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EA81 rebuild with SPFI manifold 38/38 carb


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Most readers would recognise Tweety.

 

Biting the bullet very shortly. Engine is out and as usual for me I have some radical plans. Radical plans can call for some advice and opinions though.

 

My Subaru powered trike has a VW automatic.  In the past I've had a weber 32/36 and it was sluggish off the line.  Hence the purchase of a synchronic  carbie. The desire is low down torque not a revving engine due to the auto and its restrictions.

 

My desire is to use the EA82 SPFI manifold (I have one) with a custom made adapter for the 38/38. No problems there.  I am thinking along the lines of-

 

1/  rebore 20 thou oversize EA81 pistons. 

2/  20-30 thou shaved heads

3/  Cam grind 16/56 as recommended by a friend

4/  heads ported

5/  has electronic dizzy in good condition and high output coil/leads

 

Seeking 9:0 or more compression.  Have done a search and read that the SPFI manifold should be modified so the fuel/air mix swirls. how can this be done and is it really necessary.?

 

I am aiming at a really fresh engine. Trike weighs 640 kgms.  Getting ideas from all over.

Edited by tweety
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hiclone qld have been advertising lately - that oughta give you a Kia like swirl ! I used to have some mazda TC 1300 heads with built in swirl inducers above the valve seat - nasty things when mixed with fingers poking about. Not a continued enhancement.

 

Cough * 16/56     0.235" lift

 

EA81 really not a revver so low down torque pursuit is goo idea.The crank can get a bit of flex in it and pound out the centre main bearing tunnel and develop a bit of a knock. No idea if EA81S got a better crank for its high revability

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Bumping the compression is a great way to increase your low end torque.

 

 

The high compression ea81 I have is like a tractor engine.  Loads of low end torque, and seems to hit a wall at about 4500rpm reving.

 

 

EFI is a great idea as well.

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So you want a hole shot off of the line. Seems that you have a drivetrain problem and not just carburetion. If you have a trike that weighs 640kgs and it was sluggish with a Weber 32/36, then your transmission and rear axle ratios are suspect. Have you tried changing the ring and pinion gears? Are you sure that you want a Weber 38/38? It is a lot of air for a small engine. I looked at the hiclone unit and I can not use it. It is used on petrol engines and I use gas......................sorry, I couldn't hold back on that one. Putting a swirl thingy in front of a turbocharger is really funny. There may be a way for you to experiment with 'swirl' without hacking up your SPFI manifold. There is a company in the US that makes 'swirl torque carb adapters'. Nothing for 2 barrel carbed Subaru's, so you would make your own. There are always glowing test/use reports on these units. In reality, they are said to work very well on some engines, neutral on some and very bad on some installations. The SPFI manifold is a simple device and a 'bolt on ' experimental approach is possible. www.tdperformance.com TransDapt Performance Products. They sell TransDapt carb adapter #2107, which adapts a Weber 32/36 to a carb manifold. Works great. I don't know if it will handle a 38/38 if you go that route. You will make an adapter plate to mount your carb adapter to the SPFI manifold. You have the possibility to experiment with several, grooved #2107, 'bolt on' 'swirl adapters'. Examining the grooves in the 'swirl torque carb adapters' raises several questions for an experimenter like you. How wide? How deep?  What direction and does the coriolis effect come into play? Keep us posted. Remember, no wheelies......scares the hell out of the passenger. You may have to install a sissy bar..........................

Edited by silverback
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There is a lot of history with this trike that I thought irrelevant. So I'll fill you guys in.

 

From VW 1916 went to eA81  32/36.  The VW auto is a standard piece as is the diff.  The only thing that could be suspect is the torque converter.  Either way the diff, auto and torque converter are all going to be checked and repaired if necessary.

 

I've gone down the SPFI route. Being in Oz if isnt easy replacing sensors etc when you really are guessing what the problems can be. Besides, I'm of the older gen and desire carbie now.

 

Good to realise that more compression will give it more low down torque. Exactly what I want.

 

I think the engine can be used without the swirly item until its output proves a problem to be improved.

