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Out of curiousity why does everyone use 2.5" on the crossover pipe

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Out of curiousity why does everyone use 2.5" on the crossover pipe

 
Old 09-28-2016, 03:33 PM
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He’s a busy guy but I shot his phone a txt…

I believe he was on the 218/218 @ 112 .570 lift. I know he was going 8.22 with that cam when he won drag week with his home ported 317’s on a SBE 6.0.

Mines a 224/224 @ 113 .612 lift.
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Old 09-28-2016, 05:09 PM
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So that makes clear which turbo limited engine would choke first, although that does not prove it's your only problem. The over fueling makes it sound like valves bouncing on the seat, but only fixing all the problems will help you figure it out.

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Originally Posted by Forcefed86 View Post
Hes a busy guy but I shot his phone a txt

I believe he was on the 218/218 @ 112 .570 lift. I know he was going 8.22 with that cam when he won drag week with his home ported 317s on a SBE 6.0.

Mines a 224/224 @ 113 .612 lift.
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Old 10-04-2016, 09:10 AM
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Originally Posted by Forcefed86 View Post
Sorry. It's an S400 based deal. 1.25 T4 87/96 exh wheel. 76mm billet compressor.

I know "Stock48" was going 170+ on a similar unit (same T4 housing/wheel, better 76mm wheel/cover) with his 6.0 with nice heads around 7200rpm @ 3400lbs.

If it were the turbo wouldn't I have a highish IAT indication and or more back pressure? I'm around 130* up to about 24lbs. At 28lbs it jumps to 160*.

18ish to 28lbs it traps the same 154mph with this 28" tire at 6200. With a 30" tire it went 159 @ 6200. Same deal around 17-18lbs. Adding boost with the larger tire and it didn't pick up at all.

-thanks!

Didn't you get your turbo off off ebay though?? Isn't it an Apex unit?
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Old 10-04-2016, 09:36 AM
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Originally Posted by LJMSJohn View Post
Didn't you get your turbo off off ebay though?? Isn't it an Apex unit?
Yes and no... I damaged the original APEX turbine wheel. The CHRA is now a standard BW S400 87/96. Installed the APEX 76mm compressor on it. Jose machined the 1.25 T4 housing and balanced/assembled it for me.

At 25lbs on the old 5.3 the base APEX unit (78mm x 87mm exh wheel) was good for 5mph over the standard small wheel 1.10 T4 S475 with no other changes.

Now I have the larger exh wheel mated to it. No idea how much power it's good for, but I don't see the signs of the turbo running out of steam? IATs are in check, boost doesn't fall with RPM.
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Old 10-04-2016, 11:00 AM
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hmmmm wierd...
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Old 10-16-2016, 06:03 PM
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Threw on a 1.32 T6 S480. Interestingly enough the back pressure didn't change much at all from the old 1.25 T4.


Got a few street pulls. Back pressure is still 1.8:1, even saw 2:1 at one point. So I'm thinking the hotside is the limiting factor at this point. Not sure what else it could be. Car feels sketchy fast on the street. Have it very slowly ramping in 20lbs VS wheel speed. IAT's are quite a bit lower. They peaked at 111. Around 86* ambient.

I'm sure it picked up a little, but I doubt it fixes my issue. Next track event is halloween weekend. I'll give it another go then.




The white "fuel pressure" parameter is the back pressure. I just never changed it.



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Old 10-16-2016, 07:18 PM
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Did it need more fuel at higher RPM?
If you are measuring BP near the turbo you can only read restriction past the sensor, the turbo and exhaust system past the turbo. If those did not change and it does not rev it might be excessive pressure from your pipe diameter, but the high pressure that did not change suggests a problem in the downpipe? It doesn't have any flex joints in the downpipe does it? Anything bent or broken balffle in muffler?

