Time to go Stage II!

[Alky V6]

An interesting thing about the differences in the two power curves, the 60', and the affects on converter stall that some may not be grasping.
With the Stage I configuration, and with having the torque curve dropping rather than climbing during the launch, the torque converter stall was decreasing during the launch. With the car gaining speed after coming off the line, you would expect engine rpm to rise, which would help boost to rise quicker also. What I experienced with the Stage I setup was that the rpm would stay flat for the very first part of the launch. Even though you would expect rpm to rise as car speed was increasing, the rpm stayed flat for a short time coming off the starting line.
Using an engine where the torque is increasing after the launch from the starting line, the TC stall speed will also be increasing. There will be a multiplier effect going on during the first part of the launch. Increasing car speed will have engine rpm increasing as you would expect, and with the rising torque curve, TC stall will also be increasing. The result will be a faster ramp up of engine rpm during the first part of the launch which can only help the turbocharger spool up quicker. A faster boost rise curve will only help reinforce and add to the rising torque curve.
This is all due to the fact that a particular torque converter will stall at different engine speeds depending on the engine torque input level.

 

[Dusty Bradford]

We have a customer who runs outlaw 10.5 with a small motor by today's standards. Small block. We've loosened the converter 3 times and it has gone faster each time. People get hung up on slip numbers but it comes down to what the motor wants and it's operating range. Some cars are faster with 15% slip rather than 5%. This tends to be the case with high rpm cars. If you get a converter to slip less but it drops 1800 rpm on a gear change your pulling it out of it's power range. This is the advantage of a Bruno type transmission. You run the gear ratios very close so the engine stays in a certain range and the converter can be tight.

 

[Alky V6]

We have a customer who runs outlaw 10.5 with a small motor by today's standards. Small block. We've loosened the converter 3 times and it has gone faster each time. People get hung up on slip numbers but it comes down to what the motor wants and it's operating range. Some cars are faster with 15% slip rather than 5%. This tends to be the case with high rpm cars. If you get a converter to slip less but it drops 1800 rpm on a gear change your pulling it out of it's power range. This is the advantage of a Bruno type transmission. You run the gear ratios very close so the engine stays in a certain range and the converter can be tight.

Yes. I can see that. That makes sense. The reason the sim is showing better times with the higher shift points (above 9,000 rpm) is because by the completion of the shifts, the rpm hasn't dropped down as far out of the powerband, resulting in a higher average power level through the shifts.

 

[Alky V6]

It's looking like the rpm drop will be around 1,400-1,600 rpm at shift points of 9,000 rpm. I can't get it any closer than that because the sim shows different rpm drops between the 1-2 and 2-3 shifts. It did that with the Stage I configuration too. I would match the sim to the real world 2-3 shift rpm drop, and ignore the resulting incorrect rpm drop the sim would end up calculating for the 1-2 shift.
If the sim continues to follow the 2-3 shift rpm drop more accurately than the 1-2 shift, then the rpm drop for both shifts should be closer to about 1,400 rpm.

 

[Alky V6]

A couple great quotes from a book I recently picked up and have been reading.

The author asks, "In a turbocharged engine you don't want to hold the intake valve open as long as you do in a naturally aspirated engine, do you?"
Reply from Gale Banks, "Why not?"

This is a new favorite quote of mine from Gale Banks in the same book. "Who cares what a competition vehicle runs like below its intended operating range?"

Another quote from the author out of a section of the book entitled, 'Single Versus Twin Turbos'. "Once the vehicle with a big single unit is launched using such tuning mechanisms (referring to ALS tuning techniques), the higher system efficiency takes over and the single unit will pay dividends in lower ETs."

ref: "TURBO, Real World High-Performance Turbocharger Systems" by Jay K. Miller, 2008.

 

[geno]

(I would match the sim to the real world) This makes the most sense yet,but you need to go to the track first and show us how to get a stock suspention small tire car go 1.14 in 60ft first..Just got to bust your balls because of pages and pages of techno-babble and no impressive numbers put up on the board yet. Show me the numbers like Dave Fiscus and the TSO boys do with a smaller turbo than yours and i will be impressed with all of this..Until then its all words with no real numbers..

 

[Alky V6]

(I would match the sim to the real world) This makes the most sense yet,but you need to go to the track first and show us how to get a stock suspention small tire car go 1.14 in 60ft first..Just got to bust your balls because of pages and pages of techno-babble and no impressive numbers put up on the board yet. Show me the numbers like Dave Fiscus and the TSO boys do with a smaller turbo than yours and i will be impressed with all of this..Until then its all words with no real numbers..

In the end, that is exactly the plan. To compare real world testing to the predictions of the sim. Getting the stock suspension to perform sub 1.20s shouldn't be impossible. Do you have evidence to the contrary? Is it really that hard?
All the techno-babble is just me thinking out loud. I would guess that it's extremely boring to most. Sorry 'bout that. It's just how I am. I like to share my thoughts. Hopefully, some find some of it interesting and thought provoking.

What I'm attempting to do with all this sim work is to come up with the best sim numbers I possibly can with as accurate of inputs as I possibly can. It should prove very interesting when I finally can compare the sim results to real world testing.
The latest peak bhp estimation that I've come up with for the Stage II project is 1,580 at 40 psi boost, from 228 cubic inches. 6.9 hp/cid. What's the displacement limit for a TSO engine? A maxed out TSO engine with 6.9 hp/cid should be putting out about 1,890+ bhp? Is that what they're doing?
The latest difference came with more work with the exhaust header system specifications. About a 50 hp jump from the last estimation.

