Turbocharger power requirements

[Scrambler1]

Yeah Justin we'll see what it ends up doing. I'll be leaving off a transbrake but may add a two step or a small shot to get them spooling off the line. But yes PT88 T4's.

 

[JMB Justin]

Yeah Justin we'll see what it ends up doing. I'll be leaving off a transbrake but may add a two step or a small shot to get them spooling off the line. But yes PT88 T4's.

Youll be fine off the line with a brake, I just meant from a 2500-3K hit on the street, I think it will be about 4K for 15psi.
Justin

 

[pokeytemplar]

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

Good, I didn't want to offend, only learn and your input is greatly appreciated. The above is why I wish I had access to an engine dyno. Narrow it down to just what is happening in the engine and then build the tranny, converter and gear changes to its numbers.

The trade-offs are what are so interesting in learning about all of this stuff. Learning each shortcoming and how to minimize it and also maximize each ones benefits (ie cam selection, intake design, etc etc etc.....) is the best part.

 

[pokeytemplar]

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.

Ask your man if the VGT version only has problems in diesels or is it any engine? Looking forward to seeing his response.:rock: and your build looks great!

 

[DevilDawg3097]

Ask your man if the VGT version only has problems in diesels or is it any engine? Looking forward to seeing his response.:rock: and your build looks great!

will do been busy as mother but I give him a buzz in the am and thanks

 

[Smokey]

back pressure is called "drive pressure" gotta use the right lingo
i'll sell you a slightly used hx35

 

[pokeytemplar]

back pressure is called "drive pressure" gotta use the right lingo
i'll sell you a slightly used hx35

How much HP does the drive pressure cost then? If I have read correctly Drive pressure is normally 2-1.75:1 and perfection would be 1:1. So if you are running 18psi of boost there would be anywhere from 36-18psi of drive pressure. That pressure would reduce the efficiency of the engine. That would be the "cost" of driving the turbo. Now we can accurately calculate the HP required to drive the turbos. Thanks Smokey!:rock:

 

[RedSrt007]

Lots of things go into the equation of spool times, but I have Twin 76's with a .96 a/r and get full spool around 4100rpms (which is pretty darn good).

 

[Smokey]

How much HP does the drive pressure cost then? If I have read correctly Drive pressure is normally 2-1.75:1 and perfection would be 1:1. So if you are running 18psi of boost there would be anywhere from 36-18psi of drive pressure. That pressure would reduce the efficiency of the engine. That would be the "cost" of driving the turbo. Now we can accurately calculate the HP required to drive the turbos. Thanks Smokey!:rock:

being diesel, i know turbos better then blowers, but it depends on the drive pressure ur willing to live with, i doubt thay u'll see a drive pressure that high, if so....u messed up and are gunna break shit... ive seen drive pressure that high on spray and thats it, because its more then the waste gate can handle. besides that what waste gates help eliminate, they bleed excess drive pressure out of the turbo thus lowering the drive pressure.

im running a stock turbo in my truck at 38lbs boost, drive is 45 (1.1:1)

IMO turbo>blower:burnout:

outta curiousity, why are you trying to figure this out? no matter what power adder you do, your going to lose power off something good thread tho

 

[pokeytemplar]

Read a couple of interesting things today. If the drive pressure ratio is around 1.8:1 then a belt driven setup would be more efficient. A 2.5psi increase in back pressure resulted in a 7% loss of TQ and HP in a NA environment.

 

[pokeytemplar]

being diesel, i know turbos better then blowers, but it depends on the drive pressure ur willing to live with, i doubt thay u'll see a drive pressure that high, if so....u messed up and are gunna break shit... ive seen drive pressure that high on spray and thats it, because its more then the waste gate can handle. besides that what waste gates help eliminate, they bleed excess drive pressure out of the turbo thus lowering the drive pressure.

im running a stock turbo in my truck at 38lbs boost, drive is 45 (1.1:1)

IMO turbo>blower:burnout:

outta curiousity, why are you trying to figure this out? no matter what power adder you do, your going to lose power off something good thread tho

Well let's say you want to keep "HP strain" below 2000HP (as in the strain the engine sees). If it takes 400HP to drive the turbos then the most you should push at the flywheel would be 1600HP. Much like the belt driven guys do when they size there system.

Example: If I want my twin screw to produce 1500HP at the crank. It takes approximately 175HP to "drive" the twin screw at those levels so I would need to pulley the system to produce 1700HP and also by knowing that it would determine if I needed a w245ax or w305ax to produce those numbers.

