KA-T Pressure Limits...

[Mikel]

As much as you can run without detonation. There isn't a set pressure limit, compared to the pressures of combustion, no amount of pressure a turbocharger can make will effect engine in any way. You just have to worry about detonation, which depends on Fuel quality, heat mangement, and turbo efficiency.

[Mikel]

Short answer - Take it to a dyno with a knock sensor and a wideband O2, use the fuel you will normally run in it, and have it tuned.

[95_240sx]

I dont think he is running a Piggyback or Standalone...

Rick

[AceInhole]

As much as you can run without detonation. There isn't a set pressure limit, compared to the pressures of combustion, no amount of pressure a turbocharger can make will effect engine in any way.

It's not an incorrect answer, but I'll have to disagree with that..... as running higher pressures will lead to more wear and tear on the motor (logically, as you have more pressure placed on everything from crank/ rod bearings to stress on the timing chain/ sprockets/ valvetrain). So... more boost = expect your engine to wear faster.

So, while running more boost may not lead to destroying the engine instantly, on a daily driver it should be considered that you're "kiling" the motor more and more as you increase boost pressures.

[float_6969]

most kits run 6/7lbs. I would say that is a reliable # to shoot for. Are you using some sort of FMU? Remember, boost is addictive. It's a real hard comedown if you bend a rod, or worse, break one and put it through the block. Until you can afford to do it right, keep the boost to a minimum.

[Mikel]

It's not an incorrect answer, but I'll have to disagree with that..... as running higher pressures will lead to more wear and tear on the motor (logically, as you have more pressure placed on everything from crank/ rod bearings to stress on the timing chain/ sprockets/ valvetrain). So... more boost = expect your engine to wear faster.

So, while running more boost may not lead to destroying the engine instantly, on a daily driver it should be considered that you're "kiling" the motor more and more as you increase boost pressures.

Disagree, respectfully.

Think of the amount of pressure exerted on the top of the piston when it ignites the charge. It can go well over 1000psi (that's not a typo). The actual pressure had next to no effect on any of the rotating parts.

Now, on the other hand, if your rods will only handle the load required to make 400hp, any more than 400hp will break them. BUT, it won't make a damn bit of difference to the rods if the 400hp is generated at 5psi or at 50psi.

[95_240sx]

Where does all your knowledge of KA's come from Mikel?

And you do have a good point, what AceInHole is saying is also true, and I dont understand where you linked your response and his response together...

Rick

[Mikel]

Where does all your knowledge of KA's come from Mikel?

And you do have a good point, what AceInHole is saying is also true, and I dont understand where you linked your response and his response together...

Rick

I'm saying that higher boost doesn't always lead to faster wear, boost in excess of the engine's limits, defined by about a million factors, leads to increased wear. Higher output leads to increased wear, but as long as it's tuned right, it doesn't matter if the output comes from 10psi or 20psi. More of a theoretical point I suppose, it's just bad form to use boost pressure as a definition of an engine's limits. :p

[float_6969]

Mikel, I also respectfully disagree. If your train of thought is correct, then as long as drag racers/nascar/indy/baja ect., just built thier motor to handle more hp then they motor produced, it would last just as long as a daily driver. This is just plain untrue. Some top fuel drag racers rebuild the motor every run. With increased hp (albeit from boost or compression) comes increased strain on the moving parts of the motor. The statement, "The actual pressure had nest to no effect on any of the rotating parts." couldn't be more untrue. Think about the way an internal combustion motor works. In it's basic form, it's just a complicated air pump. It gets it's energy from the expansion of the gasses during the power stroke. Now if we force air into the combustion chamber, we've already increased the amount of pressure in that chamber. Now if you measure the pressure created from an explosion in a NA vehicle and the pressure created from an explosion in that same vehicle under 7lbs of boost, the forced induction vehicle will create more pressure. If it didn't it wouldn't create more power. If nothing else, think of it like this, is it easier to squeeze a ballon with 1lb of air in it, or a ballon with 10lbs of air in it. If it harder to squeeze the balloon with more pressure in it then that ballon is exerting more pressure against you. More pressure equals more loading. More loading equals more stress. More stress equals more wear.

