2000 Tran Zam

iTrader: (2)

well right now im running open 4in downpipe... and I have a 4 in exhuast all the way back out the passenger side... I just wanna have some options so it can be quieter when I need it.

vw1320

Well in that case a cutout would suit you well. I am not sure who makes a 4" one but just a word to the wise on dmh and a couple of other ones - the motors tend to losen up and then the butterfly jams. in a half open position. I would recommend loctite on the bolts that hold the motor to the cutout as a precaution.

2000 Tran Zam

iTrader: (2)

qtp builds this stainless steel one for 75 bucks :

52172

iTrader: (2)

QTP was working on a 4" electric cutout and it should be available now. QTP make good cutouts.

Mike 01WS6

No, just tune with the cutouts opened. When you cap it up the car will run a tad richer, however that in itself is safer anyways.

My car was tuned with the cutouts uncapped, it may run a little richer and not be an optimal tune w/ the cutouts closed, but then whats the difference?...it's not gonna run optimally with the cutouts closed anyways.

vw1320

I did a little digging and qtp and dmh both list an electric cutout in 4".

QTP:
http://shop.quicktimeperformance.com...ct_detail&p=27

DMH:
http://www.nonsponsorlink.com

I can't comment on the QTP but as I said earlier the DMH is know for the motor loosening up from time to time. They do offer a 4 year warrenty and are pretty good at honoring it but who wants to deal with shipping parts back and forth and having downtime? If you don't mind the getting under the car and uncapping it by hand the manual one will do the job and technically flow better as there is no butterfly and shaft in the flow path. You never have to worry about the manual one sticking either.

Hope that helps.

boostedinaz

iTrader: (2)

Perhaps I am missing something here, but the amount of max boost shouldn't change even with the cutout open. If the boost controler is set at 15 PSI then when it hits 15 PSI it should open the WG. With less exhaust it will reach that 15 PSI quicker, but it should still open at 15 PSI regarless. Unless the WG path is restricted in some way and the added flow is simply causing creep I see no reason for the max boost to change.

I set my DSM at 20 PSI with full exhaust, then when I changed gear oil I had to drop the back portion of the exhust leaving me with a short DP only. I dorve the car for a day just for fun and my max boost never went about the previous 20. It would spool quicker but never went past the preset limit. It did this with both a manual boost controler and a electric.

Mike 01WS6

It would seem that way in theory, but on my car and many others, we gain boost, hp, and lessen spool time. You're also comparing the air demands of a 2.0L to a 5.7L or greater.

NicD

iTrader: (7)

It's not about the WG path being restricted, it usually only happens when the wastegate can not bypass enough air to keep the boost level down when you remove a restriction. For example, on my car I have a relatively restrictive exhaust for my power level and that's why I also have a dump that I can open and close for when I want to just cruise or push it when racing. When my cutout is closed I have quite a bit of backpressure and the boost stays right where the wastegate spring tells it. When the dump is open and I don't have that backpressure on the turbo it really starts to come alive and the wastegate can't bypass enough air so my minimum boost level rises a couple of psi. It can also affect your boost controller settings since most boost controllers just use a solenoid duty cycle percentage to relate to boost levels and that will also change when you decrease backpressure significantly. It's not a max boost thing but a minimum boost problem. Whether the WG is dumped to atm vs rerouted into the exhaust will also cause a different consistancy.

boostedinaz

iTrader: (2)

So basically it is boost creep caused by an under sized WG. That was my original point just poorly worded. So if someone had a proper setup, WG wise, this wouldnd't be an issue.

NicD

iTrader: (7)

Not necessarily, the minimum boost level may stay the same from a large enough WG but it can still cause a difference in the duty cycle required of a boost controller for a given boost level (for example) causing your low boost setting of 10 psi to now become 12 psi.

boostedinaz

iTrader: (2)

If you are using an electronic boost controler.

RealQuick

iTrader: (14)

perhaps with a restrictive post turbo exhaust, this causes a slower spool time which allows the wastegate to have a certain time period to evacuate exhaust for boost. Now the post turbo exhaust is not a restriction anymore, the turbo spools faster and the wastegate has less time to evacuate the exhaust, so you get a boost spike that is a few psi higher. It should level back off though to whatever the boost setting is.

This spiking is not boost creep. Boost creep is when you increase in psi above the setpoint as you increase in rpm... (whether or not you have a restricive or free pst turbo exhaust). This shows as the volume of exhaust gass increase the wastegate isnt capable of bleeding it all off...

These two circumstances seem similar (oh, I am just speculating in my first paragraph on why I think the psi spikes up).

boostedinaz

iTrader: (2)

That is the way I have seen it work. When I drove with minimal exhaust in my car with a manual boost controler it was set at 20 but would have a quick spike to about 22 then instantly settle at 20. With my electric boost controler the spike was not noticed at all.

Like you stated creep and spiking are two different things. A spike can last for a quick second and then settles. The creep is basiclaly an uncontrolable building of boost.

2000 Tran Zam

iTrader: (2)

You would think they would make a spring that can release enough pressure fast enough... whether its electrical or mechanically setup...

boostedinaz

iTrader: (2)

Well that's not really the problem. The WG spring is still at the mercy of a boost controler controling it. If everything is properly sized the stepper motor may still have a hard time keeping boost consistant at low boost levels. Personally I have never seen this even on turbo charged big blocks with a ProFecB it simply did its job, but it seems this is a common problem for F bodies.

If you are just on the WG spring itself with no boost controler then you shouldn't have this problem unless there is some restriction in the system.

ninetres

iTrader: (35)

I had my car tuned with a 3 bar and open 4" DP. When I close my cut-out (elec 4" qtp), it just runs real rich, spools for an hour, and makes a couple pounds less boost.

If your car is tuned with the exhaust, THEN you open it up......hello more boost at all RPMS, and a serious lean issue.

2000 Tran Zam

iTrader: (2)

Like I said Im sure that is exactly what happened, lol.

So in general its better to tune for it open, and then you can always close it and run less boost...

NicD

iTrader: (7)

No that's not what happened. You were running too much boost for 91 octane/timing and probably detonated when you pulled off the exhaust and ran more boost. The speed density setup on your car compensated just fine with fuel, it wasn't lean.

2000 Tran Zam

iTrader: (2)

Ah, ok, I didnt know if the tune was able to compensate for the fuel or not.

Ya, next time round Im running a minimum of 91/101 mix all the time...

I finally dropped the car off at keiths last night, lol. Hes gonna try to pull the motor today, if not tuesday and let me know whats going on.

Hopefully its just one piston that needs to be replaced so I dont have to balance and blueprint everything again.