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supercharger carb blow-through setup on ea81?


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17 replies to this topic

#1 scrap487

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Posted 07 March 2007 - 02:39 AM

anyone done this? I've been considering what it might take to do this with my weber, been working on the yellow wagon lately and the motor is stock except for a weber, but has 200k miles and proved itself indestructible so far. seems a supercharger would be less work vs turbo, and on an old worn out engine would seem to be an easier way to find out just how much more a stock ea81 can take. I might convert to spfi first though because from what I've read the computers can compensate to a certain amount of boost, where as with a carb would need a lot of extra parts/modification to get it tuned and running right without destroying the motor right away.

I'm dead serious about supercharging an ea81, and would like to do it before I rebuild the one i have in the basement so I can get an idea of just how much it can take before failure(and I've abused this particular motor w/ 200k on it heavily...) I think it would be a fun project that would be fairly cheap for what I've got. Not thinking about mad power here, just getting some hands on experiance experimenting with this stuff.

#2 mikeshoup

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Posted 07 March 2007 - 09:13 AM

I dunno a whole lot about forced induction carb'd setups so I can't help you there.

However, the SPFI might be a little strained with a supercharger. The SPFI can handle the 90HP of a stock SPFI motor easily. I don't know how much more horsepower that single little injector can handle especially since the efficiency decreases with forced induction, so you need a larger injector for forced induction engine making similar power to a n/a engine.

Limit yourself to 100HP (7lbs or so?) and I think you could use the SPFI fuel system.

#3 Reveeen

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Posted 07 March 2007 - 10:56 AM

It is, well, difficult to "blow-through" a carb. Most carbs require "normal" pressure through the venturi to work right and the float bowl(s) have to be vented to the atsmophere. Now, I'm not saying you can't do this (by modifying your existing carb, or buying a special blow-through carb) but it is going to take a skill level beyond the normal backyard type of thing.
BTW: in the late 80's, early 90's, Masarati, on their bi-turbo V-6, used a weber set-up in a blow-through situation. This might be "the ticket", if you can find/afford one, you would want the "box", carb, and all associated hardware.
If you go SPFI I *think* a standard set-up (moving the PCV valve) would stand under 10lbs of boost.

At the end of the day, turbocharging/supercharging a stock motor, simply wouldn't be worth the expense. I can't see in excess of 100hp, but I can see in excess of $500, even using junkyard parts. Maybe an EJ22 conversion?

#4 scrap487

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Posted 07 March 2007 - 03:37 PM

It is, well, difficult to "blow-through" a carb. Most carbs require "normal" pressure through the venturi to work right and the float bowl(s) have to be vented to the atsmophere. Now, I'm not saying you can't do this (by modifying your existing carb, or buying a special blow-through carb) but it is going to take a skill level beyond the normal backyard type of thing.
BTW: in the late 80's, early 90's, Masarati, on their bi-turbo V-6, used a weber set-up in a blow-through situation. This might be "the ticket", if you can find/afford one, you would want the "box", carb, and all associated hardware.
If you go SPFI I *think* a standard set-up (moving the PCV valve) would stand under 10lbs of boost.

At the end of the day, turbocharging/supercharging a stock motor, simply wouldn't be worth the expense. I can't see in excess of 100hp, but I can see in excess of $500, even using junkyard parts. Maybe an EJ22 conversion?


for a carb blow through i'd have to build a pressure box for the carb along with higher pressure and higher volume fuel lines/pump along with a a bunch of other things that adjusts the pressure of the fuel to the carb. that seems out of my budget, but doing an spfi setup(which I am going to be doing at somepoint anyways and I wont consider the cost of those parts in this project) really doesnt seem too expensive, larger injector, and then I go grab a supercharger and boost controller stuff off of a buick in a jy or maybe find one off CL or ebay, change the pulleys, do all the fab work myself, I see maybe a $400 project if I take my time. the whole point is to get experiance working with inexpensive and expendable parts working with blower setups, and also see how much more abuse and old worn out ea81 can take.

#5 Reveeen

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Posted 07 March 2007 - 04:00 PM

the whole point is to get experiance working with inexpensive and expendable parts working with blower setups, and also see how much more abuse and old worn out ea81 can take.


You could do a "suck-through" carb, though I don't know what you expect to use for a blower. I have a guy I know with a crap 2.2 turbo Dodge that seems to make 3-4 scrap engines a year.

