64 replies to this topic

[fbh]

Drat.

Just came back from a 2-hour greasemonkeying with the car - sad to say that putting two carbs on is pointless. The ports are the same size as the manifold vent, the only limiting factor is the carb throat.

Might as well just slap a big Weber on...

[Phizinza]

yeah, thats what most people do. Theres prolly a good reason for it (I think you just found it.)
Really the only reason you would do this is because it would be super cool and almost a one of a kind. Maybe some time in the future I might do something like this just for kicks.

[fbh]

heh, I might just still do it for kicks - just need to get the facilities, because right now it seems it's going to be too hard to make a pattern to build a new intake from.

Oh, another interesting note. Idle speed without airbox: 1700rpm. Idle speed with airbox and filter: 500rpm.......

[VaporTrail]

use smaller carbs, the stock carb is designed and jetted for a single carb on a 4 cyl engine, 2 carbs of that size will have great topend but suck at throttle opening and midrange. my 2 cents

exactly. I had a Holley 600 cfm 4 barrel on my '82 Brat (with built engine and exhaust). had to be extremely careful at throttle opening, or it would bog down, but once it got to about 2500 rpms, and kept it above that mark, it was awesome.

[Phizinza]

Oh, another interesting note. Idle speed without airbox: 1700rpm. Idle speed with airbox and filter: 500rpm.......

Most likely from all the sensors in the airbox making the idle lower. Or you have a really stuffed air filter. It should idle around 750 to 850 I would think. My dual carb EA81 idles at 1300 :-\ at 14 degrees before TDC.

[fbh]

quick Q: is there anything wrong with having really long drive belts? Figured if I could somehow relocate the alternator way off to the side on the other side of the engine bay I'd be able to fit two carbs on there much easier someday.

Might need to make hood scoops for it though, they'll be moved out from under the "power bulge" on the hood and the "studs" on top might just hit the hood...


EDIT: heh, an EA82 cruising along with dual, actually effective, hood scoops... heh

[Phizinza]

quick A: Longer will strech more and are more likely to break. But not too much more likely. You may need to have it pulled tighter or it may slip.

HOOD SCOOOOOOOPSS!!! I wanted on for my ute, but never got around to making my custom airbox or addin a turbo.

[fbh]

LoL, wonder what'd happen if you took one of those rather massive Edelbrock carbs and shoved it on an EA82...

[Loyale 2.7 Turbo]

Hi Guys!

I think the Dual Carb question in a EA 82 is perfectly Possible, but is a Lot of Work. I know that the Performance will increase a lot over the single Hitachi carb. But first of all, you must know that the Dual Hitachis really means Dual Troubles.

I will sugest to Use the Weber 32/36 DEGV instead of a Dual Hitachi craps.

I own a EA82 since 1985 (Well my Dad, since I was Kid) and Now it´s "Weberized" and is a Whole World Appart in better Performance than the CrapTachi. But I think just only one Weber is enough. but if you still want to put dual carbs. in a EA82, I must tell ya: "Go Weber" and trow away the Hitachi.

Also, you must visit this Site:

http://ramengines.com/_wsn/page2.html

They made custom manifolds for Subaru Engines. this Pic. is for the EA81 with Dual Intake Ports and Molded Manifold. (Also: Forget the Craptachi too):

And this is a Dual Mikuni Carbs Subaru EA81 (Forget Hitachi Too) Maybe they can help you.

So, I sugest to Use Dual Webers, it would be Fantastic! but the Performance gain over just one Weber is just -only- a Little Bit. maybe dual carbs means dual troubles; but forget about it. If you want it, you must Try it. Maybe it is a good idea to the EA82.

Send us Feedback about it.

Bye...

[mbrickell]

Anything with dual carbs has to have the carbs synched pretty well or will run like poo

They make special tools to synch carbs, i.e. the old mercury kind, etc.

Cool idea.

[DJtheGOD]

go with the twin carbies just BECAUSE no other reasons and while your at it put twin exhaust on it so that it breaths real easy..
My project '86 RX Ute(was one a Coupe) will have twin exhausts up the back of the cab(big rig style) and I intend to flick the turbo and install a supercharger why BECAUSE I CAN thats why no other reasons

[Ross]

Something to consider:

It was mentioned above that the intake runners should be short as possible - its not quite that simple. If all you're worried about is high rpm performance, that is the case, but you will be sacrificing low end performance, something most ea81 drivers arn't willing to do.

NZers, do a google search for Sub4, they do similar stuff as ramengines (4 port dual spark heads, dual carb manifolds, injection manifolds etc) - somewhere in the North island i think.

[GeneralDisorder]

You guys should do some more research - all this has been done by Subaru, and the pics are right here on our own site:

http://ultimatesubar...trudy/rudy.html

GD

[Ross]

You guys should do some more research - all this has been done by Subaru, and the pics are right here on our own site:

http://ultimatesubar...trudy/rudy.html

GD

Yes, but the chance of finding those parts (twin carb setup with no crossover) in New Zealand is almost zero.

[Scott in Bellingham]

Im very interested in this project , myself I have a Alluminum foundry and would like to cast a manifold with twin carbs SJR

[GeneralDisorder]

Yes, but the chance of finding those parts (twin carb setup with no crossover) in New Zealand is almost zero.

The point is that it can, and has been done. The twin carb setups are not actually all that rare, and even in NZ, I'm sure you have places that import used Japanese engines. That's where people in the US have found dual Hitachi setups.

