EA82 rebuild questions - for best gas mileage?

[idosubaru]

are there any particulars to rebuilding a motor for best gas mileage (highway mileage)?

 

boring over and head/work will increase power but decrease gas mileage i guess?

 

i'm getting an XT (actually an XT Turbo, but i'm installing an EA82 motor in it) saturday that will become my highway vehicle and i'm gearing it for gas mileage.

 

on a side note - does CCR rebuild long blocks only or short blocks as well? what does an EA82 rebuild cost? i sent them an email but go no reply.

[Syonyk]

Amusingly enough, the same things you'd want to do for best power are the things you'd want to do for economy.

 

Make sure there's as small a gap as possible in the rings, for best compression.

 

If you want to put higher compression pistons in, that will help.

 

Make sure the valves are opening fully and sealing properly.

 

Depending on how crazy you are, you might want to try Motoman's engine breakin method. Google for it, but he has convincing evidence that a typical gentle breakin is actually bad for the rings (and therefore compression, power, and fuel economy), and that the best method is several (many?) full throttle runs up through the RPM band (and engine brake back down) in the first 5-15 miles.

 

If I ever rebuild a boinger, I'm definitely giving his method a shot.

 

If you have the money, putting a MSD6A or Crane HI-6 in would most likely help some - multiple hotter sparks, so if the mixture doesn't catch the first time, it'll get lit by a subsequent spark.

 

And, if you're in a state you can do so, remove the stock ECU, remove all the emissions control stuff, and use a full standalone ECU to tune the engine. You can get noticeably better gas mileage when you don't have to keep a catalytic converter from melting into slag.

 

Other things you can do would be to use high quality synthetic oil, as well as good quality synthetic gearbox/differential lube, run the tire pressure high, keep the car waxed, etc.

 

-=Russ=-

[NorthWet]

Consider using the turbo cams on the non-turbo block. The decreased overlap should provide smoother running and slightly less wasted intake charge and/or less charge dilution; it will also give you a higher effective compression ratio. It will cut down on mid-to-high-rpm power.

 

Standalone, TUNABLE ECU would be useful, and some better form of ignition. I would prefer a distributorless type, just for it being potentially more accurate than something sitting at the end of a shaft that is driven by the end of the camshaft that is driven by a resilient drive system off of the semi-resilient end of the crankshaft.

 

I personally would not even try the previously mentioned break-in procedure.

[idosubaru]

awesome pat. i'll already have the turbo cams. are they definitely different than the EA82 cams?

 

i'll stick with the stock ECU for ease of use and troubleshooting.

 

i'll use standard break-in procedures.

 

what would be the best pistons to use for gas mileage? highest compression? would that be the standard EA82 pistons? i have some of those already so if there isn't much difference i'll likely use those. i can get lightweight forged pistons but i'm thinking that wouldn't transfer into much gas mileage savings.

 

i'll have a complete head job done.

[555Ron]

I personally would not even try the previously mentioned break-in procedure.

Yeah, you could start a big argument on break in procedure. Don't ever give it revs when its cold. I'm fairly sure prodrive (Subaru's rally car producers) use a normal break in procedure, so i'd stick with that. You do (imo - and most others) want to load the engine up when it is being run in (when hot)... so high gear, high acceleration, steep hill... and keep the revs below... say 3000rpm?? The extra force of the high energy explosions help seal the rings while not putting too much force on the engine that high rpms will give. The better your rings are sealed, the better the mileage.

 

You could always buy a motorbike:drunk:

[idosubaru]

end of break-in comments. i can start a new thread when i get to that point. it's not really needed now.

 

no go on the bike, won't suit my needs and i don't want one. snow, storage, passengers, long trips, rain (60 mile one way commute), DC traffic is hell, i've never driven one...

[Ross]

The shop i had my cams ground recommended "sharply" accerlerating and decelerating between 40 and 80km/h 5 times in 3rd after fully warming the engine up. I will probaly follow a similar procedure, but i will not be interpreting "sharply" as full throttle (perhaps on an N/A engine though?).

 

They also recommend never to let the engine idle below 2000rpm for the first 10 mins.

 

As for fuel economy, the best thing you can do is raise your compression ratio. SPFI pistons give you the highest comp ratio.

[idosubaru]

what's the difference bewteen SPFI and MPFI pistons? will i have to go to high grade gas on the SPFI pistons?

