Just rebuilt motor. Now have terrible mileage.

flyersfan1088 · 01-19-2003, 07:07 PM

I just had the motor in my '86 rebuilt. I had the stock iron heads ported and a bigger cam put in (224 dur @.050 .495 lift) I am now averaging 12 mpg. I am 99% sure that the cam was installed a couple of degrees retarded, which is going to be fixed. Can running the cam retarded effect fuel mileage this much? Or do engines get worse mileage during break in?

QuickVet · 01-19-2003, 08:34 PM

yes, timing can affect milage. Fix that first and then see if it gets better. Welcome to the world of more HP and less milage :lol:

Vetterodder · 01-20-2003, 12:50 AM

While 2º retarded cam timing might result in lower fuel economy (in some cases it might result in higher fuel economy), the difference wouldn't be that dramatic either way. Lower mileage during breakin isn't unusual due to ring seating issues but, assuming that we're talking about a TPI engine, only 12 mpg is way beyond what would be expected. I suspect two issues are involved in your case. One is that you're enjoying the hell out of the new engine and you've lost control of your right foot :). The other is that your computer hasn't been reprogrammed for the bigger cam and has your injectors working overtime.

flyersfan1088 · 01-20-2003, 12:29 PM

Quote:

One is that you're enjoying the hell out of the new engine and you've lost control of your right foot :). The other is that your computer hasn't been reprogrammed for the bigger cam and has your injectors working overtime.

Well, it's probably a little of both. I'm still learning about custom PROMS. I hadn't thought about reprogramming to regain economy. Thanks for the tip :)