Let's talk pipe size

This came up in conversation with a fellow turbo car guy at work, so I thought I'd pass along the conversation and get some of your input.

Basically, let's say you have a dead stock turbo 2.... Say the inlet to the turbo is 2 1/4 inches, so let's start there. Is there any reason to increase the size of that pipe from the air filter? I doubt there is a downside to having a 4 inch pipe, but fitment would be an issue. Are there gains to be had with a 2 1/2 or 3 inch pipe? Considering the actual inlet of the turbo compressor is under 2 inches.

From there, the discharge from the turbo is maybe 1 1/2 inches, maybe 1 3/4 inches? From there, the factory pipes enlarge and reduce until it gets to the intercooler inlet that's maybe 2 1/4 inches. Is there any reason to go larger than the intercooler inlet diameter?

Assuming the intercooler outlet is the same 2 1/4 inches, and the throttle body is the same size, is there a reason to have a pipe with larger diameter?

When things are modified, the question gets more complicated, My personal feeling is the factory has price restrictions to work within, but we don't, so is there gains to be had in pipe sizing?

I can tell you on a VR4. the stock turbo inlet pipes are no smaller than the diamter of the turbo inlet at any point.
turbo inlet is 1-/34 inch

I changed from stock turbo inlet pipes to some 2.5 inch exhaust pipes and filters.

I went from 298 HP to 319.

https://www.3si.org/forum/f1/diy-pre...owthru-587530/

no other changes. just pre turbo pipes.

Quite an increase! How much larger were the new filters? Same dyno too?

https://www.youtube.com/watch?v=XYaxk50h1DA

week apart. same dyno. correction factory got it to 319.

it was a single big filter through a single intake tube. then 2 filters. maybe 4x7 inches. and single pipes for each turbo

going from the factory T2 airbox, with a T1 smooth hose to the turbo to a 3" mandrel bent pipe that at the time was sucking hot underhood air gained me a consistent 1mph at the track which equates to 10hp. I then built a cold airbox around the filter but didn't get back to the track with it. So yes a bigger pipe makes a difference as the turbo has to work less to get the air. This allows slower shaft speeds and the WG opening sooner and more for less back pressure in the motor. So you gain power on both the intake and exhaust side of things.

A look at my daughters Caliber SRT4 shows that even with a turbo smaller than our Mitsu's that going bigger on the turbo to intercooler piping helps. As the outlet on one of our mitsu's is tiny the SRT4 funnels out into what would be a 2.5" diameter pipe just looking at it. And some of the other owners run a 4" inlet pipe though I think that's a bit overkill for the turbo as a 3" or so would be more than enough but I don't want to lose the fact that the factory has a cold ram air box.

Can you go too big? Yes for a point of diminishing returns. But you want the turbo to be able to grab as much air as possible, and then have someplace for it to go. 2.5" ID pipe on a slightly modded T2 isn't overkill between the turbo and throttle body. For over 300hp I'd go 3" with 4" to the turbo.

I would expect that larger post turbo tubing while leading to more HP due to reduced delta P (pressure drop), will also show increased spool up time on the Turbo due to increased volume

The factory air box/air filter is pretty small. Being in AZ I wanted to continue pulling air through the SMEC (when I still used a SMEC) so I went with a Ford V8 enclosed air filter. Last time I went to the dyno with my 2.4 in my van I made 395 horsepower. My dyno guy was curious as to how much of a restriction my air filter was so we took it off. I gain 4 hp. Not enough to risk a turbo so I leave it on. Just so you have an idea how big your air filter needs to be around the 400 hp mark. Start at post 50: http://www.turbo-mopar.com/forums/sh...triction/page3

This is all good info. So maybe a 3 inch pipe from air filter to turbo inlet with a reducer right at the compressor is beneficial

How about having charge pipes larger than your intercooler inlet - outlet and throttle body? Say the outside of a 58mm throttle body fits a 2 1/2 inch coupler. Has anyone run a larger pipe and seen gains?

On my old black/tan GLH Turbo, I had modified it with a very large Isuzu NPR intercooler. It had 2.75" I/O, so I got 2.75" mandrel bent aluminum pipe and used silicone reducers at the throttle body (2.75" - 2.25") and turbo discharge (2.75 - 2.00"). It must have used at least 4 feet of pipe just for the intercooler. For the intake, I used 3" mandrel bent aluminum with a (3.00" - 2.50") silicone transition.

I never had it to the track, but it spooled up faster than ever with a stock TII turbocharger. I suspect the large pipe slowed the velocity down and probably increased cooling (more time in IC), but it still pressurized the whole thing near instantly even though there was way more volume between the turbo and TB.

