Turbocharger power requirements

[pokeytemplar]

Your comment earlier about a supercharger vs a turbo with the same peak HP, that a supercharger gives a better average is true due to spool time. But who builds a turbo motor to run the 600hp the Roes are capable of? Us doing it are after 1000+.

Here you are doing a direct comparison to a Roe. There are twin screws out there capable of 8.3l/rev. So you could build a 10 with 30+psi of boost right from idle. The only reason a Twin screw isn't making 1000+HP is because no one has invested the time and money to do it(even though some are). Roe designed a system with a very specific goal in mind and I believe that he did an excellent job at. If his goal would have been "no traction...... ever" on a fully built engine I would assume he would have gotten a higher capacity TS to do just that. Please remember this is not a which is better battle. I am just trying to quantify the power required for the turbos to work. They are more efficient but by how much?

 

[Scrambler1]

Well the answer to your question would vary by turbo. Different size turbos with different size A/R's will cause more or less back pressure depending on what the goals were for the build. Also some people with turbos don't run mufflers, so do they make up for what the turbos cost them by having a less restrictive exhaust system?

Too many variables.

 

[JMB Justin]

Well the answer to your question would vary by turbo. Different size turbos with different size A/R's will cause more or less back pressure depending on what the goals were for the build. Also some people with turbos don't run mufflers, so do they make up for what the turbos cost them by having a less restrictive exhaust system?

Too many variables.

Exactly, a T3 turbo would certainly have higher backpressure and HP loss than a T6 turbo on a big ci. motor, and a T6 on a 1.6l honda would probably be 0-1% loss because it is not a restriction. Its the same on the superchargers, you cant generalize superchargers and say they all take X % to drive, because they are all different. A tech at procharger told me that they have a 900HP mule motor to break in the blowers and every F series is dynoed to max RPM. Their 900HP motor literally doesnt produce enough power to turn the big F3's to redline, they have to restrict the amount of air going into them in order to max out the RPM. He said the F1 series is cake to max out with that motor. It will be the same on twin screws, etc. Also the statement that a twin screw will make the same power as a turbo (on the same boost) while having peak boost off idle, I have to disagree. There are no twin screws Ive ever seen making 2000HP, and there are certainly turbo motors doing that. A properly sized twin screw vs a properly sized turbo or centrifugal (on the same boost) will trade low end for high end. A centrifigal supercharger will also never make the mid range or torque of a turbo (or twin screw) because it is based on RPM, the faster you spin it the more boost it makes, where as a turbo makes peak boost at X RPM based on sizing (typically 2500-4000 on a 6K RPM motor vs. 6K on a 6K motor on the centrifugal). So you have to decide what you want, big low end TQ and moderate HP or big midrange TQ and high RPM HP. I like the centifugals and turbos because they are more traction friendly IMO, but a big twinscrew would be a blast to drive too. BTW this is not directed at any person, just my .02 in general.
Justin

 

[pokeytemplar]

Exactly, a T3 turbo would certainly have higher backpressure and HP loss than a T6 turbo on a big ci. motor, and a T6 on a 1.6l honda would probably be 0-1% loss because it is not a restriction. Its the same on the superchargers, you cant generalize superchargers and say they all take X % to drive, because they are all different. A tech at procharger told me that they have a 900HP mule motor to break in the blowers and every F series is dynoed to max RPM. Their 900HP motor literally doesnt produce enough power to turn the big F3's to redline, they have to restrict the amount of air going into them in order to max out the RPM. He said the F1 series is cake to max out with that motor. It will be the same on twin screws, etc. Also the statement that a twin screw will make the same power as a turbo (on the same boost) while having peak boost off idle, I have to disagree. There are no twin screws Ive ever seen making 2000HP, and there are certainly turbo motors doing that. A properly sized twin screw vs a properly sized turbo or centrifugal (on the same boost) will trade low end for high end. A centrifigal supercharger will also never make the mid range or torque of a turbo (or twin screw) because it is based on RPM, the faster you spin it the more boost it makes, where as a turbo makes peak boost at X RPM based on sizing (typically 2500-4000 on a 6K RPM motor vs. 6K on a 6K motor on the centrifugal). So you have to decide what you want, big low end TQ and moderate HP or big midrange TQ and high RPM HP. I like the centifugals and turbos because they are more traction friendly IMO, but a big twinscrew would be a blast to drive too. BTW this is not directed at any person, just my .02 in general.
Justin

This isn't a very good explanation. If you improperly size everything nothing will work right and losses will be huge or gains minimal. My question is if it is correctly sized for the application how much power is lost due to the increased back pressure?

All of them are tied to engine RPM as well (some more directly than others).

I don't understand the part about the 2000HP comment.:dontknow: Like I said I am not trying to bash one over the other.

Huge low end TQ and High HP are possible they just have to be sized perfectly for the intended application. Problem is no one can afford a truly custom one-off FI system for their vehicle. Thus we are stuck making trade-offs. I am trying to find out what all of the trade-offs are with a turbo build. I understand all of the trade-offs with a belt driven solution (Twin screw, centrifugal, roots) and all of the turbo's except for the power requirements.

