2JZ overboost problem.....fixed :D

[brett_celicacoupe]

so...

without a restrictor in the exhaust, the 2JZ with stock turbos wanted to push over 20psi into the motor.

since the front turbo died on my engine it warrants me to pull the turbos off and see how the issue can be fixed.

the plan of attack is to use a front turbo exhaust housing on the rear turbine so that the wastegate actually controls boost rather then its previous function on the rear turbo of providing pre-spool.

im led to believe that the exhaust housing from the front turbo bolts in place of the rear turbo, exhaust housing.

without alterations, it is expected that the sequential system wont work properly.

the solution; somehow open the butterfly in the dump pipe (name: exhaust valve?) partially to carry out the function of the prespool previously.

hopefully this can be implemented using a jaycar motor speed controller (PWM thing) and some sort of trigger off either boost or RPM.

im going to start pulling the turbos of next monday. ive got the 2nd hand replacement turbo, although im still waiting for the front exhaust housing

not sure if this has been done before but any useful info would be handy.

stay tuned for results/pics.

[brett_celicacoupe]

okay,

pictures....

here i have put the front turbo exhaust housing on the rear turbo. you can see the difference in 'thickness' of the housing. i will probably bolt the setup in the car and measure how thick the spacer needs to be. looks around 14mm at a guess.



edit.... just noticed the flange patterns look different ??


obviously the wastegate actuator shaft will need to be shortened by probably the same amount as the thickness of the spacer

[wilbo666]

Good stuff

I'm still planning to go with the external gate just for simplicity, and saving to source other parts, but this should on paper work too!

As a note I'd use the front turbo wastegate actuator, it is much stronger than the prespool actuator (check the Aristo TSRM for test actuator pressures... I think the front is ~15psi? and the rear is like 7psi?)

But seeing as how the flanges are really different I think your plan B is a better option

Cheers
Wilbo

[manual]

I don't think this will help in anyway.

The main issue remains that the wastegate is too small to flow the air around the turbo rather then through it.

The only solution is to enlarge the wastegate (and from memory - there just isn't enough metal to port out on the stock wastegate to stop boost spike), mount an external gate to the manifold and call it a day, go to single turbo like a 2J should be ... or put in an exhaust restriction.

though props for trying i just don't think it will achieve what you want.

[brett_celicacoupe]

I don't think this will help in anyway.

orly?

so you reckon 2 wastegates wont flow more then 1 wastegate

[wilbo666]

I don't think this will help in anyway.

I also think you don't know how the 2jz stock turbo system works

Stock there is only 1 wastegate. And that is on the front turbo.

Adding another wastegate will of course help!

Cheers
Wilbo

[brett_celicacoupe]

my plan B is to modify the existing rear turbine housing to operate as a wastegate rather then a prespool.

easier then i thought to modify.


step 1. centre punch the hole and drill it in progressive sizes. my largest drill is 18mm so ill need to take it elsewhere to get it to the proper size (25-30mm i think)


you can see it comes through perfectly square on the turbine inlet. i might port it slightly later on for a smoother entry.


i found some 2" exhaust pipe and started machining it. it ended up very thin walled in the end.



the exhaust housing has a step in it. i machined the pipe accordingly


here is the hole that needs covering...


the sleeve is ready to be tapped in. nice snug fit....


and here it is tapped in





take that skeptics!

test results will come soon

[JZA70 R]

this is awesome. i love DIY shiznit.

So are you gonna confirm if the front turbo fits on the back or have you already?

[brett_celicacoupe]

have a look at the comparison photos in post 2.

flanges are completly different

[manual]

hahaha my bad

i didn't read it as running the 2 ...instead just read it as you were putting the front to the rear

its been a tough end of financial year

[PlacentaJuan]

i am doing the same thing, but am getting 2 flangeplates made up to fill the gap.

i used the no1 turbo gasket and no2 turbo gasket as a template.

the 'gap' is 26mm, minus 2mm for each gasket is 24mm so 2x 12.. thick mild steel plates should do it.

once these are back from the laser cutters i will bolt them on to each assembly, bolt the whole thing up then tack weld the plates to get the shape, then look at getting the whole thing converted into a one-piece adaprot that can be cnc'ed.

i think that once an adaptor is made, prespool can be brought on by the exhaust valve, which has an adjustment screw on it, i would just leave it open the whole time rather than trying to imitate the original prespool valve.

the compressor vavle allready has a one-way valve to accomodate any boost made by the no2 turbo before the valves open.

then you can use the no2 WASTEGATE to control boost for the no1 turbo while in single mode, (just like the prespool valve does) and the original no1 wastegate will provide the extra bypass once both turbos are onlince and hopefully control the boost.

i will post some pics once my camera is charged.

