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View Poll Results: Which way should I run with this?
#1 RS-RA STi w/VF-29 36 49.32%
#2 Built Ej25 w/Rimmer Supercharger 37 50.68%
Voters: 73. You may not vote on this poll

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Old 01-13-2006, 12:43 PM   #1
Matt Monson
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Default Supercharged Hybrid with pictures...

Here's the deal. I bought another Impreza last night. It's a '95 coupe, 5spd, AWD, rear discs, etc etc. The best of the best of the early USDM cars for a builder. And here's my dilemna. I swore that since my RS-RA STi longblock started it's life in a Legacy that it would never find it's way into an Impreza. I have also recently acquired a Rimmer Autorotor based supercharger kit. So, I have two potential swaps to do. The Ej18 is coming out no matter what. And the application of the car will be purpose built rally-x and track events. Please don't suggest anything other than the 2 options I present like a different turbo, etc. I have ALL of the parts to do either swap already in the garage with the exception of the EM and a turbo x-member.

Build #1: RS-RA STi swap. Use the Ej20G engine mated to a VF-29 turbo and 440cc STI yellowtops. Convert to modern COP ignition, wire in a WRX wiring harness and ECU and tune with ECUtek. Parts required to purchase would be the wiring, ECU, ignition system and crossmember.

Build #2: Ej25 w/Pnp'd heads and Rimmer Supercharger, v6 STi intake manifold and 400cc STi yellow tops. Again, only parts purchase required would be EM. Probably a Hydra for this application.

I know this forum is swap biased, but the AFI forum has been dead for months and most of the guys doing anything related to this have been hanging out here. So I figure this is the place to ask. Not gonna be a tool and cross post it...
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Last edited by Matt Monson; 01-24-2006 at 12:53 PM. Reason: added pics.
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Old 01-13-2006, 12:54 PM   #2
Master2192
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Go for the supercharger. The throttle response is much better, which is very important to Rally-x and the track. Even if the turbo spools up very fast, it can never match the instant response of the supercharger. Those two events, especially Rally-x, are based on time and speed.

I would put it this way, if you got up near first place, but then you missed out and got 2nd place because of 2/10ths of a second. And you could have made up that time if you didn't have any boost lag, wouldn't you switch to a supercharger? I mean, they are competitions and it would feel really good to be the winner. Especially if you made the smartest choice that got you there.

I dunno, thats what I think anyway. Be interesting to see what some other people say.
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Old 01-13-2006, 01:00 PM   #3
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Hi Matt. I remember you from the N/A forum, so I know you're definitely knowledgeable enough to pull this off. That said, I think when you look at how much work it will be fabricating the intake, brackets, pulleys, belt arrangement, etc etc to get the supercharger to fit, going standalone, and then when you look at how much more work it is going to be to run and service this thing, you will realize that a swap is a much cheaper, easier and more reliable alternative.
My 2 cents worth I'm fascinated by superchargers (my dad has a Mercedes Benz Kompressor) but all the SC threads I kept up with on the aftermarket forced induction forum convinced me that it is not worth the trouble; TONS of work, a lot of failed or non completed projects, and not particularly impressive power.
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Old 01-13-2006, 01:22 PM   #4
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hmmmmm

#1 how you gonna make wrx harness work w/ old cranks and cam pickups and how ya gonna get a vf-29 to work with the G manafold?

#2 i don't think much will top this for a purely auto-x setup why a ver 6 manafold to fit the injectors?? are you gonna change the pistons?

a wire in link, smc,used tec2/3 or even pp xmc +wideband would do as well ... lot easier when you don't ahve to deal with plug n play or obd-2

grumble grumble wish i had a 95 coupe project car
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Old 01-13-2006, 01:57 PM   #5
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yeah, I was actually wondering about the old sensor/new wiring and ECU compatability game too.

I do like the idea of the insta-response of the supercharger....and heck, there aren't that many S/C subarus out there anyway.

I was also wondering which 25 block were you considering? A new short block? okay. a used EJ25 N/A....well, eek. If this is for competition, I'd steer clear of the N/A block when thinking of FI.

I give you mad props for contemplating this undertaking. And even though Powerlabs is giving you some food for thought about S/C projects.....I'm pretty certain that you're one of the few that could pull it off. I mean, the sheer number of projects and mods that you've done and continue to do....I think you've got a damn good shot at completing this and having a successful ride afterwards.

Go for the S/C with a good strong block....so yeah, option 2. The larger displacement WITH the S/C will give you a shove right off the line....or off the apex.

Only thing to think about is not breaking a tranny with that kind of kick off the start. Ahhh, another thread

GGT
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Old 01-13-2006, 02:01 PM   #6
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powerlabs,
head over to the SC thread in AFI, and you will see a picture of the exact KIT I have. No fabrication required. I can install it in less than 2 hours.

