what is max boost on stock conquest

[crquest23]

i have an 87 widebody with an 88 ecu and a rebuilt motor with forged pistons i believe they are 8 to 1 compression and a down pipe from tep with 3 wire o2 i think the turbo is a stock 12 a not sure how to know for sure just dont want to blow another head or gasket

[psu_Crash]

Get a wideband air/fuel meter and boost till it leans out. Then don't go that high again.

I would think 15 psi is a safe level for you, but I'm no expert

I have heard of some folks running 18psi but I know the stock 12A turbo loses efficiency before that point.

[Sully]

No....

 

7.5 for 83-87

 

10.5 for 88/89

 

STSQ's!!

Edited November 25, 2008 by Sully

[86TSiGuy]

No....

 

7.5 for 83-87

 

10.5 for 88/89

 

STSQ's!!

 

These are the correct stock numbers.

If your asking how high you can turn the boost up on your 12a safely. I wouldn't go beyond 14psi without wideband A/F control, and if you do go beyond 14psi make sure your car is in tip-top shape with a good head gasket and studs.

Don't forget to read the FAQ on detonation as well.

[Sully]

just dont want to blow another head or gasket

 

I'm just talkin dookie. 15psi is all you'll want to go with the 12a

Edited November 25, 2008 by Sully

[scott87star]

Turning up the boost doesn't net much, all you're doing is turning up the pressure in the exhaust manifold even higher which adds thermal load to the combustion chambers and ...... BOOM! Y'all got to realize a turbo has a compressor AND a turbine, just paying attention to the compressor side (how much boost can I run?) is why these motors are all getting rebuilt. If you want more power open up the turbine so it can flow some air.

 

Scott

[Dquick]

Turning up the boost doesn't net much, all you're doing is turning up the pressure in the exhaust manifold even higher which adds thermal load to the combustion chambers and ...... BOOM! Y'all got to realize a turbo has a compressor AND a turbine, just paying attention to the compressor side (how much boost can I run?) is why these motors are all getting rebuilt. If you want more power open up the turbine so it can flow some air.

 

Scott

 

a fellow sq fan in the area said he can take the compressor off one of my tdo5h talon turbo's and machine it to attach to the turbine that's on the car already to make a bolt on 14b, is this kinda what your talking about?

 

alos if i have a catless 2 1/2 inch exhaust and downpipe, would turning up the boost be as bad since i've already removed some "thermal load" or have i removed any at all?

Edited November 25, 2008 by Dquick

[Caliber308]

All I can add is this: The higher you boost a turbo that was never meant to do 15 psi, The shorter the lifespan will be on it. TDO512As will push out 15 psi, the question is this.......for how long???

 

CALIBER 308

Edited November 26, 2008 by Caliber308

[scott87star]

Bigger exhaust helps for sure but is not the entire answer. You need to read up on turbo sizes and nomenclature in the FAQ section, there are several topics that cover it. Look or search for "turbo sizes", here's one.

 

Corky Bell covers it well in Maximum Boost, the short version is this: pressure in the exhaust manifold is higher than that in the intake manifold in all but a small percentage of turbo systems. In an OEM application like the Starquest, it can be 3-4 times higher (Corky recommends 2X higher for a suitable street system), so if you're pushing 10 psi into the system it could be up to 40 psi or more in the exhaust. It's a non-linear function, meaning doubling the intake pressure doesn't double the exhaust, more like triples or higher. So while at low compressor pressures you get a significant increase in FLOW through the engine relative to naturally aspirated the effect is reduced as you increase the inlet pressure at a given turbine size, the law of diminishing returns. In other words, if at 10 psi you get twice the FLOW through the engine than you would have without the turbo, at 15 psi you don't get 3X flow, more like 2.2X, and you've likely more than doubled the exhaust system pressure. According to the ideal gas law, PV=nRT, increasing pressure increases temperature or thermal load.

 

OK, off my soap box.

 

Scott

[86TSiGuy]

Bigger exhaust helps for sure but is not the entire answer. You need to read up on turbo sizes and nomenclature in the FAQ section, there are several topics that cover it. Look or search for "turbo sizes", here's one.

