Forced Induction's FI91X report!

[Dusty Bradford]

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?

The fastest TSO cars can drop 1200 and not have traction issues if the track is right. Most of your issue probably goes back to tires and suspension. You address this and the traction issue should fix itself.

As you know, there is always a trade off at some point when it comes to converters. Rpm range has more to do with this than anything..it can drop 1000 and stall 5000 if you can turn the motor to 9k. In your case. You have a turbo which is really oversized for your ci and rpm range. Because of this you will not be able stall 4000 without the n2o assist and still drop 1000 when you have power applied. It's possible it can do it when you have a lot of power out of it but you need the converter set-up with full power in mind. I'd shoot for 1000 drop with moderate power and then it should come in around 700-800 when you crank it up.

 

[Alky V6]

A 1000 rpm drop is not important to me. As you stated Dusty, a 700 to 800 rpm drop would be what I prefer also.
I realize that nitrous will always need to be a part of my combination.
The trick is going to be balancing the nitrous shot, and targeting the best stall speed that will get this turbo to 8 to 16 psi quickly enough to help achieve a 60 foot of around 1.3 secs.
The rpm and map rise really starts to turn the corner and take off at 5150rpm/129kPa. I just don't know if that would be a good stall target or should the target be at a lower point? Would targeting a stall of 5100 on the nitrous cause a launch that would be too aggressive?

 

[Dusty Bradford]

A 1000 rpm drop is not important to me. As you stated Dusty, a 700 to 800 rpm drop would be what I prefer also.
I realize that nitrous will always need to be a part of my combination.
The trick is going to be balancing the nitrous shot, and targeting the best stall speed that will get this turbo to 8 to 16 psi quickly enough to help achieve a 60 foot of around 1.3 secs.
The rpm and map rise really starts to turn the corner and take off at 5150rpm/129kPa. I just don't know if that would be a good stall target or should the target be at a lower point? Would targeting a stall of 5100 on the nitrous cause a launch that would be too aggressive?

What rpm have you had success launching at before?

On the limited tire I would guess 4400 (give or take 200) would be an ideal launch rpm. If it sticks because the boost is low at this point and your not making a ton of power, you can raise launch rpm. When you say 5100.....are you talking about 5100 being the point at which the engine will not make any more rpm? I'm thinking you need something that will allow the car to reach 4600 or more rpm easily on the t-brake and then flash to 6600 or so with the nitrous assisted launch. I can't see you being able to leave at a reasonable rpm to plant the tires without also using n2o to get the turbo up to speed.

 

[Alky V6]

What rpm have you had success launching at before?

On the limited tire I would guess 4400 (give or take 200) would be an ideal launch rpm. If it sticks because the boost is low at this point and your not making a ton of power, you can raise launch rpm. When you say 5100.....are you talking about 5100 being the point at which the engine will not make any more rpm? I'm thinking you need something that will allow the car to reach 4600 or more rpm easily on the t-brake and then flash to 6600 or so with the nitrous assisted launch. I can't see you being able to leave at a reasonable rpm to plant the tires without also using n2o to get the turbo up to speed.

With the old turbo, a good launch occurred when a nitrous shot of 190 was used to get the turbo spooled to 10-16 psi just before the transbrake was released. The rpm at transbrake release would vary from 4300 rpm/160 kPa to 4700 rpm/197 kPa. The lack of consistency was because I wasn't using a delay box until towards the end of using the T76.

What I'm thinking of is staging, setting the transbrake, going WOT, having the delay box activate a 285hp nitrous shot so much time before transbrake release, having the rpm rise to 5100 rpm/3-5 psi boost by the time the transbrake is released, and have the nitrous continue helping the turbo until 8 psi was reached. From there, the turbo alone would take over. The boost climb would have to be controlled for the 1-2 shift, then a higher boost would be ramped in after the 1-2 shift. After the 2-3 shift, another step up of the boost until the finish line.

 

[Alky V6]

I think I may have been right on with an earlier idea. I need to keep throwing more nitrous at this t/c until it bends to my submission. I played with the simulators some with higher shot sizes and the simulators love it. Everything falls into line. As the shot size goes up, the stall requirement goes down. Even to stall speeds lower than what my present stall is. The shot size that looks the most promising for the stall I'm using now is a 340hp shot. That happened to be my planned 2nd step up with the nitrous system during the next set of tuning sessions. I may make that my 1st step.

Remember. Theoretically, nitrous/alcohol hp rating = 1/2 x nitrous/gasoline hp rating.

 

[Quint]

I'll tell you that once Dusty losened ours by 400 and put in the Diod, it only drops about 700-800 between shifts if I hit them correctly. We also found that now we do not have to leave on the 2 step any higher then 12#'s or so with the drag radials set at 14#'s to yield 1.27-1.35 60 fts. This is with Nitrous only on transbreak aand once car hits 2 step. it shuts off. With the 3.42 gear and the taller tire, after the launch, its pretty tame, so long as your hooking. This car will go 8.50's, being safe (with a clean pass) and only hitting 26#'s, possibly 27#'s out back,. being the kind of turbo it is, it gives up the low end, but makes up for it on the big end major. Don, you get the converter thing working right and your car will take care of the rest, so long as your susp is working for your car as well, like Dusty said.

