How low can the cyl. compression be for the FI???

[Petersubaru]

I am just wondering, if it is feasible for my friend to convert to FI from his EA82 carb... when checking the compression, it is about 130-135 across the board...the spark plugs burn clean and the car uses about 1 qt of oil every 1200mi of highway driving and obviously the back pressure is more present..

[jeffast]

you should be fine with that all fuel injection is is an electric carb if it will run carburated it will run fuel injected

[GeneralDisorder]

Compression really isn't all that important - he's about 30-40 psi off from a new engine, and by the sound of the oil usage his valve stem seals are shot, and probably the seats are burnt causing the slight pressure reduction. But really, comp. numbers aren't that important for the engine to run, and won't by themselves cause the FI any problems at all. The SPFI system is capable of adjusting for any number of problems, and will run better than a carb simple because the carb is still jetted for a new engine and the SPFI is capable of adjusting itself to a somewhat worn engine.

 

First rule on compression numbers is that the NUMBER itself doesn't matter (within reason), it's the percentage of difference between the cylinders that makes all the difference. An engine with 80 psi on each cylinder will run fine as long as all 4 are the same or similar. And surprisingly it won't really lose all that much power - remember the engine rotates at about 1000 RPM minimum - 80 psi at starter crank speed (which even with the plugs out is around 200 RPM) is going to be MUCH higher at 1000 RPM. Compression tests are good, but people put way too much stock in the number, when all that really matters is the percentage difference.

 

GD

[Syonyk]

Agreed. Differences in valve timing or battery voltage can affect the compression, the length of the hose going to the compression gauge has a major effect, even the temperature/humidity on the day you're running the tests can have an effect.

 

Even compression & that low of oil consumption? The engine's got a lot of life left in it. A quart every few hundred miles would be cause for concern.

 

-=Russ=-

[Petersubaru]

GD.. it is good to know that the FI can make adjustments as the system wears on, unlike the carb which is set up for a stronger vacuum or air being pulled into the motor...a little history on this motor...the heads where bought thru subaru (so I am told) and together with the block have about 10,000 miles on them..so as not to make the story to long, we had to tear down the motor and replace the bearings and rings... new ones from the Nippon piston ring company useing the standard size ring ..(apparently the same ring that subaru orginally used)... the machine shop said that cylinders were only out by .001in...so the standard size seemed correct..(almost no wear at all)...I did not install the new rings, but was later informed that the new rings had a larger gap then the old ones taken out, which might give some explanation as to why it consumes the larger amount of oil

[GeneralDisorder]

Did they at least do a bottle brush hone on the cylinder walls? It could be that the new rings haven't broken in yet.

 

GD

[Petersubaru]

the brush honing was done to the cylinders (that I did see them do) and the oil consumption is far less then when it was first started up...a little side note concerning the rings.. the first set of rings were from the federal mogul group and they had to be sent back because the ring gap was even larger (a total misfit of rings to cylinders)...by the way...how will you make it known when your FI project is ready with pictures and price..

Did they at least do a bottle brush hone on the cylinder walls? It could be that the new rings haven't broken in yet.

 

GD

[GeneralDisorder]

I'll make a big hairy post about it - both here for the write up, and probably in the vendors section for the harnesses and distributors. Initially I'm doing the harness and disty, but for people that ask I might be convinced to box up an entire setup and ship it - mostly that's for folks in the areas where soobs are scarce though because around the west coast we have a ton of them. At any given time there are at least 2 dozen EA82's at each of the 3 yards closest to me, and that's not counting the small yards I don't frequent unless I really need something bad and can't find it. And these days most are SPFI it seems.

 

I took more pictures today, and things are looking good. I've sent the link to a couple people for review and sugestions. It's not ready yet, but I'll probably release the link here in a few days even before it's totally finshed. I need to get to the yard for another harness to do a pictorial step-by-step of the harness conversion process, but the weather here is REALLY, REALLY bad. Tropical storm bad - I just got back from the store, and 100 yards before the the on-ramp that I used, there was a semi trailer on it's side, and a couple cars spun out of control - cops everywhere..... just a freakin mess.

 

GD

[GeneralDisorder]

How many miles since the re-ring? It usually takes 500 or so for them to wear in.... you might find out what grit bottle brush they used. I'm assuming you got the sintered iron rings? I've only used the chrome ones from Fed-Mog myself..... they must have ordered the wrong part number or something.

 

GD