cannot make over 10 psi of boost
 

well, one by one I've handled the little issues of a new car and I'm pretty much down to the final one or two on my list. Since I finished the car it will not make over 9.5-10 psi of boost, in any gear up to 6200 rpm or so.

Here's what I have:

402 LS2 turbo-specific build, ET Performance 245cc heads, PMC sheetmetal intake, Nelson Racing headers, twin T67-76RE Precision ball-bearing turbos with twin 44mm Tial wastegates and single 50mm Tial blow-off valve. The 3.5" in/out intercooler was in the car when I bought it and the old motor could run 15+ psi of boost without issue. I have 3" mandrel bent downpipes and full 3" mandrel-bent exhaust out to the rear of the car.

The wastegates started with 13 pound springs and I run a manual boost controller on top of that. I swapped to 19# springs in the gates and tried with and without the boost controller, no change. I added a boost line to the top of the wastegates directly off the turbos, no change. I shimmed the blowoff so it cannot open, no change. I removed the air filters and then the inlet tubes (3" mandrel-bent) and no change. I pulled the inlet/outlet tubing out of the intercooler to see if there was a rag inside or something stupid, nothing. I swapped from the W2W turbo roller custom cam back to the stock LS2 Z06 camshaft; picked up idle vacuum, but no change in boost.

The turbos have .81 exhaust housings, but spool fine. Even if those were too big once it made boost it should go nuts. My laptop shows 160-165 kpa which matches my boost gauge at 9.5-10 psi, so I believe the boost reading is correct. The car runs great, but I'd really like to be able to make more boost. I am out of ideas at this point. I've spoken with Precision and Tial, no answers.

The boost comes up fine and then it's like it hits a wall and stops at 10 psi; that's why I thought the gates or blowoff were opening, but apparently not (I know the blowoff isn't as it's shimmed shut). The only other thing I can think to do is add a boost gauge off one of the turbos before the intercooler just to see what it shows. Does anyone have any other ideas?

Jody

http://www.camcojb.com/temp/ls2engine.jpg

1st off have you verified your boost guage is not faulty or has a leak in the line leading to it ?

tap off the turbos outlet scroll and run a dedicated boost gauge there to see if there is something restricting them such as a rag in the intercooler etc.

check your turbos exhaust and intake wheels for damage
verify you have no large exhaust leaks
check to be sure your turbos are spining freely and have no bearing damage
check the waste gates to make sure they do not have damage to the valves even if shut if the valve or the seat for it are damaged it can cause issues
check the blow off valve diaphram and seal/valve
check all silicones they may look ok but have a tear un the underside
check the intake and intercooler for any large holes or cracked welds

the welds can crack and be just fine under vacume but when boost is applied they will open up the seam and allow large amounts of presure out
< have seen this happen with liquid to air intercoolers alot >


thos turbos should have no problem pushing 25 psi into that engine so im going to go with most likely your waste gate or turbos themselfs have a issue.

Check your exhaust pressure before the turbo. Might be an easy way to find a serious problem(Wrong turbine wheel for your housing, damaged wheel,open or defective wastegate,...)

Do you have an easy way to check exhaust backpressure before the turbo (o2 sensor bung or something)?

I can't think of anything else (at the moment) that sacarguy didn't mention or that you haven't tried.

no, there's nothing to hook into between the engine and the turbo; you don't want an O2 on the pressure side, so the bungs are in the downpipes.

Jody

your headers look VERY blue, my guess, (which is only a guess) is that the turbos are on the small side, you could be at the surge limit at 10 pounds, have you done the math and checked the turbo maps?? it could be that the housings are the limiting factor.

you could be moving the same mass of air at 10 pounds thru the bigger heads as you weer at 15 pounds with the old ones.. and its the mass, not the pressure that matters, the ET 245 heads flow like a MoFo and on a 402 with your super optimal intake and hot side tubing, you could be outflowing the turbos

The turbos were spec'd by Precision for my combo. They are T67's that flow like T76's according to Precision, and have the larger .81 exhaust vs the more normal .68 exhaust housing. They claim they are plenty big enough for 1400 hp. I actually was thinking they were on the big side as I didn't want a laggy engine, but they're not laggy at all, come up on boost nicely. They just don't make as much boost as they should.

As a comparison, I had this engine in my GTO with a pair of GT3072R turbos that made 16 psi no problem, could have made more but that was as high as I ran them. They were much smaller turbos than what I have now.

I'm going to hook a boost gauge to the outlet of one of the turbos first to see what the boost pressure is before the intercooler, just to eliminate that as an issue. If that's near 10 psi then I'm going to shim the wastegates closed so they cannot physically open and see what happens.

