Julian@MRC

iTrader: (28)

back pressure on a FI car can lead to raised EGT's, Which can lead to knock.
Yes,
Try dataloging the Air intake temps on a TT car compared to a TN car.

Julian@MRC

iTrader: (28)

Dont get to happy, I still dont like you

BrianLG35C

iTrader: (2)

No we don't, please eloborate Sharif.

taurran

iTrader: (18)

I wasn't as concerned with the intake temps compared to the EGT's in this case.

For what it's worth, my car runs quite cool under the hood. Then again, I'm trapping all that heat in the pipes with header wrap, high temp coating, and the turbo blanket.

The only part of the intake tract that gets any warmer than the rest of the car is the intake pipe where it bolts to the timing cover of the motor. I've been trying to imagine how to change this and bolt it down elsewhere, but it's a tight fit in there and VERY close to moving belts. If not for that bolt, the intake charge pipe would be nice and cool.

Oh well, back to the original subject..

merlin3

iTrader: (4)

props to julian for taking an unbiased opinion and helping

taurran

iTrader: (18)

Hah.. well I don't think anyone has "helped" the issue. No one has yet to explain what happened to Jet's piston. I'd be surprised if anyone ever agreed on the cause.

Julian@MRC

iTrader: (28)

Are you for real?
You intake temps are probably more critical than EGT's.Thats the whole point for using an intercooler on a F/I car. The cooler the "intake charge" the denser the air,and less prone to detonation,which allows one to run more timing for more power. The higher the intake temps,the less dense the air,the hotter air is more prone to dtonation and pre-ignition,resulting in knock and higher EGT's. This would explain the inability to run lots of timing advance on the TN kits.
They go hand and hand when tuning a car. But the lower the Intake temps, the better...

taurran

iTrader: (18)

I know how a cool intake charge allows for more power, thanks.

You're getting me wrong here (once again). I was more concerned with the earlier correlation between backpressure and knock, and why this would have been a reason to tune Jet's car in the manner it was. This applies to others on this forum and might be a good bit of info. However, it's all heresay and I don't think I'll find out until we tune first hand.

Julian@MRC

iTrader: (28)

BACKPRESSURE CAN CAUSE A CAR TO KNOCK... As I have previously stated and explained why.

kostat26

iTrader: (41)

Loving this thread.

MIAPLAYA

iTrader: (3)

No need to apologize. If this is your experience so be it. Let me start by saying I am not knocking anyones ability to tune or their experience with this kit at high boost but I'm just curious how a back pressure issue can occur and be more drastic on a low compression motor as opposed to a high compression motor. Let me explain, (again this is not a flame I'm just examining both sides) Performance Factory has a car with the Turbonetics kit running 14 PSI of boost with an upgraded Tial wastegate dumping to atmosphere. The motor is stock. That motor is making power to 6200 rpms from what I can see and does not exhibit the drastic loss in power in the high end we have seen in the past. On the flip side we have Jet's car which is running a Turbonetics kit also at 14 PSI and also with a larger Turbosmart wastegate also dumping to atmosphere. Jet's car does experience a power loss in the top end. Now it has been stated that as a result of increasing back pressure at higher boost levels due to either the downpipe design or turbine section sizing, timing had to be retarded to prevent knock. The explanation appears to be that back pressure is causing some efficiency issues in the turbine section and also that the compressor is out of its efficiency range at this boost pressure. Lets look at the back pressure issue first. What are the significant differences in the two motors that could cause back pressure to be an issue in one car and not another. I think its clear to everyone the compression or state of a motor have little to do with backpressure as encountered/measured at the turbine section. If the downpipe is the same between both cars and both cars have a MUCH larger wastegate venting unneeded exhaust gas to atmosphere the only factor which could affect backpressure that is left if the remainder of the exhaust system. I don't know what exhaust AJ has or Jet has for that matter. It is possible that the exhaust system could be the only delta in backpressure here although if I recall Sharif you did try dynoing Jet's car with no exhaust which should have negated that as a variable. I think this question needs more information from the shops.

Compressor blowing "hot air" aka out of its efficiency range. Lets assume the ambient pressure is 14.7:1. This should be close to accurate being that Jet is in South/Central Florida and most of Florida is below sea level anyways. This is the compressor map for the 60-1 compressor wheel found in the 350Z Turbonetics kit:



Assuming an ambient pressure of 14.7:1 at 14 PSI the pressure ratio would be roughly 1.95. Plotting that on the compressor chart puts us in the last band of the island at 550 Crank HP (roughly based on 55 lb/min of air flow). Jet's car was making about 460 WHP with an added 15 % for drivetrain loss we see that we are even a little bit closer to the center of the island and in the second outermost band of efficiency. What does this all mean? Well the compressor is reaching the limit of efficient air flow it can provide at that pressure ratio with that amount of required air flow. Rasing boost to 16 PSI we would se similar power but more squarely in that band of efficiency. My take is that on this car and this motor the 60-1 compressor should be more then capable of flowing its full 57 lb/min within the efficiency band assuming the Ve of the motor is decent (VQ35 is has over 100% Ve) and the tuning is set this way. Again I am not disputing what people have done and seen. I wasn't there they were. I can see clearly that it is possible for the compressor to start leaving the efficiency island above 16-18 PSI on THIS motor.