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I'm guessing but if the manifold is about 6mm larger in internal and external diameter, the 38/38 larger than commonly used with heaps more air intake, that the porting to enlarge the entry at that point prior to combustion would be essential ??????   Exhaust is a short length each side with one large muffler and a joining pipe.  No smog stuff

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The SC12 supercharger in a suck thru system (fuel and air) wasnt so successful IMO.  Yes it made 100+ hp on the dyno at the fly but it was so difficult to tune at all revs. I wasnt prepared for the 14mpg.  In the end it didnt satisfy my thirst for economy and reliability.

 

Things change and now in retirement my thirst has changed to basic carb and a fully redone engine. it just might outlast me. 

 

Then I'll get buried with it....

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you missed the supercharger era of Tweety, long and sad saga though it may have been, you still got a power hike !

 

Idasho - how'd you get high comp ?

 

 

I decked the heads and am running SPFI pistons

 

Between the two the motor is running an estimated 10:1 compression ratio

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  • 4 months later...

Thanks Idasho for your replies and info.

 

The engine builder is commencing my EA81 rebuild. He has identified I had a dropped ring in number one cylinder. Plus both head gaskets blown although in the initial stages.

 

He has yet to decide on pistons to use for the rebore.  The "towing cam" Jono suggested of 16/56 with .235" lift doesnt match well with compression over 9.0:1 ratio. Add to that, in Oz we didnt get SPFI at all in the ea81 and ea82 engines so getting SPFI pistons would need to be imported here. I think he is looking at ea71 pistons and a slight decking of the heads.

 

What will be interesting is the use of the Weber 38/38.  No swirly bits yet. A friend is making up the adapter38 to manifold. Should have it next week. It's inconclusive how it will perform. I've read everything on the net about 38/38's. Some have used it on 1600cc engines and swear by them, some have used them after using 32/36 webers and note a remarkable boost in power down low revs. Many say it is too large for a 4 cylinder.

 

The intake hole on the SPFI manifold has been enlarged, nearly double in size. The exit holes of the manifold I noticed are the same size as the stock ea81. So hoping the larger manifold will supply more air and more fuel from the 38 will be a match to end up with more low down torque and take off. The 3 speed full automatic VW transmission is the culprit in terms of being restrictive. It has just had a full gasket and seal replacement and service. Torque converter was 100%.

 

I've just found an interesting website to do with 32/36 and 38/38 webers. I'll underline some important comments.

 

In the past there have been questions and much miss
information put out on the choice of a 32/36 DGEV carb or the 38 DGAS


 

1)    
The Kits utilizing the 32/36 Progressives Weber are designed
to provide the market with an economical performance carburetor conversion
that while increasing Hp also improves drivability and fuel economy over the
stock carburetor. The kits using the 32/36 progressive carburetor
is the optimum carburetor for use as a replacement carburetor for
a worn out or hard to maintain factory carb.

 


2)    
When purchased in kit form, the REDLINE kit with the
38mm DGAS carb will perform on a stock unmodified engine without any problems.
This is not going to be an over carburetion situation. It will provide considerably more
initial torque and acceleration
but the top end performance will not be
significantly improved over the 32/36 when used on a stock motor.

 


3)    
The 38mm DGAS carb should be the only consideration if the
engine is in the future or currently going to have any level of additional
engine modification. Such as headers, free flowing exhaust, a cam, or rebuilt
engine. Usually these motors will be improved over stock with oversize pistons
and towing cam. The 38 will enhance the improvements of any of these items.

The 6 cylinder engine applications are particularly enhanced by this
application. In-fact on ALL JEEP and LAND CRUSER applications with any upgrades
this is a mandatory choice. Other wise the progressive will require extensive re-calibration to work properly.
 

 


 

4)    
When using a 32/36 in the above situations will
require additional calibration and rejetting to attain the desired performance
and standard fuel economy. There is a jet kit available for just this reason.
The jetting is required due to the performance enhancements of the additional
modifications. Although the 32/36 does out perform the original, to receive the full
benefit of your investment the 32/36 will require helpful re-calibration. The
38 DGAS is the optimum choice and has a larger fuel delivery
system and the calibration to handle the broader range of improved performance
and improves substantially your other product investments.
 

