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Uh. Has it really been FOUR years since the last update? Holy cow. Just got done with my fourth read through over the years. How is the Twin Turbo coming along Rob?? Randy, do you know of any threads that would best explain the use of the pressure tap that Rob brought up? After all these years, I still come across stuff I have no knowledge of.

Desperately craving more TD history,

Mark Lucas
 

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Rob, the Pressure Ratio King has takes a pressure reading from his exhaust manifold.

Drill a hole, pre-Turbo and thread in a fitting that can hook up to another boost gauge.

The goal is to have equal exhaust pressure to Engine boost.

Perfection is 1 to 1 but rarely obtained like Rob does.

Most times the ratio is over 2 or 3 to one.

EG: 20 PSI boost=20 PSI in the ex manifold.

As Rob often says, reduce restriction aft the turbo

Thanks
Randy
 

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I'm not sure what Rob uses but I like a few feet of pre-made steel brake line.

It already has a flared flitting on one end to screw into the manifold fitting.

The other end can have a hose fitting to screw onto it's flared fitting.

Thanks
Randy
 

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Read this thread! If anyone currently frequenting the forum has not read this thread, please do. It's 100% worth it. Especially if you want to be inspired by the history of one of the fastest guys in the hobby. If there is enough demand, Rob may come back and continue the story. The more inspired we all get, the more likely it will be that one of us has an amazing idea that could take us to the next step in the evolution of the Trans4 2.2 Turbo!
 

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Discussion Starter · #66 ·
Wow, was just talking to Randy earlier and decided to look some stuff up to see if it was here. Had no clue anyone had recently posted.

Guess I'm going to have to get back on it and finish this up in the near future. Crazy how time flys!
 

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Hi Rob!!! I was actually going to try to dig around to find an email to message you about a dream about twin turbos that woke me up this morning. Almost fell over when I looked at my alerts on here and saw you had posted.
 

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Discussion Starter · #68 ·
Hi Rob!!! I was actually going to try to dig around to find an email to message you about a dream about twin turbos that woke me up this morning. Almost fell over when I looked at my alerts on here and saw you had posted.
Hey Mark, I use to get those Crazy dreams as well, Not so much lately though. Hopefully that's going to change Soon.

On the pressure tap I actually use a brass fitting in the exhaust mani, then a length of brake line to get away from the heat till I can attach the gauge hose. (18" or so, some like to coil it) Was skeptical about the brass but decided to try because of it's melting point. I've never trusted or ran an EGT gauge, but I know if I ever melt the brass fitting I'm over 1800deg's! : )

Here's a lucky/ fluky piece of info;

When I originally did the pressure tap on the Charger, I just used what I had lying around at the shop. Found an oil pr gauge with what I thought would be sufficient psi range and slapped it together.

Years later and after installing taps in several other cars we've built, I've found that regular psi gauges suffer from exhaust moisture/ debris and will start to screw up if you don't have some sort of filter in front of them.

Crazy that I just happened to chose an oil pr gauge way back then and have never had an issue since.
 

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That's awesome! I had started reading about pressure differential since talking to Randy here recently, but only because I was trying to study the effects of valve overlap(LSA), so the sources were mainly talking about how high exhaust manifold pressure is in a turbo setup. I can't believe I had never even thought about the fact that superchargers don't even have to deal with this at all, so they can benefit from higher LSA just like NA does.

You may think it's gross, but my dream was actually about running Twin Mitsubishi TE04s. My thinking I guess was that since they spool so fast that boost becomes almost uncontrollable when you just remove the cat and muffler, but they don't flow very much overall, that if you divide the pressure coming into the hot side in half, boost control with free flowing exhaust becomes achievable, and at the same time, you double your flow with two turbos that spool crazy fast. The other benefit to using the tiny TE04s is just that. Their small size. I thought about taking advantage of my ever growing pile of log turbo exhaust manifolds, cutting #1 and 2 runners off of two manifolds and bolting the #3 and 4 to ports 1 and 2, and 3 and 4. I could make adapters to angle the turbos if need be for charge pipe routing or simply to clear each other. The overall thought was to have VNT level powerband, but more power down low than VNT did since there would be significantly more flow. Maybe I'm just nuts.
 

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Discussion Starter · #70 · (Edited)
What you're describing was actually built and I believe ran around the same time I was building the twin turbo. (Thinking a year or 2 after I started) Not a very optimal design in my mind back then, but kudos to the guy for getting it together and running!

Found it! Wayback Machine

Just click on twin turbo Shadow in left column

Biggest issue for me when I saw it was the 2 exhausts merged together. One of the biggest advantages of going twins would be the Free Flowing exhaust gains!
 

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Just to be clear valve overlap isn't LSA or Lobe Separation Angle.

