Using the stock turbo & s400 or k-31 for twins

I wanted you to tighten up the bottom turbo's wastegate to experiment. You can fiddle all you want with the top turbo. But if the primary turbo is gating too soon, it will not provide enough overall airflow to meet your HP and EGT needs.

Why not tighten up the gate to where you get 32-35 out of the GT42? Do this and I'm waiting to hear back about your new found power, lower hill climbing egt's and identical or slightly higher drive pressure.
 
Big Blue24 said:
I wanted you to tighten up the bottom turbo's wastegate to experiment. You can fiddle all you want with the top turbo. But if the primary turbo is gating too soon, it will not provide enough overall airflow to meet your HP and EGT needs.

Why not tighten up the gate to where you get 32-35 out of the GT42? Do this and I'm waiting to hear back about your new found power, lower hill climbing egt's and identical or slightly higher drive pressure.
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Blue, I understand to tighten up the gate on the bottom, but i don't understand what that will do? Can you elaborate more details. thanks
 
Big Blue24 said:
I wanted you to tighten up the bottom turbo's wastegate to experiment. You can fiddle all you want with the top turbo. But if the primary turbo is gating too soon, it will not provide enough overall airflow to meet your HP and EGT needs.

Why not tighten up the gate to where you get 32-35 out of the GT42? Do this and I'm waiting to hear back about your new found power, lower hill climbing egt's and identical or slightly higher drive pressure.
Click to expand...

I'm not so sure that that range out of a gt42 will get much... I think over 27-28 psi is asking too much... just an opinion from experience. A gt4202 (biggest compressor) is good for about 90-95 lbs/min IIRC.
 
Yeah something is seriously wrong with my stocker/s400 i could hit 50 psi easy...

How tight is your spring? the wg controller from nathan.. and your boost numbers need to be 2 to one meaning if your seeing 30 psi on the top charger the bottom needs to be 15 psi.. right now you are over working your bottom charger.. Like i stated before with the smarty, stock sticks, stock cp3 i rolled 580 on a dynojet... if you want I can pm you my number and try to help ya... Tuning twins is a lot of work took me three days to get my new 62/71/13 running in tune and I am not 100% there eaither...:rockwoot:
 
luvinacummins said:
Yeah something is seriously wrong with my stocker/s400 i could hit 50 psi easy...

How tight is your spring? the wg controller from nathan.. and your boost numbers need to be 2 to one meaning if your seeing 30 psi on the top charger the bottom needs to be 15 psi.. right now you are over working your bottom charger.. Like i stated before with the smarty, stock sticks, stock cp3 i rolled 580 on a dynojet... if you want I can pm you my number and try to help ya... Tuning twins is a lot of work took me three days to get my new 62/71/13 running in tune and I am not 100% there eaither...:rockwoot:
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I tightened up the bottom gate to 26 psi it was at 29-30. This did allow me some improvement tuneing the top charger. 1 st run with the top gate turned almost all the way out was a strong 1400 deg and a max of 50 lbs of boost. 2nd run, I turned it almost all the way in to about 1/4 - 1/2 from bottoming and it allowed me to run 1250-1300 and 55 lbs of boost. 50 lbs came very quick and easy. The remaining 5 psi it had to work. I don't have my drive pressure guage so I couldn't check it. Overall egts seem a little cooler from before and it's 70 deg here. For the most part it seems better. I think turning the primary down to 24-25 will be where it should be and still allow me to make the change on top to get 60psi.
 
OSCI, hope your tuning goes well. I have an interrupted question here from the first page. JFlagg posted that the exhaust housing could be changed on the factory turbo for cooling. Why do I never hear more about this and who dose the mod?
 
Racing4funn said:
OSCI, hope your tuning goes well. I have an interrupted question here from the first page. JFlagg posted that the exhaust housing could be changed on the factory turbo for cooling. Why do I never hear more about this and who dose the mod?
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Other than loosing spool up for me, I didn't think there was anything available for the holset other than stock. I have heard that someone here in the NW is modifing the stock turbos but it's as much as just upgrading to a larger charger anyway.
 
On the Garrett web-site, the GT4202 is good for max lb/min airflow at ~3.5 pressure ratio:

http://www.turbobygarrett.com/turbobygarrett/catelog/Turbochargers/GT42/GT4202_731376_2.htm

http://www.turbobygarrett.com/turbo...argers/gt42_images/GT4202_731376_2_comp_e.gif

3.5 PR is ~ 35 psi gauge pressure at 14.5 psi atmospheric pressure feeding the GT4202 and that is where I have my GT4202 gated at in conjunction with the Super B top turbo.

You can get higher boost (higher PR) out of the GT4202 according to its compressor map, but the airflow starts dropping.

