porshhhh951

Okay whoever said supercharger's don't have lag must not own one. The only blower's that are instant power are screw-type...i.e. root's type blower's that mount on top of the manifold. Centrifical blower's have lag just like turbo's do. That's why your friend doesnt see much power gain until 4k. The only supercharger I would ever put on my car would have to be a root's type....the centrifical blower's are turbo's with a belt. There power comes much later(typically) and they do not make the power/boost ratio that turbo's do(typically) A turbo will hands down beat a centrifical blower in mid range power...and peak power all day long. That being said....a 996 n/a with its compression ratio and closed engine bay...are hard to fab turbo kits for. Hence the much larger price tag. A decent rule of thumb is 10-15 hp per psi of boost. Of course this widely depends on the application and the part's and configuration. Different car's and kit's will yield different result's. Let's talk hypothectical's for a second. Car "a" has a cen. blower with air-water cooler @ roughly 9 psi of boost. He see's decent boost pressure(let's say 5 or 6 lbs of the total 9) by 4k rpm's and has linear power till redline....gradually increasing boost pressure as his rpm's rise. Car "b" is fitted with a turbocharger and a air-water cooler @9 psi of boost. He see's full boost at 4k all 9 psi and holds till redline. We are obviously talking low load gear's here because anyone decent displacement 6 cyclinder can produce 9 psi of boost in a high load gear..i.e. 3rd,4th,5th,6th. Now depending on the size of the compresser wheel....the a/r and how the downpipe is fitted to the hotside of the turbo will drastically affect the results. But, all in all case by case a turbo will always out perform a cen. blower in ever category. Now moving on to your situation. A turbo isint really a viable means is it??? unless you wanna cough up the 20+ grand it takes to get the piping right. Is a 9 thousand doller cen. blower a good purchase in your case......hmm...I think so. Is it better than a turbo...let's not kid ourselves. If cen. blower's were better Porsche would have been using them along time ago from production. Porsche uses turbo's because they are more effecient,make more power, and put less strain on the motor. With FI car's its all about load. Another reason why I really don't see cen. blower's being better than turbo's is they are belt driven...just like the a/c and everything else....so what does that mean...you guessed it. It takes power away from the motor to run. The blower actually costs you hp...to be able to run. Anything atached to the belt's of the car sucks power.....cen. blower's are no exception to this rule. Most people use them because they are easy. But, that's where the benefit's stop over turbo's. Because they certainly do not perform better. I feel for your particular appilication a cen. blower is a viable mean's to some reliable hp. Taken into consideration the cost ratio of blower-turbo....I think the best bang for your buck is going to be the blower. Of course turbo kit's can be had for the same ammount and in most cases much much less. The problem is the platform (996) is very costly. So any upgrade you do is going to hit your wallet rather hard. I think you will really enjoy the added power...and let's face it you need it don't you. Momma's lincoln comes with 280hp. 996's are excellent car's. They handle well, they brake well, they are very ballanced and neutral in my opinion. But, the none turbo one's leave a little to be desired in the performace department. I would run not walk but, run away from a non turbo 996 all day long I don't care what bolt on's he has(btw I have done it to some of my friends) Get the power adder and go have some fun at you local track.

best wishes,
The water pumper

CarlosR

The answer to this is just a little complicated. First, it depends if you have an e-gas model or not. I believe that all the '99 C2's (not C4's) were NOT e-gas. In that case the original model (that is now shipping) will not work.

BUT, there is good news. Todd emailed me that they have a version in development for the non e-gas models (like my '99 C2 cab), and that he expected it to be available this month.

That was about 3-4 weeks ago, and I haven't heard anything since, so I'm not sure if it's ready yet or not. But it is supposedly coming.

=CarlosR=

ben in lj

"Todd/Evo did have a turbo conversion for the 3.4 L/3.6 L but it really never came out."

I would have turboed it a long time ago if not for the rear ricer spoiler requried for the intercooler. Darn glad I didn't and waited for the much more sleek, smooth (and lag free), and lighter SC.

Mitch

Carlos...I'll PM you w/ phone # and we can hook up for you to see the car/kit. I think you'll like the result if you're thinking of doing this to yours.


Gsanders...I think Ben confirmed that Todd has or just about has a kit that works for '99 C2 (without egas). Good luck.


Ben...You where right. This kit really makes a difference. Does your SC have a slight whine at idle? I like the sound and even more when you get on the throttle, personally. Any problems starting the car? I've got a slight glitch that Todd has just solved with his car and we will be shipping the brain from mine to him to adjust. Any word on your CGT?

