Ok... the `04 Cobra Mustang (4.6 liter, supercharged) is rated at 390 hp @
6,000 rpm and 390 lb.-ft. torque @ 3,500 rpm. The `05 Vette (6.0 liter, non-supercharged) is rated at 400 hp @ 6,000 rpm and 4000 lb.-ft. of torque at 4400 rpm. These specs are almost identical except for that the Cobra makes it's peak torque at a lower rpm (which is in fact better!). So, I am very confused here. The unbroken rule of the universe is that you simply can't get something for nothing. The supercharger is allowing the small 4.6 Ford to basically match the torque and horsepower specs of the larger hi-tech 6.0 Vette engine.. but what is the CATCH? There must be some downside to the supercharger (other than just the whining noise). Boy would it be nifty to have both these cars to drive and compare. Any comments? I'd love to hear from anyone who has driven both supercharged cars (such as the Cobra) and also larger engine non-supercharged cars..... comparisons?
So a 4.6L engine running 7 psi of boost will flow about the same amount of air as 6.79L normally aspirated engine. There are a lot of other factors involved in the amount of horsepower per liter an engine generates but this rule of thumb is pretty close.
I don't fully agree with this answer but I'm not an expert so I humbly await an expert to correct me if I'm wrong. Could you not add a supercharger to your 6 liter Vette's engine and reliably get that 600-700 hp you are talking about? Or since this is a "Ford Board", let's look at it from the Mustang's perspective vs. something stock supercharged like a WRX STi. I believe the WRX Sti puts out somewhere around 300hp and is a 2.4 litre
4-banger. Let's compare that to a 1998 or 1999 Mustang Cobra (pre supercharged years I think) that was putting out around 300hp. I would guess/assume/hope that the 1999 Cobra had a "strong" enough engine to allow a supercharger to be added to it without too much pre-modification? If so (yeah I know a big "if") then you could slap a supercharger on that thing and even going with just small boost you would see 400hp... heh example being the next gen Cobra (current) which are putting out that much. My point is that a larger engine from the factory gives more room to grow. A stock 4.6 liter Mustang GT engine (260 hp, 300 torque) can yes, sure be modded and modded forever. But so can a stock 6 liter Vette engine (400/400) and I believe since you are starting with so much more from the factory, you have more potential. Seems simple. I fully realize I may be wrong here. I'm no expert. Now, look at it from the Mustang point of view: Take a stock 4.6 liter 16 valve Mustang GT that is (nowadays) producing around 260 hp, 300 torque (ahhhhh yum). Compare it to a stock Acura RSX something something producing around 240/220 or whatever. Which engine do you think has more room to tweak and add stuff to? Which engine would require the least amount of money/mods to *safely* get to
350hp? 450hp? 500hp?
These were more or less the type of answers I was looking for. Adding a supercharger indeed adds increased complexity, more moving parts etc which in turn leads to reduced reliability. As well, yes, there is more stress and wear on the engine overall per power output, and thus longevity issues... makes sense. From a fuel economy point of view, a smaller displacement engine would be better I would think. At idle, in traffic, a smaller cube engine will drink less fuel than a large cube engine, etc. As well, a smaller engine in theory should be lighter and physically smaller, both good things from an economy point of view. But then again, the supercharger unit itself adds weight and needs space. In sum, the longevity issue is probably the biggest issue... with a supercharger, you are squeezing every last drop of power form a given displacement engine... it only makes sense that such an engine will wear faster and be more prone to breaking under extreme use. As I said, you can't get something for nothing. But when you consider the size / weight / economy issues, superchargers seem to be the way of the future... with the fuel situation as it is, I would think that large displacement engines will start to disappear again, just like in the mid `70's. I still stick to the saying, "there is no substitute for cubic inches". While the 5.7 liter Vette I test drove the other day was indeed impressively fast, it was still no match for the 440+ cubic inch engined cars I used to drive, certainly not in the lower-end torque department anyway. Those old beasts were ridiculously wasteful and impractical, but they had enough torque to squash your lungs against your rib cage causing difficulty breathing... now that's the kind of fun I really miss. Makes me want to build a Shelby Cobra kit car and drop in a 454 or whatever. It's neat to be able to let the clutch out at 900 rpm and then instantly have violent torque thrust (emphasis on "violent") as soon as you lay your toe into the pedal, continuously all the way up to 5,500 rpm or so... unlike most newer smaller engined cars that don't start to really "pull" at all until after 3,500 rpm or so, kinda like my GT. Still wish Ford would drop more cubes into a Mustang.
