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

[GOT-Torque]

With all things being equal, which would flow better on top. Don't care about spooling, lag, smoke, etc. Just thinking of top end flow and hp...



How would a set of twins using a small turbo "X" and large turbo "Y" compare to running the same large turbo "Y" by itself?



Would the large turbo "Y" flow more or better on the top end as a single due to less restrictions in the exhaust flow path?



Or would the twins flow more due to each turbo working more efficiently?

 

[2broke2smoke]

i'm gonna tag this one ... should be interesting



i would think the large single would be better with no concern for spooling ... lag ...



you would not have to contend with the restriction caused by the smaller turbos exhaust housing ...



like to hear what the experts have to say

 

[zstroken]

I am gonna say if the twins are sized and wastegated correctly they get my vote.

 

[oneshotkyle]

i'm kinda curious to what the pro's say also.



but i would have to go out on a limb and say if lag wasn't an iissue a big single would get my vote. simply cause there is less restriction to the flow. i believe twins are more efficient to a certain degree.



come on big turbo pro's lets here it, come and let it all hang out.

 

[zstroken]

Look at the big boys, unlimited single, but they put a limit on the size of the twins. It will take a larger single charger to make the power of a smaller set of twins. Plus your torque numbers are typically higher with the twins. This is the theory behind the twins, your taking what ever air comes out of the bottom charger and putting it through another compression stage. This is assuming your make provisions on the small charger to expel the turbine gasses without huge backpressure.

 

[DieselTweaker]

how large do you consider large??

Zach

 

[Idaho CTD]

A large single will make more power. As a single you can make upwards of 100% the lb/min. flow x 10. In twins about the best you can expect even wastegating the larger turbo is about 80-85% of the lb/min. flow x 10 of the primary. Things can vary some from this but in general it is pretty close. The upside to twins is you can spool a much bigger primary then you can run as a single to overcome the percentage difference. Another upside to twins is the ability to get more air into a given area over a fixed amount of time due to higher PR's. The down sides are keeping the head on, cost, and the difficulty of plumbing.

 

[zstroken]

A large single will make more power. As a single you can make upwards of 100% the lb/min. flow x 10. In twins about the best you can expect even wastegating the larger turbo is about 80-85% of the lb/min. flow x 10 of the primary. Things can vary some from this but in general it is pretty close. The upside to twins is you can spool a much bigger primary then you can run as a single to overcome the percentage difference. Another upside to twins is the ability to get more air into a given area over a fixed amount of time due to higher PR's. The down sides are keeping the head on, cost, and the difficulty of plumbing.

Even if the larger charger has less effeciency, shouldnt the factor of the smaller charger be taken into consideration as boosting the system efficiency. Remembering that the same charger is used in both the single and the twin setup. What is the x 10 for? Also if you can get more air in wouldn't that be more power on the top end?

 

[GOT-Torque]

My original question is based upon the fact that the same large turbo is used as a single vs. using it in a set of twins.



For example, for my setup I am using a dodgezilla and a B2 turbo. How would this compare to running a B2 all by itself? (I don't even know if it is possible, but the question still applies).

 

[Idaho CTD]

Ok for an example: If a B2 flows 96lbs/min x 10 is 960. So a B2 as a single can make upwards of 960hp. Usually this is a bit optimistic but 90% is definitely doable which would be 864hp. Now in twins a B2 primary would be lucky to make in the low 700's wastegated.



The efficiency of the 3rd gen's seems to be much higher than the older trucks. This is probably because of the higher injection pressure which leads to better atomization and more complete combustion.



Unfortunately the small charger hurts the efficiency of the big charger because it creates a restriction in front of the primary. The reason the percentages are as close as they are is because each turbo is working in it's most efficient part of it's map in addition to the elevated boost pressures.

 

[GOT-Torque]

If that was the case, then why would some classes (in truck pulling) not allow twins? If it is known that a single of the same size would produce more power, why not allow twins in the same class and just have an overall limit on inducer size?



I had somewhat thought a single would make more top end power, however I was confused by some of the rules I've run across.



Maybe it is due to the torque? Don't twins make quite abit more torque than a large single?

 

[zstroken]

I thought I had seen twins with a b2 configuration break the 1000HP mark I mean I am not talking a hx35. I am meaning a 62mm+ charger and the B2. The people I have talked to have said differently than what we are talking. Hopefully we can get some more input. Why do the tractors have singles, twins, and triple classes. I am still thinking the compound charger setup will put down better numbers than the same big charger used alone. Maybe I am way off(again ) say your top charger is increasing by 14. 7 psi well effectively that is another atmosphere, hence twice the air is no being moved through, the engine. So wouldn't that be more power?

