Compressor Surge.

[sonofsam 5]

lol, funny you should say that (again ).browsing through some japtuning mag @ luchtime today

and noticed a new forge uprated diaphragm valve, looked very sexy, not on there site yet I dont think.

But did say it wasn't prone to failure, although it looks an easy fix when they do go..

 

What the advantages with a diaphragm then? apart from being louder?!

[tom_m 0]

lol, funny you should say that (again ).browsing through some japtuning mag @ luchtime today

and noticed a new forge uprated diaphragm valve, looked very sexy, not on there site yet I dont think.

But did say it wasn't prone to failure, although it looks an easy fix when they do go..

 

What the advantages with a diaphragm then? apart from being louder?!

 

over a single piston DV? none, more disadvantages if anything. diaphrams split, pistons don't. get a working single piston if you want one sam, but the XM never ran a DV at stock boost, so you'll be fine running it like that.

[inferno 1]

i dont know the ins and outs, but ive expeirience diaphrams/single and twin pistons on each turbo car ive owned.

 

twin piston suits rsturbo escorts best.

diaphram suits cally turbo/fiesta turbo/zx(xu10) turbo

 

piston valve felt leaky on the cars other than rsturbos. the diaphram on the rsturbo made it run s*ite.

 

fitting a dv on the zx did appear to allow turbo to spool up quicker

[jim21070 2]

But the XM never ran a DV at stock boost.

 

I wonder if they did in some markets? The stock Xantia turbo trunking has blanked off spigots where a recirc valve could be fitted and three blanked off spigots on the inlet manifold.

 

Citroen-pr.net makes no reference to anything that may be connected there though. Curious

[sonofsam 5]

Their was a Topic about this a while back Jim, bit I cant find it

IIRC some cars did come with a recirc DV as standard and yes youre right it was fitted

to the cross over pipe.

I only have two spigots on the side of my manifold, but there is a boss also ready for tapping if I needed more.

[tom_m 0]

I wonder if they did in some markets? The stock Xantia turbo trunking has blanked off spigots where a recirc valve could be fitted and three blanked off spigots on the inlet manifold.

 

Citroen-pr.net makes no reference to anything that may be connected there though. Curious

 

yes i wondered about that too. the main boost hose (that runs under the coil pack) in the XM has two blanked off ports where pipes could be fitted (if anyone has spare blanks they would be appreciated mine seem to have gone walkies ) but no obvious place to route a recirc back into the inlet trunking.

[inferno 1]

ive got virtually all the xm turbo and 406 turbo blanking plugs available just tell me what pipe od u want to blank off

 

the 406 sri i have has a recirc valve...

[Sam 4]

fitting a dv on the zx did appear to allow turbo to spool up quicker

 

How is that possible?

[inferno 1]

no dv will leave pressure backing down to the turbo on throttle closed, causing turbo to stall, therefore increasing spool up time.

[pdd144c 0]

Diaphrams DVs are very prone to passing and splitting Inferno. I wouldn't advise fitted one.

 

Piston ones are much better, you just need the correct one. All depends on whether or not you have an airflow meter fitted

[sonofsam 5]

Im going to hold out getting a new for the minute, car drives fine without for now.

 

Any opinions on recirc/diverter valve, would mean extra plumbing though

Considering I'll should be running a bar of boost I shall fit one then.

[sonofsam 5]

yes i wondered about that too. the main boost hose (that runs under the coil pack) in the XM has two blanked off ports where pipes could be fitted (if anyone has spare blanks they would be appreciated mine seem to have gone walkies ) but no obvious place to route a recirc back into the inlet trunking.

 

 

Aha, found the post where the pictures are, of how the standard issue recirc gets plumbed back!

 

http://forum.205gtidrivers.com/index.php?s...mp;#entry574310

[tom_m 0]

Aha, found the post where the pictures are, of how the standard issue recirc gets plumbed back!

