Compound p/r understanding

[Chevy1925]

Is your egt going up?

Imho, you need more out of the ihi and less out of the 475. The pressure ratio on your ihi is too low so it aint doing much at all and your missing out on boost

I have a air pressure regulator on my boost line to the ihi. Its basically shut off right now and my pressure ratio is 2.78 on the 483 and 1.68 on the ihi. Im actually going to crank the wastegate adjustment arm down more than the 5 turns banks so i can get more out of the ihi (if the wastegate has no air to it and its still opening, drive pressure is opening it for me) Originally i thought it was maxing out but she aint.

This is on the tow tune though

 

[N2BRK]

My ihi P/R rises to 1.88 (1.62 on the s475 at that point), and then as the wastegate opens it drops. I show that as 12.76lbs of boost.

At the highest boost I’ve logged (51.587), I was 1.43 p/r on the ihi and 3.15 on the s475.

I get what you’re saying about sharing the load “better” , but here’s where I get confused! Let’s say that I make the same 51.587lbs of boost, but the s475 only makes 25lbs. Now my IHI is making 13.38lbs and its P/R is 1.9. Great! Except if you look at the S475, its P/R has dipped to 2.36. Go look at the compressor map and my efficiency has dropped from .74 to .68. - 6% eff loss. Did I make that up with the IHI? Without having any idea of the lbs/min flow of the IHI, I’m stuck. I can’t really understand much from its map.

What I can guesstimate is that knowing the Ihi shits the bed past 31psi as a single, and that P/R would be 3.1… maybe it’s 20lb/min? That would put it in overspeed according to the map. So if I go back to my highest recorded Ihi and ASSume 8-10 lbs/min… I’m not in a great spot for efficiency but more P/R actually hurts me not helps. I need more volume flow to get Gilligan on a higher efficiency island! If I’m wrong and flow is more like 14lbs/min, then I am smack dab on the highest efficiency island for the IHI. without knowing flow, I’m presently stuck.

 

[N2BRK]

and I just realized that the IHI idea at the end is BS. Max effort at 31psi is like 500hp and that's more like 2x the lb/min I guesstimated. It's so far off the IHI map that it threw me for a loop and I don't know WTF to think now. LOL

 

[N2BRK]

I just found a thread on a forum that mapped our LB7 turbo and it's nothing like the one I saw here. It makes things make a lot more sense. I still can't upload here, so Post 28 link: https://www.rs25.com/threads/ihi-turbo-identification-and-compressor-map-help.198104/page-2

Now I can see more clearly. SO a Max effort at 3.1 P/R and a hair over 50 lbs/min is right on the max compressor speed line on the linked map. I think that gives me some trust in what I'm seeing.

Although there's no efficiency islands drawn on that map, I think that my spread from 1.43 to 1.88 has me in a very efficient part of the map. I could possibly do better with a little more boost, but not much. A little too much more and I'll be on the surge line. I actually think it's telling me to stop here.

 

[Chevy1925]

Splitting hair lol. You need the ihi to compound the air or it becomes a restriction for the 475.

Your never going to stay in the optimum efficiency range, the idea is to have the line for cfm to cross through the center of the efficiency map for the hp and rpm range. Its never going to be perfect.

Its not like your boost is falling off in the upper rpm range (though it kinda is cause the ihi is dropping boost because you took its drive pressure away.)

 

[Chevy1925]

I just found a thread on a forum that mapped our LB7 turbo and it's nothing like the one I saw here. It makes things make a lot more sense. I still can't upload here, so Post 28 link: https://www.rs25.com/threads/ihi-turbo-identification-and-compressor-map-help.198104/page-2

Now I can see more clearly. SO a Max effort at 3.1 P/R and a hair over 50 lbs/min is right on the max compressor speed line on the linked map. I think that gives me some trust in what I'm seeing.

Although there's no efficiency islands drawn on that map, I think that my spread from 1.43 to 1.88 has me in a very efficient part of the map. I could possibly do better with a little more boost, but not much. A little too much more and I'll be on the surge line. I actually think it's telling me to stop here.

