that the total advance increases. This is something that you can play around with and is not the same on all engines. My car likes 28° best, 12°static timing and 16° of advance. I know one guy who's car runs best at 32° total, but I think that is too high and certainly is for my engine. Too much advance, and the power begins to trail off. Hope this helps. Happy Motoring!...Jim'85TE
Hi Jim,
Thanks for the ignition timing info, it is usefull right now as I just fitted a TEC3 system and am going through the setup. On the Cam timing; do I have to replace the cam wheel or can it just be moved on the cam belt to another tooth?
Thanks,
Mark (88 Turbo)
Mark,
You went with the TecIII system from Electromotive..?? Very Cool!... I lust for their systems!
How are you triggering it? From a crank or cam trigger wheel?
I would start off by having 16° total advance and have it all in by 2300 RPM, then set the static timing at 12° for a total of 28° and see how you like that. With that system, making a change later is pretty simple. But be aware, that shortly past 30° total advance, there will be a noticeable drop-off in power.
As far as cam timing, you cannot simply move the belt by a tooth as each tooth represents 18°. What you need to do is fit either adjustable cam pulleys or swap the stock 110 MOP pulley(Red Dot) in the intake cam for the 104 MOP pulley(Green Dot) on the Aux. shaft (MOP= Maximum Opening Point). All pulleys are identical, same circumference, same number of teeth. Where they differ is the keyway cut into their centers. These vary only slightly, some fraction of the width of a single tooth. By making this swap on the intake cam, you will advance the cam 6° back to it's original design setting. There is a noticeable difference in low-end torque, but the benefit is really a product of your expectations. It will not be like you dropped a Viper V-10 in the engine bay, but a slight, noticeable improvement.
With your engine, I doubt there's any benefit to playing with the exhaust cam timing at all. Besides, you'd need to buy another pulley ($100+) and any benefit derived won't measure up to the cost involved. Happy Motoring!...Jim'85TE
>> Edited by lotusguy on Friday 21st November 23:26
You went with the TecIII system from Electromotive..?? Very Cool!... I lust for their systems!
How are you triggering it? From a crank or cam trigger wheel?
I would start off by having 16° total advance and have it all in by 2300 RPM, then set the static timing at 12° for a total of 28° and see how you like that. With that system, making a change later is pretty simple. But be aware, that shortly past 30° total advance, there will be a noticeable drop-off in power.
As far as cam timing, you cannot simply move the belt by a tooth as each tooth represents 18°. What you need to do is fit either adjustable cam pulleys or swap the stock 110 MOP pulley(Red Dot) in the intake cam for the 104 MOP pulley(Green Dot) on the Aux. shaft (MOP= Maximum Opening Point). All pulleys are identical, same circumference, same number of teeth. Where they differ is the keyway cut into their centers. These vary only slightly, some fraction of the width of a single tooth. By making this swap on the intake cam, you will advance the cam 6° back to it's original design setting. There is a noticeable difference in low-end torque, but the benefit is really a product of your expectations. It will not be like you dropped a Viper V-10 in the engine bay, but a slight, noticeable improvement.
With your engine, I doubt there's any benefit to playing with the exhaust cam timing at all. Besides, you'd need to buy another pulley ($100+) and any benefit derived won't measure up to the cost involved. Happy Motoring!...Jim'85TE
>> Edited by lotusguy on Friday 21st November 23:26
lotusguy said:
Mark,
You went with the TecIII system from Electromotive..?? Very Cool!... I lust for their systems!
How are you triggering it? From a crank or cam trigger wheel?
>> Edited by lotusguy on Friday 21st November 23:26
Hey Jim,
I'm triggering the TEC3 from both the crank AND the cam (Full sequential setup). It as been a HUGE job bacause as you know my 88 Turbo came stock with the Bosch Jetronic FI system wich is mechanical so I have had to change the whole injection system (very good learning experience, but challenging). I got really lucky and managed to find a complete TEC3 system on eBay for $1100 (sensors and the lot), but then upgrading the injection system cost about another $500 by the time I got done with it. You cold actually do your carb turbo for about the same price if you really wanted to.
Thanks for the info. on the cam. I think I'll leave it be for now as I also had the head ported and polished while I had the engine out so I think I should see a good improvement from that also. I dyno'd in at 302hp before I started the project so if I get much more I'll be looking for a new gearbox I fear.
When I am done I will post a web site with photo's etc.
Cheers,
Mark
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