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MrWOT
01-22-2010, 07:31 PM
So, the recent acquisition of my 87 Conquest and it's subsequent tiny hotside on a big engine brings to light a topic that is so near and dear to my heart. Backpressure.

For valve overlap to work properly, the inlet pressure needs to be higher than the exhaust pressure, or it's going to try to revert (flow backwards, exhaust out the intake) on overlap.
You might make a little more power, because your average cylinder pressure will still be higher (called BMEP, brake mean effective pressure) from all the fuel, but at the cost of more wear and tear on the engine and the turbo, loss of mileage, and higher coolant and oil temps (it gets REALLY hot in the chamber when there is a large volume of exhaust still present under hard boost, hence the overfueling to keep things under control).

The 3S head flows very well up to a half inch of lift, well above what HKS offers. I realize people are going to be stuck with the choices we already have, because custom grinds are expensive.

Back to back testing of a 3S with stock, and all avail HKS grinds, logging EGT, a/f, ebr (exhaust backpressure ratio, ratio of intake manifold pressure:exhaust manifold pressure) and bsfc (brake specific fuel consumption, the measure how how efficiently you are making power, fuel per horsepower.) would really paint the picture, especially swapping different turbine housings on a t3/t4 frame (like .48 -> .63 -> .86 a/r )

So, you need to MEASURE your backpressure to know what to do to make your car go fast. So go do it!

Shadowlife25
01-22-2010, 09:42 PM
Perhaps an explanation on how to perform the test? :)

MrWOT
01-23-2010, 12:39 AM
Drill/tap exh man for 1/4" NPT like you would for a EGT probe, get a min of a 3ft piece of hardline tubing (fuel/brake) with said size fittings (longer is MUCH better, get the longest one you can up to 6-7ft, dampens pulses). Bend the hardline so you can get to it and put a piece of vac line on it, use a good fuel injection (bolt/nut) style clamp. Regular vac/boost gauge that will do 30psi. Higher if you are running over 16psi. The hardline is important to insulate the gauge/hose from both heat, and pressure spikes that will screw with the gauge.


edit: You know, I bet you could read it right off the EGR feed tube, never tried that though.

Freshnicity
01-23-2010, 02:48 AM
You want your intake manifold pressure to be higher then your exhaust backpressure right?

But for overlap to work right, how much higher does the intake man. pressure need to be over the exhaust backpressure? Thats what I dont understand

88st165
01-23-2010, 04:16 AM
I did this when me and my buddy build a turbo kit for my car last year. We tapped 1/8npt into the turbine housing on a garrett turbo bc there was plently of room. Ran copper tubing as it dissipates heat much faster so we didnt have to worry about anything touching it would melt (all the way up to the cowl) then rubber hose into the cabin. We had the luxury of having a hand held pressure transducer that converted the pulses directly into a voltage. We didnt measure the pressure on the intake side but we did gather mass flow rates. I dont remember where the info we got went :(

Shadowlife25
01-23-2010, 08:11 AM
This interests me.

I will have to try it soon.

WOT, you think the EGR feed would be sufficient for this?
If so, a simple threaded fitting that's the same as the EGR valve would work fine and eliminate the need for drilling, no?

joe's gt
01-23-2010, 08:45 AM
Data log with an Arduino! I got mine recently and am learning how to use it. I plan on doing the intake system at the start using thermistors and a differential pressure sensor. I believe, however, that finding a pressure sensor that can actually withstand the heat of the exhaust might be a little bit of a challenge.

Shadowlife25
01-23-2010, 08:59 AM
Joe, could you build me one of those things? :D

Use an automotive grade sensor and it should be fine. The one that actually goes into the EGR is likely perfect, and it is a simple 2 wire connection.

joe's gt
01-23-2010, 07:03 PM
Joe, could you build me one of those things? :D

Use an automotive grade sensor and it should be fine. The one that actually goes into the EGR is likely perfect, and it is a simple 2 wire connection.

haha, you don't got to do any building. Its easier to just by the pre-built board and then set it up. It takes like 5 min to set up. The hard part is the coding. I have a lot learning yet to do regarding that.