[wilbo666]

I don't see the benefit of your system over Bretts placenta?

With bretts method:
>You can use your existing rear turbo (no need to find another front turbo).
>You don't have to clock the front turbo to make it fit on the rear in the correct orientation (does the front actuator still bolt up once you've done that?)
>The number of parts you need is less / easier (1 sleeve, and drill 1 hole), no new flanges

I think brett was planning to also use the EGBV (the large valve post rear turbo) with a controller so that it does stay closed while the first turbo is boosting. and then comes open at a set PSI...if it was me I'd look at adding another VSV (and some electronic control) that could direct pressurised air to the actuator EGBV actuator based on the (unplugged) prespool VSV

Then connect the 'rear' turbo wastegate actuator to the pressure output of the rear turbo (before the IACV).

Cheers
Wilbo

[brett_celicacoupe]

leaving the EGBV open a fixed amount was another option...

however im not sure how much lag it will introduce to the front turbo

[JustenGT8]

While i admire the 'outside the square' thinking why not just a single? (come on someone had to ask ) I asume you want the stock look? or a questions of dollars

[brett_celicacoupe]

poor uni student

it was a serious option however i realised that monies i spend on the soarer is monies i dont spend on the supra

[PlacentaJuan]

oh i see i didnt realize you were modifying the 2nd turbo!!!

yes i am planning to use 2x no 1 turbos because the thought of modifying a turbing housing didnt occur to me.

i think its also beyond my capabilities and i am hoping to come up with a solution that lots of people can use (in adelaide anyway) and i think a 'bolt and play' solution is more viable.

also i dont like the idea of modifying the turbo like that, not because i dont think it would not work or have problems with longevity, but because its just how i think!!

justengt8 if i was living in sydney i would go single turbo, but in adelaide you may not put an after market turbo on a street registerable car.

also other reasons might be: a liking the sequential system, like the look of stock engine bay, dont really want 400rwkw on the street etc..

i dont think that there is going to be any argument that for a power vs dollar scenario, a single turbo will win every time

also brett, while the open area of the prespool valve we equal an area of 'x', having that same areo on the EGBV i think will cause it to overboost (or lag the first turbo) and i think that you would need a much smaller area on the EGBV considering it will be open permanently, and not opening after a certain amount of rpm is reached.

i am planning on just 'cracking' it and adjusting from there...

[wilbo666]

also brett, while the open area of the prespool valve we equal an area of 'x', having that same areo on the EGBV i think will cause it to overboost (or lag the first turbo) and i think that you would need a much smaller area on the EGBV considering it will be open permanently, and not opening after a certain amount of rpm is reached.

i am planning on just 'cracking' it and adjusting from there...

I can still see this as really not being optimal...

The rear turbo is effectively under no load when the IACV is closed... so gas will happily go past the rear turbo turbine wheel and out you exhaust, effectively bypassing the front turbo... so you've effectively added another wastegate to the front turbo...when you are trying to get it to spool...!

I think it will suck. But I guess you can try it

Why not control it in a better fashion?



Cheers
Wilbo

[brett_celicacoupe]

i tapped a thread into the rear turbo outlet and installed a nipple.

i even had the correct tap on hand

[PlacentaJuan]

I can still see this as really not being optimal...

The rear turbo is effectively under no load when the IACV is closed... so gas will happily go past the rear turbo turbine wheel and out you exhaust, effectively bypassing the front turbo... so you've effectively added another wastegate to the front turbo...when you are trying to get it to spool...!

I think it will suck. But I guess you can try it

Why not control it in a better fashion?



Cheers
Wilbo

i will be balancing this out with extra boost on the first turbo anyway.

i reckon its going to be hard to control the exhaust valve to prespool because of the different size actuator and pressures required.

it has been proven that the second turbo in stock form can survive fine with a lower prespool value from factory anyway, so my aim will be to have minimum prespool at the crossover stage and let a steel wheel and highflowing take any extra shock load, so it will be barley taking any more gas from the first turbo, than current leaks past any valves anyway.

brett why didnt you tap the nipple into the existing casting on the compressor housing?

[wilbo666]

brett why didnt you tap the nipple into the existing casting on the compressor housing?

Prbly so he could get to it at a later date.

Royal PITA to get to in car the rear turbo compressor housing is!

Cheers
Wilbo