Do these numbers look right...

[IdahoRob]

Get the tightest housing they make for the 72. You need to drive it hard.

From another thread I posted incase you don't see that one. Now any boost leaks will throw these numbers so it is important to fix all leaks no matter how small.

rough formula to figure P/R's out and then boost PSI. Then you can take a look at the maps of the chargers to come to your conclusions.

(atmospheric pressure) + (overall boost) divided by (atmospheric pressure) = overall P/R
(atmospheric pressure) + (primary boost) divided by (atmospheric pressure) = primary P/R
(Overall P/R) divided by (Primary P/R) = Secondary P/R
(Secondary P/R x (atmospheric pressure) minus (atmospheric pressure) = Secondary Boost

So in your example we'll use sea level:
14.7 + 50 / 14.7 = 4.4 P/R
14.7 + 25 / 14.7 = 2.7
4.4 / 2.7 = 1.629
1.629 x 14.7 - 14.7 = 9.255 psi

 

[chevyburnout1]

I just caught that other thread so I wont try to create a duplicate post. So if I factor in my elevation where I do my average driving it would equal out to this:

(12.3 + 50) / 12.3 = 5.07 P/R
(12.3 + 25) / 12.3 = 3.03 Primary P/R
5.07 / 3.03 = 1.673 Secondary P/R
(1.673 x 12.3) - 12.3 = 8.278psi

Comp Turbo doesn't post their flow charts but comparing to a similar Garret (which charts I could find) would put the primary at the way top of its efficiency islands and the secondary barely touching its flow islands at all. That sound correct?

 

[chevyburnout1]

So for discussion sake I'm using a flow chart for a GT4294R. It shows the most efficient area around 2.5-2.7 pressure ratio. For drivability-sakes I want to drive the charger as hard as I can to get it to that effecient P/R as quick as possible, and then pop open the wastegate to keep it at that same efficient P/R?

 

[IdahoRob]

I just caught that other thread so I wont try to create a duplicate post. So if I factor in my elevation where I do my average driving it would equal out to this:

(12.3 + 50) / 12.3 = 5.07 P/R
(12.3 + 25) / 12.3 = 3.03 Primary P/R
5.07 / 3.03 = 1.673 Secondary P/R
(1.673 x 12.3) - 12.3 = 8.278psi

Comp Turbo doesn't post their flow charts but comparing to a similar Garret (which charts I could find) would put the primary at the way top of its efficiency islands and the secondary barely touching its flow islands at all. That sound correct?

Correct, in your case you need to drive the piss out of your secondary. I doubt you will even need to open the wastegate at your fueling level.

 

[chevyburnout1]

Thanks for the help Rob! I love crunching numbers like this and it's finally making sense! I just got off the phone with Comp Turbo, ordered up their .58 divided exhaust housing for the secondary charger. And the good news is he said he could almost guarantee my CT6 atmosphere charger is just fine. Said the oil leak is more than likely due to too big of an oil feed line, especially with the volume our oil pumps can put out. Going to check that out here after work. Their customer service was top notch :thumb: Can't wait to see how it'll run!

 

[IdahoRob]

Glad to help, the internet preaches bigger is better so it must be so...

Most turbos need an oil restrictor on the feed side. The Garrets we use have them.

 

[JDub]

Ball bearinf versus journal bearing plays a large role in how much oil they need

Sent from my SPH-D710 using Tapatalk 2

 

[chevyburnout1]

I mentioned restrictors and was told not to use one on their large frame ball bearing setups. Just to get the right hose on it.

 

[chevyburnout1]

So I got my .58 housing installed last night. Didn't get to put too many miles on it but I can say daily drive-ability has improved even more. Charger's feel easier to get on top of without having to manually shift it anymore. Did a quick full throttle run and total boost peaked at about 52psi with the primary doing about 17psi. So that roughly came out to a 5.22 total PR with the primary at 2.38 PR and the secondary at 2.19 PR. With those pressure ratios it plots the data right in the efficiency ranges of both turbos! Must be doing something right as EGT's wouldn't go over 1400°

The only issue that I have now is drive pressures. Running about a 2:1 ratio across the board. Is this going to be troublesome or is it just what I have to run with right now to make these turbo's drive-able at this altitude?

 

[xtremebikr04]

So I got my .58 housing installed last night. Didn't get to put too many miles on it but I can say daily drive-ability has improved even more. Charger's feel easier to get on top of without having to manually shift it anymore. Did a quick full throttle run and total boost peaked at about 52psi with the primary doing about 17psi. So that roughly came out to a 5.22 total PR with the primary at 2.38 PR and the secondary at 2.19 PR. With those pressure ratios it plots the data right in the efficiency ranges of both turbos! Must be doing something right as EGT's wouldn't go over 1400°

The only issue that I have now is drive pressures. Running about a 2:1 ratio across the board. Is this going to be troublesome or is it just what I have to run with right now to make these turbo's drive-able at this altitude?

I would try adjusting the regulator a little at a time to open the gate and see if things improve.

 

[Bonestock]

It all depends. It's generally made a point that 3k or less drop in rail from demanded will get you just about the same power, bigger drop in rail than that and power can drop off. A dyno or track will tell just where is best for your truck

X2!

 

[chevyburnout1]

New update! Craiglist supplied me with a stock intercooler off a truck with 35,000 miles and a new Allison spin on filter for $60 bucks. Figured I couldn't pass that up at this time. It held 60psi no problem but I had the usual spots welded up anyhow. Got it installed and found numerous other leaks! Three clamps, the map sensor port, and the main gasket for the intake horn had some very decent leaks. I guess with my old intercooler leaking so bad I wasn't able to test the rest of the induction system. Got all of the leaks fixed up and am now seeing about 60psi total at the top of the shifts, with drive pressure about 85-95psi (gauge bounces). EGT's wont go passed 1500° with my fueling maxed out.

 

[malibu795]

nice

 

[chevyburnout1]

It runs great. I'm curious about James suggestion of upping the turbine wheel to a larger size, maybe combining that with my .84 housing as well when I get my dual cp3's and a looser coverter. In due time though. This will work great for the winter!

 

[DBUSHLB7]

#figuringhisshitout

 

[Chevy1925]

im bumping this up as im still trying to wrap my head around plotting twins on maps.

So ive got figuring out pressure ratios down as Robs post helped alot there.

question is, how do i know where to split the flow between charger or figure that out so i can plot them? ive gone through and done a calculated lbs/min needed for say 600rwhp which is about 85.5 lbs/min (unless i messed up somewhere). how would i divide that up between chargers of my s480 and stock turbo? pressure ratios are 2.07 at the 480 and 2.12 at the stocker. 4.4 over all.

just trying to figure out exactly what im doing as i mess with the wastegate and not stare at the EGT gauge

 

[chevyburnout1]

So are you saying if your looking at both turbo maps and you know where the pressure ratio is for each one, you're curious of where horizontally the data plot will land for the airflow?

 

[Chevy1925]

So are you saying if your looking at both turbo maps and you know where the pressure ratio is for each one, you're curious of where horizontally the data plot will land for the airflow?

yes sir!

 

[MarkBroviak]

That's where the shaft speed comes into play because that is the very important piece of the puzzle that most never have that info.:thumb:

 

[Chevy1925]

Well crap! So I guess it comes down to stabs in the dark then based off pressure ratios? Or is there something else you can use to maybe narrow it a bit? I mean the p/r kinda gives you an idea but nothing defined.

Btw, I'm not asking anyone to give up secrets. I'll do the leg work if need be, just trying to have a starting place