Turbo vs Supercharger

[David_J]

Originally Posted by JP-s-in st. louis

I have more plans not this motor but since I like this car so much and it is all but paid off. I hope to find a 3.2 or 3.4 sleeve it out to a 4.1 (alla Todd) do some head work and tune via IA, Tit connecting rods, pistons, Cams and and some N20... I figure I like this car that much and am already knee deep. So anyone who has a line on an engine please keep me in the know...

I will eventually do a wide body kit like an RSR so I can fit bigger meats under it. I already have issues hooking up. 1st is useless and 2nd is almost the same.

Now that's what I'm talking about. Making the car a blast to drive. Hell, I'm deep into mine already, so what's a little more $$$. I think I will keep mine around for the race/show vehicle but mod the crap our of it.

Josh, let's go take your car out in the snow. Let's have some fun. You said I can drive it anytime, I'll be over in 30 minutes.

-David

[MNBoxster]

Hi,

A Super is Crank Speed dependent ± the Pulley used. Power comes sooner, little spool up time (lag). But, it loses something at the top end over a Turbo due to parasitic loss (you need more boost from a Super to achieve the same HP). Roots type are less efficient than the compressors in a Turbo. Vane type are about the same as a Turbo.

A Turbo comes on later (lag), but creates more power higher in the Tach with less Boost. More complex plumbing and Oil circuit (most Supers use a self-cotained Oil System). Heat Management becomes an issue, especially on a mid-engine.

I'm not yet convinced of using either on the Boxster w/o Intercooling due to the high CR and variability of available fuel. I'm skeptical of the longevity of a Boosted M96 engine. There are few high-mileage examples, so it is yet to be proven to my mind.

But, for simplicity, the Super kits are the better of the two for the Boxster IMHO...

Happy Motoring!... Jim'99

[NickCats]

Originally Posted by MNBoxster

Hi,

A Super is Crank Speed dependent ± the Pulley used. Power comes sooner, little spool up time (lag). But, it loses something at the top end over a Turbo due to parasitic loss (you need more boost from a Super to achieve the same HP). Roots type are less efficient than the compressors in a Turbo. Vane type are about the same as a Turbo.

A Turbo comes on later (lag), but creates more power higher in the Tach with less Boost. More complex plumbing and Oil circuit (most Supers use a self-cotained Oil System). Heat Management becomes an issue, especially on a mid-engine.

I'm not yet convinced of using either on the Boxster w/o Intercooling due to the high CR and variability of available fuel. I'm skeptical of the longevity of a Boosted M96 engine. There are few high-mileage examples, so it is yet to be proven to my mind.

But, for simplicity, the Super kits are the better of the two for the Boxster IMHO...

Happy Motoring!... Jim'99

Jim,

Found another thread about this subject :

http://986forum.com/forums/showthread.php?t=4189

Look like your opinion hasn't changed much in the past year.

I am surprised you prefer the supercharger over the turbo for the Boxster, though...

Nick

[MNBoxster]

Originally Posted by NickCats

Jim,

Found another thread about this subject :

http://986forum.com/forums/showthread.php?t=4189

Look like your opinion hasn't changed much in the past year.

I am surprised you prefer the supercharger over the turbo for the Boxster, though...

Nick

Hi,

Doesn't surprise me that my information (or opinion) hasn't changed at all. I have had a fair amount of experience with Forced Induction both in Aircraft and Automotive applications. Each has their advantages and disadvantages. But these are not generic, rather, they often depend upon the application.

With the Boxster, being mid-engined, I think the Heat Management issues alone (let alone the plumbing issues) would outweigh the advantages of a Turbo. So, I would most likely choose the Supercharger route.

That's not an endorsement, at least without Intercooling, or some other way to prevent detonation given the high CR that the Boxster has...

Happy Motoring!... Jim'99

[pecivil]

Trigem2k!

When you get your turbo set up, lets hook up and you can compair it to an NA 3.4l :dance:

If you will get 270 to the wheels, it should be close to mine. I am in San Diego and would love an excuse to get up there to drive some of the canyons in Malibu!!