Jody

Stones of steel. I'd be terrified to block off the wastegates and try to force up the boost. I know you guys are all really knowledgable and this is easy peasy for you, but with the coin you've got invested, I'd be sweatin' bullets watching the boost gauge on that test run.


Jeff-

I think I could modulate it with my right foot pretty easy. I don't plan on going wot for a 1/4 mile pass, just load the engine and see if the boost swings past 10 psi. Going to check the boost on the inlet side of the intercooler now before any other changes, will post back on my findings.

Jody

10psi
 

"Hits a wall at 10psi"

Since you've eliminated all the other variables, I'd check the exhaust pressure going into your hot sides. If you're seeing over 20 PSI there (2:1), then you've found a restriction. The closer to a 1:1 ratio, the better. As a side note- do you have any EGT probes? I'm curious as to what your gas temps are hitting. Do you notice a more-than-normal rise in IAT when you're on the boost for a while?

I agree that your .81 housings are about right & should work fine, but you might be right at their limits already. I think that motor is trying to move alot more air than it currently can, hence the 'wall' effect. I think you can get 1.01 housings for those; that might be worth a try.

my thought exactly.. but check the boost before at the turbines just to be sure....

you could have another issue causing it.. some manual boost controllers need to be plumbed to both sides of the diagphram on the wastegates.. so they hold them closed by applying pressure on top to hold the valve closed till the boost hits preset, and then they release this pressure to allow the valve to open.... just make sure you havent got the hoses crossed (mounted wrong) on one or both sides so your boost controller is actually opening the valve instead of keeping it closed

Jody, sorry to hear that you are still having troubles....but we know you will figure it out.

And since you started this thread we all can learn from it! :lateral:

well, some progress made. I hooked a separate boost gauge to one of the turbo outlet housings and took a drive. That shows 15-16 psi at the turbo, before the intercooler, and the in-dash gauge and map sensor both show 10 psi at the intake plenum.

So there appears to be a big restriction in the intake system, or a huge boost leak. I think the intercooler is fine as it was on the car before without issue, but it's a definite possibility it's restricted or plugged somehow. Possibly the big 90 degree angle coming right off one of the turbos (required to clear) is affecting it, but I've had right angles on the pressure side before. Maybe the boost is pushing past the o-rings on the sheetmetal intake.

I need to get a longer piece of hose and hook the gauge to the other turbo and see if it's different. The intercooler will be a pain to remove, most of the front end stuff has to come off (grille, bumper, etc.).

Well that's a relief. PT usually doesn't get much wrong IRT turbo application.

Good luck on the rest of the troubleshooting...

Jody, I have some 90 degree bends on the pressure side of mine also! I don't remember what my pressure drop was from the turbo the the intake. I checked it about four years ago but just can't remember now. I've run boost as high as 18 psi and didn't see any high spikes in intake air temps or other issues. If you want, I can hook up a guage to the turbo tomorrow and take a reading. At least you can compare my results to yours before you go through the trouble of taking the front end off of your car. I know that your pressure drop is excessive, but maybe some real world numbers might help...

I appreciate that Ray, but hate to have you go to the trouble. My next step is to make a 3.5" bypass for the intercooler and see what happens.

Jody

Jody check your intercooler very carefully they crack and split quite often. If you can source a smoke machine and pipe it into the turbo outlet on the cold side you'll find the leak. That's how I check for leaks. I've run into that same problem quite a few times and 9 out of 10 times it's the intercooler(s).

I hope you get it fixed I want to see some VIDEO!!!!!! :thumbsup:

Jeff

found 2 psi
 

well, I found 2 psi. The nice thing (for me) about getting older is that I can laugh at myself now. In my younger days I'd never post on a board about some stupid thing I'd done. :D

I built a plug and test fitting to pressurize the intake manifold. Hooked it up to 25 psi and found a big leak. In the throttle body there was (what I thought) a blind hole out the passenger side. I'd looked at it when I installed it, and it didn't go anywhere. Well, it does, goes out in front of the throttle blade. Not under vacuum, but a direct leak under boost. Thing is, you look straight at it and it looks like a blind hole; change the angle and you can just see a passage on the bottom side joining it. I tapped it for 1/8" NPT as you see here:

http://www.camcojb.com/temp/100_0354.jpg

That now gets me to 12 psi at the intake. I can also hear some slight leakage at the intake o-rings. Very small amount, but who knows how much that may add up to total. Trying to find a stock LS2 intake to try. Don't want to spend a ton of money as I'll never use it permanently, but it will bolt right on and fit my 90mm throttle body. It's also what I had on this engine in the GTO, and had no boost leakage. If someone has one let me know.

