Questions About Turbocharging

[Guest TurboSedan]

you have never riden in a Talon or an eclipse. they whipwash you at 3500, nothin till then. and they die off at 6500.

 

actually yes my friend has a '91 Talon TSi. Aaron, you sound like you don't know much about turbocharging systems - maybe you shouldn't let the Talon or Eclipse scare you away and experience other turbocharged cars. Brian, corrections? i thought i mentioned all those but ? well i'm outta here later

joshua

[brian89gp]

perhaps a wrong choice of words there, anyway if i duplicated any of it sorry.

[slick]

What about a centrifigul (spelling) supercharger? Whats the pros and cons on them?

[91GranSport]

Here are answers for your questions, although I can be somewhat "off" on some of these.

 

1. Intercoolers work by cooling the densely charged air coming into the intake manifold. They are a must on turbocharged engines but supercharged engines can work fine without them. If you do add an intercooler to a supercharged engine you will definitely see bigger horsepower and torque gains.

 

2. When it comes to twin turbocharged engines, the two turbos can either work parallel with each other (at the same time), or sequentially (one kicks in for low to midrange and then the next kicks in from midrange to top end). When twin turbocharged engines have parallel turbochargers, then you can expect a massive kick in the back once the two turbos spool up and build boost pressure. However, there is noticably turbo lag, more so than a twin turbo using sequentially timed twin turbos. Now, with a sequentially timed twin turbo, one kicks in at lower RPMs and produces power all the way up to midrange, where the next turbo kicks in to bring power from the mid RPM to redline. The power deilvery on this time of unit is supposed to be a lot smoother and have less noticable turbo lag. Which is better? I guess that depends on what you're looking for.

 

3. Turbos don't kick in at a certain designated RPM. There's a boost gauge that shows you how much boost you're creating. Turbos are actually always running as long as your engine is on, but they won't build power until there's adequate exhaust flow. Turbos need exhaust coming out of your engine to spin the impeller and create boost. If you're creating a lot of exhaust flow at 1000RPM then you're already making power. But if your engine has very low exhaust coming out until 4000RPM then that means you won't be building power until 4000RPM.

 

4. Superchargers need lower compression. You should never (I think never) run a supercharger with a high compression ratio.

 

I know turbos are supposed to have a better increase in power than superchargers so im told. But they also sound more complicated and more work. So how do IC's work? I know turbo lag is a bit of a problem and even more if you want to go with a bigger turbo. Hence the creation of twin turbos using two smaller turbos and creating less lag. And dont usually turbos kick in around 2500rpm? If this is so there isnt much lag i mean if your ripping through the gears at full throttle that split split split second wont matter much would it? Another question. If they kick in at 2500 rpm does that mean they go when ur doing regular driving and just accelerating nicely from a stop light? Or is it just the speed of the exhaust coming out that gets em going? And with superchargers dont u need higher/lower compression? I got more questions but i think thats enough for now.

[91GranSport]

So, would it be safe to say that a supercharger is better for low end torque and a turbocharger is better for high-end horsepower?

 

a turbo, on an average application, will not make ANY more power(it might even lose some) befor about 3000-400 rpm. now the supercharger will increase power all of the way, making more boost as rpm's go up. overall, the S/C doesnt give as much of a igh end, but still helps your low end. the turbo doesnt help, and even hurts, the low end but will help the hgih end even more than the S/C

[91GranSport]

I agree with you on that. I drove a Plymouth Laser which is the same thing. It was a turbocharged/intercooled L4, 5-speed and and AWD if I can remember correctly. Thing was a dog below midrange. Funny, I think most of it's power came at 3800RPM rather than 3500RPM. It did have a lot of power after that, but it did die off at a little early. But then again the one I drove was an absolute beater.

 

you have never riden in a Talon or an eclipse. they whipwash you at 3500, nothin till then. and they die off at 6500.

[91GranSport]

Yeah, can someone please explain the difference between a Roots, Eaton, Centrifugal supercharger and whatever types are left?

 

What about a centrifigul (spelling) supercharger? Whats the pros and cons on them?

[brian89gp]

A roots blower moves air, it does not compress it. The M90 I believe moves 90CFM per revolution. Boost pressure is a side effect of the blower moving more air then the engine can gulp down. That is why the roots blower has excellent low end but dies out up top. They are horribly inefficient but have a very linear power curve and excellent low end

 

There are some roots similar blowers (whipple) that acutally compress the air along with moving it which brings the efficiency up quite a bit.

