300 turbo economy?

[Anonymous]

Howdy I've been reading for days here and am amazed at the collectinve knowledge.

I've got an 87 F 150 (Factory EFI) that I will be building a donor engine up for which is also an '87. I know I have the areodynamics of a brick but I am after better fuel economy and I was considering turbo charging. Any one have a daily driver turbo'd? What kind of mileage pre turbo vs post turbo did you see? My best tank so far was 12.8 mpg so it isn't going to take much to improve it, the current engine is tired.

I'm not expecting to run in the 14's while getting 35 mpg but I think I *should* be able to get 15-18 consistantly. One big down fall right now is the 4 sp trans with the huge jump between 3-4. I'm watching the local U wrench it yard for a 5 spd. I know I won't recoupe the money invested in new parts unless i drive the truck 200,000 miles after the mods but I'm rebuilding the engine regardless, I would like to make it as efficient as possible.

Also, what kind of levels will the stock EFI support? 200 horse? 5-7 psi? After all the reading I have done I haven't seen anyone build the stock EFI system. Is there a reason that the stock system wouldn't support very mild levels of boost?

Thanks,

Neal

 

[StrangeRanger]

Depending on how you cook the numbers the stock injectors limit out somewhere between 165 and 195 HP. Basically they're close to being maxxed out on a stock EFI system. Replacing them with bigger just takes a trip to the parts store. The trick is going to be the processor mods to support the higher throughput.

 

[inline300]

Larger injectors + adjustable fuel pressure regulator + FMU and you shouldnt have too much of an issue with mild boost, wont be efficient. FMU alone wouldnt work so well, as the 4.9 injectors are running at high psi/near peak as it is, as mentioned.


You could add larger injectors, have someone reprogram your computer but it would still require hard data to really nail it down.


If your serious about efficiency, learning about stand alone efi controllers would be in your best interest. This way you could run a boost friendly map sensor, make adjustments as needed.


Good luck

 

[StrangeRanger]

On a stock 300, operated at moderate boost in the stock RPM range, you have a choice of a T03 with Super 60 Trim or a T04 with one of the smaller trims. If you start trying to make more revs or going for big boost, you need the T04

At 8 PSI, a 300 with moderate head work should make something in the neighborhood of 225 BHP/320 ft-lbs or about 50% more than stock. That means you're going to need to supply it with slightly more than 50% more fuel than stock (boosted engines have slightly higher BSFC numbers.) A set of 24# injectors should do that nicely but you will need to work out the control mods

 

[Bort62]

swaping large injectors into a stock fuel system is not a good way to get fuel economy.

If you put 25% larger injectors in the motor, the computer isnt going to know it and it will be dumping 25% more fuel that it should.

With an AFPR you MIGHT be able to tune htis OK for WOT, but your part throttle is going to be way rich. If you change injectors, you need to reprogramm the computer.

 

[XFlow_Fairlane]

btw putting a turbo on is not going to help your milage any period. it will take a slight reduction. now you could prob get by with a steeper gear with the added power/torque which then will help your milage out.

btw my 1997 4.3L 2wd s10 only gets 22mpg (much smaller than a f150 and much better areo) so unless you go for drastic mods like steep gears narrow tires, etc then I wouldn't look for much more of an increase.

 

[GrantD]

This is somewhat related...

I realize that a turbo will not increase mileage any but do you think that you'd get better mileage than you would if you were running a larger motor N/A of the same power output?

Been curious for a while and this thread reminded me of it.

 

[XFlow_Fairlane]

sorta...

at part throttle operation it is mostly based on the efficency of the motor at that rpm....for instance...

2.3L guys report the same milage in 4th gear as they do in OD on a T5. the OD is not real steep on them and since the motor is still in the same efficency range it uses the same amount of fuel to produce the same amout of power to run at say 55mph.

BUT you take a 300 built for 400HP in turbo form and since it has a mild cam and ports under cruise conditions it is nothing more than a mild built 300" motor. now tune a 302 for 400hp and try and run it on the highway and since it will most likely have a bigger carb, cam, ports than a mild/stock motor it may get worse milage (if it is turning to slow with big ports your velocity will drop off and fuel will come out of suspension kicking up the unbirnt HC)

the turbo 2.3L guys coudl report milage in the high 20's even on a 300hp car (mostly was just a bigger turbo and intercooler with more boost) so it still used factory like mapping at cruise speeds.

just remember out of boost you just have a stock motor. if you are EFI then you can tune for real good cruise milage but still have that power tune under throttle. do a blow through carb setup and you can run a small carb to keep that lowend power.

 

[Lazy JW]

This is somewhat related...

I realize that a turbo will not increase mileage any but do you think that you'd get better mileage than you would if you were running a larger motor N/A of the same power output?....

Maybe but it would require dyno testing and BSFC numbers to prove, the difference would likely be very small. The smaller engine 'should' have less thermal loss but this may well be lost due to the turbo backpressure.

There really have been only small improvements in thermal efficiency since Sir Harry Ricardo was messing around with his "high speed internal combustion engines". He turned in some pretty impressive BSFC numbers using FLATHEAD engines
Joe

 

[StrangeRanger]

The conventional wisdom in sizing injectors is that NA engines have a BSFC of .50 lbs/HP-Hr. and boosted engines have a BSFC of .55. This means that under full load and WOT the boosted engine will use 10% more fuel than an NA engine which produces the same HP.

Ay part throttle, it depends on haw radical the build is. If you build a 300 for the 200-225 HP range, the NA camshaft and headwork aren't going to be all that radical and fuel economy will be comparable. Push it to the 275-300 HP level and the turbo should deliver better fuel economy and drivability every time