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  #1  
Unread 6th July 2018, 02:37 AM
Beachworm Beachworm is offline
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Default supercharging vs turbocharging for off road.

I recently met a guy who owns two SG foresters. One is an XT, lowered and set up for optimum on-road performance. The other is a non-turbo X with a supercharger bolted on, lifted and otherwise modified for great off-roading.

He happens to be a Subaru specialist mechanic and it is his view that turbo-charging is inherently unsuitable for challenging off-road use due to the need for high torque at relatively low revs. His solution is an aftermarket supercharger fitted as a bolt-on addition, without any other engine modifications.

I questioned him on the issue of pre-ignition, blown head gaskets etc. and he assured me he has given it a very hard time over the last couple of years without any issues. He says it pulls like a train from 1500 rpm right to the red line.


I am wondering what the general consensus is in the Subaru off-roading community. Should we all be going with bolt-on superchargers?
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Unread 6th July 2018, 02:55 AM
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I investigated this when I was considering my options for upgrading my engine. Another option I considered was the h6. I ended up going turbo and I am pretty sure I made the correct decision. I don’t know what turbo he’s running on his xt, or what gearbox. I have found that the combination of dual range box and small turbo means concerns of lag are unfounded.
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Unread 6th July 2018, 03:48 AM
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I understand his reasoning, but I really don't see the point in a subaru.

* as rally says - you can get a reasonable low range
* there are so many turbo subaru's that a turbo solution wins the economic (kw & Nm/$) and ease of tuning argument hands down.
* if you want low torque, use a small turbo (eg: the early GT foz with a TD035). Drop a low range box on it. My EJ208 TT has full boost (15psi) by 2000rpm due to a tiny VF26 which only flows about 150kW maxxed out. It has way more low down torque than my asthmatic EJ251 ever had.
* You can more easily (with bolt-on subaru bits) low-pressure (say < 7psi) turbo an NA engine, you'll get the low range NA torque, boosted mid and top, for minimal $$.
* for more demanding offroad applications where you want low down torque and smooth take offs, get an auto. An auto, lifted XT would be perfect.

The only thing I can see a supercharger really being an advantage is the linear response. Turbo's tend to come on boost in a hurry, which can be awkward.
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Unread 6th July 2018, 05:24 AM
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I’d love to drive his car and compare it to mine just to see how it goes. If he has optimised his xt for on road performance, then the tune would be different and he might be running a bigger turbo. I also assume he is running a single range box. Helping the turbo cause are the 1.447 low range and 4.4 diff ratio against what we assume is standard SG gearing in the supercharged car. Finally, the turbo engine runs AVCS that the supercharged engine doesn’t.
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Unread 6th July 2018, 05:57 AM
scalman scalman is online now
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Quote:
Originally Posted by duncanm View Post
I understand his reasoning, but I really don't see the point in a subaru.

* as rally says - you can get a reasonable low range
* there are so many turbo subaru's that a turbo solution wins the economic (kw & Nm/$) and ease of tuning argument hands down.
* if you want low torque, use a small turbo (eg: the early GT foz with a TD035). Drop a low range box on it. My EJ208 TT has full boost (15psi) by 2000rpm due to a tiny VF26 which only flows about 150kW maxxed out. It has way more low down torque than my asthmatic EJ251 ever had.
* You can more easily (with bolt-on subaru bits) low-pressure (say < 7psi) turbo an NA engine, you'll get the low range NA torque, boosted mid and top, for minimal $$.
* for more demanding offroad applications where you want low down torque and smooth take offs, get an auto. An auto, lifted XT would be perfect.

The only thing I can see a supercharger really being an advantage is the linear response. Turbo's tend to come on boost in a hurry, which can be awkward.
so you could put small turbo on EJ251 NA ?
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Unread 6th July 2018, 06:10 AM
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Yes, many people in the US have done so I believe.
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Unread 6th July 2018, 06:28 AM
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Quote:
Originally Posted by scalman View Post
so you could put small turbo on EJ251 NA ?
sure, why not.. many have done so.

There's no essential difference between turbo and supercharging when it comes to the engine. You're just compressing air and stuffing more into the intake.

Why you choose one over the other is more to do with packaging (manifolds and up-pipes versus extra belts off the crank), where you want boost (super and small turbo for bottom end, versus big turbo for top end).

Any EJ engine can be force-fed.. but you need to be wary of the limits. I think guys in the US (and here with the raptor kit) have done ok with about 6-7psi in an NA subaru engine.. while your typical EJ205 can handle about 15psi, and an EJ207 (forged) is ok to about 25.

Try here for starters: http://www.rs25.com/forums/f7/t75715...ng-na-car.html
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Unread 6th July 2018, 06:31 AM
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Superchargers have their place off-road and in the subi world in my opinion. They're just not as common as the turbo setups.

Two ways to do it:

- buy an off the shelf kit such as one from Raptor. This comes with all the supporting parts including the ECU piggy backs to make it run correctly.

- DIY your own setup with an appropriately sized charger of choice. A mate of mine supercharged his ej22e (Subarino). He used a Toyota SC14 charger running 6-7psi with a WAIC kit to keep air temps down.
It was a great setup for off-roading, boost coming on straight from idle. Best bit was that you could turn it off when you didn't need the extra power.

There are other chargers that can be used on NA Subaru engines without long term damage to the engine when done right.

So they're out there, can be loads cheaper than a turbo conversion or can be a quick conversion turn around without having to stuff around with exhaust and major wiring changes.

For off-roading I'd want a charger over a turbo - and one that can be turned on and off as needed

If you frequent the high country for off-roading a charger is more effective over a turbo, especially a large turbo...

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  #9  
Unread 6th July 2018, 06:42 AM
scalman scalman is online now
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just turbo must be cheaper because those engines allready have them so you can almost bolt in and its good. can find it from other car for cheap. where charger you need to buy new and you would need move ABS block to other place for that i guess as well. lots work and redoing stuff. i saw only one outback charged and one tribeca.
i heard EJ251 engines are not best for putting turbos on them. they just not doing that on those engines. others are way better
maybe H6 likes superchargers more.
it would be cool to have more torque on lows for sure, thats what you need on off road. thats main thing where i feel that engine just dont have enough to push car forward so its just stops.
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Unread 6th July 2018, 06:44 AM
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One of the supercharger manufacturer/distributors I contacted specifically told me not to supercharge my NA engine.
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