Sorta useless post, how much power per PSI of boost (at least, in my case)

[cygnusx1]

Maybe I'm missing something but a boost controller whether it's a grainger or electronic, does not care that you bolted on a downpipe or even run without one. It should maintain a setpoint no matter what (aside from spike). The RATE of boost climb relative to RPM and TIME may change but peak boost should always be limited by the controller and wastegate. No?

[Guest bastaad525]

Maybe I'm missing something but a boost controller whether it's a grainger or electronic, does not care that you bolted on a downpipe or even run without one. It should maintain a setpoint no matter what (aside from spike). The RATE of boost climb relative to RPM and TIME may change but peak boost should always be limited by the controller and wastegate. No?

 

I used to think this too but it doesn't seem to be the case. Someone explained the how's and why's of it pretty well, I couldn't possibly hope to re explain it, unfortunately, but yeah, going with a much larger exhaust will result in the boost pressure raising on it's own even though you didn't touch anything on your boost controller.

[Guest Loose_Screws]

It's all about flow, in and out of the engine. Consider the engine an air pump. The more air it can move, the more power it is going to make.

 

If the backpressure of the turbine (hot side) of the turbo is high, the engine is not breathing. So there has to be a balance between pressure caused by the turbo and pressure created by the turbo. While exhaust gas is pushing on the turbine of the turbo, the compressor is pushing against air while forcing air into the engine.

 

Overall, pressure is caused by restriction. So consider Flow vs. Restriction. Having flow is better than restriction, which is why some engine setups can make more power with lower boost. It is my understanding that my T3 turbo has too small of an exhaust turbine outlet to have enough flow to make major HP.

 

Consider this: If my WG is completely closed at 3,500 rpm and I am making 18psi, ALL exhaust gas is being forced through the turbine housing, restricting flow. If my WG is partially open (subsequently making only 15psi) I have less exhaust restriction and more air is actually be flowed.

 

This is my understanding of turbo systems after reading countless info on the web. I still don't understand turbo trims very well. Feel free to correct any misinformation here!

[cygnusx1]

Hey Bast! I think you can delete the "Sorta useless post...." part now!

 

Great discussion.

[wheelman]

Maybe I'm missing something but a boost controller whether it's a grainger or electronic, does not care that you bolted on a downpipe or even run without one. It should maintain a setpoint no matter what (aside from spike). The RATE of boost climb relative to RPM and TIME may change but peak boost should always be limited by the controller and wastegate. No?

 

I think I can explain this. It will leave out a few factors so don't jump on me about an incomplete picture here.

The amount the boost on a stock setup is generated by the flow though the turbine (hot) side of the turbo which is directly affected by the exhaust system. The waste gate is controlled by the pressure (vacuum) in the intake and the spring, so the gate will open a set amount for each PSI increase in the intake. When the flow rate on the exhaust side is increased the amount of pressure on the intake increases in turn opening the waste gate further which should regulate the intake pressure to the preset value, but the original setting was a balance point between the spring pressure, intake pressure on the waste gate diaphram and the flow rate of the exhaust though the DP and the waste gate outlet which has not changed. This balance point has now changed due to the better flow in the DP which will increase the efficiency of the overall system thereby causing the maximum boost balance point to be raised. At first glance it doesn't make sense but after a deeper examination you should see that it will do exactly what Bastaad525 has stated.

 

I'm not a turbo expert so if I'm wrong here please correct me.

 

Wheelman

[Afshin]

My understanding is that as you increase exhaust efficiency, you decrease backpressure and improve turbine spool up. Now since spool up is improved and the turbine spins faster, you need to bleed more exhaust thru the wastgate to keep the turbine from spooling faster and increasing boost.

In other words the turbine spools faster for the same amount of wastegate opening, which then causes the compressor to spool faster and you get more boost.

So the wastegate is still opening the same amount as before the new exhaust install, but now the turbine and hence compressor spins faster and more boost is created. Remember, the wastegate opens partially, how much it needs to open for a given boost depends on the turbo unit, flow efficiency, exhaust efficiency, downpipe....You improve efficiency and then wastegate needs to divert more exhaust from the turbine to maintain same boost.

[Guest boosted]

At this time I dont have anything to add that hasnt already been discussed . But would like to mention that this has been a good read for me and will be for others as well. Im ALWAYS interested in seeing cause and effect / before and after results even if it applies to your car and your car alone . Its and idea of what can be expected from the modifications listed .

 

Thanks bastaad525 , good read , I enjoyed it

[Guest bastaad525]

Well there you have it! Myself, I only knew that adding a larger exhaust increases the boost thru personal experience, as I saw it happen in reverse as I went from an open DP to my current setup, w/o making any changes to my manual boost controller's setting. I've also heard it said by many people on here that as they upgraded to 3" mandrel they saw boost go up 1-2psi w/o making any other changes. I never actually thought about or understood WHY it happens though... but now we have some good explanations as to the why's of it.