5 years ago, i coulda told you by memory how to plot out the map using excel but ive not done it so long, I’d have to reteach myself. I had to do this when i turboed the tracker. But that link is pretty much how it turns out when you plot it. You need to stay out of surge but dont fall off the far right side at peak rpm

 

[N2BRK]

I’ll share my excel formulas and spreadsheet. I’m also going to get more sample data and let it eat in another gear higher too .

Tomorrow is power steering pump first though. Damned leaves today!

 

[kidturbo]

I don’t think you can just add them to come up to total boost, since the secondary isn’t breathing at 14.7.

Not a compound guy, but have a little data on where the 475's lite in a straight single, or won't should say. The NLX's on Voodo spool up to about 14-17psi and seem to hit a wall that I can't overcome in the boat. In 1:1 high gear ratio, out of the hole it's 0 psi dead. But low gear at 1.15:1 is where I hit that wall. Once I break the prop load, and they spool to 21psi , they light off nicely and always maintain. The single 476 if being technical, NLX wheel performs happy 2200-4500R in a fully loaded world. Long as I keep it above 2100R and 18PSI, I can Fuel both engines back to life under any conditions. Moment one drops below 17, back to low gear, or she's rolling coal till the cows come home. 1700+ on all 4 probes. A shot of NOS right there would sure be handy.

So just guessing, but your 14.7 value not breathing sounds spot on. I'm going with 17 or above on your stock 457. Gauge values are trivial when you feel one laying on that hump, and just two psi is all ya need. I'd start high and work my back down to on that gate for driveability comfort. Burm more fuel keeping the stock one lit, but resonse should be crisper also.

 

[Bdsankey]

Personally I think your gate is opening WAY too early and you are missing out on a ton of power/midrange from the IHI.

I know it's your first time but you should be seeing way more out of the IHI overall.

 

[N2BRK]

Oh wow! Good to know!! I do have the wastegate tightened a lot vs stock, but I can certainly go more!

Fwiw - I used the wastegate hose to find the crack pressures. My stock is 7psi and max open was crazy like 90psi. My last adjustment to my stock replacement turbo’s adjustable wastegate brought it to a crack of 14psi.

 

[Chevy1925]

Oh wow! Good to know!! I do have the wastegate tightened a lot vs stock, but I can certainly go more!

Fwiw - I used the wastegate hose to find the crack pressures. My stock is 7psi and max open was crazy like 90psi. My last adjustment to my stock replacement turbo’s adjustable wastegate brough lt me to a crack of 14psi.

Don’t crank that down anymore. Instead, you need to put a regulator on the hose between the boost source and the Westgate.

You crank that waste gate down too much and you’re gonna put the spring into spring bind and it’s not gonna open enough or open at all.

 

[N2BRK]

I remember Mark saying some people hook the wastegate to the primary so it sees less signal. That’s an option too.

Before going that route, i have a PPE Boost valve that I could stab in and log the difference, leaving all else alone.

 

[Chevy1925]

You can try it, but you’re probably gonna see next to no difference.

Just get an Amazon tiny air pressure regulator.

 

[N2BRK]

No new data yet. Just attaching the excel file from the last log. I think I'd like to add a drive pressure sensor too.

 

[gmduramax]

I remember Mark saying some people hook the wastegate to the primary so it sees less signal. That’s an option too.

Before going that route, i have a PPE Boost valve that I could stab in and log the difference, leaving all else alone.

Ppe boost valve just dumps pressure out the fitting and it has a smaller opening. Do a regulator.

 

[Bdsankey]

I 3rd a cheap regulator. It makes tuning in the gate an absolute breeze compared to using a boost increase valve.

 

[N2BRK]

This ok?

Amazon.com

 

[2004LB7]

This ok?

Amazon.com

Seems like the operating range of that regulator is too high and will limit your regulation ability to the bottom of the gauge

Maybe something like this will be easier to use https://www.amazon.com/dp/B0D4L58NJ7

 

[Chevy1925]

This ok?

Amazon.com

Yup, pretty much what mine is

EDIT, either would worn just fine. Mine is a 150psi one

 

[N2BRK]

Ordered. Thanks