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Discussion Starter · #1 ·
why doesnt the supra wastegate work like other stock turbo cars?

most other turbo cars will boost uncontrollably if you pull the pressure line that controls the wastegate. like over 30 psi!

but on a tt supra you only get 18-21 pounds of boost if you pull the pressure hose depending on weather conditions.

im still trying to figure it out, but i think it has everything to do with the weak wastegate actuator for the stock turbos. can someone explain why the stock wastegate behaves this way?

im asking because I am having a hell of a time getting my HKS EVC IV dialed in.

basically the evc wont make max boost (18-21 psi) unless the evc boost solenoid is completely closed. the only way to do this is by setting the evc to 30 pounds of boost. which will only make about 18-21 because it is pretty much doing the same thing as pulling the wastegate hose by sending no pressure to the wastegate.

i was wondering if anyone has figured out a way around this?

is there a way to modify the stock wastegate to function as on other cars?

i really want to take advantage of the extra functions of my EVC IV but cant do so unless I can get it dialed in properly.

any suggestions are appreciated.


Premium Member
4,972 Posts

I've been wondering the same thing and have been wanting to post on the same subject for the last few days.

When I first installed my EVC 4 (TTC) I have it hooked up the same way the M's boost controller was set-upon the car (Blitz way) and ran the fuzzy logic learning. No on could believe how well it controlled boost. If I had it set at 1.2 bar, it would stay right at 1.20-1.21 perfectly. After time I had developed some boost leaks so the boost controller wasn't controlling boost well anymore and wouldn't learn in fuzzy logic mode anymore.

In troubleshooting things after I have fixed the boost leaks, I got the instructions from HKS and realized that they reccommended a totally different way on hooking things up, so in switching it to their install method, I found some blown vaccum lines back against the firewall that led to the pressure tank and fixed them. The boost controller made boost go to the desired level a little better,, but it would back off 0.1 bar and then spike back to 1.2 during shifts, and then trail back down, but won't work in learning mode and needs the stock boost + setting to be only.05 above, the offset to be at 50 and the boost set at 1.35 to get anywhere near 1.2 bar.

After having it hooked up the HKS way for a year and wanting to switch it ever since, I finally switched it back. However it still won't learn in fuzzy logic and exhibits the same boost spike and drop off. I was wondering if it was my pressure tank leaking and effecting the boost controller since the HKS way has you hook up one of the line to it, but now that it is not hooked up to there anymore, I am thinking it is a weak wastegate.

Some people have talked about shimming the wastegate to bring up the pressure on the diaphram/spring, and I might try this next, but I've been wondering if you can replace the wastegate w/ out taking off the turbo's.

Has anyone tried this? I know that Andi has had problems holding boost too.

Any input would be greatly appreciated.
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