Competition Twins vs. large single, which one for top end ONLY!

[GOT-Torque]

Lots of good info in this thread.



Here's some flow #'s I pulled out of another thread (I can't take credit for putting the table together):



Turbo______CFM______Racing HP____Daily HP

HX35______600________420_________330

HX40______800________560_________440

T66_______800________560 _________440

B1________900________630_________495

H2E_______1000_______700_________550

HX50______1000_______700_________550

HX55______1050_______735_________578

HT3B______1100_______770_________605

T76_______1350_______945 _________743

HT60______1400_______980_________770

B2________1500_______1050________825

HX60______1550_______1085________853

T88_____1450-1750__1015-1225____798-963

HT4B______1800_______1260________990

Big Brother_1900_______1330________1045

T91_______2000_______1400________1100

HC5A/HX82_2450_______1715________1348

T100______2600_______1820________1430

T105______2900_______2030________1595



I assume these #'s would be if the turbo was ran as a single? If it was in a twin configuration, the flow path is more restricted therefore the flow #'s would be less? (Which is the whole principle behind my original question)



Jim, that's interesting that you ran a SPS66/Big Brother twin setup before and now you are just running the SPS66 by itself. If the hp # in your sig is with the SPS66 alone, what were the numbers with the SPS66/BB setup?



Also, where would a SPS66 fall on the chart (flow wise)?

 

[CStraface]

Huge singles do offer a lot of air at a cheaper price than twins but could never be driven as a daily driver. Thanks

How big are we talking? What turbos would you consider too large for the street?

 

[GOT-Torque]

Some of the questions being asked have way too many variables affecting the answer. What generation of truck, what gears, tire sizes, amount of fuel, who is driving?



Sure you can slap a huge turbo on and manage to drive it to the local pull, so it is streetable? Define streetable? It also depends on who answers the question.





THE REAL WAY TO TELL IF YOUR TRUCK IS STREETABLE



How about this, if a woman (other than your wife or girlfriend) can drive the truck for a week with less than 60 seconds of instructions from you, then it is streetable Otherwise it is not.



You all know what I'm talking about, something like this...



Don't let it get over 1250 EGT's, don't shut it off until under 350 EGT's, don't go over 20 psi boost until it is up to temperature, don't lug the engine, don't "try" to smoke out every car that you see:-laf , don't turn this box on, and don't I repeat don't push this red button!

 

[Jim Fulmer]

The current numbers are with the 66 and (2) small stages of N2O. The 66/BB combo took me to 850 on #2 and 873 with water... ... . along time ago!



The #2 numbers running the 66 will never beat the 66/BB combo, but I love the simplicity of the single, and who needs 800+ hp all the time. I'm easier on the truck now for sure as I don't run around with the bottle open. Since making the change I haven't touched it except for a new ported housing... ... . again simple.



Jim

 

[GOT-Torque]

I don't run around with the bottle open

You are not fooling anyone here...

 

[NoSeeUm]

.....

It is a VERY large subject and I will help when I can.

Yeah and thanks.



Jim

 

[NoSeeUm]

Is it typically exhaust or intake restriction that limits most twins?



It seems to me that with properly sized compressors, multi stage compression would almost always be more efficient than single stage.



Jim

 

[Idaho CTD]

The example I made was purely hypothetical. That why it says "around". It was insinuated that a twin set up can't be made to spool as fast as your singles and that is total BS. Most twin set ups spool about 100-200rpms slower than the secondary by itself. So by dropping one compressor wheel size or by adding more fuel you can recover that loss in spool up. By dropping one wheel size your not going to sacrafice a lot of hp especially if the big charger is sized correctly.

 

[Idaho CTD]

Is it typically exhaust or intake restriction that limits most twins?



It seems to me that with properly sized compressors, multi stage compression would almost always be more efficient than single stage.



Jim

It's best if you think of it like this: Twins amplify the power capacity of the smallest turbo while keeping close to the same drivabilty/spool up as the small turbo.



Bypassing the turbine side is probably the most critical part to making big power with twins. Non wastegated primaries and undersized wastegates on the secondaries severely limit the power output of a twin system because turbo are needlessly over driven which costs hp. Two turbos take more hp to turn then one turbo so it's not always more efficient. They do have a more efficient powerband, meaning they have a broader range of usable power.



If you look at the new trucks there are basically two approaches to quick spool up and a broad powerband. The VGT's/VVT's which make a larger turbo spool quicker and then open up to relieve back pressure or a compounded set up like the new Ford. Cat has been doing it for a few years with the semi's too. But the manufacturers do it for emissions.

 

[Double J]

You all know what I'm talking about, something like this... [/SIZE]



Don't let it get over 1250 EGT's, don't shut it off until under 350 EGT's, don't go over 20 psi boost until it is up to temperature, don't lug the engine, don't "try" to smoke out every car that you see:-laf , don't turn this box on, and don't I repeat don't push this red button!

I tell everyone that now who drives it and it's only a mild daily driver :-laf



That'll be a completley diffrent story next month when the HTTss 66, 240HP injectors, etc goes on.

