Turbo Advice T25/GTX

Skilfil · Post by **Skilfil** » Tue Nov 13, 2012 2:54 pm

Hey guys,

Looking at selling the VW and using the money from it to stick a turbo on my SmurfMX5.

That megasquirt ECU comes with two full maps, either a T25 turbo or GTX, I've been looking online and it seems the T25 would be the easier more powerful option. I wouldn't mind 200hp to be my goal.. Any advice/ideas/how wrong am I?

Cheers

Post by **jif** » Tue Nov 13, 2012 3:20 pm

200 hp is a lot of fun in a car this light.. the main problem will be having enough willpower to stay out of trouble

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WideOpenThrottle · Post by **WideOpenThrottle** » Tue Nov 13, 2012 3:23 pm

200hp at the flywheel is what i got from a T3/T4 1600 GTX turbo so you should be able to get that at the wheels with a T25, providing you install bigger injectors,dyno-tuned standalone ecu [as in the M.S.] plus appropriate headers/exhaust.Intercooler would help,& so would a dual feed fuel rail & bigger fuel pump if running lean on the stock one.
Dont forget a bigger clutch is more than likely to be needed,and certed if for road use.

All up should cost you one $squillion...perhaps a bit more!

Skilfil · Post by **Skilfil** » Tue Nov 13, 2012 3:38 pm

Well its going to be a gradual process. I'm planning on doing a few things to it first to prep it for the turbo. Brakes + Suspension, and probably the seats and roll bar.

Then I'll be ready for a turbo.

SLYDIT · Post by **SLYDIT** » Tue Nov 13, 2012 9:12 pm

the GTX VJ20 turbo is a bit small really. it was developed to be small so that it would boost low down and make the most of a 4WD system off the line. (much like the WRX td04 13 turbo.) I am running the VF10 subaru turbo which is basically a VJ20 turbo except it has a much larger compressor wheel and a slightly bigger turbine housing so it makes its power at lower boost.
The T25 would be good as you can buy manifolds etc from overseas.

Kieran · Post by **Kieran** » Wed Nov 14, 2012 9:58 am

The MS comes with fuel and ignition maps to start the car and get you to a dyno you should never boost on them so you also have to factor in cost of a tune

I vote T28

chris · Post by **chris** » Wed Nov 14, 2012 10:02 am

Kieran, we don't all need to compensate our size with a bigger turbo.

Kieran · Post by **Kieran** » Wed Nov 14, 2012 10:12 am

Not a compensation if you use a re-circ and internal wastegate

punkoutnz · Post by **punkoutnz** » Wed Nov 14, 2012 10:48 am

I have a T25 on mine. I'm on full boost by around 2300rpm. I think the B6 could be well suited to a T28 but the T25 is so much cheaper and easier to find so that's what I've stuck with for now.

Skilfil · Post by **Skilfil** » Wed Nov 14, 2012 1:07 pm

punkoutnz wrote:I have a T25 on mine. I'm on full boost by around 2300rpm. I think the B6 could be well suited to a T28 but the T25 is so much cheaper and easier to find so that's what I've stuck with for now.

Do you find you're on boost on the motorway while driving? Sorry if its a really retarded question, never actually owned a turbo myself.

Post by **jif** » Wed Nov 14, 2012 1:32 pm

Do you find you're on boost on the motorway while driving? Sorry if its a really retarded question, never actually owned a turbo myself.

oh yes ... the con is that only ~20% throttle is the same as WOT (non turbo) , the pro is that you can overtake *really* quick :] (see previous comment about willpower

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Skilfil · Post by **Skilfil** » Wed Nov 14, 2012 3:43 pm

jif wrote:
Do you find you're on boost on the motorway while driving? Sorry if its a really retarded question, never actually owned a turbo myself.

oh yes ... the con is that only ~20% throttle is the same as WOT (non turbo) , the pro is that you can overtake *really* quick :] (see previous comment about willpower

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Damn lol gas must disappear like nothing? I know gas is a moot point with a turbo but don't want to set my wallet on fire just yet!

punkoutnz · Post by **punkoutnz** » Wed Nov 14, 2012 4:05 pm

No my MX5 is really good on gas when it's tuned right (currently running a stupidly rich tune, but when it was properly tuned it was getting >500kms to a tank). No you're not on boost while on the motorway, but it is available at the flick of the throttle for overtaking.

I think what jif is trying to say, is that if you give your car around 20% of the throttle then it will be making around the same amount of power as a stock car at wide open throttle. So yes if you drive it hard it will drink gas like a pack of Irish sailors, but when driving "normally" it's really efficient.

Post by **jif** » Wed Nov 14, 2012 4:18 pm

ok, i see what you mean ... steady,flat motorway cruise is still in the unboosted range, fuel economy about the same as before if its tuned appropriately (ie with a wideband o2).

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Skilfil · Post by **Skilfil** » Wed Nov 14, 2012 4:43 pm

Ahh right. Well, that definitely sounds better haha. They should all come turbo by default, its a fun car but trying to overtake up a hill is a mission. Thanks for the info I'm definitely learning as much as I can.

T28 is apparently not very well suited to the MX5? As it is, T25 seems to be very common. Would it be worth getting one of the 'brand new' GT25's off TM for $450ish when I go about getting one?

Kieran · Post by **Kieran** » Thu Nov 15, 2012 10:25 am

Most people on Miataturbo.net run at least a T28 mainly for heat management a T25 will run 7-10psi from 2-2.5rpm to redline and create alot more heat as a byproduct than a T28 because of the surface area and spool only drops from full boost at 2-2.5 to 3-3.5rpm

but when your on the track you'll be above 3000rpm constantly anyway
and on the street it just makes for better fuel ecconomy as your not on boost as much if you drive below 3000rpm
if you get a lightweight flywheel you can rev up quick enough that you won't notice the lag

There are a couple people running GT30's... F That

The GT25s on trademe are cheap Chinese crap
Read up on www.miataturbo.net you'll learn alot

SLYDIT · Post by **SLYDIT** » Thu Nov 15, 2012 8:40 pm

My suby turbo gets to 8 psi at 3000 rpm and it certainly isnt what i call laggy. if you want full boost at 2000 rpm then get a supercharger. Stomping of the gas at 100ks in 5th sees the boost gauge shoot to full boost before you can say "full boost".
The americans for some reason all seem to think that uber low rpm boost numbers are all that matters. god knows why.
Remember that the smaller turbo you have, the more energy goes into useless heat instead of power.

Mad Kiwi · Post by **Mad Kiwi** » Thu Nov 15, 2012 11:07 pm

My old t4 turbo'd engine made great boost at 2500 ish and was considerably more friendly to drive than my new engine with a t28.

Not sure if that is tune or what but miataturbo reckon of the 3 t4 versions (subaru) 1 was especially well suited to the mazda engine.

I presume it was what I had as it was a very driveable, torquey motor.