 

And yeah this thread has turned out pretty sweet... I expected it to only get a few replies of 'oh that's interesting' or 'well that's not the right or accurate way to look at it' or something along those lines... but it's actually turned into a pretty informative thread and a good conversation to boot

 

 

Unfortunately my own Z is now on a little 'hiatus' as I've found that my transmission has started leaking pretty badly and is leaving small puddles everywhere I park... so I'm kinda scared to drive it until getting this new problem taken care of. This REALLY sucks as I recently paid quite a bit extra when I was having the clutch replaced, to have the tranny completely resealed... only to have it leak much worse 6 mos later??? I went back to the shop I had it done at and just my luck they have either gone out of business in that last 6 months or moved (there was no sign indicating such)... odd since I know that shop has been around for at LEAST 10 years as I've taken other cars to them in the past. They'd always done good work but really screwed me over on this one So... hopefully I'll drop it off this tuesday at this Z specialty place I found, and have it back by the end of the week, sans ANY MORE F"ING LEAKS!!!! Oil leaks are the one problem that have been plagueing me since day one of my swap and is just driving me NUTS!

[Tony D]

I can personally attest to the longevity of a 1962 VW Bus Transmission from the time the oil stops dripping out (because you got sick of topping it off every week...) and the time the fourth gear synchro fails to hold it in gear is about 30,000 miles.....

 

So as long as it's drippin, it's got lube...yer fine!

 

LOL

[Guest bastaad525]

no way man I can't stand stand leaks... after all the work I've done, it just REALLY bugs me to have a car that leaks oil all over the place. I think I'm gonna be dealing with these problems the rest of the time that I own this car, and it drives me nuts.

 

Well I took it to a shop and paid a hefty chunk of change to have them pull the tranny, to find that the front ring seal of the tranny was completely fuffed, and the front cover of the tranny that holds the ring seal, was supposed to have a gasket, but instead there was just silicone, and that was leaking as well. I also had them replace my rear main seal on the engine AGAIN, and the speedo cable seals. This is after paying a large sum of cash to the LAST place that removed my trans when I had the clutch replaced, and had them reseal every gasket/seal on the trans... some job they did! I keep getting screwed.

 

Anyways... now at least there are no more puddles every time I park the car... not even a DROP on the ground so far. I had also just replaced the differential gasket like two weeks ago... so thats most of the major leaks taken care of.

 

Unfortunately the engine STILL seems to have minor leaks in a couple places... from the pan gasket (which I've changed like three times and yeah I've checked it for straightness as well... but maybe the block surface is warped?) at the rear of the engine, and possibly from the oil pump gasket as there's a small wet spot at the front of the engine as well, hard to tell if it's the pump or pan gasket... Like I said... it's gonna drive me nuts.

[cygnusx1]

Permatex #2. I swear by it. Put it on both sides of the gaskets and let it set up, assemble loosely for 12 hours and then full torque after that. The stuff is awesome. It is NOT crappy looking like silicones and hardens like licorice and stays flexible. It is holding Mobile 1 in my 120K mile Z motor without a trace.

[Nismo280zEd]

Now there's something I gotta try on my tranny... after my 5 speed went out a I picked up a local 4 spd for free.. leaks worse than my 5 ever did, and you can never tell where the dang leaks are comn' from... it's just wet period lol.

 

-Ed

[Guest bastaad525]

Well it's the oil pan again for sure... Got under the car and checked it out, it's leaking from the rear of the pan on the passenger side... hard to tell how bad as it's all over the place.

 

well... damn I'm so pissed right now. I'm so tired of chasing leaks on this thing. At least the tranny is taken care of... the engine I can top off easily unlike the trans, and it's a slow leak anyways. I've only had to put a half quart in about 3000 miles. But it's gonna bother me to no end until I take care of it. Well at least an oil pan gasket is something I can do myself at some point and with some place to work.

 

And no, next time I'm not using any silicone or anything like that... no way. As long as I've had problems with this gasket leaking, the only time I ever got it to STOP leaking was when the shop put on a gasket with NOTHING on it... then it stayed bone dry, but then when I replaced the main bearings I put a gasket with sealer on it and now it's leaking again.

 

The only thing I MIGHT use is Copper spray or if not I'll just use the gasket plain.

 

Question - Do I HAVE to use the L shaped metal bracket that goes inbetween the bolts and the oil pan itself? I have this sneaking feeling the bracket may be warped or something not allowing me to tighten down the bolts onto the pan enough and that's why it keeps leaking right there.

