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HP limits of the old school 4 speed?


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11 replies to this topic

#1 The Keith

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Posted 24 January 2008 - 01:17 AM

I'm tired of searching for it, I have an 83 (EA81) GL 4wd hatch with a 4 speed man, does any one know how much power the tranny can handle?

I'm used to the 5-speed and it's 300hp wall on my WRX, so I figure the older ones are even more fragile.

#2 grossgary

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Posted 24 January 2008 - 01:52 AM

what kind of horsepower, useage, how many miles do you want to put on it?

whatever you can get out of an old school EA engine will be fine....150hp or more. if this is for an EJ swap, then swap the trans as well.

there's a ton of variables and it's not asymptotic, but parabolic or something....in other words.....it's not like there's a magic number where at 234 hp it's fine and at 235 they break. so that makes your question unanswerable on one hand...or if it is answerable everyone will give a different one based on where they'd chop the curve...keeping in mind everyone's "curve" is different since this won't come down to quantitative measurements at all.

#3 TomRhere

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Posted 24 January 2008 - 04:53 AM

Scot (subarubrat) had the 4 speed behind his built ER-27 (XT6 engine) running over 200 HP. He fragged reverse trying to rock the BRAT out of a hang-up, do belive he replaced it with another 4 speed though

#4 The Keith

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Posted 24 January 2008 - 06:16 AM

all righty, thanks guys.

I was just trying to make sure it wasn't like 130 or so.

#5 Phizinza

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Posted 24 January 2008 - 07:34 AM

Its very similar to the 5 sp in construction. Its just the reverse gear that is weak.

#6 GeneralDisorder

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Posted 24 January 2008 - 09:54 AM

Confirm reverse is weak on the 4's - I blew one with a Weber'd EA81. Part of the problem is the linkage wears and will not fully engage gears. Half engagement is BAD. I would swap to the five for no other reason than to get the VASTLY superior linkage. Love all my 5's - especially in the Brat.

GD

#7 mikeshoup

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Posted 24 January 2008 - 11:45 AM

Run the 4spd until you blow it, then replace with 5spd :D

Actually, I love the 5spd for the same reasons as GD. Better linkage, and the better gearing. No more racing or dogging the engine at 25mph.

#8 The Keith

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Posted 25 January 2008 - 05:35 AM

Does a modern 5-speed just bolt on or is it a different 5-speed in the 80's?

#9 ausubaru92

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Posted 26 January 2008 - 03:21 AM

Its not so much a horsepower limit, its actually peaks of torque that will break the gearbox.

You could safely put 700HP through your box if you drove smoothly. Its usually dropping the clutch at 6000rpm that will break it.


No the EJ series gearboxes have a different bellhousing pattern, but you can make an adapter

#10 Phizinza

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Posted 26 January 2008 - 06:58 AM

EJ gearboxes also can't just use the 2 piece EA82 shaft like the 5sp EA82 gearboxs in EA81 cars. Ej boxes also use different mounting and is a little trickier then the EA82 box in EA81 swap.
EJ boxes are far superior onroad though as they have the centre VLSD unlike the PT4WD D/R boxes which are driect coupled front and rear thus making it bad onroad, and poorer handling then AWD offroad. EA82 FT4WD (or AWD if you like) are still not as good as EJ AWD as they only have open centre diff.

EA82 5sp is a pretty easy swap in a car like yours.
Just need to figure out low range linkage, crossmember mount and the centre bearing mount.

#11 The Keith

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Posted 26 January 2008 - 07:45 AM

EJ gearboxes also can't just use the 2 piece EA82 shaft like the 5sp EA82 gearboxs in EA81 cars. Ej boxes also use different mounting and is a little trickier then the EA82 box in EA81 swap.
EJ boxes are far superior onroad though as they have the centre VLSD unlike the PT4WD D/R boxes which are driect coupled front and rear thus making it bad onroad, and poorer handling then AWD offroad. EA82 FT4WD (or AWD if you like) are still not as good as EJ AWD as they only have open centre diff.

EA82 5sp is a pretty easy swap in a car like yours.
Just need to figure out low range linkage, crossmember mount and the centre bearing mount.



what?

#12 GeneralDisorder

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Posted 26 January 2008 - 01:41 PM

I'm not gonna argue and say the ea81 trans is super strong. Was the one you're talking about the one at WCSS? Cuz if it was, can you really blame it on the tranny?


Mostly it was the linkage - mudrat's cobbled together linkage never properly engaged reverse till I modified the tranny mounts to use EA82 mounts. It was half gone by that time though.

The tranny's are quite strong, yes. But almost all of them have suffered from the poor linkage design. The 5 speed and the 4 speed have almost identical reverse gear systems - just the 4 has the linkage with the tendancy to not fully engage gears.

GD




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