Forced Induction's FI91X report!
- Thread starter Alky V6
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Dusty Bradford
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Stage 2 heads and a 91mm thumper off of a V8. The large turbine side makes it hard to spool.
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GT55 would have probably worked better or maybe on of Precision's new offerings. Do the Pro Mod units come with small turbine options?
Dusty Bradford
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I didn't look into them much at PRI. I think I saw a GT55 based 94 which was interesting. There is a GN getting a pro-mod 90mm. I look forward to seeing how that turns out.
Thought I'd share a note highlighting how difficult it is to match a torque converter to a dual personality engine. Or, as in my case, an engine with three personalities.
I play with a drag racing analyzer that has given me fits trying to dial it in to match the performance of my car. The way the program is presently setup, it will be impossible to accomplish. The reason being that the torque converter capacity or stall setting is not flexible enough for a turbo engine that has little torque off the turbo, then massive torque on the turbo. Another parameter that lacks flexibility is the engine torque curve. A turbo engine has one torque curve as the engine is spooling and then has another after the engine has spooled to full boost setting. For instance, the engine can have one torque rating at 6,000 rpm as the turbo is spooling to full boost, and then it can have another torque rating after a shift that brings the rpm of the engine back to 6,000 rpm, but this time the turbo is at full boost. I may talk to the programmer to see if he's interested in looking into making the program more turbo friendly.
This is what I've found. In order to match the amount of rpm drop that I'm seeing between shifts, I have to enter a torque capacity value that gives me a stall speed of just over 4900 rpm for the torque curve that I have entered. In order for me to match the curve of rpm rise that I see in first gear from the launch to the 1-2 shift I have to enter a torque capacity value that returns a stall speed rating of 3500 rpm. So this tells me that the stall changes from 3500 rpm at launch to 4900 by full boost. Stall speed is not a rock solid number you can give a torque converter. It changes from one engine to the other, AND, changes with the torque curve of a given engine. Especially noticeable if the engine has a drastic torque value change throughout the rpm range.
So. My torque converter stalls at 2440 rpm off boost and no nitrous. Stalls at 3500 rpm with a 240 hp nitrous shot and no boost. And, stalls at 4900 at full boost (24).
I thought this might be enlightening to some.
Let's say you have a T/C that stalls at 5000 rpm off boost, no nitrous. What do you think the stall is at full boost?
I play with a drag racing analyzer that has given me fits trying to dial it in to match the performance of my car. The way the program is presently setup, it will be impossible to accomplish. The reason being that the torque converter capacity or stall setting is not flexible enough for a turbo engine that has little torque off the turbo, then massive torque on the turbo. Another parameter that lacks flexibility is the engine torque curve. A turbo engine has one torque curve as the engine is spooling and then has another after the engine has spooled to full boost setting. For instance, the engine can have one torque rating at 6,000 rpm as the turbo is spooling to full boost, and then it can have another torque rating after a shift that brings the rpm of the engine back to 6,000 rpm, but this time the turbo is at full boost. I may talk to the programmer to see if he's interested in looking into making the program more turbo friendly.
This is what I've found. In order to match the amount of rpm drop that I'm seeing between shifts, I have to enter a torque capacity value that gives me a stall speed of just over 4900 rpm for the torque curve that I have entered. In order for me to match the curve of rpm rise that I see in first gear from the launch to the 1-2 shift I have to enter a torque capacity value that returns a stall speed rating of 3500 rpm. So this tells me that the stall changes from 3500 rpm at launch to 4900 by full boost. Stall speed is not a rock solid number you can give a torque converter. It changes from one engine to the other, AND, changes with the torque curve of a given engine. Especially noticeable if the engine has a drastic torque value change throughout the rpm range.
So. My torque converter stalls at 2440 rpm off boost and no nitrous. Stalls at 3500 rpm with a 240 hp nitrous shot and no boost. And, stalls at 4900 at full boost (24).
I thought this might be enlightening to some.
Let's say you have a T/C that stalls at 5000 rpm off boost, no nitrous. What do you think the stall is at full boost?
I would suggest a loose converter with a diode, but I'm no expert...Don,If your convertor is 4900 at full boost its time for you to realize taht it is WAY WAY WAY to tight period.
What is your shift rpm?
If your not shifting at 5500 take your convertor out and loosen it and see how much better it spools.
It should be flashing to ATLEAST 3000.
Argue all you want,but you could be out racing and enjoying your car rather than trying to find another way to mask a completely obvious solution.
What is your shift rpm?
If your not shifting at 5500 take your convertor out and loosen it and see how much better it spools.
It should be flashing to ATLEAST 3000.
Argue all you want,but you could be out racing and enjoying your car rather than trying to find another way to mask a completely obvious solution.
If the engine is capable of 10,000 rpm. Probably redline with very little, if any, rpm drop at the shifts.10,000rpm
I'm convinced you're right Otto. I've had the feeling for quite some time. I'm going to play with the tune a little longer before I make a move on the T/C. The more data I have with this T/C, the easier it will be to decide what changes need to be made.
The parts aren't cheap. The more info I can pass onto them, the easier it will be for them to set me up with the right parts the first time.
I've already talked to them about raising the stall and the primary I'm using now is maxed out. I would have to send the whole T/C back to have a new primary fitted.