 

Corky Bell covers it well in Maximum Boost, the short version is this: pressure in the exhaust manifold is higher than that in the intake manifold in all but a small percentage of turbo systems. In an OEM application like the Starquest, it can be 3-4 times higher (Corky recommends 2X higher for a suitable street system), so if you're pushing 10 psi into the system it could be up to 40 psi or more in the exhaust. It's a non-linear function, meaning doubling the intake pressure doesn't double the exhaust, more like triples or higher. So while at low compressor pressures you get a significant increase in FLOW through the engine relative to naturally aspirated the effect is reduced as you increase the inlet pressure at a given turbine size, the law of diminishing returns. In other words, if at 10 psi you get twice the FLOW through the engine than you would have without the turbo, at 15 psi you don't get 3X flow, more like 2.2X, and you've likely more than doubled the exhaust system pressure. According to the ideal gas law, PV=nRT, increasing pressure increases temperature or thermal load.

 

OK, off my soap box.

 

Scott

 

I don't mean to thread jack here.

But thank's Scotty for the explanation, it's good to see somebody else apply physics to answer some of these questions.

[Technology]

Starquests don't follow the rules of physics. fuel cut is at 20 psi with a stock setup. 1G turbo eclipse mass air sensor raises that a bunch, but you cant tune with it. MAF-T will allow some tuning and remove fuel cut. Upgrade your turbo. 60-1 with E cover and a stage 3 t3 exhaust, .70 to .80 A/R will be nice on the street. then you're done.

[PDX87Starion]

A 12a boosts up to 15psi just fine. (how long ???) Just dont rev it too much past 4000. You will get a blast of torqe (which is fun on the street) but will never make big HP because you just cant rev it that high with the small turbo at that boost (too much back pressure). The lower the boost, the higher you can safly rev with the 12a.

[craig87]

dont screw around putting a 14b compressor in your stock exhaust housing your not correcting the restriction on the hot side you will notice more if you adapt the td05H housing to your exhaust manifold it can be done quite easy then you have the pick of any eclipse turbo.

[Dquick]

dont screw around putting a 14b compressor in your stock exhaust housing your not correcting the restriction on the hot side you will notice more if you adapt the td05H housing to your exhaust manifold it can be done quite easy then you have the pick of any eclipse turbo.

 

 

this is turning into a really good thread. It makes sense to to relieve as much pressure on the exhaust side as possible in order to be the easiest on the engine. i think the factory 10.5 should be good for this turbo seeing as i'd like to see good revs from it and a decent lifetime. Now by the same token without adding additional boost can an improvement in the flow on the compressor side(ICtubing and air filter etc) in and out make as much power as the exhaust? and does it mean there'll be a longer spool time?

[86TSiGuy]

this is turning into a really good thread. It makes sense to to relieve as much pressure on the exhaust side as possible in order to be the easiest on the engine. i think the factory 10.5 should be good for this turbo seeing as i'd like to see good revs from it and a decent lifetime. Now by the same token without adding additional boost can an improvement in the flow on the compressor side(ICtubing and air filter etc) in and out make as much power as the exhaust? and does it mean there'll be a longer spool time?

 

Hardpipes for the intake and plumbing, larger mas, less restrictive air box or cone filter, port & polish TB and manifolds, then get a new non-jet head casting w/ over-sized valves and HD springs, and for a little more durability do a balance shaft removal.

 

That with a 2.5" cat-less exhaust should net you a hefty power gain and increase spool time dramatically.

After that you need to deal with the flywheel which was grossly over-weight.

[Dquick]

Hardpipes for the intake and plumbing, larger mas, less restrictive air box or cone filter, port & polish TB and manifolds, then get a new non-jet head casting w/ over-sized valves and HD springs, and for a little more durability do a balance shaft removal.

 

That with a 2.5" cat-less exhaust should net you a hefty power gain and increase spool time dramatically.

After that you need to deal with the flywheel which was grossly over-weight.

 

already got BSEK,2.5exhaust no cat,ngk plugs/wires,and a k&n filter:) sounds like i'm on my way. decrease spool time you mean?

[86TSiGuy]

already got BSEK,2.5exhaust no cat,ngk plugs/wires,and a k&n filter:) sounds like i'm on my way. decrease spool time you mean?

 

Lol, yeah. I'm awesome by the way.

[scott87star]

Yeah, the bigger the hot side the longer it will take to make boost. But look at it this way, without lag you wouldn't have the big kick-in-the-rear coming. Without lag you have a N/A engine.

 

Scott

[jinx]

I wouldn't sweat all that technical stuff.

To keep it simple, copy any one of the many proven mitsu turbo combos posted.

DSM 05h machined into starquest turbine housing works very well... right up to a clipped 05 turbine wheel & 18g comoressor wheel.

