SC and TT Characteristics Compared & Discussed

[dbk]

I've tracked my GT at the road course with both the twin screw making around 600rwhp and the TT system and for me the TT is preferable. It's not because it's super duper ultra mega fast on the straights, but rather that the car doesn't want to come around on itself coming out of a turn putting your foot to the floor as much. Those few hundred rpms where you can think about it really help. Oh yeah, and the boost controller works both ways, so there's nothing preventing you from running 600-700rwhp with the TT setup at the track. I told Shelby#18 he was going to like his turbo car at the track better than the big power blower car for this reason, and after he tracked it, he concurred. That said, you can't just stick it in 3rd for the entirety of most courses. And while it still gets flaming hot at the track, it doesn't go into limp mode as fast.

 

[sandman]

Interesting, I guess you can adapt your driving style to the different power delivery. I would still prefer to be able to use the throttle to control the car instantaneously.

 

[dbk]

It's definitely different. For a more serious track rat the blower would probably be better, but I do most of my driving on the street and am not a track expert. I think part of it is that once you're used to the explosion of power above 3500 with the turbos, it's the exact opposite sensation with the blower. I drove a stock GT a few weeks ago and thought "Hey, this thing feels like it goes pretty good!" after just stabbing the throttle. Then I laid into in third all the way to 6800 and thought "Holy shit this car is slow." :lol

 

[Fast Freddy]

in addition to the mile the TT would be the way to go for a maximum effort open road race oriented GT (175+ mph average speeds)

 

[nota4re]

in addition to the mile the TT would be the way to go for a maximum effort open road race oriented GT (175+ mph average speeds)

The TT's race track applicability is far more than just top-end type of events. I'd venture to say that throughout history, there have been many, many more road course win with turbo-equipped cars than SC cars... and even if true there are a multitude of factors that would influence that.

 

[PL510*Jeff]

The various race organizations use different rules and reg's for Turbo vs Supercharged engines. Particularly when fuel octane ratings is the "kicker" when choosing between the two.

Turbo engines, such as the Porsche units, has at one time a distinct advantage in smaller displacement class racing. And the $$$ to make them work. And as everyone knows were quite successful in getting the checkered flag. Mazda successfully exploited the rules with their Wankel rotary engines, whichare said to love low octane fuel.

Today the turbo diesel engines are on the podium quite often. Using bio diesel clean fuel.

For the last three decades it seems there were many more street vehicles using turbocharging than supercharging. I imagine this this was a cost vs performance decision. The current increased use of superchargers on street motors must have something to to do with engine management systems and improved metalurgy for the various components involved. Just a guess on my part.

How about Indy GT chiming in here. Or one the Ford guys that have more "insight" in this discussion.

DBK this could be a wonderful topic for Rally V discussion open mic program.

 

[nota4re]

Well, I don't seem to get slammed when I cite the positives of the SC's, but it wouldn't be fair to discuss the topic without highlighting some of the disadvantages, as well. Here we go....

As good (great?) as the SC is on the low end, generating near instantaneous boost and power in a very linear fashion, there's that darn principal which states that there's no such thing as a free lunch. Unfortunately it is true in the case of the GT SC's as well, with the main nemisis being the trailing-off of efficiency and the power consumption of the SC itself as the RPM's increase. The belt driven SC's require a lot of engine power just to turn the SC. This is power that you will never see or measure at the rear wheels - but it is work that the engine is performing. The amount of HP "consumed" by the SC, can be substantial. In our applications on the GT, an educated guess maybe as much as 75HP for the OEM blower and likely well over 100HP for the big Whipples. Really? So where can we see this.

If we go back at look at this dyno comparison;



notice that from approximately 4200 RPM upward, the boost pressure is flat for both systems (*). But, look at how different the HP curves are. The turbo solution continues to increase the gap and look at the result at the high end - nearly 200HP difference! Again, boost pressures are the same, so what is happening? The two biggest factors at play here (both working against the SC) is that 1.) The SC is "consuming" a lot of power to turn the SC itself and; 2.) The SC becomes a lot more inefficient at generating boost and air inlet temps go up which robs power.

(*) Note: I stated that the boost pressure is flat for both the TT and the SC. How the flat boost line is achieved is VERY different. In the TT system, as the turbo spins up to the desired (adjustable) boost level, the wastegates are designed to start opening to bleed off the exhaust pressure that drives the turbos. By modulating this wastegate valve, the turbo system can maintain a nice, flat line of constant boost pressure. In contrast, the SC has no means of bleeding off pressure to meet a desired boost level and instead relies upon on an inherent decreasing efficiency to essentially run out of steam.

In summary, as good as an SC is at generating near instantaneous boost at low RPMs, they are very, very inefficient at higher RPMs (as compared to a TT) where the advantages/disadvantages are essentially inversed.

