GTO 402 w/ F1A (12 psi & E85) can't break 550rwhp

[FSAE_Junkie]

I'm trying to diagnose what has been consistent low power output out of my GTO across 3 engines. They've all been in the 12-15 psi range, all with the same F1A procharger pullied at the same ~62k impeller RPM, and none of them has made over 500-550 rwhp. And I know this isn't just due to low or erroneous dyno readings, as I've lost a roll race to a buddy of mine with a well setup NA 402 in a heavy G8 while I was on 10 psi...

I was optimistic after swapping pullies to target 70k RPM (74k is the max speeed), that I could get above 12 psi of boost and maybe break past 550 rwhp mark. Unfortunately, you can see my latest results below:
GTO_F1A_12psi_E85_6-11-21_Dyno.png
This is the raw measured torque/power, I forgot to add the SAE correction factor here, but it is in the range of 1.06 or so I believe. Now typically, backing out power on the street is a bit noisy in terms of data, but you can see there is definitely something going on here. I personally think it is related to the boost curve.

Here's a plot below comparing a pull with obvious belt slip, a pull from my prior pulley setup yielding 62k impeller RPM, and a pull from my most recent change at 70k impeller RPM.
GTO F1A Boost Comparison.png

I don't think I'm getting belt slip in the red and purple curves. I'm getting a pretty linear increase in boost vs. RPM and its not behaving like it does when there is major belt slip. I'm using the shortest belt I can fit and have it tensioned according to prochargers recommendations. I've also tried adding more tension with no effect on the jaggedness of the boost curve. So again, I'm reluctant to just say it's slip.

I would love to see a log from anyone that has a procharger or similar blower just to see what your MAP looks like vs. RPM.
It also feels like regardless of slip or not, only making 500-550 rwhp with 12 psi seems quite a bit low.

[SultanHassanMasTuning]

tune/log of the run would be good

you can make 20psi

if your fueling and timing aint right you wont make power

[FSAE_Junkie]

Sorry about that, I meant to include these the first time around. Here's my current tune and log which has a good 3rd gear pull.

This was my first time with the new smaller PC pulley, so I hit some new boost VE cells and need to add a few % more fuel. Otherwise, I'm targeting high 11's AFR on gas scale with E85.

As for timing, I'm running a flex fuel setup and targeting roughly 17* up to 20* in my last g/cyl cell.

I really don't think there's much left in this setup from a boost standpoint. I have a 7.65" crank pulley I'm planning on swapping in place of my 7.0" pulley. That should bring me up another 10% in impeller speed, but at that point, it'll out the blower around 6800 RPM.

[crew chief]

Your cylinder volume has your engine as a 5.7L not sure if this affects much but probably worth correcting.

[Realizm]

Sorry about that, I meant to include these the first time around. Here's my current tune and log which has a good 3rd gear pull.

This was my first time with the new smaller PC pulley, so I hit some new boost VE cells and need to add a few % more fuel. Otherwise, I'm targeting high 11's AFR on gas scale with E85.

As for timing, I'm running a flex fuel setup and targeting roughly 17* up to 20* in my last g/cyl cell.

I really don't think there's much left in this setup from a boost standpoint. I have a 7.65" crank pulley I'm planning on swapping in place of my 7.0" pulley. That should bring me up another 10% in impeller speed, but at that point, it'll out the blower around 6800 RPM.

Are you sure there aren't any boost leaks? If there is any belt slip, you'll often see belt powder everywhere. Something seems off with that setup for sure. I'm running a 2011 Corvette Grand Sport, LS3 (10.7:1 compression ratio), D1sc Procharger with a 3.6" pulley (7.5" crank pulley) putting the supercharger at 55k RPMs, regular intercooler and dump valve, ID 1050X injectors, LG long tubes, catless, B&B cat back, running E85 via a DSX flex-fuel kit, pushing 17-20 degrees of timing with a 58% alcohol content. Timing will go up a bit more with higher %, lower of course when running on 93 octane. I'm seeing about 13 lbs of boost in 100F weather here in Texas, 14 lbs during winter time. I'm going to guess this is about 750 rwhp, but I'm not sure (some experts here can chime in). I haven't had it on a dyno since I did some major changes but I know it makes *WAY* more power than before. I use to run a P1sc at 8 psi, 15 or 16 degrees of timing on 93 octane, with cats and that was 553 rwhp on LG's dyno. So, I'm certainly surprised to see that 550 RWHP on the F1A. Do you have any other method of checking power? Do you have a Dragy GPS performance unit, or have you had it to the drag strip? If so, what is your rough trap speed and vehicle weight? Depending on traction levels if you have a Dragy, you could see 70-100 mph times (or 60-130 if you are ok with running up that high).

I don't have a longer pull just yet, only this short one to check knock. Lambda target is 1.27/0.787 with E85, actual is 0.82 or so. I'll attach that long and my current tune setup (before it was 20 degrees straight across the bottom, but in this the latest one I removed 3 degrees to compensate for that 3 degrees of knock). Hopefully, you can compare and see if you see anything that may make a difference. What sort of compression ratio is that engine? If lower than 10.7:1, you could probably increasing timing even more. One thing that helped me get more boost out of this 6 rib D1sc was to change to the Gates RPM belt. Any other belt would slip like hell and I couldn't make above 10 PSI.

