Dan87951

Need some advice. The problem is at high rpms I'm loosing about 5psi of boost. My car is a 87 951 and has the following upgrades done to it so far, Huntley Racing Stage 3 MAF, Huntley Racing Chips, Manual Boost Controller set a 15psi boost, 3" Testpipe, Autometer boost gauge/ Air to fuel gauge, as well as the ARC2 and ARM1 gauge. At about 5500rpms my boost pressure is around 10 psi and falls to a low of 9psi and around 3800rpms my boost pressure peaks around 15psi-16psi. I'm loosing some major HP here, and was wondering if a new wastegate would fix this. I really like the price of the Lindsey Unit but will it hold 16psi to redline or even 18psi if I decide to go that high?? I hear the deltagate is a pain to install, but I heard SFR is making a cross over pipe with it already welded on?! Any ideas would be great. I'm defenitly going to install a aftermarket turbo down the road and would a wastegate that hold up to it as well. My turbo down the road is going to be something small probably not run it at 18psi boost, and what something that fits nice in the factory location.

Thanks
Dan Scully
PS: Where can I get a fuel pressure gauge for the end of my fuel rail. Also has anyone installed SFR fuel lines?

Perry 951

Definately could use a wastegate. I have the Deltagate and have 0 bleedoff..

However, you are on the stock turbo, and they are not able to hold high boost up in the revs. The "S" can do it better, but still some drop off.

I got the Huntley Stage 2 Turbo, and am running 19psi now, and it never falls off. It is so fun! Can't wait to get the MAF on it in the spring!

Dan87951

I was the stock turbo should be efficent to hold 15psi of boost close to redline. My other 951 with 200k holds 15psi boost almost till redline but fades off to about 13psi. It puzzles me.

Dan

OZ951

Use any of the dual port wastegates and you can set whatever boost your motor is capable of producing. The boost itself contributes to holding the wastegate shut until the required differential is achieved and the gate opens.

Wayne.

Danno

Yep, Perry's got it right on the nose with that one. Most likely your dropping boost is due to the turbo maxing out. Both the standard Turbo and TurboS has the same max-boost of around 11.5psi, and they both drop off to about 10psi at redline. But the non-S starts dropping at about 4400rpm while the S can hold 11.5psi til about 5200rpm.

What happens when you start upgrading with free-flow exhaust, intakes and start turning up the boost, is that max-boost is higher and so is total flow. Thus, the drop-off of the boost-curve (and the resultant torque curve) is even earlier and drops off quicker as well (because flow-limit of turbo is still the same, but total flow is higher now).

Here's a dyno chart of a stock '89 @ stock boost:


and here's a dyno chart of both an '87 and an '89 with Authority Stg2 kit (15psi):

As you can see, on the '89 with higher-boost (same stock turbo), the torque curve hits a higher peak, but it also drops off A LOT quicker than the stock configuration. Another interesting thing is that the '87 with smaller turbo builds boost faster to a lower peak, while the S turbo has more lag, but builds to a higher torque peak.

These charts came from Farzaan's excellent dyno-chart comparisons page: http://www.novustelecom.net/~fkassam/dyno/dyno.html

As for the stock wastegate, it may or may not be the problem depending upon whether the spring has weakened or not. Rodney Wiggins recently built a 400rwhp with an almost perfectly FLAT torque curve (even better than stock '89 Turbo's curve). He did this using an all STOCK lower-end (pistons, rods, crank, cam, valves) and a STOCK wastegate. I'll have a dyno-comparison with a stock car posted soon...

Anyway, it wouldn't hurt to shim your wastegate to make sure it stays shut like it should. That way you'll know for sure that your turbo is the culprit.

I posted a procedure on how to shim the stock wastegate here: http://forums.rennlist.com/scripts/rennforums/ultimatebb.cgi?ubb=search&search_forum=20
You'll have to turn down your boost-controller a little after shimming the wastegate to get the same max-boost level as before.

Dan87951

Thanks for the much needed info. The link you gave me for shiming the wastegate did not work, what do I search under? Also where can I buy a shim at or are they easy to fabricate.

Thanks
Dan

Danno

Whoops, sorry I copied & pasted from the wrong window. Here's the correct link on how to shim our stock wastegate. http://forums.rennlist.com/scripts/rennforums/ultimatebb.cgi?ubb=get_topic&f=18&t=0002 00
Shouldn't take any more than 30-45 minutes. It would actually help if you've got a 3-5 year-old kid with small hands who can reach above the wastegate to undo the two bolts that hold the hanging bracket to the torque-tube clamp.

Another example of Porsche's "service engineering" where the design engineers obviously speak a different language than the repair technicians. It really isn't that tough to make a racket that can be unbolted from the bottom with a upwards-aiming socket. But NOooo.. You're going to need the socket, a universal swivel, about 8-15" of extensions and a medium 3/8" ratchet. In fact, it wouldn't be that hard to make a QUICK-RELEASE bracket that can undone by hand even.

My other pet peeve is the one upper belt-cover bolt that's hiding the power-steering belt. If they just moved that bolt in ANY direction by 5mm, you can easily remove it.