What are your thoughts on Boost regulated cut outs?
Originally Posted by vw1320
Thats the problem with any of the boost vacuum activated cutouts - if you set them to open under boost they are too slow responding. If you set them to open under low/no vacuum they might open when you don't want them to (getting on it but not planning on seeing boost, etc.)
If a cutout is what you want (I prefer a free flowing but quiet exhaust all the time) get one of the electric ones. I would recommend getting the car tuned with them both open and closed so as to make sure its safe.
If a cutout is what you want (I prefer a free flowing but quiet exhaust all the time) get one of the electric ones. I would recommend getting the car tuned with them both open and closed so as to make sure its safe.
Teching In
Joined: Jun 2007
Posts: 32
Likes: 7
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.
Originally Posted by 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.
TECH Fanatic
Joined: Jul 2002
Posts: 1,218
Likes: 1
From: MI
Originally Posted by 2000 Tran Zam
So would it be two different tunes then... one for open cut out and one for it closed? Thearetically it would require two different boost settings due to back pressure right?
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.
Teching In
Joined: Jun 2007
Posts: 32
Likes: 7
Originally Posted by 2000 Tran Zam
qtp builds this stainless steel one for 75 bucks :
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.
Last edited by kp; Jun 6, 2007 at 11:44 AM.
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.
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.
TECH Fanatic
Joined: Jul 2002
Posts: 1,218
Likes: 1
From: MI
Originally Posted by boostedinaz
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.
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.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Originally Posted by boostedinaz
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.
Originally Posted by NicD
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.
Originally Posted by boostedinaz
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.
Last edited by NicD; Jun 6, 2007 at 12:56 PM.
Originally Posted by NicD
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.
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).
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).
Originally Posted by RealQuick
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).
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).
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.
Originally Posted by 2000 Tran Zam
You would think they would make a spring that can release enough pressure fast enough... whether its electrical or mechanically setup...
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.
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.
If your car is tuned with the exhaust, THEN you open it up......hello more boost at all RPMS, and a serious lean issue.
Originally Posted by ninetres
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.
If your car is tuned with the exhaust, THEN you open it up......hello more boost at all RPMS, and a serious lean issue.
So in general its better to tune for it open, and then you can always close it and run less boost...
Originally Posted by 2000 Tran Zam
Like I said Im sure that is exactly what happened, lol.
Originally Posted by NicD
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.
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.