[jeffp]

About the dyno charts posted on Jeffp's site, one thing I wonder about, is if that '100% bone stock 280zxt' had an aftermarket boost gauge or if they were even watching what the boost was doing. It's pretty common knowledge that freeing up the exhaust by a significant amount will result in an increase in boost, w/o changing the wastegate setting or boost controller setting. I"m thinking this probably accounts for part of why in that particular case he gained such a big improvement in power and torque. Of course the bigger exhaust made a difference, I'm not doubting that, just thinking it didn't make ALL of the difference.

The test was completed on a BONE STOCK 280zxt. The only thing that was changed from stock was the exhaust.

The waste gate actuator was stock, everything stock.

Now that I have cleared that up.

The waste gate is operated by the pressure developed by the compressor side of the turbo. The exhaust turbine side has nothing to do with when the waste gate opens. It gets 7psi and it opens, regardless of what the exhaust side is doing.

the two do run hand in hand when you get to the point that the back pressure on the EXHAUST turbine/exhaust reaches a point that the restriction in flow basically is a plug to the engine breathing, when you reach the "CROSS OVER POINT" you are done, unless you can develop more boost to have a higher level of pressure then the exhaust side, the air/exhaust will follow the path of least resistance.

The waste gate, will operate @ 7psi and open under any condition, it sees 7psi on the gate it opens, now wether it acts like a added exhaust dump or becomes part of the exhaust system to relieve back pressure, and that does happen, it will STILL open @ 7 psi.

Have you ever driven a restricted turbo car? you get to a point that the engine is at its max boost, and rpm, and even if you still have throttle left on the accellerator the engine doesn't go any faster, no additional torque. The engine is choked and can not pump additional air through the pump(or engine).

When the exhaust system is restricted and reaches its point of saturation (meaning the exhaust side and intake side pressures are equil) the pump will not produce anymore power. Now keep in mind the combustion pressures and that to also aids in the flow out the exhaust as it creates an increased pressure differential on the exhaust side ONLY, that is why some say you can go X amount over the intake pressure and the pump (or engine)will still work.

Now create an exhaust side that is far less restriction then the intake side. What do you get, correct a significant increase in flow, and less restriction, so the pump in effect now is limited by the intake of the air and not restricted by the exhaust back pressure. So your waste gate STILL opens at 7 psi, but the energy expended by the pump to move the air through the system is far less, so you pick up additional working power that was before used to operate the pumping function of the pump(or engine). What you have done in effect is to move the energy produced by the pump from the energy required to operate the pump to energy that is now freed up to make the pump produce more power for the same expended amount of energy.

Does that make since?

[Guest bastaad525]

yep that makes some sense, but doesn't explain why it has been observed time and again that boost WILL usually go up 1 or 2 psi when going with a more free flowing exhaust. I think I mentioned earlier that I myself really have no idea why or how that happens, and it didn't make sense to me, but I have seen several people say that it had happened to them.

 

I know my boost went DOWN when I went from running just an open DP to my current rather restrictive setup, from just over 7psi to now running just under 6 psi if I remove my boost controller.

[tyson]

Well here's my contribution to it all...but I am running an automatic which is in somewhat poor shape, but its my contribution.

 

81 280ZXT

~45lbs of fuel pressure

Merkur XR4TI/SVO injectors

JeffP's 3" downpipe, and only a downpipe, no cat or catback.

Starion intercooler with mandrel bent piping

14psi

Plugs/wires/MSD and all that other crap that may or may not help 1-5 hp.

No air filter

No power steering or AC hooked up, just the alternator and water pump.

Electric fan

Average ~70 degree day, not humid.

 

210HP and 235 ft/lbs

 

Horsepower still fell like a rock after about 4300RPMs or so. Fuel curve stayed around 13:1

 

I'm putting a 5 speed in soon, and will again be testing it out immediatly after its in.

[Pyro]

There is a simple formula for this! It all depends on what HP you start with before turbo charging.

 

That 8-10 hp/each psi is a very general rule and doesn't work in a lot of cases. For example, if a turbo is added to a 10 hp lawn mover engine then that would general rule wouldn't work for sure. see....

 

The turbo is just a multipler of the hp an engine already has. The multiplier is the following formula:

 

(14.7 + boost psi)/14.7 = muliplier.

 

So a engine with 10 psi of boost with a base hp of 145 would make:

((14.7 + 10)/14.7)x145hp= 243 hp. (9.8 hp/psi)

 

Of course, this assumes a perfect tune.

 

The reason bigger exhaust increases hp is because the bigger exhaust is increasing the base hp. The multiper is the same. The same goes for better flowing heads, bigger cam, etc. So the trick is to turbo charge an engine with good hp to start with.

 

The formula can also be worked backwards to find base hp. Lets say an engine is making 235 hp with 12 psi of boost. Then the multipler is 1.816 which makes the base power 129.4 hp. Then if the boost is turned up to 17 psi then the hp would go to (2.156 x 129.4)=279 hp. (8.8hp/psi)

 

A quick way to figure it is, 7 psi will add another 50% hp over the NA hp, 15 psi doubles the hp.

