[EcoCivic]

I have a couple of questions about converting my 2005 Honda Civic with a 4 speed auto to a 5 speed manual. My first question is what would the overall effect on gas mileage be if I install an EX 5 speed trans? I initially thought that highway MPG would stay approximately the same and city mileage would improve.

However, I found out that the trans that I am looking to install (An EX 5 speed, which has more aggressive gearing than an LX or HX trans) would cruise at a high RPM. With my auto, the engine runs at around 2300 RPM going 70 with the converter locked, but with the EX 5 speed, the RPM would be more like 3000 going 60. I am not sure if that would mean lower highway MPG. You would think it would, but the manual transmission has much less losses, even cruising with the converter locked, so the mileage may not drop.

The other option I have is to get an EX 5 speed trans and swap the 5th gear to a taller gear from the LX trans before I install it, which would drop cruising RPM at 60 to around 2800 IIRC. Would that help gas mileage measurably?

Thanks in advance for your input