Not without some very serious engine modifications. The Vette engine was designed as a high compression ratio, N/A motor. A smaller engine designed to handle boost will almost always outperform a larger N/A engine.
You just made my point by comparing two engines with the same hp but the WRX is half the displacement.
You can probably take any engine and build it to handle forced induction. The rub is that the cost is typically very high when compared to getting more power from a well built F/I engine from the factory. The '03+ Cobras go from 365 rwhp to around 500 rwhp for about $1,000-$2,000 in mods. Try getting a Vette's engine to increase output by 40%+ without spending way more than this amount. There are Cobra engines making nearly 800 rwhp without having the valve covers off.
Given enough money, anything is possible. I don't know many people that would spend $50k on a new Vette and then throw in another $20k-$30k for engine work to make it blower friendly and have anywhere near the potential the Cobra engine does right off the showroom floor.
In the end there is no replacement for displacement. The rub is when you factor in the cost. I have a supercharged Mustang and know what trouble it is to take a stock N/A engine and make it boost friendly. For what I have spent I could have had an '03+ Cobra AND had more hp/torque from a much more reliable engine. IMO, the '03-'04 Cobra engines are going to go down in automotive history as one of the best F/I engines ever offered in any car. It is that well engineered.
Go to an SVT dealership & test drive an 03/04 Cobra. You will know how absolutely wonderful a blower feels. IMO, I'd rather have an 03/04 Cobra rather than a pre-05 Corvette (05.. iffy... it's real nice)... and just because it's a blower that doesn't mean you're "squeezing every last drop of power" from the engine... and I'm not sure what Corvettes engine internals are made of, but 03/04 Cobras were built specifically FOR forced induction with forged internals... sure you're going to have increased wear & tear.. but you've got the internals for it. If you step on it in a N/A Corvette... you're increasing wear & tear.. same as any car. Just my .02 cents.
Michael pretty much summed it up. The Cobra engine is build for a supercharger. Forged pistons, lower compression, etc This makes it easy to bump up the power even more.
Adding a supercharger to the corvette would require big changes since the compression ratio is to high.
The >I don't fully agree with this answer but I'm not an expert so I humbly await
not really unless you run it on the track only. In everyday driving that supercharger is only producing boost when you step on it. When you don't you probably have LESS engine wear due to lower compression, and solid-engineering on the engine part that is supposed to hold up under boost.
Go test drive one, It still blows me away how much boost kicks in at an incredible low rpm rate, ...and it keeps on going all the way to
6500 rpm. whoa The drive ability is also very very good.
Low end is the *only* advantage base displacement has.
Air makes power. It doesn't matter how the air gets through the system. Any system that moves the most air will make the most power, period. The large base displacement allows for more air to be moved in the low velocity regions below 2k rpm or so. If you like to lug around, then there ya go :). Personally, I prefer today's spinners. A motor that can't make 6.5k rpm, while still making good power, is a waste, and I'd prefer it hit 8k. The power production is smoother and more refined while the forces are just as crushing. Gear a small motor appropriately and there's no way at all to tell it's small, especially if there's a pressure inducer on its intake :).
As for reliability and longevity; TANSTAAFL is still a physical principle, however, todays forced induction systems are not the primary, *direct* cause of failure on any car I know of made in the last 20 years or so. The overall mean time between failures is certainly reduced, however, the *practical* MTBF is not affected at all, as far as I can tell. The systems are very reliable and very durable. I hang with factory boosted GM's and Fords that have tens, even hundreds of thoushands of miles. It's not that rare, especially for cars that are left close to stock.
