EA81 twin carb

littlewhiteute · Post by **littlewhiteute** » Sun Oct 14, 2007 8:07 am

Hi guys,

I know that there was a factory twin carb EA71, was there ever a factory twin carb set for the EA81 1800 engine?
And if so, was it brought to Australia, and in which cars?

stinky · Post by **stinky** » Sun Oct 14, 2007 8:34 am

Yeah, there was a factory EA81 engine, I think it was built for rally versions of the car. They can be very hard to find the proper ones, not so hard to find ea81's with the twin-carb manifold bolted on. I've owned one of each, and found a fairly big difference with the former driving way better.

littlewhiteute · Post by **littlewhiteute** » Wed Oct 17, 2007 5:50 am

How do they compare to a single 32/36 Weber for power and fuel economy?

I'm rebuilding an EA81 with a tiny cam (207@.050), multi angle valve seats etc for efficiency.
This is my first "hi po" Subaru engine, have rebuilt heaps of other engines, mainly V8s, any further tips greatly appreciated.

stinky · Post by **stinky** » Wed Oct 17, 2007 10:38 am

I definately got more pull out of the dual carb engine than when I had a weber, fuel economy difference wasn't really noticeable with standard driving.

timmo · Post by **timmo** » Wed Oct 17, 2007 5:09 pm

i think there was a dual carb manifold & carbs on ebay the other day

timmo

BRUMBI · Post by **BRUMBI** » Wed Oct 17, 2007 5:14 pm

there is one on ebay

littlewhiteute · Post by **littlewhiteute** » Wed Oct 17, 2007 5:55 pm

Yes, I know of that set, I'm very keen on it.

Thanks guys for your comments.

Phizinza · Post by **Phizinza** » Wed Oct 17, 2007 8:28 pm

Yes, EA81 did come with a Dual carb model. But theres a little more then just a manifold and two carbs.
I have one of these and it starts at the two carbs. But the heads are also different. The valves are the other way round (exhaust inlet inlet exhaust, instead of the standard inlet exhaust exhaust inlet) like the EA82 engine. The valves are larger then standard. Because the valves are swapped the came is also different.
From the factory they were suppose to have 100hp. Thats a lot more then the standard 78hp of the time (pre 84.)
I'm building custom manifolds for mine so I can have a weber or something like that on top of each head. I'm also looking at increasing compression a fair old bit and running some high octane fuel. Hoping for 140hp+, but I'd be lucky probably.

littlewhiteute · Post by **littlewhiteute** » Wed Oct 17, 2007 9:15 pm

So the twin carb manifold won't fit single carb heads? The flange spacing appears to be the same.

Gannon · Post by **Gannon** » Wed Oct 17, 2007 10:09 pm

Phizinza wrote:From the factory they were suppose to have 100hp.

Where did you see that?

I find that hard to believe, seeing the EA82T with 7psi of boost and MPFI can only manage to push out 115hp from factory

BRUMBERTY · Post by **BRUMBERTY** » Wed Oct 17, 2007 10:17 pm

In fact there were two factory twin carb tunes....
100hp and 120hp

Both competition motors

HP = Torque x revs..

imagine what the 120hp unit revved to, I know they had bugger all torque
as I ran one with 11:1 compression.

Scary.

sublime · Post by **sublime** » Wed Oct 17, 2007 11:30 pm

littlewhiteute wrote:Yes, I know of that set, I'm very keen on it.
Thanks guys for your comments.

If you look closely at the dual carbs and manifold on eBay at the moment you will see that it is from a EA71 not EA81. The manifold will be too short for an EA81.

steptoe · Post by **steptoe** » Wed Oct 17, 2007 11:40 pm

good spotting sublime

the EA81 twin carb manifold will fit a standard EA81 , you don't need to have the heads and cam. Phiz sounds like you are trying to develop your own safari style manifolds. What we need is an engineer and foundry in china to produce our dreams cheaply. Want power from an EA81 look up sub4.co.nz who have their own heads and roller rockers and stuff and get 140HP !!!