 

why did they use lower compression pistons in the MPFI?

[NorthWet]

what's the difference bewteen SPFI and MPFI pistons? will i have to go to high grade gas on the SPFI pistons?

 

why did they use lower compression pistons in the MPFI?

I can't remember offhand if there is a difference, compression wise. SPFI are more common, so I think that is why they are most often recommended. Forged pistons aren't going to affect your mileage, unless they are higher (but still workable) C/R.

 

After higher compression, the biggest single thing would have been a better fuel management. The Subaru system, especially earlier versions, were relatively primitive and erred on the side of caution (and emissions). Might be good for 10-15% improvement. Something to think about down the road.

 

I am not sure what is available as options for rings. Once upon a time I think that it was claimed that Moly coated/filled rings had less friction than chromed rings; might be bad memory or Old Wives' Tale. If there is a difference, it would be minimal, especially at our low piston speeds.

 

Regarding the cams, the only ones that I have seen FSM specs on was from an 85 FSM. (And that FSM is on loan at the moment.) In general, turbo cams have very little overlap.

 

And, there is gearing... but you said engine.

[idosubaru]

i was wondering about gearing as well...but was going to wait on that one since i've never done internal trans work. i'd like to have the 3.7 gearing of the auto in the manual. the rear would be easy...but i'm guessing no easy way to do the front diff gearing? anyway to swap that from an auto into a manual? how nice it would be if the front diffs were perfectly swappable!

[Ross]

I can't remember offhand if there is a difference, compression wise. SPFI are more common, so I think that is why they are most often recommended.

 

 

I believe the MPFI engine has a CR of around 9:1, as opposed to 9.5:1 for the SPFI.

[Syonyk]

On this topic, what kind of gains have people seen from going to a Megasquirt or such, as opposed to the stock ECU? I know that with emissions removed, you can lean things out a bit and get better economy, but I haven't see actual numbers posted.

 

... otherwise, I guess I'll just have to do a MPFI swap in mine and test it out.

 

-=Russ=-

[jacobs]

Amusingly enough, the same things you'd want to do for best power are the things you'd want to do for economy.

 

Make sure there's as small a gap as possible in the rings, for best compression.

 

If you want to put higher compression pistons in, that will help.

 

Make sure the valves are opening fully and sealing properly.

 

Depending on how crazy you are, you might want to try Motoman's engine breakin method. Google for it, but he has convincing evidence that a typical gentle breakin is actually bad for the rings (and therefore compression, power, and fuel economy), and that the best method is several (many?) full throttle runs up through the RPM band (and engine brake back down) in the first 5-15 miles.

 

If I ever rebuild a boinger, I'm definitely giving his method a shot.

 

If you have the money, putting a MSD6A or Crane HI-6 in would most likely help some - multiple hotter sparks, so if the mixture doesn't catch the first time, it'll get lit by a subsequent spark.

 

And, if you're in a state you can do so, remove the stock ECU, remove all the emissions control stuff, and use a full standalone ECU to tune the engine. You can get noticeably better gas mileage when you don't have to keep a catalytic converter from melting into slag.

 

Other things you can do would be to use high quality synthetic oil, as well as good quality synthetic gearbox/differential lube, run the tire pressure high, keep the car waxed, etc.

 

-=Russ=-

I was just reading about the normal break in procedure for the old "Mobil economy run" was to remove the air cleaner, drive on dirt roads with a chase vehicle in front of the car being broken in. They didn't say how many miles it took though.

[84gl]

the ea 81 2wd 5spd trans was the highest geared of all the 5speeds 5th is .725 and the axle is 3.7

[zyewdall]

what's the difference bewteen SPFI and MPFI pistons? will i have to go to high grade gas on the SPFI pistons?

 

why did they use lower compression pistons in the MPFI?

 

I have a stock SPFI EA82, and it takes lowest grade of gas (85 octane here in colorado) if I'm driving it around on the flatland. If I head into the mountain, it pings on low grade going up hills (especially in hot weather) so I have to switch to mid grade (87 octane).

 

My method of increasing the gas mileage for my subaru is going to be putting a VW diesel engine in it -- it seems you just can't get much better than mid 30's with a gas engine in a subaru, but a diesel should have no trouble getting high 40's.