 

[Red Stroke]

GOT-Torque

THese are the number I come up with for a S3 and S4 configurations.

Here is a brief Schwitzer lineup, the first number is frame size ie: S300, S400, or S500, the second and third numbers are the compressor size ie: S362 would be an S300 with a 62mm compressor wheel. Again, 2. 25kg's in 1lb, the designations are kg's per second, and lb's per minute. Volumetric flow rate can be converted to mass flow by multiplying by the air density. Air density at sea level is 0. 076lb/ft3



S362 0. 48kg/s ~ 65lb/m 855 CFM

S364 0. 55kg/s ~ 75lb/m 987 CFM

S366 0. 59kg/s ~ 80lb/m 1053 CFM

S465 0. 66kg/s ~ 90lb/m 1184 CFM

S471 0. 74kg/s ~ 100lb/m 1316 CFM

S475 0. 81kg/s ~ 110lb/m 1447 CFM

S510 1. 19kg/s ~ 160lb/m 2105 CFM



Also some HX Turbos



HX50 0. 75kg/s ~ 101lb/m 1328 CFM

HX60 0. 95kg/s ~ 128lb/m 1684 CFM

HX80 1. 3kg/s ~ 176lb/m 2315 CFM

HX82 1. 5kg/s ~ 203lb/m 2671 CFM

 

[GOT-Torque]

Double_J, funny video, it is definately a sickness. My wife uses those same words... .

 

[mclunas]

Double_J, funny video, it is definately a sickness. My wife uses those same words... .

my girlfriend doesnt even like to take it to the store

 

[Double J]

Double_J, funny video, it is definately a sickness. My wife uses those same words... .

I keep telling my wife I need to be admitted for this sickness. :-laf

 

[WPeschel]

my girlfriend doesnt even like to take it to the store

My GF wont give it back..... The other day I was riding with her and she raced a dodge datona truck... . That guy got beat by a girl... .

 

[Forrest Nearing]

The example I made was purely hypothetical. That why it says "around". It was insinuated that a twin set up can't be made to spool as fast as your singles and that is total BS. Most twin set ups spool about 100-200rpms slower than the secondary by itself. So by dropping one compressor wheel size or by adding more fuel you can recover that loss in spool up. By dropping one wheel size your not going to sacrafice a lot of hp especially if the big charger is sized correctly.

they don't spool up as fast... you can make them spool SOONER by going smaller on the turbine, but the boost needle doesn't swing as FAST as it does on a single turbo... due to intake and exhaust restriction...

 

[Jim Fulmer]

they don't spool up as fast... you can make them spool SOONER by going smaller on the turbine, but the boost needle doesn't swing as FAST as it does on a single turbo... due to intake and exhaust restriction...

Agreed, funny how my truck makes max power now 400 RPM sooner.



Jim

 

[NoSeeUm]

It's best if you think of it like this: Twins amplify the power capacity of the smallest turbo while keeping close to the same drivabilty/spool up as the small turbo.



Bypassing the turbine side is probably the most critical part to making big power with twins. Non wastegated primaries and undersized wastegates on the secondaries severely limit the power output of a twin system because turbo are needlessly over driven which costs hp. Two turbos take more hp to turn then one turbo so it's not always more efficient. They do have a more efficient powerband, meaning they have a broader range of usable power.



If you look at the new trucks there are basically two approaches to quick spool up and a broad powerband. The VGT's/VVT's which make a larger turbo spool quicker and then open up to relieve back pressure or a compounded set up like the new Ford. Cat has been doing it for a few years with the semi's too. But the manufacturers do it for emissions.

Thanks much for the answer.



I got to thinking about this some more, actually allot more. (OT - I am trying to tune my twins). Your comments about Hp got me stumped a bit.



When you talk about turbo Hp. I am guessing what is meant is the pumping losses generated and the required Hp the engine needs to rise to overcome them. I am assuming the pumping losses can be shown with increased drive pressure. Other wise, to the engine, the exhaust is just waste heat.



A little background in my thinking. From what I know about Hp and fans / compressor fans (limited knowledge) is that if you hold compressor efficientcy constant the Hp requirement is based upon two things. Change in pressure and the change in flow volume. I suppose to some extent compressor RPM is a factor, I am not sure how much. But I believe the major effect is the change in flow volume.



So lets say we compare two turbo systems that are equally optimized in their application. Each is moving 900 CFM @ 45 psi. One is a single turbo set-up, the other is a twin. How would the total Hp requirements compare for each?



Jim

 

[blacksheep4x4]

So if I had a truck that sees light to light action, Drag racing, mud bogging,

and is used as a back up trailer transport truck(mostly small 5th wheels and travel trailers) would I want twins or say a big turbo like the silver bullet? This truck has Dynomite Diesels 90hp injectors, smarty & Quadzilla race box, AFE progaurd 7 stage2 , banks high ram intake and MBRP 5" turbo back exhaust.

 

[Forrest Nearing]

you throw towing in the mix, I gotta give the vote for twins