A question for all you DSMers

Okay, so I ran doors with a 2nd gen talon TSi last night...the only mods he had were a K&N cone filter and he had the boost upped from 12psi to 16 psi...well I talked to my "friend" this morning(he drives a N/A talon) and he says there is no way I shoulda kept up and that the car I raced was probably slow as fuck because 16psi is too much for a stock 4G63 and he probably blew a bunch of seals and had no compression...okay so my question is, is 16psi too much for the 4G63, or was this guy just butt-hurt? Thanks in advance

No it isnt

okay, thanks.

16 is about as high as you want to go on the stock turbo, but you can run 30+ psi on stock blocks if the car is setup and tuned properly ;)

You have similar estimated 1/4 mile times as a near stock turbo DSM. I'm not surprised. Like 95 GSXracer said, in short... yes the guy doesn't know what he is talking about. Increasing boost to 16psi is exactly the right thing to do, and the guy you raced probably knows more about his car than your N/A friend. As for how much boost a stock motor can run... if you remember that boost doesn't equal power, you can run 30psi on a smaller turbo on a stock motor fine, but may not be able to run 20psi on a bigger turbo. In reality, I'm not the only person who has run 20+psi on a stock turbo and stock motor.

Okay, I'll be honest, I'm an idiot when it comes to turbocharging...what does increasing the boost do? Doesn't it make more horsepower, at least in theory? I mean, I don't think you would up your boost and risk having something go wrong without it making you more horsepower...

most boost is just more pressure on the air flow. more air flow means more power, if set up right. but a 16lb on this car is not the same as 16lbs on another. in therory a 14lb eclipse could be faster than a 16

Is 16psi too much for the 4G63t? Thanks in advance

No it isn't. I was pushing 16 with my old TC. As for him having his boost set to 16psi, alot of people exaggerate. When I first had my 91 TSI it was only pushing 8 and this other guy was claiming his 95 Tsi was pushing 16. Now I have AWD.. might I add and we were already coasting before we started to take off so he had the advantage. When he said go I just kept pulling on him. :grinno:

most boost is just more pressure on the air flow. more air flow means more power, if set up right. but a 16lb on this car is not the same as 16lbs on another. in therory a 14lb eclipse could be faster than a 16

Exactly, and not only is it in theory, it's true 100% when comparing two different setups(turbos, excluding other supplementle factors). Airflow is what makes power, and is more important. Like it's been mentioned, you can have a car that runs 20psi and make close to 400whp, and on a smaller turbo, run the same boost and make 300whp. To give you an easier understanding, at the same water pressure; which will put more water on a fire to put it out, a fire hose, or a garden hose?That analogy may help you understand what's being addressed here.

This is also the same reason that you cannot measure an engines maximum capabilities in psi, or cfm, or other measures. The only thing that can actually measured it's max output, is when it's measure in HP. This will always tell you the exact amount of stress that's being put onto the system.


Also, 16psi is not anywhere near the 4g63's capabilities, in simple terms. (provided supporting mods are in place)

okay, okay, but on a stock 4G63 turbo, wouldn't 16psi be better than 14psi, all other things being equal? I'm so confused.

If everything held equal. Meaning, same car, same engine, same turbo, same setup, then more psi=more power.

If everything held equal. Meaning, same car, same engine, same turbo, same setup, then more psi=more power.


On a restrictive setup, more boost may not net enough of an icrese in airflow to make any more noticeable power though. This applies in particular to maxed out turbos and restrictive setups. Take a 14b at 25 psi, raise it to 27. You'll only get it in the midrange, which will result in more torque, but no more peak power. And after boost drops you are creating a lot of heat, and could even drop hp a bit. Just for the sake of nitpicking :icon16:

Damn...forced induction is so complicated...lol

There's a lot of things that come into play...you can think of boost gauge reading as air that is not getting into the motor also. A stock head for example can't flow as much air as a well ported one, so...say all things remain the same but port the head, your boost reading may have been say 20 but now it's only 18.. boost reading goes down but HP goes up as more air is getting into the motor.


Also with high boost levels on a small turbo the turbo will be out of it's flow map and the booseted air will be heated up equaling less true air flow into the motor due to the density of the compressed air being lower.

FWIW A 14b can run up to about a max of 25 PSI on a mildly modded motor.

Okay, I don't know shit about DSM cars, either 1st or 2nd gen, but is the 14b the stock turbo on the 4G63?

Okay, I don't know shit about DSM cars, either 1st or 2nd gen, but is the 14b the stock turbo on the 4G63?

yes it is. the most common upgrade is a 16g of some sort.

Yes it is. And 10.5's statement that boost pressure is a reading of airflow that can not get though the motor is absolutely correct. Think of boost as excess airflow. Some of that excess airflow will get through the motor, some wont. As pressure goes up the force pushing the air through the motor goes up, so you do get more through. But looking at PV=nRT, pressure is heat, and the inverse of density. That what we are talking about when you get to that point of diminishing return, where you are geting sliiightly more airflow, but LOTS more heat.

Manual 1g turbo's had a 14b. Auto's turbo 1gs had a 13b, smaller. 2g turbo's, both manual and automatic, had a t-25. The 14b is the best of the bunch.

shit I have a eclipse and im still lost in this turbo stuff I dont know much about this at all but thats why we are here is to learn.

A lot of good info in this thread, but unfortunately it can't all be asked and covered. Some of the ideas that most people might not understand are:
1. A boost gauge reads boost that is NOT going into to the engine. (thanks 10.5sec92AWDTALON)
2. psi doesn't equal power, here's a short explanation: boost pressure (psi) can only be compared to another pressure if you're talking about the same engine, turbo, and mostly the same supporting mods. Say I installed a part which let the engine flow better. It's not hard to imagine that the boost gauge would read less. The air that couldn't go into the engine before can now.. less boost, more power. There are many other examples.