 

[BradyWilliams]

There are many factors to consider when choosing a turbo set up. We make large singles that have raised the bar and continue to due so as we come out with better products. Twin turbo sets as in compounded twin turbos have the ability to spool up better than a huge single, but not as well as a large single like our Super Phat Shaft turbos or our new Silver Bullet turbos. We have made our Twin Turbo sets to be larger than most as the need for hp has been going up. Twin Turbo sets have the ability to deliver higher boost pressures and more air volume at a cooler temperature. This is what you will need to make bigger hp and help keep EGT's in check. Twin Turbo sets can run high turbo drive pressure (exhaust back pressure) if not configured right. Running exhaust through two turbos can produce high drive pressure. By selecting the right types of turbos and sizes the drive pressure can be kept down. Huge singles have been used to sled pull with. They DO NOT spool very well and are set up on engines that are tuned to run in a specific RPM range and hp range. Large singles are easier to afford than twins. Twins do offer value in performance but are more money than singles. Huge singles do offer a lot of air at a cheaper price than twins but could never be driven as a daily driver. Thanks

 

[BradyWilliams]

This subject can go on for pages. I don't want to go too wild here but may add more later.

 

[RonA]

I thought I had seen twins with a b2 configuration break the 1000HP mark I mean I am not talking a hx35. I am meaning a 62mm+ charger and the B2. The people I have talked to have said differently than what we are talking. Hopefully we can get some more input. Why do the tractors have singles, twins, and triple classes. I am still thinking the compound charger setup will put down better numbers than the same big charger used alone. Maybe I am way off(again ) say your top charger is increasing by 14. 7 psi well effectively that is another atmosphere, hence twice the air is no being moved through, the engine. So wouldn't that be more power?

Do not confuse boost pressure with lbs/min of air. My SPS 62/K31 combo makes 64psi of boost at 500 hp. My SPS/B2+ makes 670 at 63psi. Much more air, 1psi less boost. Same 32psi on primaries. The only air you actually get to the motor is what the primary is putting out. The top charger helps get the bottom going, and then basicly gets in the way.

 

[zstroken]

Do not confuse boost pressure with lbs/min of air. My SPS 62/K31 combo makes 64psi of boost at 500 hp. My SPS/B2+ makes 670 at 63psi. Much more air, 1psi less boost. Same 32psi on primaries. The only air you actually get to the motor is what the primary is putting out. The top charger helps get the bottom going, and then basicly gets in the way.

I know Ron, that is why I said 14. 7psi instead of 40 psi(plus 14. 7 just happens to be atmospheric) for the boost of the small charger. Actually it isn't much more air, it is just that the air your using is much more dense. I would be curious to see if you had a temperature probe on the inlet charge and see if there was much of a difference in the air temp. Too much pressure is just heat, you have to find the point of where the added pressure doesn't make it too hot, which decreases the density. We are back to why do they let the single charger setups be unlimited and they put the size limit on the twins.

 

[Idaho CTD]

In my opinion they let the singles be unlimited because they have a much narrower power band. So at the bottom end (taking off) they aren't as good as twins and when the sled bogs the truck down you fall off the charger, so to speak, sooner then you would with twins. Running a restricter for say a 3. 0 inducer class doesn't neccessarily hurt the guy running twins because he can be using a turbo with a 3. 5 inducer and a restricter. He will make more power than a guy using a 3. 0 inducer turbo and no restricter. The part that hurts the twin guys is that most of these classes have inducer size restrictions small enough that they can easily be ran as a single. For example: the 2. 8 inducer class is only a 71mm turbo and many people run those as singles and can make a fairly broad powerband with them. If they were to raise the sizes to say 3. 4" then you'd see way less people running singles that big because they are considerably harder to spool creating a narrower powerband.

 

[Idaho CTD]

Twin turbo sets as in compounded twin turbos have the ability to spool up better than a huge single, but not as well as a large single like our Super Phat Shaft turbos or our new Silver Bullet turbos. We have made our Twin Turbo sets to be larger than most as the need for hp has been going up.

This is false. You can make a twin set up spool as well as any single and make more power than any single. For an example: You take the 66mm Silver bullet as a single. It spools at say 1800rpms. Now you take a 64mm Silver bullet (it spools at 1600rpms as a single) in a twin set up. With a big enough primary you can make way more power with the twins then the Silver 66 and still spool at 1800rpms.



What does your "Big Brother" primary set up flow?

 

[BradyWilliams]

Spool up is relative to fueling as well as turbo configuration. I have a Silver Bullet on my truck. With the TST on 5, I see positive boost pressure by 1500rpm and spool up from there is VERY FAST. If I put a Silver Bullet on a Stock truck with no fueling then you maybe correct at 1800rpm. We also make smaller turbos like our Super Phat Shaft 62 or our Silver 62 which spool very fast. Then we can use our . 70 A/R housings which make even faster spool up. Since the smaller turbo is there to help in spool up then yes you can configure the twin set to spool quicker with a turbo that spools quicker. The air flows are affected by the large turbo and interupt the air flows on both sides of the turbo. This always affects the spool up of the twin set. Yes you can configure the twin set to spool well and yes you can make big hp with twin sets. A top turbo that is too small will limit hp capability even with a very large bottom turbo. (Quick Spool And Low HP) I do realize that I did not give every piece of information that could be brought up. I did state that I may chime in again to further clarify my statments and to add more information to this thread. I have not talked about all of the information that can be brought up and talked about. It is a VERY large subject and I will help when I can.

 

[Jim Fulmer]

Brady, kind of remind me of the 40-B/B setup that I built and ran, then how much better it did after I swapped out the 40 for a SPS 66, much better combo!



Jim