If you look at a cam from the end the V shape that's the LSA.

Sometimes called LCA for Lobe Centerline Angle.

LSA/LCA are the only cam specs in cam degrees, not crank

Below is the lobe separation angle between an intake and exhaust lobe.

There is some corelation but overlap and LSA are different.

Not trying to be picky just getting on the same page.

Thanks
Randy




That's awesome! I had started reading about pressure differential since talking to Randy here recently, but only because I was trying to study the effects of valve overlap(LSA), so the sources were mainly talking about how high exhaust manifold pressure is in a turbo setup. I can't believe I had never even thought about the fact that superchargers don't even have to deal with this at all, so they can benefit from higher LSA just like NA does.
 

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I remember that Twin Mistu Shadow Rob !!

Out of curiosity do you think your Holset could be bettered with twins??

Not any twin setup but limited to using our 8V cylinder head etc.

Thanks
Randy

PS: This thread reminds me why you are the Pressure Ratio King !!

What you're describing was actually built and I believe ran around the same time I was building the twin turbo. (Thinking a year or 2 after I started) Not a very optimal design in my mind back then, but kudos to the guy for getting it together and running!

Found it! Wayback Machine

Just click on twin turbo Shadow in left column

Biggest issue for me when I saw it was the 2 exhausts merged together. One of the biggest advantages of going twins would be the Free Flowing exhaust gains!
 

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Absolutely not the same thing, but they are hand in hand. That's what I get for posting right when I get up in the morning. I totally misspoke. I meant to say LOWER lobe separation angle.
 

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This information about the twin mitsus is invaluable! Can't believe that they merged the exhausts, though. As he says, the twins don't spool as fast as a single mitsu. Obviously because each turbo is pushed by only half of the engines exhaust gasses. Merging the turbines into one output elbow compounds this issue and in my opinion cancelled out the benefit of the reduced exhaust gas input to better control the mitsu overboost problem. Having two of them would allow you to run dual open 2.5 exhausts without overboosting! With regard to the fueling issue because of the cycles, this is something that can be tuned for. I don't actually know if you can use MPTune to change the pulsewidth of injectors individually, but you certainly can with Megasquirt.
 

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Discussion Starter · #75 ·
I don't know if it could be bettered or not, (thinking negligible diff)but the twin turbo was born out of the need for something that didn't exist back then. Turbo technology has grow in leaps and bounds since, specially when it comes to smaller engine displacements. So to go to the trouble now, just to be at the same place (I think at best) as a good single, is no longer worth the effort IMO.
 

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You should be pleased someone read your late night post at the TD graveyard!!

LSA is important as it's # in cam degrees is the same as the installed # in crank degrees.

To elaborate, that's for a cam installed straight up, with no advance or retard.

LSA and LCA are the same numbers but are totally different things.

LSA is a non adjustable figure, LCA is where the cam is installed.

LCA is the installed centerline or ICL and used for cam degreeing.

Not trying to be difficult, just trying to speak the same language!!

LSA sets the torque output and overlap sets the rpm range.

Thanks
Randy




Absolutely not the same thing, but they are hand in hand. That's what I get for posting right when I get up in the morning. I totally misspoke. I meant to say LOWER lobe separation angle.
 

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One more thought on camshafts with our Engines.

"LSA sets the torque output and overlap sets the rpm range".

Most of us make great torque but few of us make any decent HP.

Gary Donovan once stated anyone can make torque, HP takes brains.

Our Engines don't like overlap due to our typically high pressure ratio.

Reducing the pressure ratio successfully allows a cam with more overlap.

With a low P/R, a Turbo Engine likes a cam more like high HP N/A cam.

Rob makes great HP and is known as the "pressure Ratio King".

Everyone knows we don't have a big cam selection to choose from.

I'm curious to hear anything Rob has to say on the topic!

Thanks
Randy

 

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Discussion Starter · #79 ·
From the very beginning I always thought a great turbo build would pretty much mirror a great N/A build. In all the years since I have yet to find any evidence of it being any different, but Yes, PR has to be observed And you need more than a paper degree in understanding to grasp it.

As this conversation goes on, I will eventually ask a mod to separate it into a spin off thread so we don't add more pages to the Charger thread then necessary. No issue with it till I start to revisit the original topic in the next month or so though.
 

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Well said and there is a general consensus that our Turbo Engines require less overlap.

One might say a higher pressure ratio requires a lesser amount of overlap.

Or, the lower the pressure ratio the higher amount of overlap is favored.

Obviously, you are way ahead of us in regards to pressure ratio.

Not trying to be argumentative and enjoying the conversation.

Sadly, activity on our forums is rapidly dwindling.

I suppose FB has taken over the world.

My wife and family do FB but I dont.

I'd probably embarrass her!!

Thanks
Randy
 
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