I did have it on the dyno once and it made 198 WHP/270 WTQ with 14psi. The dyno operator (Brent at PFI) was laughing when the boost would hit hard down low.

Attachment 63788

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Originally Posted by iTurbo

On my old black/tan GLH Turbo, I had modified it with a very large Isuzu NPR intercooler. It had 2.75" I/O, so I got 2.75" mandrel bent aluminum pipe and used silicone reducers at the throttle body (2.75" - 2.25") and turbo discharge (2.75 - 2.00"). It must have used at least 4 feet of pipe just for the intercooler. For the intake, I used 3" mandrel bent aluminum with a (3.00" - 2.50") silicone transition.

I never had it to the track, but it spooled up faster than ever with a stock TII turbocharger. I suspect the large pipe slowed the velocity down and probably increased cooling (more time in IC), but it still pressurized the whole thing near instantly even though there was way more volume between the turbo and TB.

I did have it on the dyno once and it made 198 WHP/270 WTQ with 14psi. The dyno operator (Brent at PFI) was laughing when the boost would hit hard down low.

Attachment 63788

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Is than on an otherwise stock t2 engine?

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Originally Posted by shadow88

Is than on an otherwise stock t2 engine?

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Actually, it was a junkyard '89 2.5L TI from a Caravan with about 180k miles. I only put new gaskets and seals in it, but didn't touch the rotating assembly. I did have to get a remanufactured cylinder head because that and the cam were wasted. Manifolds and TB untouched (from a TII Maserati TC), but it did have a stock TII turbocharger and full 3" exhaust and grainger valve boost control.

Intake, charge pipes, intercooler upgrade and 3 inch exhaust on 14 psi? What size is the maserati throttle body?

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Originally Posted by shadow88

Intake, charge pipes, intercooler upgrade and 3 inch exhaust on 14 psi? What size is the maserati throttle body?

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It was a junkyard TII Maserati TC top end. Just a stock 48mm TB. Even the 16v ones only have a 48mm.

I was very lucky not to hit overboost on the dyno. It still had factory overboost protection (no adjustable zener, which I did later to get to 17 psi).

I ran a 09+ ram 1500 hemi intake on my omni. It was 3.5 inches. Worked real well.
https://drive.google.com/uc?export=d...boVx59AI05Gcqy

3 inch filter to 3 inch pipe to 3 inch compressor housing, out 2 inch compressor outlet, to 2 1/4 inch pipe that goes to 2 1/2 inch, then to 2 1/2 inch intercooler, then back to 60mm pipe and hoses all the way to the 52mm throttle body.
Made 367whp at 26psi on E52.

http://www.thelostartof.net/tryingbe...ewbattery1.jpg

Maybe I do need a bigger throttle body.

Before the turbo you want as little restriction as possible while maintaining smooth flow. Larger pipe helps (to a point as has been mentioned). The smooth, cool flow will yield more power than turbulent hot flow.

Post turbo the theory from physics is that you should avoid size transitions is because each transition will reduce efficiency. My personal "recipe" is a pipe size that matches the turbo outlet to the intercooler. After the intercooler either the size of the intercooler outlet (usually about the same as the throttle body), or one pipe size larger if it can fit.

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Originally Posted by thedon809

I ran a 09+ ram 1500 hemi intake on my omni. It was 3.5 inches. Worked real well.
https://drive.google.com/uc?export=d...boVx59AI05Gcqy

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What was there before? Any other changes? Any guess on power gains?

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Originally Posted by Reaper1

Before the turbo you want as little restriction as possible while maintaining smooth flow. Larger pipe helps (to a point as has been mentioned). The smooth, cool flow will yield more power than turbulent hot flow.

Post turbo the theory from physics is that you should avoid size transitions is because each transition will reduce efficiency. My personal "recipe" is a pipe size that matches the turbo outlet to the intercooler. After the intercooler either the size of the intercooler outlet (usually about the same as the throttle body), or one pipe size larger if it can fit.

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Let's say you're using an air filter minder type of device. http://filterminder.com/ If it indicates no restriction, could there be gains to a larger pipe? Obviously cold air and smooth transitions are preferred.

Maybe I'm reading it wrong, but your second paragraph says to me that transitions will reduce efficiency, yet suggest one size larger than throttle body which would require a reducer.

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Originally Posted by iTurbo

I did have it on the dyno once and it made 198 WHP/270 WTQ with 14psi. The dyno operator (Brent at PFI) was laughing when the boost would hit hard down low.

