1JZ-GTE VVTi BOV Mod

tye-bo

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#1
Tired of the turbo kicking in at 3000rpm? Tired of having no low end torque?

If you perform this modification to you OE BOV, you essentially turn it into a standard BOV and it works of the push pull principle. It is very simple to perform this mod, remove the BOV and get a 1/8" NPT fitting with a 1/4" nipple, and drill out the open air vent hole that is on the side of the BOV that points down when installed. BE CAREFUL NOT TO DAMAGE THE DIAPHRAGM, THAT IS RIGHT INSIDE OF THE HOLE, then use some thread sealant on the NPT fitting and screw it into the BOV. This is what it will look like when this step is done:

IMAG0744.jpg

Then attach a line from the intake manifold port (the one that isn't normally being used) to the NPT fitting, like this:

IMAG0747E.jpg

Next, disconnect the line that goes from the turbo to the ABV VSV and connect it straight to the BOV, I connected the other line back to the VSV so I don't just have open ports.

IMAG0741E.jpg

Then you are done! Now your turbo will feel much more linear, and you won't have boosting issues when you turn up the pressure!

If you have any questions, let me know.
 

Rafa

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#2
Thank you so much sir for the write up...
When im ready to turn up my boost ill do this mod thanks alot..
 

te72

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#4
Interesting... now I'm thinking that this idea may work in reverse as well, correct? In my case, I have a bit too much boost too early, and it causes me to hit fuel cut at ~17psi. Now, I have an adjustable blow off valve, could I turn the screw to loosen the spring on the BOV to basically act as a controlled bleed off of pressure? Engine is a 1j on MAP by the way, so I'm thinking that it shouldn't cause the engine to run rich from the lost air.

If I'm way off, someone please set me right here... I'll tinker with it this afternoon and see if my theory makes any sense.
 

te72

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#6
Haha, if it were that simple, it would not be an issue man. I have the boost controller set on its absolute lowest setting (Turbosmart MBC), with the gate system removed to prevent spiking (which was causing fuel cut). Thing only hits like 12psi without it, but with it, it keeps climbing right on up to about 17psi and hits the dreaded fuel cut. I just want that 15psi sweet spot on the twins... :p
 

tye-bo

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#7
This mod is only for the 1JZ VVTi (factory single turbo), not the normal 1JZ with twin turbos, so it may not have the ABV VSV. The factory VSV actually puts boost on the other side of the diaphragm to open the BOV below a certain RPM. My guess is for emission reasons, and then when it hits a certain RPM (3000 or so) it slams shut usually spiking like crazy. When this happens there is no low end power at all, and when the boost kicks in it hits like a ton of bricks. I wanted a more linear feeling turbo, so I performed this mod.

ONCE AGAIN, THIS IS NOT FOR THE STANDARD TWIN TURBO 1JZ
 

te72

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#8
Makes sense, but thanks for clarifying. I loosened up my BOV a bit last night before going home, and it seems to have alleviated the fuel cutting by limiting the boost right where I like it, but it was still cutting out in the morning in the cool air, so I will tinker with mine a bit more.
 

tye-bo

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#9
When I was using the factory ECM, I noticed I could boost a lot higher in 1st and 2nd, than I could in 3rd. Also I turn it up as I go up the mountains, but that's because I have a MAF and since it's based on air density and flow, it allowed me to run a little more boost. Are you running an electronic or manual boost controller?
 

te72

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#10
I'm running a 1j on stock twins, also it is MAP based rather than the MAF of the vvti engines. Running a Turbosmart manual boost controller, on its lowest setting.

Good news is, I've gotten it to where the BOV spring is loose enough, it only hits fuel cut maybe once or twice in 2nd gear. Before loosening the spring, it would hit fuel cut 4-5 times. On mine, the turbos themselves are becoming a restriction (and a major one at that) around 4500 or so, so the boost stabilizes around 16-17psi, and I don't have any breakup after that point.
 

Orion ZyGarian

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#11
Brad, you may have your boost signal sourced wrong. I'm guessing it's right after the turbos and before the intercooler. The pressure drop isnt kind to the signal; you really want it right before the throttle body.
 

te72

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#12
Interesting... the pressure signal is right off the turbo outlet on the stock twins. I'm trying to actually LIMIT my pressure... oh wait. I think I see what you're saying. If I get the signal closer to the throttle, it should see a more accurate pressure level? I do wonder though, how much pressure do you lose to a stock 1j intercooler..?