#6 970subaru

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Posted 07 March 2007 - 09:01 PM

this is somewhat of an oversimplification but:
you need at least 3 things to blow through a carb: a fuel pump that can do about 4-6 psi higher than the highest boost you will run, a boost sensitive rising rate fuel pressure regulator(rrfpr), and a thing called a pitot tube which is like a boost port that the intake of it is facing into the intake stream so it is reading not only the pressure of boost, but also the pressure of the incoming air stream. its a concept taken from airplanes.
so you set your base fuel pressure to whatever you need it at, and plug your boost line into the rrfpr then it increases fuel pressure 1:1 with psi from the pitot tube. since the pressure inside the fuel bowl will be slightly higher than normal your jetting can remain close to stock. you have to boost reference every port on the carb that would otherwise be referenced to the atmosphere.
keep in mind, I dont have a f#cking clue about hitachi or weber carbs, I only know mikuni bike carbs namely CV's and VM's so all of that above may totally not work. I know you can blow through some webers because VW people do it all the time with turbos. it may be totally possible to blow through a hitachi but mjor pitfalls of blow throughs are crushing floats from boost, getting incorrect metering, and tearing diaphragms. also getting something to seal to the carb so you not leaking off all your boost.
best blower to run would probably be a eaton M62 off those pontiac things because they are dirt cheap on ebay and not too big but you will have to either get one off a mercedes that has a boost controllling clutch or run a recirc valve.
another option would be to use a propane mixer setup and either blow through that or draw through which would be pretty freakin sweet but add at least $300 to your project.

#7 mykingcrab

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Posted 07 March 2007 - 09:50 PM

Exactly right. This pressure sensitive regulator (970subaru say)is the key to old school blow thru.at an idle the fuel pressure is low (like stock),as soon as boost is detected by a pressure switch, it instantly raises fuel pressure.There is a clear glass window on their fuel reg.(RFPRR), you can see it trickle at an idle and when you hit the gas ,you can hear it swich,and see it start dumping fuel full blast.on/off-on/off. that quick..

MELLOYELLOWs brother in cal has a 2000cc stock vw water cooled vanagon/autotrans in a jane plain looking rail,But when the garrett t4 goes to 11psi (and no shifting delay)it pisses off the high dollar long travel rails. at the top of the hill they all come over to see what kicked their butt. :mad:
In the back of hot VWs magazine,there is an add for the BOOK.How to turbo any engine. mellowyellows contemplating this on an ea81.I THINK THIS WOULD WORK KILLER ON ANY EA81 Me personally, id just end the problem of need for more power,and get the equally reliable EJ22.+adapter+wire harness.if you dont want to be difficult,buy a rubbermaid container and throw the EJ harness in there and in the sparetire compartment.Done.

Heres som pics of an ea81 with a blower. The carb looks like a stromberg SU.(brittish)look at the bottom of this page for similar threads Supercharger for EA81Posted Image
Posted Image

#8 Uberoo

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Posted 07 March 2007 - 11:45 PM

never mind the carb,where can I find the blower?

#9 RenaissanceMan

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Posted 08 March 2007 - 12:07 AM

That would be a Toyota SC12 or SC14 supercharger, I got one sittin in storage. Unfortunately mine's not for sale ;)

-Mike

#10 970subaru

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Posted 08 March 2007 - 12:44 AM

like i said above-
eaton m62 off a pontiac, mercedes kompressor or maybe even one off a mini cooper S but those are smaller. ebay.

#11 scrap487

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Posted 08 March 2007 - 01:27 AM

^^^ you guys rock... I'm gonna have friday or saturday off work and hit up a junkyard and get some parts, will update with what i've found then. in one day you guys posted like what it took me a week+ to find, and then some extra I didnt find on top of that. I love forums.

So, for those who know, would you suggest blow through carb or go to spfi? also, any thoughts about intercooling? would it be any good for a low end project like this because i know where I can pick a decent one up practically free...

#12 joostvdw

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Posted 08 March 2007 - 09:52 AM

^^^ you guys rock... I'm gonna have friday or saturday off work and hit up a junkyard and get some parts, will update with what i've found then. in one day you guys posted like what it took me a week+ to find, and then some extra I didnt find on top of that. I love forums.

So, for those who know, would you suggest blow through carb or go to spfi? also, any thoughts about intercooling? would it be any good for a low end project like this because i know where I can pick a decent one up practically free...


I don't know how easy they are to come by in the US, but renault 5 turbo's also have blow through carbs and with some work (manifold mostly) you can make it work on any car

suck through is also an option, added benefit is the petrol cooling the compressor, I don't think an IC would work properly (petrol condensing and stuff) then, so high boosts are a no no.