If you guys are spending 7k for the kit, and 2k for install, why not just go with a 3.4 conversion, with no detonation potential, no real heat issues, and no worries about going to FI on a high CR motor?

Theres no way I would go to FI on with the CR the M96 has with no IC.

I have an eaton SC on my E36 318i with no IC and the CR is 10:1. And that is pushing it but it only gets up to 6 psi. But it kicks ass when a E36M3 can't pull on me in a little ol 318 :dance:

I would imagine that they tune the ECU to accomodate the additional fuel required to match the FI, for either system, right?

[ohioboxster]

Yes Jim but what do you do if the car doesnt detonate? You know even when my car continues to run for trouble free mile after mile I have a feeling there are people that will say "Fluke" or "Lucky". I just dont understand why several people say the car will detonate due to the compression ration. I drive my car everyday without issue. Let me clarify, Im not looking for an endorsement or even convince you of anything but just want you be aware 5 lbs of boost does not make the car detonate.

[David_J]

Upgrading a 3.2 to a 3.4 doesn't seem a logical choice for what you get. I mean, my 3.2 only has 24000 miles. Why would I want to upgrade that to a 3.4? Adding a SC to a 3.2 sounds like a good choice for me.

-David

[MNBoxster]

Originally Posted by ohioboxster

Yes Jim but what do you do if the car doesnt detonate? You know even when my car continues to run for trouble free mile after mile I have a feeling there are people that will say "Fluke" or "Lucky". I just dont understand why several people say the car will detonate due to the compression ration. I drive my car everyday without issue. Let me clarify, Im not looking for an endorsement or even convince you of anything but just want you be aware 5 lbs of boost does not make the car detonate.

Hi,

I never said your car detonates. What I said was that at anything over 8.5:1 CR, detonation becomes a concern. At 11.7:1 CR, it becomes a major concern.

Your car may be detonating at certain times and you're unaware of it, it may be doing so under certain conditions (Ambient Temp, Load, Fuel Quality, etc.). The DME may be compensating for it by using a detuned MAP, I don't know, I haven't studied your specific installation and all it's pertinent parts and those of the motor itself. But, if you are at times detonating, it's probably not enough to grenade the engine, but what are the longterm effects?

The rule of thumb is that anything over 10:1 CR requires Intercooling to be safe from detonation. Porsche doesn't force the M96 engine in any of their cars, what do they know that we don't? The Turbo uses a different engine. The TT engine (M96/70) is similar to the M96, but also very different - 8.4:1 CR.

Adiabatic Heating (a Gas rises in Temp if it is compressed) raises the Charge Temp 11°/1 PSI (10.9°/1 PSI to be precise). So, at 5 PSI, your intake charge is 55° hotter than the Ambient Air entering the Intake. On a 60° day, this means a lot less than on a 98° day, because the Charge temp would be 115° on the 60° day, but 153° on the 98° one. This heated charge will reach a detonation threshold (approx. 268°) a lot sooner in the compression stroke (where it is further compressed and heated) than Ambient Air charge would, which is what the engine was designed for (Pistons, Bore, CR). This means the engine must produce a spark sooner to compensate. How much sooner is it capable of? I don't know. How soon is too soon? Again, I don't know. But, it's the not knowing which concerns me.

Also, one bad batch of fuel and you could have serious problems. That's just too much risk management for me I guess...

Happy Motoring!... Jim'99

[JP-s-in st. louis]

Originally Posted by David_J

Now that's what I'm talking about. Making the car a blast to drive. Hell, I'm deep into mine already, so what's a little more $$$. I think I will keep mine around for the race/show vehicle but mod the crap our of it.

Josh, let's go take your car out in the snow. Let's have some fun. You said I can drive it anytime, I'll be over in 30 minutes.

-David

I can spin the tires thru 3 in the rain and you want me to go out in snow...hahahahaha

I would not even make it up the hill on my street.