The one item I would like some more clarification on is what deltas could present backpressure sufficient enough to maul the power band as it has been reported on one car but not be a factor on another despite similar exhaust/wastegate setups. For the last time, I'm not questioning anyones ability here I'm just genuinely interested in this as it seems to be an anamoly I can't explain. I won't claim to be an engine expert as I am not but I know enough that backpressure can't be caused by compression.

taurran

iTrader: (18)

I KNOW IT CAN, but I was interested in IN THIS SPECIFIC CASE, it absolutely did.

Get it?

Oh well, at this point I think I'd be better off talking to this pencil lead sitting on the table here. I've gotta run anyway, I'll check in on this later.

DomZ

Loud Noises

No but seriously, can't we keep things...um..not so personal?

Stailey

wow, thats some big font

chris'smax

iTrader: (5)

+1 backpressure can lead to greater thermal loads.


BTW Julian did you get my pm?

TENGAI

iTrader: (5)

All of this is why I'm going to be personally involved in my own build. If something goes wrong, there's nobody to blame...

Everybody f'ks up. No matter what you do to prevent it otherwise. What or who's fault it is at this point is all lost in this BS arguing. Somebody just needs to tear down the engine and find out what the problem really is. Then it's just a matter of fixing it and getting back on the road stronger than before... Unfortunately, taking risks with FI means that you may end up on a losing side of the table. No matter what you do to reduce the risk (i.e. built engines, finding the right shop for tuning / install, etc.) there's always a chance that **** isn't going to work out.

Good luck man.

Julian@MRC

iTrader: (28)

Mia,
You and I both know there are long winded technical expenations from an engineers stand point of what something "SHOULD" or "SHOULD NOT" do....And there are REAL WORLD scenarios of what it "actually does".
Your long winded explenation would imply that both myself and Sharif do not know how to tune a TN kit..
YOu know it yourself the 38mm wastegate dump back into the piping causes a restriction as well as causes the kit to notoriously overboost.

Sharif@Forged

iTrader: (92)

Mia, you bring up some good points. One thing to remember, is that AJ's car is tuned on a dyno jet. The 2500lb inertia drum results in less taper towards redline (due to the heavy drum free spinning at high speeds), which gives the appearance of powering being made further in the power band.

On our Dyno Dynamics, a constant and linear load is applied to the rollers, so you have a much more precise indication of what is actually happening at higher RPM, once the rollers are spinning at 120mph or more.

And can someone link me to AJ's dyno chart? IIRC, it was really choppy, and all over the place.

MIAPLAYA

iTrader: (3)

Clearly you didn't read beyond that line in my post. I stated no less then 4 times I'm not questioning you or Sharif or your ability to tune a car. READ MY POST. I actually stated that I can see how the compressor could be nearing the limit of its efficiency at 14 PSI. If you still don't get it that means I'm agreeing with your earlier post that at 14 PSI the turbo is near the end of efficient air flow. Stop being so damn defensive and read. My remaining question is what part of the motor could cause a backpressure issue that prevents power to redline in one car but not another all other things being equal. I am not arguing real world vs lab. I am asking YOU and the OTHER SHOPS what is the delta. What in a low compression motor would cause increased back pressure rates over a higher compression car? If you can't answer this then move on. I'll say it again, I AM NOT QUESTIONING YOUR ABILTIY TO TUNE A CAR. I AM NOT QUESTIONING SHARIF'S ABILTIY TO TUNE A CAR. I AM NOT QUESTIONING JEREMY'S ABILITY TO TUNE A CAR. I AM ASKING WHAT ASPECT OF A LOW COMPRESSION MOTOR WOULD CAUSE TWO CARS WITH THE SAME COMPRESSOR AT THE SAME PRESSURE RATIO WITH A SIMILAR EXHAUST SYSTEM TWO HAVE DIFFERENT BACKPRESSURE VALUES. I hope that is clear enough for you now.

Audible Mayhem

iTrader: (48)

i just want to appologize to sharif, sorry for saying anything to discredit you. i am a good honest person and get caught up in this drama sometimes. its all just stupid. sometimes you have to back up and take a look at the whole picture.

we are pretty much the hardcore racing metal militia of the Z community, its got to be the fastest, loudest, lowest thing around, we let our arrogance overtake our professionalism sometimes, nothing good comes from name calling and so forth...




of course we are rival shops, we will just let the cars performance tell from here...