I want to try a 280 shot with the system and get some data before pulling the trigger.
With Don's small ci engine it should be over 6k at full boost imo. Maybe 6200-6300 And it shouldnt drop below that on shifts or its hurting performance.
It's hard to explain how the T/C capacity works with the program. Real world, at the launch, the stall is around 3,540 rpm on the nitrous (240 shot). The rpm rise and roll out is slow. About what you'd expect using a 3,540 stall t/c with a turbo that doesn't start to spool until about 3,900 rpm. Still being able to clock a 1.66 60 foot due to the nitrous by a wide margin.
Before the shift to 2nd, with the turbo spooled to 238 kPa by 7,400 rpm and still on a very steep climb straight up, the t/c stall characteristic changes and it acts like a 4,900 to 5,100 stall t/c. What I mean by that is, the rpm drop during the shift is about what you'd expect out of a t/c that stalls at 4,900 to 5,100 rpm. The drop is from 7,400 to 61-6,200 rpm. Typically, a 900 to 1,200 rpm drop depending on the rpm at the shift point. With the program, in order to get that amount of rpm drop during the shift I have to use a 4,900 to 5,100 rpm stall setting, while to simulate the launch I have to use a stall setting of 3,540 rpm. So the program actually simulates the launch very well, up to the point of the 1-2 shift. Then, to simulate the rest of the run, I have to use a stall setting of 49 to 5,100 rpm in order to match the real world rpm drop that I see during the shifts. What the real world stall is when at full boost, I don't know. I just know that using one stall setting with the simulation software will not allow a real world output.
What I do like is when I use the stall setting of 5,100 rpm along with a 285 shot for the whole simulator run. The thing is, that's 5,100 stall with the 285 shot. So, what do you think the stall would be without the 285 shot? That's the stall speed I need.
As it is now, a 240 shot raises the stall speed of 2,440 to 3,540 rpm. An 1,100 rpm increase. So to get a stall of 5,100 with a 285 shot, does that mean a stall off the nitrous of 4,000 rpm? Or lower? And if lower, how much lower?
Before the shift to 2nd, with the turbo spooled to 238 kPa by 7,400 rpm and still on a very steep climb straight up, the t/c stall characteristic changes and it acts like a 4,900 to 5,100 stall t/c. What I mean by that is, the rpm drop during the shift is about what you'd expect out of a t/c that stalls at 4,900 to 5,100 rpm. The drop is from 7,400 to 61-6,200 rpm. Typically, a 900 to 1,200 rpm drop depending on the rpm at the shift point. With the program, in order to get that amount of rpm drop during the shift I have to use a 4,900 to 5,100 rpm stall setting, while to simulate the launch I have to use a stall setting of 3,540 rpm. So the program actually simulates the launch very well, up to the point of the 1-2 shift. Then, to simulate the rest of the run, I have to use a stall setting of 49 to 5,100 rpm in order to match the real world rpm drop that I see during the shifts. What the real world stall is when at full boost, I don't know. I just know that using one stall setting with the simulation software will not allow a real world output.
What I do like is when I use the stall setting of 5,100 rpm along with a 285 shot for the whole simulator run. The thing is, that's 5,100 stall with the 285 shot. So, what do you think the stall would be without the 285 shot? That's the stall speed I need.
As it is now, a 240 shot raises the stall speed of 2,440 to 3,540 rpm. An 1,100 rpm increase. So to get a stall of 5,100 with a 285 shot, does that mean a stall off the nitrous of 4,000 rpm? Or lower? And if lower, how much lower?
Dusty Bradford
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You should have enough data for Marty with your 0# boost test. He needs to be a good bit looser down low while sacrificing as little up top as he can. When our 9.5 was desinged, it comes out of the box in this configuration already.
You will always have to use the nitrous but he should be able to get it so that a 200 shot is plenty to get it spooled quickly.
When I shift at 7,400, I feel that I'm lunging it out a little longer than I should. If I shift anywhere between 6,900 to 7,400, it usually yields a rpm drop to the same point of 6050 to 6150 rpm.
With the proper T/C, what rpm drop should I expect?
Remember that a 285 shot with nitrous/alcohol is not the same as a 285 shot with nitrous/gasoline.
Dusty Bradford
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With your engine size I would look for no more than 800. It's just to small with that size turbo to be pulling it back hard on the shift.
When a combo is well matched you can get a converter that pulls back 1000rpm and slips 3-4%. When a combo isn't matched well you have to give up some efficiency to keep the engine in the power band and you'll see the car run faster with 8% slip than it will at 4%.
The rpm pull back on the shift is not a problem with this engine and this turbo. The power is pretty flat from 6000 to 7400 rpm. The boost actually spikes with no drop below the controller set level at the end of the shifts, so the exhaust energy is there to keep this big turbo spooled within that rpm range. The problem with the amount of rpm drop as it is now is purely traction. The tires get shocked pretty hard. I'm also assuming that by going higher with the stall speed will make the rpm drop at the shifts smaller. Am I incorrect with that thinking? Can a t/c that stalls at 3700 to 4000 rpm off nitrous and off boost still have an rpm drop of 1,000 rpm? And if it can, will it shock the tires less and still have good coupling on the top end?