 

A centrifical s/c is basicall the compressor side of a turbo that is belt driven. This actually compresses the air and has a very sloped power curve, until the compressor wheel is spinning a certain speed there is little to no boost but when it hits its efficency range bam!, you got a hell of a lot of air. A centrifical s/c easier to mas produce due to basically only needing bracketry made up (which is easy for a large company to do, difficult for a DIY'er) and is packaged smaller then a roots or turbo. The CSC is also RPM only dependent which leads to a predictable power curve and it is easier to drive.

 

A turbo is a turbo, it has the highest efficiency (usually) of the 4. One interesting note is that the turbo rely's completely on exhaust velocity and is completely independent of engine rpm. A CSC, if it has 6psi at 4000rpm, then it will always have aroudn 6psi at 4000rpm at any engine load. A turbo thrives on engine load and is heavily dependent on it. Engine load = high exhaust velocity and rpm's = high exhaust velocity, it is a balance between the 2 of those as to when a turbo will spool up. Spooling up is referring to the time before the turbo gets into its efficiency range and starts pumping out serious air.

 

As for highs and lows, the roots and whipple style are good for drag racing because boost is instantanious, with 8 and below second quarter miles there is no time to wait for a turbo to spool or a CSC to spin into its efficiency range. A roots blower is also very streetable because of that, power without the need to rev then engine much at all. A CSC is good because it rely's on engine rpm and is more predictable. A turbo in my opinion is better then a CSC, you might have lag but that could be a plus. While you are cruising at light load (the CSC might be into boost depending on RPM, even at low engine load) the turbo will not be spooled up which means better gas milage, if you can live with some turbo lag and a engine that will pull like hell at 2k under load but 4k with low load is slow as hell, then i say turbo it is.

 

It comes down a great deal to personal preference, roots blower or a CSC/turbo. A turbo is much easier for a DIY'er to do, and a CSC is much cheaper for a company to produce in kits, and a roots is just a roots.

[91GranSport]

Brian, you are the fucking king of forced induction.

 

Seriously though, thanks for the info. Shit, I learn more here than I do tinkering with cars.

 

BTW: One last thing, what is an "Eaton" supercharger? Is it the same as the roots? If so, then there are only two types of superchargers, Roots/Eaton/Whipple and Centrifugal superchargers.

 

A roots blower moves air, it does not compress it. The M90 I believe moves 90CFM per revolution. Boost pressure is a side effect of the blower moving more air then the engine can gulp down. That is why the roots blower has excellent low end but dies out up top. They are horribly inefficient but have a very linear power curve and excellent low end

 

There are some roots similar blowers (whipple) that acutally compress the air along with moving it which brings the efficiency up quite a bit.

 

A centrifical s/c is basicall the compressor side of a turbo that is belt driven. This actually compresses the air and has a very sloped power curve, until the compressor wheel is spinning a certain speed there is little to no boost but when it hits its efficency range bam!, you got a hell of a lot of air. A centrifical s/c easier to mas produce due to basically only needing bracketry made up (which is easy for a large company to do, difficult for a DIY'er) and is packaged smaller then a roots or turbo. The CSC is also RPM only dependent which leads to a predictable power curve and it is easier to drive.

 

A turbo is a turbo, it has the highest efficiency (usually) of the 4. One interesting note is that the turbo rely's completely on exhaust velocity and is completely independent of engine rpm. A CSC, if it has 6psi at 4000rpm, then it will always have aroudn 6psi at 4000rpm at any engine load. A turbo thrives on engine load and is heavily dependent on it. Engine load = high exhaust velocity and rpm's = high exhaust velocity, it is a balance between the 2 of those as to when a turbo will spool up. Spooling up is referring to the time before the turbo gets into its efficiency range and starts pumping out serious air.

 

As for highs and lows, the roots and whipple style are good for drag racing because boost is instantanious, with 8 and below second quarter miles there is no time to wait for a turbo to spool or a CSC to spin into its efficiency range. A roots blower is also very streetable because of that, power without the need to rev then engine much at all. A CSC is good because it rely's on engine rpm and is more predictable. A turbo in my opinion is better then a CSC, you might have lag but that could be a plus. While you are cruising at light load (the CSC might be into boost depending on RPM, even at low engine load) the turbo will not be spooled up which means better gas milage, if you can live with some turbo lag and a engine that will pull like hell at 2k under load but 4k with low load is slow as hell, then i say turbo it is.