I personally just think trying to look at a mechanical gauge while driving to monitor back pressure is incomprehensive. It would be much more effective to have sensors logged electronically with rpm which would allow you to see back pressure as it related to rpm and you could also use the gear ratios to relate back pressure to speed.

My only concern with those automotive pressure sensors is the time constant. If it has a slow time constant, it might never reach its peak value before you let off the gas to shift gears in the lower gears. The only way to tell really, is to have the sensor and test the response time. Typically they don't give you that response time information. But in general, I think the 2 hoses and pressure sensor is good enough for government work :p

Klue
01-23-2010, 09:12 PM
thought i might throw a couple things out there♠
a. spent gas does not have the effect your describing on the engine. Its quite the opposite, spent gas actually cools the combustion charge, and dilutes its creating a more eco friendly burn HENCE EGR (exhaust gas recirculation). Power wise it doesnt help, but its actually the exact opposite your describing. The engine runs cooler, and produces less NOX which is what EGR was designed to alleviate.

b. 99% of STOCK cam'd turbo cars have VERY VERY little overlap because it again works quite the contray to what your describing. When you have a overlap on a turbo car your pressure from the intake charge goes OUT the exhaust valve during the overlap cycle.
To support what im saying is the fact that if your turbo car( this applies most to turbo because of the high intake pressure) has more overlap than it needs then your essientally pushing your Air fuel mix out the ehxuast valve to get burnt as it hits the super hot turbo, they have a name for this too its called ANTILAG/STAGING/AFTERBURN or 100 other names.

back to the discussion, for a turbo car its perfectly accecptable to have a high back pressure between the exhaust valve and turbo as this is what spins the turbo, the pressure being built on this side. Now if you have back pressure on the opposite side of the turbine(downpipe side) THEN you have some back pressure issues. It would be interesting to monitor this as I dont have any really numbers to add to my section here, but I think its more energy than its worth.

MrWOT
01-23-2010, 09:33 PM
I'm sorry, you don't know what you're talking about.

EGR doesn't cool it physically at ALL, it slows the reaction speed because it's supposedly non-reactive (inert) gas. It's similar to water injection. (btw there is such a thing as cooled EGR, but we don't have it)

As for overflow on overlap, that would only occur if you had high boost at way lower rpm than the cam was efficient at. Like if you had 272s on a stock ct26. And then you'd blow you shit up because of the SUPER HOT, SUPER DENSE exhaust gas flowing backwards and staying in the chamber, triggering preignition and or detonation and melting your pistons/blowing gaskets. With a big turbo, you're not on boost at low rpm, not an issue.

Why do you think things with anti-lag are made from things like inconel? Even then they don't last long, it's the heat..

What you are talking about only occurs on supercharged engines because they are always on boost, even under the cam efficiency band. And it doesn't matter, because then exhaust pressure is always lower than intake pressure, so it just wastes gas and raises emissions.

edited for spelling.

Klue
01-24-2010, 02:57 AM
before you go throwing around talks like I don't know what im talking about you can easily do some reading on the internet.
a.I dont know how you minsunderstood, BUT egr does cool the combustion event. look it up.
b.overflow on overlap what are you talking about? have you ever heard a N/A motor with overlap on idle blap blap blap pop, you wonder why it doesnt do that at high rpm?
c. super hot and super dense? thats gr10 physics and a oxy moron, as well as being impossible. incase you were sleeping in that class, as a property of matter when something heats it expands, making it less dense.
d. i guess you could bring up that point to the guy who drives a ct20 272 cammed mr2 to track events all day he certainly hasnt melted anything.
c. the anti lag im talking about is not air injection like you have seen pictures about, im talking about creating a combustion event outside of the chamber to power the turbo.

