igtabg1

I posted this on tech but thought i would post here as well to gain some feedback with the few rear mount turbo guys we got here.
Good morning,
I have been getting the bugs out of the my Single rear mount turbo setup on my c5 corvette. I looking for some advice to possibly an idea where to check on resolving my boost issues. First a little info about the car.
2001 C5 corvette:
Stock 4l60e with 3600 stall.
Stock bottom end.
Comp lsr cam 231/239 113
stock 243 heads
melling oil pump
ls7 lifters
Head studs
BTR springs with supporting mods.

Now with my cam only setup mentioned above the car did 400 + hp on the dyno and i was running in the 7's in the 1/8.
After my rear mount setup I am currently only able to make 5lbs on a 10 lb waste gate spring.
Turbo setup:
stock manifolds
3 inch exhaust feeding a t4 flange with a on3 turbo 78/75 with a .96 ar exhaust housing.
55 mm or 60mm waste gate (sorry i cant remember at the moment)
2.5 aluminum cold side
A&a early gen intercooler
4inch tube that feeds from intercooler to throttle body
2 bar map SD tune.
Manual boost controller runing directly off the wastegate.
down pipe is 3inch pipe with vband that is approximately 15" long.
oil feed is 4an and drain is 10an both with one way check valves pre turbo and post turbo, along with remote oil pump.
Yes i have checked for exhaust leaks and cold side leaks and there are none currently present.




After testing the car at the track last night it wouldnt make more than 5lbs on a 10 lb spring. I have not ran the car without the boost controller that will be my next step, but i am also looking for other things to cross of my list in hunting this boost issue. Sorry for the lengthy post, but I didnt want to leave anything out. Any help would be greatly appreciated.

Thanks,
Chuck

junk c5

Obviously you already know to take that boost controller off and run it off the spring alone. Make sure your vacuum lines are properly place.

Your wastegate does not seem to be in the optimal position. But since you are currently not over boosting, I would not worry about that.

If all else fails, go to the hardware store and get an expansion plug for one half of the cold side plumbing and a PVC fitting for the other side. Use your silicone to affix the cap. Tap the PVC fitting with a compressor airline fitting and put pressure to it with your compressor regulated down and look for leaks. See if the cold side maintains a constant pressure.

Smoove

Is the wastegate SIGNAL reading directly off the compressor?

If so...you're seeing more pressure(boost) at the compressor, than you would see likely at the intake(length of piping-intercooler-etc. Maybe get the SIGNAL from the intake area, which would keep the gate open. I would change that if thats the case. However, if you have a 10lb spring, and only seeing 5...you may have piping issues, as in maybe the wrong diameter or a boost leak, even tho you tested them. How did you test them, pressure readings between joints(couplers) or are you smoke testing the pipes? I would smoke test as that method has helped me in many cases.

Also wastegate, make sure the fire ring is installed cause THAT will definitely cause a problem. You said yo don't have exhaust leaks, just make sure you don't have crappy gaskets at the manifold. If you're using anything other than factory MLS gaskets, or remflex,...I would change them. That's all I got man.

junk c5

Damn fire ring got me once. lol

stevieturbo

Draw a schematic of how YOU have the boost control plumbing configured including details of whatever controller you are using.

Long hoses to/from any controller are never a good thing.


Or just buy a decent electronic controller, it will make life easier and mean you can ensure all hose runs to/from the control solenoid are short.

And you have what spring fitted ? And what boost does this offer on spring only ? And what is the lowest boost you need to run ?

junk c5

Boost leash electronic boost controller.

StatmanRN

Agree with above. But...Are you sure the turbo itself is in good condition? Not familiar with the brand. Sizing seems about what most singles run. New or used?
Also, verify your boost pressure with a known gauge.

igtabg1

Thank you guys for the advice. The turbo was bought new. There is no shafts play on either the exhuast turbine or the compressor side. I do have the fire ring installed because like most of you guys I have made that mistake before. I made a video of me testing my wastegate and it seems like the wastegate is opening around 6 lbs. So I will be trying a bigger spring to see if the car will make 10 lbs. Heres the link https://youtu.be/zPyJaQZX32E.
I have also posted a sketch of how my boost controller is installed

the turbo has a add a port on the silicone coupler. I have thought about removing the add a port and tapping the compressor housing and putting a nipple on there.
I would love a electronic boost controller however I might have to save my change for now until late I get one, I have been loowing at the aem electronic boost controller. Please keep the advice coming, I plan on testing some these things this weekend and I'll report my findings back.

stevieturbo

What MBC is it you're using ? And presumably you're blowing into the bottom chamber of the gate ?

AEM Tru Boost would be a total waste of money. It's no better than an MBC other than easier to adjust from the car.

GFB, Gizmo, Turbosmart etc etc all make budget closed loop controllers which will work much better.

But some answers to the previous questions and some testing will help decide what is needed without spending too much.

The MBC whilst not perfect should still work well if everything else is good.

igtabg1

Hallman pro boost controller. And yes it's blowing into the bottom port on the wastegate. It's basically a knock off tial, I even have a tial spring in there. I bypassed the boost controller and ran a vacuum line from the vacuum block at the front of the car to the wastegate. After I test in mexico I'll report back with my findings.

junk c5

I've run my wastegate without any vacuum lines. Just off spring pressure and didn't relay on any signal lines to the wastegate.

TommyTomlin

After reading this, if I had to guess.....I would go with the fact that tss a rear mounted turbo, with what appears to be only the wastegate tube wrapped being the problem. Heat is what spools these bad boys and Id imagine you just don't have enough back there. Ive seen it before where a full wrap and moving the compressor closer to the engine has solved this exact problem.

StatmanRN

I'd agree that rear mounts are inherently prone to spooling problems and that the wrap should help. However it shouldnt effect the total boost it will eventually achieve.

junk c5

My rear mount got to 15lbs just after the intersection. Once the boost starts coming in its on and cracking.

igtabg1

whats the specs on your setup?it looks like it makes boost quick.

I did test the car a little bit in mexico. Both these test bypassed the boost controller. First i ran the car with the supplied vacuum hose from the front of the car to the wastegate, ditched the add a port silicone coupler and it made no difference. Then i took the vacuum off the wastegate and ran "spring only" and although it felt a bit stronger it only resulted in 5 lbs on the top end. My next test will to be trying a high psi spring and see where that gets me.

junk c5

The motor was a stock bottom ended ls1. PRC heads, turbo cam and ls6 intake. Turbo was an MP T70 w/.68 ar housing. It was a little laggy from a dead stop but within 75 feet it's at 15lbs. Best 60 foot was a poor 1.98. The exhaust was 3 inches all the way back and the cold side was 2 1/4 from the turbo all the way up front. I've tried different cold side diameters and found the small the tubing, the quicker it spoiled obviously due to the lesser volume on the smaller tubing. With such a small ar housing, I'd imagine the turbo was just about tapped out at 600 RWHP.

I think your going in the right direction. Run the wastegate without a signal on a slightly larger spring. I've got a box of 10-12 springs I've used over the years. Its going to take a few spring changes to get you where you want to be, providing you don't have a pressure leak in the cold side.

stevieturbo

The w/g should never see vacuum. Ever.

Apply boost pressure only to this ( unless using some other form of high pressure air source )