 

[Dusty Bradford]

I think I may have been right on with an earlier idea. I need to keep throwing more nitrous at this t/c until it bends to my submission. I played with the simulators some with higher shot sizes and the simulators love it. Everything falls into line. As the shot size goes up, the stall requirement goes down. Even to stall speeds lower than what my present stall is. The shot size that looks the most promising for the stall I'm using now is a 340hp shot. That happened to be my planned 2nd step up with the nitrous system during the next set of tuning sessions. I may make that my 1st step.

Remember. Theoretically, nitrous/alcohol hp rating = 1/2 x nitrous/gasoline hp rating.

The real test will be once you get to the track and start working on 60ft times. The sims are good for testing theories but getting the tire to plant and accelerate the car is something only track time will prove. You will need a lower launch rpm and a larger n2o shot to get the car to hook with a super tight converter. The idea would be to get the converter to flash higher as you launch.

 

[Chevota]

I think I may have been right on with an earlier idea. I need to keep throwing more nitrous at this t/c until it bends to my submission. I played with the simulators some with higher shot sizes and the simulators love it. Everything falls into line. As the shot size goes up, the stall requirement goes down. Even to stall speeds lower than what my present stall is. The shot size that looks the most promising for the stall I'm using now is a 340hp shot. That happened to be my planned 2nd step up with the nitrous system during the next set of tuning sessions. I may make that my 1st step.

Remember. Theoretically, nitrous/alcohol hp rating = 1/2 x nitrous/gasoline hp rating.

?Turbo spline?

 

[Alky V6]

?Turbo spline?

I'm running a THM400. Yes. Turbo spline comes stock.

Quint and Dusty. Thanks for the info. It all makes perfect sense.

I'm hoping that a 345 shot will increase the stall at the launch to about 3900 rpm. With the 245 shot it's 3540 rpm. With that large of a shot increase, if nothing else, it should leave on the nitrous alone rather well, I think. It should also quicken the spool time. Judging from past changes, that will happen to one degree or another. Testing will be the only way to find out.

 

[Chevota]

If the big shot doesn't work I've got an option on the shelf you can try. Although yor spool tune would drastically change it'd be a cheap(free) test.

scott wile

 

[Alky V6]

If the big shot doesn't work I've got an option on the shelf you can try. Although yor spool tune would drastically change it'd be a cheap(free) test.

scott wile

Thanks for the offer Scott. Let me give the nitrous a chance first.

Has anyone done a search on Youtube on nitrous explosions? Very interesting stuff.

 

[norbs]

I don;t understand, why you are risking the motor with that much nitrous, when the correct stall is all you need. Do you know how risky a 345 shot can be at low rpm?

 

[Chevota]

I don;t understand, why you are risking the motor with that much nitrous, when the correct stall is all you need. Do you know how risky a 345 shot can be at low rpm?

Maximum efficiency would be my guess

 

[Otto J]

I don;t understand, why you are risking the motor with that much nitrous, when the correct stall is all you need. Do you know how risky a 345 shot can be at low rpm?

To each his own but I don't know why he ever went with such a big turbo unless he wants to run in the 7s with it.
Any 88 will spool up without Nitrous and cary him to low 8s.

 

[Alky V6]

The short term plan is to get it to 8.50. After it's there, then I'll make the decision what to do next. I went with the 91 because I felt I could make it work to max out the potential of this stage I and then be adequate if I decided to put together my stage II parts. Of course, if I did that, it would mean major chassis changes. Right now, the economy is not cooperating with that plan.

I already answered that one Otto.

You're absolutely right Scott.

Produce a 1.3 or better 60 foot. Run the turbo in the 78% efficiency zone and lose as little as possible to the t/c.

When done right, the nitrous can be less stressful on the engine than boost at low rpm.

 

[Alky V6]

Otto. Don't forget.

The actual hp with a nitrous/alky setup is less than that with a nitrous/gasoline setup.

 

[Alky V6]

Theoretically anyway. I hope.

 

[Alky V6]

Otto. Don't forget.

The actual hp with a nitrous/alky setup is less than that with a nitrous/gasoline setup.

Ooops. I meant Norbs.

 

[Alky V6]

Seriously though. You wouldn't believe how the simulator came around when I started increasing the nitrous. The torque converter started to take on the appearance of pure gold. It looks to be a perfect combination. The cylinder pressures were surprisingly reasonable up to the point that a fair amount of boost started building by the high 4,000s rpm. I'll just need to pick and make sure that a target boost is not exceeded during the spoolup through the peak torque mid-rpm range. Should be a piece of cake with the new boost controller.

A long time ago I talked to Marty about my combination and asked about raising the stall. He was very reluctant to do that. He said it would require a change to a less efficient primary. I'll always remember what he said before we ended the conversation. "Why don't you just throw more nitrous at it?" You know. He may have been right.

 

[Quint]

To each his own but I don't know why he ever went with such a big turbo unless he wants to run in the 7s with it.
Any 88 will spool up without Nitrous and cary him to low 8s.

Otto, yes the 88, would eliminate the need for nitrous, but lets look at how many buicks are honestly running mid to low 8's with an 88. We have seen a few, but most are back halved cars, running much bigger tires and lets be honest, pushing way more then 26-30#'s boost, more like 37-42#'s, which means lots of rebuild cost. Fiscus is the only guy right now that I know with a stock styl susp, running faster then 8.50's most of the time. The Reason a few of us crazy guys run something different and bigger, is to NOT have to push our cars that Hard to hit a number. Should we ever want to go faster, then we have the heads and the turbo already to go for a later build. :smile: