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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 02-24-2016, 07:37 AM
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Originally Posted by 94 slow View Post
Phil,
This is one he'll of a thread.

How would you tackle a rear mount setup? Say 5.3-6.2L, T4 mount, 1000hp goal in a first gen Camaro. The wheel base is approximately 108".
Same principals, size for max hp, keep the pipes as short as possible, coat and wrap.
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Old 02-24-2016, 07:42 PM
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Originally Posted by engineermike View Post
I would argue that pressurizing 1200 deg F exhaust gas to 45 psia adds heat of compression and increases the temperature to about 1800 deg F, thus giving it the energy it needs to quickly spool the turbine.



The same thermodynamic principals govern.



I haven't taken these measurements, but I would bet that it doesn't cool much on it's way to the turbine. After all, the exhaust gas only spends about .008 seconds in the crossover pipe.
I enjoyed the commentary from the last page. Much explained as I understand it.

I feel the enthalpy is the primary factor in judging the available energy but I haven't seen any discussion regarding Bernoulli's principle regarding the theoretical lift the pressure differential across the turbine, as the gasses flow across the wheel as it rotates at given gas & turbine RPM velocities/ enthalpy values, plays into this.

In other words I see the importance of understanding turbine efficiency as it relates to enthalpy retention across the turbine.

So that the gate sizing, determining the reaction rate to a delta change in gaseous mass by venting residual exhaust gasses is a function of this efficiency based on available enthalpy, gas velocity & turbine efficiency.

Your thoughts?

Last edited by gtfoxy; 02-24-2016 at 08:03 PM.
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Old 04-19-2016, 04:09 AM
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Just read through thise whole thread, twice! Some awesome information in here, that's for sure. One question I have for you Phil, is how you go about determining the FPS of exhaust gas out of the head, and then what FPS that translates into with the various size pipes?

Cheers
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Old 04-20-2016, 07:55 AM
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Originally Posted by Ben. View Post
Just read through thise whole thread, twice! Some awesome information in here, that's for sure. One question I have for you Phil, is how you go about determining the FPS of exhaust gas out of the head, and then what FPS that translates into with the various size pipes?

Cheers
I used some basic formulas from Max Boost and started a rough spread sheet. I highly doubt that they are accurate to whats really going on in the engine BUT they have given me a guideline that seems to hold pretty tight on every setup that we have tried with it. My calculator did combine max engine RPM, max boost and VE to get a working number. I am sure there are some thermodynamics that could have been added in but for what I am doing is not needed.

When you get down to the nitty gritty and start looking at cross sections of the exhaust valve/valve seat, exhaust port, header flange, header tube, crossover pipe, neck to the turbo you will find some decent information there alone.

IMO, a great basic setup would be truck manifolds and a 2" crossover, that will take care of probably 90% of the builds here.

Seems like the trend is to go with an oversized header, oversized crossover and use a smaller turbine and A/R combination.

I think you should use what I consider the correct size header and crossover which will allow you to step up the turbine and A/R and still get better spool and lower backpressure out the back
door.

I think the valve seats I measured were 1.46 ish depending on the head and size of the valve with an 8mm stem, you do have 8 of those vs 2 - 2.5" or 2" pipes.

Last edited by Phil99vette; 04-20-2016 at 08:00 AM.
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Old 04-22-2016, 12:25 AM
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Thanks for the help on this one Phil, much appreciated. I'm glad you've mentioned valves and valve area, as this is one I've been dwelling on, while trying to work out how to calculate the air speed out of the exhaust port, especially considering the valve is closed most of the time. Is it easier to make an overall assumption based on air in = air out? Then divide by the number of cylinders to get the appropriate runner sizing?

One conclusion I've drawn is: although temperature and pressure from combustion effect where the speed of sound is, they don't effect the volume of air moving through the system as such, and therefore won't effect the speed of the gas flowing through the exhaust manifold and turbo, it only gets hotter and denser. Is this correct?

Appologies for all the questions, I find this topic very interesting and would like to get my head around it so I can size up any turbo system on any car without having to get spoon fed answers from someone like yourself.
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Old 05-16-2016, 07:47 PM
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Originally Posted by Ben. View Post
Thanks for the help on this one Phil, much appreciated. I'm glad you've mentioned valves and valve area, as this is one I've been dwelling on, while trying to work out how to calculate the air speed out of the exhaust port, especially considering the valve is closed most of the time. Is it easier to make an overall assumption based on air in = air out? Then divide by the number of cylinders to get the appropriate runner sizing?

One conclusion I've drawn is: although temperature and pressure from combustion effect where the speed of sound is, they don't effect the volume of air moving through the system as such, and therefore won't effect the speed of the gas flowing through the exhaust manifold and turbo, it only gets hotter and denser. Is this correct?

Appologies for all the questions, I find this topic very interesting and would like to get my head around it so I can size up any turbo system on any car without having to get spoon fed answers from someone like yourself.
I am not really hung up on the technical small points per say. I do know that 1 3/4" headers and a 2.5" crossover can make enough power to go 160-165 mph to the 1/8 in a 3300# car. Multiple cars have done it so I know it works.
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Old 08-01-2016, 07:58 AM
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does anyone make a 2.5 to a 2.25" vband setup?
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Old 08-02-2016, 11:40 PM
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^ yes, but damn if I can find it now. i swear CRMB listed it in their catalog.

