MY 930 Torque/Horsepower Curve
 

Porsche 930/911 Turbos up to 1989 are well behaved and can be forocious (At least the ones I have driven). My question is: My particular 911 turbo (1987) seems to have a torque curve that comes on hard around 3200 and begins to diminish above 4200 RPMs. It pulls very strong. Example; Going from second to third getting on the freeway I leave 2nd gear at 4200 and hit 3rd and the RPMs will be about 3000 and then you have to wait a second for the boost to come back on...Is this normal? My car would be awesome if you went from gear to gear on boost.. I would think that .8 bars of boost would generate a longer torque curve into the 5K RPM range ( above the 4200 RPM peak ) remedying this phenomenon. Does anyone else experience this 4200 RPM peak torque. Can it be cured?

Thanks

Bob

My '87 comes on boost about the same time yours does, but it pulls hard all the way up to redline. Then I'll shift it. I really don't feel the boost falling off. When I shift from 2nd to 3rd I'm still in the boost range. My car is completely stock.

Just a guess here, but maybe you have a faulty wastegate or BOV bleeding off the pressure. Basically what I'm saying is that your car is probably making boost, but it's not getting to the engine.

Bill,

Your car pulls as hard from.. lets say 5K-6K as it does from 3200-4200 RPMs? My boost is there... but just doesnt pull as hard....Maybe I have an ignition problem (Advance)?????? Anyone have any Ideas?

Bob

Is your engine stock?

Brian,

Yes...has the fabspeed exhaust muffler and BMC intake...Other than that Bone stock....Will a stock engine pull as hard from 5-6K like it does from 3500-4500???

Bob

No.
Stock engines are done at 5500rpm, one reason for the long-geared 930 tranny. I don't think that changed until the K27 was used in the 965.

Try to find others who have stock cars and get their impressions. You could very well have a small issue robbing your power, it's hard to say from a few typed words.

My car is stock and when it comes on boost it feels linear and very smooth all the way up to 6000 where I normally shift. When the clutch is released for that next gear my boost needle jumps right back up instantly and the gauge reads full boost. My full boost is at .7 and it hits the same mark EVERY time. I never got the feeling that the boost starts to let off or the car doesn't pull as hard.

I don't want to argue with Brian cause he does know his stuff and you should listen to him. I'm just saying what has been my limited experience.

I would like to install a K27 HF ...Will this help the top end?

Bob

Actually Bill, it is hard to tell from the seat of your pants that the power is dropping off. You can see it clearly on the dyno. That is why Bob needs to hear from folks like you, who actually own a stock 930.

The HF is likely overkill for a stock engine. I'd try the generic K27-7200 or equivalent. Depending on the engine type (930/xx) your exhaust system is likely holding you back.

I'm think the recirculating assembly is at fault (as suggested earlier as the BOV).
If you are not on a budget then headers & a K27HFS is the way to go.

My stock '87 930 feels like Bill's does, above. Only difference is that the boost gauge pegs at 0.8. Otherwise, feels pretty linear from my seat-of-the-pants gauge.

See, your car is stock and my car is stock and we get different boost numbers. I'm sort of confused by this too. Not to hijack, but I've heard the US cars stock springs were .7 and Euro cars were .8. Can someone clarify this for me?

I have a .8 spring I'm planning on putting, but haven't got around to it yet.

A good place to start would be a dyno run.

Bob, does your car loose power in 1st gear?

Your car should be powerful enough to not feel a drop off in 1st and probably 2nd gear. I would suspect a problem if you feel the power dropping off in the lower gears.

As for the stock boost discrepancy, it could be in your gauge. Stock boost gauges are not the most accurate. It could also be the springs. They may be 20+ years old or one may have been replaced by a 0.8bar somewhere along the way.

Brian,

No it doesnt. Also I forgot to mention it has a 1 bar spring. Thats why it boosts to .8. That shouldnt matter. I drove it this morning and nailed it getting on the freeway and she pulled up to ~5k when I shifter. I did notice a consistent hard pull until it started missing a little bit then I shifted. She sure runs great when its cool outside. I'm going to replace my fuel filter and check the fuel pressure this weekend. Got a clue why it has a subtle miss under boost? What would you check first....Timing advance? Fuel obviously??


Bob

if the car begins missing (breaking down) at higher rpms you may need a set of plug wires
I have seen this several times in the past (even with brand new wires so buy the best available)

Robert, get a proper gauge hooked up to test your boost pressure properly. I am wondering if you overboost and the safety switch cuts in.

If you have a 1.0bar spring but are only seeing 0.8bar you have a boost leak, which would manifest itself the way you describe. Generally it is caused by a faulty O-ring on the intercooler or throttle body.

The overboost protection switch kicks in at 1.1-1.2bar, close enough to sometimes cause issue when using a 1.0bar spring.

I was told that the boost pressure should read .8 indicated as it begins bleeding off the over pressure. When you hit a smidgen over 3k with your foot atleast half in the throttle it comes on like afterburners. I have been reluctant to just stop on it (FLoor it) because I guess i'm afraid of breaking it. Everybody says the engine was designed to take the abuse..But coming from a High Perf. VW background I've had things break that werent supposed to. Does the engine mind reving up frequently to 5K RPMs plus.

Bob,
An engine with stock head studs and rod bolts has a safe redline of ~6200rpm or so. Unfortunately a stock engine is done by 5500rpm so you're just making noise after that point.
Your car? I have no idea. Unless you know what's in the engine it is impossible to say.
My engine has ARP head studs and rod bolts. I shift at 7000rpm and it begs for more. My power likely runs out before 6500prm but the momentum keeps the engine in boost through the gear changes.

I don't understand about the 1.0bar / 0.8bar deal. If you have a 1.0bar spring you should hit and sustain 1.0 bar from ~3000rpm or so to redline. If you are bleeding down to 0.8bar on a 1.0bar spring you have a leak.

How does your boost controller fit into this? If you have a 1.0bar spring then 1.0bar is the lowest setting you should have. The boost controller would hold off the signal until the preset (above 1.0bar) is hit and then dump the signal to the wastegate which then pops open. Is this how your controller works?