 

[Alky V6]

Gene. I wonder if the TSO guys could go even faster if they were allowed to use a larger turbo.
Seems to me, the turbo size restriction is meant to control top end performance. I'd bet they could go faster.

 

[Dusty Bradford]

Of course they could go faster with a bigger turbo or with twins. But that's the limit placed on the class and that's what they have to deal with.

 

[Dusty Bradford]

Another quote from the author out of a section of the book entitled, 'Single Versus Twin Turbos'. "Once the vehicle with a big single unit is launched using such tuning mechanisms (referring to ALS tuning techniques), the higher system efficiency takes over and the single unit will pay dividends in lower ETs."

ref: "TURBO, Real World High-Performance Turbocharger Systems" by Jay K. Miller, 2008.

The part in bold...........discredit's everything this man has to say.

Unless you have a big enough single and compare it to some very small twins, this guy couldn't be more wrong.

Take TSO for example. Run a 47-88 up to 40psi with backpressure at 65psi. Now put twin 70's on it at 40psi boost/ 37psi bp and the twins will run circles around the single.

 

[Alky V6]

The part in bold...........discredit's everything this man has to say.

Unless you have a big enough single and compare it to some very small twins, this guy couldn't be more wrong.

Take TSO for example. Run a 47-88 up to 40psi with backpressure at 65psi. Now put twin 70's on it at 40psi boost/ 37psi bp and the twins will run circles around the single.

Wait a minute. Who claims that you have to run high exhaust backpressure with a large single? You're picking one turbocharger model and building a universal claim using just that one example?
Haven't you learned anything from what I've been doing?

 

[Alky V6]

With the Stage I, I documented 28 psi boost with only around 22 psi exhaust bp with a large single turbocharger. Using the same turbocharger with this Stage II project, I plan to see around 37 psi exhaust bp while generating 40 psi boost pressure.

 

[Alky V6]

The part in bold...........discredit's everything this man has to say.

You should do a little research first on who this person is before you go off criticizing him like that.

 

[Dusty Bradford]

Wait a minute. Who claims that you have to run high backpressure with a large single? You're picking one turbocharger model and building a universal claim using just that one example?
Haven't you learned anything from what I've been doing?

And what model is he using to support his claims? It would take a severely undersized set of twins for a given engine not to make more power than a oversized single. It appears he is using one example and building a universal claim himself.......

 

[Alky V6]

And what model is he using to support his claims? It would take a severely undersized set of twins for a given engine not to make more power than a oversized single. It appears he is using one example and building a universal claim himself.......

This is something I learned myself quite a while ago. Large turbine housings tend to be more efficient than smaller turbine housings. Nevermind the compressor side for now. Anytime you can use a hot and/or cold side that is more efficient, you will make better use of energy, and will waste less of it.
Take a better look at Mr. Miller's statement again. "Once the vehicle with a big single unit is launched using such tuning mechanisms (referring to ALS tuning techniques), the higher system efficiency takes over and the single unit will pay dividends in lower ETs."
I highlighted the part of the statement that you decided to leave out of your opinion. This part of the statement is very important.
Some have learned that if you can manage to get a large hot side spooled up in a reasonable fashion, you will end up with better efficiency and use of the available exhaust energy.

 

[Alky V6]

Another point that Mr. Miller makes in his book, that some don't seem to realize or take into consideration, is the inefficiencies of each turbine assembly, and compressor side, for that matter, brought about by the running clearances between the wheels and their housings. Anyone that has ever dealt with the jet pump of a jet boat understands where I'm coming from. And you, Dusty, working with clearances inside a torque converter should understand this too. A twin turbo setup simply doubles or multiplies those types of inefficiencies.
As pointed out in Mr. Miller's book, there are other considerations where it comes to choosing a single over a twin setup. Street use versus strictly drag use being a primary consideration. But, for strictly racing, if a proper turbo can be mounted and sized for the application, and a sufficient anti-lag strategy can be employed, the large single will be more efficient, waste less energy, and will allow more power to make it to the rear wheels, hence lowering ETs. As long as that extra power can be successfully transmitted to the ground.

 

[norbs]

You might have 2x the clearances, but 2x the flow with twins ......I tend to agree with Dusty here.

 

[Alky V6]

You might have 2x the clearances, but 2x the flow with twins ......I tend to agree with Dusty here.

2 times the flow?
Norbs, do you know how to size a single or a twin setup to an engine?

 

[norbs]

Yes, just use Dusty's example of a twin 70's vs gt47-88. Bring up the maps and figure it out.

 

[Dusty Bradford]

The only scenario where this applies is where the engine is small enough that an extra large single can be sized to keep the backpressure at 1:1 or under which is where twins would operate.

He really needs to venture out and look at every racing sanctioning body rules. Twins are either outlawed or run at a heavier weight because they will make more power. Inefficiency's caused by twice the clearance between the housings due to having 2 turbo's and extra heat loss through 2 turbine housings is nothing more than a theory that can't be proven on the racetrack.

I use a 118mm turbo on a 531ci engine. I could swap to twins right now and pick up an easy 300hp. One local guy just made the swap from running a 114mm turbo on a 427ci engine. Car maxed out at 168mph in the 1/8th. Swapped to twin 88's and has now ran 174. More efficient compressor along with a drastic reduction in backpressure produced a huge hp increase.