Within the enthusiast community I know just as many broken N/A motors as I do boosted motors, for any given specific output level. In the end, the power output and operating conditions define longevity. Forced induction merely makes it easier to break a car, it isn't the root cause of failure.
While the initial cost of the induction system may be higher, in the end, the performance results are far more monetarily effective. There are many boosted cars that can easily hit 700+ bhp for a modest cost. Building even a large base displacement motor to reach that normally aspirated is just as costly, if not more so, because there are no systems that can attain that without taking the motor apart and having professional work done to the intake and exhaust tracts. Not to mention the balancing work that will be necessary. For everyone but the guys with their own shops, tools, and experience, the cost is pretty substantial.
Finally, you mentioned squeezing a small motor to death with boost to get it perform well. That may have been the case a decade ago, but I don't think it's true today. Even the tiny motors are built better out of better materials. We've got tiny motors now spinning to 9 grand off the show room and they do just fine. For domestic boosters, the current supercharged 4.6 produces about 420 bhp out of the box. With the factory blower it's capable of just shy of 550 bhp. With a power adder swap it will make 800+ bhp. I don't think, in stock trim, it is being pushed anywhere near its limits. If one were to leave the car alone, it should last a long, long time.
And where does that GT redline? Take your big block up there once ;).
I have a roots blower. Peak torque (588 ft-lbs) doesn't hit until 2.5k but it's within 5% by about 2k, so I have to wait an extra thousand before I can roast them. Then my car pulls through 6.5k (it's down to 440 ft-lbs by then) . I have to shift only because the blower is rpm limited. When I repair that my car will pull through 7.5k easily.
I priced out getting a 'Vette to 550 bhp normally aspirated. After I got my breathing under control I noticed it was cheaper to just put a blower on it :). And to make one spin more? Fuhgettaboutit.
Eh, the S197 SVT Cobra will be a 5.4. But that's still a small motor in my book. Thank goodness :).
Boost and RPMs cause engine wear. When I pulled my 1975 500 cid engine out of the junk yard, the cylinders only need to be honed, not bored out. Longevity is the "catch".
One more point I have to add... almost a counterpoint, but not quite -
When the engine is designed with a lot of safety room (a stock 302, for example, or even the new 4.6 GTs), it's quite possible to throw a blower on it and call it a day. There are people with 180,000 mile 5.0's that throw a blower on it and still have a reliable car. Not enough to get numbers in the 500-600 range, but it's still a vast improvement.
But, when the engine is already running high compression and cast parts (as is most definately the case with the N/A 4.6 DOHC cars), strapping a blower on is like building a time bomb. I've heard horror stories of guys dyno-tuning a supercharged early DOHC at a fairly low amount of boost and still blowing them up relatively easy.
I don't know the specs on the 6.0 Vette engine... but if it's high compression and cast parts, beware putting a blower on it. This was some of the complaints out of the hot rodders when Ford released the 5.0 cammer. It makes a ton of power for its size, but the cast internals and 11:1 compression (or somewhere thereabouts) made it nearly impossible to artificially aspirate. An option should be available for 8.5:1 compression and all forged internals to allow for blower/turbo installations.
Blown Mustangs are everywhere, but I don't see too many blown LT-1's and LS-1's. Most of those are nitrous-powered. There's probably a reason for that.
Yeah, but part of the high power these engines put out is because they HAVE the high compression numbers. Dropping these numbers would drop hp numbers. I remember in my younger days messing around with 2-stroke engines. We would shave the heads of and gain some hp's. (we'd also ruin the big-end and little-end but ahwell :-) )
The companies making blowers for the Corvette want to charge twice as much as a similar blower for the Mustang.
The forged internals will handle the added stress well enough, but they don't get very many buyers with such a high price.
A problem that I can also see is that the automatic in my
1994 Corvette doesn't appear to be built strong enough to handle the added power. I am already getting about
375 hp and am afraid of twisting the transmission case if I add a blower.
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