Differential pressure gauge?

[Mr Whippy]

Is there such a thing, and/or is it easy to rig one up?

Basically, I'll very shortly have my intercooler all piped in, and in the interests of efficiency I want to check the pressure drop and temp drop

Now, I've got two pressure gauges, but not knowing how well each is calibrated, and not having a really fine scale, even 1psi out each might make my reading vary from 0psi loss to maybe 4psi loss.

Is there any common way of having a pressure gauge read relative to another input, rather than atmospheric?

I guess there might be some available, with a 2nd input that is left open for pressure wrt to atmosphere.


If anyone has any handy tips or tricks to get the differential only (as this is what is signifcant and important for this test) then that would be great


I'm not sure what I'm doing for temps yet, I have a plan to use the air temp sensors from my model car as they go out to 100degC, and seem pretty accurate in the 0-60degC range.

Does anyone know of anything really cheap, say sub £50, that will measure temps before/after somehow? It'd be nice to have the two readings side by side with the pressure drop one, so I can have a passenger plot the efficiency at 500rpm intervals...

Cheers

Dave

[CNHSS1]

sure Corky bell covers it in his Maximum Boost book or A.Graham Bell in his Forced Induction book (both worth a read anyway if youre into turbo applications)

people like maplins sell cheap digi readouts and thermocouples which would be fine for pre and post temps too, or a decent meter that will take multiple thermocouples and then switch between the two?
also what about rigging up a 'manometer' setup connected to input and output of I/C? wouldnt give you a pressure reading per se, but would show the variance and how much it changed during boost rise on the dyno? i suspect that the restriction (if any) wont be linear, its likely to be acceptable up to a given boost pressure, then ramp up as the boost goes high. if it doesnt change at all/much at your max boost, then the setup isnt restrictive

Edited by CNHSS1 on Thursday 4th September 12:08

[Mr Whippy]

Ah I have Corky Bell's book, but he uses two gauges, and then takes the differential...

I might have to have a scout on Ebay for a cheap gauge and butcher it's atmosphere side with a tap for another input so it reads the differential


Right, sounds like a trip to Maplins then. I need a few other bits from there anyway... getting ready for another wallet raping (but at least I can actually check intercooler efficiency, which seems to be rare amongst almost everyone who tunes cars )

Cheers

Dave

[Howitzer]

Use 2 gauges, then swap them and note any difference.

Most gauges will have a calibration well within what you want to measure.

We used to set a 10KPA drop across our charge coolers when testing.

Dave!

[CNHSS1]

Howitzer said:

Use 2 gauges, then swap them and note any difference.

ha ha, why do i never think of the easy ways! great tip that :-)

[Mr Whippy]

CNHSS1 said:

Howitzer said:

Use 2 gauges, then swap them and note any difference.

ha ha, why do i never think of the easy ways! great tip that :-)

Doh! Very very good plan

I'll have to do a few runs one way then swap and note any differential

Thanks for that, makes my life a little easier... but I still think most boost gauges are too small scaled to be really handy here.

My setup is ~ 160bhp, 21psi, 4000rpm peak, K03/GT15 sized turbo. What kinda losses would be acceptable? I'm hoping for no more than about 2psi peak... (thats quite a small gap on the gauges)



Tis quite a large cooler...




Thanks

Dave

Edited by Mr Whippy on Thursday 4th September 12:49

[stevieturbo]

Tis quite large, but chopped in half, so will be more likely to pose a restriction.


Most pneumatics shops will sell various gauges for about £5ea.

Hook them up to various parts you want to measure...and for cheap(ish) logging, get a video camera if you're stuck lol.

Im sure there are differential gauges out there, and there are definately pressure differential sensors for logging purposes.

[Mr Whippy]

stevieturbo said:

Tis quite large, but chopped in half, so will be more likely to pose a restriction

Hehe, yep, not so great cross section wise, and is essentially very long too!

I tried to fathom Corky Bells suggestions for the ideal intercooler, and this seems close. Ideally it'd be better being taller, and narrower and still a twin-pass design, reducing the internal length, and increasing the cross sectional area. I think 3" depth is ok for my application though.