If you are going SPFI (which to me is the simplest/best option) you might want to consider running a second injector, or maybe a second TB+injector ;)

oh and definately get a wideband O2 sensor/boost gauge/oil temp gauge,

#13 Loyale 2.7 Turbo

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Posted 08 March 2007 - 10:40 AM

Anyone has Tried to make that on a EA82? ...
:confused:



#14 Ross

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Posted 09 March 2007 - 05:31 PM

So, for those who know, would you suggest blow through carb or go to spfi? also, any thoughts about intercooling? .

Don't rule out a suck through setup, much easier to set up than blow through - the carb needs no mods running this way. Like everything, it has its disadvantages (throttle lag may be noticeable, and i've heard that they can be a prick to start sometimes), but i'd say it would be a better option than blow through...

#15 970subaru

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Posted 09 March 2007 - 06:28 PM

better no, different yes.

#16 BoostedBalls

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Posted 09 March 2007 - 08:47 PM

for a carb blow through i'd have to build a pressure box for the carb along with higher pressure and higher volume fuel lines/pump along with a a bunch of other things that adjusts the pressure of the fuel to the carb. that seems out of my budget, but doing an spfi setup(which I am going to be doing at somepoint anyways and I wont consider the cost of those parts in this project) really doesnt seem too expensive, larger injector, and then I go grab a supercharger and boost controller stuff off of a buick in a jy or maybe find one off CL or ebay, change the pulleys, do all the fab work myself, I see maybe a $400 project if I take my time. the whole point is to get experiance working with inexpensive and expendable parts working with blower setups, and also see how much more abuse and old worn out ea81 can take.


You don't really need a box to surround the carb. I've done it many times without on different engines. The dual throat webbers and delortos are best IMO but a nice edelbrock performer 500cfm 4 barrel would work great also. They are extremely easy to blow through. I suppose if I were doing a blowthough on an ea series engine, I would go with dual downdraft delortos, like the ones you see on VW's. The jetting would already be in the ballpark too if you followed a buildup from a 1600-1776cc VW to copy. If you were looking for just cheap, easy and still fast- I would go with a single side draft webber or del attached to a garrett turbo from a mid 80's 2.2l Chrysler product and use it in a draw-through setup. They have the carbon seal that you need for the vacuum on the inlet of the compressor, they are all over ebay really cheap too. You could expect 150-180hp easily with that kind of setup. The drawthrough is a lot easier to tune also. And you don't have to worry about a special fuel pressure regulator, intercooler, BOV, etc. It isn't the ultimate in power but it will be enough to eat a stock WRX in the 1/4 mile.

#17 psylosyfer

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Posted 26 March 2007 - 05:28 AM

I'm clueless on trying to make a blown ea81, but I do know FI engines are commonly blown on (american V8's) higher flow fuel pump and larger injectors, Do the job. Other than that reprogramming the ecu, seem's to be a biggy to get good results, then they finish by improving the exhaust flow.
Hot Rodders do this all the time. Last one I was around, went from 285 HP. to 500+ at wheel's on new dyno, If memory serves it was a 5.0 liter ford. Did not start at 500+ took a bit of trial and error on the engine management settings.
I think the first run after all the hardware was on,was under 400HP, Done from a laptop on newer cars. How are you going to "tune" A subaru ECU?
It was a 5.0 ford I remember now because the owner was telling us he bought a Roush setup as It is the only one that won't void ford warranty.
Back in the day I put a blower on a 400 pontiac in my GTO, got the blower from a big rig diesel, (471 gmc) and put two 4bbl carbs on top (carter AFB's mech sec.), didn't know how too put boost before the carbs, after worked fine, looked good and left getting at the carbs easy. Never got to a dyno, but went fom mid 12's to just above 10's.

#18 psylosyfer

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Posted 26 March 2007 - 05:38 AM

On the question of cooling Roush includes twin cooling units (heater core type radiators that bolt under the car behind the radiator horizontally at the bottom of the main radiator.
Used two (for fit) instead of one big enough to stand alone. a restrictor to reduce water from the engine to the blower pump,(something about not starving the blocks supply).
Also included plumbing ,an electric water pump for the blower only, and various hardware, I think the cost was a bit over 4K,

Why not copy them, Using a tranny cooler or two for cooling the blower, I'd run from the engine radiator through the tranny cooler then to the blower, To keep the mix as cool as possible (the denser the more power). Then to the block , and back to the radiator.
Anyone have any thought's on how this would work (or not work)?




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