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Mounting EGT probes

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Mounting EGT probes

Post by jmc on Mon Aug 03, 2009 6:08 am

I've got a Defi EGT probe to fit to my stainless 4 branch manifold. Defi recommend simply drilling and tapping a hole in the manifold (and to do it down near where the primarys connect), but I've also seen ones which have a welded on boss on the manifold and placed up near the cylinder head. Is there a right / wrong way to do this, and is there anything I need to look out for?
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Re: Mounting EGT probes

Post by mrbeige on Mon Aug 03, 2009 6:55 am

I would think you'd want it where all the primaries meet, as if you just had it one primary, you might miss one of the cylinders burning really hot??

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Re: Mounting EGT probes

Post by dirtytorque on Mon Aug 03, 2009 7:48 am

I'd have to disagree with Stu on that.conventional wisdom states you want it as close to the head to get a good indication of cylinder temps.
Cylinder number one will run hottest on a g60 so i'd put it there.
In fact that is where I have mine.
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Re: Mounting EGT probes

Post by mrbeige on Mon Aug 03, 2009 8:02 am

I understand you'd want it close to the head to get the 'highest' reading, but don't you run the risk of missing something? Then, I suppose if you have an issue with high exhaust temps, it's normally from all four cylinders??

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Re: Mounting EGT probes

Post by kevhaywire on Mon Aug 03, 2009 8:36 am

Agree with Dirty torque, ideally EGT should be 2" to 3" from the exhaust valves to get accurate readings, especially with turbos, which is easy to do with a log manifold. Not so easy with 4 branchers.

On this occasion I'd personally go with the collector scenario and make sure the primarys are well insulated as to not lose heat. Reason being if the other 3 cyls are running too lean or too rich, you'll get false readings. The sum of all 4 cyls is the reading you want. I'd be tempted to put an egt probe in each primary 2" from the exhaust valve if cost wasn't a factor. You would see in an instant which cylinder is having an off day then!

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Re: Mounting EGT probes

Post by dirtytorque on Mon Aug 03, 2009 2:46 pm

I guess ideally you'd want to run 4 really,but how much is too much?
I'm labouring under the impression that all 4 cylinders should be running to very similar conditions and so I chose to use one cylinder as a snap shot for what was going on in all four.

I guess as a good compromise one in the collector and one in one of the runners would be good.
I'm happy with just the one tbh as I also have a wideband in the collector area which should also hint at problems.
And i take all my spark plugs out regularly to have a read of those too.
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Re: Mounting EGT probes

Post by JNLRacing on Mon May 17, 2010 2:07 am

In an ideal world EGT temperatures are measured 4" away from the back of the exhaust valve. Unfortunately this means running multiple probes. So you either grab an average of all 4 at the collector and accept it will read a tad low or measure 1 cylinder at the top of the runner 4" away from the back of the valve and hope it is the hottest of the 4.

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Re: Mounting EGT probes

Post by jmc on Sun Jun 13, 2010 10:54 am

Thanks JNL. I got it fitted in runner 1 in the end, but further down (about 8" down). As durtytorque said, the no1 cylinder would be the hottest running on a G60.

Ok, here's a question. Assuming it's left for a couple of mins to stabalise, is the temperature purely dependant on air:fuel ratio? From what I've read, higher temps mean a leaner mixture, so is it really a simpleas that. I seem to be getting very specific temperatures depending on what I'm doing (poottling round town, cruising at '70' on the motorway, and the more spirited B road driving).
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Re: Mounting EGT probes

Post by mrbeige on Sun Jun 13, 2010 10:57 am

I would think a higher engine loading would also produce higher temps??

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Re: Mounting EGT probes

Post by Yandards on Mon Jun 14, 2010 2:11 am

mrbeige wrote:I would think a higher engine loading would also produce higher temps??

Higher load will produce higher exhaust gas temps link here to PDF see page 14 but as you can the effect is not linear.

What is more interesting based on that series of tests is that the peak temperature is achieved just after the pipe join (4 into 1 style manifold). There is in fact a variation of some 100+ degrees C when comparing the manifold to downpipe thermocouple to any of the ones taken directly from a cylinder outlet.

This will be down to the gas merging into a single tract which will cause both turbulence and, due to the design of the exhaust manifold in this case, there is a rise in temperature due to a reduced overall internal diameter of the pipework. There is probably also a rise in exhaust gas speed at this point thanks to the increase in temperature (should result in some increase in pressure as well).

So, you should see peak temperatures around 10cm downstream of the manifold join but this will only be any use if all the cylinders are in the correct trim. The problem is that as the main reason you will get a cylinder burning hot is down to a dodgy injector the only way to monitor this is by placing an EGT at all 4 outlets.

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Re: Mounting EGT probes

Post by jmc on Mon Jun 14, 2010 11:16 am

Hhhh, I'd forgotten about load here, and it explains why it runs hot on part throttle when motorway cruising as it should be running leaner there. The whe I go on WOT the temp briefly drops as it goes rich, before coming back. My temps seem low though - 900-1150 degrees F. Must be where I have my probe, with it being further away from the head. Thanks guys, nice PDF document by the way, good to see some actual data on the zircotech coatings.
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Re: Mounting EGT probes

Post by dirtytorque on Tue Jun 15, 2010 12:06 am

/\/\/\

Yup underload the engine will obviously be producing more energy and thus more heat. Smile
Any thing that changes combustion characteristic will effect EGT,i.e advance/afr.

900 to 11500 F?

Mine seems to be about 400 degrees celcius at idle.
roughly 900+ on load from memory.
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Re: Mounting EGT probes

Post by kevhaywire on Wed Jun 16, 2010 4:42 am

I see similar temps to dirty, also in degs C. 400ish at idle, 550-600 crusing around 50-60, 700-800 cruising from 80-100mph. In boost it peaks at 950.

