ACSGP

So if I do buy the 951, where do I get this offset cam key?

V2Rocket

http://www.928motorsports.com/parts/...aft_keyset.php

ACSGP

So this basically moves the torque curve lower. Interesting. But you lose top end, which I guess can be compensated with a hyrbid turbo set-up and a re-mapped ECU.

V2Rocket

The 951 will be slightly different, but I lost nothing at the top end.
I have done dyno testing of my car with every modification and advancing the camshaft not only brought on the torque sooner and stronger, but it still made MORE power at the high end of the RPM range than stock.

There really is NO downside to the advanced cam - the peak power RPM is moved maybe 2-300 down...not something you'd notice...but the gains everywhere are immensely noticeable.

I promise you...when you put the key on and drive it the first time, you'll wonder where it's been all your life.

dmjames

Some of us have wondered if running with the advanced cam could have much of an impact on emissions, and there's not been any real consensus to this point other than suspecting that it's not likely to be a big change on an otherwise well-running car. I'm living in a county with emissions tests, and the last test was before I installed the cam key. It'll still be a little while, but once I do have the next round of test results, I'll post both sets for reference.

951Dreams

In theory, you lose top end. But if I understand the engineering correctly (and I may not) our power curve is controlled (limited) by other things, mainly the AFM and heads themselves. The engine is capable of much more, but is limited by its ability to breath. Part of the reason they take to turbo's and 16v's so well.

I saw someone who did all the math, and it was way over my head, but if you remove the air/exhaust restrictions this engine would peak at something like 7300 RPM. I think that takes into account cam profile and the works, just removing the breathing restrictions (and accounts for being able to inject enough fuel).

That's useless in practice, since stock the DME limits RPM's to 6500, and 7k is the max with most aftermarket chips. Porsche just didn't design the parts for over 7k. So advancing the cam timing a couple of degrees may lower the MAX HP, but it lowers it to like 6800 or so RPM. So it's outside the range of normal operation still.

Even if it lowered it to 6400, most would never see that either. And you would have power loss due to valve float long before you saw the decrease from the change in cam timing. (Turbo springs or aftermarket super heavy springs might limit this effect of course)

So, in short, the power curve you see on the dyno is not due to the engine reaching it's max potential, but is limited due to a combination of of other factors. So while in theory the cam key lowers your max power, you never reach that range with max power anyway, due to other factors..... or so I've been told.

Some things to keep in mind. This is directly from Jon Milledge, a fairly well known cam grinder in the 944 world:

1) The numbers we are throwing around are crank degrees, not cam degrees. In other words, we are talking cam timing, but the numbers are degrees of crankshaft timing we are advancing the cam. 4 degree cam timing = 8 degrees crank timing, and that would cause valve collision. Period. So when they talk about 2 or 4 degree timing keys, they are talking advancing the cam 2 or 4 degrees crankshaft degrees. In cam degrees it's really only 1 or 2. I guess the guys at 928 decided that 1 and 2 degree keys didn't sound as awesome as 2 or 4 degrees? Dunno. But there you have it.

2) Jon also told me that at 4(2) degrees you're really kissing the pistons with the intake valves. There is really no room for error here. I think we was being slightly dramatic, because I haven't yet heard of anyone bending valves with a head that was shaved. So there is some leeway. Luckily as belts stretch it retards the timing slightly, so that's a good thing at least. So the bottom line is, if you do use the key, make SURE to time it perfect. If you're off a tooth normally, no biggie, off a tooth advanced, with a already 4 degree advance?? They'll more than kiss likely.

(I will say, I think the Lindsey adjustable cam gear will allow up to 6 degrees. So it seems you do have a little play left at 4. But Jon's comments don't make me feel good about more than 4)

mrgreenjeans

Yes, this has been a corrective thing since the day the car was introduced.

The proper designation IS '85.2 or '88.2 and not the 1/2 or .5 method of saying it.

All one has to do is to refer to the Porsche original Warranty and Owner's Manuals to confirm. It is written right there on the cover of the book.
Where the 1/2 came from is anyone's guess, but it stuck. When the internet became our source of conversing, the incorrect model designation went into full on wide spread usage on every forum.
But, it isn't the way the Porsche factory says it or denotes it in their numerology. Or their parts descriptions or model designations. It follows the same sequence of upgrades such as the part number on your oil filter. Or motor mounts. The last (.#) is the final generation of upgrade.

Porsche is doing the same model separation today with their generation 2 - 991 which is undergoing significant changes, and as I have seen it written already they refer to it as 991.2

Small stuff, but it does bear repeating for clarity and correct descriptions of the models, so 40 years from now it's not forgotten and people are wondering what is really what. Was there a half year ? Was there a .5 or 5 generations of the 944 ? No, only 2. The '85.1 and the '85.2 and for the 951, when it got the boost in power mid year '88 to 247 hp, it became the turbo S during the '88.2 model run. Which did revert to , as mentioned above, the '89 turbo for the final full year of production for North America.