 


5)    
While the 32/36 progressive carb will improve your fuel
economy on a stock motor over the OEM carb. The 38 Synchronous carb will not
get less fuel economy than the OEM carb.

Edited by tweety
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I am sitting on a 32/36 that actualy came off an MGB, ran well, pull well and was quite impressive around the 80 mph mark. The SU's went back on for the authentic look . Amusing the comment re not really suitable for 4 cylinders, no ida how that would come about, with four cylinder capacities ranging from say 1200 to 2600cc ! My 1800cc probably sucks just as much air at 100 kph than a 4000 cc six ! It sucks as much fuel !

Your engine builder is taking into account the light weight of Tweety so some of the design aproach may not be so good in heavier Subes ?

 

I ran 'flat top' EA71/EA81 pistons with my 16/56 on petrol - no problems

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I'm happy to have chosen the weber 38 based on their advice that if your engine has been rebored with tow cam etc it will be ideal.

 

The 32/36 progressive is ideal to replace a standard carbie and for ultimate economy.

Edited by tweety
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Ea81 ports and intake manifolds are 35mm. You can fit a larger manifold but the ports in the heads will still be 35mm. There are also three sharp right angle bends inside the heads to kill flow. This is why the 32/36 doesn't have a higher top speed than the standard Hitachi.

 

As you know, the dgas is 2x38 and it's synchronous. It may feel like it has more power low down because it won't take much throttle opening to get full flow through the ports.

 

If you tune it right, you should get the same fuel economy at cruising speed, but you'll have to be very gentle on the throttle to get good economy around town.

 

Airflow through the venturis will be very low at low engine speed, which may cause poor fuel atomisation. This would cause a flat spot when you floor it unless you inject a good dose of fuel through the accelerator pump; another potential for poor stop/start economy.

 

Personally I think it's too much carb for 35mms ports, the 32/36 flows enough for at least 120hp.

 

I'm not going to say don't do it though. Nothing ventured, nothing gained etc. But if you find you get terrible economy around town, I'd suggest swapping the carb for a 32/36.

Edited by cubastreet
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Trike only weighs 640 kgms.  The bigger issue for me is the VW auto. On a dyno the ea81 is bled 14 hp with the auto. That's a lot. Even a low weight of 640kgms the 32/36 seemed sluggish, always wanting to open up the second throat.

 

I concede that when I cruised at 85kph on a club run once it achieved 35mpg (Oz gallons) likely only the first throat was open.

 

I live in the country here in Oz. I wont be riding in city traffic much. Hence the choice for the 38. I dont have concerns now but for a while I did.

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another thought - is the twin Hitachis Tony - they open two primaries togther, with two more secondaries to go, same smooth flowing bends as any EA inlet manifold really. You will be pioneering, and even if you gain a follower trying same, it'll be a different horse, much lardier than Tweety. Your new engine will have some mighty fine vacuum to draw the fuel through whatever you fit up. Have I said I am getting impatient with this ???

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  • 3 months later...

Tweety is alive again.  Few days ago a goos mate attended to help sort out why the new engine wouldnt fire.  Turned out the distributer was 180 degrees out. Also had the digital speedo connector on neg when it should have been on positive.

 

Anyway, the 38/38 carb so far looks like a good match along with the SPFI manifold. Got to run the engine in.

 

th_MVI_0054.mp4

 

Thanks to USMB and Ausubaru guys for all your advice and comments.

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  • 3 weeks later...

Haha.

 

update.  I havent ran the engine in yet. Done only about 20 miles making adjustments/mods rather to the cooling system. Engine runs good although too much throttle at low speed gives a hiccup, like too rich.

 

Am waiting for a new stock coil then run in commences. Nice hills around here for some climbing. Then the engineers report.

 

and will report here the results eg economy, power etc.

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