just wondering what everone thinks the 2.4 can handle in terms of actual PSI before the engines takes a dump...im personally aiming for about 10psi on a t3/t4 50 trim .63a/r w/stg3 wheel....i think it may be pushing it...but who knows it could suprise us all
In the stock configuration with no valvetrain mods, you can expect to top out at about 14 to 15psi.
Clear
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Dynoed at 450HP
Hahn Turbo Stage IV with valvetrain upgrades
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Don't forget about the rest of the running gear. Not so sure about the automatic trans I only have a CAI and cat back exhaust and my trans is leaking from some wear. I don’t feel that I have driven it that hard to have the trans leaking. It appears to be working ok just leaves a little puddle in the garage.
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Don't forget about the rest of the running gear. Not so sure about the automatic trans I only have a CAI and cat back exhaust and my trans is leaking from some wear. I don’t feel that I have driven it that hard to have the trans leaking. It appears to be working ok just leaves a little puddle in the garage.
shouldn't happen - swap the stockers back in and take it in
just wondering what everone thinks the 2.4 can handle in terms of actual PSI before the engines takes a dump...im personally aiming for about 10psi on a t3/t4 50 trim .63a/r w/stg3 wheel....i think it may be pushing it...but who knows it could suprise us all
One thing to consider is that it is not the amount of boost that kills things in an engine. To give you an example a small GT2554 on the 2.4L @10psi is not the same as a GT3071 @10psi and that would not be equal to a MP62 flow @10psi either. Boost pressure is just a measurement of the restriction of flow through the engine that is why we see higher boost pressure with the supercharger on cars that have a restrictive exhaust, even though they make less power to the wheels. One of the things that bends things up inside the engine is cylinder pressures which also has a direct impact on how much torque the engine makes. The higher your cylinder pressure is after combustion the more force on the piston and the more transferred throught the rods to the crank and depending on the angle of the crank determines how much torque the engine produces. The biggest thing we need to find out is at what cylinder pressures do things in the engine start to get twisted .
One thing to consider is that it is not the amount of boost that kills things in an engine. To give you an example a small GT2554 on the 2.4L @10psi is not the same as a GT3071 @10psi and that would not be equal to a MP62 flow @10psi either. Boost pressure is just a measurement of the restriction of flow through the engine that is why we see higher boost pressure with the supercharger on cars that have a restrictive exhaust, even though they make less power to the wheels. One of the things that bends things up inside the engine is cylinder pressures which also has a direct impact on how much torque the engine makes. The higher your cylinder pressure is after combustion the more force on the piston and the more transferred throught the rods to the crank and depending on the angle of the crank determines how much torque the engine produces. The biggest thing we need to find out is at what cylinder pressures do things in the engine start to get twisted .
So, are you saying that a boosted car benefits from a little "back-pressure"?
Jackknife
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So, are you saying that a boosted car benefits from a little "back-pressure"?
Jackknife
There is always going to be a pressure differential between intake and exhaust, even when not using any output from the turbo or s/c as they are always spinning. (a turbo less connected than a beltdriven s/c) The unit's boost is generally a measurement of the increase of this pressure differential. Without changing pulleys you cannot cause a s/c to overspin while operating, it has a designed in max rpm, regardless of what you do up or downstream. A turbo on the other hand will spin as fast as the exhaust gas can cause it to go, if you remove restriction you can potentially see the turbo run too fast for its own good. A littl ebackpressure helps moderate teh output for street driving.
Just like when we talk of adding 14.7 psi boost, we always ignore the fact that at sea level we already have 14.7 psi in the air around us. And thus a reason that unless tuned for the Denver or higher altitudes, a boosted vehicle, while exceeding the performance of a non-boosted vehicle in the mountains, will fall short of its sea level output. A turbo's max output is regulated by not only size of the unit, location in the stream, wastegate operation, but also downstream restrictions in the exhaust. Eliminate restrictions downstream from the turbo outflow (which is basically exhaust) and you will raise hp. Keep the wastegate shut longer and you also will raise hp. "Real" racecars don't run mufflers or CATS, nor do they use airboxes, just velocity stacks. Less retrictions at both ends, but if they didn't build more strength into the engines themselves they would blow up more often. There is a margin of safety in the design of the ecotec that allows for a certain level of higher output prior to "building" the engine. There is a GM book on it and somewhere on this forum a link to it. An ecotec can easily (with enough $$$) be built to spit out in the neighborhood of 900 hp, IIRC. Will a 2.4 boosted to ahigher output than a LNF be as durable and reliable over time? Possibly not, but that's the risk you take when you mod.
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So, are you saying that a boosted car benefits from a little "back-pressure"?
Jackknife
"back-pressure" is a double edge sword. Scavenging is what we are looking for when tuning an exhaust and when it comes to supercharged and naturally aspirated motors exhaust gas velocity one of the important factors in scavenging. Scavenging is trying to get all of the waste gases from combustion out of the cylinder and filling it with as much fresh charge as possible.
