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EA81 NA Mods Questions


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15 replies to this topic

#1 Waterboxerz

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Posted 18 October 2003 - 01:00 AM

Hi all! I hadn't been able to put much time into my '80 1800 GLF 2WD coupe for a while, but my roomie and I finally got into a house, with a garage! So the project begins...

Pulled the motor out and disassembled it. Blown headgasket on the passenger side made for some ugly oil in the pan and some minor crud in the bores. Both heads were cracked into oblivion. They have since been rewelded an rebuilt. Lifters have some carbon crud on the faces, and the cams a little pitted. Crank looks okay, but it'll definitely need new rod bearings.

My plan is to send the cam off to Stratus (if they're still doing Subie cam regrinds), and have the crank cleaned up by a reputable machine shop. The heads were done by a good shop, and were decked .040 each to accomodate the Stratus cam. From what I understand, this bumps the compression ratio up from 8.5:1 to around 9.2:1. Are those numbers reasonably accurate? Also, I remember reading somewhere that the 1600cc Subie pistons would fit the EA81, and that they increased the compression ratio too. Is this true, or merely smack talk? Finally, could the engine accomodate both the 1600cc pistons AND decked heads? I'm sure I'd be getting close to having interference between valve and piston, and I'd rather find out now instead of during reassembly. If it might work, does anyone know where I can get some 1600 pistons?

I intend to use this car for autocrossing, and possibly some rallycross, and have a little fun on the street with it, presuming that I can mod it that much and still get buy with hi-grade pump gas. I'd seen a fair bit on EA-81 aero applications, and the power numbers looked pretty good. I do plan to change the pully sizes to prevent the water pump from cavitating at higher RPM. I'm also looking at ways to modify the intake manifold to fit on the now-shorter longblock, unless anyone knows of a set of Baby Del'Orto manifolds for EA81s.

I feel that old Subies get no respect around here, and I figure that if I can get this car running well, I can back up my sig line. Thanks in advance for any info.

Sean L.
'80 1800 GLF Automatic beige coupe
Huntsville, AL

Stalking an '80 GL beige wagon as well!

#2 GeneralDisorder

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Posted 18 October 2003 - 01:38 AM

The EA71 pistons do indeed increase the compression - to around 9.5:1 in a normal engine. CCR will even put them in for you if you ask them to on engines they build.

GD

#3 Hondasucks

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Posted 18 October 2003 - 09:18 AM

but .040 off with 1600 pistons, I don't think I know of anyone with an EA81 like that. I really don't know if you'll have valve interferance or not... you could assemble the block with the 1600 pistons and measure it up... put heads on and check for interference...

#4 Waterboxerz

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Posted 18 October 2003 - 06:51 PM

Sure. If the pistons are thick enough, would it be feasable to spot-face 'em a bit for valve pockets?

And where can I get my hands on a set of EA71 pistons? :D

#5 StormTrooper

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Posted 18 October 2003 - 08:36 PM

all of your ideas are very valid, and actually match the same research i have done myself...go check out this links of airplane sites, you will be amazed by the plethora of knowledge and business' that cater to building your own Sube performer...

http://groups.yahoo....p/airsoob/links

#6 Qman

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Posted 18 October 2003 - 08:51 PM

The difference in the pistons is barely visible to the naked eye. .040 is standard for the aviation side of the house. The problem you will run into is that the intake will no longer match correctly. It brings the intake ports closer together. I milled my heads .020/ea without ill effects and the intake still matched up. The power gains are quite noticable.

It is true that you will need to decide with pure torque or HP. You can go to the high end with either one. If you are running high r's then go with the HP grind. The torque will be there in that rpm range. The valves won't interfere as they are closed when the piston gets that high.

BTW, I am running two different high performance motors. Both are running 1600 pistons and big cams. One is built for HP and one is built for torque. Do not bore the cylinders. They have a bad tendancy to spin the sleeves during operation.

#7 GeneralDisorder

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Posted 18 October 2003 - 09:57 PM

If it's just a matter of the intake holes, and if .020 lined up still, then your only talking .020 to get the holes to line up with the heads shaved to .040.... couldn't you just drill out the intake manifold holes a little bigger and still use it that way? Maybe shave on the intake passages to take off the edge where they got offset.... just a thought, and I've never done it, so maybe there's a reason you can't?

You mentioned that sleeve spinning before Ken - by "operation" are you refering to the boring operation itself, or are you saying they will spin when you put the engine into operation (ie: running)? If so.... how does CCR do their engines? There must be a method that ensures this won't happen - do they just re-sleeve the block? I'm just curious because I intend to build an engine for the wagon eventually.

GD

#8 Dante

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Posted 18 October 2003 - 10:47 PM

Wow--there's some great info. here. Thanks for those links Storm Trooper...100HP...140HP...170HP...WOW! I can't wait to get my hands on one of these cars. I'll have my trailhead car AND a project car :banana:

#9 StormTrooper

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Posted 18 October 2003 - 11:50 PM

I think one caa accomplish those high hp ranges by mixing the know-how of the junkyard/machine shop antics of most soob-heads, and the pristine engineering of the airplane freeks...