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Old 10-16-2016, 08:07 PM
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Hard to tell on the fueling due to the constantly changing "E85" around here. I believe this tune targeted 11.0 on E85 last outing. I filled up right before making the passes today and I'm pretty sure the gas station was putting out E70 now. Tune went rich all over... In the low 10's. So hard to tell. (i"ll test the fuel tomorrow).


This is the entire exhaust system. 4" straight through with 4" butterfly. With the dump closed it uses the 2" kickout on the side for quiet cruising. Not even 2 feet of pipe. I'm out of other things to try... I can take the exhaust dump off the tip, but I can't see that doing a whole lot.

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Back pressure is being taken at the #1 runner.

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Old 10-17-2016, 07:38 AM
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With that sensor location you likely are reading the pipe problem. Sounds like you answered why people use 2.5 tubing!

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Old 12-01-2016, 07:57 AM
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So I went with a new billet S480 T6 turbo. The back pressure didn't change much. Was still 2:1 @ 20lbs at the #1 runner. So I moved my back pressure rig over to the new 1.32 T6 housing (one side of the scroll) and back pressure dropped to 1.4:1 @ 20lbs. Got a couple street pulls and it pretty much does the same thing. Noses over around 6k.

Brought it to the track for the last event of the year. Immediately popped the planetary on the trans first run. So no more data till next year.

Also figured I wasnt really running a true 2 hot-side. Im running 16g 2 tubing with 1.87 ID from each manifold. Still feels like Ive hit the flow limits of this hotside diameter wise. Unless its the new GM LS7 lifters, Im not sure what else could be holding me back.



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Old 05-18-2017, 08:12 PM
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https://www.physicsforums.com/thread...t-duct.241856/

What we used in jet engine school to understand airflow thru the engine and ducts. Hope it helps.
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Old 09-23-2018, 03:11 PM
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Back from the DEAD!

I'm working with a 4.2L V8 9.5:1 40v

Currently i'm running full divided...2.25in piping off the manifolds for ~4ft, then 2in piping for ~3ft, and finally 2.25in for 6ft, into the T4 1.0ar divided housing (yes, you guessed it....rear mount).
It was easier for me to grab 2.25 piping at the time but my turbo response isnt great and the research i've done has taught me a lot. I'll be dropping that last 6ft down to 1.75in piping.

My thought process was even though the manifolds are jet hot coated and piping is wrapped (304ss) and the turbine housing is jet hot coated as well, i need to increase/maintain velocity going into the turbo since it inevitably cools down and loses velocity due to wall friction, bends, and everything else).

This thread was really helpful in confirming my thoughts on how to increase response! We'll see how it goes in the next couple weeks!

This whole thread was a great read.
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Old 10-02-2018, 11:56 PM
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Me too, I'm running a remote mount twin turbo LS3 and it has race long tube headers with merge 3" collectors, I step them down to 2.5" but am now thinking I should step them down from collectors to the size of the T3 turbine inlets. I wrongly thought plenty of flow to the turbos was better for backpressure
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Old 10-03-2018, 01:38 PM
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Originally Posted by Bazman View Post
Me too, I'm running a remote mount twin turbo LS3 and it has race long tube headers with merge 3" collectors, I step them down to 2.5" but am now thinking I should step them down from collectors to the size of the T3 turbine inlets. I wrongly thought plenty of flow to the turbos was better for backpressure
You will probably do better with stock exhaust manifolds with 2.25" pipe and wrap the manifolds and pipes all the way to the turbos. You need to keep the heat and velocity high for remote turbos and long tube headers lose a lot of both quickly.
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Old 10-08-2018, 08:00 PM
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I think these images say a whole lot about some of the info in this thread. Check out how small the exhaust runners are...


Scania 730hp V8 Semi Engine



An entirely different application to here I know, these motors have world leading technology in fuel economy, emissions, and power for the semi truck market. 730hp at 1900rpm, redline at 2400, and 2600ft/lb of torque from 1100rpm to 1400rpm. But 730hp is 730hp! Yes, the runners look smaller than they are because it's a big 16L V18, but back when the ancestors of this V8 was running half the power they ran proper stainless headers with much larger primaries.... and half the power.

