Twincharging with Screw-Type SC instead of Roots

[jbond]

Twincharging an engine that features a screw-type supercharger (ie it already has internal compression) in my mind has the following advantages and disadvantages:

Disadvantages:
It would still feature parasitic loss when the supercharger is "bypassed" and the turbo is powering away at higher rpm

Advantage:
The efficiency being better than a roots blower, would mean lower temps and more power

Can one of the gurus post their thoughts? PatPrimmer and Warpspeed had a lot to say on previous TwinCharge topics.

In short: what is the suitability of screw-type SC for twincharging project?

PS: I really have the twincharge bug! help!

 

[Scirockett]

check it:

http://mr2.com/TEXT/SuperChargerInfo.html

looks like toyota is no stranger to SC clutches and bypass valves. Even though some may think the setup stucks, it has a lot of merit considering it was done at the OEM level in 87-89! infact, it's described to be similar to, if not actually being, the eaton type onboard bypass/wastegate.

it may not seem like bypassing and disengaging a SC would not offer much gain, but it's one more piece that add's to overall efficiency/performance of the motor, and it's happening now more often than not on OEM vehicles. Here's how I look at it: I know how much power I currently make with the turbo, and I don't want to lose any of it. ie, once the turbo spools, I want the same unrestricted, fresh, cold air that I get now w/o a SC. It's a hefty wish, and has warts, could be done other ways, but I've been bitten by the TSI bug.

monster fmic is a must. Not a big fan of a/w ic's because of all their damn components. (ha ha My plan is the existing monster fmic between the turbo and TB/engine. The little TSI uses an a/w IC in the intake manifold. how compact.

 

[Jamin2]

Nobody has referenced the best old thread in this one yet, so here it is - thread71-174690.

I'm new here, I found that old thread on Google while researching the possibility of twincharging my car vs a bigger blower vs straight turbo. It is the best technical discussion i've ever had the pleasure of reading in any forum on any topic I think, and I thank all who participated - especially Pat and Warpspeed - for the fantastic information. I am DEFINATELY going twincharged now. Maybe I can contribute a little, too.

It seems to me after much looking around, that starting with a supercharged engine or an engine for which well developed supercharging kits are readily available rather than a turbo motor would be a far simpler begining point. Fabbing up a turbo system involves an exhaust manifold flange and some pipes (okay not really, but it IS easier) and intercooling should you desire it is simpler. Adding a supercharger involes a custom intake mani and mounts, removing something or finding room for the extra pulley not to mention finding a correct size belt and new tensioner settings for the extra drag - and now you get to cool the air you compressed, which is a lot more involed than a front mount air-to-air common in a custom turbo setup. I mention this because in subsequent threads I see a lot of people talking about adding a blower to this or that turbo motor for a twincharge, and that seems overcomplicated to me.

I'm starting with a great ice of work, the GM LSJ EcoTec. I wish to bring in a new (I hope) idea to the twincharging discussion, that of using a remote-mount turbo for the system. It seems to me that this would have several benifits. Firstly, as remote turbo guys are always saying, cooler operating temps and less heat transferred to the compressed air. Since we're compressing it again, cooler to begin with can't possibly hurt. Secondly, we can run a real header system before the turbine. Yes, the positive action makes this unecessary per se, but it occurs to me that in combination with a properly proportioned wastegate mounted near the front of the system and well before the turbine, further "tuning" of this complex exhaust equation becomes possible. Just a thought.

Lastly a question. The discussion has focused on a lesser pressure blower fed by a higher pressure turbine for the most part. I feel that keeping my blower PSI up (stock is 12-12.5) should make for stronger low end response, and blowing a few extra PSI at the top end via the bigger than normal turbo up top would flatten things out. Maybe less peak power this way, but a much flatter curve. Correct me if I'm way off here.

The plans forming in my head now would invlove a GM stage 2 type arrangement bumping the redline of my 2.0 to 7k rpm, spinning the blower slightly faster with a slightly smaller pulley delivering 15-ish known PSI, and affixing a GT30 or 35-ish turbo out back with a long tube header system and high-velocity tuned exhaust with a custom wastegate mounted up front to make the motor think the exhaust is a lot bigger once the turbo is up to speed - reducing overall backpressure and keeping things cooler and happier. I'll take a hit on overall pressure, I don't think I'll be starving for power, LMAO. The existing HPTuners suite for the LSJ would give me a fairly wide level of control over the fuel and spark without messing with standalone stuff, and the existing boost-bypass from GM makes that (very good) discussion moot for me as well.

I'm also thinking an E85 conversion makes for less overall thermal units of power, but more resisitance to the obscene boost levels and detonation for a lot less $$ than VP105, lol. This will be daily driven on a fairly frequent basis!

Thoughts? Feedback?

 

[Jamin2]

Can't figure out the edit funtion yet? LOL

Forgot to mention that I'd be thinking no more than 8 psi from the turbo, tops. Based on teh excellent info provided previously, that should get me more than enough boost - I might keep it in the 4-6 psi range from teh turbo! Just a little more up top where the blower gets out of it's efficiancy range.

Thanks for reading...