Ken, if I'm not mistaken, the amount that you shave on the head should be dependant on the type of cam grind you do, as shaving the head X-amount will adjust the valve geometry that is influenced by the Y-amount of cam grinding...So wouldn't the amount of shaving that the heads need totally depend on what you're looking for in terms of low-end torque, or top-end HP?

I'm truly all concept here, as I have only recently begun to research what's needed to acheive what's desired out of the EA engines...

#10 Waterboxerz

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Posted 19 October 2003 - 01:06 AM

Since the nature of this beast is gonna primarily be an autocrosser, I'm looking for the power up near the top of 2nd or 3rd gear. All the running I've done so far with my roomie's MA70 NA Supra and my Audi GT have kept the engines near the rev limit in those two gears.

As for the cylinders, all I intended to do was a light dust-up with a bottlebrush hone. Nothing too tricky.

On the manifold, I'm considering pulling a spare off a junker motor, and welding the bases to a set of 34mm Dell'Orto manifolds from a single-port Beetle, and then matching the ports. Lotta work, but this thing could be a hoot with dual carbs.

:D

#11 Waterboxerz

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Posted 19 October 2003 - 01:24 PM

Does anybody know anything about Badger pistons? Two sets for 1600/1800 on eBay, one's .030 overbore, and the other's .040 overbore. Not sure if this will give the compression ratio I'm looking for, and I'd prefer not to bore the block unless these pistons would actually improve the ratio.

Thanks in advance. Now back to cleaning the block.

Posted Image

:D

#12 Waterboxerz

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Posted 22 October 2003 - 10:18 PM

Got my cylinder heads back from the shop yesterday, and they're looking pretty good, except for the dorky "tattletale" warranty stamps that fail if you overheat the heads. They did a good job of welding and replacing the valve seats, and taking .040 off too. I'm almost ashamed at how clean they are as compared to the rest of the block. Here's the "before", note all the damn cracks! The one on the #3 cylinder almost penetrated the water jacket!

Posted Image

And here's the finished product!

Posted Image

Got a stamping kit to mark all the pistons before popping then out of the block. Was somewhat of an exercise in futility, once I got a good look at the #3 piston. I suspect they're not supposed to look like they've been gnawed on.

Posted Image

So, here are my current questions:

1) I have heard rumors of the later EA81s having bigger valves than fossils like mine. Is there any truth in this? When I had the heads rebuilt, I was tempted to ask them to get the later valves, but I figured that I needed to research this story further before acting on it.

2) I talked with a buddy of mine who's been building racing VWs for many, many years, and he brought up an idea which had occurred to me, but I simply hadn't asked yet: Has anyone ever "pinned" the bores on an EA81 to keep 'em from spinning? If I have to bore the cylinders, the discussions of spinning the bores worries me. I inquired as to the extremity of boring .030 on the engine, and my friend laughed it off, saying that the figure is essentially a 1st overbore on American iron. However, I doubt that figure is a blowoff on a Subie. Any feedback would be appreciated.

3) If boring the block is bad, then can anyone suggest a good source for a set of new or good EA71 pistons? I'd prefer to go with stock size, but I'll work with whatever's available.

Thanks!

- Sean L.
'80 1800 GLF coupe owner and worshipper :D

#13 Qman

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Posted 22 October 2003 - 10:40 PM

1) Yes, the hydraulic motor's have bigger valves.

2) I have heard many bad things about boring the cylinders on a Subaru engine. I do not know if pinning would help or not. I also think it's a heat dissipation thing as well.

3) I used used pistons in mine. Had them mic'd and checked for roundness. Then just used stock rings and bearings. CCR rebuilds all retain stock specs. They get alot of cores and measure everyone to find the good ones that are still within spec.

#14 TomRhere

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Posted 22 October 2003 - 11:02 PM

I take then that the sleeve's can not be replaced. Anyone one with an answer as to why they can't? Just curious is all.

Remember someone on here saying he had .050 over pistons for his. That would jump the CC's up a bit.

Got a set of MPFI heads here, with a bad crack between the valves in one cylinder. It's big enough that the valve seat came out. Wonder if those could be repaired?!?

#15 StormTrooper

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Posted 23 October 2003 - 12:46 PM

BTW- Who knows what "Forged Pistons" are?? RAM Performance sells an EA81 rebuilt kit with Forged Pistons...:cornfuzz:

#16 Guest_subu luvr_*

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Posted 23 October 2003 - 12:53 PM

forged/cast/billet

billet is machined from a solid block
makes nice parts, but they are soft

cast is melted, then poured into a mold
nice parts but they are brittle and usually heavy


forged is heated, then beaten into shape
has cast's strength, but not the brittle
has machined parts detail but is harder

forged is the only way to go ;)




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