Adjust turbo pressure by variances in wastegate rod length..

[HJ2]

Dear colleagues,

I just found this piece of text over here:
http://www.lotustalk.com/forums/f3/lets ... ndex3.html:

"I had to replace an engine in one of mine. I bought the car from a girl that just ran it out of oil. She and here boyfriend bought it, and they broke up. I bought it for a song. Should have been carrying a gun and wearing a mask. I STOLE it. Anyways, at the time I knew one of the Lotus guys that was on the M100 project. He told me that the engines were literally taken out of the crate from Isuzu and put in the cars. ONly difference was the location of the turbocharger and I think the alternator. I replaced that engine with one from an Impulse that I bought used with 37K miles on it, from a dismantler. It was the EXACT same engine. We used to get more HP out of them by decreasing the wastegate rod in length. I put a turnbuckle on mine so that I could regulate the boost. Lotus told us how to do that...well I should say that one fo the guys from Lotus was at LOG and he told us how to do it. "

To me, as a novice, it looks like it realises the same effect as a MCB, but without the dangers involved in adding a more or less 'controlled' leak in the plumbing. Of course adjustment has to be made whilst taking care not to exceed injector spec's as we don't want the injectors to deliver more fuel than they can deliver..

What are your thoughts about this?
Is the original author a member of the forum?
It sounds interesting enough to do some research...

[Specky]

This sounds familiar, the other month a wastegate diaphragm assembly came up on eBay, it was said to have been removed off a protype M100 many years ago. This provided more power.... Blah... Blah...

When I glanced at the photo on th eBay add it appeared to be standard, l would say the differential area of the internal diaphragm and distance of travel is the secret, at the moment I can't see how a different lenght rod would work. The two points of attachment are ridged. (even if one can actuate under vacum pressure). So on that Theory only a nominal length will fit, you could however change the rod (shorter or longer), but spacers or reworking the diaphragm mount would be a must.

If I was to change a bit of the sytem, it would be the wastegate diaphragm to actuate at a higher differential pressure.

Just thought you could shorten the rod and have a constant stream of hot gasses through the wate gate, get it wrong and you've got a self induced siezd wastegate and a loss of power under hard acceleration.

[racerstev]

I've been thinking along ths route..

http://cgi.ebay.com/ebaymotors/T3-T3-T4 ... 0505248069

You would need a aftermarket boost controller to take advantage of it though. It's main advantage is to keep the
wastegate closed at higher boost levels, seems they can open from the backpressure in the manifold.


Steve Lockett

[HJ2]

I've been thinking along ths route..

http://cgi.ebay.com/ebaymotors/T3-T3-T4 ... 0505248069

You would need a aftermarket boost controller to take advantage of it though. It's main advantage is to keep the
wastegate closed at higher boost levels, seems they can open from the backpressure in the manifold.


Steve Lockett

That looks OK.

I'm SURE I've seen an adjustable waste gate rod here on the forum somewhere, but never realised what it does, nor have I read any success stories.
Does this porker thingey has the same operating length as the Elan (or isuzu for that matter) / is it interchangeable?

[Enright]

I bought a 2nd hand turbo off eBay ages ago to keep as a spare, just in case.
It had a threaded and joined portion in the actuator rod which you can see in the Wiki's Wastegate Wiggling guide.
(Edit in response to Specky's post below: I had always assumed that it was a bodge, but in hindsight perhaps it's just another of Lotus's own "variations" )
I ported the wastegate on the turbo but as yet have never had the need to use it. However if I did, with the far more elegant method of boost control that Alan's chips offer, I would just set it to standard and let the software do it's job.

[Specky]

Mine has the adjusting rod as standard, but I thought that was just for rigging it to it's nominal length....

Here's a picture, excuse the head torch in there, I needed the light...

zebra.jpg

TTFN

[rip]

Doesn't the ECU simply open the wastegate 'a bit more' until the boost is at target..or it is fully open?
I can't see how the size of the actuator rod would affect this.

[HJ2]

like in closed loop?

[Enright]

Doesn't the ECU simply open the wastegate 'a bit more' until the boost is at target..or it is fully open?

As I understand it, that's pretty close. the Boost Solenoid swiches many times per second and controls the air feed to the actuating diaphragm. Air pressure as a control by it's very nature has a 'lag' or smoothing capability built into it, so that fast on/off switching is translated into a percentage of time/range open or closed. I believe that the limits are defined by the duty cycle from (I guess) 0 to 100 percent.
Oh and you're right, it's monitored by the MAP sensor (sensing air pressure) and fuel/spark advance et all are set from this.

I can't see how the size of the actuator rod would affect this.

I believe that if you bear in mind the above example then the wastegate should be 50 percent open at 50 percent duty cycle if set correctly.
So if the rod is shortened it will reduce the percentage opening against the same percentage of duty cycle.
The system will have to maintain a higher duty cycle to produce the same result, which doesn't necessarily present a problem (apart from wear of components) until you hit 100 percent duty cycle.
At this point the wastegate may only be open, say, 3/4 but as the ECU can do no more, turbo boost pressure would rise uncontrollably. It's like having a partially siezed wastegate.
If set wrongly you'd hit boost cutoff.
I don't like the sounds of an out of balance system. Our chips are as cheap as, well, chips really (!), and work WITH the components and safety features rather than against or around them.
Standard performance enhancement route for me thank you!

[HJ2]

I came across this:

http://www.youtube.com/watch?v=p12g1PpI ... r_embedded

So adjusting the rod does not change anything in boost settings at all, as i was corrected earlier above, but it does another thing: With adjusting you can get a little pre-load so at all operating temperatures you know that 'close' is realy close, no matter what! This keeps it from leaking boost when the ECU thinks its closed since the wastegate can be controlled one-way only (thru the solenoid controlled pressure line) and the other way it's the diaphragm that pulls it back.

In short: Use it to correct zero position and reduce hysteresis
I don't have the adjustment on the rod, but when assembling the wastegate bracket there is a little negative play so a little pre-tension is applied to the dome anyway.

If not adjusted correctly you can loose valuable boost pressure or keeps the turbo from spinning up fast where you don't want it, so correct setting is worth the trouble. With a 'fixed' rod length there is nothing to worry or change.