Boost dropping near redline; is my PT51 maxed out running 11.45 ET?

[Syclone0044]

Hey guys, hope nobody minds if I ask here about my 91 GMC Syclone, I know tons of you guys run the same turbo in similar weight Turbo GM V6's :biggrin:

Old Stock Heads/Cam Results
When my truck was mostly stock with just a 2700 Yank lockup converter (700R4 trans), 93 octane & SMC dual nozzle alky kit (100% methanol), stock 28# injectors, and a little tuning, it ran a best of 11.8 @ 112 MPH around 23-25 PSI. I run a ball-and-spring manual controller from Boostvalve. The boost control looked like this (pink line). The red line peaks are 1-2nd, 2-3rd, TCC Lockup, and 3-4th:

Nice and flat, right?

New Stock Heads/Cam Results
Last fall I converted from the stock "swirl port" ~160cfm heads to late model Vortec truck heads that flow 227cfm intake, 171 exhaust. I also swapped from the stock 179/191* roller cam to a 218/218 115 LSA custom XFI roller cam. Obviously this greatly increased the flow of the engine. I quickly found what felt like the limit of my turbo at 16-20 PSI. I do all my own tuning with a wideband, laptop datalogger, and realtime chip emulator. I went to the track and made 6 passes, the fastest 2 were at the lowest boost (16-20) and the 4 runs I ran 21-22 PSI were the slowest runs. The slowest run was 11.65 @ 116.2 and the fastest was 11.45 @ 117.7.

I noticed the boost doesn't seem to maintain flat any longer. With the extra 800 RPM of the new heads & cam (4700 RPM redline before, now 5500 RPM), it seems like the turbo can't keep up? Here's what it looks like on my best run:

One thing I did was port the PTE turbine housing internal wastegate opening. I only opened it a bit and concentrated more on smoothing what used to be a 90* entry from the turbine. Is it possible the extra surface area is pushing the flapper open at redline?

Or is the turbo just tapped out? My truck is full street trim, full weight (3650# race weight with me in it). Could I have already maxed out the PT51 at only 11.45? I thought guys with heavy GN's could get this turbo into the 10s.

Race Videos
Here's a video of my best pass 1MB Windows WMV9, 640x480 High Resolution, 44kHz sound.
If that link doesn't work, here's the low-res YouTube version.

For complete detailed build info on the truck, see my webpage.

I also have more videos here.

Thanks in advance for your help!

 

[RUQWKNF]

#1 You need a Heavy Duty actuator to hold the flapper shut under WOT, now that you have extreme exhaust flow compared to before.

It's good that you smoothed out the housing, but did you make sure to note the carbon ring on the turbine housing before porting out the wg hole? Can you double check to make sure the puck is completely covering the hole?
If you have the standard PTE SyTy kit, they came standard with a standard spring wastegate. You would have to get a heavy duty wastegate actuator from PTE with no brackets welded to it, at the same time, order one E cover backing plate clamp, and have someone weld that new backing plate clamp to your new HD actuator in the same configuration as the actuator that you already have.

#2 With the extra exhaust flow, you could very possibly have a back pressure issue at the higher boost levels, which is causing the motor to strain at higher boost levels.

This is very typical once you start doing things to let the motor breath easier.
Example: A stock Buick motor with a PT70 3-bolt slapped on, might have to run 32psi to run 125mph, you throw a good set of flowing heads and a roller cam and you might only have to run 22-23psi to run 125mph. This is just an example but you get the idea.
It's all about freeing up back pressure. You're graphs look like boost is falling off due to the actuator coming unsealed from the housing. Ala bleeding off boost.

If it were me, I would try the HD actuator first, and make a back pressure gauge. Run the truck again at your given boost levels, 16psi, then 21-22psi and see if the boost level is steady. As well as making sure the back pressure is not through the roof. 16psi of boost at the intake should not be 32psi on the back pressure gauge. And 22psi at the intake should not be 44psi on the back pressure gauge. If either are past the 2:1 ratio (2psi of back pressure for every 1psi of intake boost), you have a serious back pressure issue, and it's time to upgrade the turbine wheel and housing.
Which, to my knowledge, I'm not sure if PTE can machine the SyTy turbine housings to accept the 65 turbine wheel, or the HPQ turbine wheel. With your mods, the 65 wheel (P-trim replacement) would be the minimum I would go with on a good breathing 4.3L Sy. Another thing you have to remember is, you have a 4.3L, vs the heavy Buicks with only a 3.8L. There are some serious flow differences at work here between the two combos.

Hope this helps a little.

Patrick

 

[Syclone0044]

Forgot to include a pic of the engine in the 1st post, I can't seem to Edit my own posts either..

 

[GNVYUS 1]

Very clean engine bay.

I'd try the HD actuator also but I have a feeling you're turbo is done up top.

With 4.3 cubes those heads and roller cam it's most likely out of breath up top at that rpm, you pretty much have a Mustang motor running on that small turbo. Those guys run much bigger ( though on 8 cylinder ) but a PTE 62/65 ( 67mm billet comp wheel ) and seems like the turbo for you to keep it streetable.

Are you still running the 28lb injectors?? I'd be curious to see what your Duty Cycle is even with the Alky.