Jaxx,
I already looked into those issues. It really is as simple as changing the sensors, crank gear and pullies. And installing a 90 degree bend on a vf-29 isn't rocket science.

On the SC, the v6 manifold because I have it with the rails and injectors. The way the kit is designed, the TB mounts on the SC plumbing, so I am rerouting the throttle cables over there anyways. Initially, I wouldn't change the pistons, but would start work on one of my spare shortblocks to run 9:1 TWE pistons. O

Or the other idea I batted around was using the RS-RA heads on an Ej251 bottom end. Given that the RA heads have a 57cc combustion chamber versus the 46cc chamber of the Ej25 heads, I could get a healthy drop in CR that way as well...

I will confess that I am definitely leaning towards the SC, but figured it would be a good way to generate some discussion...
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Old 01-13-2006, 02:07 PM   #7
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Go for the SC Matt. The RS-RA deserves to be in a legacy. It would just be way cooler. Plus I am a fan of that impreza its light so it doesnt need as much overall power to be fast. plus the throttle response from the SC for auto/rally-x would be awesome.

The hydra looks good. Thatis what i wanted and think ultimately I will go with one as well. Have you made sure they have a harness to work with the 1.8 harness? are you going to swap in an RS harness?
what are you gonna do to your blue RS now?
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Old 01-13-2006, 02:22 PM   #8
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Oh, I didn't know you had a kit... My bad. That does simplify things then

How about a crazy thought; TWINCHARGING... Someone out there already has an STI that's supercharged and twin turboed... I think a SC with an electromagnetic clutch (a la Merc Kompressor) actuated by a pressure switch once the turbo spools up and makes boost would provide tons of power WITH low end torque... Plus you could gear the SC super low so it would be spinning 1PSI of boost right at idle and make tons of power off the line.
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Old 01-13-2006, 02:57 PM   #9
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hmm.. this is a dielemma.

i personally want to see you do the supercharger, simply bc i love looking at complex belt setups and im sure you could pull it off well.

BUT i want to see someone run the EJ205 elec on a EJ20G, and it seems perfect that you do it instead of me do it. so thus is my vote biased. that and im courious to see what a RS-RA is capable of bc its such a funkalicious thing.

as far as which setup would be faster, they probably be very close to the same if the driver adjusted the settings to it. (gearing, style etc). so thats not that big a deal.

do whichever one floats your fancy, or toss a coin on it!

grumble grumble- jaxx are you hungary? should i toss you a GC8 cookie to play with?
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Old 01-13-2006, 02:59 PM   #10
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GGT,
Don't have an Ej257 STi bottom end anymore. But I have got 3 spare Ej251 bottom ends. This thing is only going to be putting out 6-8psi, so I am not terribly worried about the bottom ends. If I fubar one, I will just replace it with another one. Contrary to the big turbo big power guys, I don't consider open deck Ej25's pos's. And worst case, I've got a closed deck Ej20G I could SC if the others do proove unreliable. In short, as I mentioned, there will be very little shopping done for more parts to make this happen...

I've got 2 spare trannies...

BMXpunk,
I haven't looked into the Hydra far enough to see if they make a harness for it. But I ain't afraid to cut wiring. And I've got a spare MY00 RS harness if I need different connectors. Or, as Jaxx mentioned, I have about 5 options I can pursue for EM...


As to your question about the RS? It's back on it's old build schedule. The Pnp'd head should be in the car in a couple of weeks. Picking up this supercharger kit, a '99 WRB RS Coupe (for my girl), a 1970 911 Targa, and now this '95 GM, all in the last month, has reignited my monster frankensubie mechanic within. I now sit at my desk all day just waiting to get home and get into the garage to play with my toyz...

And Diz is trying to work a deal to pick up Bugman's old car (home of the Ej20G w/Ej22t heads hybrid we built) so that he has a rally beater to build as well. Life in teh Ghetto Garage is good right now...
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Old 01-13-2006, 03:34 PM   #11
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nice.

so you going to NA build your pnp heads motor?
supercharger the 95. only idiots dont believe in open deckable boost
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Old 01-13-2006, 04:01 PM   #12
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You got it. Can you guess what's going to happen to those RA gears we were discussing?
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Old 01-13-2006, 04:03 PM   #13
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hmm point taken about compression ..
is the SC even capiable of more than 8 psi ?
if its not then i cant see lower than 9 to 1 being any advantage espialy with the air to water IC

how about the pnp heads +high compression pistons +standalone em in the 911 (wonder if josh at cobb still has those 2.5 indvidual throttle bodies) woooot