The 968 was to receive the numerical designation 944 S3 but it was significantly different enough to warrant it's own model number in Porsche's thought processes. We were at the factory and at Weissach during the last of the 968's pre- production testings and saw many cars driven on the streets of Weissach and in the countryside on two lanes, as they got shaken down just a few months before intro to the public. Our liaison at the factory spoke about the concern in getting the right model designation and they felt it didn't sound correct to call it the 944S3. Perhaps public questioning thru product development questionnaires confirmed this,

Hence: 968.
( And thus, there is no warranty book in your car which has 944.3 written on the cover.)

951Dreams

The real story here is that MGJ was asked what they should call the new 944, and MGJ said 968. Don't let his modesty fool ya.

As always, thanks MGJ for the clarification. I'll be calling it the CORRECT 85.2 from now on. I'd seen both and wondered myself, and now I know!

black944 turbo

From experience I would leave the car stock with a chip only. If you have to have more low end get a good maf kit (vitesse, rogue). The maf will transform low end power and is easily reversible.

V2Rocket

I smogged my car with the cam advanced, failed for other reasons...
I set the cam straight up, and the emissions numbers were nearly identical.

I know a lot of "smog motors" had retarded cam timing, but the 944 engine was 10 years after the first smog rules were implemented and was also a fresh engine design (not a modified 50s/60s engine like US V8s)

The reason for failing was faulty O2 sensor wiring causing the car to go stupid rich...

V2Rocket

Got to clarify this...
The degrees quoted on the cam key/gears are cam degrees, not crank degrees. If 4 degrees advance would cause valve contact, then how is it possible to run the engine with the cam a full sprocket tooth advanced (9 cam degrees)? There is still a good bit of wiggle room here.

And the 944 engine, as stock, will not ever make peak power at 7000rpm, or 6500rpm, or 6000rpm.
The stock camshaft/manifold combination is totally done with airflow by 6000rpm. I have done a lot of testing on the dyno and with my car as a 2.5L on the early camshaft the power curve goes to a flat line past 136whp...there just isn't enough cam, or cc's in the engine, to pull more air at that point. Peak power is between 5500-5800rpm, cam advanced or not.
See:




The cylinder head flows fine, probably enough for 200hp NA. In turbo terms, that should be around 400hp at 1 bar, assuming everything else (TUNE, turbo, exhaust, intake piping+AFM delete) is up to snuff. A year or two ago I parted out a 2.5L 951 engine that was making over 425hp at 16.5psi, and the cylinder head and intake manifold had nothing done to them but a light sanding to clean up casting flash, the ports/valves were otherwise stock.

The late 944NA camshaft has 1 more mm of exhaust lift, and 8 degrees more exhaust duration, and was worth 4hp by itself when Porsche implemented the change on series 944 engines (all other internal parts, and the engine tune, were more or less identical from 85-1 to 85-2). So a tiny change in cam was +4hp.

So you can keep the stock cam and run it advanced for a buttload more power at all RPM ranges, the car idles better and is so much stronger everywhere...or you can get a new cam designed for your turbo, intended RPM range, etc and really maximize things. The difference is, advancing the stock cam is $24 or so, and a new aftermarket cam is $600-$1200, depending who you buy from.

The AFM of course is the first restriction to deal with, but that's not what we're talking about here.

mrgreenjeans

As I went into a bit of a long diatribe about the model designation, I will only clarify and re-state one thing about that and add it here.

The actual model designation on the second series warranty / owner's manual books found in the glove box of our cars, is actually printed :

944/2.
Not actually 944.2 as I wrote, and certainly NOT 1/2 as is commonly and mistakenly spoken and written. I can actually see some reasoning behind how some may have mis-read those covers and thought they saw a 'half' or 1/2 instead of 944/2. The eye didn't capture the loss of the '1' , but instead "saw" a 1/2 , so now thinking and saying it that way instead of seeing and saying the model as "second series".
The part lists descriptions are actually more accurately designated with a decimal following the model.

Hope this clears up any misconceptions.

jeff968

I think the ship has sailed on this one. Most car enthusiasts refer to mid-year introduction cars as .5 referring to half a model year later. This goes way beyond Porsches.

mrgreenjeans

BUT,

is that totally correct thinking ?

odonnell

As long as you're understood clearly. I (and I think many of us) have seen all sorts of monickers for them... 944/2, 85.5, 85B, late 85... "correct" is subjective. But that's just me being subjective.