 

[DevilDawg3097]

I talked to him today, he is checking, and he said to get rid of that new style, youll have nothing but problems, also your 35 is close to the flow but with the hx 40 it can easily be upgraded and run the 50 inerts there is 1.5mm differance in the 50's housing that bolts to the manifold. But you stumped him too and now you have him curious becuase he said in 30yrs that is the first time anyone has ever asked him that:marchmellow: So as soon as I hear from him I will let you know.

 

[JMB Justin]

Properly sized is very vague, properly sized for what, max power, max spool time, max torque? at what boost? what HP level? There is so much more than "properly sized". The 2000hp statement was a twin screw vs. turbo, Ive never seen a twin screw making 2000HP but there are certainly 2000+ HP turbo setups, so does that mean the twin screw isnt properly sized or...??? A twin screw will not make the same max horsepower as a turbo setup given "properly sized" vs. "properly sized". I guess the real question I have is whats the difference, if a "properly sized" turbo will make more power than a "properly sized" supercharger and you want more power, then why will the amount of power loss play a role in your decision since no matter what it will be a larger power gain than the alternatives. The real deciding factors would be when you want your power and how much you want, which is also how you determine "proper size" for any power adder.
Justin

 

[DevilDawg3097]

Hey justin just for shits and giggles If in the future ( an article on a mustang pokey gave me) thats where the Idea came from a supercharged turbo A) would it be possible removing restrictor plates and adding a turbo nothing huge ( I only know holset specs so) comparable to the size of a hx 40 is it doable 2 when a turbo kicks in on a setup like that what happens to the s/c because I know It can not flow or keep up once the turbo is wide open?

 

[Scrambler1]

Pokeytemplar, let me give you an example of two very different "properly" sized twin turbo setups. Same basic engines are far as displacement and ability to move air. The numbers aren't exact but very close.

1. Twin 76mm turbos, setup to be full boost 3500rpm, 1500hp.

2. Twin 88mm turbos, necked down A/R for full boost at 3500rpm, 1500hp

Both do the same thing. The larger turbos are doing less work to make the same boost but the exhaust side is restricted to still spool up relatively early. Spool up from zero will be a little slower on the larger turbos but with full boost realized at the same time. The larger turbos obviously have the capacity to make more power but are limited by BOV's.

So which is more efficient, the smaller turbos working harder (more heat) or the larger turbos with more exhaust restriction?? I really don't know but that is two ways to tackle the same problem with very similar results.

 

[blackviper]

And now we start on compounded boost setups. I've certainly given this alot of thought. The easiest way would be to use a similar setup to the STS.

 

[DevilDawg3097]

And now we start on compounded boost setups. I've certainly given this alot of thought. The easiest way would be to use a similar setup to the STS.

Thats it, it was on the tip of my tongue and i couldnt find the article. I think I would be able to keep it all up top with a log style manifold. I am just curious as what happen to the s/c whenn it can not keep up does it act as a restricter or flows what the turbo is feeding it?

 

[blackviper]

The S/C should not create a restriction. It should simply multiply the boost it receives. Compare PSI to atmosphers in theory.

 

[Scrambler1]

Devildawg, google compound boost, that's what you're talking about.

It's a very cool idea, instant roots blower torque with turbo power up top. The shop working on my truck recently built a compound boost mustang. This cool idea comes with a couple caveats...

1. Tuning it is a HUGE pain
2. Since the supercharger becomes the restriction you get very very high manifold pressures to make the same power up top. I am not sure what the longevity will be.
3. Damn it's expensive!!

I understand the setup is a monster to drive and a blast on the street. I'd love to see someone do this on a Viper motor. I'd be more temped to try a setup like a diesel truck where a small turbo spins up the larger one. I think the results would be very similar with a large displacement engine like ours.

 

[Scrambler1]

Here's a link to a diesel compound turbo setup for a Cummins engine click here

Justin what would you think about something like this for our engines? The piping may prove to be a bitch. The Cummins has enough room on the passenger side of the block for me to stand in the engine bay.

 

[pokeytemplar]

Whoa now I wasn't trying to get into compound boosting Devildog! I am glad your guy knows what I am talking about and look forward to his answer.

Justin, I seem to have offended you. I have stated this over and over that I am not trying to do a which is better battle. I will always agree that turbos are a more efficient use of power they do have their limitations though.

Scrambler, you are the closest to what I am talking about Two setups both produce the same power at the same time however, the bigger turbo with the lower A/R (to decrease lag) will be creating more back pressure to spool the turbine. That twin 88 most likely will be making less HP at sub 3500rpm due to the increased back pressure. The twin 76 more HP at sub 3500 but looses out in the top because it runs out of "wind". I cool comparison would be dom's dyno sheets from the first and second turbo setups (if they were done on the same dyno and no other mods done).

