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Discussion Starter · #1 · (Edited)
As above with perhaps pics.
Thanks
So I've been reading about the pulley. What is the science behind this???
 

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There are lots of threads on green dots. I just had mine done last year. It makes the car to spec of how the engine was designed. My impression is that it ran slightly better off-boost, no discernible change on-boost.


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I only drove the car once before switching to the green-dots so my experience is limited. Seems like the idle is lumpier and it pops and burbles more on downshifts (which I like). It definitely pulls more smoothly and progressively down low until the boost comes on but I made several other changes that may have helped with that as well.
BTW...I only drove the car once before refitting the pulleys and cam belt because I checked the tension after the initial drive using the frequency method...it was ZERO hertz, too loose to get any reading at all. The only thing my phone could pick up was a slight 114Hz buzz from the fluorescent lights in my garage.

I got my pulley from Steve at SJ Sports Cars...read the posts and you'll see you already have the other one. Get the blue belt and tensioner bearing from JAE...my bearing was well on its way to failure too.
 

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As above with perhaps pics.
Thanks
So I've been reading about the pulley. What is the science behind this???
The science behind it is simply changing the cam timing. In a fixed camshaft system, IE, no type of variable valve timing, the camshaft profile, valve opening, piston location, etc etc etc, can only be tuned for maximum intake air charge velocity at one RPM range. My understanding(note, my understanding is often hazed, and wrong), the cam for the Esprit was tuned to provide the best fuel/air charge at the lower RPM levels, as the Turbo would supplement air/fuel at upper RPM's. However, for emissions reasons, the cam timing was advanced, slowing velocity, to produce a leaner mixture at idle and off idle prior to boost. The green dot pulley retards the cam timing slightly, improving low RPM performance, per my understanding, and again, my understanding, when Lotus related, is often wrong. With V-Twin pushrod, aircooled twins, I generally have a better understand...

So basically, when you bolt on the green dot pulley, and align the dots, the intake cam shaft will be moved a couple degrees retarded, I seem to remember that I read 3 degrees somewhere once, but I'm probably wrong.

As I understand it, the green dot pulley can also be used on the exhaust camshaft, though the gains aren't as good?????? Really hazy on this one BTW
 

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How will this affect smog?
 

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Wingless Wonder
1988 Esprit Turbo
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How will this affect smog?
My '88 has 104 MOP cam wheels (green dot) on both intake & exhaust, and the emissions tester guys say it passes the sniffer test handily. :up:
 

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My '87 Hci has them and they are great. Chunkier idle, better low end throttle response, and a tad more upper end too, IMO.

Plus, it sounds so cool to say your car has green dot cams..... doesnt it? :coolnana:
 

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My '88 has 104 MOP cam wheels (green dot) on both intake & exhaust, and the emissions tester guys say it passes the sniffer test handily. :up:
Great thanks!
 

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My '88 with green dot cam pulleys passed the stringent bi-annual California sniffer test on rollers a couple years ago without a problem. If it passes here, it probably won't be a problem anywhere else. :)

Roy
 

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My '88 with green dot cam pulleys passed the stringent bi-annual California sniffer test on rollers a couple years ago without a problem. If it passes here, it probably won't be a problem anywhere else. :)

Roy
Good to know, now where can I get a pair and what is the cost on them?

Thanks,
 

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Wingless Wonder
1988 Esprit Turbo
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Good to know, now where can I get a pair and what is the cost on them?
You already have one, on the auxilary cam wheel (chargecooler pump or distributor pulley, depending on year)

So, you only need to buy one more.

The Usual Lotus Parts Sources often carry them (I think JAE produced their own). About $100 - $150 last time I looked.
 

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You already have one, on the auxilary cam wheel (chargecooler pump or distributor pulley, depending on year)

So, you only need to buy one more.

The Usual Lotus Parts Sources often carry them (I think JAE produced their own). About $100 - $150 last time I looked.
Thanks!
 

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So I've been reading about the pulley. What is the science behind this???
"By Design" - the 104 & 107 cams are designed for 104 MOP timing. That's were they run the best.

All Non-Federal / Non-Emissions Carb Turbo 910s
Intake 104 (green) / Exhaust 104 (green)
nominally correct / nominally correct

The cams were re-timed for emissions purposes, first in the USA, later everywhere. The 910, in good condition, will pass the emissions test in most areas in the original, design-correct 104 (green dot) MOP condition. However, Lotus was on the hook for warranty costs (including emissions) for the long term, and wanted a wider margin of safety. Therefore, the engine was designed cleaner that required so that age, wear and lack of maintenance wouldn't push it into a failure condition during the warranty period. The changes included retarding first just the intake cam, and later both cams.

