Compound p/r understanding

[MarkBroviak]

I highly recommend moving the wastegate reference from total boost to atmospheric turbo boost to slow it down and it will also make it easier to adjust the gate accordingly. The stock gate was never designed to operate compounded so it opens way too easy in that setup. You are also looking to make half the pressure from the big turbo so for instance you would like to see 60psi total boost and 20-30psi of that should be coming from the atmospheric turbo to keep everything happy and not risk overspeed of the big turbo.

 

[N2BRK]

Thank you, Mark!

 

[kidturbo]

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

That's the best turbo advice I've heard in a long time.. Back when I earned this nickname, was running a cheap Bypass regulator teed into the waste gate on my TurboCoupe. Basically it just allows ya to dump part of the pressure between the compressor and gate. $20 regulator, tee, vac hose, and you can dial that gate from drives seat until you find your happy spot.

 

[N2BRK]

I decided to do this in 2 steps. First step was tonight. I plugged the pressure port on the IHI to WG and ran the WG to the S475 crossover pipe. No regulator in between, and no adjustment of the WG rod. I wanted to just see the effect prior to install of a regulator.

The low and midrange feel MUCH stronger. I did a little running around to check numbers and decided that it was safe to make a log similar to the prior, with the only change as noted above. 4wd, small hill, max out at about 80mph.

S475 is now contributing a max of 18psi vs 31 before! The IHI is contributing 17psi at max boost instead of 6psi. Max total boost is now 56psi vs 52psi. S475 P/R is now a max of 2.2 vs 3.14 before. IHI P/R is now a max of 2.1 vs 1.8 before.

Noteworthy - the IHI now makes max boost at the same time that the S475 does. In the prior setup, it maxed out at at just under 13psi and then the wastegate blew open and it dropped like a stone to 6psi and the S475 went ape and carried the heavy lifting.

Step 2 was to add in the regulator and adjust. Based on the above numbers showing 18psi S475 and 17psi IHI, and P/R 2..2 and 2.1, I feel like I kinda hit goal already and could skip the addition of the regulator, no? @MarkBroviak really nailed this in a KISS sorta way, LOL.

 

[Chevy1925]

You can pretty much skip it if you want. May need it of you up the fueling/tune down the road but cross that bridge when you get there

 

[Bdsankey]

This is a great thread as I plan on doing similar with my father's LB7 (SAC100%, 10mm, 64mm supercore/480, built trans).

 

[N2BRK]

I'm glad to hear that! It was a little bit of a PITA to get the info needed to do this properly. I think that a lot of guys that install these compound kits must not mess with them much. The difference between when I started to now is night and day. The tune has cleaned up a ton too.

Thinking aloud, if my replacement IHI didn't come with an adjustable wastegate, I might have been one to just leave it all alone too. The problem was that XDP sells an OEM replacement turbo with adj WG and has ZERO support on how to adjust to factory specs. It arrived with the wastegate partially open at rest, lol. They finally admitted on the phone that they have no idea what to do with it and maybe I should follow Bank's instructions to set it up, LOL.

My next step is that I'd like to add a drive pressure gauge and log that as well.

 

[MarkBroviak]

You really want to go off the deep end, get the Hewitt Industry dual needle gauges and run one for the high pressure turbo and one for the low pressure. Orange needle for drive and green needle for boost and your brain will really go ape shit when you have a visual for the data! https://hewittindustries.com/product/108-10x/

 

[N2BRK]

Brother, you’ve met me. You know I’m cross-eyed enough without that double demon-needle gauge!!!!!

I took mom to the range today to pop some cans; her 73rd birthday. Truck is strong with the new WG settings! Great drive there and back.

 

[malibu795]

You really want to go off the deep end, get the Hewitt Industry dual needle gauges and run one for the high pressure turbo and one for the low pressure. Orange needle for drive and green needle for boost and your brain will really go ape shit when you have a visual for the data! https://hewittindustries.com/product/108-10x/

Basically a repurpose dual air tank truck gauge.. I got one from ISSOPRO in my FL70 for system air

 

[N2BRK]

Airflow questions, please

I'm sitting bored with a pissed off knee from yesterday's tangle with a mudhole on my dirtbike, LOL. So I'm just mind-wandering about this... no complaints right now - far from it! It's working better than ever. Tows my little enclosed dirtbike trailer great!

I never really pinpointed where the IHI is on its compressor map, because I didn't know airflow. I think I have a good SWAG now, so I'm going to share and see if anyone can correct me or confirm that it's close enough. Maybe I can extrapolate to run this through excel and show a bigger picture in the future.

I'm just going to consider full output for now, since I don't have any way to measure airflow. I'm est airflow at 80lbs/min for this truck. Hoping that's "ok", I take the P/R of the S475 at peak output and use it to divide 80 into the corrected IHI's airflow. That comes to 80/2.25 or about 36lbs/min. At that same point, PR on the IHI is 2.17. Looking at that map that I linked to shows it about perfect on target.

FWIW if I had drive pressure monitoring set up, ( I don't yet), I think that it would be more accurate than the above, right?

One more word on the IHI compressor map. We really don't have the OEM compressor map for the lb7 turbo that I can find anywhere. There's one floating around here that I tried to use initially, but it has to be wrong. It shows about 20lbs/min before wanting to make ka-boom, but we know that it can do 59lbs/min max. The link that I used in this thread seems to be accurate, but it doesn't show the efficiency islands. So there's a lot of guesstimating here. I'd love if someone has more data to share!

 

[N2BRK]

Ok, so that map is not the lb7 it's the LML. I did more digging and found from where that guy mistakenly took that map and it's an LML. I did find another map though that seems correct - max flow looks to be about 55'ish lbs/min which seems about as I'd expect.

 

[N2BRK]

I don’t know how I missed this until now, but something hit me like a ton of bricks- the XDP “ihi” replacement turbo I’m running has a 10 blade compressor wheel vs 11. And of course since XDP has no info on their own turbo, I guess I have no map. lol. Maybe I’ll toss my OEM wheels in it next summer and see if my butt-dyno feels anything.

 

[JoshH]

I highly recommend moving the wastegate reference from total boost to atmospheric turbo boost to slow it down and it will also make it easier to adjust the gate accordingly. The stock gate was never designed to operate compounded so it opens way too easy in that setup. You are also looking to make half the pressure from the big turbo so for instance you would like to see 60psi total boost and 20-30psi of that should be coming from the atmospheric turbo to keep everything happy and not risk overspeed of the big turbo.

Mark, maybe I'm thinking about it wrong, but if you run the regulator boost reference line to the atmosphere turbo, wouldn't you increase the risk of overspeeding the atmosphere turbo? As boost increases on the primary, you open the wastegate more driving the atmosphere turbo harder thereby continuing to increase the work it is doing and slowing down the stock turbo.

 

[N2BRK]

I think what will help is to take what you stated (correctly): "as boost increases on the primary, you open the wastegate more driving the atmosphere turbo harder...". But now add to that - "Which is less than if we sample the total boost with the reference line, and blow the wastegate open sooner."

You are correct in what it's doing, but not considering that the total combined boost will exceed the S475's boost way sooner.

Proof of this is that before relocating the reference, I had it sampling the total boost and I was making over 30psi from the atmo S475, and now it's making 18psi.