 

http://forum.205gtidrivers.com/index.php?s...mp;#entry574310

 

http://forum.205gtidrivers.com/index.php?s...st&p=575432

 

and theres my post with the XM bay in showing the blanks

[jim21070 2]

I've done some calculations regarding surge and whilst I'm only a beginner at turbo stuff and may well have made a total hash of it, I have found the following:

 

I have had to use T3 maps as they were all I could really find that gave any clarity and there are lots of various impeller "trims". 40, 50, 60, super 60 and so on which significantly affect the results. I'm assuming a 40 trim for the standard turbo as factory fitted.

 

I have assumed a compressor efficieny of 60% and a Volumetric Efficiency (VE) for the engine of 0.9 (typical figure for a mild cam I'm told). I've also assumed we're at sea-level and not half-way up a mountain.

 

At full RPM the compressor is operating very well away from any surge regime. In fact it is not running efficiently at all and the operating point is well to the right of the "efficiency island" on a 40 trim and improving as the trim goes up. The compressor runs even less efficiently as the boost is increased toward 14 psi (1 Bar) suggesting to me that the engine needs a bigger turbo even when running stock boost. PSA have very much sized the turbo to favour low/midrange grunt with not much scope to get much more from it unless the turbo is swapped for something a bit bigger.

 

However, the compressor will very quickly run over to the surge line as the revs fall and the volume of air flowing reduces (i.e butterfly closed or closing) and therefore I'd say that a DV is essential even when running standard boost and when fitted should help the turbo spool up better.

 

One thing that surprised me was what a difference an efficient intercooler makes to airflow.

 

With no intercooler and the engine running at 5800 RPM, it will move 15.8 lbs/min of air at a temperature 104F (sorry for the imperial units ) above ambient.

 

Have an 80% efficient intercooler and the flow goes up to 18.3 lbs/min at a temperature only 20F above ambient. In cubc feet per minute (CFM) thats 226 against 261. Quite a useful rise and a very useful reduction in inlet temperature. This is where the biggest gains should come so Sam, your original giant intercooler really was the way to go

 

It has been an interesting exercise and a good learning exercise. A heck of a lot of assumptions has been made and many may be wildly inaccurate. It does show the general trend though.

 

So in short:

 

1. There is not much point in raising the boost much above stock;

2. Fit a DV;

3. Fit the biggest and most efficient Intercooler you possibly can

 

My Xantia will be getting a DV very soon

 

Now, in my stash I have a standard Nissan 200SX intercooler. I wonder....

Edited March 27, 2007 by jim21070

[tom_m 0]

i might be wrong, but i think the compressor is a 48 trim

 

oh and good work btw jim

Edited March 29, 2007 by tom_m

[johnrobertgordon 0]

Has anyone with a xu10cjte ever had an....ahem.....play with an mi16 205? bet it would be pretty close!

 

Yeah, your engine has! From a standing start I took the lead, but as I snatched for second the longer powerband of the MI gave him an edge, Was very close though, once both cars were up to speed the gap remained the same.

[johnrobertgordon 0]

yes i wondered about that too. the main boost hose (that runs under the coil pack) in the XM has two blanked off ports where pipes could be fitted (if anyone has spare blanks they would be appreciated mine seem to have gone walkies ) but no obvious place to route a recirc back into the inlet trunking.

 

 

Thats because the engines without the re circ have a different plastic pipe going from the airbox to the turbo. The other half of the circuit stars on the cast ali pipe coming across the top of the engine, mine was blocked of by a rubber bung.

[johnrobertgordon 0]

no dv will leave pressure backing down to the turbo on throttle closed, causing turbo to stall, therefore increasing spool up time.

 

 

You should actually get a quicker spool time if you use a recirc as the wasted boost gets dumped back into the intake and spools up the turbines. If any of you had recircs as standard and have ditched them you will see a drop in the performance as the ecu map was writen fot the extra boost it provided.

[pugrallye 0]

in addition to jims post: quality intercooler is a must, but its core construction not physical size that matters (well its just core surface area really), you can pay 200 for an ebay jobbie front mounted intercooler and its actually less efficient than a std. production intercooler, trouble is you never know how well the cores are made til you cut them up lol

[sonofsam 5]

Would agree with that. The huge FMIC I had was probably just a cheap copy and made to look

good with all it's shinyness, were as the MR2 IC I use now has good core and good end tank design

and is perfect for 230hp