Losing boost at 6400rpm. Help!

[jdub]

Jay - 1)Is 6400 RPM about where your torque peaks on the dyno?

2)- Did you have the exhaust ports ported larger?
3)- Are you running oversize valves?

4)-Do you have an EGT gauge...if so, what does it read when this happens?
5)- Specifically, are you seeing an EGT increase as you approach 6400 RPM that continues as you go to redline?

6)- What is the exducer size (turbine wheel) for the PT67 vs the 35R?
7)- Is the turbine housing approx the same size?

8)- One last time...what are the specs for the BC cams you are running? Lift, duration and overlap.

 

[suprahero]

Jon, I'll answer these to the best of my knowledge and thanks for checking in.

1) no, I think my torque peak is somewhere around 4500rpm, but I'll have to check one of my dyno graphs if I can find one.

2) No. I haven' had anything ported since I had it built before it tore up in March.

3) I am running stock 1jz valves on both intake and exhaust.

4) No I don't have an EGT guage. Do you recommend one? If so which one?

5) I don't know.

6) I have the .68 on this pt67 and I had a larger one on the 35r. I think it was a .92 or something like that.

7) almost identical.

8) specs on cams are as follows:
Intake: Duration: 272* Lift .343
Exhaust: Duration 272* lift .343
Overlap: -1.0 ATDC-------- -9.0 BTDC

Intake opens -1.0 atdc and closes @ 39.0abdc
Exhaust opens 47.0bbdc and closes @ -9.0btdc

Lobe seperation 114*

Duration @ .050" Intake 218* Exhaust 218*
Lobe lift Intake .343 Exhaust .343

The 35r was having the exact same results as the pt67 and the cams are the same as well. Hopefully something is wrong that I can find with a little help from my friends that are smarter than me............:1zhelp:

 

[jdub]

I have an Apexi EGT gauge...it's a good investment. I have mine mounted in the turbine housing, just behind the flange.

9) Does your boost peak at torque peak, then flatten out to you lose boost at 6400 RPM?

10) Are your adj cam gears set at "zero" or at a reference +/- after you degreed them?

11) I need to know the diameter of the turbine wheels, not the trim. Or, is .68 and .92 the housing A/Rs?

What I'm getting at here (and back 250 posts ago) is those cams have a lot of overlap (10 degs) for a turbo motor. Plus, your exhaust path is stock from the valves to the manifold...the 1J head was optimized for small twin turbos.

There is a condition called reversion when you have too much overlap in cam timing on a turbo motor. During overlap, both the exhaust and intake valves are open. The problem is not flow across the cylinder from boost, but from back pressure due to restriction from the exhaust valves, ports, turbine housing, and turbine wheel/outlet. When back pressure = boost pressure, your turbo efficiency (and engine efficiency) drops like a rock...boost will flatten out and drop as RPM increases.

Boost will peak some where around torque peak and flatten, then drop. EGT will increase as well due to increased cylinder temps from the back flow of exhaust. Your problem IMO is not RPM dependent, but pressure dependent that occurs at RPM.

I was under the impression the peak/fall off occured a bit earlier with the PT67 vs the 35R?

 

[IJ.]

The thing to keep in mind on this one was "it DID run right at one stage then changed"

 

[jdub]

Yeah...I know. I'm trying to figure out what changed
(I suspect it's in the cam timing)

 

[IJ.]

Points @ J >>>>

 

[buckshotglass]

I still think the I/C is full of something, limiting flow.

 

[jdub]

Buck - He's already checked the IC.

 

[buckshotglass]

ok. I know it's a long shot, but I thought he said it was fine from before. I didn't know he actually checked. Once again, I stand corrected. :goes back into hiding.

 

[IJ.]

Can't imagine what could block an IC that wouldn't kill the engine in the early stages of it blocking?

 

[buckshotglass]

I just thought they don't get cleaner as time goes on. A flow restriction may not show up until it's ability is maxed out. I know it's a reach. It would be cool if I was right though.

 

[IJ.]

Yep but what would be restricting it?

 

[jdub]

Mice! Rats! Squirrels!
(it is Alabama you know )

 

[IJ.]

Sisters, cousins?

 

[buckshotglass]

Dirt.
It's dusty down there, in Bama.
Wouldn't too small of an I/C limit boost, if the turbo was too big for it? I know it was big enough before, but maybe it got smaller, due to mice and crack baggies.

 

[jdub]

Cousins are fair game in Alabama

 

[IJ.]

I thought J ran a "cousin filter" ummmm errrr air filter to keep crap out?

 

[buckshotglass]

There you go again IJ, throwing facts around.:nono:

 

[suprahero]

I have an Apexi EGT gauge...it's a good investment. I have mine mounted in the turbine housing, just behind the flange.

9) Does your boost peak at torque peak, then flatten out to you lose boost at 6400 RPM? I will do a few datalog pulls tomorrow and post them up tomorrow evening so I can show you exactly where it falls off. My boost actually fluxuates a little up and down and then falls off @ 6400rpm.

10) Are your adj cam gears set at "zero" or at a reference +/- after you degreed them?They are set at 0. I tried adjusting them, but I didn't get any difference at all. I plan on going to the dyno this week and adjusting them there though and seeing if it affects anything. I feel better adjusting them on the dyno where I can watch everything instead of watching the road.