I'm sure a racing version of this motor would benefit from upsizing and maybe going to headers for top end cfm - but it does prove the point that small runners staged like this can build incredible velocity and ENOUGH cfm to make the power. These trucks make the Cummins signature series motors look like weaklings, with 600hp available from 1230rpm where the top Cummins is at around 470. Along with the 750hp Volvo motor these are the pinnacle of big power semi diesels, and they would be using headers if that made more power on less fuel. Thoughts re application to the LS turbo motors?
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Old 10-10-2018, 06:57 AM
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Originally Posted by Bazman View Post
I think these images say a whole lot about some of the info in this thread. Check out how small the exhaust runners are...
An entirely different application to here I know, these motors have world leading technology in fuel economy, emissions, and power for the semi truck market. 730hp at 1900rpm, redline at 2400, and 2600ft/lb of torque from 1100rpm to 1400rpm. But 730hp is 730hp! Yes, the runners look smaller than they are because it's a big 16L V18, but back when the ancestors of this V8 was running half the power they ran proper stainless headers with much larger primaries.... and half the power.

I'm sure a racing version of this motor would benefit from upsizing and maybe going to headers for top end cfm - but it does prove the point that small runners staged like this can build incredible velocity and ENOUGH cfm to make the power. These trucks make the Cummins signature series motors look like weaklings, with 600hp available from 1230rpm where the top Cummins is at around 470. Along with the 750hp Volvo motor these are the pinnacle of big power semi diesels, and they would be using headers if that made more power on less fuel. Thoughts re application to the LS turbo motors?
That is interesting. But I would like to point out that a V8 half that size is 8 litres.....so more or less half the power most likely...so that is 375hp.....aren't many years of 6.6L Duramax more powerful than that? Granted, much higher rpm and not as much torque though....What diameter are the Duramax manifolds?
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Old 10-10-2018, 08:27 PM
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Originally Posted by 1CAMWNDR View Post
That is interesting. But I would like to point out that a V8 half that size is 8 litres.....so more or less half the power most likely...so that is 375hp.....aren't many years of 6.6L Duramax more powerful than that? Granted, much higher rpm and not as much torque though....What diameter are the Duramax manifolds?
No idea re Duramax manifold sizing but not fair comparison as you said. Scania peaks its 730hp by 1900rpm compared to 3000 for the Duramax. The Duramax does not even achieve peak torque until 2250rpm. A Scania motor hot rodded to peak at 3000rpm would be quite something. These big motors regularly exceed 1,000,000 miles at 50 ton gross with outstanding fuel efficiency. They're a huge step up in technology from a Duramax and are the Rolls Royce of truck engines, though some would argue the Volvo 750hp sits alongside. MAN, Mercedes, Cummins, Detroit, Cat (cough) etc don't make anything in that power bracket that can match the efficiency

Here's a marine version that is not so worried about emissions:
https://www.scania.com/content/dam/s...076M_846kW.pdf

1046hp by 1800rpm and 1150hp at 2300. Obviously a Duramax can be built to make 1150hp too - but will burn a lot more fuel doing it and have a life likely around 1/10th, or 1/100 if it had to pull 50 ton lol

Notice the picture of the 1150hp version in the link above looks more like what we would expect - with twin turbos and a different (but still high velocity) exhaust manifold. I
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Old 10-16-2018, 02:09 PM
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The massive power and torque at low rpm boggles my mind LMAO.
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Old 03-11-2019, 04:44 PM
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Sooo...... 2.25 is the aimed cross pipe?
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Old 05-20-2019, 03:45 PM
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Originally Posted by panda240ss View Post
Sooo...... 2.25 is the aimed cross pipe?

I run 2.25 on mine. seems to run good. Pulls to 7000 with a 222/234 cam (5.7)
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