 

[Fubar]

Every word in this thread is tainted with personal preference. And that's all it boils down too, so lets just tell it like it is

Turbo=more efficient
SC=more manly

/thread

 

[BlackICE]

Boost is not the best indicator of potential power, Boost is dependent on factors other than air flow, such as discharge temperature and exhaust savaging to name a few. A better measure would be to plot air flow through the MAF (MAF counts) and torque vs. RPM. You will find as you already said Kendall, that at the top RPM range for equivalent air flows the TT will make more power than the SC, but MAF counts instead of boost would give a better picture if the greater efficiency of the TT system. Blowers have a sweet spot, when exceed, their volumetric and adiabatic efficiency falls off. TT in general have the best adiabatic efficiency of any forced induction system.

View the PDF files for a 2.2 and 3.3 liter twin screws.

 

[ChipBeck]

In all seriousness if I had to choose a car with linear power and one with a more abrupt delivery I would pick the linear for obvious reasons.

The SC has more linear power delivery AND far more abrupt power delivery. The older Heffner Twin Turbo GTs have larger collector pipes and boost comes on at about 4000 RPM. The newer ones like mine with the smaller collector pipes come on at about 3500 RPM. I have now witnessed 3 expensive Supercars swap ends and crash with major damage coming out of a corner. All 3 had lost it when that instant supercharger hit broke the rear tires loose. Even above 3500 RPM the power delivery of my TT is a lot smoother than my old SC provided. I feel a lot safer and more secure putting 850 TT HP out on the track than I felt with 650 SC HP at the track. My TT never feels like it want's to swap ends, my SC was eager to bring the tail around.

Chip

 

[skyrex]

I don't think this thread is intending to be pro one system or the other. I always wondered why some of the multi-GT guys had one SC, whipple or regular, and one TT. I understand better now because they are two totally different feels. I love them both, but honestly you have to drive both before you can make a clear judgement. But debate is what make a country or a Forum great. :cheers

I do miss seeing the supercharger spinning in the rear view occasionally though......:biggrin

 

[sandman]

The SC has more linear power delivery AND far more abrupt power delivery. The older Heffner Twin Turbo GTs have larger collector pipes and boost comes on at about 4000 RPM. The newer ones like mine with the smaller collector pipes come on at about 3500 RPM. I have now witnessed 3 expensive Supercars swap ends and crash with major damage coming out of a corner. All 3 had lost it when that instant supercharger hit broke the rear tires loose. Even above 3500 RPM the power delivery of my TT is a lot smoother than my old SC provided. I feel a lot safer and more secure putting 850 TT HP out on the track than I felt with 650 SC HP at the track. My TT never feels like it want's to swap ends, my SC was eager to bring the tail around.

Chip

I’ve seen plenty of N/A , Turbo’ed and Blown cars spin, hell I’ve spun mine at 135mph in turn 1 at Thunderhill. It nearly always a case of driver error! Being in a turbo car will not save your ass anymore than a blown car will cook it! Anecdotal evidence aside what it comes down to is driver competence. The “swapping ends” comment regarding the blown cars keeps coming up; well I want a car that I can transition from understeer to oversteer with my right foot and I want it to happen right now. I would argue to use a TT gal to her fullest extent on a road course you as a driver will be taxed more to keep the gal on boost to get her fastest possible lap time. DBK mentioned putting the blown car in third and running all the way around the track and he is correct! That is the beauty of the blown gals, gobs of torque all through the rpm range. It makes a very easy, very forgiving car to drive on a road course.
As far as which system is right for you, it is your choice and I begrudge no one on their decision. It seems as if some want the TT to be presented as the be all end all set-up for the GT. For many it may be but for me the turbo system’s as presently presented are a non starter.

 

[nota4re]

True Colors!

I don't think this thread is intending to be pro one system or the other.

It certainly WASNT intended to be a pro one system or the other. I think I'm being labeled the TT guy.... but I still have the OEM supercharger (w/pulley) and the cost entry barrier for the TT would be lower for me as I my credit myself the install costs! Despite this I am, at least for now (lol) still a SC guy.

My issue is that I am easily corrupted and I blame my "friends" for corrupting me!!! I remember some heated discussions I had with AlohaGT a few years ago over the bumper delete mod. I told him that he was crazy, he would ruin the car, it looks weird.... and then he finally said well, you need to do it or tell me who can because I'm gonna get it done. Reluctantly, we did the mod. And damn him..... seeing the car in person, knowing the kit and what's behind it, knowing it could be easily reversed, etc.... a couple of months later my car had a bumper delete! Not long after, Gaby asked me to install one of the first Kip Ewing CF binnacle and gauge panels. "Holy crap, Gaby, do you know what that stuff costs? Let's spend the money on some go-fast parts!" Yep, you guessed it, a few weeks later I had the CF gauge panel and binnacle in my car too. (Do yourself a favor and sit in a car with this mod and you'll get sucked in just like me!!)

