Z

Based on having seen somewhere easily over a thousand 928 dyno pulls, on a DynoJet, SAE corrected, not counting spikes from misses or lifting abruptly, no funny business manipulating the correction factors, very typical numbers are:

S4 5-speed- 265-270rwhp
S4 Automatic - 250-255rwhp

Some people are probably better off not dynoing their cars. I saw one car that looked great. The owner didn't have much or any experience with other 928s, thought the engine was in great condition and running strong. It wasn't. Slowest S4 I've ever seen. He was happy until he saw the dyno numbers. It did 175rwhp. Sometimes ignorance really is bliss.

jorj7

Mine was 262-263 rwhp on a Dynojet when I first got it (ie stock). Later dynoed 251-252 rwhp on a DynaPack while still stock.

killav

Good gracious, to get down that low on an S4 would take bad hall sensors, knock sensors, faulty flappy, way jacked up cam timing, clogged cats, bad MAF, vacume leaks and God knows what else.....

Bill Ball

My 89 S4 auto bone stock except RMB (minimal to zero effect) was consistently 262 RWHP on a Dynapac over a couple of years at about 130-150K miles. I've seen as low as 250 and as high as 270 RWHP on decent S4 autos.

rgs944

Sean you are talking about wheel right?

GregBBRD

I personally think that is a "bit" optimistic, for an automatic, from what I've measured, but not by much.

I would think that if you got an "exceptional" engine, with everything at the "high end" of factory specifications, that might be real.

GregBBRD

Yup. Completely agree.

GregBBRD

See end of post 16.

rgs944

So it sounds like around 260 at the wheels and close to 300 at the crank would be a likely average.

928 at last

I pulled 260 rwhp, best of three, 267.5 torque, stock. (With the top end refresh, and new sensors).
77 degrees farenheit, 28% humidity, 28.94 in.hg pressure....10:27 in the morning, engine fully heat soaked.

928 at last

Figure on 20% parasitic loss throught the tranny, so roughly 325 chp.

Courtshark

I pulled 267 on a dynapack in my now-sold 88 auto, which had a refreshed 89 motor with about 4k miles since the rebuild at the time, bone stock.

jcorenman

Wait a minute, aren't you the same guy who's been saying that he wasn't going to dyno his car because he didn't care about numbers?

I'm not giving you a hard time (much), and please don't dump a pile of crap all over me again. I'm just saying that your sudden interest in horsepower numbers is kind of amusing.

It doesn't matter what people "think" horsepower is, it is something that can be measured. The factory spec for the S4 (brand-new everything) was 316 bhp, that is SAE horsepower measured at the crank. If you take that number and figure 15% loss with a 5-speed that gives you around 270rwhp, and a Rogerbox with 18% loss would be around 260rwhp, that's rear-wheel hp on a chassis dyno with SAE correction. Which is pretty consistent with what's been reported here and elsewhere. So I think the factory number for the S4 is pretty good, on average. (GT's are different, but that's not what you asked).

That's for a new car. A 25-year-old car will be lower, depending on what sort of condition it is in. "Refreshing" the things that need refreshing is helpful, but doesn't add any horsepower-- it just gets you back towards where the car started. And don't overlook the MAF, it is the key component for fueling.

As for power-adders, don't believe everything that you read. Many folks report big numbers for x-pipes, but remember that they are swapping cats as well as adding the crossover. An x-pipe with new 100-cell cats (or no cats) will certainly outperform a set of melted, clogged factory cats. I do not know of anyone who has done the apples-to-apples comparison and just added the x-pipe without changing cats. I am not saying that x-pipes don't add hp, they do. But doing a proper before/after is not simple.

Will you be at Sharktoberfest? I think there is a dyno in Anaheim.

SeanR

Yes. Btw, my "before" dyno was a dead 250hp. This was before x-pipe and intake refresh. After was the 289.

AO

Here a 'BEFORE" dyno sheet from a 1990 928 S4 (auto) with an x-pipe and no cats. This is the same dyno that i used last weekend where I posted 490HP.