Gannon · Post by **Gannon** » Thu Oct 18, 2007 6:39 am

BRUMBERTY wrote:HP = Torque x revs..
imagine what the 120hp unit revved to.

A very important point a lot of people often forget.

Yeah i agree it would have to rev to get that power, but surely not a very useable powerband.

This is the first time ive seen horsepower numbers like these posted for the ea81, but i'll admit i have never really paid much attention to ea81s

littlewhiteute · Post by **littlewhiteute** » Thu Oct 18, 2007 6:20 pm

sublime wrote:If you look closely at the dual carbs and manifold on eBay at the moment you will see that it is from a EA71 not EA81. The manifold will be too short for an EA81.

What's the length difference of the manifolds?
The seller gave me his measurements and although I don't totally agree, it must be correct for EA81.

sublime · Post by **sublime** » Thu Oct 18, 2007 10:58 pm

littlewhiteute wrote:What's the length difference of the manifolds?
The seller gave me his measurements and although I don't totally agree, it must be correct for EA81.

I am not really sure of the differences in length. It would not be much, at a guess 15 to 20mm? Does anyone on the forum have the length of a EA81 manifold?

There are other differences that make me think it is for a EA71. There is the way the air cleaner housing sits on the carbs. EA81 carbs (both single and dual) have a thread in the middle that air cleaner assembley mounts to or is tightened down on. The carbs on eBay do not have this mounting arrangement, you can, however, see the brackets on the outside of the carbs for mounting the EA71 air cleaner which is the blue one in the pictures marked with SEEC-T.

There is also the position of the thermostat. On all the EA81 manifolds (again single and dual) I have only ever seen the thermostat on the drivers side. On EA71 manifolds it is positioned in the middle, just like the one on eBay.

Perhaps I am wrong. Others on this forum might even be able to add more information or let me know I'm wrong, I just feel it would be annoying to buy something that does not fit.

Phizinza · Post by **Phizinza** » Fri Oct 19, 2007 9:42 am

littlewhiteute wrote:So the twin carb manifold won't fit single carb heads? The flange spacing appears to be the same.

Nah, they will fit. It's just there is more to the dual carb motor then carbs like lots of people believe. The manifolds do have the same placing and everything.

Phizinza · Post by **Phizinza** » Fri Oct 19, 2007 10:06 am

sublime wrote:There are other differences that make me think it is for a EA71. There is the way the air cleaner housing sits on the carbs. EA81 carbs (both single and dual) have a thread in the middle that air cleaner assembley mounts to or is tightened down on. The carbs on eBay do not have this mounting arrangement, you can, however, see the brackets on the outside of the carbs for mounting the EA71 air cleaner which is the blue one in the pictures marked with SEEC-T.

My original air box for the dual carbs (although looks quite different to that one, looks more like a standard one) has two wingnuts on the inside holding the base to the carbs and then only two holding the lid to the base. It doesn't have the wing nut that fits to the carb out the outside of the airbox like the single carb models do.

As for HP, I have seen in several places 100 and 102hp figures. I can't remember where I saw it but I saw a photo or scan of an original spec sheet from a Subaru dealer with the 102hp figure on it.

I ran mine with standard 9.5:1 compression and she had a good 10 to 15 % more power right the way through the rev range then the stock rebuilt EA81 my brother had. And just for the record that stock EA81 had 170psi on all 4 pots. And with the second carb she used to be able to rev up and beyond 8500rpm. EA81 FTW! Now I just need to give her a rebuild and some more compression, etc.

One more thing, the thermostat housing on the manifold is different to standard and dual carb EA81's... It looks more and more like a EA71 manifold. Although I can't say if they swap over or not.

Xtreme_RX · Post by **Xtreme_RX** » Fri Oct 19, 2007 11:03 am

The EA71 manifold WILL NOT FIT the EA81...
Been there done that.....

littlewhiteute · Post by **littlewhiteute** » Fri Oct 19, 2007 8:08 pm

EA81 manifold bank to bank for inner bolts: 420mm, outer bolts: 525mm, port centres: 472mm, off my stripped engine.
8500 rpm? I'd be over the moon if I can pull 6500.