Jody

i got a stock ls2 intake. PM me

I have one as well.

Let me know if you need it.... You can swing by my shop and pick it up, I'm in Richmond right off the San Rafael bridge.

not even close those t-67 can support over 700 horsepower each no way they cant supply more then 10 psi to that motor he would be having to make 1000 rwhp at 10 psi to out flow those turbos.

did you change the cam shaft profile to much over lap can easily cause such a issue

well, I found the reason I'm having a problem with the boost levels. The intercooler was not built for this power level, and simply won't support my airflow needs.

I have a 24" wide by 12" tall and 3" thick core with side tanks. So the unit has air flowing horizontally, which is very restrictive with that config of a core. If I could swap to a vertical unit, the same size core would be much more efficient as it'd be 24" wide and only 12" long. Unfortunately that won't fit without a complete re-doing of the front end of the car. According to Bell my intercooler config and size is only real efficient up to 400 hp or so............. :(

The tech at Bell guessed the exact boost drop of my combo just off the intercooler specs and boost level into the core; I didn't have to tell him. My plan is to bypass the intercooler for now and plumb the turbos directly into the throttle body and run water injection as I have in the past. It may not be ideal but it definitely works and I'm sure the power difference will be huge.

Thanks for all the help, it is much appreciated.

Jody

or you could mount two water/air intercoolers in each fender in front of the tire! or re-map the EFI and run E85 and full boost, sans IC... mut the water/meth injection is propably the best and quickest fix

I think the easy thing to do for now is bypass the intercooler, build new custom pipes up to the throttle body, and keep the present intercooler in place in case I sell the car in the future and the guy can live with the lower boost.

I'd go E85 if it was readily available out here, but it's not. There's one place supposed to be opening up this month, but I want to do Power Tour and longer cruises, so unless they get a good network of E85 stations out here I have to stick with pump gas.

Jody

Jody,

Sorry kinda off topic but I was wondering what kinda of HP does it have a 12 psi (or current state) and what would you expect at 18 psi? No other reason than curiosty...I am guessing it is BIG POWER

12 psi feels like 700-750 hp. 17-18 psi should be 1000+ hp.

Jody

Thanks, it was strictly for my :drool: purposes. :thumbsup:

There, fixed it for you.

:P

[that's actually sad but true Troy. It's stupid that 700 hp feels pedestrian................. ;)

Jody

Well at least you got to the bottom of it! So there's no way of fitting a proper size IC or two?

sure I can, but it'll require a fair amount of fabbing and some re-pinting of the front inner sheetmetal. Would be a cool winter project I guess, but for now I want to get the boost up and enjoy the car.

Jody

LOL, tell me about it... that's why my ball bearing PT-61s should be here next week, the extra 125hp/150 ft-lbs or so over the Procharger at the same boost level are badly needed. :lol:

I think there is something seriously wrong with both of us. :yes:

yeah you guys are sick! :yes: can I be your friend!!? :unibrow:

jody, bell intercooler built mine we made 1000 hp with 9lbs of boost. just need to put it in the camaro
rick k:cheers:

yeah, I just can't fit the size needed without some mods, and I don't want the car down right now. 9 psi? Never seen an LSX make anywhere near that power at 9 psi.

Jody

Of course we can make it fit... start cutting! :unibrow:

The intercooler I had Bell make for me is good for 1500 cfm @ 10 psi with less than 1 psi pressure drop across the core and is about the size & flow capacity that you'll need for your combo; actually you might even want to go a little bigger for more charge air flow area. You could go a little shorter on the core for easier packaging and it won't give up that much in terms of efficiency; for this particular core thickness & width (27" x 3") Gerhard said 6" tall was the absolute minimum he would go, 8" was the "sweet spot" in terms of weight & size vs. cooling efficiency, 10" was better still for cooling, and 12" would be starting down the overkill & diminishing return point in terms of cooling efficiency vs. weight, size, and increasing pressure drop.

http://home.comcast.net/~swedish_che...lercdsmall.jpg

I agree though, drive the car now and save the project for winter... and knowing the configuration of the nose of your car and especially since it's all painted & detailed it's going to be a tough task to fit a properly sized intercooler up there.

Glad to hear you got it figured out...:)

Jody,
Is this car going to be sold before the 2009 power tour? Sounds like you have buyers lined up...tell Charley to wait. Is the car going to be at Sema? You built one hell of a hot rod! I can't wait to see what you build next...besides the 2nd gen camaro. Fantastic job:thumbsup:

I have no plans to sell it. I'll be at SEMA, don't think the car will though.


Jody

Don't anyone offer him any money till after Power Tour 2009.

I thought it was going to be in a vendor booth at sema...damn