95ONE

Kinda different at the same psi eh? (Blue vs. Green)

Whats especially interesting is how the 15 and the 17 psi give practically the same hp. (Boost drops to about the same at 6k rpms due to compressor maxing out no matter what it boosted earlier. )
(Green Vs. Red)

Oh yeah. This is BEFORE I did the intercooler install. 2.5" exh., Filter, Autothority chip set. All is same for Stock Wg. vs. Dual Port 38mm.

Just thought I'd clarify the difference between the two boost levels. Practically NOTHING different up top. (Obviously from almost identical boost loss up there.)

RRRandy

So, blue is stock WG @15psi and green is DP-Wastegate @15psi, nothing else different? That means that the DP wastegate alone is giving you 32HP!? And the only other mod is the Autothority chip. That’s a pretty clear chart. Interesting to note that the increased psi did not change things much. Do you think there is another factor that may be bottle-necking power and preventing the 17psi from showing more gains?

eclou

Despite the same top end HP, you should notice that the torque curve climbs proportionally to the boost. Mine hit about 300 ftlbs with that config.

schnellfahrer

That's a 26/8, right?

95ONE

No. Thats a 26/6 stock 1986.5 951 turbo.

Yes. the torque did improve much in mine also, I just didn't post it up on the graph because there were too many lines. But it's because the torque peaks sooner in the rpm band and the turbo can keep up there. but when the blower runs out breath up high, it all equals back out to the same as the 15psi setting. (Which at that point is more like 12psi.)

And YES! there is a bottleneck. The compressor! It's just straight up too small and can only blow a certain amount of CFM at those rpms. So no matter what boost you start out with. Say 20psi if I wanted to. The horsepower amount at that rpm (5700)will still be almost exactly 256hp because the compressor cant send more that about 13psi at that rpm, regardless of how high it boosted earlier in the rev range. That is the whole reason I posted this. TO show you guys, no matter how much boost you throw at the stock compressor, it's not going to gain ANY more power on that mod alone past 15psi. (Maybe a few more from momentum.)

So, end result, if you want any more horsepower than that, (Sans head porting and cams - which will be optimimized by a larger turbo anyway) Just start out by changing the turbo. Don't try to turn up the boost past 17-18. (It does help alot in torque down low and us track guys know the importance of that out of a corner.)

95ONE

Nothing else was different between these two runs. STRICTLY wastegate. I was sure to keep that constant. Yes! 32 hp! That's why I posted the earlier "HOLY COW" thread. I had the same reaction to that upgrade as you did.! - NO. the other mods were filter and aftermarket straight through type muffler 2.5"

Read above post about why Max HP didn't change much.

schnellfahrer

256rwhp from a 26/6 is quite nice.
Most charts I've seen top out at around 240rwhp.
Do you have a chart with torque?

Mike1982

Yea, that is a nice chart. I had about 242rwhp and 297rwtq running 17psi and 14ish at redline last year. This is one main reason I am changing turbos this winter. Need to get a nice new turbo that can actually produce power and keep it! My mid-range isn't bad but you can feel it does fall flat on top. The maf/piggyback did help mine to get more upper end power but that can only help so much.

kevincnc

Sorry this is probably a stupid question, but can someone explain where the power is coming from? If the stock and DP wastegate both hold 15 PSI, what's the difference? I thought the only reason to improve the wastegate was if it couldn't hold the pressure that you want.

95ONE

yes! the stock wastegate can't hold the exhaust pressure. so it struggles to get to 15. BUT>>>>>>>> It IMMEDIATELY lets go and drop to 9psi. Therefore. It is almost NEVER at 15psi and mostly at some crappy lower one. (Old springs, poor design, bad cyclic valve, whatever the reason.) SO to answer your question, They don't BOTH truly hold 15psi. The Dual Port hangs on to it until the compressor weazes out, and the stock wastegate jut taps 15psi and starts letting go immediately even though the stock turbo can handle more.

RRRandy

That’s awesome. By straight-through exhaust, you mean test tube in stead of cat…but other wise stock?(stock being 2.5” ‘en all). How much to you think the chip is helping? By that I mean to ask; without the chip, would you expect to see the same gains between the SP-WG and the DP-WG?

porshhhh951

if your running the same boost levels yes. The higher the boost level the more effective the DP wastegate will become aparent.

95ONE

the difference would be same on stock chips. IF there wasn't a boost cut on the stock chips.

RRRandy

95one, If you are running a manual boost controller, then there is no way the chip can cut boost, right?

95ONE

Honestly, I am not qualified to answer that question! I'm not sure how the DME/KLR work together. I know the klr can still "read" the amount of boost the engine is receiving. But I'm not sure how it handles the method of "boost cut" Be it through iginition or it's own cyclic valve. I'll do a search........good question.