I think as it stands it's borderline on my requirements for cross-section (advertised as 400cfm or something mad, but by Corkys calcs thats if it were not cross-flow when you work it out), so I think for a low revving diesel it shouldn't be too bad... a friend has used this setup already and had 150bhp quite nicely, but if it's loosing maybe 4psi and I could get an intercooler at say 2psi, it's a fair old extra bit of work when the turbo is already approaching the edge of it's envelope at that kinda power!


This is the main reason I want to test it all anyway, then I can check these important areas and basically get some feedback on what is reasonable or not


When you say pneumatic shop, do you have any examples of what types of shop that might be Sounds like a daft question but I honestly don't know. Will a place that sells industrial compressors, airlines, air ratchets etc be a good place to start?

Thanks again

Dave

[Mr Whippy]

Hmmm, had a plan while browsing Maplins.

I've found decent thermocouples and multimeter so should be able to see temps (not sure exactly how I will see both at once, might ask a Maplin person if you can do that somehow )

But then pondered using the boost sensors these cars have in the HDi110 models (loads about). I can get them cheap off a scrapper, get the table of output vs pressure, and away I go there too. Just mount two and do the same as above (and check them for accuracy of course)


Now, time to go start messing with electrical thingies and do some reading

Dave

[stevieturbo]

Yes, anywhere that sells compressors or air tools should have stocks.


I'd say ideally, Mr Bell would have down a top-bottom flowing core, as opposed to sideways.

Interestingly....most of the custom US builds are top-bottom flowing, with many short tubes for minimal restriction.

Whereas over here, most tend to be side-side for some reason.

[Mr Whippy]

Interesting you should mention the USA and their top to bottom pipes, as I've found one I quite like over there that is a much better config for my desired app just as you describe. It's basically the same as the old 1.9Td 306's were intercooled on the top, short tubes, wide flowing tanks and a wide core.

Tanks top and bottom, about the same width as mine, same depth (3"), but it's about 50% the height (so only really loosing the bit that sits behind the number plate/bumper), and it has 2.5" inlets rather than 3" which is just impractical really... so maybe the pipes that bend round into the engine bay will land in almost the same places too which is handy!


Main reason for wanting to test so much, is I'll likely order one as soon as it's all setup and working, and try it as well, and if it's better then I've done a good thing

Cheers

Dave

Edited by Mr Whippy on Friday 5th September 00:45

[Daveuk9xx]

Measuring differential pressure across the intercooler is straightforward enough. You fit a tapping to the pipework upstream of it and another downstream. You connect the upstream tapping with plastic tube to the high pressure side of the differential gauge and the downstream tapping to the low pressure side of the gauge. That's about it.

You can turn a normal gauge into a differential one if you can fit an extra tapping to it on the atmospheric side of the diaphragm. Depends how it's sealed as to how easy that is. If the case is sealed with a vent hole in it then you can glue or solder a spigot over the vent. If the case is unsealed you'll need to seal it with silicone or something similar first.

Dave Baker

[Mr Whippy]

Yeah, I was having a look at some temp corrected manometers, but they were fairly steep. I'd love to get one, but at ~ £120 it's just a bit too much right now...

I think I'll just get a good pair of multimeters (if I can get the HDi110 boost sensors reading onto them), a pair of thermocouples, and maybe take a look at the boost sensors off the HDi110, as they will be cheap as chips from a scrapper and probably as accurate as any analog gauge...

Then I can just get my lovely assistant to sit in the writing things down as I drive


I like the video camera idea suggested above, if I can get two multimeters and get my sensor pairs showing the differential output (say one is 0.1v and the other 0.2v, the difference is 0.1v... but I'm not sure if that works if the sensor output isn't linear, I need to do some test case maths to check), and just have one showing temp diff and the other pressure diff

Now I just hope the intercooler and intake system as a whole is at least reasonable... that said it's quite fun trying to optimise these kinds of things rather than just cranking the boost up more

Dave

Edited by Mr Whippy on Friday 5th September 10:05