924Board.org

[joecitizennn]

I have a 1988 924S. 2.5L engine SOHC. It has 140 K on the clock, but is in excellent runniing condition. I finally found an oppertunity to open it up. It had very rapid acceleration up to 100, slow acceleration to 110, and there it stopped. Why? I dont think it was a problem with a worn out engine, because this car is such a rapid accelerator, and I have found no faults with the engine while working on it.

[Chrenan]

I would think something is wrong, that car should go to 140.
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1987 951 - M193 Version for Japan

[Khal]

Is it an automatic?

Even so, she should easily to 120mph (on its way to about 140, like Chrenan says)
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'80 924 Turbo

[Chrenan]

Even my 924 goes to 110 easily, and the only thing stopping it going any faster is my own fear.
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1987 951 - M193 Version for Japan

[gohim]

Did you have the headlights up?

Did you have the sunroof open?

Did you have the windows open?

What size tires do you have on the car?

How much air in the tires?

What tranny (already asked by another, but no answer from you)?

What were you carrying in the car?

What grade of gas?

[924guy]

i seem to recall getting my 87 924s auto(RIP) over 120 a few times, so theres definatly an issue with an 88 being stuck at 110... could be a bunch of things though... give the colective the answers to the above questions and im sure well come up with some ideas..
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Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
Performance by Pasha

[joecitizennn]

I was using regular gas.
I think my tires are 205 60 15 or something running 25 psi cold.
It was nitetime with my headlights open.
I had the car floored at 110 until I went down a steep hill where it rose to 119, and then receded back to 110.
My sunroof and windows were closed.
I must ovserve that 110 mph in that car is very calm compared to my miata. The porsche seems to just be happily cruising at that speed.

I have noticed no hesitation on acceleration, or any other type of rough running. Sometimes with my windows down I smell exhaust while driving. The car has enough power to squeal its tires on pavement, and glue you to your seat up to 100, so I am at a loss.

maybe need to open up my air intake?

[joecitizennn]

sorry, I have a manual tranny, to answer your questions. A loud manual tranny, I might say, but it is manual. It has a conventional 5 speed shift pattern with reverse at the lower left. I have it topped off tieh 80-90 or something.

[gohim]

Everything sounds okay so far.

Except...

The tire pressure that you report is low. Your tire diameter will be smaller as a result.

Have you ever had your speedo check with the tires that you are running?

The reason why I asked about your tires size is because tire size will affect the speedo's accuracy. The 924S came with 195/65/VR15 which are a different size in diameter (tire manufacturers each seem to have a difference in opinion as to what size any tire really is). A 205/60/15 from one manufacturer is not the same size as one from another manufactuer), so the speedo reading is probably going to be a little low.

Open headlights will dirty up the car's profile and trim 3-5mph from the top speed. The same thing for opening windows, or opening the sunroof. Open them all up as the same time, and you create a huge amount of drag.

Turning on the air conditioner, or the defroster will load the engine down, as the ac compressor clutch engages, reducing the hp available to push the car.

Running low octane gas will cause knocking under load and reduce hp output. The factory specs were run in Germany with better gas.

[Khal]

[timstar92404]

if the engine runs okay and accellerates good then timing/ fuel should be good right....

maybe the throttle cable isn't adjusted correctly.

I doubt something like your headlights being up or an automatic will make a 924S 110 mph....

even the 78 na is suppose to go up to 120mph manul 4 speed and like 115mph for the automatic......

the 924S automatic should go 130+ at least.
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78 924 sold.
85.5 944

[ideola]

[Joes924Racer]

Not saying the engine is wore out casuse 140 isnt alot of alot
though it could be enough to wear out a component like a lobe
on a cam, its quite the game sorting these things out you have
know the go of your engine.
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[924guy]

though i would definate
another thoght is brake dragly agree that wind resitance and tire pressure will affect top speed, im still wondering if that would result in a 15 to 20 mph drop , that sems a bit much for the conditions reported. Timstar may be onto something with the throttle cam adjustment, or perhaps, its something as simple as having a floor mat bunched up under the accelerator, or some other hangup thats not permiting wide open throttle? easy enough to check by having someone mash the gas pedal and checking the throttle cam to see if it is opening fully..
another thought is brake drag, though i would think that would be noticed at much lower speed..
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Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
Performance by Pasha

[Ozzie]

My NA auto had absolute rubbish acceleration and it was caused by poorly adjusted throttle cam and auto cable adjustment.
The adjustment required measuring the angle at rest for the cam and adjusting to 29deg.
Mine was closer to 40deg. Made a huge difference.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance