Why does GM choose to go with roots over centrist? Seems that the centrics are more popular with the after market crowd. Is it that roots are more reliable overall making them more attractive to the manufacture that has to support warranties vs. centris that are less expensive to install for the after market consumer with more expandability? Just curious if others have more insight into this.

 

Because eaton rotors are cheap at a production level as eaton is a OEM supplier. Its far cheaper to manufacture in all aspects and they dont have to fit the car with a air to air intercooler.
Reliability and power have nothing to do with it.
Because as many of us know, centri's are just as reliable and make far more power.

 

Yes and no.

Eaton superchargers have lubrication systems that don't require service till beyond 100k miles and the centrifical self contained units require fluid changes every other oil change or so. It's just one more liability where warranties are concerned.

 

Most centri's are oil fed, not self contained. Only certain models and prochargers are self contained. So this point is moot, oil fed units would require no further service than a regular scheduled oil change. No different than any factory car or truck turbo application.

 

Actually the majority of modern centrifical superchargers are self contained these days save for a handful of race units I believe....

Regardless...I've never had a centrifical go 100k without a refresh where I've had several MP112's that did. Six of one half dozen of another

 

Define majority?
All prochargers are..

Vortech/Paxton make a COUPLE that are self contained and they make oil fed versions of the same units. Self contained units were simply designed for people that didnt want to drill holes in there oil pan in a AFTERMARKET situation.

The majority of blowers produced are still oil fed as well as nearly all turbochargers. Just a fact, so once again, that is not a issue.

Screw blowers, such as the MP112, sure they have gone 100K, but ive also seen MANY screw blowers eat nose bearings at half that. I believe we have several members in the F/I sections here that have gone many many miles on centri blowers, usually it wasnt the blower that failed, they pushed there stock engines to hard and blew them up and went to bigger blowers upon rebuild. I know of two members personally that have gone over 100K on vortech S-Trim oil fed units with no problems.

Reliability becomes a issue when you start going to extreme belt tensions to hold small pulleys in high horsepower applications (900 whp plus) In a normal situation, such as what the MP112 or TVS1900-2300 is normally operating in, there should be little issue with failures of any kind. A centri has less moving parts, in a smaller package, essentially a belt driven turbo, turbos go hundreds of thousands of miles without needing to be rebuilt, as long as extreme belt tension isnt causing premature bearing wear, a centri blower will be no different.

I still stand behind my line of thinking, they are not used because screw blowers are cheaper to produce and easier to package.

 

This! Twin turbos would be even more expensive.

 

Cheap and easy to package are the key reasons. Also I think eatons are less likely to throw belts. Can you imagine the warranty claims with thrown belts? Plus with a well designed system running at reasonable boost the low rpm torque of the PD blower would make the car feel faster than a centri at similar boost pressures.

 

Belt reliability is all based on pulley alignment and belt tension. The big names in corvette blower systems do not have any issues with throwing or breaking belts if properly installed. I know two guys that have daily driven blower cars and the belts have lasted as long as they would with a non blower setup. Were just replaced when they showed wear and cracking like any other serpentine belt.

Its really the price and packaging as we both stated. There is no other good reason they havent made the change to centri setups or turbos on these things.

 

Damn, the best and brightest engineers this country (and others) has to offer and they can't figure this out. Bunch of dumb aaasssses! How much fun would a centrifugal blown sports car be at very mild boost levels on 91 octane fuel....with no methanol? There's the question those dumb engineers have to deal with.

You sound like you have this figured out. How much money do you think the OEM's save, on a per unit basis, going with the cheaper/inferior p/d blower? Surely the light bulb would go off over at least one of these dimwit's brains. Imagine all the prizes and promotions he would win if he just had a smidge of your insight!

 

Actually they make two that aren't self contained...

 

Hehe...the sarcasm be mighty heavy in here

For the record...Ford actually produced the '55 T-bird with a Paxton centrifical supercharger (as a factory option).

 

Because being an OEM supplier isn't cheap or easy. It is more than just GM buying parts from a place. Quality systems, ISO certs, JIT system, six sigma, lean, etc need to be in place. Right now the centri companies really aren't in a position to be big 3 suppliers. That leaves GM with companies like eaton that are OEM suppliers and with what they offer.

 

Agreed. Torque under the curve is where it's at for OEM applications. And that's where a PD or properly engineered turbo system excel. Packaging a turbo system on a C6 is far from ideal in my opinion, which leaves PD type blowers.

Another important thing to consider is noise. The Vortech blowers I owned were far from quiet. The blow-off valves even more so. Quite a bit of engineering would be required to make a centri blower suitable for an OEM application. Look at what BMW had to do for the centrifugal supercharger on the Aplina B7 (i.e. a clutch on the blower, an electric "restrictor plate", etc.).

 

Was it just me, and was I seeing things, or did the blower on the LT4 have a separate belt aside from the main belt for the drive components?

Couldn't tell real clearly for the shots I looked at, but that is what it appeared to me?

 

I do believe pretty much all of the previous gen Roots blown LS motors had a separate drive for the blower. Interesting to note that the 2015 Z will have a 1.7L TVS blower. Smaller blower will definitely limit the upside for those that want to push for more. With VVT and even more instant boost than the bigger blowers, that's going to be one torquey little package. 625 engine hp and more on the tq side. Leaves GM quite a bit of room if they want to do a C7 ZR1 in a few years. Seems to me that they'll need to drive all four wheels at those bigger power levels. I wonder if they left any room in the C7 chassis for front wheel drive. Going to be a tight fit.

 

i cant think of a single manufacter that uses a centrifugal blower. , ford, chevy, jag, mercedes, range rover, etc.. all roots style superchargers. i know in the 50's and 60's a few cars had centrifugal superchargers, but i believe thats about it. ie: positive displacement blowers may make less peak power, but they have a much better trq curve vs a centri blower.

 

4wd isn't needed, you just need good torque management systems. These are run of the mill on MB and above cars these days. The systems have been there on Ferraris for years now. You simply need to know the amount of torque the engine is producing at what rpm and throttle position. Link that to traction control system and the engine will reduce power (reduce timing) to limit torque. The key is getting the frequency fast enough that you can't 'feel' the power loss when the car starts to slide.

 

On and I heard about the smaller blower to! Getting 600bbp + out of the 1.7 ltr unit is amazing. Think I heard GM will be spinning the little thing to about 20,000rpm! As you mentioned looks like there will be a lot of headroom for a ZR1 car.

Also interesting is they are running approx 10.0:1 compression ratio on the LT4. That's quiet a lot for a oem. Shows you how much DI can help when it comes to controlling the fuel burn.

Shame GM didn't go twin turbo though! That would have been really impressive!

 

I think you're right in that GM probably will use tq management vs going with all wheel drive. But.....tq management is another way of saying that you can't use all of the power. All wheel drive would sure be sweet with 750ish hp going through all four wheels. Now, you're talking supercar. If GM offered that, I'd buy it, leave it stock, and just enjoy it. Naaaaaa, probably not