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Best way to gain C.R. with EA81T heads


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16 replies to this topic

#1 TheSubaruJunkie

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Posted 09 August 2003 - 02:11 PM

Well... its getting closer to the time to build my engine. Im going to be using EA81T heads and intake manifold. Coupled with a standard EA81 block.

The EA81T's compression is somewhere around 7.7:1 and the EA81 is something like 8:1 or something.

Should I try to increase my C.R. with the EA81T heads by replacing the pistons? Or shaving the head? I was planning on having the heads shaved anyhow, but not sure how much I should have shaved off.

Also... I am planning on using the VW FOX, CIS-e EFI system. Anyone know if there will be any complications with that and the EA81T intake manifold and throttle body?

-Brian

#2 MilesFox

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Posted 15 August 2003 - 03:10 AM

use the pistons from an ea71 hatch motor. hatch pistons in an ea81 block will give you the same 9.5 compression of an ea82 spfi block

I got to see oh noah's setup in person. the bosch unit satin the spare tire, and the airflow moved over a disc inside that actuated the ffuel flow valve. his was connected to an xt spider intake, but you will have to connect yours to the ea81t's throttle body. as long as you can get your plumbing to fit you should be alright. its all amatter of conjuring up the right size pices. its one of those creative ventures.

the throttle body on the manifold will determine how much flow will go into the motor, and thus it will pull through the bosh unit. you will be pulling your air through the disc on the bosch unit instead rather than the subaru's flapper door.

#3 CIS Subaru

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Posted 16 August 2003 - 10:00 AM

I wouldn't shave those heads if I were you, at least not very much. They're such a rarity that I'd tend to want to keep them stock. You probably already know that shaving the heads interferes with the intake mounting and the valve adjustment.

The standard EA81 has 8.7:1 compression and the EA71 has 9:1.
Since you'd be using different heads than either of these engines, it's kindof hard to say exactly what your compression ratio would be with either of those pistons.

Miles, do the EA71 pistons make 9.5:1 in a EA81 because the EA81 has different rods? I don't see how else they would make MORE compression in the EA81 than in a EA71.

As far as the CIS goes, I don't think you'll have any fitment troubles with the intake. You should be able to use Subaru front axle nuts to hold the CIS injector holders in place, though the nuts may need to be trimmed with a dremel tool in some places. Like Miles said, you'll just have to piece together an intake that works for you. If you could find the piece that attaches to the throttle body from a '85-'86 non-turbo (the piece that says "4wd Turbo" on the turbo models) that would probably be a big help for you. I might still have such a piece if you're interested.

Also, I haven't measured yet to see if VW Rabbit injector hoses are long enough to reach from the right side fender location (where the Fox airbox is designed to sit) over to cylinders 2 & 4. You may want to leave your battery in place and just install the airbox by the firewall where I put mine. That would also help you when it comes to connecting up the fuel pump (if you put the fuel pump in the spare tire area like I did).

#4 TheSubaruJunkie

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Posted 16 August 2003 - 12:23 PM

Yeah, my CIS will most likely be mounted where you have yours. In the spare tire area. Im also going to rig a air filter box that will fit snug against the hood, and i'll have a hood scoop to feed it.

Will i still need fuel injection holders even tho the EA81T heads are MPFI and already have the FI boss's?

-Brian

#5 soobme

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Posted 16 August 2003 - 01:35 PM

I was looking @ Adams EA81T intake and heads yesterday, and it looks like U sould be able to just drill the hole in the heads (for the stock injectors) to take the CIS injector holders. But I could be wrong on that. If that will not work, U could have a machine shop make U 4 injector holders out of aluminum that way they could be welded on, then they will expand and contrackt @ the same rate as the head.

#6 TheSubaruJunkie

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Posted 16 August 2003 - 02:01 PM

What would happen if we used EA81T injectors. Or aftermarket injectors that will fit inside the EA81T heads??

WRX1AB, not sure if anyone remembers him, but he had to replace 2 of his injectors on his EA81T and he used some injectors from a Kawasaki Ninja.

The EA81T heads are so rare, if I dont want to shave them then I sure dont want to modify the injector boss's.

