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Test pipe - fuel consumption?

Test pipe - fuel consumption?

Test pipe - fuel consumption?

(OP)
On another forum I regularly visit I came across an interesting thread, when replacing the catalyst for a less restrictive hollow test pipe will increase or reduce mpg?. So which one is it, I am curious to hear your answers. Thanks

RE: Test pipe - fuel consumption?

It should improve the fuel consumption slightly, due to the reduced backpressure.

In practice it seems daft to chase a few % improvement in mpg in exchange for a large fine... but that's your choice.

Cheers

Greg Locock

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Test pipe - fuel consumption?

It may also loose a little due to fuel being drawn over during the scavenging process at TDC overlap.

This might partly offset the gains from lower blow down pressures.

Regards

eng-tips, by professional engineers for professional engineers
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RE: Test pipe - fuel consumption?

I think you used to be able to gain about 10% with respect to the early pellet type GM converters.  Maybe a little more if it wasn't in "like-new" condition.  That was 25 or 30 years ago.

Relative to a modern high flow converter in good condition I don't think you'd be reliably able to tell the difference (your driving probably varies more widely).  Aftermarket high flow units can flow over 500 cfm (some well over that figure), which indicates a level of backpressure comparable to (and quite possible lower than) a high performance aftermarket muffler.


Norm

RE: Test pipe - fuel consumption?

One also needs to be wary of changing the effective length of your exhaust system by removing a restriction, assuming it is a tuned exhaust.

-Reidh

RE: Test pipe - fuel consumption?

Greg,

How can a cat increase back pressure but not have an acoustic effect?  We don't actually deal with catalytic converters in our industry, so I am by no means an expert on the subject.  I had assumed that if it has enough restriction to affect back pressure that it would change the effective length of the pipe.

Reidh

RE: Test pipe - fuel consumption?

Sorry

I should have said no significant /measurable/ effect.

Yes, obviously it has some effect.

Cheers

Greg Locock

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Test pipe - fuel consumption?

The removal of the restriction will increase overall airflow into the engine, meaning more fuel will need to be added to compensate for the increased air.

You will have more power availiable, therefore the fuel consumption will go up.  Of course in a steady loading condition, you will have the same or slighlty better fuel economy at less throttle openings.

RE: Test pipe - fuel consumption?

A cat may have negligible effect on noise but some say a DPF can replace a muffler.

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