The other question I would wonder, being MAP based, it fuels based on manifold pressure, rather than airflow, correct?
 

destrux

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#13
About 2psi, sometimes more. Even with aftermarket intercoolers pressure drop is an issue, although not as bad. I see 1.5psi with my core that's sized for 450hp.

I seem to recall reading a reason not to source the boost signal from after the IC... I can't remember where I read that or why not to though. Possibly something about boost spiking because the pressure takes time to go from the compressor, through the pipes, through the IC, through more pipe, then back to the wastegate actuator through a long hose. A short hose from the compressor outlet to the wastegate is best for reducing spiking.

You might find that you go from low RPM overboosting to boost spiking during spoolup. Either one will kick the boost cut in.

Maybe experiment and see if it works anyway, that's what I'd do.
 

f00g00

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#17
Great article but what do you do with the turbo compressor outlet? block it off or just T it to the B source? He never mentions that, just says to move to B.
 

te72

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#18
A short hose from the compressor outlet to the wastegate is best for reducing spiking.

You might find that you go from low RPM overboosting to boost spiking during spoolup. Either one will kick the boost cut in.

Maybe experiment and see if it works anyway, that's what I'd do.
Actually, strangely enough, I had about 6-8' of line for the last Turbosmart MBC I had (an in-cabin type), and it didn't hit boost cut unless it was really cold out. So, I'm wondering if the longer hose didn't allow enough of a delay to keep the boost from rising too fast.

In other words, with the hoses JUST long enough to reach the boost controller and where it hooks up to, the boost was really fast spooling and spiked really bad, really early.
 

Orion ZyGarian

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#19
Yes, block it off. You don't need that one for boost control. I'm not sure why it is placed there, to be honest. Might be some other magic/science behind it :dunno:
 

f00g00

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#20
Its just the typical factory design there to open the wastegate and probably didn't count on aftermarket mods. I have a small stock outlet just in front of the throttle body that has a restictor after about 3 inches of hose so Ill T in there and give it a try.
 

Orion ZyGarian

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#21
That I understand, especially at stock boost levels; but you'll find them on big, fancy, aftermarket turbos as well. Even the EFR series uses them, though maybe because they go for the idea of "here's half of what you need with a turbo kit, built right into the turbo."
 

te72

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#22
That was a good thread on Turbo Miata, but I'm actually having the opposite problem. Too much boost with a boost controller (even on the minimum setting), but without it, I only get maybe 12psi, 13psi tops.

I'm wondering if a slight restriction somewhere might not be in order...
 

Twadecook

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#23
Tired of the turbo kicking in at 3000rpm? Tired of having no low end torque?

If you perform this modification to you OE BOV, you essentially turn it into a standard BOV and it works of the push pull principle. It is very simple to perform this mod, remove the BOV and get a 1/8" NPT fitting with a 1/4" nipple, and drill out the open air vent hole that is on the side of the BOV that points down when installed. BE CAREFUL NOT TO DAMAGE THE DIAPHRAGM, THAT IS RIGHT INSIDE OF THE HOLE, then use some thread sealant on the NPT fitting and screw it into the BOV. This is what it will look like when this step is done:

View attachment 59635

Then attach a line from the intake manifold port (the one that isn't normally being used) to the NPT fitting, like this:

View attachment 59636

Next, disconnect the line that goes from the turbo to the ABV VSV and connect it straight to the BOV, I connected the other line back to the VSV so I don't just have open ports.

View attachment 59637

Then you are done! Now your turbo will feel much more linear, and you won't have boosting issues when you turn up the pressure!

If you have any questions, let me know.
Thanks for this great write up gonna try this out but I have one question what size tubing did you use? 1/4" the hole way I believe the intake port size is 1/8od and the nipple pipe would be 1/4od with 1/8 nipple..
 

Twadecook

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#24
NVM did it and it works rather well again I appreciate this is a great little trick. I just used a 1/8np x 1/8barb fitting.