Tuning Twins

Good thread guys. Have a set of twins here from E.D. going on a friends 2nd gen. Gonna be my first set tuning.
 
inline6power said:
I agree but after talking to ed, and forced they both agreed that the 1.32 housing and the 96 wheel was what my problem was so I am anxious to see if they were right. It was weird cause like I said as a single the b rocked in spool up but as soon as I put the bottom charger on it all went away. No boost leaks, so I have no clue what else would cause it to not spool. Only thing is changed was putting the bottom charger on.

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Interested in what you found out. Cant argue with those guys but it seems to me tightening up the primary turbine would bring it in quicker at the cost of spooling the secondary.
 
I won't argue that a smaller turbine on the primary won't help out. It will make a huge difference. But the larger turbine wheel will still come on strong, just a bit later in the RPM band. Still need enough fuel to drive them properly. The exhaust goes into the secondary's housing and expands, helping drive the wheel. But when it expands it loses energy, heat and velocity. Then it goes to the primary and tries to expand again to drive the wheel. I think properly matched housings on the chargers make a big difference, along with turbine size. But the mass volume of exhaust needs to be there to drive them. Wow I'm really rambling this early in the morning
 
Well all is good now. It was a couple of issues. Truck now spools around 1850 compared to 2300. Out the new turbo on, started and had a miss. Check light on. Checked and death code. Checked fuel pump and it's dead. Run to Browns, got a new vp, new raptor, put it all in late last night and wam, truck is a pleasure to drive now. Still need more fuel to get it to really spool like I want but between the new so pump, fuel pump and turbo, one of those three fixed the problem lol.

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inline6power said:
Well all is good now. It was a couple of issues. Truck now spools around 1850 compared to 2300. Out the new turbo on, started and had a miss. Check light on. Checked and death code. Checked fuel pump and it's dead. Run to Browns, got a new vp, new raptor, put it all in late last night and wam, truck is a pleasure to drive now. Still need more fuel to get it to really spool like I want but between the new so pump, fuel pump and turbo, one of those three fixed the problem lol.

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I believe it was fuel, 1850 isn't bad at all. Glad you got it worked out
 
I have a stupid question but could someone explain what you mean by drive pressure?

Thanks Jake
 
Been trying to tune newly installed twins on a 99 vp truck. S.O pump, mach 7's, edge drag comp, fass pump. 60/68/12 over an S475 billet wheel, 1.1ar. Secondary has a drive pressure style waste gate actuator. Seeing 62lbs total boost, 25lbs from the primary. Cant get them any more balanced. Adjusting the wastegate tighter or looser will alter total boost and spool up but cant bring the turbos any closer to 50/50. Best balance I have seen is 58 total with 23 from the primary. This is my first set and it has me stumped. No leaks. Truck runs good. Seeing 10lbs by 1600rpm. Need more fuel? External waste gate needed?
 
ENafziger said:
Not a stupid question, and you're not overthinking things. First off, you're way ahead of most people who just say "set the secondary at twice the boost of the primary". However, as you know, boost ratios and PR are NOT the same.

I went through this about a year ago as well, with my 62/476 install. It's somewhat hard to find helpful, technically accurate information on tuning twins (at least from what I could find). Nonetheless, here's what I've found out on mine.

You're going about it right, in that you want each turbo to share half of the "work"...and this means running equal PRs. However, from what I've experienced, it's not possible for this to happen in reality. You can adjust the wastegate on the secondary so that PRs on the two turbos match at one condition, but they won't match at any of the other conditions.

Since the secondary begins to spool much faster, its boost climbs quickly to about 10 psi before the primary begins to make a pound or two. The secondary continues to build boost faster, up to the point that its wastegate cracks. When the wastegate opens on the secondary, the primary begins to pick up speed much quicker. This (obviously) is because the primary is now receiving a larger percentage of the exhaust flow, and it's "higher quality" exaust due to the higher temperature of the wastegated exhaust...it is also beginning to get into the mass flow rate of air where it was designed to operate.

