where does the gas milage go.

[fordkid68]

hello-

I was just wounder what performance up grades couse the gas milage to go down more. I mean I know all up grades couses the gas to go down but what does it the most. is it carb, intake, cam, heads and so on.


thanks
ford kid

[joinrdie]

The cam and carb are the big ones, to my understanding.

[rbohm]

the biggest single factor is cam selection. too large or too small and fuel economy suffers. when you build an engine you need to first figure the rpm range the engine will spend 80% of its time in. you then pick parts that compliment each other. after that it is a matter of tuning the combination. one example, my old 289 in my mustang. on the road it would get 25mpg, and int he city it would get 17mpg. i actually had the wrong cam in it but it wasnt too large for what i wanted. if i used a cam with less overlap and more lift i would have gotten better mileage.

[fordkid68]

well I will be spending most the time in the city. I usually only drive highway on the weekends. so whats A good rpm to go with. I dont know what the shift point will be. I do know it will be going in an automatic.


thanks
ford kid

[rbohm]

ok you want a cam that will work in the off idle to 4500 rpm range. two cams i recomend that will work nicely and make good power are the comp cams 260 high energy and the edelbrock performer(NOT the rpm) cam. along with these cams, use the edelbrock performer intake, again not the rpm, and a set of windsor jr heads, assuming you are building a 302 or 351w engine.

[fordkid68]

I am building A 260. will those cams and the intake still work. or did you mean all those sugestions were for A 302 or 351.


thanks
ford kid

[rbohm]

everything will still work with a 260, just watch the valve size. check to make sure the valves dont hit the cylinder walls, they can be notched for clearance as needed with in reason. usually a 1.94in/1.60ex fits but just. the reason i said assuming you were building a 302 or 351w, is because you didnt indicate what you were building, and if you had a six or a 390, for example, the recomendations would have been a bit different, but not much.

[fordkid68]

good cuz I was looking at the parts that you sugested and I like them more every time I look at them.

sorry for not indicating what size engine I have.


thanks
ford kid

[rbohm]

when you buy the heads, buy them bare and buy one each a stock chevy intake valve 1.94 and exhaust valve 1.60. that way you can test fit the valves and head to the block. do this after you buy the cam. that way when you or your engine builder checks the valve to cylinder wall clearance you have the actual lift numbers to use. i dont think you will have a problem, but definately check.

[fordkid68]

yea I was planning on buying the cam first. just didn't know there was A good reason to.

and I see what you mean about checking the clearance. thanks for bringing it up.


thanks
ford kid