Should I install a boost gauge?

[WannaWagon]

I've had two other turbo cars (both gassers) and installed aftermarket boost gauges in both. I have found these gauges to be a valuable tuning tool, especially a gauge that has a wide vacuum reading. But I'm now getting to know my first diesel car and wonder if I should do the same. Is such a gauge really needed in a diesel? Who here has installed a boost-vac guage in their diesel, and have you found it to be useful?

[Brian Carlton]

I have a single boost gauge that I install on both of them when I need to troubleshoot something. However, it is just temporary and the gauge is removed after the testing is completed.
I don't think you need the gauge all the time unless you have "dialed up" the boost beyond factory specs.

Originally posted by WannaWagon
Who here has installed a boost-vac guage in their diesel, and have you found it to be useful?

I find it a MUST to have a boost gauge when tuning a Turbo Diesel. The vacuum part of the gauge is wasted space on a diesel, the is no measurable amount (By a cheapo auto store style standards) of vacuum present to make use of it. I believe sunpro makes a plain 0-15PSI gauge. This would be all you need since our engines cant stand more than 13psi without an intercooler.

My boost gauge.

Yes it has a vacuum side. It was only $15 at autozoo and had the correct fitting to place directly into the intake plug near the overboost sensor.

[The Warden]

A boost gauge is a good idea, but IMHO the "necessary" gauge to add is a pyrometer. Even on a stock engine, it's a good idea to monitor your exhaust gas temperature IMHO.

The only reason I don't have one on my 123 is $$

[Brian Carlton]

I agree with Tim. A gauge for exhaust temperature is far more valuable than a boost gauge. I do believe it's possible to do some damage at 13 psi boost, 90 degree ambient, if the power is on for more than 90-120 seconds. A pyrometer would warn you of this where a boost gauge will not.

Originally posted by The Warden
The only reason I don't have one on my 123 is $$

Check with performance truck/diesel shops (ATS, etc.). In tulsa I had one shop quote me $180+tax for the gauge, sensor, wiring, manifold drill/tap (Including removal/install of the manifolds+turbo), and installation.

As with The Warden, $$$ at the time was the only reason I did not get it.

[WannaWagon]

Originally posted by Brian Carlton
I agree with Tim. A gauge for exhaust temperature is far more valuable than a boost gauge. I do believe it's possible to do some damage at 13 psi boost, 90 degree ambient, if the power is on for more than 90-120 seconds. A pyrometer would warn you of this where a boost gauge will not.

If this is true, wouldn't a boost gauge be a cheap way to avoid this problem if you can't afford an exhaust temp gauge? At least with a boost gauge, you would know when you're maxing out the turbo for a long period.

82-300td: Are you saying there's really no vacuum to read on our engines? Is that why there's no point in getting a gauge that also reads vac? Or are you saying most bargain gauges won't show vacuum accurately? (Sorry, but I'm still learning my way around the diesel world). By the way, I like your gauge install in the dash vent, but I'm not willing to give up one of my vents for that purpose -- it's too hot where I am!

[Brian Carlton]

Originally posted by WannaWagon
If this is true, wouldn't a boost gauge be a cheap way to avoid this problem if you can't afford an exhaust temp gauge? At least with a boost gauge, you would know when you're maxing out the turbo for a long period.

Here is a cheaper way than a boost gauge:

When the engine is above 2500 rpm and your right foot is 2/3 of the way down, or more, you are in full boost. Now, full boost, of itself, is not the problem. The problem occurs when full boost is used for an extended period of time in warm/hot ambient temperatures. How long is "an extended period of time"? How hot is "warm/hot ambient temperatures". I have not a clue.

But, the exhaust temperature gauge will know. That's the defining parameter for engine damage.

[jbaj007]

I have a permanent boost gauge and a EGT gauge.

My boost gauge is just a modified "economy" gauge from a 126 gasoline engined car (It should be somewhere in the archives). Now that I have it, and have dialed in my Dawes style boost controller, I really don't think it's that necessary as a permanent gauge. But, it's fun to look at. A temporary gauge, "Tee'd" into the boost line to the ALDA would work just as well for setting boost during initial set up of boost pressure, either through use of a controller or adjusting that difficult waste gate spring.

EGT gauges and probes are available from suppliers for the ultralight aircraft hobbyists. Much cheaper than I could find anywhere else. I use a Westach, but there is no reason this wouldn't work with a K-type probe:http://www.recreationalmobility.com/cgi-bin/recreation/35185.html

Probe should be as close as practical to exhaust port (there is a formula to use). I like mine pre-turbo.

At .9 bar boost and with an ALDA tweak, I haven't ever gone over 1100ºF, maybe not even 1050º, even uphill for several miles with heavy "throttle". FWIW.

As with all tweaks there are NO guarantees, so test at YOUR own risk.

[Brian Carlton]

Originally posted by jbaj007


At .9 bar boost and with an ALDA tweak, I haven't ever gone over 1100ºF, maybe not even 1050º, even uphill for several miles with heavy "throttle". FWIW.

Finally, a man with some data.

1) What was the ambient temperature on the long climb?

2) Did the engine stabilize at 1050-1100 or could it have been still climbing?

3) What was the peak engine water temperature during the climb?

This is the info that will tell us whether a 617 can take long periods of heavy boost.

[R Leo]

Originally posted by Brian Carlton
I agree with Tim. A gauge for exhaust temperature is far more valuable than a boost gauge. I do believe it's possible to do some damage at 13 psi boost, 90 degree ambient, if the power is on for more than 90-120 seconds. A pyrometer would warn you of this where a boost gauge will not.

But what is the 'danger' number? 600°? 800°?

[Brian Carlton]

You know, Randy, this varies based upon engine type and design. I was curious about the same thing, so I e-mailed MBZ to see if I could get a straight answer.

I won't hold my breath, however.

[Pete Burton]

What is the "typical" failure mode during extended boost? Is it piston seizing due to thermal expansion? New pistons for my 617 were about 90.25mm at the top, 90.7 at the skirt, placed in a 90.9 stock bore, so that's about 0.65mm clearance at top. With a 1000F temp rise that 90.25 would grow by about 1.2mm (.0000133 x 1000 x 90.25) and the bore would grow about 1/2 of that, because it's steel. I doubt it would ever go that high because the piston crowns are also contacting intake gases,etc and there are so many other factors, but it seems to me that an extended boost time provides opportunity to expand the pistons the most. Add to that an older engine with carbon buildup on the sides of the pistons and more blowby which would leave less room for expansion...

[jbhebert]

Depending on the motor design, extended boot will usually do one of two things:

On some motors (arguably ones that aren't up to the task of turbocharging), the high boost will cause a head gasket failure. Occationally, if the high boost causes enough heat, the head can warp.

On other motors, the pistons will begin to melt long before the head/block integrity of the motor even comes close to being compromised. The temperature at which this will occur varies from engine to engine. I've heard that extended EGTs exceeding 1100 degrees F will melt a Mercedes piston. I, personally, would try to keep them under 1000.