There are a lot of theoretical things that are hard to guess at. If you learn how things work in reality (example: on a 2g turbo, t25, 16psi DOES make more power than 14psi), you will get the concepts afterwards. Why isn't 20psi on a t25 faster than 16psi? Well, it sounds like it should be, but for the minimal power it does make in the mid-range of the RPM band... it creates a lot of heat which makes 20psi a bad idea on pump gas, which will detonate at such heat.

Anyway, I'd be happy to stab at other concepts but don't forget that everyone looks smarter if they do their research first then ask a specific question instead of saying "I don't know anything about turbos, what is a wastegate" etc... A lot of knowledge is just experience and hearing that 16psi on a t25 is faster than 14psi, or that you can run about 25psi on a 14b. Only some of it is knowing that, say, a certain turbo would be more efficient.

Just because I'm in a good mood, and I'm putting off dropping a mean deuce that is probably going to cripple me, I'll explain my favorite "concept." Since it applies to this thread...

Boost vs Airflow and volumetric efficiency and displacement. As I stated earlier in this thead, I think, more airflow at the same (or less) boost, is the balls. Airflow is power, boost is heat. Now, to offer some tangible measureable data. On a 2 liter, its typical to get 40 lbs/min at 20 psi on a decent sized turbo (20g and up) and stock cams/intake/head. Add cams to that, and you get ~4 lbs/min improvement in flow at that same boost. Thats a 40 hp increase, without adding heat (knock). The added cylinder pressure (cylinder pressure and power are the same, or more acurately, torque, but both are mathematically linked anyway) will increase the chances of knocking but its very linear and predictable (unlike increasing timing, which can increase cylinder pressure (knock) exponentially after some point).

25 psi was good for 47-48 lbs/min, or about the max a 20g will do. Note that at 25 psi a 16g will do ~35 lbs regardless of cams/mods, since thats its limit ;) In the case of a 14b, 30 lbs/min at 25 psi. A sheetmetal intake is good for a few more pounds of airflow at the same boost.

All this added airflow is added power, without added heat (boost, see ideal gas laws/adiabatic compression). This is bigtime if you are running pump gas! Race gas will "bandaid" all this BS, and thats why you can max out 16Gs and 14Bs and not knock, on relatively stock setups.

Add a stroker into the mix and things get real fun. 20% displacement increase will yield 20% airflow increase if VE remains constant (unlikely, but its close enough). This is how I was able to hit 64 lbs/min at only 29 psi last time at the track. I was getting 60 lbs/min on a 60-1 at less than 25 psi. I ran that on pump gas with no knock.

Its important to note that if you increase a motors volumetric efficiency (cams, head, intake, larger turbine wheel, free flow exhaust, less restrictive MAS, etc) beyond the flow capabilites of the turbo, boost will drop as demand goes up. This is exactly what you see with a t25 on a stock 2g set to say 18 psi. Once the turbo can keep up with airflow demands, airflow will flatline and boost will drop. Note that boost is dropping, but airflow (power) is not! I've datalogged this on several setups. Take a 20g car with cams and sheetmetal intake set to 30 psi, and you will see the same thing, boost dropping at high rpm, airflow maxed out. In these cases, less boost is not less power. The two are not perfectly linked like people tend to think. :)

So I hope that people at least pick up on the relationships between boost, heat, knock, cylinder pressure, and power, and the fact that boost and airflow arent the same thing, with airflow mods making the difference. And also that low boost and high airflow is key especially on pump gas. This is why people love strokers in daily drivers, including me. I'm tempted to build up a spare block into a little strocker for the 1g. :)

Very nice explanation, Kev! In case anyone really wants to get into the complexities of turbocharging, go pick up the book Maximum Boost by Corky Bell. Just about everything you need to know (up to a point) is in that book.

And Kevin, I think you meant the 14b maxes out at ~30lbs/min, not 20lbs/min ;)

Whoooaaaa, brain overload of turbo information, you guys really know your shit...that helps out a lot guys, thanks....shit while I'm here, why is the 14b better than the T-25?

Kevin, I must say that must be the 50 bagillionth time you have written that same post with comparing boost, and airflow, and it still kicks ass.

Anyway, the 14b has a higher flow capacity, roughly 30 lbs/min like guitar said, and that info has been data logged many times, so it's a fact. As for the t-25, it's flow capacity is less then that of the 14b, thus it cannot create the same horsepower. Basically, that's what kevin was saying, well, part of it. (it can make more power at the same boost)

Yes, I am a dumbass. I changed it to 30 lbs/min. T25 is about 22 if I rmember correctly. So when I say that a 14b is an awesome upgrade for a 2g, its onw obvious why. Almost 50% more airflow (power making) capaciy.

Kevin, I must say that must be the 50 bagillionth time you have written that same post with comparing boost, and airflow, and it still kicks ass.


Thats the funniest thing I've read all day. I probably do repeat the same info all the time. If nothing else I guess it helps me remember it :icon16:

Simply, the 14b is bigger than the t25... there doesn't need to be much explanation for it. Bigger fans flow more air at the same RPM. Needs a more powerful motor though.. which in turbos is the time it takes to spool, lag.

Also the abaility to use more air. If you are maxing out the flow of the motor with one turbo, a bigger turbo can not move any more air. But typically a bigger turbo has a bigger hotside, which will allow a little more flow. I went from a 6h 20g to a 6h GT40 56 trim, and at 25 psi there was no difference in flow between the two ;)