I have my STI RA V-Limited engine waiting to be dropped in to my '96 WRX.

I want to put a new turbo on the engine before putting it in the car but can't decide which turbo to go for.

What would be best and why,the 18g or the 20g ?

My current mods include-Apexi power fc and commander,550cc injectors,walbro 255 fuel pump,fuel reg,hybrid front mount intercooler with hard pipes,gt spec headers and up-pipe with full Hayward and Scott exhaust system. I also have an Sti 5 type-r 'box and an Exedy organic clutch with lightened and balanced flywheel.

 

If you have STI Heads with 8k rev limit Id defo go 20g. If I had a 7k rev limit id go 18g myself on a 2.0 Litre.

 

With the current WRX engine I had a 7k rev limit. Could I fit the Sti engine with a 20g and when I get it mapped have the 8k rev limit ?

 

its the internals that limit the rpm, that's why sti lumps with stronger internals have an 8k limit. So regardless of the map you will have an 8k limit on sti lumps and 7k on a wrx lump.

hth

 

So in that case,if I have the Sti engine with 8k rev limit,will I be best to go for the 18g or 20g ?

 

20g; because it has more top end grunt which you can use with the 8k limit

 

I'd say it depends on your intended usage as well...

I've got the 20g on a WRX and it's very toppy, with peak power being made at 6200 rpm. I don't mind as the car's not driven that much in town etc, but it still spools too late for my liking (in those conditions, once the revs go past 3500 it flies ).

If you pootle around a lot and don't like stirring the gearbox too much, then go for an 18g imo.

Here's my graph: http://www.bilar.co.uk/subaru/graphs

My wife likes the car though


I think on the road, where you're likely to have lower revs every so often, an 18g car will outrun a 20g one (although I may of course be wrong on this one).

 

So,with the 20g and my mods what sort of power could I expect ?

 

I'd agree with Henrik. Mid range is actually better on my 18G than on the 20G I had for a very short period of time. Had to change it as the spool was poor.
Yes 20G better for the top end is figures are your thing but on the road when moving I'd say there was very little to chose between the two. Not sure what they are like on Classics mind as my comparisons are on a Newage Sti.

 

depends on both the type and quality of your supporting mods...anywhere from 360-400 I'd imagine having had a quick butchers at your specs.

 

get an md321

 

But that's like £1200 !! An 18g or 20g from Andy Forest with my 2 TD05's in exchange will only cost me £400

 

My 20g is a bit slow low down, but come on strong to 1.6 bar by about 4500 to 7000.
The turbo can only deliver a max of 400 bhp anyway, and mine does roughly 360/380 depending on which RRoad you believe.

For road driving the 18g may be the best for low/mid range. The 20 g pulls harder 'high' mid to top end.

Rob is right about the 321, but the stock Sti innerds will bend literally if mapped to hard. A well mapped 321 on a 'steel' 2 ltre/2.33'2.5 is a killer turbo as Rob and I know from different ends of the game.

 

Well Andy Forest says go for the 20g as the RA engine breaths well and will work well with the 20g. He said the spool up between the 2 on this engine is minimal

 

20g on a stock Sti V3 engine with a few supporting mods:
DropShots.com
Not too laggy?

 

Seemed to go well to me

I'm really not sure what to go for. I don't want to buy one of the turbo's then regret it and wish i'd bought the other

General thoughts seemed to say the 18g will be better for road driving and as mine is a daily driver that could be the best for me.

 

Just been out for a blatt, and here are my thoughts:

With the old td04, it was possible to have fun at 35-45mph, as the turbo would kick in early in second gear, producing a nice rush of power.

With the 20g the fun starts at 40mph in second gear, but soon you're up to 80mph, which is just way too fast to for the normal roads (imho etc), so in a way, the td04 equipped car was better on the road and the 20g is worse (because it's too fast? )

The 20g *really* needs a track or motorway speeds to come into its own (again, 3rd gear is the best imo), and it needs to be kept on the boil to be fun (I don't think it's got anything to do with the map, as it's a Bob R map).

Our scooby is quick becoming something that is suitable only for the track, which may not be a bad thing (clio 197 cup for the road, here I come)

 

There is a lot of sense in the comment above imho.
I have had mine on now for 3 years, and the car does about 3K mile/year, plus about 12 hillclimbs a year.

The pull over 5000 especially in 3rd on the road makes the car very very fast, and you catapult between the bends etc, but you will scare sleepy people when overtaking.

However, you do not have to drive flat-out!
My AndyF mapped car is about 360/380 bhp and 350 lbft and with the Type R trans it is very easy to drive slowly as well as keeping it boiling (ie over 4000)

It is not a hard work car to drive, but that is the secret of a good tune in any car.

Remember the 20 g and the 18g for that matter will need appropriate supporting mods all over the engine plus a good 20g to start with.

AndyF supplied my tweeked 20g.
I have a huge thread I did about fitting it all and the mods and the end result, but it is huge!

Graham.

 

I had a 20g on mine for about 600 miles and then swapped to an 18g. It just didn't suit a five speed box and I was always in the wrong gear.

 

I hear what you're saying... I'm thinking a 2.5 lump might be the way forward here

OT: Does a car that's driven on trackdays need to be MOT'd etc (essentially, does it need to be 'road legal')?

 

I think the secret to your car there is the higher rev limit as well... mine's a bog standard WRX, so I've got a 7000rpm limit and badly flowing heads and my gear ratios are too long.

I don't want to get rid of the turbo as it's a great piece of kit (and it was a grand as well ), so hopefully once the tranny breaks I'll pop an STI 6-speeder in and that will give me shorter gears and should rectify the 'omg i'm doing 90mph' "problem"

Would anyone care to comment on if changing heads for better flowing ones (early sti?) would yield more torque lower down?

 

I guess Sti cams would be abetter 'swop'?

Pulling constant 8000 revs in competition sure helps with the boiling bit!

 

18G - more driveability. Not that far off from a 20g.

Buy and 18G and spend the change on some other mods for the car...

 

The 18g and 20g from Andy F are the same price