+1 for seeing a g (or k or early 207) run on usdm computer
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Old 01-13-2006, 04:05 PM   #14
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i want to see you make some genius supercharged gc. turbo is too standard for subarus. be different! run some crazy EM and make wads of power
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Old 01-13-2006, 05:29 PM   #15
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Jaxx,
The 911 is far to valuable as an original car to put an Ej series engine it. The 68-73 911's are the hot ticket right now. Plus I bought it with a purpose. I am going to do some restoration work on it and give it to my father as a gift.
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Old 01-13-2006, 05:48 PM   #16
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You know my opinion, but I'll give it publicly. Slap that supercharger on a frankenmotor & see how long it takes to pop. Someone else besides me needs to take the 'last motor popped' title.
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Old 01-13-2006, 06:50 PM   #17
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If you'd buy something you weren't afraid of breaking, you could do that...
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Old 01-13-2006, 07:02 PM   #18
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8 PSI in a supercharged EJ25 will make about 220chp. That VF29 will make 280whp. Problem solved
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Old 01-13-2006, 07:09 PM   #19
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Quote:
Originally Posted by Matt Monson
GGT, Contrary to the big turbo big power guys, I don't consider open deck Ej25's pos's. And worst case, I've got a closed deck Ej20G I could SC if the others do proove unreliable. In short, as I mentioned, there will be very little shopping done for more parts to make this happen...
I wasn't so concerned with the 'deck-ness' of it...look at some of the boost numbers of the EJ205 with Stage Kits 457+ ...what I was thinking about were the internals. Sorry, should have specified. Pistons, cons and crank.

Are the internals of a EJ251 and a EJ205 any different in strength? (using the EJ205 as a reference point as that is a boosted motor and the EJ251 wasn't from the factory)

What trannies do you have in inventory?

GGT
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Old 01-13-2006, 07:34 PM   #20
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Quote:
Originally Posted by Scoobie Steve
8 PSI in a supercharged EJ25 will make about 220chp. That VF29 will make 280whp. Problem solved
I am going to have to beg to differ. My Ej25 with Cobb spicy cams makes 220chp. I am figuring the SC'd engine will be more in the neighborhood of a stage II WRX at 275chp or so. In a 2500lb car I think that will be plenty. And the SC can support a fair bit more than 8psi. That's just how it is tuned currently...

To be honest, I will probably get bored of the car after a year or so, sell it off, and go back to looking for a BD to put the RS-RA w/VF-29 into.
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Old 01-13-2006, 07:37 PM   #21
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Quote:
Originally Posted by Gator GT
I wasn't so concerned with the 'deck-ness' of it...look at some of the boost numbers of the EJ205 with Stage Kits 457+ ...what I was thinking about were the internals. Sorry, should have specified. Pistons, cons and crank.

Are the internals of a EJ251 and a EJ205 any different in strength? (using the EJ205 as a reference point as that is a boosted motor and the EJ251 wasn't from the factory)

What trannies do you have in inventory?

GGT
The car the SC kit came off of ran for several years without problems with rods or bearings or whatnot. It did eventually blow the top off a piston because it was underfueling. But the funny thing is it had full compression from the rings while the top was totally destroyed from detonation. It was only the #3 cylinder.

I have spare '98 and '00 trannies with minor issues. But I work for a tranny shop and can fix them really quickly if I need to...
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Old 01-13-2006, 07:44 PM   #22
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I voted for the supercharged option. Cause like others have said already.. You have instant power with the supercharger, as long as its not a vortech type, which i know its not. Turbo lag in sport like autocross or rallycross, where you have alot of varying corners, low speed, high speed, the supercharger i believe would be more consistent for a driver to utilize best.

I can't wait to see this summer how i do in auto-x with the new engine in it, compared to the last time i was out, with the ej251 in it.
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Old 01-13-2006, 08:04 PM   #23
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Quote:
Originally Posted by Matt Monson
I am going to have to beg to differ. My Ej25 with Cobb spicy cams makes 220chp. I am figuring the SC'd engine will be more in the neighborhood of a stage II WRX at 275chp or so. In a 2500lb car I think that will be plenty. And the SC can support a fair bit more than 8psi. That's just how it is tuned currently...

To be honest, I will probably get bored of the car after a year or so, sell it off, and go back to looking for a BD to put the RS-RA w/VF-29 into.
You made 60hp with cobb cams??
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Old 01-13-2006, 08:09 PM   #24
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build #1 IMHO

but

build #2 seems more unique

but

I still vote build #1 FTW!
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Old 01-13-2006, 08:28 PM   #25
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I am old school at 45

History show Superchargers are hard on everything! all car supercharged, Thunderbirds, MR2, Nissan Frontier, all dead like clockwork at 60K miles. I have look at most old SCCA runoff and racing records and supercharger have proved to be failures!

I could be wrong! And somthng different is cool.

either way a 95 project car find is cool!
Red Or White or black! 1 more teal car with beige interier and I will PUKE!
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