Finally got to validating & installing a wastegate on a supercharged setup. Pictures and story below. Enjoy!

I'm running a Novi 1200 SOS kit with a 2.8" pulley. Pulley was purchased from ASP Racing and arrived 1 week after ordering. Pulley is steel (you have the choice of Al or Steel) and have been coated by Carbinite Racing for anti-slip mitigation.

http://autospecialties.com/
http://www.carbiniteracing.com/

Pre-coating, bare untreated steel.


Post Carbinite Racing treatment. Feels like sandpaper and does indeed work!



The pulley will produce ~18 PSI of boost and wanted to limit it to approx 12 PSI. My first attempt to execute this was with a Boost Limiting Valve (BLV) from 928 Racing. This is a very simple device; ball & spring which can be adjusted to bleed boost at a certain spring preload.


Unfortunately, the BLV failed to purge the volume of air I was trying to bleed and did not work for this application. Top 2 plots below are with the ball completely removed from the BLV and shows that boost was not being limited. We had to stop the run at 7000RPMs due to excessive boost levels.


Back to the drawing board. Purchased a Tial MVR Wastegate which is built for turbo applications. This unit comes with a handful of springs at no extra charge! Below some comparison pictures.






The Tial has almost double the opening size and should do the job just fine! Here's how I rigged the system.






It's a very snug fit, but works with clearance to spare. I installed a 11.6 psi spring for these runs. FYI, here are the springs Tial provides


Dyno indicated that the Wastegate did its job. The boost does seem to bleed below the target set point. I'm thinking this is happening as wastegate valve is being pressed more open as the pulley is producing more boost (PSI). Anyway, I'm happy with the results as far as boost limiting goes.

The bold line is my new 2.8" pulley setup @ 12 psi; thin line is my baseline 4" pulley at 9.5 PSI. There is definitely more area under the curve and will give the midrange I'm looking for!



Unfortunately I hit a wall at 6800 RPM where HP flat-lined and Torque fell off. Looks like I'm hitting some type of restriction and can't figure out why. If anyone can help, please let me know here https://www.s2ki.com/s2000/topic/971...-less-peak-hp/

Old setup made 387 whp, new setup is 353 hp

(yes the torque Y-Axis scaling is wrong)



That's all for now.

edit: I just bought a MAC controller and will update this post with new results.

 

I think your dropping power rather then maintaining it, because that's exactly what your boost is doing. You bleeding down back to your original 9psi rather then bleeding at 12psi and holding. Your also spinning the blower faster, which means hotter IAT at that 9psi net then previously. This set up may work in theory, but may not in real world due to the mechanical nature of whats going on. If you could electronically effect the opening and closing of the waste gate in a variable fashion at any rpm, you might have better luck.

 

An interesting route, now needs to be massaged but you get the good bit, a 45 mm turbosmart hypergate would be an easier fit if someone wants to go this route.

 

Great idea, hope you can work out the bugs.

 

What about restricting the intake?

 

Awesome install solution. Try a different spring or boost controller and see if you can dial it in.

Restricting the intake would cause torque to fall off and HP to flat line. That's because HP is directly correlated to cfm, and once you hit Max cfm you can't go higher. HP and torque are mathematically linked via rpm, so if HP is constant and rpm keeps rising, torque must drop. Interesting that the dyno charts show that happening with this setup. I preferred a BLV or wastegate over an intake restrictor to avoid torque dropping off, because I thought they would just vent excess boost without affecting cfm flowing into the engine. Maybe that assumption is invalid?

 

That's a great bit of info (thank you for that); didn't know that HP directly correlates to CFM. IF that's a fact, then this may be what's happening here ???

I'll be installing an electronic boost control solenoid to see if I can maintain the 12 psi without dropping boost. I'll redyno/retune and see what happens.


Edit: Found this formula below, which indicates that the blower is in an inefficient range and producing less volume at higher RPMs.

Peak Airflow (lbs/min) = Power Level (hp) * Air to fuel ratio (x:1) * BSFC /60

 

This is a great idea. You are making less peak hp because the boost is drooping off too much at redline. A Mac boost selonoide controlled with an aem ems should be ablue to fix this by closing the wastegate a little more by redline. Also another problem is that your maxing out your blower speed just to run 12 psi, when will make your 12 psi of boost not as good as 12 psi of boost from a smaller pulley because the air will be hotter.

Realistically if u want 400whp with good mid to bottom end just run a good turbo setup using a small turbo like at bb gtx3071r.

 

That will help the issue. Your wastegate is seeing all the boost at once and opening wide open quickly once you hit the spring pressure of the wastegate. The boost now vents and cannot recover in time. Remember in a turbo application you are venting exhaust gas, not boost, which has way higher volume that needs to be evacuated than your setup which evacuates air. Hence, any wastegate you install will err on the side of venting too much, too quickly. A good electronic boost solenoid that can ramp its own duty cycle based on the boost it sees gradually as you build boost will catch your wastegate in time and make sure it doesn't open too much.

You are basically creating a boost leak in your system with this method. It is not going to be very easy to dial in the correct parameters. Wastegates on turbos are much more forgiving, as the exhaust gas isn't pressurized and largely still continues down the main exhaust path. Your boost is wanting to escape out the wastegate too readily since it is the path of least resistance.

 

Actually it's not. Boost is a linear function and builds up as a function of RPM. Without a wastegate it's like the green line below



When on the dyno, I see the wastegate cracking open very so slightly and increasingly opening with RPM. The wastegate opens more (purging more boost) as the blower is building more PSI, up to ~18 PSI worth.