Regards

HBacura

It would be the other way around, where the turbo would be less destructive if you don't go all out crazy with the boost. We can all agree the major advantage of a SC is there is minimum lag, but at the same time the SC is constantly running, putting more stress on your engine, while a TC you have control if you want to apply boost. You can drive 100 miles a day and never really use the TC if you don't push the car. Plus boost controllers and turbo timers really help regulate boost and the wear on your engine.

My experience from a SC is it's great at first, but after you get used to it, it leaves you wanting more.

ben in lj

hey mitch.

i don't remember hearing a whine at idle and yes i have the "warm" start problem that todd apparently is close to getting a fix for (if not already fixed).

the cgt is an august build so hopefully it'll be hear by late sept/early oct.

glad you are enjoying your car. it's just such a better (different) car with that extra power.

NiveK

no actually the Turbo will ALWAYS be more destructive on your engine, 1st, the turbo has to run off the the exhaust pressure, 2nd it causes much higher heat for your air, even with the intercoolers, now that being said, i would like to have a TT personally , but if we where talking just upgrading my 996, no, because the engine internals would need to be upgraded to handle the extra power and heat that a turbo creates, which is sometimes true of a SC if it really knocks the power up

porshhhh951

ummm no offense what-so-ever intended but, I have to completely disagree with what you just said. While turbo's do generate more heat(need the inertia to spin the impeller) any decent running intercooler or water injection system can get the temps to below atmospheric easily. Super charges are always spinning at least a little because of the belt and the pulley...but, I have to say even that is minimal in itself. I had owned serveral cen. blown car's and they really don't build alot of boost down low. They have lag just like the turbo. I think really the only superchargers that are going to drastically hurt the life of the motor...or atleast enough to notice it would be root's type(screw type) because they actually are instant power....so you are running boost all the time.

anyways that's my .2 cents.

NiveK

well i would imagine they both actually do more damage than not having them at all, which one is obviously up for debate, but i can tell you from my experience's ive always had problems with turbo's and reliability, none with SC's, but im sure it's just like anything you use, some have problems some don't

flatair

Facts:

Centrifugal superchargers are the same thing as turbocharger compressors, only difference is that the turbo compressor is driven by an exhaust turbine, the centrifugal supercharger is driven by a pulley or gear drive (most are pulleys).

Centrifugal compressors (turbos and cent. superchargers) build boost exponentially to shaft speed. This means if a centrifugal supercharger is spinning at a ratio directly related to engine speed, the boost will develop exponentially, as will the power. If you gear the centrifugal supercharger to produce lots of boost at low engine speed, you'll end up overboosting and overspeeding the compressor at high rpms. Thus centrifugal supercharger inherently have a 'soft' low end, and produce all the power at the top end (as shown by any dyno sheet).

Turbochargers have lag, centrifugal compressors do not. Lag is time taken for the turbo impeller to get up to max speed, which is not directly related to engine rpm (rather exhaust flow). A well designed turbo system will have *better* bottom end than a centrifugal supercharger, because the lag will be minimal and the turbo will hit max boost well before 3000 rpm, right about when a centrifugal supercharger starts waking up.

Positive displacement superchargers have power everywhere, because they're not using rotary compressors force air into the engine (which essentially 'throw' air from the center of the compressor wheel to the outside, kinda like a sling). Positive displacement units are using lobes or screws to 'stuff' air into the engine. So the amount of air being pushed into the engine is relatively constant and directly proportional to engine speed - so you have the same proportion of extra air being pushed into the engine at any engine speed. The exception is at very low rpms, where some units can back leak a bit - you'll see a flat torque curve on positive displacement units, but they soften just a wee bit at very low rpms.

Centrifugal compressors are much more efficient at what they do than positive displacement units. The positive displacement units 'beat up' the air as they work, which produces heat (roots lobe type are the worst, screw type are better). This heat decreases power, and increases risk of engine damage. Heat can be mitigated by intercoolers, but comparing positive displacement to centrifugal, centrifugal will produce more peak power.

Turbo is the best, but most complex solution. Turbo has the efficiency of a centrifugal compressor, lag can be managed by good matching of turbo size to engine, there's no parasitic loss, and a well matched turbo can hit max boost as low as 2000-3000 rpm. Lots of stuff to go wrong though, and if your boost control fails, you'll overboost and kill your engine. There's also a tendancy for amateur 'tuners' to 'up the boost' without doing things right. boom.

