How much HP increase with Test pipe

not much

any teeny weeny increase is not worth the major exhaust stink that you will get. Go with the Hyperflow. No smell and the same seat of the pants increase.

I know because I lived with a test pipe on a 308 QV for 7 years.

 

I have the same experience as Tommy... you *will* notice that your car revs up faster and sounds better with a test pipe, but the exhaust smell will be significant. I got rid of my test pipe and put on a Hyperflow cat I got from Ricambi... it flows 95% of what a test pipe does and sounds just as good, but without the smell and is environmentally friendly.

 

Have owned several Euro spec cars. Porsche 930S, no cats, no gas smell. Euro TR, no cats, no gas smell. Just my personal experience.

 

When I run my Euro '85 QV without cats, no exhaust smell.

 

couple points, the early CIS like carbs does not have a feedback for the fuel trim, so the use cats will only clean the air provided your injection system is running right, outside of that you can cause problems if you run to rich as the cats have a propensity to ignite :O

for the later versions of CIS there is a feedback to the fuel system for trim, removing the cats should not really make that much of a difference in smell as the O2 sensor will try and lean out the mixture. but this will create a problem as the mixture can be leaned to much and then you run into detonation and burned pistons. most people who remove the cats with a functioning O2 sensor have to send a 'dummy' signal back to the FI so that it doesn't run lean. for the net effect it's not worth the risk or cost, go with high flowing cats and enjoy the clean air.

and yes I still think that cats on carb'd or early CIS is a dangerous idea as there is no feedback.

 

They don't and this is a point that I have always wondered about. Would a disconnected O2 sensor give the eye-watering exhaust I and many others experienced with US cat free cars (mine is an 84)? My CO was adjusted countless times with no improvement but my O2 sensor has been disconnected since before I bought it in 1997.

 

"later versions" as in the 328 series only? Was the lambda system on all the injected cars 80 on?

 

If I recall correctly early US versions used ke jetronic with lambda feedback. The early Euro spec system was k jetronic. No feedback if I recall correctly. Could be completely off base though.

 

I don't have the year at which ferrari started to use the lamdba feedback, my Nov 1981 build mondi has the just the basic k-jet, no feedback. but the 328's should have the O2 sensor by then.

Disconnecting the O2 sensor puts it into open loop, a richer mixture. the lambda is also controlled by a thermo switch for the ECU to know when to take readings from the O2 sensor. I'm not sure if the early K-lambda records faults for this when the O2 is disconnected.

the CO adjustment is strictly an idle control setting.

 

My 1988 Swiss Market 328 came with a "catastrophic converter" but no O2 sensor/no feedback circuit/no frequency valve.

It did come with an exhaust gas temperature probe, "slow down" light etc.

Erich

 

I guess that's why everyone who sees that my O2 sensor is not hooked says not to worry about it.

I suppose if I get a new one and hook it up the only change I'll see is about 1 mile per gallon increase. I may not be worth the bother.

 

What I have been taught about replacing Cat converters is that it depends on the ' eneration' of catalytic converter hat your car originally came wit. The earlier 80's 'pellet' filled converters were quite obstructive and like the thermal reactor muffers, you will get a gain in hp replacin them with a straight pipe, resonator OR newer technology cat like a hyperflow. For newer technology catalytic converters with the more 'honeycomb' type catalyst the exhaust losses are far less, and there is not as much to be gained hp wise.

I think the hyperflows are a good (if a bit overpriced) option, although I would like to see a CFM rating on them if anyone has one. Any newer technology cat with he appropriate flow rating will work pretty well.

The catalytic converter does act as a sound silencer, and that is figured into the sytem (usually).

That all said, it is especially amazing the improvement gained on some specific cars by cat removal and muffler upgrade...

Good luck!

 

That is true. Without the cat it is a lot "throatier"