Can't rev past 5k

[Kindred]

I've been driving my car like an old woman due to my massive oil leak. Well, the leak seems to have resolved itself, so I went out with a couple of friends to play at the track. Something new that I've noticed today is the fact that my car suffers from a total loss of power after 5k rpm. I can't even rev past it in neutral. Could this be a symptom of a clogged cat?

[Tim]

Could be that you have a rev limiter also.


Regards,

Tim

[Kindred]

I forgot to mention that I've hit my rev limiter many times in the past. It's between 6200 and 6400.

[Tim]

I see.

I was thinking of Canadian cars - from what I've heard they have governors that prevent them from going over 100 mph or something. Correct me if I'm wrong, though...


Regards,

Tim

[MY5TERE 1]

no governor on fi festies. can't say about carb ones tough

[Kindred]

So does anyone have any ideas as to what the problem might be or how I can troubleshoot it? I don't want to waste money on a new cat if that isn't the problem.

[Tim]

Poke all the stuff out of the catalitic convertor with a poker or piece or pipe or something and reinstall it. The car should still pass emissions inspections and you'll gain an extra couple of HP.

I did that to mine and it passed the Texas inspection.


Regards,

Tim

[FB71]

Uh, I dispute that power increase statement, Tim. And I know where to find the dyno pulls to back it. I'm adjunct staff at Penn College of Tech in Williamsport PA, and the head of the Automotive Tech Management program there (Dr Ron Garner) has data from one of his students. He did dyno pulls on a car (don't remember what) with a good cat, a hollowed cat, and a piece of straight pipe. I do remember it being a FI 1980's car. The straight pipe made the most hp, but at a higher rpm than stock. The cat made the best hp and torque #s, and the hollowed cat made the worst. This was attributed to the exhaust gases being permitted to expand in the hollow cat body, then being forced to re-compress to exit. And every state can have a different pollution test. I can tell you Uncle Fester didn't pass with a converter, and would blow the test away with no cat. We here in MD are subject to the dreaded IM240, where they dyno our cars to see volume & mass of pollutants emitted during simulated driving. Its a real joy, lemme tell ya.....

[Kindred]

We also are subject to those IM240 tests here in AZ. My car blew it away under load, but was very close to failing at idle last Dec.

[MY5TERE 1]

the best solution to find out if your cat is clogged would be to take it off and run the car. see if it revs freely. also examine your exhaust pipe. look for crimps that would severely restrict exhaust flow. if your cat is the problem, buy a delete pipe or pull one off a junker. i have almost 400,000km on my festy and have never had a problem with the cat. but on my old 626 i had to remove the cat because it made a really bad stinky smell. i guess that's what they do when there clogged.

[Tim]

Uh, I dispute that power increase statement, Tim. And I know where to find the dyno pulls to back it. I'm adjunct staff at Penn College of Tech in Williamsport PA, and the head of the Automotive Tech Management program there (Dr Ron Garner) has data from one of his students. He did dyno pulls on a car (don't remember what) with a good cat, a hollowed cat, and a piece of straight pipe. I do remember it being a FI 1980's car. The straight pipe made the most hp, but at a higher rpm than stock. The cat made the best hp and torque #s, and the hollowed cat made the worst. This was attributed to the exhaust gases being permitted to expand in the hollow cat body, then being forced to re-compress to exit. And every state can have a different pollution test. I can tell you Uncle Fester didn't pass with a converter, and would blow the test away with no cat. We here in MD are subject to the dreaded IM240, where they dyno our cars to see volume & mass of pollutants emitted during simulated driving. Its a real joy, lemme tell ya.....

Well, I wasn't expecting an ambush like that!!! ops:

I was going from personal experience - the stuff inside the cat was loose and I poked it out, and did feel a slight increas in power. Could be my imagination, though. I thought that the less stuff between the exhaust manifold and the outside, the more power you got. This piece of wisdom was imparted to me during a summer job as a small engine mechanic.

Can't argue with the facts, though...

I don't know what they put us through in Texas, but if I read the paperwork right my car passed the emissions test with flying colours.


Regards,

Tim

[HappyMom]

I was thinking of Canadian cars - from what I've heard they have governors that prevent them from going over 100 mph or something. Correct me if I'm wrong, though...

Canadian cars are limited to 160km/h. I've hit the limit several times in my 91 Jetta in 4th gear. The Festiva was probably excluded from this limiting thing, because the stock ones max speed is than 160 km/h to begin with.

And FB71's statement about hollowed cat being inefficient because the gas has to suddenly expand and then suddenly contract is basic fluid dynamics.

[FB71]

I wasn't attacking you, Tim. Just wanted to toss in my $0.02. Keep up the good posts!

[Tim]

No problem!

Better a right anwer than a wrong one...

:lol:



Regards,

Tim

[FB71]

Normally, you're right Tim. The less restriction to the atmosphere, the better the exhaust will flow. A hollowed out cat actually adds restriction under higher gas velocity, due to gas expansion in the flow stream. You probably did feel an increase in power if your catalyst bed was deteriorated and loose. That caused erratic flow of gases, resulting in excessive backpressure. A good cat can actually straighten and accelerate gas flow. Not to say all converters add power. Some are engineered to restrict the flow intentionally. But on our little cars, I find they perform better with the cat intact, at least in stock form. Now, increasing airflow and fuel delivery, more exhaust flow can really help.....