Im trying to add something to your topic, dont try to bash me man! especially not with things like i dont know what im talking about. dont let my post count fool you, i got a pretty good understanding of how these things work :)

joe's gt
01-24-2010, 04:40 AM
I will throw my 2 cents now. lol

a. I think you guys both misunderstood each other on the EGR thing. Klue made it seem to MrWOT (and to me at first) as if he was saying that the EGR cooled the charge mixture when you both meant to say that the EGR actually dilutes the mixture which causes a cooler combustion event and therefore less NOX.

b. don't have enough experience with this to have an opinion

c. I agree with MrWOT on this one. While gases do expand and become less dense when they heat up, there is one variable that is being forgotten...volume. the exhaust gases are being forced into a much smaller volume within the exhaust manifold and before the turbo which actually makes it very dense. So I agree that the exhaust gases are dense before the turbo. As to what effect this has with cams, pressures, etc., I don't have enough practical experience to have a valid opinion.

d. Its true that anti-lag greatly decreases longevity. Is the ct20b exhaust housing less restrictive? If it is, then that is why he is not blowing shit up cuz there is less back pressure. If it isn't any less restrictive than the stock ct26, than great for for him, but I still think longevity would be greatly compromised. If its a track car tho, he probably cares less so its not even an issue.

e. This is pretty much as I understand it as well. Its a continuing combustion event after the cylinders. However I don't know whether its actually ignited afterwords or just an already started combustion event that continues past the valve and into the manifold/turbo?

MrWOT
01-24-2010, 08:32 AM
before you go throwing around talks like I don't know what im talking about you can easily do some reading on the internet.
a.I dont know how you minsunderstood, BUT egr does cool the combustion event. look it up.
b.overflow on overlap what are you talking about? have you ever heard a N/A motor with overlap on idle blap blap blap pop, you wonder why it doesnt do that at high rpm?
c. super hot and super dense? thats gr10 physics and a oxy moron, as well as being impossible. incase you were sleeping in that class, as a property of matter when something heats it expands, making it less dense.
d. i guess you could bring up that point to the guy who drives a ct20 272 cammed mr2 to track events all day he certainly hasnt melted anything.
c. the anti lag im talking about is not air injection like you have seen pictures about, im talking about creating a combustion event outside of the chamber to power the turbo.

Im trying to add something to your topic, dont try to bash me man! especially not with things like i dont know what im talking about. dont let my post count fool you, i got a pretty good understanding of how these things work :)

I'm not trying to bash you, but the things you're saying aren't accurate, and you stated them as if you are very well researched on the subject while telling me I am wrong, putting me on the defensive? sorry if I came off as an ass.

a. My problem is in your wording "cools the combustion charge", "cools the engine", this isn't accurate. It makes the "event" cooler, as in, lower peak pressure/temperature, because that is where NOx forms. But it will heat the crap out of your intake charge. The reversion we are talking about, cylinder backflow from the exhaust manifold, isn't like EGR. And taking really hot exhaust, then compressing it with the piston, puts a serious heat load into the piston.

b. It's not because it's going out the exhaust, some of if is, surely, but you're hearing that because having too much duration at low rpm will go far past the point of cylinder fill. The cylinder gets filled, the intake is STILL open, and the flow backs up.

c. Joe got it, you have limited volume, and flow WILL go towards the point of least resistance, be it the turbine, the wastegate, or your cylinder with the open intake valve.

d. show me, seriously. No way he isn't DUMPING fuel on it to keep it alive. Pif anyone is going to track a setup with 272s on a hotside that small, it would have to be water injected, alky, something exotic, no way he keeps it alive on pump gas.

e. I understand what you meant perfectly. Anti-lag systems are prohibitively destructive. Hence why they are only used in racing events, where people have budgets, big ones.

MrTurrari
01-24-2010, 11:31 PM
The reversion we are talking about, cylinder backflow from the exhaust manifold, isn't like EGR.
Yes it is exactly like EGR just a different path to get there. They use it in VVTI engines to do the same exact thing.


And taking really hot exhaust, then compressing it with the piston, puts a serious heat load into the piston.
Although it does transfer a little more heat into the piston during compression it is not as much heat as the reduction from having it there reducing the amount of burnable air/fuel mixture. The average temperature goes down so it is not an issue. The piston actually ends up having to transfer less heat away into the cooling system when you have exhaust gas reversion.


b. It's not because it's going out the exhaust, some of if is, surely, but you're hearing that because having too much duration at low rpm will go far past the point of cylinder fill. The cylinder gets filled, the intake is STILL open, and the flow backs up.
Uhhhmmm what? :D You don't get popping sounds because the cylinder is full and the air stops flowing. That happens every time the valve shuts. It couldn't be a very loud sound either with the little amount of energy involved. The sound comes from unburned mixture being ignited in the exhaust manifold and that rapid expansion makes a pop sound. If you are hearing the noise coming out your intake it is because both valves are open when this happens.

It has been mentioned but I think people are not putting enough weight on something, you can not meaningfully talk about back pressure without also talking about RPM and power band. An engine is a dynamic system and all engines, the way they are designed, will have places where the pressure in the exhaust is significantly greater then what is in the intake and vice versa. It's unavoidable in both NAs and turbos. For turbos specifically you usually want and need that while the turbo is spooling to get it going as quickly as possible. The reversion is a side effect but it in no way hurts the engine. It has a plus side too because it cools the cylinder in preparation for going to full boost and decreases the chance for detonation.

On the other side of the coin when your turbine starts to restrict flow in the upper RPMs if you're still in your power band, well you will be slower. :) That happens because it reduces scavenging (yes turbos do that too) and that can even become reversion if it is bad enough. Waste gates tend to keep exhaust pressures from getting too high though and keep that from happening unless they are themselves too small. It can also get bad if you have a poorly matched compressor and turbine.

I believe that is what the point of this discussion is, to size the turbo to itself and to the engine. I think that pressure readings could be valuable in doing that if you also look for where in the powerband they are occurring. High pressure when you are spooling is good (or at least not bad). It means it spools faster. High pressure at redline, again that can be ok because you picked one that would spool quickly. High pressure at peak torque or peak HP, very bad, your turbo is too small, too big, the compressor and turbine are not properly matched or your wastegate is too small.

You are not likely to blow an engine because of too much back pressure and it really isn't going to increase wear and tear on the engine. Toyotas stock engines pretty well demonstrate this because they intentionally put smaller turbos to spool quickly and make midrange torque. Now using higher duration cams with the stock turbo... I would worry about the turbo not the engine because you are going to be spinning it faster and you might have the possibility of surging. It's like putting the same turbo on a bigger engine.

MrWOT
01-24-2010, 11:56 PM
Yes it is exactly like EGR just a different path to get there. They use it in VVTI engines to do the same exact thing.

True that that is done in VVT engines, but show me a single turbocharged engine that uses said strategy?

I'm not talking about EGR, which is irrelevant to this thread because EGR doesn't operate under boost, for a bunch of good reasons, and even if it did, having the exhaust flow backwards will cause several other things that simply rerouting exhaust won't and can't do. That is what I mean :P

OK, now that EGR has NOTHING to do with this thread again :laugh:

If you've got a turbo making say, 10psi at 3k. At 7k your exhaust manifold pressure is more than likely going to be more than twice your inlet pressure, EGT is going to be well over 1400F. The fact that it's mostly inert is the only reason things don't go downhill much more rapidly because of the retardation effect.

You show me a motor with a small hotside and big cams, and I'll show you scuffed bores/pistons. No way you can combat coefficient of expansion, especially with prolonged use :ohnoes:

As for the sound thing, he's not talking about popping, he means a loping idle :p (i think)

MrTurrari
01-25-2010, 03:57 AM
Since Toyota stopped making turbocharged cars when they went to VVTI there aren't any, however there is no reason not to and I'm sure they would have had they continued to make turbos. It would be an awesome mating for total control over turbo spooling and top end power.

EGR does work under boost just not WOT. When you cruise down the highway you are still under boost even if that boost doesn't register as a positive pressure. Ok that one may be semantics but it is true. The turbo is raising the manifold pressure and the EGR is open. Anyway what are those things that putting exhaust in through the exhaust valve rather then into the intake manifold does? Other then going through the exhaust valve is a little trickier to do and gives you a cleaner intake. :)

Your logic is flawed with the pressure in the manifold. The pressure will be whatever is needed to keep the intake side at your set boost point. The wastegate bleeds off the rest. Pressure in the exhaust manifold is going to vary because the turbo has one efficiency curve and the engine has another. If the hot side is too small you will reach a point where it can't keep the boost at the set pressure, the wategate will close, boost will fall and the exhaust manifold pressure will rise. This happens with the stock 3sgte and ct-26 when you try to run 15psi. It is not by itself harmful to the engine.