Same thing would hold true for the turbos. If you want "x"HP at the crank then you need x turbo. Only problem (or opportunity) here are a lot more ways to get to "x"HP with turbos than there are with belt driven systems. Singles, Duals, Quads, compounds, etc......

 

[Smokey]

how ever you build it....its gunna be one sweet ride

 

[dnz28]

Turbochargers have to be picked out for the application, It Can be as efficent as a blower or better, Its a real trade off if you want less drive the turbo will then be more efficent but it will take forever to build boost. but if you want to take a hit in alittle hp but gain power where its needed and make the powerband wider you want drive pressure. its all in what your after, thats why turbos are so loved. Also a turbocharged engine will respond to engine load better than a charger. then with cutting drive pressure your peak boost will be limited.

also your test would not work
if you put a restrictor on the end of the intake inlet to spool the turbo, you would no longer have the compressed gas leaving the engine so turbo would either not come to boost or take for ever to get there.

 

[pokeytemplar]

Turbochargers have to be picked out for the application, It Can be as efficent as a blower or better, Its a real trade off if you want less drive the turbo will then be more efficent but it will take forever to build boost. but if you want to take a hit in alittle hp but gain power where its needed and make the powerband wider you want drive pressure. its all in what your after, thats why turbos are so loved. Also a turbocharged engine will respond to engine load better than a charger. Also with cutting drive pressure your peak boost will be limited.

I agree it is all in the design goal. For all out power in the SRT-10 rams I cannot find any fault in using turbo(s). Being traction limited as they are the turbos are the perfect fit for big number builds.

My build is not as traction limited because I have full time AWD. I am leaning more towards the broadest powerband possible without as much concern on "peak" HP. I don't have pockets deep enough to win that battle and I really want a daily driver not a dyno queen . At first I will build it as an NA build (560ci) with the CR set for FI after the tune is perfect. It really all depends on how much power I can get NA. If the power down low is already unusable (constant wheel spin:rock: ) then I will do turbos. If not then I will do a twin screw setup.:dontknow:

 

[dnz28]

i like turbos and they just out perform chargers, but in my mind turbos are for teens that have wet dreams of hatchbacks with wings, nothing better then american muscle with a blower. sound, visual, and power. i guess im old school.

 

[pokeytemplar]

i like turbos and they just out perform chargers

I wouldn't necessarily agree with the statement. What if your goal is 1000ft/lbs of TQ from 2000-6000RPM? Turbo is unable to spool fast enough to give 14+psi at 2000rpm and then still be able to flow well enough to continue to provide that boost (or more) at 6000RPM. If you want NO LAG then turbos are not an option and a centrifugal is out as well. If you want efficiency then a roots blower is out leaving only a twin screw. If turbos out performed charges then chargers wouldn't exist. Each has its place/purpose.

 

[bigike]

Heat spools turbos................. How much heat can you create against a given surface area.?

 

[pokeytemplar]

Heat also causes detonation. How much back/drive pressure until detonation occurs? How much reversion reduces the efficiency of the engine and by what percent?

 

[WOT]

Pokey, on some high output engines, there have been examples of drive pressure ratios less than 1. That means that for example if you are making 30psi boost, it is taking less than 30 psi to drive the turbine. In that case, you actually are gaining power (besides the fact that the boost gains you power) due to the fact that the 30 psi on the intake side pushes down on the piston during the intake stroke and makes up for the 30 psi pressure on the exhaust side. With optimized cam timing, you have a 0 hp cost for the turbo. This was supposedly done with a very large turbo and A/R, for a stationary engine.

Of course this wouldn't work during transient conditions (coming off idle, shifting gears, etc). But, it just shows that you can have a turbo with no HP cost at certain states.

 

[pokeytemplar]

Pokey, on some high output engines, there have been examples of drive pressure ratios less than 1. That means that for example if you are making 30psi boost, it is taking less than 30 psi to drive the turbine. In that case, you actually are gaining power (besides the fact that the boost gains you power) due to the fact that the 30 psi on the intake side pushes down on the piston during the intake stroke and makes up for the 30 psi pressure on the exhaust side. With optimized cam timing, you have a 0 hp cost for the turbo. This was supposedly done with a very large turbo and A/R, for a stationary engine.

Of course this wouldn't work during transient conditions (coming off idle, shifting gears, etc). But, it just shows that you can have a turbo with no HP cost at certain states.

Interesting.... If there is any drive pressure though there is a cost to driving the turbo. The cost is a lot less but there is still a cost. We see a benefit from FI because our gains are more than our losses.