Phil99vette

iTrader: (11)

Same principals, size for max hp, keep the pipes as short as possible, coat and wrap.

gtfoxy

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?

Ben.

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

Phil99vette

iTrader: (11)

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.

Ben.

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.

Phil99vette

iTrader: (11)

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.

Nali6.2

does anyone make a 2.5 to a 2.25" vband setup?

truckdoug

iTrader: (25)

^ 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

Nali6.2

was hoping for a vband but whats 1 more weld lol. thanks for the link just ordered them

Phil99vette

iTrader: (11)

I would not use a vband to neck down a tube size, use a reducer cone from cone engineering or the link provided above.

Forcefed86

iTrader: (4)

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!

Forcefed86

iTrader: (4)

Anyone find the limit of a 2” hotside? I think I may have...

https://ls1tech.com/forums/forced-in...l#post19405404

Forcefed86

iTrader: (4)

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 2” fully divided hot side. Going by weight/trap I’m around 1000ish crank (160 @ 3100lbs 6200rpm) It feels like I hit a wall around 6k. Car completely stops pulling. I was running a 30” tire. Installed a 28” 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 IAT’s went from 130 to 160. I’mnot sure whats happening here. Also it revvs clean to 7k in 1st. And converter slip is around 3%. Not sure where the power is going…

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

Phil99vette

iTrader: (11)

I think the turbo might be the problem. Tell us about what turbo is on this thing.

Forcefed86

iTrader: (4)

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!

j88l98irocz

iTrader: (44)

I'd bet your t4 housing is the restriction.

Forcefed86

iTrader: (4)

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.

Phil99vette

iTrader: (11)

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.

Forcefed86

iTrader: (4)

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.

427

iTrader: (3)

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