So now we're doing these TT conversions (damn Heffner). Over the top. Why the heck would someone spend that kind of money for a TT kit when the GT already runs like a raped ape with just a pulley/tune, let alone a nice Whipple upgrade? These people have more money than sense!!!
We finish the first TT upgrade and we are VERY impressed with the kit, all of the quality components, the elegance of the car that can make power from "wasted energy". Then there's the damn sound. C'mon, we've talked about the unique Ferrari sound and no matter who you are, you just have to love the Ferrari exhaust note. It's like that too with the TT. Mind you, it doesn't sound anything like a Ferrari, but it has that unique, "I'm gonna rip your head off if you let me" sound. Intoxicating.

The system is growing on me. I am trying to resist. Once finished with Apollo's car, we take it for a shakedown drive. Low boost, mostly cruising around, but a few dashes to 5000 RPM. Hmmm, this is pretty darn cool. I though the car would feel dead, but no. It is "free-er" now and seems to like to rev quicker. (I think the car wants to get to the sweet spot of those turbos.) And oh, once under way that exhaust note has its way with you! But, I am strong. I shake it off. We have a great dyno tuning session and we deliver the car to Apollo. I have survived and I haven't spent any money!!!

Next up is Skyrex. Of course, install number 2 goes a lot faster. We complete the kit in one week and again come to the point to test drive the car before heading to the dyno. We set the boost low as we primarily want to check the car for driveability, leaks, anomalies, etc. I drive this car at night. The roads are empty. The exhaust again is oh-so-sweet! The evening is cool. I let the car run up to 5K or so a couple of times before taking her back to the lift. The bug has bitten me harder. This car just feels strong. Yes, the butt dyno can easily detect that the direct linkage between the throttle pedal and instant torque has been broken. There is NO doubt about this! But in its place is a car that seems more familiar. A car that has a fuse. When you hit the knee of the power curve, there’s just no putting into words how every interval of acceleration just feels twice as strong as the previous one. Uncontrollable? No way. The car is NOT violent. It is so different than a SC car. Honestly, I don’t want to like this set-up. My pocketbook doesn’t want to like this set-up. I loved my bumper. I loved my dash. I love my SC! There’s nothing wrong with these things that Ford designed “oh so well”.

So there you have it…. am I biased? Yeah, a few weeks ago if you told me you wanted us to take off a perfectly good SC and replace it with a not-so-inexpensive TT system, I’d say you’re as nutty as…. well, uh, as nutty as DBK or Chip. (And then there’s Apollo who ditched a 4.0L Whipple.)

Kidding aside, I started the thread to try to enlighten forum members with my hard-to-describe experience. Start with some fundamental pros and cons knowledge, etc. etc. But I guess the real test is to hop a ride in one. The numbers are definitely increasing so the chances of getting a ride is better! One final tip… if you want to hold on to your wallet, bring ear plugs. For me, that under-the-surface whir of the twins is definitely part of the “I want one” equation.

Conversion job #3 is arriving tonight from Hawaii, compliments of a 747. We pick it up in the morning. Help me before it is too late – this one may send me over the top! I can probably negotiate a good price on a nice Gen 2 Whipple in lieu of labor…. but that’s not what I want! (Did I mention that I hate CARB?)

 

[BlackICE]

I think CARB is the biggest impediment to getting a TT for CA owners. When the urge for a TT hits you, just say CARB 10 times.

 

[soroush]

not suprising on a "build" motor.

I believe because not alot of people are doing "build" motors.

well Im very "suprised" that's not the case!

 

[Mullet]

well Im very "suprised" that's not the case!

:lol

 

[ChipBeck]

It looks easy.

I’ve seen plenty of N/A, Turbo’ed and Blown cars spin, hell I’ve spun mine at 135mph in turn 1 at Thunderhill. It nearly always a case of driver error! Being in a turbo car will not save your ass anymore than a blown car will cook it! Anecdotal evidence aside, what it comes down to is driver competence. The “swapping ends” comment regarding the blown cars keeps coming up; well I want a car that I can transition from understeer to oversteer with my right foot and I want it to happen right now. I would argue to use a TT gal to her fullest extent on a road course you as a driver will be taxed more to keep the gal on boost to get her fastest possible lap time. DBK mentioned putting the blown car in third and running all the way around the track and he is correct! That is the beauty of the blown gals, gobs of torque all through the rpm range. It makes a very easy, very forgiving car to drive on a road course......It seems as if some want the TT to be presented as the be all end all set-up for the GT.

