4psi Jump on the 2-3 Shift???
10-17-2009, 01:19 AM
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4psi Jump on the 2-3 Shift??? Ok, so while doing some tuning tonight, it was discovered that on a WOT pull, I am seeing a steady 7-8psi all through 1st and all through 2nd, and then as soon as it makes the 2-3 shift you can watch the boost jump right up from 8-12psi...
Keep in mind this car is stock drive train wise...stock gears stock converter, so on the 2-3 shift we are seeing it drop from our 5,800 shift point to roughly 3,800....We are guessing that its the fact that the Turbo is moving so much air that when we hit that shift and the RPMs drop so far, the motor cant use up the air fast enough and we end up jumping the boost and of course lean out....(Im fairly sure that the psi will again fall as the RPMs come back up, but I didnt verify that last night)
The car in question has a Single MP T70 with a 38mm TiAL Wastegate....
I figure I have two options.... ONE buy a TiAL 44, or TWO, Buy a converter so my RPMs dont take such a dive.....
Thoughts?
Keep in mind this car is stock drive train wise...stock gears stock converter, so on the 2-3 shift we are seeing it drop from our 5,800 shift point to roughly 3,800....We are guessing that its the fact that the Turbo is moving so much air that when we hit that shift and the RPMs drop so far, the motor cant use up the air fast enough and we end up jumping the boost and of course lean out....(Im fairly sure that the psi will again fall as the RPMs come back up, but I didnt verify that last night)
The car in question has a Single MP T70 with a 38mm TiAL Wastegate....
I figure I have two options.... ONE buy a TiAL 44, or TWO, Buy a converter so my RPMs dont take such a dive.....
Thoughts?
10-17-2009, 11:12 AM
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Do you agree though that if the shift extension was alot less (Converter), it would probably hold ok? I dont see why it wouldnt... The 38 really does control it fine until that shift extension on the 2-3 shift...
Last edited by LS1Silverado05; 10-18-2009 at 01:47 AM.
10-19-2009, 01:46 PM
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100+ Views and only 1 response??
Does anyone agree OR disagree with me that throwing a converter in the mix should help alleviate the problem since it only happens on that drastic RPM drop...
Does anyone agree OR disagree with me that throwing a converter in the mix should help alleviate the problem since it only happens on that drastic RPM drop...
10-19-2009, 01:59 PM
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Here's my opinion. The wastegate should not allow any more boost than what it is deisgned for (spring and or/controller). I would assume you see boost creep due to the turbo being under a high rpm spin (upshift, rpms drop with current pressure) which loads the turbo and the wastegate cannot release pressure fast enough.
2 things.
1. Wastegate too small.
2. Wastegate Plumbing/Routing/Placement
Have any pics of the routing?
2 things.
1. Wastegate too small.
2. Wastegate Plumbing/Routing/Placement
Have any pics of the routing?
10-19-2009, 10:01 PM
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I agree 100% with your opinion.... and I already know about the different mounting situations as well as the limits of the gate...(mine not being optimal with roughly an 80* mounting, but it IS reading both pipes, and it is NOT going against flow...but its not a perfect situation as far as the gate goes)
My question is this: since it is clearly a function of the rpm drop during the shift extension of the 2-3 shift, and a converter would drastically cut the drop in RPMs, and allow the rpms to stay up (as they do on the 1-2 shift), wouldnt you think that a converter would effectively give me that breathing room on the gate at its limits at the lower psi setting?
Im in no hurry to throw on a bigger gate since usually even a gate that has trouble controlling lower psi's will do fine controlling higher psi....
I think I might throw a converter in and post my findings....cant hurt, Ill be wanting a converter soon anyway...and if it doesnt work, Ill throw on a TiAL 44 minimum.
Thanks for the post....
My question is this: since it is clearly a function of the rpm drop during the shift extension of the 2-3 shift, and a converter would drastically cut the drop in RPMs, and allow the rpms to stay up (as they do on the 1-2 shift), wouldnt you think that a converter would effectively give me that breathing room on the gate at its limits at the lower psi setting?
Im in no hurry to throw on a bigger gate since usually even a gate that has trouble controlling lower psi's will do fine controlling higher psi....
I think I might throw a converter in and post my findings....cant hurt, Ill be wanting a converter soon anyway...and if it doesnt work, Ill throw on a TiAL 44 minimum.
Thanks for the post....
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10-19-2009, 10:19 PM
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i wouldnt be so much worried about youre gate as i would try and figure out why youre losing signal strenght to the gate so it can hold it from spiking as it did. ive seen gates only release 1 side of the motor have solid boost control with no spikes or creeps. according to this it goes totally against everyone's theory but you can look at 75% of the turbo setups on trucks and they only vent one side of motor and have no issues.
if youre losing signal strenght then that will cause youre issue, are you using the intake for reference or turbo? i prefer using the turbo for signal source.
are you using a boost controller or going off the spring
if youre losing signal strenght then that will cause youre issue, are you using the intake for reference or turbo? i prefer using the turbo for signal source.
are you using a boost controller or going off the spring
10-19-2009, 11:00 PM
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Signal Strength huh? Never really thought about that... I have the reference plumbed into the intake pipe after the intercooler since I wanted to read the psi after the pressure drop of the IC....it goes through a Hallman Pro MBC, and straight down to the gate... ]
10-20-2009, 03:12 PM
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Signal Strength huh? Never really thought about that... I have the reference plumbed into the intake pipe after the intercooler since I wanted to read the psi after the pressure drop of the IC....it goes through a Hallman Pro MBC, and straight down to the gate... ]