11) I need to know the diameter of the turbine wheels, not the trim. Or, is .68 and .92 the housing A/Rs?That is the rear housing A/R.

What I'm getting at here (and back 250 posts ago) is those cams have a lot of overlap (10 degs) for a turbo motor. Plus, your exhaust path is stock from the valves to the manifold...the 1J head was optimized for small twin turbos.

There is a condition called reversion when you have too much overlap in cam timing on a turbo motor. During overlap, both the exhaust and intake valves are open. The problem is not flow across the cylinder from boost, but from back pressure due to restriction from the exhaust valves, ports, turbine housing, and turbine wheel/outlet. When back pressure = boost pressure, your turbo efficiency (and engine efficiency) drops like a rock...boost will flatten out and drop as RPM increases.

Boost will peak some where around torque peak and flatten, then drop. EGT will increase as well due to increased cylinder temps from the back flow of exhaust. Your problem IMO is not RPM dependent, but pressure dependent that occurs at RPM.

I was under the impression the peak/fall off occured a bit earlier with the PT67 vs the 35R?

I wouldn't think the peak or fall off would be quicker with the pt67, but I could be wrong.

The thing to keep in mind on this one was "it DID run right at one stage then changed"

Yes it did run right before. I need to call Blake monday (dyno tuner) and see if he has it on file where the cams were set at. I may go to the dyno monday with some racegas and adjust the cams back to where they were when I went to the Texas meet.......although I did end up blowing it up on ther way there...........:aigo:

Yeah...I know. I'm trying to figure out what changed
(I suspect it's in the cam timing)

I will do some research and find out monday what the cams were set too Jon.

Points @ J >>>>

I take full responsibility of this screw up Ian...........:cry:

I still think the I/C is full of something, limiting flow.

It's full of air and that's it. I took it off and dunked it under water not to long ago to check it for leaks. I don't remember any squirrels crawling in while I hooked it back up, but I do appreciate the thought.........now, go work on your car.........:evil2:

ok. I know it's a long shot, but I thought he said it was fine from before. I didn't know he actually checked. Once again, I stand corrected. :goes back into hiding.

I'm used to be corrected Dave. It's not so bad once you get used to it.

Buck - He's already checked the IC.

\
^what he said.

Cousins are fair game in Alabama

All my cousins look like bear bait...........:aigo:

I thought J ran a "cousin filter" ummmm errrr air filter to keep crap out?

I removed it a while back just in case that was what was causing me to lose boost.

 

[jdub]

I was under the impression the peak/fall off occurred a bit earlier with the PT67 vs the 35R?

I wouldn't think the peak or fall off would be quicker with the pt67, but I could be wrong.

I thought the 35r was causing it since I"d replaced everything else, so I bought a pt67 from a local guy here. It does the exact same thing, only sooner now.

^^^ This is where I got the impression.

Any idea on the diameter of the turbine wheels?

If it's the cam timing (overlap), accuracy and details are very important. It will be a balancing act to adjust to a point where back pressure doesn't cause reversion and your dynamic compression doesn't go up to the point where you blow the motor.


What you posted in your build thread on cam timing:

The cam are set as follows. Exhaust +8 degrees and the intake is -4degrees.

The car has NEVER ran lean under boost. It has ran lean under normal driving before but this was after the fact. I ran it home lean on purpose to keep as much smoke as possible from exiting my exhaust so the people behind me could see. I was told it would be fine as long as it wasn't lean under boost. The person that told me this can chime in if he wants too.......or not.

Red, the motor had roughly five hundred miles on it when it started smoking, but it was very little smoking at first. It wasn't until we got past Louisiana that it started smoking horribly.

What would the AFR's need to get to, to detonate the engine like it did?

Looking at your cam specs, you eliminated all overlap (actually went 2 deg negative overlap) with the above settings, assuming these adjustments were made from an installed "zero" (degreed) reference...your dynamic compression shot way up as a result. I would not go back to these settings.

Jay - You are going to need to get an accurate degree on your cams. It is imperative you know that the lobe centers are (exh & int cam) when the motor is at TDC before you do any test runs. Once you get the reference points, that is the cam's installed "zero"...every adjustment must be made from that reference. It is very possible your overlap is even larger with the adjustable cam gears pointing straight up. For review: http://www.enginelogics.com/camdegree.html

This should help: Your BC 272 intake cam has an installed centerline of 110.00 degrees ATDC. The exhaust cam has an installed centerline of 118.00 degrees BTDC. This is calculated from the specs you provided...reality may be +/- as much as 1 deg in your 1JZ head.

What kind of crank damper are you using? It would be a good idea to check your damper once you figure out where TDC is. The damper index should be pointing at "zero" on the scale above the crank. This will be useful to set initial ignition timing after you do all this...just add/subtract degrees based on where the damper index is pointing with the #1 cylinder at TDC.

Once you have the installed zero, you need to reduce the overlap...advance the exhaust cam and/or retard the intake cam. Personally, I would start with E+2/I-2 from the reference, then retard the intake cam 1st (in 1-2 degree increments) after you see what the 1st run does. After a -2 deg change on the intake cam, go to the exhaust cam and do the same thing (in + 1-2 degree increments). Use caution going smaller than 2-4 degs of overlap.

I highly suggest you write all the results down for future reference