 

It comes down a great deal to personal preference, roots blower or a CSC/turbo. A turbo is much easier for a DIY'er to do, and a CSC is much cheaper for a company to produce in kits, and a roots is just a roots.

[TGPilot]

Thanks Brian...I definitely learned something this morning. I honestly didn't know there were so many forms of forced induction! I am a turbo man through and through...to hear the turbo begin to sing and have a car throw you into the seat when it comes to life...daddy likey!

[brian89gp]

I was thinking Eaton was just a brand. There are the: roots style, twin screw (whipple), and the centrifugal

[timg]

Here are answers for your questions, although I can be somewhat "off" on some of these.

 

1. Intercoolers work by cooling the densely charged air coming into the intake manifold. They are a must on turbocharged engines but supercharged engines can work fine without them. If you do add an intercooler to a supercharged engine you will definitely see bigger horsepower and torque gains.

 

First, Intercoolers are even MORE important on Roots blowers vs turbos. The less efficient a supercharger or turbo is, the more likely it is that it will need an intercooler. On a given engine, it's likely that a turbo could produce 10 psi before detonation occurred due to detonation caused by high intake temps. A roots blower on the same engine might only make it to 6 or 7 psi because of the much lower efficiency of a roots blower. In virtually every case, superchargers need to be intercooled MUCH more than turbos. This is a VERY common misconception.

 

Everything else you said was very good. A turbo can be designed for zero lag and a powerband that starts at idle and dropps off by 4k. They can also be designed with significant lag and a powerband that begins at 4k rpm. My turbo will make full boost at VERY low throttle openings if the engine is above 4k rpm.

 

Tim

[Guest TurboSedan]

perhaps a wrong choice of words there, anyway if i duplicated any of it sorry.

 

thanks for the info brian,

 

'all hail the iron duke?' hahahah

 

joshua

[brian89gp]

perhaps a wrong choice of words there, anyway if i duplicated any of it sorry.

 

thanks for the info brian,

 

'all hail the iron duke?' hahahah

 

joshua

hehe, I think i put that in my sig during one of the 3.4 vs 3800 debates

[Aaron]

as for the whipwash thing i said, TimG said the same thing. you can tune for low or for high end, but not both unless your redline is at like 5k or MAYBE 6k. i rode in Lukes TGP, 5-speed 12psi, and it had shitloads of low end tq. spooled at like 1500. so nice, it had soo much tq i was shocked that i beat it. it just hammered you in the seat. but, it died off at 5k. and just let go by 5.5, nothin after that.

[Power-Glide]

BTW: One last thing, what is an "Eaton" supercharger? Is it the same as the roots?

 

The Eaton supercharger is essentially a Roots blower pump, with one substantial design wrinkle; each rotor has been twisted 60 degrees to form a helix. The two counter rotating rotors have three lobes, which intermesh during operation. These twisted rotors, along with specially designed inlet and outlet port geometry, help to reduce pressure variations resulting in a smooth discharge of air and a low level of noise during operation. This arrangement also improves efficiency over traditional Roots superchargers. With helical rotors and an axial inlet the Eaton supercharger can be spun to up to 14,000 rpm, thereby reducing package size.

[slick]

So is there a way to buy a CSC type supercharger by itself? I've only ever seen them come in kits, and it seems like it would be an easy way to get some boost, as making brackets are no problem.

[91GranSport]

Thanks again for the info. Damn, you should be a fucking engineer already. Okay, here's the situation. We're all going to start working for GM now...

 

Shawn, along with yourself, will be the powertrain engineers.

I'll be part of the design team.

Hazmatic will provide the beer and entertainment.

 

Sound cool? Shit, we can take over GM easily!

 

BTW: One last thing, what is an "Eaton" supercharger? Is it the same as the roots?

 

The Eaton supercharger is essentially a Roots blower pump, with one substantial design wrinkle; each rotor has been twisted 60 degrees to form a helix. The two counter rotating rotors have three lobes, which intermesh during operation. These twisted rotors, along with specially designed inlet and outlet port geometry, help to reduce pressure variations resulting in a smooth discharge of air and a low level of noise during operation. This arrangement also improves efficiency over traditional Roots superchargers. With helical rotors and an axial inlet the Eaton supercharger can be spun to up to 14,000 rpm, thereby reducing package size.

