Stillen exhaust upgrade effect on gas mileage

[chad1200]

i read in the very first post in the modification database from G_whizz that the Stillen exhaust kit actually reduced gas mileage! how is this so?

[C-Kwik]

Any exhaust that results in more power can increase gas mileage. But there are a lot of factors that play into this and any increase in efficiency would be quite small.

If the exhaust in question increases volumetric efficiency at the RPM's you drive in most and especially the RPM you cruise in most, then it can help so long as you drive the same way you did before you installed the exhaust. My own experience is that this never happens but everyone is different. In case you do drive it the same way, the increased pumping efficiency is where you'll find the benefits.

However, it is also possible that you can decrease gas mileage. First off, if you become a more aggressive driver post-exhaust, then this can easily occur. As i said, I tend to be more aggressive as I can enjoy the exhaust much more when I rev it out. I'm sre many others are the same way. Secondly, if you are heavy footed either way, the increased efficiency will lead to slightly higher airflow, which also results in more fuel being injected.

Now bear in mind, aside from a change in driving havits themselves, any gas mileage differences would be small and more than likely, quite negligible. I really would not put much thought into gas mileage when thinking about an exhaust purchase.

[Q45tech]

OBD2 ecu are very very accurate in setting injection time to yield 14.7 AF so the more air you allow the engine to ingest the more fuel is used.

MPG Gains from exhaust primarily went away with carburetors.

However the frictional pumping losses to allow the exhaust gas exit can decrease IMEP [part of working friction] still for a fixed rpm the effects are minimal say 1% at best.

If oem could improve MPG they would as a 1 MPG improvement can save them $500-$1000 in Federal taxes allowing them to lower the selling price of the vehicle...........or to just make more profit.

[joe603]

Q45, you have to remember that there are other factors in play for manufactures to consider. If the cost of the improved exhaust that would result in better MPG were less than a standard system, they would do it. However, I'm sure that they would save more money making the cheapest exhaust possible first, than worry about performance after.

It's all a balancing act in the quest for more economic profit.

Chad1200, I don't think that G's MPG problem is due to the stillen exhaust. We're still waiting for his troubleshooting results...

[chad1200]

i guess i'll just have to wait and see. it couldn't be all that much, anyway.... i hope. super unleaded in DFW - $3!!!!

[BigWill]

i guess i'll just have to wait and see. it couldn't be all that much, anyway.... i hope. super unleaded in DFW - $3!!!!

Wow... I wish I could pay fifty or sixty cents less per gallon like you! lol

We get absolutely RAPED here in So Cal.

Although, as a rule, the Europeans are paying in the equivalent neighborhood of $8/gallon for their petrol.

[G_whizz]

Hey Big Will...nice new pic in the sig