KC911

I remember when Loren first appeared here on Rennlist back in '03 (and later on Pelican) and began his online chip pi$$sing contests. In the beginning, he wouldn't concede that even the '84-86 chips could be "improved" (i.e. as Porsche KNEW what they were doing), and that anyone who percieved an "improvement" was simply an idiot and was "feeling things". To my knowledge, he's never conceded that chip timings "can" be SAFELY advanced if one is willing to run the higher octanes (particularly those of us outside of CA that have access to 93). I'm just a "backyard" hack, but I know the earth isn't flat .

Keith
'88 CE coupe

scarceller

Keith,

I don't want a pissing match as it is not my style. I simply wish to improve our understanding of the facts.

The fact is that the 87-89 factory chips bumped the timing up about 3deg at WOT above 4K RPM. This is a FACT! not speculation.

Then we see in this thread that the factory also bumped the Octane requirement up from 87 to 91 for 87-89. I'm just wondering if these are related?

Just want folks to think about this.

KC911

I think that applies to ALMOST everyone of us .

Hester

Can someone post the advertised performance statistics for the 84 through 89 models?

Back in the day, we used to bump the base timing up a few degrees and run premium to go faster than the kid next door. In a short while, we would get sick of buying premium and listening to the car ping at low RPM under load and knock the timing back. That was back when men were men and engines had distributors with vacuum advance.

Based on everything we've learned in this thread, its safe to say that the advanced timing in the 87-89 ignition maps (and maybe increased compression) is why Porsche changed the fuel requirements to 91.

Putting "chips" in those 84 to 86 cars is a cheap way to unlock performance because it does exactly what we were doing in high school: it advances the timing. The downside is that you have to run higher octane (and therefore more expensive) fuel.

KC911

I don't have the specs in front of me, but hp increase was 10 for the '87-89s over the '84-86 versions.

scarceller

Here are the WOT Timming maps from 2 factory chips, one from 84 the other from 89. You can clearly see that the 89 chip bumped timming up after 4520RPM.

scarceller

Here are some specs I found on the net:

1984 Carrera - shows 200hp@5900RPM
http://auto-specs.zercustoms.com/p/p...fications.html

1988 Club Sport - shows 214hp@5900RPM
http://auto-specs.zercustoms.com/p/p...fications.html

EDIT: I had a link to specs on the 89 Speedster but the specs where wrong, I removed the link.

Did not find the 89 base Carrera spec, sorry.

Peter Zimmermann

Correct: (USA versions) - 207 DIN @ 5900 ('84-86) and 217 DIN @ 5900 ('87 89).

JBO

My SC owners manual says run 87, but according to most of you I should ignore that and run premium (which is what I have always done, and usually Chevron), but I'm not sure it's not a waste, with 8.5-1 CR and a rebuilt top end and thus without carbon buildup. I am concerned now that my local Chevron station pumps now say "now contains 10% ethanol", which I don't think is a good thing.

Dave Thomas

JBO, we've had 10% ethanol for at least 15-20 years here, never any problem in anything I've used it in, including a 12:1 CR auto-x car, Saab Turbo with CIS, '88 Carrera, etc. No fuel line or hose problems, nothing. I'd have to check my archives, but I *think* the fuel and car manufacturers are OK with ethanol at least to 12% or so? There was a discussion on Pelican a few months ago - you might do a search there.

Oh yeah - put me down in the "loudmouth shadetree" column

Peter Zimmermann

You are correct, Porsche recommends RON 91 lead free fuel for 180 hp engines, and RON 98 for the RoW 204 hp engines. 91 RON = 87 (R+M)/2 (the number most-often used in the US). Somewhere along the way that recommendation cut things a little close, especially for Lambda-equipped '80-83 SCs, which can have a tendency to ping with the ignition timing set to factory spec. That ping disappears immediately when premium (91/92 (R+M)/2 octane) is used. I've always recommended Chevron Premium because: (1) the potential for 87 to ping, and (2) the concentration of Techron in Premium is higher.

