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Does anyone happen to know how exactly the boost gauge reads. I've noticed a little turbo lag and would like to know when the engine has positive pressure (boost), compared to vacuum (before the turbo spools up). Im not near my car presently, but the gauge only has a 1-0 as the max I think it was, then before it a series of lines. Anytime the gauge moves is that reading boost? Usually I see it around the middle of the gauge to slightly past it once the turbo comes up. What is the middle of the gauge in measurement of boost (Bar, PSI?)
 

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....as soon as the butterfly opens, you are producing boost. Between 1950 rpm to 5,150 rpm the turbo is working effectively.

Turbos do not need to arrive at a particular RPM to provide boost. Even at idle, the turbo is providing boost -- there is still a gas flowing at the turbine.
Turbo lag? yep, the bad one.
1. Since turbo relied in exhaust gases, you need the engine to pump more gas to spin the turbo faster.
2. How do you quickly spin up the turbo? This is a very complex issue. This is based on the turbo design. The size of the turbine & compressor - the length/size of the piping - the size of the intercooler & so on. A small turbo that has a light turbine blade and a small inlet will spin faster but will run out of breath at higher rpm. On the other hand, a larger turbo with a large volume of inlet will spin up slower but it will provide more boost at higher rpm. One will quickly spool and the other is a late spool.

The analogy is: try blowing at the sandwich bag -- as oppose to blowing in a grocery bag. How many times you will inhale/exhale before filling the bag with air? (inhale/exhale is the same as engine rpm's)

Big is not always better in turbo configuration. Response is the key.
 

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"....as soon as the butterfly opens, you are producing boost. Between 1950 rpm to 5,150 rpm the turbo is working effectively."

Don't forget about the vacuum actuated bypass valve that relieves ALL boost pressure until being overcome, that's when the turbos boost finally arrives.
 

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Does anyone happen to know how exactly the boost gauge reads. I've noticed a little turbo lag and would like to know when the engine has positive pressure (boost), compared to vacuum (before the turbo spools up). Im not near my car presently, but the gauge only has a 1-0 as the max I think it was, then before it a series of lines. Anytime the gauge moves is that reading boost? Usually I see it around the middle of the gauge to slightly past it once the turbo comes up. What is the middle of the gauge in measurement of boost (Bar, PSI?)
The middle of the 88 Esprit boost gauge is 0.5 bar (7.24 PSI) and maxes out at 1.0 bar (14.48 PSI).

The boost gauge is 0-1 bar (14.x PSI). The 88 Esprit is limited to 0.65 bar (9.5 PSI). Terminology-wise 'positive pressure is anything greater than 0 - vacuum is 30 to 0 inches of mercury.

A combination vacuum/boost gauge will go from 30 to 0 to 15 -from vacuum (30-0) to boost (>0 to 15 or beyond).

If your boost gauge goes beyond 0.65 bar (the tick mark to the right of middle), your stock engine is at risk of damage. There are several subsystems on the 88 Esprit that limit RPM or fuel in that scenario (assuming your waste gate is malfunctioning).

When I'm driving to work, my 88 Esprit starts producing boost around 2300 RPM and tops out at 0.5 bar - something is sticking on my car as it should do 0.65 bar - sometimes it does 0.50 or 0.6 and sometime 0.65 bar.
My guess is the waste gate is tired - will probably have it looked it at next service.
 

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When I'm driving to work, my 88 Esprit starts producing boost around 2300 RPM and tops out at 0.5 bar - something is sticking on my car as it should do 0.65 bar - sometimes it does 0.50 or 0.6 and sometime 0.65 bar.
My guess is the waste gate is tired - will probably have it looked it at next service.


I lot of heat there, yeah the spring could be tired, try turning the wastegate rod 1 full turn & lock it.. it should go back to 0.65
 

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Discussion Starter #10
Its sounds as though my turbo is working correctly as I suspected. Is the vacuum actuated bypass valve located on the side of the airbox or am I mistaken, this is a Bosch CIS car.
 

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Its sounds as though my turbo is working correctly as I suspected. Is the vacuum actuated bypass valve located on the side of the airbox or am I mistaken, this is a Bosch CIS car.
The airbox valve is the Fuel Cutoff mechanism. It bypasses the metering unit on throttle over-run, to minimize burning fuel shooting out the exhaust when you let off the throttle. -eek-


The turbo control/wastegate is the hard pipe that comes off the turbo, down to the waste gate on the left side of the engine (onto the tail end of the exhaust manifold). Too much boost pressure, and the wastegate diaphragm will open a poppet type valve in the manifold extension, so that exhaust gasses bypass the Turbo and reduce boost.

