Pete M - "Either way, unless you have a super restrictive intercooler or something, i don't think it'll make much difference."

If you cool your charge air... you will have a pressure loss. Typically it will be 1-3 psi depending on IC core design. If you're looking to change it 1-3 psi..its a quick easy way.

Biggy72 - "I'm just curious how you propose to actually make one work with only one solenoid? Where does the other side of the actuator plumb into that makes it any better? "

The bottom port is connected to your boost source, the top port is connected to your solenoid which is then connected to your boost source. like so...


There are several reasons why this is MUCH better than running solely off spring pressure...
Springs open at a linear rate. So as your boost pressure increases the valve creeps open, bleeding off exhaust pressure necessary to spool the turbo (pressure and temperature differential across the turbine wheel). So you're making the turbo "laggier" than it should be. with teh twin port actuator you can keep the gate closed with FULL Spring pressure (Upper Port pressure+ spring Pressure - Lower Port Pressure= pressure applied on wastegate valve) so if your upper port is the same as your lower port...your spring pressure is holding your valve shut. Your EMS controls the solenoid and keeps the unmodified boost signal to the top port 2-3 psi prior to the desired boost level. At that point the pressure at the top port is blocked via the solenoid (0psi + spring pressure (maybe6psi) - Boost pressure (say 10psi)= -4... your valve is going to open very quickly... maintaining your boost level.

Beyond that...there are gear dependant maps, RPM based boost control, time based boost control, etc.

Single port actuators in comparison are quite inferior and harder to accurately control the wastegate valve compared to dual port gates.

Ernie,

You're right, except do you know what sort of boost pressure these engines run? With the restrictor and 12k you can't be running a very high boost pressure. With that said you would then need a dual port actuator with a very very very light spring in order to set the whole thing up the way you proposed, because otherwise there would never be a large enough pressure differential to open the thing.

Maybe i'm wrong here, but why would cooling the gas necessarily change its pressure? This isn't an adiabatic process (by definition). It was my understanding that the only reason you get a pressure loss is due to friction from the relatively high velocity air going through all the fins.

We've seen about a 2 kPa (0.3 psi) drop across our intercooler at peak boost. I'd call an intercooler with a 3 psi drop an absolute disaster. 20 kPa of pressure loss is worth over 30 degrees of intake temp (assuming a bar of boost and ~50 degree intake temps). Maybe that kind of loss is typical in street cars, but it sounds terrible.

Pete M,
Well when your intercooler is 24x12x5 and you're running 40lbs of boost on a 67mm turbo 3psi of pressure drop "isn't bad".

"Typically it will be 1-3 psi depending on IC core design." The more restrictive the IC the more pressure loss. As you were saying the pressure loss is due to the friction in the core. yeah you're right.

What kind of intercooler thermal efficiency are you seeing from your IC then? Whats your compressor discharge temp, post IC temperature, ambient temperature, and the pressures at those same points.

I don't have the data in front of me, but 120-140°C compressor discharge, 40-50°C post IC for 20-30°C ambient is in the ballpark. Loss is about 2 kPa at peak power, somewhat higher by rev limit. This is all on about 16 psi of boost, although boost is heavily rpm dependent.

It's hard to actually get useful numbers for some of this stuff, because we're rarely on throttle long enough for anything to get to a steady state situation, and the core is sized far too small for steady state dyno loading. Thermal inertia tends to dominate on track.

I'm really impressed with 16 psi. We're not up and running yet, but from all of my calcs I'm hoping we can hit 12psi at peak. You guys are running the gt15 aren't you?

16 psi is the approximate boost at peak power. It's more like 18 psi 1000 rpm lower. We rarely hit that on track though, except on a launch or if the driver exits in the wrong gear. We let it run the boost there because it doesn't seem to mind and it was just a number in a table. It's actually far more prone to detonation higher in the revs, even though the boost is lower.

One of our drivers was briefly stuck in 4th at aus last year. We were on full boost then. Our record last year in testing was 25 psi of boost when one of the drivers hit upshift at 6,900 rpm with the turbo fully spooled. Was firmly on overboost cut by that point though, so doesn't really count.

And yes, last year we used the 15v. Haven't made our final decision yet for this year.

just curious...the teams that are running with turbos, are you using head shims at all?

quote:

Originally posted by joshiepoo:
just curious...the teams that are running with turbos, are you using head shims at all?

As in a thicker head gasket? No. We (well, team members before my time) did that initially in testing in 04, but decided that it was not a very good solution. Stuffs your squish and the lower compression isn't great for efficiency anywhere you're not on full boost. My advice, build yourself a det can and try it with stock compression first. Start at low boost and conservative timing, be careful and you'll be surprised at how much boost you can run with stock compression.