These temps are inline with a few other guy's I've asked, and stock 1.8Ts EGT at 750 deg C at 80mph too, so I'm fairly happy my tune can't be too far off the mark Very Happy

My EGT probe is a few inches in front of the T3 flange where all 6 runners converge, so approx only 4-5" from the head as it's a stumpy little log mani. Certainly for turbo engines, this seems to be the best pick up point, but it does run the risk of losing the turbine wheel if the probe breaks off.

From monitoring EGT for 3 years on mine, I've learned that with the VR6 at least, it's the timing that has the biggest overall influence on the temperatures.

I don't know the G60 lump at all, but 900 - 1150 F (482 C to 621 C) under hard load says to me, too rich? The unburned fuel is cooling the gas temps down. Are you getting black smoke under boost JMC? Although you might not be getting enough smoke to be seen in the rear view.

I know that when my tune was pig rich and dipping into the 10s, early 11s, the EGTs fell right down, and the black smoke was quite amusing!

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Re: Mounting EGT probes

Post by jmc on Wed Jun 16, 2010 10:38 am

Yeah, I think it might be slightly rich Kev - plugs are saying that to me though, not smoke in the rear mirror (can't see that at all). I've had a couple of mates driving behind me and they haven't spotted any smoke on WOT either. Mine is definately further down and away from the head than most as well.
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Re: Mounting EGT probes

Post by Yandards on Wed Jun 16, 2010 11:59 am

jmc wrote:Yeah, I think it might be slightly rich Kev - plugs are saying that to me though, not smoke in the rear mirror (can't see that at all). I've had a couple of mates driving behind me and they haven't spotted any smoke on WOT either. Mine is definately further down and away from the head than most as well.

It's digi managment striking again, without a throttle pot the ECU cannot run accurate MAP prediction which is essential to a good fuel/air mix under acceleration and therefore clean running.

It's a shame as no-one seems to have setup a decent aftermarket system to get the best from the G60; everyone who owns one knows they have good days and bad days when you stick your foot down. On the good days they really really fly but the inability of the engine managment to give a consistant level of performance is really annoying.

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Re: Mounting EGT probes

Post by kevhaywire on Thu Jun 17, 2010 4:35 am

Hmmmm, I can't see the EGT dropping a few hundred degrees C over 5-6" personally. What kind of advance are you running in boost?

I guess the EGT probe / gauge itself could be under reading?

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Re: Mounting EGT probes

Post by jmc on Fri Jun 18, 2010 3:00 am

From memory the cam is 6 degrees BTDC. Not sure on the advance in the map though. Must admit I have never been 100% happy with the map. At the moment though I'll have to put up with it - haven't the time or money to do anything further with it.
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Re: Mounting EGT probes

Post by dirtytorque on Mon Jun 21, 2010 12:37 am

/\/\/\ I just think ecu itself is not sophisticated enough to make accuarate(by today standards) air fuel mixture predictions.idle/WOT switches and CO pots all point to the managmements systems limitations.Also It was never designed to be the brain of a car with 250 bhp.

I am only running a MAP sensor and I hit my afr targets consistently.I have a tps but I am in no hyurry to wire it up if indeed I ever do.I'd expect my throttle response to maybe improve but I have no motivation to wire it up att.
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Re: Mounting EGT probes

Post by Yandards on Wed Jun 23, 2010 10:01 am

dirtytorque wrote:/\/\/\ I just think ecu itself is not sophisticated enough to make accuarate(by today standards) air fuel mixture predictions.idle/WOT switches and CO pots all point to the managmements systems limitations.Also It was never designed to be the brain of a car with 250 bhp.

I am only running a MAP sensor and I hit my afr targets consistently.I have a tps but I am in no hyurry to wire it up if indeed I ever do.I'd expect my throttle response to maybe improve but I have no motivation to wire it up att.

A throttle pot should make a fairly big old difference to engine response under acceleration. If you consider a MAP sensor even with MAP prediction it is only ever responding to changes in the inlet manifold; the same can be said of the lambda probe. A throttle pot provides the ECU with a 'what I want' signal and gives the ECU the ability to switch over to MAP prediction far faster.

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Re: Mounting EGT probes

Post by kevhaywire on Mon Jun 28, 2010 7:05 am

Yeah TPS adds a nice 3rd dimension to the map but it's not essential on old cars like ours. Modern cars rely on TPS a lot for handling and traction control etc. We only really need it for throttle pump enrichment and maybe over-run control. MAP alone is more than enough to fuel these old motors quickly and reliably Very Happy

God this forum has practically ground to a halt recently! Whistle

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Re: Mounting EGT probes

Post by dirtytorque on Mon Jun 28, 2010 4:25 pm

kevhaywire wrote:

God this forum has practically ground to a halt recently! Whistle
Lol,yeah.Is it the recession biting?
No one playing with cars anymore?
lol
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Re: Mounting EGT probes

Post by jmc on Tue Jun 29, 2010 4:28 am

dirtytorque wrote:Lol,yeah.Is it the recession biting?
No one playing with cars anymore?
lol

It is a bit like that with me - not so much spare cash, and being in the process of buying a house doesn't help.
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Re: Mounting EGT probes

Post by kevhaywire on Tue Jun 29, 2010 6:45 am

Same here. I'm not on the breadline but I can't afford to lavish parts the beast with some luxury parts at the moment Sad

Gotta save £200 for an Iphone4 upgrade when it's finally available. I never thought I'd see the day where I choose to spend on a phone instead of the car!!

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