EDIT- I didn't read your following post clarifying that you were stating that there wasn't neccisarly a relation between boost and motor wear. Theoretically, you are correct, but in a real world application, there is a direct relation between power output and engine life. And generally, if the engines are tuned the same, more boost will create more power and shorter engine life

[Mikel]

Mikel, I also respectfully disagree. If your train of thought is correct, then as long as drag racers/nascar/indy/baja ect., just built thier motor to handle more hp then they motor produced, it would last just as long as a daily driver. This is just plain untrue. Some top fuel drag racers rebuild the motor every run. With increased hp (albeit from boost or compression) comes increased strain on the moving parts of the motor. The statement, "The actual pressure had nest to no effect on any of the rotating parts." couldn't be more untrue. Think about the way an internal combustion motor works. In it's basic form, it's just a complicated air pump. It gets it's energy from the expansion of the gasses during the power stroke. Now if we force air into the combustion chamber, we've already increased the amount of pressure in that chamber. Now if you measure the pressure created from an explosion in a NA vehicle and the pressure created from an explosion in that same vehicle under 7lbs of boost, the forced induction vehicle will create more pressure. If it didn't it wouldn't create more power. If nothing else, think of it like this, is it easier to squeeze a ballon with 1lb of air in it, or a ballon with 10lbs of air in it. If it harder to squeeze the balloon with more pressure in it then that ballon is exerting more pressure against you. More pressure equals more loading. More loading equals more stress. More stress equals more wear.

Reread my statement, I said the power output IS a good defination of the limits of an engine. Boost pressure doesn't matter.

Try this, run 5 psi from a T25 on stock fuel. You should be fine, right?

Try 5psi from a T88 on stock fuel, you won't be fine. Boost pressure does not equal output

[float_6969]

read my corrected post

[float_6969]

I was talking to too many ppl and it took me too long to type that original response. by the time I was done, there were 2 posts after it. Sorry!

[Mikel]

Yeah, like I said, it's more a theory discussion than anything.

To get back to the original topic - Either get it dyno tuned, or check around with other people running a similar setup.

[float_6969]

speaking of widebands, those would be for tuning use only, correct? I know a lot of ppl use EGT to measure their fuel ratios but I'd really like an accurate way to get real AF ratios invehicle. I know a wideband will run you close to a grand for everything, but does it last any longer than a regular O2 sensor? Just a thought I guess.....

[AceInhole]

As much as you can run without detonation.

This is mainly the point I disagreed with. On a KA you can run a good 20psi on pump gas without detonation, but the pressures of combustion due to that 20psi (assume manifold pressure at close to constant temp vs. NA) will crack a ring or piston. You're saying that the original poster, as long as he has enough fuel, can run 20psi daily???

Now:Quote »Think of the amount of pressure exerted on the top of the piston when it ignites the charge. It can go well over 1000psi (that's not a typo). The actual pressure had next to no effect on any of the rotating parts. [/quote] Except that pressure becomes a direct force onto the wrist pin, which exerts a force (of that 1000psi* the piston head area) onto the rod, then the rod bearings, which then exerts a torque onto the crank, which translates into a force on the crank bearings as well as the flywheel. Seems like a lot of rotating parts being effected by pressures in the combustion chamber, which go up dramatically when boost is raised.

[Mikel]

speaking of widebands, those would be for tuning use only, correct? I know a lot of ppl use EGT to measure their fuel ratios but I'd really like an accurate way to get real AF ratios invehicle. I know a wideband will run you close to a grand for everything, but does it last any longer than a regular O2 sensor? Just a thought I guess.....

A wideband lasts about as long as a regular O2, but the sensor itself is only ~$200 to replace.

[float_6969]

thats what I said....

[float_6969]

Thanks Mikel

[Mikel]

This is mainly the point I disagreed with. On a KA you can run a good 20psi on pump gas without detonation, but the pressures of combustion due to that 20psi (assume manifold pressure at close to constant temp vs. NA) will crack a ring or piston. You're saying that the original poster, as long as he has enough fuel, can run 20psi daily???

Yes. With proper fueling, no detonation, I would see no problem in 20psi.

Quote »Now: Except that pressure becomes a direct force onto the wrist pin, which exerts a force (of that 1000psi* the piston head area) onto the rod, then the rod bearings, which then exerts a torque onto the crank, which translates into a force on the crank bearings as well as the flywheel. Seems like a lot of rotating parts being effected by pressures in the combustion chamber, which go up dramatically when boost is raised. [[/quote]

So the piston crown, which can see in excess of 1000psi in regular combustion, will be affected by another 20psi? I doubt it. I've run well over 20psi in my GN, the pistons are nothing special, not even forged, cast. In fact, lots of people have run over 25psi on racing fuel. In the Supra, people run over 30psi on good gas. These motors are not made of unobtanium. True, they can hold the horsepower, but the horsepower isn't the issue I'm talking about, it's the boost pressure.

[float_6969]

Mikel-if I'm understanding you correctly, your saying that if 2 motors, creating the same hp, but one with more boost, it won't make that much difference in the life of the motor. Am I correct in that assumption? If indeed that is what you are saying, then yes, I totally agree with you. But in all actuality, that isn't true. There is a relation between boost and output. No, more boost doesn't wear the motor out faster, the hp created from using more boost wears the motor out faster. But that is like saying that cigarettes don't kill you. Well technically, no, cigarettes DON'T kill you, it's your body's response to the cigarette smoke that kill you. So in a weird technical way, yes you are right. But in a real world situation, there is a link between boost and hp and more hp shortens the life of the motor. So from that we can say that as boost increases, GENERALLY hp increases, and as hp increases engine life decreases.

[AceInhole]

Yes. With proper fueling, no detonation, I would see no problem in 20psi.

So you're saying that the stock rings and bearings won't be affected by more stress, exponentially greater than stock?? And that since there is no additional stress, a boosted motor will last just as long as the same motor running naturally aspirated. Those are bold statements, my friend.

Quote »So the piston crown, which can see in excess of 1000psi in regular combustion, will be affected by another 20psi? I doubt it. [/quote] 20psi of an air fuel mixture will lead to a lot more than 20psi in the combustion chamber once the mixture is ignited.

Quote »I've run well over 20psi in my GN, the pistons are nothing special, not even forged, cast. In fact, lots of people have run over 25psi on racing fuel. In the Supra, people run over 30psi on good gas. These motors are not made of unobtanium. True, they can hold the horsepower, but the horsepower isn't the issue I'm talking about, it's the boost pressure. [/quote] Whatever... you're apparently not understanding my original post, or the following posts. I know people have run insane amounts of boost on stock engines. What I'm questioning is the reliability and life span of such engines.

[float_6969]

Ace, what he's saying is theoretical and not really possible. I think he's saying that if you have 2 motors with the same output but running different different boosts, they would have the same lifespan. But now that I look at it that way, I don't agree with what he is saying either....

[Mikel]

So you're saying that the stock rings and bearings won't be affected by more stress, exponentially greater than stock?? And that since there is no additional stress, a boosted motor will last just as long as the same motor running naturally aspirated. Those are bold statements, my friend.

Nope, saying that the same motor NA and boosted making the same amount of power will be equally reliable, actually, I would give the upper hand to the boosted motor, as it would be using smaller cams and less rpms.

Quote » 20psi of an air fuel mixture will lead to a lot more than 20psi in the combustion chamber once the mixture is ignited.[/quote]Yep, by way of burning more fuel, and producing more power. The boost pressure itself is irrelevant.

Quote » Whatever... you're apparently not understanding my original post, or the following posts. I know people have run insane amounts of boost on stock engines. What I'm questioning is the reliability and life span of such engines. [/quote]

I understand, I just don't agree. I agree that higher output = less life. I don't agree that higher boost pressure (without relation to higher output) = less life. If the motor will only hold 350rwhp, and increasing the boost to 20psi will make the output exceed 350rwhp, then yes, it will break the motor, but not as a result of the manifold pressure, as a result of the output.

I'm just disagreeing with the people that say "XXX motor will only hold 12psi"

12 psi from what? A T25? A T76?

12 psi on 87 octane? on 100 octane? on 116 octane?

I completely agree that every motor has a limit in output. It doesn't however have a boost limit. How can you tell someone how much boost they can run without knowing what size turbo they have or what fuel they intend to run?

[AceInhole]

I would give the upper hand to the boosted motor, as it would be using smaller cams and less rpms.

Then... it wouldn't be the same motor, would it....

Quote »Yep, by way of burning more fuel, and producing more power. The boost pressure itself is irrelevant. [/quote]Boost pressure in the manifold at near constant temperature will always yeild the same amount of power though. So, boost pressure is only irrelevant if your disregard that the extra power you're making comes from the extra boost.

Quote »I understand, I just don't agree. I agree that higher output = less life. I don't agree that higher boost pressure (without relation to higher output) = less life.[/quote]So basically, you're agreeing with me, since higher boost pressures will lead to higher output.

Quote »I'm just disagreeing with the people that say "XXX motor will only hold 12psi"

12 psi from what? A T25? A T76? [/quote]12psi from whatever the FMax Stage I kit uses apparently.

Quote »12 psi on 87 octane? on 100 octane? on 116 octane?[/quote]being a daily driver we'd have to assume premium fuel. Either 91 or 93/ 94 depending on where you live.