-Brian

#7 CIS Subaru

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Posted 17 August 2003 - 12:13 AM

If you used EFI injectors, then you would have to use some sort of EFI system instead of CIS. :confused:

There shouldn't be any need to modify the heads at all. You can't mount the CIS injectors IN the heads because they are much longer than the EFI injectors.

I made adapter plates to hold the CIS injector inserts, but it turned out that I could have just threaded the inserts into Subaru front axle nuts and used some of the original Subaru injector mounting hardware to hold the nuts in place.

#8 TheSubaruJunkie

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Posted 17 August 2003 - 02:34 AM

Ok... so i guess there's a difference between the CIS and standard EFI injectors.

Looks like i have to put more thought into this. I really dont want to modify the heads to fit CIS injectors.

-Brian

#9 GLCraig

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Posted 17 August 2003 - 03:44 AM

You could go the megasquirt route

http://www.bgsoflex....megasquirt.html

The Volvo and VW guys who have switch to MS from CIS feel that it's a big improvement

#10 TheSubaruJunkie

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Posted 17 August 2003 - 09:55 AM

True, but how much configuration is involved with the MS system?

-Brian

#11 CIS Subaru

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Posted 17 August 2003 - 02:58 PM

Brian, you got the wrong idea.

I was trying to say that there is NO NEED FOR MODIFICATION in order to use the CIS injectors.

I did nothing to the MPFI intake I used in my conversion. What I was suggesting for you was that you thread CIS injector inserts into Subaru front axle nuts, and fasten those to the heads using the existing injector hold-downs. That way you wouldn't damage/modify the heads at all, and they'd be ready to accept CIS injectors.

You might have trouble with your hood scoop idea. At the very least it will be harder to implement than you are thinking. The problem is that air travels UP through the airflow sensor plate in the CIS airbox. You would have to plumb your scoop to a duct that ran to the bottom of the airbox to get what you want.

If you need help with anything CIS related, feel free to shoot me an email. (that goes for anybody)

#12 TheSubaruJunkie

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Posted 17 August 2003 - 03:21 PM

Your the 1st on my list Noah. (as far as help) just need to gather thoughts and idea's.

I know the air travels up... i was thinking of cutting a hole in the bottom of the spare tire holder, running a 90 degree angle of PVC pipe, maybe 3" in diamteter to a filter box that will fit snug against the hood.

Need to get the engine 1st tho... so lets worry about that. I understand the CIS injectors fit into CV nuts, which is good. Not sure if I would use actual CV bolt... maybe a real bolt of the same thread pitch. I'm not sure if I want to jerry-rig it like that tho. Sounds like a good idea, but if I have to do it that way, might as well pay a proffesional to alumi-weld the bolts to the heads themself.

Noah. I no longer use ICQ, too much of a hassle. Do you use any other chat software?

-Brian

#13 CIS Subaru

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Posted 18 August 2003 - 10:16 PM

I hardly ever use ICQ now either. I'm so busy these days that I'm lucky to have time just to check the board and my email. I'll look into getting AOL IM going again when I get time.

As for the whole injector mounting thing, I know that the axle nuts sound like a rigged up solution, but it's really a viable way to use the factory mounts with CIS injectors. A slightly better solution would be to make aluminum adapter plates like I did:
Posted Image
Sorry the labels are hard to read, but I think you can make it out.

#14 TheSubaruJunkie

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Posted 18 August 2003 - 11:02 PM

Adapter plates sound better. I think i may go that route.

-Brian

#15 WRX1AB

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Posted 03 January 2005 - 06:50 AM

True, but how much configuration is involved with the MS system?

-Brian


don't screw with teh compression! ad a turbo!

#16 TheSubaruJunkie

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Posted 03 January 2005 - 09:24 AM

ALready done rich :) Look at how old this thread is. Since then, ive had a Turbo EJ22 & now I have a Turbo EA82 in my RX :)

-Brian

#17 MorganM

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Posted 03 January 2005 - 10:52 AM

ALready done rich :) Look at how old this thread is. Since then, ive had a Turbo EJ22 & now I have a Turbo EA82 in my RX :)

-Brian


Did you go with the EA71 pistons?

How much did you mill off the heads?




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