Overboost after porting wastegate

[texaselite]

Finally got the car back after porting wastegate, CAS replacement, timing belt replacement, 2.25" Piper with/Sports Cat and ceramic downpipe. Much quicker, but touched 1 bar while punching it and felt fuel cut-off for a second (let go of pedal immediately) and saw CEL switch on for about 10 seconds. Haven't even put in my Everest chip yet. Not sure if the weather here in Houston (has been in 40-50s at night with little humidity) was reason for greater airflow, but not sure what I can do now. Any advice?

[Steve A]

Welcome to the club

Out of interest what size did you port it to

[texaselite]

20mm as suggested by most

[Steve A]

20mm as suggested by most

As did I

Wouldn't it be wonderful if you fitted your chip and it cured it, can't see that happening though

[texaselite]

I know, right...not sure if I just sell the chip or install it now. Had I known overboost could still be an issue, I would have ported to 22+. Didn't think the extra flow from a 2.25" system would have been an issue. Can't afford to have the turbo re-ported at this time, already poured tons of extra $ into the car.

[Steve A]

Piper did mention 22mm after I already did and put it back on

I'd give your chip a go just to see how it effects the cars performance

[texaselite]

Yeah, I guess it can't hurt to try the chip..maybe it will "reset" the ECU and work properly. I guess I am not THAT concerned b/c I am rarely going to be pushing the car to the extremes where overboost is an issue, just pisses me off that after pouring so much $ into the car, it's not perfect.

[steve matthews]

If the flow can not pass through the down pipe then it will not matter what you bore the wastegate to.
Just a thought
Steve -w- wastegate at 21mm, 2.25 exhaust no cats and Alan's switcher with custom maps.
And no overboost.

[whippit]

i have a 2.5 with a precat eliminator, switcher , ported to 21mm never had overboost with this set up,

i had overboost with just the exhaust fitted, i fitted the chip and it helped, its worth a go doesn't take long

[HJ2]

Steve's got a point.
If the downpipe throws off the balance between core - and wastegate flow... There's no use in porting over say, 21mm.
In my treat i allready suggested that piper needs to add a deflector for the wastegate flow, just like the original lump . I'll go have a talk with my welder first...

The pre car eliminator keeps the flow directly after the turbo intact since it uses the original downpipe. So everything points to this, hence the clever but expensive design of the Knox pipe!

Don't worry, we'll solve this together, but perhaps it is wise to keep everything in one treat ?

[norman lovie]

i have a 2.5 with a precat eliminator, switcher , ported to 21mm never had overboost with this set up,

i had overboost with just the exhaust fitted, i fitted the chip and it helped, its worth a go doesn't take long

thats pointing towards the ecu - boost controller - control parameters - how it responds to the observed rapidly rising pressure - the chip may have re mapped this response which is good stuff because most don't bother
if you don't have the response parameters matched to the change in hardware, you get pressure overswing until the system is able to react and bring it back via opening the actuator - unfortunately we don't have access to modify these parameters ( time to think about a mappable ECU)- but you can play with a few mechanical aspects
you can open up the choke in the boost controller, this makes the response to the actuator quicker ( BBR use this the opposite way i.e. they choke it back to hold back opening the actuator - i.e. pay a fortune for a small bit of plastic with a hole in it)
you can also fit a choke - as a damper - to the MAP sensor - if you can slow down the MAP sensor response until the over boost swing stabalaises then you can stop it triggering over-boost fuel cut
but if the overboost is actual creep and it's sustained then both these measures will be overcome and it will still trigger over boost cut - just a fraction of time later

try a longer hose with a small choke in it feeding the MAP sensor - i,ve seen this done by simply putting a tie wrap round the hose and experimenting with the tightness of the tie wrap to see if you can damp out the over swing

[HJ2]

Hmmzzz.. It's only in the top range that the overboost occurs. You can see the pressure slowly rise till cut-off level and the curve is already flattening or better at the top. So the system being to slow to respond.... i don't think so.

[norman lovie]

Hmmzzz.. It's only in the top range that the overboost occurs. You can see the pressure slowly rise till cut-off level and the curve is already flattening or better at the top. So the system being to slow to respond.... i don't think so.

ok that is classic creep,versus over-swing
there is a device that can help - a blow off valve / dump valve - a bit more advanced than the typical vacuum operated one that vents on a closed throttle - you get ones that also have an adjustable upper boost vent level - quite a good additional safety device

[HJ2]

There are several topics about this, but the use of a dump valve would definitely not be my cup of coffee to cure things like overboost.
My overboost returned only after the fitment of the Piper downpipe. Nothing else changed.
The goal of the custom pipe is to improve overall flow, not change the balance between core and bypass flow. I want to first try to change the downpipe to my best knowledge.. If that does not work, Then the total flow is just to much and the balance is not the problem. I then will try over-porting.

[ccb056]

I've been doing some calcs and I think 20mm is way to small for a 2.25" system with PCE.

You want 22mm for 2.25" with PCE and 24mm for 2.5" with PCE.

Here's why:

Stock exhaust diameter is 2" and stock wastegate is 16mm. Let's assume that the precat is a 30% flow restriction (not sure on this, just the number I used). This means the the precat changes the effective area of the stock exhaust from 2027 mm2 to 1419 mm2. The area of the wastegate is 201 mm2. The ratio of stock areas (exhaust/wastegate) is 7.1

To maintain the same flow characteristics, you want the upgrade to have the same ratio.

A 2.25" pipe has an effective area of 2565 mm2 (with PCE). To get the the stock 7.1 ratio you need a wastegate diameter between 21mm and 22mm (7.4 and 6.7).

Of course, a better estimation of the precat restriction would yield more accurate wastegate diameters.

[HJ2]

Good input.!

[whippit]

The science doesn't explain my setup though, 2.5 ported to 21mm never had overboost at all ,
you've not much metal to play with in the standard flap, i had about .8 around the flap going to 21mm,
its doable i suppose enlarging beyond this point, a little engineering needed though,

[HJ2]

Whippit,

I think the pre-cat eliminator does not change the balance. The Piper downpipe does, since geometry is different (balance is worse) between turbo exit and exhaust section. That's why your setup differs! (the downpipe is the same)

For the record: I Ported to 21-ish mm. I have the 2.25" exhaust Empty pre-cat housing, no main cat and an Everest Chip.
No overboost issues, until i changed to the Piper downpipe.

[steve matthews]

Take the pre-cat out of the equation.
If the wastegate is not functioning due to flow restrictions you get overboost.
Trying to modify the system prior to the down pipe is not addressing the problem.
A simple bench test of the flow parameters of the down pipe is in order.
In my opinion Piper should have done this prior to distribution.
Not trying to needle anybody but could you be getting more performance from this
modification if done correctly.

Steve

[HJ2]

Take the pre-cat out of the equation.

Steve

Take it out of the equation, and the Piper downpipe can change 2 things: Improve total flow (i believe that) So if everything behind is able to cope with the difference, the total balanced pressure difference will increase. = faster spool up time and flawless running if the wastegate can keep up.
Also the pipe can throw of the balance (I hope not, but it looks like it), decreasing the flow through the wastegate, but increasing the flow through the main pipe, (but combined still increase total flow) thus changing the control characteristic of the turbo control set-up for the worse... resulting in over boost.

Or am I missing something other obvious here?