 

[HighPSI]

Correction.....a PTE 6265 does NOT have a 67mm Billet Compressor Wheel. The PTE 6265 has a 62mm Billet Compressor Wheel and 65mm Turbine Wheel. Wasn't sure if this was just a typo. ~ Holly@Hartlineperformance.com

Very clean engine bay.

I'd try the HD actuator also but I have a feeling you're turbo is done up top.

With 4.3 cubes those heads and roller cam it's most likely out of breath up top at that rpm, you pretty much have a Mustang motor running on that small turbo. Those guys run much bigger ( though on 8 cylinder ) but a PTE 62/65 ( 67mm billet comp wheel ) and seems like the turbo for you to keep it streetable.

Are you still running the 28lb injectors?? I'd be curious to see what your Duty Cycle is even with the Alky.

 

[imjoesnuffy]

Dont know if this is like comparing apples to oranges but I pushed mine to 25-27 psi and managed an 11.09 @ 123 with a 1.67 60 ft. Mods in my sig. My heads were massaged, it looked like someone did a home made port job on them. Not anywhere near a pro port job.

Not sure if you are pushing it hard enough?

 

[bison]

Dont know if this is like comparing apples to oranges but I pushed mine to 25-27 psi and managed an 11.09 @ 123 with a 1.67 60 ft. Mods in my sig. My heads were massaged, it looked like someone did a home made port job on them. Not anywhere near a pro port job.

Not sure if you are pushing it hard enough?

Hes pushing it pretty hard. The truck is probably heavier than your GN and eats up a lot more hp to go the same mph because of the AWD. He needs a stiffer spring in the actuator to prevent the taper off. I have a high tension spring in mine and its cranked in several turns and it still tapers off slightly up top. Thats with a GTQ wheel in a Precision .85. Anytime you run anything really hard you are limited by the backpressure/actuator tension. If i had an external electronic boost controler on it like an AMS with an external gate i would easily be able to overcome the backpressure with the CO2 charge.

 

[noway55]

Can I jump in the middle of this with a similar problem?

I posted on the SYTY.NET board and not much assistance so far.

I have been reading around here for a few months since buying the Alky Control. Glad I spent the extra bucks based on my reading!

Here we go... Similar problem, boost falling off.

It seems to make more boost at part throttle and hold it but when I go WOT, it fades away

The other issue is using TunerPro to scan with, my RPM's seem to be jumpy, I dont know if this is real or is this typical of tunerpro?

Thanks for any input.

Again, sorry to jump in but I think I have same type issues here.

Turbo is a 60-1 trim T04B

Using AEM TruBoost controller set to 90 which is pretty much max setting.

Thoughts? Suggestions?



TPS.Boost...MPH...RPM
54....22.06.....53...4125
61....22.92.....53...4050
66....23.27.....54...4050
72....23.27.....55...3825
78....23.61.....55...4000
89....23.27.....56...3725
98....22.75.....57...3950
100...22.58....58...4000
100...22.06....58...4150
100...21.54....59...4425
100...21.02....59...4350
100...20.51....61...4375
100...20.16....61...4400
100...19.65....61...4450
100...19.3......62...4500
100...19.6......63...4375
100...18.61....65....4575
100...18.44....66....4600
100...18.27....66....4475
100...18.1.....67.....4500
100...17.92....67....4575
100...17.92....67....4525
100...17.75....68....4475
100...17.58....69....4300
100...17.41....70....4650
100...17.41....70....4525
100...17.23....71....4625
100...17.23....71....4500
100...17.06....71....4325
100...16.89....72....4450
100...16.89....73....4225
100....16.54...74....4600
100...16.54....74....4500
100...16.37....75....4225
100...16.37....75....4475
100...16.2.....76.....4375
100...16.2.....76.....4400
100...16.03...77.....4225

 

[BEATAV8]

My PT51 couldn't keep up after a heads/cam upgrade. Same symptom you have here.

 

[dgoodhue]

Turbo is a 60-1 trim T04B

A T04B is a small compressor housing especailly with upgrade heads and cam. Usually most people use T04E with 60-1 wheel (and that is considered a mild turbo). I wonder if it can't supply enough air at WOT?

 

[dgoodhue]

Hes pushing it pretty hard. The truck is probably heavier than your GN and eats up a lot more hp to go the same mph because of the AWD. He needs a stiffer spring in the actuator to prevent the taper off. I have a high tension spring in mine and its cranked in several turns and it still tapers off slightly up top. Thats with a GTQ wheel in a Precision .85. Anytime you run anything really hard you are limited by the backpressure/actuator tension.

Syclone weight similair to a GN. Stock weight is 3550. Yes, the AWD does have more driveline losses compare to 2WD. I have never see any exact numbers but I would guess another 5-7%

 

[noway55]

Forgive me, I am a little new at the turbo stuff...

1st of all, what is required to change the spring out on the actuator.... and where would I get one and what would I know to ask for?

2nd.. Lets say the turbo can't keep up. What do I have to change to go bigger? Does that mean custom exhaust work to put in a new housing? I can bolt stuff on but dont do any welding if that's required.

I would assume I could unload this turbo, it's only got about 1000 miles on it. Most of them easy breaking in the new motor.

 

[brian_k03]

your out of turbo, you'll need to go bigger if you'd like boost to continue to climb.