Thus, when you reach this point, the primary now begins building boost much quicker than the secondary. As such, neither of the turbos spool linearly with respect to each other. The small one spools quicker at first, and tapers off as the wastegate cracks. The big one is slow at first, and gets a kick in the pants as the secondary's wastegate opens. Because of this non-linearity, I've not found a way to maintain a constant shared PR across the speed/load operating range of the engine.

The best I've been able to do, is to set the wastegate on the secondary such that you are at a 1:1 PR ratio with the two turbos at about 75 - 80% of full horsepower. This allows the small secondary to spool quickly and get you going. At full 100% hp, the primary will be doing more work than it should; however, for daily driving, this has worked better for me. It does make the primary have a higher PR than the secondary at WOT, but it allows the PRs to be more closely matched in the 40 - 75% throttle range where I normally tow/drive/need boost at.

For an all-out-best dyno number, it may be better to match PRs at 100% load, but I've found for a daily driver/work horse, a little lower does better. For what it's worth, with my ~650 hp worth of fueling, the 476 primary never sees much more than 25 psi on a WOT run. Thus, unless you are too heavily fueled for the set of twins you have, I don't think there is much tuning to be done with the wastegate setting on the primary...as long as you aren't letting it crack before 25 or 30 psi and "wasting" exhaust energy.

Again, the above info may or may not be accurate, and may not be the best way of doing things. It's just what I've found to be true with my limited knowledge and my setup.

--Eric
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Great info Eric..

For my ATS Aurora Plus 5000 (HE351 over ATS 5000) to spool faster, I should have the waste gate open a bit sooner to dump more hot air into the larger bottom turbo?? I'm more concerned with turbo and faster boost efficiency than over all horse power gain.
 
rlawless said:
Great info Eric..

For my ATS Aurora Plus 5000 (HE351 over ATS 5000) to spool faster, I should have the waste gate open a bit sooner to dump more hot air into the larger bottom turbo?? I'm more concerned with turbo and faster boost efficiency than over all horse power gain.
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Id want the wastegate to stay shut longer to help with spoolup.
 
homewrecker said:
Been trying to tune newly installed twins on a 99 vp truck. S.O pump, mach 7's, edge drag comp, fass pump. 60/68/12 over an S475 billet wheel, 1.1ar. Secondary has a drive pressure style waste gate actuator. Seeing 62lbs total boost, 25lbs from the primary. Cant get them any more balanced. Adjusting the wastegate tighter or looser will alter total boost and spool up but cant bring the turbos any closer to 50/50. Best balance I have seen is 58 total with 23 from the primary. This is my first set and it has me stumped. No leaks. Truck runs good. Seeing 10lbs by 1600rpm. Need more fuel? External waste gate needed?
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What's the problem? Looks good to me. I saw similair boost when I had my setup close to yours. Have you checked drive pressure? That's what id worry about vs spliting the boost equally.
 
Yeah. Spoke with Chris ( E.D. ) and he says its ok for the fueling we're working with. Got a lighter spring from stainless to try on the wastegate just to see if we can get the s400 spooling a little quicker. Next time the truck is in town im gonna check the drive pressure.
 
homewrecker said:
Yeah. Spoke with Chris ( E.D. ) and he says its ok for the fueling we're working with. Got a lighter spring from stainless to try on the wastegate just to see if we can get the s400 spooling a little quicker. Next time the truck is in town im gonna check the drive pressure.
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What psi does the primary start coming on?
 
bsmith said:
Id want the wastegate to stay shut longer to help with spoolup.
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That is kinda what I thought, but then reading Eric's comment:

"When the wastegate opens on the secondary, the primary begins to pick up speed much quicker. This (obviously) is because the primary is now receiving a larger percentage of the exhaust flow, and it's "higher quality" exaust due to the higher temperature of the wastegated exhaust...it is also beginning to get into the mass flow rate of air where it was designed to operate".

I was gonna try that...

I did try it today, I took two & half turns off the waste gate pressure and it seems to spool pretty good but not sure if it's faster, but the EGT's are @ 1400* @ WOT where before 1250* was maxed... But I'm still more concerned about towing than HP. Gonna try two turns past (tighter) than ATS's settings (is 7.5 turns) next time (going 9.5)..

