Supercharger or Turbocharger for AutoX, and Track

[FRS Justin]

All in all I must admit I'm beginning to see why a S/C is favorable to some people. I myself love my turbo's and probably will never go back to a S/C unless its a muscle car with a big ass BDS system on it, have to give props to the S/C guys

[Sleepless]

Originally Posted by FRS Justin

As far as response of a F/I setup, that is entirely based on tuning of the F/I product while the big name S/C companies have done a fairly good job on this a turbo can be tuned to respond the same based on design. Pipe sizing and Exhaust housing sizing Impeller sizing all go into making a system work well or not at all.

It is impossible for a purely turbo setup to have the same throttle response as an NA or SC setup. The Only ways I'm aware of to get a turbo car to have the same response is to add an SC for initial boost or to an electric motor to spin up the turbo instantly. In racing they have used fuel dumping to keep the turbo spooled up, but that isn't viable if any sort of fuel economy is desired.

[jwvand02]

Originally Posted by FRS Justin

You make a excellent point in the first paragraph from a consumers point of view, which I did not consider. I was more into the efficiency of the F/I method point of view. So in my opinion it wasn't really a "fallacious" statement, but I can see your point of view, In all 3 paragraphs from a consumers point.

Yeah, if that came off like a three paragraph lecture directed particularly at you, sorry, it wasn't my intent. Fallacious may have been a bit strong of a word, but I do figure if OP is asking he is definitely a consumer so that's the viewpoint I think matters. The last two paragraphs were really intended to be my two cents only, given my experience with both (albiet turbo on a different platform.)

[jwvand02]

Originally Posted by bfrank1972

Hah I do get your viewpoint - but I guess what I was getting to is stress on the motor - it has to work harder to put down 350rwhp than the turbo car. I was completely oblivious to this point until I joined in a thread with Moto Mike a while back. He sort of illustrated it to me - the motor has to work to produce 350hp at the rear wheels AND take on turning those rotors on top of the motor. Just for example, let's say mechanical failure rate for rods and/or pistons increases dramatically around 425 ft-lbs at the crank. The turbo car putting down 350rwhp will have a lot more headroom than the supercharged car.

That's an interesting point, I hadn't thought of that. I guess it means that supporting mods may have to come at lower levels of power on some platforms if you're using a SC, which is definitely a downside if you're shooting for that kind of power.

[FRS Justin]

Originally Posted by Sleepless

It is impossible for a purely turbo setup to have the same throttle response as an NA or SC setup. The Only ways of getting a turbo car to have the same response is to add an SC for initial boost to an electric motor to spin up the turbo instantly. In racing they have use fuel dumping to keep the turbo spooled up, but that isn't viable if any sort of fuel economy is desired.

Why is it impossible to have the same throttle response. I'm not talking from idle but lets say 2500rpm and up, true driving conditions. I understand that I could take a 671 blower change the pulleys to run 22% overdrive and the bottom end would be extreme and the top end would suck but I want to focus on basic systems like I originally posted. A true apples to apples comparison.
Not trying to be difficult just want to learn

[FRS Justin]

Originally Posted by jwvand02

Yeah, if that came off like a three paragraph lecture directed particularly at you, sorry, it wasn't my intent. Fallacious may have been a bit strong of a word, but I do figure if OP is asking he is definitely a consumer so that's the viewpoint I think matters. The last two paragraphs were really intended to be my two cents only, given my experience with both (albiet turbo on a different platform.)

No offence taken at all it was very well written and received. I should have considered the consumer point of view and I missed that.
The whole what is better or best is a question with many answers and I will remember this and grow from it. I truly appreciate the respect shown and the way people discussed their opinions because at the end of the day I left the table with more knowledge than I sat down with.

[totopo]

Originally Posted by FRS Justin

Why is it impossible to have the same throttle response. I'm not talking from idle but lets say 2500rpm and up, true driving conditions. I understand that I could take a 671 blower change the pulleys to run 22% overdrive and the bottom end would be extreme and the top end would suck but I want to focus on basic systems like I originally posted. A true apples to apples comparison.
Not trying to be difficult just want to learn

It's because an engine at 3500 rpm with out gas produces less exhaust and hence boost than an engine at 3500rpm at WOT. It's more of an issue with road racers and street driving. Let's say you overdrive into the corner (or overspeed onto a freeway onramp, oops): you trail brake super late, turn in with minimal to no throttle input, sweat your pants, then you see the corner exit and you realize oops, you slowed down TOO much, you have plenty of rear traction available, so you go from minimal gas to mashing. It takes the turbo a split second to actually deliver the power, since it needs exhaust to spool up (whereas the SC is still making the same boost it always makes), and that can be frustrating and loose time. It is manageable by driving skill, but it is hard and not as "fun"

If you have gran turismo 6 you can have an excellent example of turbo lag if you try to drive that ayrton senna ridiculous POS 97T lotus (900bhp out of 1.5L...) and it illustrates why it can be difficult to road race with a lot of turbo lag.

[FRS Justin]

Originally Posted by totopo

It's because an engine at 3500 rpm with out gas produces less exhaust and hence boost than an engine at 3500rpm at WOT. It's more of an issue with road racers and street driving. Let's say you overdrive into the corner (or overspeed onto a freeway onramp, oops): you trail brake super late, turn in with minimal to no throttle input, sweat your pants, then you see the corner exit and you realize oops, you slowed down TOO much, you have plenty of rear traction available, so you go from minimal gas to mashing. It takes the turbo a split second to actually deliver the power, since it needs exhaust to spool up (whereas the SC is still making the same boost it always makes), and that can be frustrating and loose time. It is manageable by driving skill, but it is hard and not as "fun"

If you have gran turismo 6 you can have an excellent example of turbo lag if you try to drive that ayrton senna ridiculous POS 97T lotus (900bhp out of 1.5L...) and it illustrates why it can be difficult to road race with a lot of turbo lag.

I can't imagine that scenario you just stated, I would be like hold my beer this is going to hurt!! I'm just a simple drag racer and drive on the street.


Ok serious note tho, I have read of rally racers over in Europe who have to do what you stated and they came up with deleting the BOV to and I quote " make the throttle response more crisp" I have never done it so I can't tell you anything about what happens when you do it. I've always been happy with how my custom designed turbo kit works. I really feel no lag on the street or just tooling around.




I'm sure a real professional could tell or feel it but I can't I'm more worried about the back passing the front when I floor it than lag. It is one angry car when you get on it I will try to find a video from the inside of the car and post it.

[FRS Justin]

Originally Posted by FRS Justin

I can't imagine that scenario you just stated, I would be like hold my beer this is going to hurt!! I'm just a simple drag racer and drive on the street.


Ok serious note tho, I have read of rally racers over in Europe who have to do what you stated and they came up with deleting the BOV to and I quote " make the throttle response more crisp" I have never done it so I can't tell you anything about what happens when you do it. I've always been happy with how my custom designed turbo kit works. I really feel no lag on the street or just tooling around.




I'm sure a real professional could tell or feel it but I can't I'm more worried about the back passing the front when I floor it than lag. It is one angry car when you get on it I will try to find a video from the inside of the car and post it.

Here is a article I found describing the BOV delete



<a href="https://www.facebook.com/primeperformanceauto/?fref=nf">Prime Performance

July 31, 2012 ·





BOV DELETE EXPLANATION
Many people ask us why we delete the blow off valves on our Gen4 swap cars. Here is a technical explanation. (borrowed from mr2oc.com)
1. The compressor wheel doesn't create pressure. A lot of people don't realize this. It imparts massive velocity onto the incoming charge. That velocity is then converted to static pressure via Bernoulli's principle by the two diffusers- the double wall at the exducer exit and the scroll.
What does that mean in terms of surge? It means that "boost" that is forced back through the diffuser (which operates as a nozzle in reverse) is converted back into velocity. Pressure never acts on the compressor wheel. The velocity of air being forced back through the scroll will ALWAYS be less than the velocity coming off the wheel (due to losses in conversion from V to P and back to V). Add the velocities together and you essentially get a slowdown of air coming off the compressor wheel (notice I didn't say slowdown of the compressor wheel itself?). This slowdown oscillates as air slips backward past the compressor wheel and air velocity speeds up and slows down.
2. Those changes in velocity change the loading on the compressor wheel. Thrust loads from both the compressor and the turbine act in the same direction. That is why a turbo only needs a single thrust bearing. That oscillation has a hammering effect on the thrust bearing. Under full throttle surge, this can damage the turbo as there is a massive thrust load from the turbine, which is operating at a much higher pressure differential. When you lift off the throttle to shift, that massive thrust load from the turbine side is gone. The small oscillation is now acting well within what the thrust bearing is designed to deal with, since there's less than half the thrust loading during off-throttle conditions.
To get an idea of just how much loading the turbine side adds to the equation, bear in mind that a turbocharger's turbine discharge generates enough thrust that people actually use turbos to build jet engines.
3. As for "keeping the turbo spooled between shifts," well, that's a crock too. Impeller speed is affected primarily by the loss of drive pressure on the turbine. The turbo loses speed at a ridiculous rate as soon as there's no exhaust to drive it because its mass is relatively close to its axis of rotation.
Keep in mind too that an average 16g sized impeller pair at full boost is spinning with the same rotational energy as a 15lb engine flywheel at 4000rpm. It took a large pressure differential of super-heated gas (air AND fuel) to spin it up to those speeds, the effect of slowly decompressing the charge pipe through the compressor inlet will be negligible in comparison. There's maybe a small percentage change in speed between the two setups, but the faster speed with the BOV is negated by the fact that:
4. Turbochargers are positive feedback devices. The more boost you have, the most boost you make. Opening the throttle again with 10psi still in the pipes to drive the turbine spools the turbo significantly faster than starting over from 0psi. This is easily confirmed by datalogs. Boost recovers about twice as fast between shifts when shifting fast without a BOV than it does with one. It's a simple matter of the fact that there's still energy in the induction system to re-spool the turbo when you don't dump all that energy out of a BOV. Race engineers have known this since the 80s. That's why you will never see a proper turbo race car with a BOV- it costs literally seconds per lap to throw away that energy

[xwd]

Generally you use an anti-lag system in a proper race car. Running the car at higher boost levels and closing the throttle while the pipe is still pressurized isn't a very good idea (no BOV). I've had a car with ALS and you keep the turbo spooled via dumping fuel or other means and the throttle plate is still open somewhat so air is still going into the engine.

There are some modern turbos like the EFR from B-W that have great throttle response especially on/off boost. GTX series from Garrett aren't terribly far behind. However it always takes time to spin up turbo impeller to build boost unless you are using something like ALS to keep it spooled off-throttle.

A twin-screw supercharger like the Sprintex internally compresses air and if it didn't have an internal bypass valve it would make boost all the time, even at partial throttle. An Eaton TVS used in the Cosworth/Edelbrock/Harrop kits is a roots type and still requires air moving through the engine to compress so it won't really make boost at partial throttle.

I'm not sure how having an oil/water fed turbo and dealing with boost control is not more complex than a supercharger.

[FRS Justin]

Originally Posted by xwd

Generally you use an anti-lag system in a proper race car. Running the car at higher boost levels and closing the throttle while the pipe is still pressurized isn't a very good idea (no BOV). I've had a car with ALS and you keep the turbo spooled via dumping fuel or other means and the throttle plate is still open somewhat so air is still going into the engine.

There are some modern turbos like the EFR from B-W that have great throttle response especially on/off boost. GTX series from Garrett aren't terribly far behind. However it always takes time to spin up turbo impeller to build boost unless you are using something like ALS to keep it spooled off-throttle.

