Hiya!

 

Could someone please explain, in easy to understand term, how the diameter of the hole in the boost jet relates to a particular amount of increase in boost. I will be installing a JWT ECU chip & induction system in the very near future and need to know what "gas tourch welding tips" to get. I'm not looking to push the envelop too far.

 

Any info would be very welcome.

 

Thanks

 

Danny

 

PS - any suggestions where to get the "boost jets"?

For the best explanation take a look on www.twinturbo.net, in the tech section. There is a section on upgrading the turbos and boost.

 

Basically, the stock car opens the wastegate when there is something like 9psi vaccume in the wastegate hose.. hence no more boost as it's opened the gate venting the excess gasses... the boost jets go in the waste gate line and with the restriction (boost jet) means it needs more pressure to open this wastegate...

 

The smaller the jet the more restriction, the gate opens later, more boost.

 

Don't plan to go over 12psi on stock injectors and ecu unless you realise the effects! Personally I would reccomend not to do it without an ecu upgrade.

 

 

Tech section... http://www.ttzd.com/tech/ecutech.html

 

Just foudn this for you... http://www.twinturbo.net/

FAQ section...

Look up this...!!!

"Could someone explain boost jets to me? "

That'lll be this then :-

http://www.twinturbo.net/ttnetfaq/FAQpages/boostjets.html

 

Can anyone tell me what size jet approximately equates to what boost ? I don't have an accurate boost gauge installed yet !

From what I've read it varies from car to car (which is a tad odd.. But I guess it's down to the health of the turbo's and vacuum lines)..

 

See ; http://www.twinturbo.net/cgi-bin/ttnet_viewmsg.pl?forum=main&msg_id=674168

 

Concensus is that you want to start with .045 tips and if they are too small (too high boost) swop up a size, too low boost, down to .035..

 

Without an accurate boost gauge you're risking very horrible things though...

 

BTW - Jez - the actuator hoses (wastegate actuator) are operated by positive pressure, not vacuum There is a rated spring inside the actuator which presses against a diaphram. Above a certain pressure, the +ve pressure overcomes the spring and opens the wastegate. A higher rated spring gives a sharper boost response, but raises the minimum boost. Boost can also be adjusted by altering the preload (how much the spring is already compressed/extended by) by lengthening or shortening the actuator rod.

Never seen that done on a Z though.

 

And just for completeness.. The stock actuator is set to 7psi (safety boost), the ECU bleeds off pressure via the solenoids to raise boost to 9psi normally, and closes them to switch into safety boost mode. Therefore, if the ECU does *not* send a signal to the solenoids (something is wrong, perhaps) then you'll always default to safety boost.. (i.e. disconnect the solenoids - look - safety boost... but code 55 on the ECU..)

 

Az

 

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Stage: Rather Ill

 

[This message has been edited by aaronjb (edited 09-10-2001).]

Ok, another question regarding the Zeds ability to gauge the boost level at any given moment: If the stock boost gauges are deemed to be innaccurate, what about the sender unit that tells the ECU what boost level is currently running? For example, when in 'safety' boost, what is measuring the boost, or is some valve opened somewhere in the actuactor line, and 7psi is *assumed*.

 

Forgive my sorry-arse for not knowing what is probably common knowledge

 

------------------

Simon

The ECU has no idea what boost the car is running (other than via the MAF readings, which is uses purely for injector timings)

 

Common misconception that 9psi is the norm and safetyboost is the 'odd' boost.

7psi is the norm, 9psi is attained when the ECU *opens* a solenoid valve on the wastegate actuator hose to bleed off some pressure. So to go into safety boost, the ECU simply no longer opens the solenoid, allowing the actuator to see the full boost pressure.

 

Az

This is very obvious, and initially quite confusing, when using a Techtom, because most of the time the BSCV (Boost Solenoid Control Valve) is OFF. Then once the engine temp goes above 59 degC it turns ON, thereby allowing the boost solenoids to do their job and increase boost to max. If for whatever reason the car is in safety boost then I expect BSCV would be permanently OFF.

(Glenn - you need to play with a Techtom m8)

1mm jet approx 12psi

0.8mm 14psi

will vary on air temp\ size of turbos any other mods. these are just guidelines.

 

Hmmm, interesting reading, cheerZ for that Az mate

 

I was thinking the same about Glenskis motor Andy, Techtom session would be called for in his case I reckon.

 

Tim - I reckon Glenskis solenoids are disconnected........

 

Az

 

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Stage: Rather Ill

He's got a boost adjuster thingy right, so are the solenoids controlled by that, or are they disconnected when that is installed ? So if that doesn't work, then it's standard boost all the time ..... whaddya reckon ?

Bingo Andy, I think you just hit the nail on the head... Yeah - lots of toys but doesn't know what they are, thats our Glen isn't it...

 

Now, to install a boost controller, you unplug the stock solenoids, so they are now closed - wastegates seeing the full pressure, therefore boost is limited to 7psi (so called safety boost)...

 

So if his boost controller is turned off..Yup, he'll get safety boost (and code 55 on the ECU)...

 

Think we hit the nail on the head here?

 

Glen, where are you!?

 

Well done AndyP.. If you're right that is

 

Az

 

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Stage: Rather Ill

And back to the top we go ... wheeeee!

 

Seriously, thanks to everyone who posted replies to the original post. The links made for some very interesting reading.

 

It is my understanding, and please correct me if I'm wrong, that with the JWT ECU upgrade in place I can safely run at 14psi boost (i.e., 0.8mm hole in boost jet - thanks Tony).

 

All I need now is somewhere that sells these tips - any suggestions?

 

Thanks again guys!

 

Danny

Danny, boost-jets actually are MIG-welding tips.

So any DIY-shop that sells MIG-welders should also have "boost-jets"

 

-Eric

Danny,

Just my personal opinion, but I'd start with 12-ish and then go up to 14 if all is well. As has been said before actual boost will vary with car, weather etc and you don't wanna run 16 by mistake ! Also, double check your timing is dead on before you start. It should be 15 deg BTDC, the JWT chip will twiddle with it further up the rev range, but that is all relative to the base figure.

If you buy a JWT chip the boost jets and fitting instructions come with the kit!

 

Simon

Glen has also got an AFC on his car if I remember rightly! But last time I conversed with him a while back he said he never switches it on coz he didn't know what it did.

 

Bless him!

 

Sure that isn't the AFC on his radio

 

He did say something about a speed controller ... (I think) ...

Excellent feedback - thanks very much!

 

Right, so I'm off to a DIY shop to look for MIG welding tips - B&Q perhaps?

 

I'll be doing the following before I put the chip & boost jets in:

 

1. de-restrict stock exhaust

2. verify that timing is correct

3. replace sparkplugs with propper NGK PFR6B-11B's

4. install JWT intake kit (still on the other side of the pond )

5. install JWT ECU

6. install boost jets (start with 1mm hole = ca 12psi right?)

 

Oh yeah, and I need to do an oil & cooling change ... keep putting it off.

 

Cheers all

 

Danny