Doesn't the stock Holset gate only 3 cylinders? If so, are you measuring the really high drive pressures on the gated or ungated cylinders?

Before you ask... I haven't measured drive pressures yet with this Super B/GT4202 combo, but I am not worried since my prior smaller primary turbo setup (BD twins) was ~1:1 drive:boost up to ~55 psi. The Super B (HTBG) gates all 6 cylinders.
 
metal_miner said:
On the Garrett web-site, the GT4202 is good for max lb/min airflow at ~3.5 pressure ratio:

http://www.turbobygarrett.com/turbobygarrett/catelog/Turbochargers/GT42/GT4202_731376_2.htm

http://www.turbobygarrett.com/turbo...argers/gt42_images/GT4202_731376_2_comp_e.gif

3.5 PR is ~ 35 psi gauge pressure at 14.5 psi atmospheric pressure feeding the GT4202 and that is where I have my GT4202 gated at in conjunction with the Super B top turbo.

You can get higher boost (higher PR) out of the GT4202 according to its compressor map, but the airflow starts dropping.

Doesn't the stock Holset gate only 3 cylinders? If so, are you measuring the really high drive pressures on the gated or ungated cylinders?

Before you ask... I haven't measured drive pressures yet with this Super B/GT4202 combo, but I am not worried since my prior smaller primary turbo setup (BD twins) was ~1:1 drive:boost up to ~55 psi. The Super B (HTBG) gates all 6 cylinders.
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I just looked, the stocker gates all 6, there is no divider in the exhaust. housing.

I don't have any knowledge about the maps, and honestly don't know what i'm looking at/:bang Yours' is gated at 35, is that right. thanks
 
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osci, it baffles me that you achieved lower egt's by opening the GT42 gate at lower boost pressure. All that my mind could think of is possibly the lower charge air temp is creating more mass flow of air into the stock holset and thus more air molecules are being crammed into the motor.

I still think you will make more power and have better egt control by gating that GT42 at around 35 psi like metal miner pointed out.
 
My advise:

Set the primary to gate at 32-35 psi.
Try to tune the top turbo from there to find the perfect spool up, egt, and HP sweet spot.


When you tighten up the MPI spring all the way so as to keep the Holset wastegate closed till high drive pressure. When do you start to see boost pressure from your GT42 primary turbo? Do you see boost in the cold pipe when your overall boost is around 10 psi, 15, 20, where/when exactly does the GT get into the game and start making substantial boost in the coldpipe between the stages?


Secondly, I assume that by tweaking the top gate, you can control how soon the GT42 gets spooled up but bypassing exhaust around the top secondary and feeding hot exhaust to the GT. If you open up the top gate, like take the spring keeper off, can you spool the GT without the Holset doing any of the work?
 
Big Blue24 said:
osci, it baffles me that you achieved lower egt's by opening the GT42 gate at lower boost pressure. All that my mind could think of is possibly the lower charge air temp is creating more mass flow of air into the stock holset and thus more air molecules are being crammed into the motor.

I still think you will make more power and have better egt control by gating that GT42 at around 35 psi like metal miner pointed out.
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It sure would be nice if someone in the seattle area had a similar set who could show me just whats going on. I'm guessing on which way to go and each day gets more confusing.
 
Drive pressure guage is back in and I will be leaving tommorow camping. I will know if this made a change asap, once I leave my driveway.
 
We'll see, so far just driving around here 20 psi boost = 25-30 drive pressure.

Dave, For some reason i can't find my drive pressure guage and therfore had to make another one.
 
osci said:
We'll see, so far just driving around here 20 psi boost = 25-30 drive pressure.

Dave, For some reason i can't find my drive pressure guage and therfore had to make another one.
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I bet it's where you left it.

Hanging on my garage wall......

Dave
 
Since I turned the primary down I seem to be getting better results. Temps were 80 deg outside. Towing my 12k 5 th and gross 21k on flats averaged 800-900 egts. Pulling an incline 1200 egts and up to 212 wtr temps. Drive pressure is alot better, at 45 psi i had 50 lbs of drive pressure. Never ran it above 45, but at 50 before I was 75. Most of the time I ran on l-1 on my juice (375-400) hp , but didn't notice any difference on 0 and just the injectors (350) hp. Planning on turning the primary down to about 23 and see how it works along with looking into an aftermarket intercooler.
 
Any updates to this thread? How are the twins working out for you? I'm thinking about going with the stock/S400 setup myself. How much could I expect to pay for this setup?
 
metalli445 said:
Any updates to this thread? How are the twins working out for you? I'm thinking about going with the stock/S400 setup myself. How much could I expect to pay for this setup?
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Gave up on fighting drive pressure issues and much happier now.
 
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