[topless94style]

For all you guys who know alot of shit about forced induction answer this. So far from what ive learned you can set turbos so the lag is where you want it. Why cant you get a twin turbo set up, set one turbo so there is no lag and have it die out around 4K, but set the other turbo to kick in around 2.5k-3k and have that last almost the rest of the power curve? That way you have forced induction throught the whole curve and nonstop slam back in ur seat power?

[Power-Glide]

You could try to do a setup like that... Problem is how do you divide the system? The better TT setups will split the banks of the the motor and use a common plenum to build common boost in, more exotic setups will even completely divide the engine banks and have two "sealed" and completely separate systems each fed by one turbo. What you are proposing would require both turbos(of different sizes to account for spool time) to feed into a common plenum, but when the first is boosting and the bigger turbo is not you would simply be backfeeding the second turbo and venting your boost. This would be vice-versa in the high range when the first or smaller turbo dies off and can't supply the CFM demand. Essentially the impellers would be fighting each other at both ends of the rpm range.

Now I'm not really good with T or TT setups but this is what occured to me.

 

Although it's a ford, this a good read for turbo guys:

http://www.hotrod.com/techarticles/42798/

[92turboLE]

this my friends is why you get creative and do what im doing. CSC and turbo. The CSC will provide the gas pedal mash power at the low end and then the turbo will carry that up on the high end. Basicly im goign to tune it so that the max boost on the CSC will be around 6-7 and then the turbos boost will be set around 8 or 9. With the turbo boost set so low, and the wastegate tuned right, the turbo wouldnt start spooling until about 3200-3500 rpm, plus with the blower providing a little bit of load, that should work out nicely and i should be able to tune the turbo and wastegate quite easily.

 

wish me luck.

 

also, you can find paxton blowers all over EBay - just do a search for paxton blowers (they are CSCs)

 

- Justin

[Aaron]

problem. the supercharger wont just die off at 3500 tho, it will still be making boost. so now you have 6-7 max psi from the blower, and then 8-9 psi from the turbo. now i dont think you can just add, but 14-16psi is a fuk of a lot of boost, especially for an aged motor that isnt dependable as it is(3.4 DOHC). as for the 3.1, i think a well tuned turbo would do just fine. bigtime spool at 2k, but it will still pull to 6. if any of you have ever ridden in Lukes TGP, it is a monster off the line. mega torque and it carries it well to about 5-5.5k. so with this low of a redline, a well tuned turbo will do just fine.

[Power-Glide]

Boost doesn't add up like that, if you have a supercharger making 9psi, and a turbo putting out 11psi, they won't make 20psi combined.... It will only make 11psi.

[Ribbie]

this my friends is why you get creative and do what im doing. CSC and turbo. The CSC will provide the gas pedal mash power at the low end and then the turbo will carry that up on the high end. Basicly im goign to tune it so that the max boost on the CSC will be around 6-7 and then the turbos boost will be set around 8 or 9. With the turbo boost set so low, and the wastegate tuned right, the turbo wouldnt start spooling until about 3200-3500 rpm, plus with the blower providing a little bit of load, that should work out nicely and i should be able to tune the turbo and wastegate quite easily.

 

wish me luck.

 

also, you can find paxton blowers all over EBay - just do a search for paxton blowers (they are CSCs)

 

- Justin

 

A CSC blower is RPM dependant. Therefore does not make sufficient boost until it reaches a certain RPM and continues to make more. Then your problem will be the turbo boosting at the same time your CSC blower comes into its power or PSI output (some else mentioned this as well).

 

All of that said, you are looking at a plumbing NIGHTMARE.

 

Good luck though

[91GranSport]

Good luck to you, dude. I know you're going to need the following:

 

1. Lots of money.

2. Lots of time.

3. Lots of IQ.

 

this my friends is why you get creative and do what im doing. CSC and turbo. The CSC will provide the gas pedal mash power at the low end and then the turbo will carry that up on the high end. Basicly im goign to tune it so that the max boost on the CSC will be around 6-7 and then the turbos boost will be set around 8 or 9. With the turbo boost set so low, and the wastegate tuned right, the turbo wouldnt start spooling until about 3200-3500 rpm, plus with the blower providing a little bit of load, that should work out nicely and i should be able to tune the turbo and wastegate quite easily.

 

wish me luck.

 

also, you can find paxton blowers all over EBay - just do a search for paxton blowers (they are CSCs)

 

- Justin