How ethanol affects things I don't know, but I do know that ethanol's RON number is considerably higher than the gasoline it's added to, so one might think it can only help (maybe 87 + 10% ethanol is a good thing). On the pump that delivers gas + ethanol are the listed octane ratings different?

Hester

Cool. Scarceller got us some specifications to compare an analyze.

The 84, 88, and 89 all had the same 3.2 liter flat six with a few differences.

The 84 and 88 had the same bore and stroke but the 89 had a smaller bore with a longer stroke. The reported specifications show the same displacement for all three years (3164). As far as I can tell, there are only two variables that effect the swept volume of the piston as it travels the length of its stroke in the bore; bore and stroke. A piston traveling a stroke of 74.4mm in a 95mm bore produces a swept volume (i.e., displacement) of 3164 but a piston traveling a stroke of 75mm in an 87mm bore should produce a swept volume of 2675 not 3164. If the 87mm bore specification on the 89 is right, it should be a 2.7 liter flat six. Maybe the published specifications are wrong? Am I missing something?

The 84 and 88 had a compression ratio of 9.5:1 while the compression for the 89 is a reported 10.3:1. “Compression Ratio” refers to the ratio of the displacement of the piston as it travels the length of its stroke in the cylinder bore to the volume remaining between the top of the piston and the cylinder head when the piston is at top dead center (the “Squish Band”). You can increase the compression ratio by either decreasing the size of the Squish Band (e.g., by “milling the head” or by using a domed piston) or by leaving the head the same and increasing the displacement either by increasing the bore or lengthening the stroke. As I mentioned in the previous paragraph, the 89 bore and stroke should have produced a smaller displacement which would have lowered the compression ratio. Either Porsche made the Squish Band significantly smaller in 89 which enabled them to decrease the displacement and increase the compression ratio at the same time or the specification that we have for the bore in the 89 is wrong.

Cam timing can effect the dynamic compression ratio. The static compression ratio is based on the volume that the piston displaces between the bottom of its stroke (Bottom Dead Center or BDC) and the top of its stroke (Top Dead Center or TDC). The intake valve does not necessarily close at BDC but can stay open until after the piston begins to travel up through the bore on the compression stroke. The dynamic compression ratio is based on the point in the compression stroke when the intake valve closes and compression actually starts. If the cam is not closing the intake valve until later in the compression stroke than BDC, the dynamic compression ratio will be lower than the static compression ratio. By lowering the dynamic compression ratio, the engine will become less likely to produce auto-ignition from lower octane fuel. Thus, two engines with the same bore, stroke, and squish bands can have different fuel requirements.

All of this is giving me a headache and all it has done has brought me back to the conclusion that, although it may be a waste, erring on the side of better fuel with more octane is best. There are way too many variables for a non-engineer like me to consider. Now, the ethanol debate should be interesting.

Peter Zimmermann

Hester: Not sure where those numbers came from, but they're not correct. All 3.2 liter Carreras are 95mm (bore) x 74.4mm (stroke). The numbers wouldn't even work for an '89 Turbo, which was 97mm (bore) x 74.4mm (stroke), which gave 3.3 liters. I'm not aware of an 87mm x 75mm ever being used by Porsche in a 911 automobile...the closest would be a 2.7 liter Boxster that was 85.5mm x 78mm.

scarceller

Peter,

If you know those HP numbers in those links are wrong for sure I'll be happy to edit the post and pull those out. Wrong numbers are Bad.

Hester got those from my prior post. I put in a few links to a web site with specs but the site is NOT a Porsche site.

scarceller

Peter,

I'm sure your HP numbers are correct. I posted a few links to some specs I found but I think those specs may be wrong. If you are 100% certain on the HP numbers you posted:

I'll edit my prior post and remove the links all together.