Turbo car issues at higher RPMs

RED09GT

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I am having trouble with the car above 5000 rpms.
On the data logs, the load peaks at around 4300-4500 rpms and falls to N/A levels by 6000 rpms. The MAF counts peak at just over 5000 rpms and then go up and down slightly until I let off. The car pulls hard to around 5300 and then struggles from there on.
The MAF counts are lower than I had with the stock motor and the same turbo kit so something is keeping this motor from breathing.
The IAT (sensor relocated to the intake manifold) temperature rises sharply as soon as the run is finished with it sometimes pegging the range of the sensor. Lito was figuring it to be a back pressure issue so I tried a few things but I've now tried just about everything that I can think of other than dumping the exhaust but the problem remains, Lito is tuning it so I am convinced that it is a mechanical issue. The boost is still registering the 11-12lbs on the gauge all the way until I let off.

Here are the details:

Engine:
Shortblock:
0.020" over stock aluminum block
Stock Stroke Cobra Crank
15cc dish Diamond Pistons
Eagle H-beams
Deck height shaved to 0.004"
Top rings: 0.021-0.023" gap
2nd rings: 0.025-0.026" gap
Crank end play 0.003"
Main clearance 0.0015"
Rod clearance 0.002"

Heads:
Hand ported bowls and valves unshrouded in the combustion chamber
Stock valves
Milled 0.015", 48 cc combustion chambers
TFS 15410 springs (300 lbs/inch) Brand New
stock retainers, keepers,followers, and Lash adjusters

Cams:
Bullet racing 227/227 @0.050", 265/267 @0.006", .550/.550 lift
LSA 115.5, degreed to 108.5 ICL (2 degrees advanced)
Locked out phasers
New timing chains, tensioners, and guides
TFS adjustable crank sprockets

Motor calculates to 9.34:1 CR with the simple online calculators
Stock intake, stock exhaust manifolds

Turbo Kit is a powerhouse kit.
Turbo is a BW S369 SX-E with a 0.96 turbine housing, 3" V-band downpipe.
I have since swapped the original Precision 6776 turbo back in place but the logs look just about identical.

Exhaust: 2 1/2" coming off the manifolds, merging to 3" up pipe. 3" downpipe to stock cat-back, with Magnaflow 2 1/2" axleback exhaust.

Here is what I have tried so far:

Tested for boost leaks from the turbo to the throttle body, found one, replaced one coupler-minor improvement.

Converted the wastegate from merging into the exhaust to dumping it-small improvement but not much

Compression test to verify cam install and make sure things are okay bank to bank:
All cylinders between 159 and 171 psi, 6 out of 8 were between 164 and 166 psi.

Swapped from a 0.88 exhaust housing to a 0.96 housing, small improvement but the problem is still there .

Swapped back to my original turbo, precision 6776 with a 0.81 exhaust housing, spools a bit quicker but the problem up high remains.

Boost leak check all the way to the cylinders and fixed a big one at the #1 cylinder Fuel injector boss and that has not improved things, other than the spool time.

Any other suggestions? The car is seeing less air passing the MAF than it did with 3 less pounds of boost with the stock motor and the same turbo kit. The load reaches a higher peak than the stock motor/turbo kit but falls off instead of remaining steady to past 5500rpms. I bought a pressure sensor so I am going to try and log boost pressure today and I'll report back. So far, I have tried to "undo" any changes that I made from how things were configured prior to building the motor but I am out of things other than starting to tear the motor down. Please help!
 

Flusher

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I have a question about the compression test numbers. Honestly, I don't have much experience with these engines or the data logging capabilities. I do have a lot of experience with OHV engines and modern manufacturing/machining processes.

Seems to me that 12PSI is a pretty wide range. If the unshrouding work was ground by hand, as opposed to being machined with a seat & guide cutter, there could be some variation in chamber volume. I can tell you, when equalizing chambers, a few 1/10s of a CC sure seems like a lot metal to remove from the chamber. That is opposed to the few drops of water needed to zero the burette.

You mentioned stock valves, were the seats cut? Did the head porter verify that the valves are sealing?

To give you an idea of how far the chambers have to be off, my last teardown of my BBC (boat engine), I really wanted to know every intimate detail. My as-cast heads varied +/-0.2cc in all eight cylinders. I did have a few valves that weren't sealing properly. A leakdown test indicated 15% leakage at the rings. The spark plugs were clean, but looked a little lean. The compression test indicated 160PSI across all eight cylinders. Definitely time to freshen it up.

How do the spark plugs look? Did Lito see any anomalies in the data logs that might indicate an internal mechanical problem?
 

RED09GT

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10% is usually acceptable as far as static compression test results so I don't think that would be responsible for this amount of power loss. I didn't test all of the chambers but the 4 I tested were within 0.5 cc, which is much better than the over 1cc variance that I measured with the stock heads.

The seats were ground by hand and I tested them with water and did not get any seepage in 1 hour of time. That all being said, the heads and valvetrain will be the first place I look if it ends up being an engine issue.

The only things that Lito pointed out as anomalous were the load, the MAF counts, and the IAT spike after the runs were over.

Spark plugs are a normal light-tan color, no spots, no oil, nada.

Logged the boost and it is holding to the boost controller setting right to when I let off the throttle.


I am going to do a couple logs in N/A form so we'll then know which way to look.
 

RED09GT

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The N/A logging did not go well, the car struggled past 4500 rpms and the log of airflow and load were ugly.

I pulled the valve covers last night and everything is still in place, no broken parts. I'll keep digging when I get a few minutes.
 

RED09GT

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Left side head gasket popped between cylinders 6 and 7, the two low ones from the compression test. No breaches to the water jacket or crankcase so no major collateral damage.
Going to have the deck and head surface checked after I get home from work next month.

It probably happened during break-in with some of the stale gas left in the tank, shit happens.
 
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