twin tuning help

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nickg9785

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Mar 14, 2012
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ok so i have a 62/65/12 over s475 with a 1.32 ex housing. 5x.016 injectors stock 181 dvs 17.5* timing. i finished the truck last wendsday and when i drove it for the first time with the twins i was not impressed at all, it was extremley laggy. i adjusted the afc, got a little better, then i swapped out my 181's for a set of 191's egts were through the roof and smoked like a train. i tried switching out the afc spring with a tigter on but no help. would burry the gauge in seconds, so i swithched back to the 181s. now im seeing about 18-20 lbs out of the bottom turbo and about 50 overall. before with the 191's i would see about 22-23 and 55-60 overall. that seems low to me since before when i was running just a single 62 i would hit almost 55 and the truck was way more responsive. now you hit it off the line and it goes nowhere. and im not impressed with the power. i know theres more in there i just need to find it. i do not have a drive pressure gauge now so i dont know when my secondary turbos wastegate is opening. i have it blocked off now and thats the best ive been able to get the truck to feel power wise. i know it should open arounf 20-25. anyone have some tips or tricks id really apreciate it. thanks guys
 
I'm with Casey on the tuning and wastegate is opening too early. Might even try a tighter turbine housing on the primary, but plenty of setups running exactly what you've got!
 
I ran that exact setup a while back, only with 024 DVs. It ran great, spooled extremely quick. Use shop air and set the secondary gate to crack at 25psi, then fine tune it from there. I was getting mid to high 30s out of the primary, total boost was in the 80s.

A 1.10 on the primary would spool even quicker, but you'd probably need an egate. The 1.10 for the 88/96 wheel is pretty pricey and a little hard to find too.
 
Pull the cold pipe between turbos and see exactly what the 62 is doing. Tight convertor and 2 to 300 slower spool with extra turbo could make a turd out of any truck.
 
how exactly do you set the wastegate on the secondary? it has the set screw on the elbow. i took the hose off and put regulated air to it and it doesnt fully open untill i put about 40psi to it. do i just pop the rod off and legthen or sorthen the rod?
 
So it takes 40psi of air to open the gate alone. But technically while your driving down the road, you have drive pressure assisting the boost actuated diaphragm to open the gate. On top of that, you are using total boost to open the gate. So so if the gate is opening at say 30psi(with drive pressure assisting) the secondary may be pushing 18psi of boost. Just random numbers. Screw in the boost elbow to hold the gate longer. I got tired of messing with mine and went to a spring gate.
 
I took the elbow out of the comp wheel and put a plug in it. I just put the stock elbow back in one without the set screw and at now at wot the bottom turbo is pushing 18-20 and overall is like 45-50 max. I'm about to just switch to the spring style gate
 
nickg9785 said:
how exactly do you set the wastegate on the secondary? it has the set screw on the elbow. i took the hose off and put regulated air to it and it doesnt fully open untill i put about 40psi to it. do i just pop the rod off and legthen or sorthen the rod?
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At what pressure does it start to move? Mine is not fully open until 70psi, but it starts to open @ 25psi. What's your preload on the gate too? If that's too low your gate could be blowing open too early. To adjust, hold the gate closed with the rod un-attached. Now adjust the rod so it just fits. Then add 3-5 full turns for pre-load.
 
Drothgeb said:
At what pressure does it start to move? Mine is not fully open until 70psi, but it starts to open @ 25psi. What's your preload on the gate too? If that's too low your gate could be blowing open too early. To adjust, hold the gate closed with the rod un-attached. Now adjust the rod so it just fits. Then add 3-5 full turns for pre-load.
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I'm thinking its blowing open too! Show us some pics of your setup.
 
Well I checked the wastegate again and it only started to open around 40psi. So I adjusted the rod so it would start to open around 15. Now I'm making almost 28 at the bottom and just about 60 overall. Deffinatly more responsive off the line now. But still had more left in it I feel
 
ok so i did a little more messing around. if i pinch the wastegate hose off i can burry my 60psi boost gauge so i dont really know overall numbers but my primary boost drops to about 18-20 wot, before with the wastegate set to start moving at 25psi i would make 28psi out of the primary but only about 55 overall. anyone have any ideas this thing is driving me nuts.
 
You need a drive pressure gauge to see what is going on. What is the fuel pressure like at wot?
 
last time i checked fuel pressure was around 40ish wot, ill have to get a dp gauge. but say drive presure is way high what would be causing that, under fueling?
 
When I had lift pump problems my drive pressure and EGTs were not controllable. Drive pressure is very controllable on mine with the HX35 waste gate I'm using. It does sound like it just needs more tuning! A gauge makes tuning much easier.
 
nickg9785 said:
ok so i did a little more messing around. if i pinch the wastegate hose off i can burry my 60psi boost gauge so i dont really know overall numbers but my primary boost drops to about 18-20 wot, before with the wastegate set to start moving at 25psi i would make 28psi out of the primary but only about 55 overall. anyone have any ideas this thing is driving me nuts.
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So what's happening here when your wastegate opens earlier is your bypassing your secondary wheel and retaining more heat and exhaust energy in the exhaust allowing you to drive the primary harder. When you hold it closed longer your loosing drive energy and heat by forcing more of the exhaust thru the turbine wheel. This imparts less drive energy in the primary, but while driving the secondary much harder. Basically your shifting drive energy between the two turbines by adjusting the waste gate. Just tune it till you find the sweet spot. A tighter housing on the primary would likely help, and a DP gauge.
 
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