I have pictures of the wastegate off the manifold....



+++++++++++++

Eddie, I got a kick out of your very specific boost gauge criteria. The boost gauge ain't THAT accurate! rotfl Although the wastegate control IS a calibrated piece.

Maybe Jamie can say if the calibration holds OK on a twenty-year-old piece?
 

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[snip]

I have pictures of the wastegate off the manifold....

----

Eddie, I got a kick out of your very specific boost gauge criteria. The boost gauge ain't THAT accurate! rotfl [snip]
I live to amuse those around me rotfl

The boost info I got somewhere (I believe the driver's handbook or service notes). None of the gauges in the Esprit appear to be accurate - the needles love to bounce around, but hey, it's all I got to work with :panic:

Here's a picture of my waste gate - can someone tell us:
If an 88 Esprit is suppose to produce up to 9.5 lbs of boost, why is the waste gate tag saying '7.0 lbs'?

 

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Discussion Starter #13
Okay, gotcha I know what the wastegate is, and I had it apart recently to check the diaphragm and actuator rod, its in surprisingly good shape for the position it is at on the exhaust header. I heard from another member that will probably chime in that the 9 PSI on boost is only on the non US cars, as mine is the same 7 PSI.
 

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1987 and 1988 Lotus Notes, in the engine specs section, says "Maximum boost: 9.5psi"
So far, no one in US reported 9.5 psi wastegate; all are 7 psi.
Do not know why.
My suspicion is that Lotus decided to play safe on US market, perhaps due to sh*#y gas here. In Europe it is hard to get gas lower than 94.
 

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1987 and 1988 Lotus Notes, in the engine specs section, says "Maximum boost: 9.5psi"
So far, no one in US reported 9.5 psi wastegate; all are 7 psi.
Do not know why.
My suspicion is that Lotus decided to play safe on US market, perhaps due to sh*#y gas here. In Europe it is hard to get gas lower than 94.
Then Lotus must have tweaked the boost gauge too?

This is on my 88 Esprit - USA spec - this claims to be 0.6 bar (about 9 PSI)

 

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Wingless Wonder
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The Lotus gauges are not necessarily accurate, but they ARE consistent.
:rolleyes:




My car sees about 6.5 bar on the gauge before the wastegate opens, just a couple needle-widths past Sleek's.


Perhaps the answer is, that when the WG opens, ALL the exhaust doesn't bypass the turbo. Just a portion...so a WG that starts to open at 7 PSI still allows the turbo to produce 9.5 PSI of boost?


Comments from the Experts? :UK:

PS: Eddie, did you put your own red-line on the tach? :no: Maximum engine speed is supposed to be 7000 RPM on Bosch cars (7200 on GM MPFI), not 6000...:coolnana:
 

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Perhaps the answer is, that when the WG opens, ALL the exhaust doesn't bypass the turbo. Just a portion...so a WG that starts to open at 7 PSI still allows the turbo to produce 9.5 PSI of boost?


Yes, there still gas going to the turbo. The function of the wastegate when open is to slow down the ROTATION of the turbine blade. It will spike a little bit but not a drastic a 9.5 psi. Your wastegate perhaps setup a little higher than 7psi.
The spring gets the beating from the heat, it's difficult to get an accurate tention. If the wastegate is old, chances are the spring & diapram are tired.
 

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Discussion Starter #18
That photo by sleek is exactly where my boost gauge will usually top out. I too was wondering about the redline marking on it, as mine has none at all.
 

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If the wastegate is old, chances are the spring & diaphragm are tired.
My wastegate is currently out of the car. Is it a valid test to apply 7 PSI to the turbo line to see if the valve opens (starts to move) at that pressure?

Can I (should I) apply washers inside the diaphragm housing to "calibrate" it?

:confused:
 

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My wastegate is currently out of the car. Is it a valid test to apply 7 PSI to the turbo line to see if the valve opens (starts to move) at that pressure?

Can I (should I) apply washers inside the diaphragm housing to "calibrate" it?

:confused:
Buy this: Mityvac MV8255 PVC Vacuum Pump, 16cc w/ Gauge, DC
Put the internal wastegate back to the turbo. Plug the turbo wastegate hose to Mityvac. Pump---> while watching the gauge & the rod moves.
You can shim the external wastegate spring but 99.9% of of the internal wastegate is fixed and you can't open the canister unless you break it.
However, some internal wastegate has a adjustable rod, turn that 1 full turn...good as shimming the spring. Not too much though.

http://img11.imageshack.us/img11/6967/wastegate2.jpg (internal wastegate)
Clockwise more tension -- counter clockwise less tension.
if 1 turn did not change the reading -- replace or buy a new wastegate.
 
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