port, polish and cam - economy hit?

[RockDoc]

I'm thinking of doing some gas-flow work on a second head to swap onto my 3FE, and I'm curious what effects in terms of milage I might expect?

I'm pretty sure the port and polish work shouldn't have a negative effect, but I'm curious if stepping up to a "hotter" cam would? The truck is my DD, so a bit more power when needed would be nice, but not if it's going to up fuel consumption. All the stuff you read on top-end modification focusses on getting more power, with little mention of effects on economy.

So for those of you who have done similar top-end work on your engines, did you notice any change in economy? Like I said, I'm particularly interested in the effects of changing to a longer duration camshaft...

Thanks,
Curtis.

 

[cody c]

dumping money into a 3FE eh?
I just got back from edmonton half an hour ago, i should have let you take the small block'ed 80 for a drive. We drove to the north end of Edmonton from calgary and filled it up on about $68, and i think i can get better than that when i get it tuned up a little better as i think it is running rich- o2 sensor issue.

But anyways, i think it depends on how aggresive of a cam you have and if you can keep off the skinny pedal with the extra power, the port and polish should help though. I dont think youll impair mileage too much.

 

[RockDoc]

dumping money into a 3FE eh?

Don't intend to spend much more than the cost of a used head, and some new gaskets, and maybe a cam set if I thinks it's worth it. I don't have the money, time, skills, facilities or interest to do a full swap. The engine is in good shape (just did an oil analysis a couple months ago), but I want to go through and change out some things (rad, hoses, fan clutch?, gaskets, ...), do a de-smog and test out some stuff I've been reading up about. I like to putter in my free time, and this should be a good chance to learn.

I just got back from edmonton half an hour ago, i should have let you take the small block'ed 80 for a drive. We drove to the north end of Edmonton from calgary and filled it up on about $68, and i think i can get better than that when i get it tuned up a little better as i think it is running rich- o2 sensor issue.

One way or both on the milage? On any highway but the QE2 I usually get about 15 m/gal (US) keeping it below 110, but that damn highway always has me going ~120. Truck loves that speed, but it really sucks back the gas.

 

[PhilC64]

Depends on the grind of the cam you're going to use, but you'd probably lose mpg's. In all likelyhood you're going to be extending the duration of the intake opening. The longer the duration from the stock duration, the more air/fuel mix you're dumping into the cylinder. The more power you make the more gas it'll take.

I haven't checked but even just hogging out the intake and exhaust ports would give you more hp and torque. Then again if you do that you might as well get a newer cam. You also might have to play with the fuel injection to avoid a lean condition in that case. Like I said I haven't looked into it myself.

Remember it's a tractor motor. You really can't do too much to it to make it faster.

 

[RockDoc]

Related question (and bump to stay on page one ):

Are there any differences in a 3FE head from '88 to '92. I'm pretty sure there were harness/sensor differences, but is there any reason a '91 head wouldn't be a good choice to pick up and work over for an '89 3FE?

 

[PabloCruise]

I read somewhere they changed up some things in '89...

I think Pappy wrote it in his 2FE write-up: http://bushrat.hdcruisers.org/3FEconversion.pdf

 

[RockDoc]

I read somewhere they changed up some things in '89...

I think Pappy wrote it in his 2FE write-up: http://bushrat.hdcruisers.org/3FEconversion.pdf

Thanks, took a quick look. Everything mentioned in the writeup is wiring/peripheral rather than the head itself.

 

[ntsqd]

Anything that improves the efficiency of moving air through the engine will be a plus to economy as well. It is how you tune the engine (cam timing, A/F mixture, etc.) that effects the end result.

Key thing is to keep the port velocity up. Making the ports bigger decreases this unless you're also increasing the normal operating RPM.
Blending the transitions to have smooth flow is more important than making things big. Highly recommend reading David Vizard's various books on this topic. There is also a book out there called "Practical Gas Flow" (or something very like that) that gets high marks.

Longer duration isn't what you want for a low speed engine. More lift is what you want. Actually more area under the lift vs. duration curve is really what you want, but getting that without increasing duration usually means more lift. Converting to hyd roller lifters would be a bonus as then the cam lobes could have far more aggressive opening and closing ramps, but I've no idea how much of a PITA that would be to do to one of these engines.

 

[RockDoc]

There is also a book out there called "Practical Gas Flow" (or something very like that) that gets high marks.

That's the book that has me interested in working the head

Anybody have a number for the lift of the factory cam? That seems to be the only factor I know nothing on. Someone with a cam sitting around and a set of calipers?

 

[silicon_toad2000]

port and polish the exhaust ports will help mpg, anything that helps get the exhaust out other than the piston pushing it out is a plus.
Opening up the intake ports will let more fuel and air into the motor at any given throttle opening, more power but more juice. Flow through the intakes doesn't mean too much when you have a half closed throttle in the way. Polishing the intakes can be a little detrimental and a bit of turbulence helps promote a more even air fuel mix.
Don't forget if your are porting the heads to make sure you get the manifolds match ported. No point in smooth flowing heads if the manifolds don't quite line up.
A three angle valve job will also help the airflow get around the edges of those valves.

 

[Mace]

Port and polish is basicaly a waste. It ends up making the truck sluggish in the low end.

A good cam (almost everyone makes the same cam for a F series motor) will give you the most benefit.
Or milling the head for inctreased compression.

And none of these things will do much for mileage. Your best option is to just go ahead and drive more carefully.

 

[D'Animal]

You could possibly use a 2F short block?