I already had the 2.5's welded on when I decided to neck down and used these to get me to 2.25

http://www.ebay.com/itm/2-25-to-2-5-...dW4EpJ&vxp=mtr
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Old 08-03-2016, 07:25 AM
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Originally Posted by truckdoug View Post
^ yes, but damn if I can find it now. i swear CRMB listed it in their catalog.

I already had the 2.5's welded on when I decided to neck down and used these to get me to 2.25

http://www.ebay.com/itm/2-25-to-2-5-...dW4EpJ&vxp=mtr
was hoping for a vband but whats 1 more weld lol. thanks for the link just ordered them
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Old 08-07-2016, 03:08 PM
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Originally Posted by Nali6.2 View Post
was hoping for a vband but whats 1 more weld lol. thanks for the link just ordered them
I would not use a vband to neck down a tube size, use a reducer cone from cone engineering or the link provided above.
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Old 08-07-2016, 05:02 PM
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Or grab some 16g steel and cut them out yourself... $40 to neck down some tubing seems steep!

Thats 2.5" to 2" from 73Runabout's setup. Turned out pretty slick!
Attached Thumbnails Out of curiousity why does everyone use 2.5" on the crossover pipe-cut1.jpg   Out of curiousity why does everyone use 2.5" on the crossover pipe-cut2.jpg   Out of curiousity why does everyone use 2.5" on the crossover pipe-cut3.jpg  
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Old 09-26-2016, 11:48 AM
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Anyone find the limit of a 2” hotside? I think I may have...

https://ls1tech.com/forums/forced-in...l#post19405404
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Old 09-27-2016, 09:36 AM
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Originally Posted by Phil99vette View Post
Considering 2.5" will support 2400hp
2.25" will support 1800hp
2" would support 1000hp.
Is this quote about a cross over specifically?

I have a factory headed 370, mild 224/224 @113 .610 lift cam. Using factory truck manifolds and 2Ē fully divided hot side. Going by weight/trap Iím around 1000ish crank (160 @ 3100lbs 6200rpm) It feels like I hit a wall around 6k. Car completely stops pulling. I was running a 30Ē tire. Installed a 28Ē tire and the problem is worse. The 160 trap drops to 154. Same trap and RPM at 19lbs as it is at 25lbs. More boost does nothing. Back pressure is 1.8:1 and is pretty steady. Fuel consumption jumped 20% and IATís went from 130 to 160. Iímnot sure whats happening here. Also it revvs clean to 7k in 1st. And converter slip is around 3%. Not sure where the power is goingÖ

If the hot side was maxed diameter wise, would it indicate higher backpressures or not? Think Iím at the hotside limit? What are the symptoms of a maxed out hot side?

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Old 09-27-2016, 09:39 AM
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I think the turbo might be the problem. Tell us about what turbo is on this thing.
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Old 09-27-2016, 09:41 AM
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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!

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Old 09-27-2016, 06:45 PM
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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!
I'd bet your t4 housing is the restriction.
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Old 09-27-2016, 08:25 PM
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Originally Posted by j88l98irocz View Post
I'd bet your t4 housing is the restriction.
As mentioned the t4 87/96 wheel S476 combos have made tons more power than I am... also I'd see it in the back pressure readings if I was maxing out the T4 housing.
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Old 09-28-2016, 01:17 PM
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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!
similar unit
better 76mm wheel and cover
nice heads

Those are all kinda loose comparisions.

The other combo probably makes 200 hp more or so based on trap speed alone, would be interesting to see the exact differences. Garrett posted some new turbos and someone reported that they are making 100+ more at the wheels than a comparable max performance effort turbo.
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Old 09-28-2016, 01:38 PM
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Looking at his thread here's the specifics...

8.12 @ 171. 365 cubes, 3420lbs, 7500 RPM, Mild port on TF 220 heads. 76mm ETR-HO billet comp. wheel, with a smaller 92mm vs my 96mm turbine wheel. 1.25 T4. Housing.

Head info:
Short side radius and bowl worked. Heads have the factory TFS valve job. I'm [email protected]", 270 [email protected]", and over 300 by .500" on a tight bench
Car made 1195 hp on 25psi and 14.5 deg of timing.

I can't see my turbo being tapped at 20ishlbs at 6k on untouched factory 317 heads... Jumping into an 80mm compressor doesn't sound like a horrible idea though... Just afraid it won't fix my issue.

Last edited by Forcefed86; 09-28-2016 at 01:45 PM.
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Old 09-28-2016, 01:53 PM
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The cam specs will be what makes a turbo drive over itself in matching combo's. Cylinder head flow will change boost pressure/power, but hp is connected to turbo on these smaller types generally. If your turbo is into problem area it will work better if you slow the engine down, that will lower the air consumed tremendously. If that is the case you need a turbo that can move more pounds per hour at your pressure ratio to speed up.

Kurt
Originally Posted by Forcefed86 View Post
Looking at his thread here's the specifics...

8.12 @ 171. 365 cubes, 3420lbs, 7500 RPM, Mild port on TF 220 heads. 76mm ETR-HO billet comp. wheel, with a smaller 92mm vs my 96mm turbine wheel. 1.25 T4. Housing.

Head info:

Car made 1195 hp on 25psi and 14.5 deg of timing.

I can't see my turbo being tapped at 20ishlbs at 6k on untouched factory 317 heads... Jumping into an 80mm compressor doesn't sound like a horrible idea though... Just afraid it won't fix my issue.
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