Engine/Transmission (1998.5 - 2002) Post Turbo EGT Advantages?

[MacGreenie]

Is there an advantage to post turbo EGT readings? I let mine cool down to 300 pre-turbo before shutdown after an idle of a minute or so (longer if towing).



I have a dual Westach EGT/Boost guage reading pre-turbo already.



There is some discussion about using switches on thermocouples that leads me to believe this introduces errors into the reading of a calibrated thermocouple. It would be nice to just buy an additional thermocouple and double the guage's capabilities with a little Radio Shack switch.



Would I possibly need a dual EGT guage with dual channels for dual thermocouples (Westach has one on their site) or a whole separate one instead to avoid this thermocouple error?



I understand the introduction of a switch or relay containing dissimilar metals to the thermocouple can throw your accuracy out the window.



Mr. Guage Happy

 

[HC]

For turbo cooldown monitoring, the "post" location is the better way to go. I've got mine post-turbo, and I'm very happy with that location, but my engine has only the mildest of mods and the vast majority of folks in TDR strongly believe in pre-turbo mounts, which gives a faster and more accurate response for all issues EXCEPT cooldown.



I do not believe that the advantages of having both pre and post readings is worth the extra trouble if you already have a pre-turbo reading. Remember, more than 90% have no pyro at all, and many don't bother to cool the turbo at all. But I would say, cool all the way to 300 every time. With my post turbo mount I sometimes cut it off a little higher.

 

[rweis]

I'm going to install pre and post turbo pyro and one boost / EGT gauge. HOWEVER, Westach does have a EGT rotary switch with extended leads to connect two pyros to one gauge. The switch is a high quality copper contact switch. It is on their web page. I thought I could get by with a RS switch, but not sure what errors it introduces. Probably not significant, but I try my dam. ness to do it right once, hence the switch.



my . 02



Bob Weis

 

[cam4g63]

The one disadvantage to using the probe before the turbo is that of having the probe tip fall off and run through the turbo. Yep, it can and has happenned, but it is pretty rare. The Autometer and some of the other K-types are pretty stout, so they don't worry me. But the faster reacting k-types have thinner tips. My probe will stay post turbo as long as I have a warranty.

 

[rblomquist]

TDR member Michael Huges talked to Westach via email about this (his setup is probably what you saw; the one with the switch from radio shack). Anyway, Michael was nice enough to PM me what Westach said:





-----------Quote from Westach support--------

Yes you can switch the egt probes. We do this all the time, we have 2,4,6 and 8 position switches for this purpose. As long as you use a good quality switch there shouldn't be any problem.



I looked at the link you sent and it is perfect. I noticed that you switch both leads. We will common the white leads to the gauge then switch the black. But that it to save some wires, especially when you get to those 6 and 8 positions.



The person that is telling you that there is some error there is correct but that amount of error is so slight that it can't be seen on an analog gauge. The correct way of running thermocouple wire is to run it all the way to the gauge but then you have to merge the thermocouple wire to the copper meter leads anyway. We just do it further away. As long as that cold junction is away from the heat source ( or extreme cold ) it is fine and happy.

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Have fun!

 

[rodmeyer]

I took my o1 to a diesel mech. here in portland to have gauges installed. He installed it post turbo. I asked him why he installed it post turbo. He works for frieghtlinner,says thats where all egt probes are installed on the big rigs. I guess thats good enought for me.

 

[Gary - K7GLD]

All the EGT limits I have seen relate to what is coming outta the engine - so to me the short answer as to best probe placement is as CLOSE to the engine as possible for most accurate readings, rather than *after* the turbo and further away from the engine, where you must then "guess" or "factor in" what you THINK heat losses really are in between...

 

[HC]

Originally posted by rodmeyer

He works for frieghtlinner,says thats where all egt probes are installed on the big rigs. I guess thats good enought for me.

I agree with you, but partly because my rig is only lightly modified. Commercial rigs are designed to stay cool running hard; and designed to stay within certain power limits. So stock, or near stock, either the commercial "big rig" or our "little" truck would be good to go with a post turbo mount.

If someone has heavy fueling modifications, then they need an extra measure of protection, and may want to lean towards a pre-turbo location for that reason.



I'm not trying to disagree with you; only pointing out that the answer will be different for different people.

 

[rodmeyer]

HC,I agree with you. So say my rig has a ez and dd1s ok. This is a mildly bombed rig. I'm not a hot rodder,just a ordinary driver who tows occasionally. Post turbo is fine right?

 

[HC]

In my opinion, yes. If you have the boost elbow hooked up on the EZ, you're probably running very close to stock as far as EGT's go, because the extra boost lowers your max EGT, while the injectors and extra fuel tend to raise it. I had an EZ for awhile with 275's, and once I connected the boost elbow I couldn't get the EGT within 100 degrees of my previous "high".



That said, in my opinion the whole point of having an EGT gauge, in either location, is to know where you usually run, and then "back off" when you see numbers way above your norm. If you're not willing to back off a bit, then what's the point of having an EGT gauge, except for cooldown???

 

[Joseph Donnelly]

The other posts pretty much summed it up. Pre-turbo is better for reading max egt to protect your engine. Post is maybe a bit better for cooldown monitoring. Countering the comment that if the probe breaks it could kill the turbo (if the probe is pre-turbo), I can say for sure that if the turbo grenades, it will wipe out a post-turbo probe. If you are running the $150 Autometer comp probe, that hurts.