 

[pokeytemplar]

OK I will play the compound boost game but please start another thread. i am trying to stay on topic here.......

 

[yellowfever#154]

Go to the yellowbullet and ask there. Thats were my answer to your question came from.

 

[Scrambler1]

Scrambler, you are the closest to what I am talking about Two setups both produce the same power at the same time however, the bigger turbo with the lower A/R (to decrease lag) will be creating more back pressure to spool the turbine. That twin 88 most likely will be making less HP at sub 3500rpm due to the increased back pressure. The twin 76 more HP at sub 3500 but looses out in the top because it runs out of "wind". I cool comparison would be dom's dyno sheets from the first and second turbo setups (if they were done on the same dyno and no other mods done).

Yes but the added heat of the smaller turbos robs efficiency. So the larger turbos are less efficient down low and the smaller ones are less efficient on the big end. I guess I'm trying to say that I don't see a way to really compare which is more or less efficient overall. You could narrow it down some by comparing street use or track use. Also I was pulling the RPM's out of thin air but you could get both of those setups to hit full boost at 2500 rpms on a 500+ ci engine.

I need Stinker to get his truck running again as I was really comparing his truck to mine if he is still changing to larger turbos. I'm currently having a twin 88 setup put on my truck. Our engines are very close in overall build and it will be interesting to compare the dyno sheets. I'll also be curious to compare mine to Dom's since he's running such a big single, again similar engine.

If you want to really confuse things we can introduced water cooled, different bearing types, etc.

 

[pokeytemplar]

Properly sized is very vague, properly sized for what, max power, max spool time, max torque? at what boost? what HP level? There is so much more than "properly sized". The 2000hp statement was a twin screw vs. turbo, Ive never seen a twin screw making 2000HP but there are certainly 2000+ HP turbo setups, so does that mean the twin screw isnt properly sized or...??? A twin screw will not make the same max horsepower as a turbo setup given "properly sized" vs. "properly sized". I guess the real question I have is whats the difference, if a "properly sized" turbo will make more power than a "properly sized" supercharger and you want more power, then why will the amount of power loss play a role in your decision since no matter what it will be a larger power gain than the alternatives. The real deciding factors would be when you want your power and how much you want, which is also how you determine "proper size" for any power adder.
Justin

Justin,

None of this is for me to make a decision on which to buy. It is based on my curiosity of how much the turbo power "costs".

My NA power levels will determine if I do a turbo or twin screw build. Remember I am not building the same ol' 10 mine is a little (no A LOT) different.

 

[pokeytemplar]

Yes but the added heat of the smaller turbos robs efficiency. So the larger turbos are less efficient down low and the smaller ones are less efficient on the big end. I guess I'm trying to say that I don't see a way to really compare which is more or less efficient overall. You could narrow it down some by comparing street use or track use. Also I was pulling the RPM's out of thin air but you could get both of those setups to hit full boost at 2500 rpms on a 500+ ci engine.

I need Stinker to get his truck running again as I was really comparing his truck to mine if he is still changing to larger turbos. I'm currently having a twin 88 setup put on my truck. Our engines are very close in overall build and it will be interesting to compare the dyno sheets. I'll also be curious to compare mine to Dom's since he's running such a big single, again similar engine.

If you want to really confuse things we can introduced water cooled, different bearing types, etc.

Your build could prove the answer then (specifically for your build). Do the three steps from my first post and you would be the closest at actually measuring the amount of power required for your power levels. I know that there are a million different variables out there that make each one unique. It would just be really neat to quantify the losses (other than just saying "less than a belt driven one")

 

[JMB Justin]

No offense taken at all, its merely a discussion and I put in my .02. I can overlap doms sheets but they wont tell you much since it has to be in MPH (lost tach signal, so torque reading is all screwed up) and he did a gear change from 4.11 to 3.73 so when read in MPH, they dont line up.

No matter what you will trade low end for top end on a turbo setup with no other power adders, its just a matter of how much you want to trade. Doms original motor without heads/cam picked up over 600whp with the turbo kit, no internal changes made at all, full boost in the 2800 rpm area, his new turbo picked up 850-900whp over his motor NA, but full spool at 3400rpm approx. on the street (full spool depends on the amount of boost obviously). Looking at his new sheet, even on pump gas it picks up 500+whp from 95 to 115mph, and on race gas it picks up over 850whp from 95 to 125MPH (pulls to 150 in 4th).

I do have to disagree with Joe in the statement that twin 88's can spool at 2500rpm on a viper motor (or even 76's for that matter), Tonys was spooling low to mid 3000's with 67's and im guessing your using Precision PT88 T4's which are also journal bearing. Even ball bearing wont make that much difference on this application, at best 3-500 rpm. I would guess on the dyno, 4K+ RPM spool (to 15psi), on the street, probably mid to high 3000's (heavy QC will certainly help). I really cant see how Doms single T6 88 (with the smallest exhaust side) would spool after your twin t4 88's, but ive been wrong before. Typically in a viper twin PT88's is a 4K+ spool.
Justin