LS3-D1sc-E85.hpl
6-18-21-flex-fuel-spark-up-step2.hpt

I'll try to get a 3rd gear pull from 3000 rpms to redline at some point and see if that gives you better comparison data.

[cadillactech]

The intake manifold pressure really does oscillate all the way up to peak boost once it passes about 18PSI. Couple spots you drop over 1 PSI.

If you look at Realizm's log, his intake manifold pressure is smooth with no dips or drop in boost as the RPMs increase.

How is the BOV/re-circulation valve set up on your car?

[FSAE_Junkie]

Lots of good comments here. I will say that I think there are at least 2 distinct issues at play here.
1) A 402 with 12 psi should be making more power than I am. Probably closer to 700 instead of 550 I would think.
2) An F1A at 70k RPM’s should be making more than 12 psi on a ~400 rwhp NA engine.
I’m choosing to look at #2 first, because that seems easier to hopefully diagnose.
I did discover 2 sizeable boost leaks. The first was a 5/16” port on the side of the LS2 manifold that I had capped off a long time ago, but the cap had dry rotted substantially and was now a full ?” dia leak. At 12 psi, this would flow about 1.5 lbm/min. Unfortunately, this probably isn’t worth more than about 0.5 psi. After fixing that, I still couldn’t build pressure in the intake tract with my air compressor; The red Procharger race valve was leaking substantially onto my foot. The valve is 11 years old at this point, so I figured I would go ahead and get a rebuild kit since they are pretty cheap. On disassembly, I didn’t see any reason it should have really been leaking other than maybe the Teflon seal being worn, but after putting it back together, it sealed better enough that I could at least get to 10 psi. I’m hopeful that it had some role to play in the low boost or maybe even the erratic boost.

I’m still not 100% ruling out belt slip, but I’m not sure how conclusively verify without building a tach setup so that I can read the procharger pulley RPM. Realizm, that is good to hear about the Gates RPM belt, I’m skeptical how well these Gates green belts can hold given that they are so stretchy. I do have an RPM belt I haven’t installed yet, but it’s for a larger crank pulley (7.65 vs. 7.0) that I’m waiting to install. I didn’t want to confound things too much with more impeller speed as of yet. I guess I could just buy an RPM belt for my current pulley combination, but was sort of hoping avoiding spending another $70 on a belt for this interim setup.

Realizm, I'm looking through your log and I think there's some things to be gleaned from this. I'll have to make another post covering some of the comparisons. But yes, certainly if you could a 3rd gear pull all the way up, that would be even more interesting to look at. I assume your log above is from 2nd gear?

[cadillactech]

Lots of good comments here. I will say that I think there are at least 2 distinct issues at play here.
1) A 402 with 12 psi should be making more power than I am. Probably closer to 700 instead of 550 I would think.
2) An F1A at 70k RPM’s should be making more than 12 psi on a ~400 rwhp NA engine.
I’m choosing to look at #2 first, because that seems easier to hopefully diagnose.
I did discover 2 sizeable boost leaks. The first was a 5/16” port on the side of the LS2 manifold that I had capped off a long time ago, but the cap had dry rotted substantially and was now a full ?” dia leak. At 12 psi, this would flow about 1.5 lbm/min. Unfortunately, this probably isn’t worth more than about 0.5 psi. After fixing that, I still couldn’t build pressure in the intake tract with my air compressor; The red Procharger race valve was leaking substantially onto my foot. The valve is 11 years old at this point, so I figured I would go ahead and get a rebuild kit since they are pretty cheap. On disassembly, I didn’t see any reason it should have really been leaking other than maybe the Teflon seal being worn, but after putting it back together, it sealed better enough that I could at least get to 10 psi. I’m hopeful that it had some role to play in the low boost or maybe even the erratic boost.

I’m still not 100% ruling out belt slip, but I’m not sure how conclusively verify without building a tach setup so that I can read the procharger pulley RPM. Realizm, that is good to hear about the Gates RPM belt, I’m skeptical how well these Gates green belts can hold given that they are so stretchy. I do have an RPM belt I haven’t installed yet, but it’s for a larger crank pulley (7.65 vs. 7.0) that I’m waiting to install. I didn’t want to confound things too much with more impeller speed as of yet. I guess I could just buy an RPM belt for my current pulley combination, but was sort of hoping avoiding spending another $70 on a belt for this interim setup.

Realizm, I'm looking through your log and I think there's some things to be gleaned from this. I'll have to make another post covering some of the comparisons. But yes, certainly if you could a 3rd gear pull all the way up, that would be even more interesting to look at. I assume your log above is from 2nd gear?

Glad you found the boost leaks! Hope that takes care of it, I saw your LS1Tech thread, hopefully it is not a mechanical issue, fingers crossed!

If you know any high end automotive repair shops, they may have a PicoScope oscilloscope and if they have the prop shaft balancing add on kit you can use the photo eye on that kit to measure pulley speed. Takes some creative set up but I have done it! Too bad you aren't closer and I could do it for you on the dyno.