 

[DigitalGT]

I'm a newcomer to this particular arena so go easy, but I do have a fair amount of experience with compound forced induction having successfully twincharged a 2.5L V-6 engine for a customer/friend in the past. I've tuned a few different twincharged engines over the the last 10 years and I'm also slowly doing another twincharge build on my own car, an '03 SVT Focus which is what has led me to this site.

What I don't understand is everyone's fascination with copying VAG's design and placing the blower before the turbo. VAG had the luxury of placing the induction components in whatever order they wanted and using an expensive servo operated valve along with complex control logic to fix the inherit flaw present in modern OEM engineering.........fuel economy. Their design takes a fairly old idea and uses every trick to reduce as much parasitic drag as possible even though an unloaded and bypassed Roots blower takes little power to turn.

I'm not an OEM (thank God) so fleet fuel economy ratings and accountants don't drive my design choices. My current list of intake obstructions (in order) is: filter, turbo, air to air intercooler, throttle body, blower, air to water intercooler, intake valves. The blower and air to liquid IC came assembled together in a purpose built intake manifold. The entire unit is mounted tidily on the back side (transverse front driver) of the engine. A fairly large heat exchanger (6"x24"x1") is mounted in the rear of the car with some duct work to supply atmosphere through it at speed and 6" fans at idle. A cast manifold couples the turbo to the head and the charge is fed through a medium sized FMIC. A recirculating (don't like the ricer psshhhht) bypass is used before the throttle body and the whole thing is tuned with a MAP based standalone. There are some other black boxes and variables thrown into the mix like water/methanol injection but they aren't related to the big picture here.

The whole thing runs smoothly with no compressor switchover drama. When the turbo comes up to full boost it simply blows through the supercharger without incident. The powerband is as predictable as any other turbocharged car. The blower makes the engine behave as a larger one and the turbo does it's normal thing. It's sort of like driving a 3.5 L. turbo 4 cyl instead of a twincharged 2.0 L.

 

[DigitalGT]

Jamin you posted while I was writing.

It seems we're on the exact same track. I use an M62 roots blower kit which by itself put out 12 psi. The turbo is a GT2871R which is internally gated (unlike the GT30 or 35 you're planning on) the electronic boost controller is set for 8 psi low boost and 12 psi high boost. The engine is built so it swallows the high pressures without issue. The tires are only 215s though and even with a limited slip, the low boost setting is overkill. Granulated rubber on demand in the lower three gears.

You're absolutely right about using a kit solution for the supercharger. I wouldn't have liked the chore of intercooling a roots blower and fabricating mounts. As you can see from the pic, this kit made it very easy for me.

 

[Warpspeed]

Scirockett,
Yes the Toyota supercharging system was way ahead of it's time in so many ways. The only real problem was the "economical" construction of the rather cheap and nasty strait two lobe blower, which is non rebuildable. The bypass system is excellent, but unfortunately it is not readily transferable to another vehicle, because of how the whole thing is integrated into a very complex inlet manifold casting. Functionally, it is well worth studying and copying. A truly great effort by both the bean counters and the engineers at Toyota.

Jamin2
Starting out with a supercharged engine is the only way to do it, either OEM, a commercial blower kit, or do it yourself.

Changing the pulley drive ratio and/or the turbine a/r enables you to set it all up to predominantly have either the characteristics of a supercharged engine, the characteristics of a turbocharged engine, or the best of both without the disadvantages of either.

Jamin, there is no edit function here. Once you hit 'submit' there is no going back.

DigitalGT
Definitely on the right track with this.
I too am baffled by some peoples ideas about doing this in really strange complex ways that only introduce extra problems.

 

[jbond]

Digital GT and Jamin2, do you guys have pics you can post up?

Digital GT, I couldn't see that SVT SC Kit that you posted up, the link didn't seem to work. Try this:

To include an image in your post:
]img

http://www.mysite.com/images/happy.gif

]
edit: Change the first "]" to a "["

 

[Jamin2]

Digital GT - I didn't go into details about teh engine I'm using, as I believe there's a fair amount of info out their about the LSJ. We are on a VERY similar track, lol - the LSJ uses an M62 from the factory, blowing 12 psi pver a 9.5:1 compression ratio. They designed a very trick intake manifold with integrated laminouva (sp?) air to water intercooling, and a barely adequate front mounted heat exchanger. The intake mani doesn't flow quite as smoothly as we'd like, but it gets the job done. Luckily my car is blessed with an abundance space between the front bumper mounts and the radiator, so plumbing in a larger HE is cake, with room to spare for an air to air for the turbo, a popular mod is the HE from a Mustang Cobra plumbed inline with the existing HE, don't evenbother removing it. Good for 20 degree drop in IAT's. Okay - too much detail, lol.

I would really like to hear more about the '28in that setup. I was thinking GT28, but after reading up on the other thread I figured I'd jump a size or two, lol. I've seen a GT30 (don't recall the trim) in action on a 2.4 liter four, and it made full boost by 3400 rpm - with 12 psi worth of blower, I'm guessing that GT28 ramps up REAL fast, lol.

