Best Shift Points

[sundaypunch]

My take is that in any engine, keeping the rev's down will extend it's life. In my daily drivers I shift low, drive responsibly, keep up on maintenance and have had great results. Over 200k with no engine work on several cars at various times.

The Porsche is my fun car and I drive the hell out of it. I usually try to shift in the 5k range and regularly take it up to the redline. While it has been able to handle this my guess is that the engine would last longer if I took it easy on it. That's not why I bought it.

Would you rather buy a used engine from a car that had been babied or driven hard?

[rick-l]

Originally posted by nostatic
As Sherwood said (and I asked early on), "best for what?" The Carreras have a shift indicator light that must be telling you the "best" shift point,

Has anyone taken apart a Carrrera tach to see what turns on the CASIS light durring wide open throttle acceleration? Is it strickly RPM? Know what that RPM is?

[Rot 911]

Originally posted by rick-l
Has anyone taken apart a Carrrera tach to see what turns on the CASIS light durring wide open throttle acceleration? Is it strickly RPM? Know what that RPM is?

The only thing I ever did with my CASIS light is disconnect it.

[rick-l]

Originally posted by Kurt V
The only thing I ever did with my CASIS light is disconnect it.

Some one said that when you pull the wire that sends the fuel injector pulses to it it still does the RPM thingy.

[Rot 911]

Originally posted by rick-l
Some one said that when you pull the wire that sends the fuel injector pulses to it it still does the RPM thingy.

Huh? Not sure what you mean. I pulled the wire and my '86 Carrera kept running just fine.

[masraum]

For your 911 Never pay any attention to the CASIS light. It was put there for the US gas guzzler crap.

In my 3.2 the owner's manual says to never shift any lower than ~2600 rpm (actually there is a chart with minimum shift points per gear, I believe the chart says
Minimum Shift points
1st gear 2600
2rd gear 2500
3rd gear 2400
4th gear 2600

My owner's manual also says what Jack Olsen said earlier "Never lug the engine..."

My opinion
During normal driving I say shift anywhere between 3500 and 4500, during spirited driving shift anywhere between 5500 and the rev limiter.

On the freeway I am generally cruising between 3200-3800 (unless I'm going over 80, yes I am often speeding). If the speed drops down to 60 then I drop back to 4th and run the car in the mid 3000's.

For a 3.2 the best shift point for acceleration is approx redline.

For your Jetta, who knows. For acceleration it would depend on peak power and gear ratios, but I can tell you that each car feels different and has a very different torque curve. My '88 loves to hit redline, but my wifes pontiac that has a dohc 4 cyl which shows very similar peak hp and torque (not values, but rpms at which the values occur) really dislikes being revved to redline, it falls on it's face well before redline. It's torque curve seems to be weaker above peak and fatter down low.

[thabaer]

It's basic fizziks guys, picking a fixed rev point to upshift for max accleration is bogus if you don't account for gear change variations. Maximum accleration comes when you shift to maintain maximum available thrust at the wheels, peak engine horsepower just boils down to revs*torque.

Plot the rear wheel torque across the revs for each gear, as the torque falls off you want to shift about where the thrust would drop below what the next gear has (or redline!).

[rick-l]

Originally posted by Kurt V
Huh? Not sure what you mean. I pulled the wire and my '86 Carrera kept running just fine.

On my 88 if you hold the pedal to the floor the CASIS light comes on somewhere in the orange band. A common way to disable the light is to pull the wire from the DME. Looking at the schematic I'm guessing that wire sends the injector pulses to the tach. I recall someone also saying this didn't disable the top end feature.

[svandamme]

i don't understand what the point is,
put me in any car, and i'll shift where appropriate
it's not rocket science now is it?!!?

you press the loud pedal, and if you feel it's not accelerating as fast any more , then you shift up

every car is different, and you can feel when to shift
you can discus the ideal upshift on two 89 carrera's, but the truth is what's ideal for A , is not for B

euro gearboxes are a lot more sporty, us gearboxes are lame, maybe not every model , but i can confirm it to be so on a 944S2 with a CASIS light >> lame gearbox

other than the gearbox, every engine will have a different curve some engines wear out faster, others have small upgrades. etc etc...

so realistically ... what's the point discussing it... drive it and listen to your ears and feel it in your lower back...

i never even look at my RPM indicator.... in any car...

[masraum]

Actually I think the US gearboxes were more sporty for the '88 MY. Generally closer gears is sportier, and the difference in gearing in '88 is that the Euro models have a slightly higher 4th and 5th, otherwise they are the same (Euro meaning RoW, but I think Swiss gearboxes were different than both the RoW and US).

[RickM]

Is the Shift indicator in any way controlled by the ECU or strictly RPM based?

[masraum]

i never even look at my RPM indicator.... in any car...

Those F1 guys (and most other racecars) must have them for a reason...

[masraum]

The CASIS light is controlled by the ECM, because it takes more into account than just rpm. The rpm that the light comes on changes according to throttle opening which to me says that vacuum or throttle position is also a factor.

[svandamme]

Originally posted by masraum
Those F1 guys (and most other racecars) must have them for a reason...

ever heard an F1 car?
then imagine sittin in one, with earplugs with a radio ...and a helmet on top ...you can't hear the differences in your engine noise well enough to use it for shifting...

don't compare apples with oranges, it doesn't work

EDIT and any street driver, who needs an RPM indicator for his shifts... is a danger since that means his attention is on his dash, instead of on the road... one fraction of a second lost because your reading your tach , adds up to a lot more reaction time lost to brake for a child crossing the street, or another car crossing or hitting something , or road debris...

[Bill Verburg]

Actually I think the US gearboxes were more sporty for the '88 MY. Generally closer gears is sportier, and the difference in gearing in '88 is that the Euro models have a slightly higher 4th and 5th, otherwise they are the same (Euro meaning RoW, but I think Swiss gearboxes were different than both the RoW and US).

Different but not necessarily sportier

[masraum]

OK, looks like the 3.2L cars with the 915 were sportier in the RoW, but I still am pretty sure that the 3.2L G50 cars were more closely geared in the US. Actually, I think that chart is wrong in the middle if my books are right.

this probably won't format well, but I'll see what i can do...

88 G50 US
Gear ratio _Overall___Top Speed in Gear
3.5_______12.06____39.96
2.0588____7.09_____67.93
1.4090____4.85_____99.25
1.125_____3.88_____119.53
0.8889____3.06_____151.28
88 G50 Euro
3.5_______12.06____39.96
2.0588____7.09_____67.93
1.4090____4.85_____99.25
1.0740____3.70_____125.19
0.8611____2.97_____156.16

[svandamme]

could be, haven't driven all those, but it is true for the 944 S2
sat in one last weekend, and it had no power in 4th and 5th

[svandamme]

and again , the the table just prove the futility of discussing the optimal shift point... to many different gearboxes, to many different engines, to many unknown variables....

gotto feel when to shift, not calculate

[beepbeep]

Well I'm still claiming that optimal accelleration trough gears will only be achieved by choosing shift points that maximize sum of swept areas under power curve for particular run trough the gears.

Prove me wrong.

[masraum]

Goran, you are, of course, correct. A graph of engine power is needed to get the best shift points for accelleration.