underpowered?

stckinaz · 12-17-2001, 06:31 AM

So we finnaly got the '69 up and running and i drove it the 40 miles to town and back. This thing seems waaaay underpowered. I have yet to pull a compression check but that is on the way this week.

I'm not sure speeds and such because the spedo is broken but i am guessing that i can run (maybe) 45mph up-hill in 3rd at 4000rpm. Does this seem about right for the rest of you 912 owners out there?

wastintime · 12-17-2001, 10:41 AM

What speed transmission do you have? If you have a 5 speed then it is a little off, more off with a 4 speed. According to my Owner's manual 3rd gear and 4000 RPMs should coincide with going 60mph with a 4speed and 50mph with a 5speed (for a '67 I don't know how much it may have changed by '69). Of course if you were going uphill that would probably explain the deviation.
Are you just noticing the RPMs or does it not want to accelerate? See if it wants to accelerate in 4th or 5th (whichever is highest for you). If it's still accelerating at a good rate I wouldn't worry too much. I have webers and headers on mine, I don't know if you do or not, but my 912 will accelerate uphill in 5th pretty nicely even at speeds around 50-60.
It's an old 4 cylinder, it's got to have higher RPMs to maintain speed than a 911. Also the 911 tended to accelerate better at higher RPMs while the 912 likes lower RPMs maybe you just don't have a feel for the gears yet, especially if you have a 5-speed. If you ever read Porsches for the Road, old motor trends, or old car and driver magazines, they have some very good info on how to drive the 912... specifically the transmission.
It'll probably help once you get the speedo working too. Hope this helps some.

Andrew

Efrain68912 · 12-17-2001, 11:42 AM

4000 rpm in 3rd gear (I have a 5 speed) worked out to a little over 45 mph in my car this morning. I use 205/55/16 tires on 16 inch wheels.

Efrain
68 912 Coupe

stckinaz · 12-17-2001, 01:10 PM

its a 4-speed, not sure of the tire size off the top of my head. Webers & k & n's.

acceleration in 3rd isnt to bad but forget it in fourth, the only thing i can do in forth is go faster downhill.

wastintime · 12-17-2001, 01:31 PM

There is definitely something wrong there. If you have a 4 speed you should be going about 15mph faster at 4000 RPMs (how steep was the hill though?), Especially with Webers. See if your compression check yields any out of the ordinary results. It could be fuel, carbs, etc... too. It sounds like your car is definitely underpowered for some reason though. Good Luck.

Andrew

Green 912 · 01:41 PM

Whadaya want? It’s a 912! The stock 912 isn’t known for high horsepower but if you set them up right they will handle real well. You might be able to improve the power and torque some. Make sure that the motor is all tuned up and that you have full throttle. I know the last one seems dumb but incompletely opening throttles are a lot more common that you might think. Compression tests are the most over used and under telling tests out there. Too many things can flaw the validity of the results. A somewhat better indicator of the top end is the leak down test but it too must be done correctly. I have seen motors with somewhat low comp # rip up a track.(for a 912 that is...)

wastintime · 12-17-2001, 01:47 PM

Just another thought... I would definitely check to see how much fuel the engine is getting. I'm really paranoid about fuel delivery problems in these cars, and that's a good way too lose acceleration... Also like green said, the throttle is a good place, check the linkage, see if both carbs are doing an equal share of work, etc... You should be able to accelerate in 4th though regardless of stock horsepower. I've had both a 4speed and 5speed in my car, and both would at be able to accelerate in higher gears.

josh912 · 12-17-2001, 10:48 PM

AH, webers! The throttle linkages for the solex provide only 2/3 throttle on the webers! Check the throttle by pulling off the air cleaners, give it throttle, and see how far the butterflies turn. If they turn completely vertical you have full throttle, if not, you need to adjust or replace the linkages.

As for the lack in power, make sure its tuned up, has good compression, all the things mentioned by the other posts. If its running well, you should be able to accerate in all gears just fine.

jac912 · jac912's Garage

To quote one of our own "timing is everything". As a kid I would diddle with the timing on my 65 Mustang Gt "Hi-Po" and test for highest top speed. I won't admit to doing the same thing today.