OK, lets look at some numbers

[bbjones121]

All research I did on rebuilding the toyota 2zz engine for a FI install in a lotus elise pointed out that it is actually a turbo that can achieve greater hp than a supercharger. This may not be true for high displacement engines, but I think drag cars use them because they have the traction for high torque off the line, not because they are more powerful. Superchargers would probably be more consistent, which is extremely important when counting milliseconds.

I'll take a shot.

There are tradeoffs for both turbochargers and superchargers. Superchargers are mechanically driven by the engine to create boost. The benefit is for the most part they make their boost throughout the RPM range and instantaneously create that boost right along with throttle inputs, however because it's a mechanical linkage they also take a good amount of HP to run on the high-end to create that boost so it limits the overall output more than a turbocharger would.

Super chargers come in a couple different varieties, roots-type and centrifugal type. A roots type like a twin-screw is the most common, they sit right on top of the engine and suck in air directly. A centrifugal type is basically the business end of a turbo that is mechanically driven instead of exhaust driven. A roots type like what mn_vette said gives low-end boost and tends to run out of steam up top. A centrifugal type is like a turbo where it makes boost at high rpm, down low you experience mechanical instead of induction lag which makes centrifugal type superchargers feel similar to turbos

A turbo spins independently from the engine using exhaust to generate the boost. They tend to be much easier on an engine and give their numbers with far less sacrifice to fuel economy and reliability when compared to a supercharger. A turbo multiplies it's output with it's own output, the boost puts more air in the engine, the engine gives out more exhaust, the exhaust spins the turbocharger.

A supercharger doesn't have the benefit to take advantage of it's own output like that, it takes HP to run and somwhere along the curve the HP it takes the engine to spin it will outweigh the HP it creates causing a drop off on the top end for roots-type blowers, and mechanical lag down low for centrifugal type. However, because superchargers are mechanically linked the boost follows the engine instantly and throttle response is preserved.

Turbo's overall are a better and much more cost-effective way to achieve power numbers. However, a Supercharger will allow you to go more balls-out on power while sacrificing less throttle response at the expense of being expensive, much higher in maintenance and much harder on the engine.

There's a good section that summarizes all of this in this wiki article http://en.wikipedia.org/wiki/Supercharger

All in all, I believe you can make higher HP with a supercharger which is why drag engines tend to use those instead of turbos. But for a track car, turbo's allow for more reliable output as a supercharger would eventually eat the engine in most cases.

[Wayne Presley]

A turbo will always make more power than a supercharger at the same boost level. This is due the HP required to drive the SC. On a centrifugal SC on a small block 302 making 450 RWHP (14psi), the SC takes between 75-80 HP to run the blower. A turbo car at the same boost level makes 500-510 RWHP.

[Gollum]

Air Temp/Density also matters when comparing the two. A turbo pushing peak HP numbers on an application that's actually in the sweet spot of it's compressor map can be over 75%, much higher than any roots style supercharger I've seen, and also rivals the best screw type as well. Then when you combine the fact that very few roots or screw type supercharging systems do anything to cool the air after the outlet it's no wonder a turbo has very little challenge beating out the conventional supercharger setups.

Now, if we're going to compare an 80's turbo without an intercooler to an OEM roots (like an eaton), I bet PSI for PSI they're nearly equal in HP.

Now, centrifugal superchargers are well suited to using an intercooler, but will still require a small HP loss to be driven, and usually to avoid absurd whine have heavily helical cut gears, which increase rotational friction. Just like how a straight cut gear in a tranny will be stronger and have less power loss, the gearing in a centrifugal supercharged is no different. There's always going to be a balance of noise and power loss. Ever notice how the most efficient centrifugal's on the market are also the noisiest? (ATI Prochargers) Granted the compressor engineering has a lot to do with it, but reduced friction is a good part of it too.

[BrandonDrums]

All research I did on rebuilding the toyota 2zz engine for a FI install in a lotus elise pointed out that it is actually a turbo that can achieve greater hp than a supercharger. This may not be true for high displacement engines, but I think drag cars use them because they have the traction for high torque off the line, not because they are more powerful. Superchargers would probably be more consistent, which is extremely important when counting milliseconds.

I buy that, sorry about the bad info. Another guy even pointed out that turbo's are banned from top-fuel dragsters. The added power is probably why.

Fact fail!

[wjfawb0]

I prefer roots superchargers on street cars for quick torque and less shifting. I suspect driving a large V8 with a turbo is a lot more satisfying than a small four cylinder, though. The two STIs I had were fun, but the turbo lag even on a stock turbo wasn't nearly as enjoyable as having 450 lb-ft of torque instantly at 2500rpm. If I had an 1800lb car with a WRX drivetrain, I would want it tuned using the stock solenoid system and a nice linear power increase to make the car more predictable and less likely to swap ends suddenly going down the road. In my cars I've always foudn right foot control to be the most effective way to keep it under control.

[iamnottelling]

I actually feel smarter as a result of reading this Forum...

Thanks for all the great explanations (CoG with breaking & Turbo vs. Supercharger)

- Just another young engineer -

[Twinspool]

I actually feel smarter as a result of reading this Forum...

Thanks for all the great explanations (CoG with breaking & Turbo vs. Supercharger)

- Just another young engineer -

Wait until you get to upper division classes. Heh.

I'd be very curious about the demographics of the average FFR buyer. I gather that many of the owners are, ahem, well seasoned. From a business standpoint, the 818 is utterly brilliant in its more youthful focus and could expand the FFR customer base far outside of the range it has been in.

A thousand thanks for making this car. You have me seriously interested. Based on conversations I had with GTM and Roadster builders, I assumed that an FFR kit was something that I wouldn't be able to do until I had $50k and idle time a plenty.

[PhyrraM]

I'd be very curious about the demographics of the average FFR buyer. I gather that many of the owners are, ahem, well seasoned. From a business standpoint, the 818 is utterly brilliant in its more youthful focus and could expand the FFR customer base far outside of the range it has been in.

I've often wondered the same thing. When the original 'single donor C**ra' came out I seriously wanted one, however in my mid-twenties, he 10K price simply wasn't possible. In today's money that is....$7K? A significant discount vs. the O.G. Roadster. So a (time adjusted) lower kit cost would open the doors of opportunity even sooner for many would be builders.

Also consider that the 818 is likely to be even less restrictive than the original Roadster in terms of an appropriate donor.

IIRC, the roadster need a very specific year range of Mustang ('87-'93?) for the required suspension parts, motor mounts, wheels, etc. to work with the kit without modification. As the years progressed FFR started adding options and variations to the kit to support other Mustang generations. If the 818 kit mirrors the Roadster or GTM coupe as far as reused donor car parts (a big 'if' at this point), almost any Subaru will do. If you can forgo the turbo motor (only 1800lbs, remember?), you can pick up a running Legacy/Impreza for as little as $500. That puts the cost as low as $11,000 for the supreme budget builder.

Here's an idea:
FFR can offer a less complete kit for (no seats, wiring, instuments, lighting, etc). Basically strip out anything not related to the chassis or basic body and sell it for...what?....$7,000? That would really open up the gates to younger, less established buyers. Of course, there would eventually be tons of unfinished kits on Ebay. I suppose that wouldn't do much for the 'FFR is not a kit car' image they have spent a lot of time developing.