Again you will generate less heat when more exhaust gas remains in the cylinder not more. You are retaining more heat but also producing less on the next event. Using a big cam with a small hot side will just keep you from making the power you could have made if you would have sized it right. Your EGTs will be lower because less energy is being used and I will guaranty you will never get close to 1400F at WOT. These engines can take 1450-1550F for extended durations anyway.

Freshnicity
01-25-2010, 04:46 AM
Since Toyota stopped making turbocharged cars when they went to VVTI there aren't any, however there is no reason not to and I'm sure they would have had they continued to make turbos. It would be an awesome mating for total control over turbo spooling and top end power.

EGR does work under boost just not WOT. When you cruise down the highway you are still under boost even if that boost doesn't register as a positive pressure. Ok that one may be semantics but it is true. The turbo is raising the manifold pressure and the EGR is open. Anyway what are those things that putting exhaust in through the exhaust valve rather then into the intake manifold does? Other then going through the exhaust valve is a little trickier to do and gives you a cleaner intake. :)

Your logic is flawed with the pressure in the manifold. The pressure will be whatever is needed to keep the intake side at your set boost point. The wastegate bleeds off the rest. Pressure in the exhaust manifold is going to vary because the turbo has one efficiency curve and the engine has another. If the hot side is too small you will reach a point where it can't keep the boost at the set pressure, the wategate will close, boost will fall and the exhaust manifold pressure will rise. This happens with the stock 3sgte and ct-26 when you try to run 15psi. It is not by itself harmful to the engine.

Again you will generate less heat when more exhaust gas remains in the cylinder not more. You are retaining more heat but also producing less on the next event. Using a big cam with a small hot side will just keep you from making the power you could have made if you would have sized it right. Your EGTs will be lower because less energy is being used and I will guaranty you will never get close to 1400F at WOT. These engines can take 1450-1550F for extended durations anyway.

Heres a question regarding that. Might be a stupid one, if it is, my bad.

When your running camshafts with a longer duration and a higher lift then factory, does that allow you to flow more air into the combustion chamber then the factory cams?(im guessing yes).Edit: I mean fill the combustion chamber with more air/fuel mixture

So if your running the same hot side on the CT26, with the larger cams(lets say 272). Whats the back affect of that exactly? Your flowing more air, in the same sized hotside, would it become restrictive and allow exhaust gases to be forced back into the combustion chamber and not letting enough "fresh" air/fuel mixture in?

Ehh sorry, trying to better understand what you and WOT are talking about.

joe's gt
01-25-2010, 07:01 AM
Heres a question regarding that. Might be a stupid one, if it is, my bad.

When your running camshafts with a longer duration and a higher lift then factory, does that allow you to flow more air into the combustion chamber then the factory cams?(im guessing yes).Edit: I mean fill the combustion chamber with more air/fuel mixture

So if your running the same hot side on the CT26, with the larger cams(lets say 272). Whats the back affect of that exactly? Your flowing more air, in the same sized hotside, would it become restrictive and allow exhaust gases to be forced back into the combustion chamber and not letting enough "fresh" air/fuel mixture in?

Ehh sorry, trying to better understand what you and WOT are talking about.

That's the way I interpreted it Will. While larger duration is good to a point, there is also the point where the overlap is too long resulting in exhaust gases in the combustion chamber, diluting the mixture, resulting in less power. The increased heat caused by the exhaust is actually offset by the lower heat it causes in the combustion event. That's just the way I interpreted it.

However, I am confused by the too much back pressure causing the turbo not being able to keep the set amount of boost and the wastegate actually closing? Can you possibly explain that MrTurrari? I guess I don't fully understand how that is happening.

Freshnicity
01-25-2010, 07:35 AM
That's the way I interpreted it Will. While larger duration is good to a point, there is also the point where the overlap is too long resulting in exhaust gases in the combustion chamber, diluting the mixture, resulting in less power. The increased heat caused by the exhaust is actually offset by the lower heat it causes in the combustion event. That's just the way I interpreted it.