Warpspeed - thanls for the quick and direct reply, it's exactly what I was needing - knowingthat either track works without problems. this being my first blown car (I've owned many a turbo), I've become somewhat addicted to teh feel, lol. I may, down the road, bore/stroke this poor thing to 2.5 litersand upgrade to a TVS blower (1.32 liters/rotation vs the M62's .962). I want lots of low and midrange power, but with more total power than a blower alone cn deliver. I was all but resigned to going turbo and dealing with the difference in power delivery. I am now VERY excited to get this going!

 

[jbond]

Jamin2, I think that the GT2856R (commonly called the GT28R) is too small for a 2L (in fact that turbo comes stock on some OEM 2L so it's definately on the small side)

My car is a 3L V6, and twin turbo'd (so 1.5L feeding each turbo) and is being built for GT28RS (about 550rwhp).

Given that you will be running a SC for low down grunt, you no longer care about a quick spoolup turbo. On top of that, remember that you 2L running with a SC at 15psi is acting like a 4L N/A. So any GT28 is too small for your application!

 

[DigitalGT]

I don't have finished pictures of my twincharged conversion yet. The car is currently on stands in my garage undergoing ANOTHER clutch replacement and the oiling system is being upgraded with a 2 quart oil accumulator, braided hose and an oil cooler.

I do have this shot of the blower though. Sorry the other link didn't work.

 

[HoofHarted]

I need to replace the oil in the gear section of the supercharger, unfortunately after searching I can't find what type or viscosity ,mainly the latter ,to use can somebody please suggest a type of oil. Somebody suggested Diff Oil like a 85w 90.

Thanx

 

[patprimmer]

Manual transmission gear box oil. After all it is a one speed gear box

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[DigitalGT]

I wouldn't use MTX gear box lube. Several OEMs have supercharger lube designed specifically for Roots blowers. I buy mine from the local Pontiac dealership but only because it is the closest GM car dealership to my house. You want "GM Vehicle Care Supercharger Oil" and it comes in 4 ounce bottles. You need two bottles. Part # 12345982. It costs about $7 a bottle.

 

[HoofHarted]

here's the response straight from Steve Padfield of Vortech Engineering: "[Vortech's] maintenance-free lubrication system uses engine oil that is pre-filtered and injected directly onto the drive gears. We chose this configuration as opposed to a `self-contained' setup because engine oil provides faster warm up, excellent reliability, and superior cooling. The lubrication oil benefits from continuous filtration, being routinely changed along with the engine oil (instead of an additional maintenance action). This system also offers the best opportunity for thermally stable operation. Vortech firmly believes this is the best method to feed and care for a supercharger."

Any Thoughts on the matter?

 

[DigitalGT]

Vortech intentionally designs their blowers around the idea of using the existing engine oiling system for lubrication. Magnuson, on the other hand, designs around a self-contained oil bath. I don't see a centrifugal blower as having smaller tolerances than a modern engine and, as such, see no reason why filtered engine oil (which is certainly good enough for the highly stressed powerplant) can't be used.

I'm a big proponent of using what the OEM recommends if for no other reason than to eliminate a warranty dispute later down the road. Obviously I leave myself very open to the idea of upgrading but sometimes mother really does know best. So long as the oil supply is post-filter and regular oil changes are made, I see no flaws in Vortech's logic. If it's good enough for the 100,000+ RPM center cartridge of a 1600° F. turbocharger, it's good enough for a blower.

That my humble grease monkey opinion. I'm sure someone else can geek it all out for you or reference some white paper somewhere to "prove" me wrong however.

 

[HoofHarted]

I Know what you mean about getting blown by facts. Um I think they wanted the oil filtered because they were using tiny oil jets to spray oil on the gears. Possibly they didn't want them getting blocked.

I'll have a look to see how hard it is to adapt a oil jet system to the charger.

 

[patprimmer]

The gears are similar to gear box gears in design and operation. They don't know what they drive. Normal manual transmission gear box oil does work I use it in a 6:71 no problems I think it was 80 weight. I never paid that much attention. It was left over from oil I bought for a manual box I rebuilt about 20 years ago.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[stimpee]

Whipple and Opcon/Autorotor both recommend 15/50 or 20/50 synthetic motor oil for the gearboxes in the twin screw compressors.

 

[HoofHarted]

Pat I can see where you're coming from in that they are just two gears costantly in contact and motion, and that Normal Manual Transmission oil would work. If I Were to use this then i would just change the oil regularly.

I'll try to find i similar rating to those two types of oil, but if i cant then im not gonna bash my head. At the end of the day Im sure it's a marketing sceme because people think it's a supercharger it SHOULD have exotic oils, fully synthetic will only do.

 

[Warpspeed]

I have run synthetic engine oil in roots blowers with a sealed oil case for high mileages without any problems. The oil always stays very clean. The only danger is that if one of the seals leak, the fairly small volume of oil contained in the blower gear case may leak away unnoticed. If you are a typical hotrodder or enthusiast, there is probably not much chance of that ever happening.

There is probably still an argument for using the main engine oiling system in an OEM application, where the blower gear case oil level may never get checked. At least the blower is always full of oil, and it gets changed when the engine oil is changed.

At the end of the day, I don't think it really matters either way.