 

So a mild 350 chevy (350hp/400ftlb) with 15psi of boost would make 700hp/800ftlbs. (23hp/psi)

 

That 8 to 10hp/psi rule works for engines that start out with 120 to 150 hp without a turbo.

 

14.7 psi is atmospheric pressure.

[Guest bastaad525]

sorry dude but that formula rarely seems to work very accurately. I've seen other formulas that give a possible range and seem to work a bit better.

 

in my case the formula is a bit off, and not because of my car not being 'in perfect tune' quite the contrary, that formula gives me a number way LOWER than what my car has.

 

Though no one knows a for sure number on what the L28ET would make with NO boost, it has to be less than 140-145hp, since that's what a regular N/A L28 makes, and the much lower compression of the ET motor must drop power at least a little bit.

 

So figure, I'm running 13psi

 

14.7 + 13 / 14.7 = 1.88

 

1.88 x let's just say 130 hp = 244hp - 15% drivetrain loss = 208 rwhp

 

obviously, quite a bit lower than the 240rwhp I'm putting down now. So...does my car have a better-than-perfect tune? heheh just jiving you, but yeah that just shows that that formula doesn't really work. You said the 8-10hp rule applies well to motors starting with 120-150hp, that's right in the range of what the L28ET starts with if you take away the stock 7psi of boost (which most people seem to forget to do), yet I saw significantly more than 8-10hp gained per psi.

 

That formula also doesn't give nearly the same increases for every 1psi increase as what I saw in my own case.

 

There are also other issues that formula doesn't cover, like the turbo's efficiency increasing or decreasing as the boost setting changes.

[Pyro]

The formula works perfect because it is based on basic science. You can't make energy from nothing. If the data that goes into the formual isn't good then the data out isn't good either. There are endless varibles when it comes to engine tuning so if there is an error with the formula there is an error with the tune or engine components.

 

Why do you take 2x drivetrain losses? 130 hp already accounts for the drivetrain losses. Why take out another 15%???

 

1.88 x 130 = 244 which is pretty close to 240.

 

So, it looks like your engine is making 127 hp (base), working the formula backwards using 13 psi and 240hp. It seems very reasonable to me.

 

If you turn the boost up to 17 psi then you could expect 274hp max (2.156 x 127 hp) if the all other functions are performing correctly (a/f ratio, turbo performance, ignition performance, cooling, exhaust, clutch. etc)

 

it works!!

[Guest bastaad525]

Pyro you need to remember when you think engine horsepower numbers, to differentiate between hp at the flywheel and hp at the drivewheels.

 

 

My motor made 240hp AT THE DRIVEWHEELS, on a dyno. That equates to about 280hp at the flywheel (the way manufacturers rate hp, so compared to the L28ET's stock 180 hp factory rated at the flywheel, at 7psi of boost).

 

I was estimating that the L28ET would make about 120-130hp at the flywheel if there was no turbo boost. A good L28 non turbo with higher compression on the order of 8 or 9:1 made about 140hp at the flywheel (and would put around 120hp to the wheels). You have to minus approximately 15% from that to get the rough hp at the wheels. When I said 130hp I was NOT already accounting for drivetrain losses. I would expect an L28ET with no boost to put close to 100hp to the wheels.

 

You are probably thinking the L28ET is good for 130hp at the wheels, because they are rated for 180hp, and it actually would put down a bit more than that (stock L28ET's make about 145 at the wheels). BUT that 180hp at the flywheel rating is INCLUDING the stock 6-7psi of boost... we're trying to estimate how much the motor is good for with NO boost. If the equation is 14.7 + 13 (the amount of boost I'm running) / 14.7 then it has to be compared to what the L28ET would make with no boost otherwise the equation is worthless.

 

 

Alternately, you could use the 180hp number and then only factor in boost added on top of the stock 7psi into your equation to try to figure the new horsepower, though I have a feeling that wouldn't be very accurate either. But lets do it anyways.

 

14.7 + 6 (the amount of boost I'm running over the stock boost) = 21.7 / 14.7 = 1.48

 

1.41 x 180 hp = 253 hp AT THE FLYWHEEL

 

Again, I'm making around 280hp at the flywheel. So actually, doing it this way gave me a number a LITTLE closer, but it's still giving me nearly 30 hp LESS than my motor is making... which by your rationale doesn't seem to make much sense. I would expect this formula, if accurate, to give me a number HIGHER than what I'm actually making, as this could easily be explained by a less-than-optimal tune or the motor's lack of efficiency. But how do you explain my motor making more power than this formula predicts? Is my car just tuned THAT good? I assure you, it's not... running mostly stock EFI with a 'bandaid' RRFPR for extra fuel, and a very erratic fuel curve... not an optimal tune, by far.