Can any of you knowledgeable turbo heads give me a bit of advice please (other than don't eat yellow snow!)
My turbo system has, from the original car, a recirculation dump valve, i.e. when it dumps the dumped air feeds into the turbo inlet. What are the
implications of changing this configuration and fitting a dump valve that dumps to atmosphere and I blank off the old dump line to the turbo inlet.
The only thing I can think of is that there may be a continual recirculation feed through the dump valve when the turbo is at idle and the engine is
not accelerating or under load and by blanking this off the full pressure will be felt on the inlet of the engine. This may upset the fuel air ration
and run weaker with all the associated problems.
The engine is a Lancia Thema 2l Turbo 8V
Cheers
Nick
wont that confuse the ecu ?
If the car uses MAF for fuelling then you will need a twin piston dump valve so that the ECU doesnt get confused.
it will be fine.....the dump allways feeds after maf (if you have a maf) so the air is not extra and doesnt need metering....
all you will gain is a nice phssst when you change gear with a atmospheric dv....
if you do have a maf you will need a twin piston type such as a bailey dv26...a single piston will cause idle issues, this is because when the engine
is at idle it is running on vaccuum and will pull the valve open causing an air leak...the manifold doesnt go into posotive untill the turbo starts to
spool....
Why do you want to change? If it ain't broke...
It will be fine. You may just get a little over fueling on over-run, but nothing more. Nothing is recirculated at idle, and is only recirculated through when lifting off the throttle after load on the engine
I disconnected my recirc valve and put a dump valve in the line to the throttle plate. Mine does not have a MAF sensor. Works fine.
See
Picture linky
Steve
Great reples guys thanks
Excuse the ignorance but what is MAF (Mass ai flow?). How will it confuse the ECU other than changing the air flow characteristics. The idle is a
little high compared to before I did the mod.
Seeing as you seem to your stuff here's another one that maybe you could help with. When at idle the waste gate is closed, when I rev the engine
to about 3000 I would have expected it to open once the RPM is stabalised or on overrun but it remains closed. It will move under pressure from a
bike tyre pump but not under normal running.
The length of the inlet tract from turbo outlet through intercooler and into the inlet is a bit longer than the original so is this a case of the
turbo not being able to stabalise the pressure enough to open the waste gate?
Nick
do you have a boost guage fitted??
what boost are you running??
your waste gate probably wont open untill around 0.8bar....it will only open at its set level, under boost, that will only occur under load, not by
just reving the engine...
what boost controll do you have??
the maf mass air flow meter, meters the amount of air being consumed by the engine and helps to determine the amount of fuel needed, i think on some
ecus you can use a different lamba sensor (wide band) to do away with it, but i may be wrong??
There are some advantages in using a non recirculating dump valve in turbos (essentially centrifugal superchargers). They have a CR so you end up with
higher parasitic losses and a hot inlet charge if you recirculate (though they are good for passing noise emission tests). You'll use a little
power pulling air through the filter just to dump it of course...
Meanwhile with a Roots type blower (which has no compression ratio) a recirculating valve is better as it prevents you having to pull air through the
filter just to dump it out.
quote:
Originally posted by Nick Davison
Seeing as you seem to your stuff here's another one that maybe you could help with. When at idle the waste gate is closed, when I rev the engine to about 3000 I would have expected it to open once the RPM is stabalised or on overrun but it remains closed. It will move under pressure from a bike tyre pump but not under normal running.
Guys
Many thanks for the posts once again, very useful.
I do have a MAF then and the recirc line did feed back into the intake after that so not a problem.
Good to know that I shouldn't see the waste gate operating without load, I don't have a boost gauge fitted but there is one on order so I
will be able to see how the boost profile works when it has been fitted. The turbo boost is quite low as it is from the Thema and not the integrale
so I would guess that it will be around 0.8bar.
Plans for next winter are to change the electrics, turbo and some of the fuel injector system for an 8v Integrale system then I can change the mapping
and bring in a few more hp - my target is 210 which I understand is achievable without engine mods. Some say 235 is good without engine mods, it
would be nice but there will be reliability trade offs with that and I have spent enough time making the thing so want to have fun now!!
It has been on the road for all last season and was an immense amount of fun, need to do the small changes now in time for May.
Many thanks again
Nick
Boggle
The boost control is pure compressor air pressure (as a servo tapping to the waste gate actuator) operating on the wastegate but controled by an ecu
actuated soloniod, which is I guess either on or off bleeding servo pressure to close the wase gate. The DV is survo inlet pressure initiated with
the aid of a spring which I think is fairly standard.
Cheers mate
Nick
If I may add a bit, being a Fiat/Lancia nut...
You have Bosch L-Jetronic on the Thema. As others have said, this has a MAF that measures the air going in and fuel is added accordingly. If you use a
simple dump valve you get two unwanted effects:
1) as you drive, the engine will run rich momentarily after the dump valve operates - not too bad
2) at idle, the dump valve stays partly open and a lot of air that has been metered will be lost, leaving your engine idling very rich - bad
The Integrale uses Weber-Marelli injection, which has no MAF, so no problem using a dump valve.
Cheers R
i thought it was magnetta marelli on the intergrale?
[Edited on 25/2/10 by boggle]
Now your going to ask me which one is fitted?
Not sure but can check tomorrow when I'm home.
Rachaeljf you say if I use a simple dump valve it will run rich at idle, is there any way round that, maybe a different DV?
Also if you are a Fiat Lancia nut, do you have access to any spares etc? For the future as you never know!
Nick
i think he means a single piston type...
you need a twin piston ie a bailey dv26
Yes I did mean a "simple" DV rather than the Bailey twin piston extra pricey one.
Magnetti Marelli is the auto electrics manufacturer. They teamed up with Weber to make the Weber-Marelli IAW mapped injection/ignition system.
I have two sheds full of Fiat parts!
Cheers R
i used to have a lancia prisma 1600 gt and ending up having to buy another just for parts......it was on an A plate and was an amazing car....
shame the rust killed it...
I think that is the same story for all Lancias sadly, the best bits are in my car!
I will hold my breath and have a look for a Bailey dv26.
Rachaeljf, you may be becoming my best friend! Do you have a 131 gearbox?
Nick
No 131 gearbox, sorry. Very rare now I would say! I only have later, FWD stuff.
Hi, another point to note is that without a filter on the DV it is likely to suck a little unfiltered air in at idle! Not many DV's come with a
filter and the amount of air taken in is small but appreciable!
Not gonna be much dust about if it rains all summer of course!
quote:
Originally posted by rachaeljf
1) as you drive, the engine will run rich momentarily after the dump valve operates - not too bad