It appears that more was read into my comments than was stated. I never claimed that any type of car couldn't be spun, or that a TT car would save a poor driver. I'm not a driving expert but those that I have listened to tell me that smooth will beat abrupt anyday. If "the swapping ends comment regarding the blown cars keeps coming up", perhaps it's because there is something to it. The comment that a supercharged car, "can transition from understeer to oversteer with my right foot and.....happen right now" is confirmation of what I was talking about. For an amateur track driver like myself in a Ford GT that has no traction control and no stability control, the hammer blow quickness of the SCs torque delivery must be controlled with a deft right foot to keep the quick transition from understeer to oversteer that you mentioned from turning into a bit too much oversteer. I had no expectations as regards my TT's ability on a track. I bought it to acquire a 200 mph Texas Mile T-shirt. I had driven my car with its supercharger on a track several times and I expected the turbochargers would make my track experience more difficult. At Spring Mountain Raceway in Nevada I experienced the exact opposite result. The smooth power delivery was confidence inspiring. There were about 10 Ford GTs there that day, most of them piloted by better and more experienced drivers than myself. A number of other supercars were in attendance as well. Absolutely nothing on the track that day could run with my twin turbo Ford GT. Running down and passing the supercharged Ford GTs was like shooting fish in a barrel. On the track in my car with the supercharger or the turbochargers I was always between 3500 rpm and 7200 rpm. At those engine speeds turbocharger boost is both quick and smooth, my supercharger's power delivery was immediate and abrupt. My comments are not theory or conjecture, they are the observations of my actual experience with both systems. I'll take your word for it that an expert driver could take advantage of a superchargers ability to rapidly transition the Ford GT from understeer to oversteer. But that's a little beyond my skill level. Some of us would argue that a car that transitions from understeer to oversteer instantly with a stab of the throttle is not the "more forgiving" car.

I evaluate snow skiing equipment the same way. I don't buy world-class skis that require Olympian abilities to extract their maximum performance. I prefer more forgiving skis that make me look like I'm better than I really am.

The TT is kind of like that. If supercharged cars at Spring Mountain Raceway Supercar Weekend were better track cars than my TT, OK. I know most of the drivers at Spring Mountain that day were better and more experienced than me, OK. The driver of a highly modified Supercharged Audi R-8 who was a member there and intimately familiar with the track, utilizing that rapid transition from understeer to oversteer, had the tail of his car come around in a corner and impacted the wall on the inside of the turn cooking off both airbags, ouch. But somehow, at the end of the day, a fat old man who had never driven that track before, with very limited track experience, driving an inferior lag prone TT that supposedly took a lot of work to keep "in boost", set the fastest times of the day. It was probably just a fluke.

All the best.

Chip

 

[Luke Warmwater]

Seems like and I say that because I have not been on a track with either, that a SC application would be easier to deal with when needing to apply controlled power when exiting a corner. Turbos need to lite and have a "hit". SC are like sowing machines. There is a direct connection between the right foot and the power delivery. With a turbo(s) you push peddle and then wait for the hit. Once one becomes accustom to the timing of that hit then certainly they could master the art of maximum exit velocity but there will still always be timing involved when compared to a SC application.

 

[sandman]

Seems like and I say that because I have not been on a track with either, that a SC application would be easier to deal with when needing to apply controlled power when exiting a corner. Turbos need to lite and have a "hit". SC are like sowing machines. There is a direct connection between the right foot and the power delivery. With a turbo(s) you push peddle and then wait for the hit. Once one becomes accustom to the timing of that hit then certainly they could master the art of maximum exit velocity but there will still always be timing involved when compared to a SC application.

Exactly what I was trying to say! Thank you for putting it in a concise form.

 

[Superfly]

Wow, what a great thread and read!!! My $0.02, I have my SC on my GT with a pulley/tune and I love it. But when the time comes, I'm going to do the Turbos. I have optional larger turbos on my 911, and I don't have the dreaded lag, then again it may be because of the way I drive it. I've driven my buddies cars with smaller turbos, and while they spool a little quicker, they also don't come on as hard higher. I like that hit. Also, I find I tend to drive my GT around town at 4500 and lower rpm (trying to stay in boost) whereas I tend to drive my 911 around town at 3000 and higher rpm (again, staying in an area where I can get fast boost). A subtle difference in wording, but a big difference in how they feel to drive. Basically the GT pulls like crazy from lower rpm, but the turbo pulls like crazy from higher. So as long as the turbos are kept spooled, they totally rock. And as for tire shredding torque, well, my 911 will spin all 4 tires if I launch hard, I'm pretty sure any TT GT will do the same if you wanted. Maybe not as much as a SC GT, but then again, tires are pretty darned expensive, so that may not be such a bad thing........

Anyway, the GT is an awesome car in any configuration. I'd just like mine to one day be TT'd. :banana