When the exhaust valve opens on your engine pressure inside the combustion chamber that is there from combustion is higher than in the pressure in the exhaust manifold causing air to rush out of the cylinder when the exhaust valve opens. The smaller that opening is, the higher the velocity will be of the air exiting the combustion chamber, since this high velocity slug of air is moving at a high rate of speed it will have a lot of momentum to it and as the exhaust valve starts to close it will continue to flow air out until the valve closes. If you have things timed and sized very good that exhaust flow can not only get all of the exhaust out of the cylinder, but also help bring in a fresh charge into the cylinder. As you increase the size of the exhaust (valves, runners, primaries, exhaust) the velocity of the air leaving the head will decrease to the point that pressures are not as high and those pressures can equalize before the the exhaust valve fully closes and you will not get as good as scavenging as you would have with a smaller exhaust. Finding the right balance between these two is dependent on many different variables, what RPM you are looking to run at, exhaust cam profile, lift, duration, header design, etc.
Since a turbo is a exhaust restriction in itself and can limit the exhaust flow, turbo cars do respond differently to exhaust because the energy in the exhaust is what drives the turbo. Typically you want an exhaust system that keeps as much energy in the system as possible until it gets to the turbo and then you can get away with a larger exhaust than if you were Naturally aspirated or supercharged because you are not concerned as much with the scavenging effect.
Also positive displacement superchargers do not like to push against pressure, so as you lower the pressure on the intake side of things, there will be less parasitic loss from the supercharger freeing up more power to be used by the wheels. That is why a positive displacement supercharger is happier moving 600CFM of air at 3psi than at 10psi.
The engine is still a 2.4L and will breathe 2.4L of air for every two revolutions, what will change is the mass of the air since we are now pressurized with the supercharger. The best analogy I can think of to visualize this is a cylinder with air in one and liquid oxygen in the other (really pressurized air ) even though both have the same volume, the liquid has a lot more mass, hope that makes sense.
Anyway the answer to the second part of your question really depends on the exhaust, but you could have an exhaust system that performs like you describe. We are still doing some testing for the intercooled supercharger to see where the real bottle necks are in the stock exhaust set-up.
I know that didn't really answer questions exactly but hopefully gives you and idea that there are a lot of variables when it comes to designing an exhaust system.
Anyway the answer to the second part of your question really depends on the exhaust, but you could have an exhaust system that performs like you describe. We are still doing some testing for the intercooled supercharger to see where the real bottle necks are in the stock exhaust set-up..
Dave,
I hope you will be able to test the redline/gxp dual outlet exhaust as well as the stock 2.4 single outlet. I suspect the redline has less restriction because it is louder, has a much larger volume muffler and two outlets. It was designed to handle 260HP in the redline/gxp (with the added restriction of a turbo), why shouldn't it work well on a stage II SC? I've read that a turbo will add about 33% more backpressure than just the muffler. There are a few of us that went this route to gain the dual exhaust look for our 2.4's and are happy with their sound and looks.
Dave,
I hope you will be able to test the redline/gxp dual outlet exhaust as well as the stock 2.4 single outlet. I suspect the redline has less restriction because it is louder, has a much larger volume muffler and two outlets. It was designed to handle 260HP in the redline/gxp (with the added restriction of a turbo), why shouldn't it work well on a stage II SC? I've read that a turbo will add about 33% more backpressure than just the muffler. There are a few of us that went this route to gain the dual exhaust look for our 2.4's and are happy with their sound and looks.
We will see what we can do to get our hands on one to test.
Next question: I assume a PD supercharger coming "on line" will have about the same boost
at any RPM (since the belt and pulley system is a constant)...but, the volume of air traveling
through the cylinders will vary with RPM, will it not?
If this assumption is correct, then for most of the engine's RPM range the "restrictiveness"
of the exhaust (within reason) should have only minimal effect on power...only at high RPM,
for example, should headers make any difference. Is this so?
Jackknife
A S/C is always spinning, and you have I think correctly identified that at idle or low torque requirement it does not come "on line" I notice this in my own S/C'd GP. The dash indicates boost in what I presume to be psi. It would be the simplest measurement, and if I am not mistaken, psi can build with rpms, but is not directly related to it. For example, when riding with my wife, the boost indicator never lights up (its a horizontal series of bars, numerically ignorant) she rarely punches teh accelerator. When I drive and ask for a little more aggression from the engine - I get it back with a varying bright light display. So I am assuming that psi will vary as well with a S/C, yet the underlying difference between s/c and t is that teh s/c usually comes "on line" quicker at any rpm.
The volume of air traveling through the cylinders at any specific steady state rpm will be almost identical among 3 engines of equal displacement; n/a, s/c, and turbo. What boost does is compress the incoming air charge, making it more dense, eliminating free space between the atoms. Since combustion process is based on a close to nominal air/fuel ratio by mass of 14.7 at normal atmospheric pressure (coincidentally identical to standard bar air pressure at sea level 14.7 = 1 atm) any increase in mass of the air must, to complete an efficient combustion process be balanced by an increase in mass of fuel. When on boost, you will obviously use more fuel per rpm than when not on boost. MPG savings on boosted vehicles come about because of teh use of a smaller displacement engine for the times when extra hp is not needed, such as steady state highway speeds.
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) even though both have the same volume, the liquid has a lot more mass, hope that makes sense.
