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Old 30-07-2001, 10:05   #1
Chuck
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Max Boost with standard turbo

Anyone know what the max pressure obtainable of the standard turbo is?
Anyone taken the hoses off the actuator to prove it??
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Old 30-07-2001, 10:12   #2
blade
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Re:Max Boost with standard turbo

Not sure if the question is about the engine or turbo.

If I remember correctly, standard engine is safe to 1.2bar. Upgrade the bolts, and it is safe to 1.6bar. After that con-rods and pistons please!

The turbo is good for around 2bar before flow rates become an issue. Gas flowing inlet/exhaust and turbo, and with different turbo internals, then 2.5bar is possible. These are continuous pressures, intermittent peaks may be higher.

What are you trying to do exactly?
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Old 30-07-2001, 10:35   #3
Chuck
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Re:Max Boost with standard turbo

I'm just interested to know a what the highest pressure the turbo will deliver, I have heard 1.8bar.
At present I'm getting 1.4, but no matter what I do with the actuator I cannot get any higher. I'm using a Gemms ecu to control the boost, at the top end in 5th i can get 1.6bar, but say in second with the actuator fully closed can get no higher than 1.3bar.
Is my actuator releasing boost?? maybe i need a new one.
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Old 30-07-2001, 11:37   #4
Lightspeed
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Re:Max Boost with standard turbo

This is why I was asking for the compressor maps.

Asking what maximum boost the turbo will make is an incomplete question.
What you need to know is:-

What is the maximum pressure ratio at what flow rate and what efficiency?

There are several limiting factors with a turbo compressor.
1. Maximum flow rate - air flow - not boost level. Two different turbos can supply engines of the same horsepower with the same mass flow rate of air at different boost pressures.
2. Compressor efficiency - drive the compressor too hard and the efficiency will suffer - ie. the air will heat up too much. You will waste exhaust energy (driving the turbine) on heating up the air instead of compressing it. That is why a turbo must be correctly sized - if you push it out of an efficient working range the boost can go up as the power decreases with hotter intake temps.
3. Maximum pressure ratio - what is the maximum boost level attainable at what flow rate and at what efficency.
4. Maximum compressor speed (rpm) - most turbos are working at over 100,000rpm. Drive them too hard and the centrifugal forces (centripedal accelerations for you perfectionists) will bend the compressor (or turbine) blades outwards and destroy the turbo.

All of this information is contained in a turbo compressor map. If anyone out there has one for the evo's 4,5,6,TM,7 I'd be very interested. You can save a lot of people in this forum from having to replace blown turbos. I have learnt the hard (and stupid!!!) way (with the help of a few friends) the importance of good data when it comes to turbos. Most aftermarket tuners (not all) haven't got a clue - yeah mate this turbo's good for 400hp.......yeah, right - ask for a compressor map, every time.
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Old 30-07-2001, 11:42   #5
Chuck
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Re:Max Boost with standard turbo

Emmmmmmmm!!
Within your answer was that a yes, I can get 1.8bar from a standard turbo? or less
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Old 30-07-2001, 11:44   #6
Braf
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Re:Max Boost with standard turbo

Are you still using the stock exhaust? Perhaps exhaust backpressure is hampering turbo efficiency? It may also be that your turbo is not too healthy. I would like to know what is happening with your setup!
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Old 30-07-2001, 12:00   #7
Lightspeed
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Re:Max Boost with standard turbo

That was an - I don't know - I can't find a copy of the evo 4 and later compressor maps.
2 bar - pressure ratio 3 is about limit for most small turbos - but often you are approaching an overspeed condition and the efficiency is compromised - esp. at high engine rpms when the air mass flow rate is higher.

Your problem sounds strange - max. boost at top end in 5th and lower boost in 2nd. Does the GEMS use knock control like the standard ECU? Possibly limiting boost and retarding the ignition for a knock situation. Are you still using the standard Boost solenoid?

Something else to consider.
If your boost seems limited - pressure test all your piping - adaptor on the turbo inlet with a tyre valve and a foot pump (preferably an air line with a good regulator) does the job (out of gear, handbrake on!!!). Soapy water on all the joints and check for bubbles and hissing. If the hoses have ever been removed it is likely that you will find a couple of leaks.

Small boost leaks can overspeed a turbo as it tries to pump too much air without reaching the pressure limit set by the wastegate.

Might also be your dump valve not holding enough pressure.
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Old 30-07-2001, 13:52   #8
Chuck
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Re:Max Boost with standard turbo

Thanks for the advice. All Pipes are metal with Samco joints, HKS Intercooler, HKS Induction with metal piping, Super Drager with De-Cat.
Only thing could be is HKS dump valve, but I thought they'd handle more boost than that. I am trying a new actuator soon, as when i reduced the arm length boost did go up .15bar but still not as high as it should do. Gems does have knock sensor, no det, and have turned off knock sensor to make sure no retard on ign. Still only boosts to 1.2-1.3 bar, even with actuator hose off. I'm guessing if the actuator turns out ok then the wastegate housing it leaking if so I'll dump the lot and get a HKS turbo, Wastgate and manifold.
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Old 30-07-2001, 15:23   #9
Claudius
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Re:Max Boost with standard turbo

There comes a time where the turbo will only be heating up instead of giving boost, but at your current levels, I would doubt that that's the case. It seems your ECU has limitations depending on gear selected in it. Probably safer but not very fun...
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Old 30-07-2001, 15:33   #10
Chuck
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Re:Max Boost with standard turbo

How can the quality of your ECU reduced boost????
I can control boost all across the whole rev range, no problem, just i can't get anymore.
If the acutator is not connected the ecu isn't even able to control the boost.
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Old 30-07-2001, 17:00   #11
Evoboy
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Re:Max Boost with standard turbo

Chuck,
How good is yr boost guage ? Check it , they can become inaccurate and even non linear when old , or if a crap quality gauge which most are btw.
How are u sensing manifold pressure ? , yr sensor cud be screwing up.

Standard waste gate actuators often become weak or fail prematurely , so after above check it out.

Regarding turbo boost pressure , certainly u can increase the pressure from the standard turbo , but 2 increase above standard by a factor of 2 or more is not realistic.
Why do u think Mitsu wud install an oem turbo with that much in reserve? They wudn't!

As already stated , turbo's are carefully matched 2 a given engine , because running a turbo beyond OR UNDER it's optimum efficiency will heat the inlet charge air and reduce it's longevity/reliability.
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Old 30-07-2001, 17:02   #12
Evoboy
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Re:Max Boost with standard turbo

Chuck,
How good is yr boost guage ? Check it , they can become inaccurate and even non linear when old , or if a crap quality gauge which most are btw.
How are u sensing manifold pressure ? , yr sensor cud be screwing up.

Standard waste gate actuators often become weak or fail prematurely , so after above check it out.

Regarding turbo boost pressure , certainly u can increase the pressure from the standard turbo , but 2 increase above standard by a factor of 2 or more is not realistic.
Why do u think Mitsu wud install an oem turbo with that much in reserve? They wudn't!

As already stated , turbo's are carefully matched 2 a given engine , because running a turbo beyond OR UNDER it's optimum efficiency will heat the inlet charge air and reduce it's longevity/reliability.
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Old 23-08-2001, 19:59   #13
The Anarchist
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Re:Max Boost with standard turbo

Remove the plastic grommet all you need is a srewdriver.[img]http://194.93.140.171/graphics/happy1.gif border|EQU| 0 align|EQU| absmiddle ><!--e1-->
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