924Board.org

[joecitizennn]

My gas mileage got a little worse since I installed a cat in place of a straight pipe. Is this supposed to happen? The core of the cat is squeaky clean, so there are no restrictions besides the cat internals themselves. And yes this is a OEM porsche catalytic converter.
_________________
87 924s
88 924SE gone
447 hp cgt clone
87 924S gone
84 944 sold
83 944 sold
89 turbo S LSD, ABS etc
86 951 white rocket
85 944 sport everything.
84 944 sold.
87 944 sold

[johnathan1]

For such a small change in MPG...it could be any number of little problems. When was the last time you replaced spark plugs, wires, cap & rotor, injectors, o2 sensor, vacuum leaks...or an improperly functioning air flow meter?
_________________
-1977 924, 4-Spd...Gone
-1987 Toyota Supra Turbo, Pearl White, BPU, 300RWHP @ 10psi.
-1989 Mercedes-Benz 300SEL

WARNING: MAY CONTAIN TRACES OF AUDI OR VW!

[joecitizennn]

The entire ignition system is new with less than 5k on it. The injectors are as clean as a whistle. (I have had them out within the last 500 miles) Functionally the car is awsome. When driving on the interstate to come to NC the car was getting 27 mpg. I have not taken exact mileage lately, but it is falling just short of 300 miles to a tank. I dont think that is 27mpg.
This post is just probing what a catalytic converter does to mileage. I know it eats a little power. If someone can tell me "no a cat does not hurt fuel economy" or "yes a cat does hurt fuel economy" I will be happy.

As far as fuel consumption goes, I am comparing figures that I got driving at freeway speeds, to figures that come from frequent starts and stops, and driving short distances at constantly changing speed. That adds a second variable.

So my question still stands. Does a cat change fuel economy?
_________________
87 924s
88 924SE gone
447 hp cgt clone
87 924S gone
84 944 sold
83 944 sold
89 turbo S LSD, ABS etc
86 951 white rocket
85 944 sport everything.
84 944 sold.
87 944 sold

[Mike924]

No question - cats lower mpg, end of story.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[joecitizennn]

Thank you! Now the question is, how much to they lower it by?
_________________
87 924s
88 924SE gone
447 hp cgt clone
87 924S gone
84 944 sold
83 944 sold
89 turbo S LSD, ABS etc
86 951 white rocket
85 944 sport everything.
84 944 sold.
87 944 sold

[!tom]

Less than the difference between highway driving and stop-and-go city-style driving.
_________________
78 924 NA
5-lug

[geddes66]

For that matter... so does colder weather and winter fuel mixes. Has it gotten colder since you installed the converter?
_________________
The Porsche is now my son's, my car is cooler, slower but cooler.

[joecitizennn]

Ohhhhh I forgot. I installed a LT1 v8. Maybe that is why my gas mileage sucks.
_________________
87 924s
88 924SE gone
447 hp cgt clone
87 924S gone
84 944 sold
83 944 sold
89 turbo S LSD, ABS etc
86 951 white rocket
85 944 sport everything.
84 944 sold.
87 944 sold

[Mike924]

Easy thing to overlook.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[Rich H]

did you wonder why there were spare sockets on the dizzy...?
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec