1jz overboost the same problem as 2jz?

[Lunchie]

Hey guys im about to buy a new 1jz auto soarer and Im just concerned about how a turbo back exhaust will effect the boost.

The car has 130kms on it and it has been well serviced so im not concerned about it blowing up on me. I have heard that the 2jz will spool around 18psi with a 3inch pipe off the turbos but im not looking to go over 14psi-1bar so i was think around 2.5inch from the turbo right through?

Any intelligent thoughts guys?

Also want a definitive answer on what these auto tt's run stock/lightly modded down the 1/4.

Any help would be great

Cheers

Lunchie

(P.S) aint it great i finally got a toyota guys ?no more rs legacy blowing up

[Silent Knight]

As I said earlier they act like any other turbo car would without efficient Boost Control.

Once you start opening her up and letting more air flow etc your boost will also rise. You can't stop it from doing so unless you have a decent EBC to control your boost with.

Fuel Cut in the Soarer is 1bar (14.7psi?) and stock boost from memory is around 10-12psi. I'd say with just the exhaust done you won't hit fuel cut unless you start her up on a very cold night and nail it straight away. Once you throw an IC into the equation you'll definitely hit it.

Stock TT Auto 1/4 is around 14-14.5s depending on driver and track conditions.
Stock TT Manual you could probably get that down to 13.7/13.8 providing conditions are suitable.

[Lunchie]

so do you think a 2.5 inch straight through from the turbo would be ok?

[postfach]

I've got a 3" straight through on mine, but its from the end of the factory downpipe, i get 13psi boost just from that and intercooler. i was warned against replacing the downpipe as well (by a fairly reputable person), as apparently i would overboost.

[Lunchie]

hmmm good point... i might just go with a 3 inch from the down pipe.... those ct12's aint exactly big

[spencer]

Check out the Cressida and Supra 1jz forums for shit loads of info on standard twin setups and everything else 1j related . 2jz only has a wastegate in one of the turbos this is what leads to boost spiking to 18psi + when a 3" exhaust is fitted. 1jz doesnt suffer as badly and 3" should be fine but boost controller would be the go. EBC, 3" pipe, twin dumps and an intercooler does for some nice gains

[postfach]

a boost controller cant lower the boost below the level its at without the controller, it can only change the gain and/or increase boost. if you put an exhaust on and it made you boost 16psi or whatever, installing an ebc isn't gonna fix that.

[spencer]

yep true fuel cut defender or what ever is the go then EBC to up the boost (well not to much on the twins). I have an hks FCD here for when I get to that stage then the megasquirt

[Silent Knight]

True that EBC can't lower stock boost but it can control it so that you won't spike and hit fuel cut...

[Dell'Orto]

Surely the stock downpipes would be restrictive enough to hold boost low, even with a 3" exhaust?

[the fallen303]

we found quite a good responce from changing the original Y dump pipe setup. i have 3" custom dumps with a reversed rear turbo through to 2 3/4" straight through to single rear "muffler". no overboost problems. took off exhaust and just ran dumps for shits and giggles one day, ran up to 1 bar, but sat nice and stable.

[2jayzgte]

The problem for the overboosting is the internal 20mm wastegate the only way to control the boost is use a EBC with stock front pipe and catback system or use a full 2.5-3inch system with a venturi or some sought of restriction in the front pipe another way to go is leave the cats in the front and mid pipe...But the big thing is the increase in flow and the small wastegate cannot handle this.

I run a full 3 inch system on my Supra I run the U.S spec turbo's with the big difference being that the U.S setup has a 30 mm internal wastegate that can manage the extra flow and thus control the boost spike.

[the fallen303]

coryn, buddy, pal, can ya hook me up?