miles per gallon after performance upgrade

[Russ]

I have a fairly stock 200 that I have added a t-5 overdrive tranny to. I have some minor additions such as headers, duals, pertronix but nothing significant. Otherwise the motor is stock. I get 28 mpg in freeway driving at 70 mph.
I am considering some extensive changes during a rebuild such as a hotter cam, Mike's aluminum head, two barrel carb etc. My question is what experience have some of you guys had as far as changes in your miles per gallon before and after significant modifications?
Thanks,
Russ

 

[CobraSix]

I have almost what you are trying to get to.

If I'm lazy on the throttle and drive it like it was a 1v carb, I can squeak out 25-26MPG at 70. Prior to that, with the 1V, mild cam, electronic ignition, and T5 I got around 28 MPG as well.

 

[rbohm]

8) if you keep your mods mild, and err on the side of low end torque and mid range performance, you can maintain, and possibly increase the fuel economy you are getting now. it is all in the combination, and how you tune it. for instance years ago i rebuilt the engine in my mustang, 289 2v engine. i added a performance cam that increased power through out the rpm band, added headers and a 4v autolite carb. my city fuel economy went from 17 to 19 mpg, and my freeway economy went from 22 to 25 mpg. and oddly enough the cam i selected was more for mid range and higher rpms.

the other thing you need to consider is what compression ratio you are going to use. higher is better, to a point, but remember to keep it low enough for proper street operation. 9.5:1 should do nicely.

one more thing deals with carburetion. it is tempting to run a 500cfm holley carb, but a smaller autolite, say something in the 300-350cfm range, will do much better overall.

 

[pikesan]

I've seen a few posts about making PERFORMANCE mods that ask about mpg. Why spend all that time and money then skimp on the cam in the name of mpg? For me if I'd make changes like that I'd stick my foot in it every chance I got to enjoy the work I'd done.
To each his own but dang! Life's too short to be sweat'n 2-3 mpg ain't it?

 

[rbohm]

I've seen a few posts about making PERFORMANCE mods that ask about mpg. Why spend all that time and money then skimp on the cam in the name of mpg? For me if I'd make changes like that I'd stick my foot in it every chance I got to enjoy the work I'd done.
To each his own but dang! Life's too short to be sweat'n 2-3 mpg ain't it?

8) my point is that if you select your components properly, and match them properly, you dont need to make the choice of performance and mpg. the problem is that most people pick the biggest cam they can find, add the largest tube headers, and the bigest carb they can put on, leave the stock 2.80-3.20 gear in place, and then wonders why their car performs like a sick dog, and has the fuel economy of the average 747 at take off.

match the components to the rpm range the engine will spend 80% of its time in, and you can get excellent performance, and still maintain decent fuel economy.

 

[woodbutcher]

I second rbohm.Have seen poorly selected components KILL performance and economy.Example.High rise manifold with a pair of 750 Hollys,2in primary tube headers,and
3in exhaust pipe.The guy wondered why his daily driver was such a PIG.Cam was designed for IIRC 3500 to 6500 rpm.
Leo

 

[CobraSix]

match the components to the rpm range the engine will spend 80% of its time in, and you can get excellent performance, and still maintain decent fuel economy.

This is why I choose the 260H cam. That, and I don't like lumpy sounding engines. But since I rarely rev my engine past 4500, who cares if I make power at 6000 (especially since my rev limiter is set to 5200)? I wanted street performance, which for me is low end torque and mid range power which makes a car fun to drive, nice to idle, and relatively good on gas.

biggest impact on my mileage now is my lead foot from having the power and wanting to use it.

But like rbohm and woodbutcher said, you can have both performance and mileage if you select your components properly. Having mismatched items only result in poor performance and poor mileage.