A twin-screw supercharger like the Sprintex internally compresses air and if it didn't have an internal bypass valve it would make boost all the time, even at partial throttle. An Eaton TVS used in the Cosworth/Edelbrock/Harrop kits is a roots type and still requires air moving through the engine to compress so it won't really make boost at partial throttle.

I'm not sure how having an oil/water fed turbo and dealing with boost control is not more complex than a supercharger.

I run a separate boost control to free up maps for tuning higher boost levels. If I was running the average turbo kit low boost I would just use the boost control in ECUTEK and forget about it. My turbo is a precision no water lines just one line in and a return out. So its comparable as far as complexity.


The only way deleting the BOV helps is by leaving a volume of air in the pipe so if your shifting by letting off the gas and then right back on their is less volume to fill and improving the boost response time.
When the air slams into the throttle blade it will flow back to the turbo and exit behind the impeller and out the antisurge holes.
It can take the pressure going out the antisurge ports it's designed to but a turbo hates surge at WOT that's a recipe for destruction.


I'm going to do more research and find out exactly what's up with this BOV delete. I'm curious. Thanks XWD for taking the time to explain the S/C differences

[CSG Mike]

Originally Posted by FRS Justin

A properly setup turbo will smoke the tires out of a corner.....The top is a Kraftwerks S/C the bottom a Spencer Fab turbo setup..


Please explain how More wtq at lower rpm will not pull out of a corner and lag...


234 wtq at 3200rpm all the way to 6k rpm v/s S/C max wtq 200 at 5800rpm is going to pull better...

http://bfy.tw/3RDV

Smoking the tires means you're spending all that power spinning the tires and creating smoke, instead of accelerating.

Originally Posted by FRS Justin

Why is it impossible to have the same throttle response. I'm not talking from idle but lets say 2500rpm and up, true driving conditions. I understand that I could take a 671 blower change the pulleys to run 22% overdrive and the bottom end would be extreme and the top end would suck but I want to focus on basic systems like I originally posted. A true apples to apples comparison.
Not trying to be difficult just want to learn

Because turbos have to spool. You don't go from low RPM to high RPM instantly. In neutral, can you instantly pin redline by flooring it? No, there's still a bit of a delay. The turbo has to similarly increase its RPM over a period of time, and then in addition to that, compress enough air to start generating boost.

That's why the new NSX is a hybrid; the electric motor(s) hides that spoolup time.

[CSG Mike]

Originally Posted by FRS Justin

I run a separate boost control to free up maps for tuning higher boost levels. If I was running the average turbo kit low boost I would just use the boost control in ECUTEK and forget about. My turbo is a precision no water lines just one line in and a return out. So its comparable as far as complexity.


The only way deleting the BOV helps is by leaving a volume of air in the pipe so if your shifting by letting off the gas and then right back on their is less volume to fill and improving the boost response time.
When the air slams into the throttle blade it will flow back to the turbo and exit behind the impeller and out the antisurge holes.
It can take the pressure going out the antisurge ports it's designed to but a turbo hates surge at WOT that's a recipe for destruction.


I'm going to do more research and find out exactly what's up with this BOV delete. I'm curious. Thanks XWD for taking the time to explain the S/C differences

You're thinking WOT box, similar to flat foot shifting in Ecutek.

You cut power output (fuel and/or spark), but you keep your foot on the gas, so the BOV doesn't actuate. This lets you shift without loosing your boost, so when the power returns your turbo is still spinning (slightly slower) and still generating near peak boost.

Normally, if you lift on a shift, your BOV lets all your boost out, your engine is no longer generating exhaust gas, and is actually *dragging* your turbo to a degree to slow down the turbo's spin.

[FRS Justin]

CSG Mike,


With you specializing in track driving I'm sure you know exactly what feels right and wrong. I don't have any experience tracking a car so I will take your word on it. I would be a fool to tell you I know what it's like coming out of a race track corner and how to apply the power. I have seen various professional Rally drivers run turbos but that is another type of racing so I would assume things might not work the same in what you do.
Anyway:


I would like to wish you and your family a very Merry Christmas.