1983-85 USA Emissions Carb 910, and...
All 920 2.0 Turbo
Intake 110 (red) / Exhaust 104 (green)
......... 6° retard / nominally correct

1986-88 USA Emissions Bosch 910, and all...
1989-96 SE, S4, S4s GMP4 910.
Intake 110 (red) / Exhaust 100 (blue)(really 97)
......... 6° retard / ............. 7° retard

The 100 MOP blue dot pulley is really 97 MOP, they just rounded it up when naming it. All other pulley MOP's are accurate as marked.

The following doesn't apply to the Turbo engines, but while I'm at it...

Federal 907 Emissions (C-Cam wants 110 MOP)
Intake 100 (blue, 97) / Exhaust 110 (red)
.......... 13° advance / nominally correct
....... (110 - 97 = 13)

On the 907, advancing the intake increased the overlap by 13°, increasing the amount of co-mingling between the intake and exhaust gases. The net effect is a lot like Exhaust Gas Recirculation, and reduced the oxides of nitrogen.

*~*~*

The effect of an MOP change is opposite on the two cams.

Intake cam: LARGER MOP retards, and SMALLER MOP advances.
Exhaust cam: SMALLER MOP retards, and LARGER MOP retards.

Advancing the intake and/or retarding the exhaust increases the overlap.
Retarding the intake and/or advancing the exhaust reduces the overlap.

*~*~*

Converting back to 104 MOP (green dot) pulleys simply puts the cam timing back to were it was originally designed to be. The result doesn't unleash a horsepower monster, but there is some power improvement, and a noticeably increased sense of urgency about the engine. Better throttle response.

Boost covers a multiple of sins, and more boost makes more power ("Boost... it does an engine good"). So once the boost comes in, the difference between green dot and emissions timing becomes less noticeable, as the difference is lost in the greater boost power surge. But the engine will feel more responsive and powerful off-idle and during low boost conditions, like driving in traffic.

You'll also detect a little more cammy idle, and a gruffer voice off-boost... not bad things when you're idling through the drive-in, trying to impress the push-rod V8 boys.

If you want more power for your buck, up the boost (and chip the GMP4 cars). If you just want the engine to run better, and feel more responsive, especially in traffic, the pulley swap is easy, and doesn't put significantly more stress on the engine & drivetrain (like more boost would).

*~*~*

All Turbo 910/ 920 engines came from the factory with a 104 MOP (green dot) pulley on the Auxiliary shaft (distributor/ oil pump). So, as a freebie (over-looking a little extra labor while you're replacing the timing belt), you can swap the Aux and Intake pulleys, putting the green dot on the Intake.

The intake cam has more impact on the engine's personality and power output than the exhaust cam has. Off boost, atmospheric pressure is all there is to push air/fuel into the engine, and any intake improvement will be felt.

After combustion, pressure in the cylinder is so high that the gas "WILL" flow out when the exhaust valve opens (it's called "Critical Flow", and no minor obstruction is stopping it !).

Yes, changing the exhaust cam timing also makes a difference on the dyno, and if you want the maximum power/ best running engine, then buy another green dot pulley and re-time the exhaust cam as well. But the improvement due to the exhaust cam timing change will be smaller, less noticeable than produced by the intake cam timing change.

If you're on a budget and just want to capitalize on a relative freebie, then simply put the green dot auxiliary pulley on the intake cam. If you're just going to change one, then the intake is the one. Not as good as both, but the price is right.

There is a front and a back to the pulleys, and you have to make certain you install them the correct way around. Don't screw that up!

Regards,
Tim Engel
 

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It may sound like a simple thing to do but then there are the "While you are there" things to do. Among them include:
Replacing the water pump
Sealing the cam towers
Replacing the timing belt
Adjusting the valves
If you have a lot of mileage, rebuilding the turbo
A tune-up replacing filters and spark plugs

Point is you won't notice any difference if the rest of the motor is not in good shape. Like most projects on a Lotus it is never "just" anything.
David Teitelbaum
 

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Discussion Starter · #16 ·
Understanding much more.
Thanks Guys.
Mike
 

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I got my pulley from Steve at SJ Sports Cars...
Is that the pulley SJ claims can be installed either side forward? There's one timing dot per side, and no IN or EX marks? If so, the claim isn't technically correct. The error is small, but... how anal retentive are you.