However, I am confused by the too much back pressure causing the turbo not being able to keep the set amount of boost and the wastegate actually closing? Can you possibly explain that MrTurrari? I guess I don't fully understand how that is happening.

Same question. You'd think if the wastegate closed, not letting some exhaust gases bypass the turbine you would overboost and possibly experience compressor surge if its not vented correctly? I dont know, dont know enough about it. MrTurrari an WOT let us know

MrWOT
01-25-2010, 06:11 PM
The difference in egr and reversion is the temperature and percentage/dilution of cylinder volume filled. egr empties to the intake manifold, where it disperses quickly because it isn't a large percentage of the total gas volume.

Reversion, on the other hand, is a much larger percentage of the cylinder volume than egr, because it's going to continue to flow backwards until equilibrium is reached, if it ever is, or until the valve closes. It lowers vac in the cylinder, lowering the pressure differential across the intake valve. Running hard boost? Fuel will still be burning on exhaust and will give off it's heat there, it's not still going to be burning by the time it reaches the intake manifold on egr. Heats everything in the chamber.

Apples to oranges, the fact that they both involve exhaust getting back into the cylinder is pretty much all they share in common :P You would need extremely precise vvt control to use the vvt kind of system with a turbo exactly because of the pressure differences you're talking about at different rpm depending on load.

You may use less heat for work, but you're still going to put out plenty of BTUs, and when those BTUs aren't converted to work on the piston, they dump their heat right into the gas, unless you're actually not able to burn as much fuel, which isn't the case for the kind of volume EGR provides, or even reversion unless you've got some crazy cams, will still be plenty of room after the exhaust is closed, afterall, it's only on overlap around ~TDC. It will still burn, just won't burn well and it will be hot. It's a power problem because the intake stroke starts on the exhaust stroke. You need the flow to be moving the right direction with the exhaust still open to make power because of the inertia of the charge, the more inertia it has, the more it will continue to fill the chamber after bdc while the valve is still open and the piston is rising. You have a certain amount of valve curtain time with a cam, fill time is so limited per cycle at high rpm, it matters.

Take a look at this. edited: (Really, read that, pretty good thread)

http://74.125.155.132/search?q=cache:YIH1bJGlFJ8J:www.yellowbullet.com/forum/showthread.php%3Fp%3D1507803


4) If you are now relying on exhaust manifold pressure to move ex gas out the WG, you are probably increasing ex mani backpressure. Great, you have boost under control now, right? A higher exhaust manifold to intake manifold pressure ratio will produce bad scavenging on the exhaust stroke, and contamination on the intake stroke, especially on high overlap cams. The higher the backpressure, the lower your detonation ceiling becomes for your given fuel. It also means having to run less timing advance.

joe's gt
01-25-2010, 07:21 PM
So what I am seeing is that there are 2 conflicting opinions here? MrTurrari states that exhaust gases left within the cylinder actually create a diluted mixture and a cooler combustion event and therefore less power, while MrWOT states that the dilution of exhaust gases left in the cylinder are insignificant to the volume of the mixture and the real problem lies in the immense amount of heat causing a lower detonation point and the need for less timing advance and therefore less power. I guess I have to do some reading of my own. Either way everybody is in agreement that there is a loss of power, but the method by which there is a loss of power seems to raise a difference of opinion.

MrTurrari
01-26-2010, 01:57 AM
Heres a question regarding that. Might be a stupid one, if it is, my bad.

When your running camshafts with a longer duration and a higher lift then factory, does that allow you to flow more air into the combustion chamber then the factory cams?(im guessing yes).Edit: I mean fill the combustion chamber with more air/fuel mixture
Not a stupid question at all. The simplified short answer... in theory yes but it depends.

You have to add RPM into the equation to really understand what is going on. With lift, depending on the ramp speed of the cams and shrouding of the valve in the combustion chamber, you are increasing the curtain area for parts of the intake cycle effectively making a bigger hole into the cylinder and in some cases actually increasing duration by a little. This bigger hole does have the effect of increasing cylinder filling at most RPMs but it can also amplify the negative effects of longer duration cams at low RPMs. Also you may have RPMs where other things are going on that keep it from filling as much like reversion or an incorrect runner length for the cams and RPM you are targeting.