Frankly tho, if you have any fabbing skills, it's not all that hard to cut plates for the head intakes, and carb base, and braze or weld on some tubes in-between, and nipples for the coolant cross-over. Dual carb theory is the same as it is for any of the VW flat fours, so there's plenty of reading material at your local library.

The problem is.... the head castings for the EA81/EA82 carb/spfi engine's don't flow well. This is fixed one of two ways - forced induction, or different/modified castings. If you can TIG alum. then you can do exactly what SUB4 does, and dual port the stock heads. Just bore into them, and weld in some tubes for intakes. I'll do it myself if I ever have the money for a decent TIG box.

GD

[fbh]

I've done a fair bit of digging around under the hood - if anyone can slide me a technical drawing of the EA82 (inc. heads) and the intake manifold's carb base then I think I'll be able to draw us up a plan for a manifold, incorporating coolant, vaccuum lines, inter-carb linkages etc.

this sound like a good plan to anyone?

[Ross]

The point is that it can, and has been done. The twin carb setups are not actually all that rare, and even in NZ, I'm sure you have places that import used Japanese engines. That's where people in the US have found dual Hitachi setups.

Frankly tho, if you have any fabbing skills, it's not all that hard to cut plates for the head intakes, and carb base, and braze or weld on some tubes in-between, and nipples for the coolant cross-over. Dual carb theory is the same as it is for any of the VW flat fours, so there's plenty of reading material at your local library.

The problem is.... the head castings for the EA81/EA82 carb/spfi engine's don't flow well. This is fixed one of two ways - forced induction, or different/modified castings. If you can TIG alum. then you can do exactly what SUB4 does, and dual port the stock heads. Just bore into them, and weld in some tubes for intakes. I'll do it myself if I ever have the money for a decent TIG box.

GD

Yeah i know you can easily get the standard dual carb setup, but thats not what they are talking about.

I really doubt that it would be worth modifying the standard heads to be four port - heaps of prototyping and flow bench work (unless you have access to CFD software??) would be needed to get satisfactory performance.

Sub4 offers their (proven) parts so cheap it seems a waste of time to me.

[Ross]

I've done a fair bit of digging around under the hood - if anyone can slide me a technical drawing of the EA82 (inc. heads) and the intake manifold's carb base then I think I'll be able to draw us up a plan for a manifold, incorporating coolant, vaccuum lines, inter-carb linkages etc.

this sound like a good plan to anyone?

Yeah, thats the way, shouldn't take too long if you're using a 3d package like solidworks/inventor.....

Doubt you're gonna find someone with pre drawn plans tho...... You might have to get the vernier out!

[fbh]

from taking off the manifold yesterday I saw the port in the head is pretty much adequate to feed the cylinders. Remember, only one cylinder at a time will be sucking through that hole, and unless you get some radical new cams, that hole will pretty much be sufficient.

The hole itself is about 1" to 1.5" in diameter at a guess. However, the main barrel of the Hicrappy carb is 0.75" or so - probably even less:banana: so in the end, the idea is to double-up the carb to allow the thing to run more freely - and on top of that, to just be able to say "I did this"

[fbh]

Doubt you're gonna find someone with pre drawn plans tho...... You might have to get the vernier out!

Oh hell, with my in-chiropractic-progress back? gonna be murder

very interesting thing just came to mind. At university, we have a machine that can "print" 3D shapes. Forgot what they call it, but you can basically create a 3D object straight out of Solidworks. ABS plastic. Hmm, anyone up for a plastic manifold? :grin:

[mortimc]

Fused Deposition Modeling (FDM) You can use is to make a mold if you know anyone who can do sandcasting. We've used this process at the Vehicle Research Institute at WWU to make intake runners. Worked well...

Clayton
Bellingham

[Phizinza]

The point is that it can, and has been done. The twin carb setups are not actually all that rare, and even in NZ, I'm sure you have places that import used Japanese engines. That's where people in the US have found dual Hitachi setups.

GD

As said before we are not talking about a normal dual carb setup like I have. We are talking about two carbs, one of each head. If you had read all the replies it might of helped, but I forgive you. Theres so much to read on this forum it just gets nuts.


back on topic. well, not quite.
http://www.sub4.co.n...25hpengine2.jpg
if you look at that (the Sub4 dual port heads) running twin manifolds and two throttle bodies (its a EFI engine.) you may get an idea what has been done. I still think smaller, shorter manifolds would be better.

It was mentioned above that the intake runners should be short as possible - its not quite that simple. If all you're worried about is high rpm performance, that is the case, but you will be sacrificing low end performance, something most ea81 drivers arn't willing to do.

I don't see a point in going to dual carbs unless you are just after high RPM. My car is just as slow as a normal EA81 down low. It only gets into its own when I get to 3500RPM really. It might have 5 more hp then a stock one below that RPM. So that said, I think we're only after high RPM power here. (which I must say, is awfully fun when I get to 6500RPM and it keeps going easy. And the sound:slobber:....)

[Monte]

I've run dualies on VW's before, not a big deal. Run the throttle cable to one carb (master) and run linkage to the other (slave). There's a tool used to balance them, basically you adjust the throttle linkage to the slave carb to open or close the throttle and get a reading on the intake air flow and make them match. There wasn't any balancing piping or anything like that. The carbs were small so the mileage didn't suffer, but you still get more flow and power.

Monte

[fbh]

hmmm... any idea where I could get my hands on such a tool, or how I could make one myself?