UkLegacyT

Hi all, not too clued up on the electronics side of the car, so was hoping somebody could help.
what i want to do is install a gauge etc to monitor the exhaust temps.
questions:
what parts do i need, and where could i get them?
also, where is best to mount the sensor? best in up-pipe pre turbo, or will the downpipe do, immediately rear of the turbo flange.
lastly, what temps do i want to stay below? (before or after turbo, wherever sensor is).

thanks
ian

Pavlo

You can buy some off the shelf, the SPA dual digital ones in Demon tweeks look good value.

You're best of putting in the header in my opinion, drill and tap a 1/8" npt thread, and fit a stainless compression fitting.

The temperature sensors tend to be stainless sheathed thermocouples, which need either a dedicated gauge or a regular thermocouple box.

Sensors can be had from RS/Farnell expect to pay about £8, connector about £3, generic box to plug into about £100-£300, some allow 2 connections.

Email me if you want anything more specific.

Paul

UkLegacyT

thanks mate

i'll have a look at the guages in the tweeks catalogue, not noticed them before
what does that expensive box do then?

ian

Pavlo

Thermocouples have a very low output (microvolts) that isn't linear. The box of tricks measures the voltage output, linearizes it, and uses Cold Junction Compensation to correct the voltage due to the thermocouple effect where the wires are terminated in the box. It then gives you a temperature, which is nice.

You can build a similar box using an IC that does it all in one go, and a LCD voltmeter for about £30 by the time you put it in a box. If you built the DIY AFR thing, you will probably manage. The circuit is very simple and can be done on vero board. I might be doing one myself.

The SPA gauge is quite cheap, but it's not clear whether you need the extra EGT interface if you buy an EGT specific gauge.

Paul

UkLegacyT

yeah its the price of the box thing that puts me off.

why dont you have a go at making one. then make a second and sell it to me

Chris.Palmer

I think all SPA Guages run a 5v input - I don't think the EGT ones come with the thermocouple & amplifier (these cost a lot extra, somewhere between £100-£200)

You can buy hand-held thercouple meters for around £30 & good K-Type thermouples for about £15 - OK for testing - but not so good for a fixed install.

If you want to go the DIY route the LM335 is a Centigrade all in one package that does cold-joint compensation.

If you don't want to tap your manifold or downpipe (You can buy downipes with EGT bosses already fitted) etc - you can also buy jubilee clip k-type thermocoules that clamp around the exhaust - these will of course read a lot lower - However - having said that - placement of the thermocouple dramatically alters readings (eg either side of turbo can be 100c difference).

IMHO - EGT is only really any good for comparisons before & after mods etc. Ask on here for appropriate of=r max EGTs I'd be surprised if you get a definitive answer - eg 800c max measured in downpipe?!

Yet another project Paul - how many on the go now

[Edited by Chris.Palmer - 8/20/2002 1:07:03 PM]

Pavlo

already done it for something else. the clamp pipe isn't any good in my opinion, not only does it read lower, but also much slower.

I found a type K compatible meter in maplin for £30 which looks good, I emailed you the details.

In fact it's so cheap, i'll probably get one, then you can just leave various thermocouple permanently in place and swap over the connectors.

RS do a good range of sheathed type K thermo couples. probably the one with 1.5mm stainless sheath, about 200mm long out to be enough, then it's terminated onto a length of glass fibre protected wires. Cost about £10 for the thrmocouple and compression fitting to mount it in a header. Although andy just drilled a 1.5mm hole in the header and fitted it with exhaust paste.

The good thing about thermocouples, is that you can plug any type K in to a type K meter and it doesn't need recalibrating (well, not for accuracy of about 1-2 degrees).

edited to add the lm335 is no good for this type of aplication, and tend to be limited to 100'c, infact they are often used to generate the cold junction compensation temperature for thermocouples, as they use a silicon junction that is temperature dependant.

Paul

[Edited by Pavlo - 8/20/2002 1:20:35 PM]

Andy.F

That's the way I do it Paul, three different plugs can plug into my standard handheld display. Looks a bit of a bodge but that is in keeping with my cars concept

FWIW my EGT in the uppipe is 245C @ idle 620C @ 80 mph cruise. 750C road thrash and 840C during extended (6laps +) track use.

Andy

Jay m A

iTrader: (2)

I have an Autometer EGT guage, about £85 +VAT from Scoobymania. How accurate it is I don't know, but its used for comparison reasons only. With the kit is everything you need - gauge thermocouple, lead and 1/8 NPT boss, all you have to do is mount the probe and gauge. It reads in deg F, FYI its mounted in the headers - Idle <600F, 80mph cruise 1150F trackday 1450F.

I think all the guages come as complete kits - HKS, Blitz etc its really a question of how much you want to spend

Justin

Pavlo

£85 sounds like a good deal, the autometer stuff is good value. I don't think looks are that critical, as you generally are only interested when on the track or doing some specific testing.

It's not like you need know your EGT whilst on the pull!

"we can go as fast or slow as you like love, we're only at 500 degrees..."

paul