With duration you are changing the resonant frequencies of the engine so that you are basically filling the same amount per cycle, just at a higher RPM. This happens because it increases the time available for the air to equalize into the cylinder at any given RPM. Now of course there are all kinds of other things effecting that like piston speed and the flow through other parts of the engine but generally it is true that an increase in cam duration moves the whole torque curve to the right.

In addition, that increased piston speed actually turns out to increase cylinder filling as well because it creates a greater force to move the air in. Which is one reason why cams not only move your torque peaks to the right they also increase them. And if you can get the other parts of the engine to resonate at the same frequency as the cams... well you get an even bigger increase.


So if your running the same hot side on the CT26, with the larger cams(lets say 272). Whats the back affect of that exactly? Your flowing more air, in the same sized hotside, would it become restrictive and allow exhaust gases to be forced back into the combustion chamber and not letting enough "fresh" air/fuel mixture in?

Ehh sorry, trying to better understand what you and WOT are talking about.
Again you have to look at RPM and flow. A hotside that is restrictive at one RPM is not necessarily at another lower one. The CT-26 flows really well from 3000-5500rpms on a 2.0 liter but the 272 cams haven't come into "phase" yet at those RPMs. The turbo builds back pressure and causes reversion and because of the overlap gives you even less power to spool the turbo.

When the cams do come into phase at around 5500rpms you have the opposite problem. Now the engine wants to breath but the small turbo can't flow any more without a exponential increase in pressure. It basically can't keep up with the demands of the engine so the boost on the cold side starts to drop, which causes the wastegate to close in an attempt to keep the pressure up and you get the problem MrWOT is describing. High exhaust manifold pressure and low intake manifold pressure. The part we are debating is whether or not the reversion it causes is harmful to the engine. In respect to that it is important to remember that it is much harder for reversion to happen at higher RPMs. You need a lot more pressure difference because the overlap period is so much shorter.

Freshnicity
01-28-2010, 06:33 AM
Makes a lot more sense now.

Would it be a better choice to then either stick with 272 cams, and get a turbo with a "less" restrictive turbine side to be able to flow up in the higher RPMs for when the cams have come into effect?

Or simply stick with the CT26 and get cams that are less aggressive, little more mild to fit into the CT26s flow range?

Id be interested in seeing someone from here measure there EBR to there MAP(think its MAP right?) on a stock 3sgte. Anyone ever done it?

MrWOT
01-28-2010, 06:16 PM
CT26 would be in it's best efficiency on 256s (for what's available anyway...)

joe's gt
01-29-2010, 01:24 AM
Id be interested in seeing someone from here measure there EBR to there MAP(think its MAP right?) on a stock 3sgte. Anyone ever done it?

From my research regarding differential pressure sensors for monitoring pressures of the intake, I think the difficult thing is finding an affordable pressure sensor that could withstand the temperature of the exhaust gas.

Freshnicity
01-29-2010, 06:35 AM
From my research regarding differential pressure sensors for monitoring pressures of the intake, I think the difficult thing is finding an affordable pressure sensor that could withstand the temperature of the exhaust gas.

Like Mario said, EGT sensor. Or something along the lines. They DO have to have something, someones measured there EBR before.

All this information is really helpful. I want to learn all of this stuff. Trying to take advantage of all your guys knowledge to grow my own lol.

Also thinking of swapping a 3s into my Celica after the 2 is running, so the information on the CT26 and cam choices is a big help

joe's gt
01-29-2010, 07:16 AM
I'm sure its been done before, but the question is cost. A temperature sensor is an ENTIRELY different sensing element than a pressure sensor and can withstand higher temperatures. I personally haven't seen an "affordable" pressure sensor that can measure in an environment with that amount of heat (although I haven't really looked in depth).

Yes, its a simple concept to measure it, but the problem lies in finding a sensing element that can actually withstand the intense heat. You HAVE to make sure the temperatures are within the sensors operating conditions or your results will be inaccurate and meaningless.

The complication lies in the cost of the measurement device itself. Look around at pressure sensors and mechanical gauges and see what their operating conditions are. My assumption is that most, if not all, affordable gauges won't be be able to operate under exhaust gas heat conditions.