Centrifugal supercharger is efficient, and will produce alot of peak power. Less parasitic drag than positive units. More efficient=less heat=safer for your engine at a given power gain when compared to positive units. They're relatively weak on the bottom end. Also easier to fit in a tight engine bay. Max boost is achieved at redline, not 3000 rpm - so in theory a 350 peak hp car with a positive displacement blower and a flat torqe curve would likely match or beat a centrifugal blown car with 400 hp peak in a street encounter.

Positive displacement units less efficient, but torque everywhere. They make your 3.4 flat six feel like it has %50 more displacement. Great for 'moderate' power gains (i.e. 50%). Not good for high output systems, i.e. not a good unit to make your 3.4 put out 500 hp at 20 psi. boom. Hard to fit in tight engine bay. Most parasitic drag.

I personally like the idea of intercooled positive displacement units for the 3.4, as I wouldn't be looking for more than an extra 100 hp on these cars.

Yes I'm bored at work

CarlosR

Flatair,

Thanks for the informative and lengthy post. Given the fact that the 996 motor is not noted for its durability, it seems to me the centrifugal blower may be the safest route to take, at some sacrifice of low-end performance.

=CarlosR=

BC

...There is legitimacy in your statement about a softer low end boost curve on a centrifugal. This is actually a transmission saving feature if you think about it. But if you DID want a more robust boost curve down low, then you would gearthe Centrifugal for lower RPM boost. But what you said about over-spinning - that can be solved with a simple Waste-gate type apparatus before the intake. You gear the Vortec or whatever for maybe 20psi of boost at 6500 rpm, but you make sure it bleeds boost over say 15psi. You have enlivened the boost curve down low, and you haven't over boosted the top end. Inneficient? Well, turbos do the exact same thing.

Oh, and that engine bay you saw earlier with Gretch's post? Don't anybody screw with that car when its together. Its called Displacement AND boost. Its a great combination.

flatair

But if you DID want a more robust boost curve down low, then you would gearthe Centrifugal for lower RPM boost. But what you said about over-spinning - that can be solved with a simple Waste-gate type apparatus before the intake.

Good idea, the wastegate solution, but that doesn't solve the compressor overspeed problem. A big problem with centrifugal compressors is that to make any noticable boost they need to spin quite fast, say 50,000+ rpm. Now lets say you have a 'normal' centrifual supercharger setup that generates 10 psi at 100,000 rpm for the compressor at engine redline (say 7000 rpm for a nice round number). Boost will be a couple psi at a compressor speed of 50,000 rpm (3500 rpm engine speed). So now we want the full 10 psi at 3500 rpm, so we gear it 2x higher - problem is when we rev to 7000 rpm, we have the supercharger spinning at 200,000 rpm!!

Now I'm just using ballpark 'round' numbers for ease if illustration, but your typical turbo/centrifugal supercharger should be limited to maybe 130,000 rpm MAX. After that, you're going to have problems - best case scenario is the supercharger fails, locks up, snaps belts, etc...worst case scenario is compressor grenade which can be pretty nasty. What we need is a variable drive centrifugal compressor that varys the gearing from high to low as the engine rpms rise - I think rotrex (sp ???) makes something like that and a couple of shops have tried to use them with mixed success.

http://www.rotrex.eu.com/

Brad

BC

Flat-

I do believe that the SCs from say vortec are rated to around 60,000 rpm.

This Link: http://www.vortechsuperchargers.com/...ts/t-trim.html

Shows that the T-Trim, which is a good fit for the CFM needs of MY car, the 928, (as well as the S-trim), tops out at 55,000 rpm. So if you spin it for 20psi, as I stated, at say, 7k or 6800, then you will have NO issue with over psinning. I am saying spin the unit to within its perameters, but outside of the bost curve that YOU wanted up top, and bleed it off over the number that you DO want.

Webtool

I read the Rotrex site and was interested to learn they use a blower transmission based on the elastohydro-dynamic drive principle which Jean Kopp perfected for use on his Variator designs back in the '40's. The variator is a precision drive which will hold speed over no load to full torque to better than 0.5% but they are expensive and fairly heavy. It struck me that for this fairly basic application of variable speed, the best answer might be to use simple split sheave pair pulleys, a drive similar to what snowmobiles use. The variable radius could be controlled by boost or rpm or load, or whatever the best mix is for progressive volume and pressure over RPM.