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zebra

Pros And Cons Of Wastegate Feed Positions

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So ive been thinking and doing some testing on my 1jz twin turbo.

For those that have driven a Stock turboed 1jz they will know they are a bit lazy onto boost.

So my theory is because the internal gate pressure feeds are on each compressor housing the actuators are always seeing boost, my testing was to have a boost gauge reading off one of the actuator lines, and driving around they are seeing a few psi just crusing at light load and more when accelerating away from a standstill. Which is probably why the standard BOV/recirc valve is always open until +ve pressure is reached in the Plenum, so fitting an aftermarket BOV has helped boost response quite a bit.

Now, standard boost on these things is around 8psi, so the actuator springs are quite soft.

IF I were to move the lines to the actuators to the Plenum they will see vacume driving at light load, so in theory the gates should be completely shut, hence bringing the engine upto full boost earlier/quicker because the internal gates aren't bleeding off exhaust gasses in the turbine.

It makes sence to me to move these lines and block off the standard pressure feeds, but I would like your advice before doing so, because the engine bay is a head f**k to work around.

I would also fit my EBC to help things along too.

Cheers

Andrew

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I think once you crack that throttle the slightest bit the entire system will be seeing the same pressure so i doubt it will make a difference....not familar with jzs tho

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Nah -15" of mercury in the plenum and 3-4psi in the cooler pipes at 110km/h in top gear.

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But seriously....

I didnt know you had a reference to the plenum at the same time to see the difference

Only if the sping it really soft i cant see it moving by 3psi....Have you tested the actuator to see what pressure it starts to move?

I guess one way to find out.......DO EEET!

Ps. Check ur intercooler to make sure it doesnt have an old sock or something in there :unsure:

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All turbo cars will have more pressure in the cooler pipes than the plenum at low throttle, eg the RB26 turbo shuffle. (kinda different due to the ITBs but same concept)

I have 2 boost gauges lying about btw. (maybe even 3 lol)

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Ironically i wanted to tap a pressure source from the comp outlet on the 26 hence keeping the hose run short as possible to send to the boost controller >actuator to see if i could have elliminated some spike....never got around to it tho

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Probably gonna get laughed at being that i'm not overly experienced with turbo stuff, but could plumbing the waste-gate feed line into the plenum cause over-boosting or compressor surge when you drop the throttle on boost? Ie would the waste-gate see vacuum while the turbo is still going with the throttle closed?

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Just before the throttle body is best IMO. It also helps boost stop dropping off in the high revs. There is a bit of lag and pressure drop for the air to get through the piping and intercooler. U can use this to your advantage by making the wastegates lag too, bringing on boost earlier and harder.

After the throttle is dodgy IMO because U can be at 80% throttle and the turbos want to keep on making boost. U can hear it on cars setup like this. U back off the throttle a bit and u can hear the turbo spinning up like crazy.

Edited by bradsm87

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Had an in depth disucussion with one of my mechanics the other day on this as well...if you remember i've got a gt3076r on a 2jz and i'm not holding boost properly at top end...general consensus agrees with your theory to take the boost feed for the wastegate or ebc off the plenum post throttle body...that way your wastegate or ebc is controlling boost according to the actual pressure that your engine is getting as opposed to the pressure in the pipes before any pressure losses through the cooler etc...

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^^^ yep but thats bandaiding a problem not fixing it.

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Do you think my idea will work on the 1j Trent?

I dont have boost control issues, just chasing a bit more response.

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Thanks Trent...i guess it is a bandaid solution...i've yet to try it but if it allows me to stop the 2psi drop i'm getting then maybe it'll do for now...

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the problem with taking your wastegate feed off the plenum is that it makes the feedback loop very slow to react. when your turbo makes boost it has to fill the outlet piping, down to the intercooler, the cooler itself, the rest of the piping and make its way through the throttle body before pressure starts travelling down the vacuum line to the actuator in order to control boost. you will end up with poor boost control.

you are much better off fitting a simple ball-and-spring boost controller like the turbotech one well advertised on SAU and available on ebay. that will keep the wastegate completely shut until the desired level of boost is seen and you can take the boost feed right off the compressor housing meaning your feedback loop is nice and short. it also means you don't have to replumb everything you can just whack the T valve in the middle of what you've got and see if it helps.

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yer may be slow to react but 90% of actuators open 3-4psi below target pressure anyway, so by creating this delay your reducing gate creep coming onto full boost. i've always run my boost source of the plenum (my cooler piping doesnt have any nipples) for years on a few different cars and have never had any problems with boost control, its always been very good. also it helps stop boost drop on gearchanges, not that you'd ever notice it with a stock turbo

Edited by JonnoHR31

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yer may be slow to react but 90% of actuators open 3-4psi below target pressure anyway, so by creating this delay your reducing gate creep coming onto full boost. i've always run my boost source of the plenum (my cooler piping doesnt have any nipples) for years on a few different cars and have never had any problems with boost control, its always been very good. also it helps stop boost drop on gearchanges, not that you'd ever notice it with a stock turbo

on most gtr's we run it that way but they dont see vacuum in the plenum.

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yer may be slow to react but 90% of actuators open 3-4psi below target pressure anyway, so by creating this delay your reducing gate creep coming onto full boost. i've always run my boost source of the plenum (my cooler piping doesnt have any nipples) for years on a few different cars and have never had any problems with boost control, its always been very good. also it helps stop boost drop on gearchanges, not that you'd ever notice it with a stock turbo

I ran my R33 that way woth no dramas as well.

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Just before the TB is definitely better than plenum. GTR's run in plenum from factory because they have ITBs. I don't think vacuum would be very good for the diaphragms in actuators either. The boost you want to control is the boost at the engine, what boost gauges and map sensors see. This is why i think on the throttle side is better than at the compressor outlet.

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