I'd port out all the hotside while its apart

[Dquick]

I wouldn't sweat all that technical stuff.

To keep it simple, copy any one of the many proven mitsu turbo combos posted.

DSM 05h machined into starquest turbine housing works very well... right up to a clipped 05 turbine wheel & 18g comoressor wheel.

I'd port out all the hotside while its apart

 

yes but it sounds like the exhaust of the car is where there's alot of power to be made, while theoretically reducing EGT's and overall engine stress. i'm very new to forced induction, mostly played with v8's but it seems that making a "fast"(not necessarily drag racing) engine is a balancing act of engine torque and turbo sizing.

 

i read a article recently and a guy had used a pajero exhaust mani. on a starion g54b and the only difference you could see right off was a larger port on the turbo end..

[Caliber308]

yes but it sounds like the exhaust of the car is where there's alot of power to be made, while theoretically reducing EGT's and overall engine stress. i'm very new to forced induction, mostly played with v8's but it seems that making a "fast"(not necessarily drag racing) engine is a balancing act of engine torque and turbo sizing.

 

i read a article recently and a guy had used a pajero exhaust mani. on a starion g54b and the only difference you could see right off was a larger port on the turbo end..

 

The choice of which turbo you want to install depends on how you plan on using the car. Figure that out, and post back.

 

CALIBER 308

[Dquick]

^not the first to tell me this, i'm torn between just taking it to fourteens, or makin it my main project and shooting for a 13 sec, autox capable street car.

[TurboRaider]

A good start would be to ask a differant question...

 

How about what is a reasonable boost instead of what it the MAX boost.

 

The problem is its really hard to define what your max boost should be. The greater the boost the greater the stress. At some point you will shorten the life of the motor. It is impossible to tell how much shorter at any given level, there are just too many factors.

 

We can offer anecdotal information such as my fresh stock engine ran 15 PSI for years without any issue. That was with a good stock fuel pump, fresh rings, new bearings, fresh turbo and a properly torqued head gasket.

 

The factory did a recall on the rod bearings because the originals were not holding up. So if you have the original bearings on an 88-89 your setup is allready on the edge.

 

If your turbo bearings are already a bit weak and grooved up with a bit of coking added in, your head has a tiny warp and your head bolts need to be re tourqued you may not last very long at stock levels.

 

What is reasonable is give you a boost range that on a decent stock motor you should reasonalby safe. IMHO on the 88-89 motor, assuming it has good rod bearings that is 15 PSI. You can go past that but the gains drop off really quickly so IMHO the gain is too small for the increase in risk.

 

After 15 PSI its time to look at a few mods to increase power. You may even consider making the mods first.

 

At the very least I would evaluate the condition of the motor even at stock boost levels to make sure it stays in one piece. The car is 20+ old and most likely needs some TLC.

 

Kevin C

[Dquick]

A good start would be to ask a differant question...

 

How about what is a reasonable boost instead of what it the MAX boost.

 

The problem is its really hard to define what your max boost should be. The greater the boost the greater the stress. At some point you will shorten the life of the motor. It is impossible to tell how much shorter at any given level, there are just too many factors.

 

We can offer anecdotal information such as my fresh stock engine ran 15 PSI for years without any issue. That was with a good stock fuel pump, fresh rings, new bearings, fresh turbo and a properly torqued head gasket.

 

The factory did a recall on the rod bearings because the originals were not holding up. So if you have the original bearings on an 88-89 your setup is allready on the edge.

 

If your turbo bearings are already a bit weak and grooved up with a bit of coking added in, your head has a tiny warp and your head bolts need to be re tourqued you may not last very long at stock levels.

 

What is reasonable is give you a boost range that on a decent stock motor you should reasonalby safe. IMHO on the 88-89 motor, assuming it has good rod bearings that is 15 PSI. You can go past that but the gains drop off really quickly so IMHO the gain is too small for the increase in risk.

 

After 15 PSI its time to look at a few mods to increase power. You may even consider making the mods first.

 

At the very least I would evaluate the condition of the motor even at stock boost levels to make sure it stays in one piece. The car is 20+ old and most likely needs some TLC.

 

Kevin C

 

very nice sir, but how do i evaluate without tearing it apart? also it's a 87 with 76k on the clock.

Edited November 29, 2008 by Dquick

[Caliber308]

very nice sir, but how do i evaluate without tearing it apart? also it's a 87 with 76k on the clock.

 

Stock TDO512A at 10 to 12 psi. There's your answer.

 

CALIBER 308