Attachment 63788

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very close #'s to my 2.5 that was in my daytona, 2.5 tucked under 87 T2 top end, ported exhaust manny, S60 turbo, 3" straight pipe side exit from the turbine wheel back. 2.5" intercooler tubing through a cummins i/c and a 3" air filter to turbo pipe. 12psi on a grainger valve.

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Originally Posted by shadow88

What was there before? Any other changes? Any guess on power gains?

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Just had a cone filter on the turbo before this. No clue on power gains. I switched a lot of things at the same time.

Big as fits and straight as possible.

Was a tight fit in an omni. My lancer has a 3" setup. Gonna change it up when I move the battery.
https://drive.google.com/uc?export=d...7ER_RfUjtiyX8j

Quote:

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Originally Posted by shadow88

Let's say you're using an air filter minder type of device. http://filterminder.com/ If it indicates no restriction, could there be gains to a larger pipe? Obviously cold air and smooth transitions are preferred.

Maybe I'm reading it wrong, but your second paragraph says to me that transitions will reduce efficiency, yet suggest one size larger than throttle body which would require a reducer.

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For the first question: probably not.

For the second question, you are correct. The reason for the 1 larger size is bends...slow the air down for turns.

So we agree the air filter to turbo pipe should be as large as you can fit all while keeping the airflow smooth and cold?

I liked iturbo's Theory that the larger charge pipes pre and post turbo would allow longer time crossing the intercooler core and thus, reducing temperature.

Everyone seems to agree there's no gains to having a larger-than- throttle body pipe leading from intercooler to throttle body?

Well theoretically. large pipes between IC and TB could help some .
possibly part of plenum size when TB is open at FT.. depending on flow restriction from plenum to pipes.

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Originally Posted by masterjr33

Well theoretically. large pipes between IC and TB could help some .
possibly part of plenum size when TB is open at FT.. depending on flow restriction from plenum to pipes.

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Wouldn't the plenum volume technically be all the way to the turbo under WOT conditions?

Strictly on pipe size, turbulence and heat (by compressing slightly) would happen if there was a neck down at the throttle body, no?

Quote:

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Originally Posted by shadow88

So we agree the air filter to turbo pipe should be as large as you can fit all while keeping the airflow smooth and cold?

I liked iturbo's Theory that the larger charge pipes pre and post turbo would allow longer time crossing the intercooler core and thus, reducing temperature.

Everyone seems to agree there's no gains to having a larger-than- throttle body pipe leading from intercooler to throttle body?

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A lot of really fast guys have posted that they run a cold side pipe to the TB which is larger than the TB itself. I think Stephan ran a 3" pipe?

My plan is to switch to a water to air I/C. The one I was looking at has 3" I/o. I want to run 3 inch pipes and a 70mm throttle body when I do that to go along with a ported +1 swirl and f5 cam.

Cpl things to keep in mind, and never forget, it's about the entire system working together.

So, going to 3" I/C pipes for eg. What turbo are you running? How much air does it flow at target boost pr? If you go too large on piping and your turbo does not flow a sig amount of CFM the system will suffer. (Drivability and transient response)

On the other hand, and as a few have mentioned, if your turbo is pushing sig more CFM than our little 8V mtrs can swallow, it is most likely stacking in the system, so going to larger volume pipes and relieving some of that, as well as Slowing down the flow for better cooling becomes beneficial.

When I went to 3" I/C pipes on the Charger, Everything got better. There was a time I considered water cooling for consistency. After the change to 3" charge pipes and the AtA I/C in the Charger now, I can hot lap the car and lose nothing at the track. Before the change I would lose 2-3mph on a second "hot lap" pass.

I'm thinking the significantly shorter run of intercooler piping will help to some degree with the water to air. I currently have a to4e 50 trim with .63 housing, stage 2 turbine with your mandrel 3" swingvalve. I'm thinking a gt3076r or similar will be my next turbo.

ok , a little tangent here
we know we lose something from "flow" when we add a 90* turn but how might that 90* turn be affected if we transition from oval to round or vs versa as we turn that 90* ?

examples (editing in links in process)

www.summitracing.com/int/parts/tfs-315b800/overview/

http://www.amazon.com/d/Automotive-E...bow/B078WK55MV

would most likly need to run the design through a air flow computer.
make sure all the areas are built correctly.

There are engineering "rules of thumb" for efficiency loss percentages for turns, transitions, length, diameter, etc... No need to guess.

From my experience, I lost no response or spool time going from the non-intercooled 2.5L, to the Isuzu NPR intercooler and 4+ feet of 2.75" pipe connecting it all. Turbochargers are high volume/low pressure pumps. It pressurized just as fast as ever after the intercooler install. It was still "point and shoot" being a 2.5L in a light car.