aristomkii

Hey guys, I'll soon be receiving my car from the land of the Rising Sun.. Anyways, It's a stock 4spd Auto 2JZGTE VVTI MKII. I am looking for clarification on OVER-boosting issues.

I have read numerous reports regarding JDM TT being weaker than USDM which is fine and I acknowledge that.
I have found alot of conflicting information about JDM Aristo 2JZ VVTI's overboosting/not overboosting from doing 3'' or 4'' exhaust setups. My car has complete STOCK exhaust and I am wanting to put a 'Boost Controlled Exhaust Cutout' on my Aristo. The diameter of this cutout is 4''.
I am wondering if I can put the cutout on the downpipe somewhere or wherever I can fit it in order to be able to get exhaust gases out the fastest with the least amount of restriction.

Mods to be had:
-Obvious maintenance and fluid changes...
--4'' Boost controlled exhaust cutout for restrictive stock exhaust system (cutout opens @ 1.0bar)
---Voodoo MBC - (stock boost is 0.7/0.8) wanting to up the boost to about 1.0bar or 1.15bar and keep it there for precations of the TT's grenading? - Can I go higher than 1.0bar without fuel cut defender? -- I've saw conflicting reports on this matter as well.
----AEM 340LPH fuel pump (Next year)
My last point is also confirming that as long as you stay below 18psi (suggested max for JDM ceramic TT's) the AFR stays at 10.0AFR when WOT correct?


Here is some information/forum posts that I found to help aid/ give me ideas/confirmations or even confuse me more lol. Cheers!


1. solution to jdm twins overboosting with 3" exhaust --> https://www.clublexus.com/forums/per...3-exhaust.html

2. Aristo swapped and no fuel cutoff --> https://www.clublexus.com/forums/per...el-cutoff.html

3. Electronic Exhaust Cut-Outs Pros and Cons --> https://www.clublexus.com/forums/per...-and-cons.html

badblackgs

iTrader: (1)

4 inch exhaust is a complete waste of space, money, time, thought, etc...
the stock jdm turbos outlet is only 2.5 inches at the outlet from the turbos. yes going 3 inch does show to improve spool up and power but than it just has to be choked back down to stop over boosting. im currently running 3 inch mandrel bent exhaust from turbos back but i have a 2 1/4'' restrictor ring. when the weather is cold like in the 50's, itll over boost easily and hit fuel cut quickly. but when its in the 80's sometimes it wont boost cut.
i get the idea what your going after, a self regulating exhaust restriction that will help keep the stock twins from overboosting. but if its made out of 4 inch exhaust, even with the side valve shut itll still over boost.
do what everybody else that running stock jdm twins. 3 inch exhaust with 2 inch restrictor ring. than run a manual boost controller to up the boost.
unfortunately, you cant have your cake and eat it too with jdm twins. you either run a restrictor ring, stock exhaust with atleast one cat, or get ready to overboost. installing a boost cut device that will allow the engine to keep increasing rpms will just lean the engine out and risk hurting it.

Letsride

What badblackgs said is correct. 4" is a waste of money on the stock twins. I have a restrictor plade made to overcome the over boosting on 2.5 to 3" pipe. The stock twins have metal blades and will be fine once precautions are taken.......however. I wont push them beyond 15psi. You have not mentioned any upgrades to the tranny.........that would be my first concern.

aristomkii

I think you guys are misunderstanding my goals here (Only if I'm totally not out to lunch lol). I want to keep the complete stock Aristo exhaust setup with an exception of POSSIBLY a Aftermarket Downpipe/Custom made 3 or 4 inch diameter piping mated to a 4 inch diameter Boost-Activated Exhaust cutout that only is open over 1bar of boost (like shown in the pictures above.)
I would assume that this combination with the OEM exhaust system will keep it relatively quiet for long highway trips, but will allow the exhaust to flow more freely out the exhaust cutout when WOT. I'm not so worried about overboosting as I've heard it's not an issue on MKII JDM Aristo's especially with a EBC/MBC; (I guess if no one has a definitive answer I guess I'll have to be a guinea pig. As I've read people have issues with overboosting while many don't at all) I'll be getting a manual boost controller and won't put my boost above 1bar or possibly 1.15bar if it doesn't fuel cut (which I'm not entirely sure either as I've read no issues with fuelcut @ 1.15bar in some cases.)

I have plans to go single turbo + transmission cooler + Fuel Cut Defender (if it fuel cuts over 1bar which it might) + ecu tune + other supporting mods I will need. Sooner or later, either when the Twin turbos go, or I have enough money/time to do so. My immediate goals with this car are to get anywhere between 350-400hp/tq. Single turbo I would hope for atleast 500-650hp at the most. My last point also is (auto transmissions here are a dime a dozen so idc if i blow one up; you can't even give them away here basically lol). Here is a video of a stock JDM MKII 2JZGTE with BPU mods to obtain 400hp with a list of what he did. This is essentially what I want to get to before I single turbo swap it.

- 1ST RUN BOOST CONTROLLER DEACTIVATED @ 85 kPA (0,85 BAR, 12,3 PSI) with peak 96 kPa (0,96 BAR, 13,9 PSI)
- 2ND RUN BOOST CONTROLLER ACTIVATED @ 113 kPA (1,13 BAR, 16,3 PSI) with peak of 137 kPa (1,37 BAR, 19,8 PSI)

I have a few questions are you guys running 2jzgte vvti or non vvti? USDM turbos or JDM? What's your full exhaust setup? Aftermarket or custom made? I just hate the idea of having a 3 or 4 inch downpipe only to put a 2 inch restrictor ring in it... seems counter-intuitive to me IMO.

Thanks for the replies I appreciate all feedback and take it into consideration!