"IF" the pulley's MOP was 103.5 (there is no 103.5 Lotus application), then the MOP would be 103.5 with either side facing forward (flip the pulley, rotate 4-teeth). The pulley would be universal, but it would also have half a degree of MOP error built in.

If the pulley is really 104 MOP when installed properly, then installing it "backwards" will result in 103 MOP. Convenient, not disastrous, but not accurate or optimal, either.

There is no accurate "install it either way, it doesn't matter" pulley, but there is marketing.

*~*~*

On the other hand, few 9XX engines end up with the cam pulley timing dots accurately aligned anyway. There are a number of parts in the stack-up, and they all have tolerances. Squabbling over half a degree doesn't make a lot of sense when the stock engine probably has more built in error than that anyway. If you're a perfectionist, buy a set of adjustable pulleys and learn the complexities of setting them up.

Regards,
Tim Engel
 

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It may sound like a simple thing to do but then there are the "While you are there" things to do. Among them include:
Replacing the water pump
Sealing the cam towers
Replacing the timing belt
Adjusting the valves
If you have a lot of mileage, rebuilding the turbo
A tune-up replacing filters and spark plugs

Point is you won't notice any difference if the rest of the motor is not in good shape. Like most projects on a Lotus it is never "just" anything.
David Teitelbaum
If you make installing/ swapping the green dot pulleys the prime motivator, then the little "while you're in there" tasks might take over. And, of course, it's never easy to evaluate a performance upgrade on an engine that is in an otherwise bad state of tune. Goes without saying.

But my approach has always been to do the pulley swap as one of those sidebar "while you're in there" tasks that's tacked onto a more important primary job... like replacing the timing belt and shimming the valves. And, oh, while I'm in there, why not rebuild the water pump, replace the front main seal, and swap the cam pulleys. In which case, the difference is more noticeable on an engine that's otherwise running well.

Glass half full, glass half empty. ;-)

Regards,
Tim Engel
 

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If you make installing/ swapping the green dot pulleys the prime motivator, then the little "while you're in there" tasks might take over. And, of course, it's never easy to evaluate a performance upgrade on an engine that is in an otherwise bad state of tune. Goes without saying.

But my approach has always been to do the pulley swap as one of those sidebar "while you're in there" tasks that's tacked onto a more important primary job... like replacing the timing belt and shimming the valves. And, oh, while I'm in there, why not rebuild the water pump, replace the front main seal, and swap the cam pulleys. In which case, the difference is more noticeable on an engine that's otherwise running well.

Glass half full, glass half empty. ;-)

Regards,
Tim Engel
My points exactly. And now you are pulling the motor because of all of the things you are doing and it is the PERFECT time to do the gas tanks! Look at how I can spend other people's money! Time to open the transaxle for inspection and replace the circlip and maybe the syncros.
Getting serious again, if you are doing the pulleys I would also do a compression test. If you have good history on the motor you know if it is time to do all the rest and how much oil it consumes. That and the mileage you are getting can give you a good picture of the general health of the motor and how much you should do. The timing belt is a no-brainer if you are anywhere near the end of it's life. All the rest is a judgement call. That and how big a hit your budget can take. Just keep in mind anything you do in addition can lead you on to do other things. Don't go down the path of just doing the pulleys if you don't know that the general condition of the motor is good. If you "just" do the pulleys and find you have to do other things you will quickly see you should have planned for them and pulled the motor.
David Teitelbaum
 

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The "as sold" configuration is:

1986-88 USA Emissions Bosch 910, and all...
1989-96 SE, S4, S4s GMP4 910.
Intake 110 (red) / Exhaust 100 (blue)(really 97)/ Jack-shaft 104 (green)


WHAT IF we swap pulleys in the following order:

Intake 104 (green) / Exhaust 110 (red) / Jack-shaft 100 (97) blue
?
Such set-up would reduce the overlap from 44* to 38*, increase SLA from 104* to 107*, and advance the Int. cam by 3*.
And, according to Garry, 110 MOP at the exh. reduces tendency to detonation.

I rechecked my old e-mail. Garry Kemp's N/A rally motor ran 105/111 MOP and made 285hp!

His reasoning on the 107 degree lobe separation was comparing it to
various other turbo motors of similar vintage - the Ford RS 200 (108),
Porsche 911 turbo (108), and Lancia Delta S4 (109) which were all potent
road cars with successful race histories.

So without knowing whether that timing would be optimum, it's in the ball
park for road going turbo motors of the day.

Your thoughts?
 
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