I don't want to over do the drive pressures though..
 
rlawless said:
That is kinda what I thought, but then reading Eric's comment:

"When the wastegate opens on the secondary, the primary begins to pick up speed much quicker. This (obviously) is because the primary is now receiving a larger percentage of the exhaust flow, and it's "higher quality" exaust due to the higher temperature of the wastegated exhaust...it is also beginning to get into the mass flow rate of air where it was designed to operate".

I was gonna try that...

I did try it today, I took two & half turns off the waste gate pressure and it seems to spool pretty good but not sure if it's faster, but the EGT's are @ 1400* @ WOT where before 1250* was maxed... But I'm still more concerned about towing than HP. Gonna try two turns past (tighter) than ATS's settings (is 7.5 turns) next time (going 9.5)..

I don't want to over do the drive pressures though..
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True but if it opens too soon it slows down the spool time.
 
rlawless said:
That is kinda what I thought, but then reading Eric's comment:

"When the wastegate opens on the secondary, the primary begins to pick up speed much quicker. This (obviously) is because the primary is now receiving a larger percentage of the exhaust flow, and it's "higher quality" exaust due to the higher temperature of the wastegated exhaust...it is also beginning to get into the mass flow rate of air where it was designed to operate".

I was gonna try that...

I did try it today, I took two & half turns off the waste gate pressure and it seems to spool pretty good but not sure if it's faster, but the EGT's are @ 1400* @ WOT where before 1250* was maxed... But I'm still more concerned about towing than HP. Gonna try two turns past (tighter) than ATS's settings (is 7.5 turns) next time (going 9.5)..

I don't want to over do the drive pressures though..
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Your secondary spools much sooner than the primary. If you wastegate it too early, you won't have as much mass flow over the secondary turbine to get it lit up harder, and will still be under the threshold for the primary.
 
Tate said:
Your secondary spools much sooner than the primary. If you wastegate it too early, you won't have as much mass flow over the secondary turbine to get it lit up harder, and will still be under the threshold for the primary.
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I have set the WG set to start opening @ 25 PSI = 6 turns (ATS said 7.5) and it is completely open about 37-38 lbs...

It seems to run best there.. Anything lower then I can see a constant smokey haze at lower rpm even at 10-15 lbs. of boost. (SW7 @ TM3)

ATS has it setup for the WG to gets its pressure from the bottom turbo... I don't think the top turbo is @ 25lbs. when the WG starts to open, I believe it would be more, but how much? I'm gonna put a gauge on it to find out.

I figure each turn of the rod equals about 1.6 lbs. starting at the lowest setting you can go, which is 15 lbs.
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I did some reading in diesel tech magazine, they had the gate on the secondary set at 60 psi on a tow twin setup. I had mine set at 25 and it sucked balls, set my gate to stay shut longer and wow what difference! No where near as hot either.
 
I messed around with my WG settings today after putting a gauge to the primary charger I could tell what my over all boost was when the primary charger started opening the WG on the secondary charger...

I changed the WG to start opening @ 29-30lbs. it's fully open @ 40lbs in which it spooled the primary charger way faster than before when set to open @ 24lbs. The HE351 top turbo is working in its max efficiency range of 30-40lbs. when the primary relieves it of its duty... I can see why ATS uses 7.5 turns on the WG rod, it starts opening the WG @ 26-27lbs. I went 9 turns WG starts @ 29-30lbs.

Total boost jumps right up to 40lbs. which is when the primary charger is opening the WG @ 29-30lbs... The secondary then lights off and Oh Boy it's on then... It pulls very hard and steady til the top end then runs outta fuel using SW4 settings...

Primary charger maxes out around 45lbs and total boost is 55-60lbs. it keeps building but I let off of it (going to fast for me).

Smarty @ SW4, TM3, TQ & RP Default spools very very fast and the EGT's push right on up to 1500 around 110 MPH I then let off the pedal... I don't want to see 1500*
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