Quote »I completely agree that every motor has a limit in output. It doesn't however have a boost limit. How can you tell someone how much boost they can run without knowing what size turbo they have or what fuel they intend to run? [/quote] We know what turbo he has. We know what fuel system he has. He has an FMax Stage I kit. However, we also know he intends to drive the car daily. My original post, and disagreement with your post, was that with a daily driver, the additional wear from running higher boost should be taken into consideration.

The original question:Quote »My question is how much pressure could i hit my 35k mile DOHC KA on a daily basis vs the max i should hit when im trying to kill that heavily modified V-8 without the worries of blowing the motor..??[/quote]It seems as though I considered his daily usage of the car, while you took it as simply how much he could boost without blowing the motor. My point: the more he pushes to the limits of his boost, or the more he runs higher boost levels in general, the faster his engine will wear. I simply wanted to clarify that while the engine can take higher boost pressures as long as it doesn't detonate (your post), you wouldn't want to run the car that high for extended periods of time (or even too much in small increments) if you wanted the motor to last, as most people would like their daily drivers to do.

[Mikel]

Higher boost pressure will not always lead to higher output.

Yes, in most cases it does.

All I'm saying is that using manifold pressure as a reference for tuning is a bad idea, way too many variables. If he can run higher boost without detonation, it will have no ill effects on the motor, assuming the motor is capable of handling the higher output.

A better question would be "how much power can I make on a stock motor, reliably"

If it's 350rwhp, he can run as much boost as it takes to get to 350rwhp, assuming he's not overrevving the turbo, or running into detonation.

[AceInhole]

Higher boost pressure will not always lead to higher output.

In this case: same motor, same turbo, same intercooler, same fuel system. Yes. Higher boost pressures will lead to higher output. If he was already running at the limit of his turbo's efficiency, then no. It may not lead to higher output. Right now, he's supposedly running at a "safe" boost level. (9psi where his setup reportedly can handle 11-12).

Quote »All I'm saying is that using manifold pressure as a reference for tuning is a bad idea, way too many variables. If he can run higher boost without detonation, it will have no ill effects on the motor, assuming the motor is capable of handling the higher output. [/quote] but, saying it will have no ill effects neglects wear on the engine. In reality, it will add to wear on the engine. I consider that an ill effect. Perhaps you don't.

Quote »A better question would be "how much power can I make on a stock motor, reliably"[/quote] I assumed that question was implied with the statement:Quote »My question is how much pressure could i hit my 35k mile DOHC KA on a daily basis[/quote]Anyways, to answer the original question: TY Yap running the FMax Stage II setup ran ~10psi for a couple years with no probs. Pushed the system to 14.5psi later on, but I recall him saying something about not wanting to run that through summer."RobTheChef" with the FMax Stage I setup has over 100,000 miles on his engine (not 100k on the turbo setup), but I'm not quite sure what he ran for boost.With setups similar to the FMax Stage I kit, and stock internals, I wouldn't go above 10psi for a daily driver. Beyond that you're almost doubling the load on the engine, but it's really up to how long you'd like your engine to last.

[Mikel]

Whatever, we're essentially agreeing, and arguing semantics. It's just a pet peeve of mine to use boost pressure as a reference point.

I saw the text list of your parts, do you have any pictures of your setup? Sounds similar to what I am planning, though I plan to run over 20psi

[AceInhole]

Whatever, we're essentially agreeing, and arguing semantics. It's just a pet peeve of mine to use boost pressure as a reference point.

Yup. It's a pet peeve of mine when people blame a setup having more power than another on one turbo being larger than the other.

Quote »I saw the text list of your parts, do you have any pictures of your setup? Sounds similar to what I am planning, though I plan to run over 20psi [/quote]

Thread jack :p

http://www.engr.uconn.edu/~corrales/240/

[Mikel]

Yup. It's a pet peeve of mine when people blame a setup having more power than another on one turbo being larger than the other.



Thread jack :p

http://www.engr.uconn.edu/~corrales/240/

lol, I hear ya.

Nice setup by the way. I want to do some kinda off the wall things to a turbo car, like methanol injection, etc. I'm scared to try it on the Supra, as the motor is expensive as hell. I figure a 240SX would be a fun test bed/daily driver, especially since the motor costs ~$500 in the event that I cause a catastrophic failure. I'm also planning to design my own manifold and have a fabricator I know build it.

[Mikel]

BTW - Do you have pics of the manifold?

/Thread Hijacking complete