New cobalt SS 21psi and only 260hp?

[Metalhead852]

I don't get it explain? Why wouldn't it produce more.

2008 Chevy Cobalt SS Test Drive: 260-hp Barnstormer Is GM's Best Sport Compact Ever - Popular Mechanics

This combination provides a high specific output (260 hp at 5300 rpm and 260 lb.-ft of torque from 2000 rpm) with rather economical performance—Chevy is claiming 22 mpg in the city and 30 on the highway. Controlled by an electronic wastegate, the Borg-Warner twin-scroll turbo supplies boost at very low revs, yet can pump as much as 22 psi 21 psi when required for maximum power.

[BobbySi]

Originally Posted by Metalhead852

I don't get it explain? Why wouldn't it produce more.

2008 Chevy Cobalt SS Test Drive: 260-hp Barnstormer Is GM's Best Sport Compact Ever - Popular Mechanics

This combination provides a high specific output (260 hp at 5300 rpm and 260 lb.-ft of torque from 2000 rpm) with rather economical performance—Chevy is claiming 22 mpg in the city and 30 on the highway. Controlled by an electronic wastegate, the Borg-Warner twin-scroll turbo supplies boost at very low revs, yet can pump as much as 22 psi 21 psi when required for maximum power.

LOL!!!! Made 380 on 10PSI untuned.

[mitsukaiSI]

mighty fine domestic engineering is the answer^

[Izzy]

Lots of companies with stock motors push higher PSI numbers through their motors than ones who drop in a turbo later. Granted, this does seem pretty high though. I'd assume that the Ecotec can handle more boost than that, honestly.

[mitsukaiSI]

my question is why only 260 at the crank on 21 psi?

[Izzy]

The STi pushes 14.5PSI to get to 300hp on a 2.5L motor. Big difference from the 7-something PSI that Civics push to get some crazy numbers. I'm not a turbo guru, but I do know that most companies with turbo'd cars do run at higher PSI because they know the car can handle it.

Heck, even my Volvo could handle 2x the PSI as a boosted Civic can, but only put out 160hp and 170lb/ft at 12 PSI. LOL.

[Metalhead852]

^ my question also. I mean I've already heard great things about ecotec's but at 21psi someone should be doing some amazing things.

[volvo9]

How big is the stock turbo though? Back in my Turbo days I could run 15 lbs on my Volvo but the turbo did it inefficiently. If I dropped in a bigger turbo I could run the same ammount of boost and make a crap load more power, and then would have needed fuel system upgrades. There's more to turbos than boost.

That is still a lot though.

[BlackHFP]

My guess is that they are running a crazy low compression ratio. Probably something close to what the old Mitsubishi 4G63's ran in the early 90's. They ran a 8.0:1 from 89 - 94 and about a 8.5:1 from 95-99. With a small turbo and 19 or so psi they would put out similar numbers.

The reason we get such high HP numbers with low boost levels is because our compression ratio is already high. Adding a turbo or s/c effectively raises the compression ratio. The reason you do not want to run high compression with forced induction is pre-detonation. The lower the compression ratio the more air you can pump in without igniting the gas from hot spots on the piston. The reason some people here can get away with it without blowing their engine to smitherines is because (and I hope) they use good gasoline.

Factories have issues putting boost onto high compression engines because they cannot control what kind of gas you put into your engine. For a good safety margin they can put in a computer controlled boost controller and low compression pistons. Then if a consumer puts in cheap gas they can retard the timing and cut boost to keep the engine from crapping out. Thus you end up with 21psi, low compression, decent on gas, and relatively safe engines.

I don't know what the actual compression ratio is but my guess is around the 8.0:1. It may be a place to start though.

[BlackHFP]

Looks like they are running a 9.2:1. That means they must be using a tiny turbo to cut down on turbo lag.

[Izzy]

I wanted to say something about compression, but didn't want to be called an idiot later on. Thanks BlackHFP.

[RJRacing]

Originally Posted by BlackHFP

Looks like they are running a 9.2:1. That means they must be using a tiny turbo to cut down on turbo lag.

Bingo, its a small turbo and in the high RPM's the boost drops 5-7psi to prevent detnaition. Many manufacutrers do this like on the EVO and Acura RDX.

[BlackHFP]

Originally Posted by Izzy

I wanted to say something about compression, but didn't want to be called an idiot later on. Thanks BlackHFP.

I will take that chance! Wouldn't be the first time.

[RWatters]

Originally Posted by RJRacing

Bingo, its a small turbo and in the high RPM's the boost drops 5-7psi to prevent detnaition. Many manufacutrers do this like on the EVO and Acura RDX.

Bingo. Something as simple as an ECU-reflash and my money says they'll have huge gains.

The K20Z3 makes great power because of it's high compression ratio, but it'll require a much more serious tune and it won't last nearly as long as a low compression motor that was built for boost from the get-go.

The new Cobalt SS is going to be a pretty damn strong car off the floor. Motor Trend clicked off a 13.9 @ 103 which isn't bad for stock. They come with a launch control and no-shift-lift (so you don't lose boost between shifts). Road and Track claimed it's the best handling FWD car in quite some time (besting even the Mazdaspeed 3). Then you get into the fact that it set the FWD production record at the 'Ring, beating the previous record holder by around 15 seconds I think it was? So yeah, I would say that's some pretty fine domestic engineering considering their MSRP isn't even $1000 more than an Si I don't think.

The previous SS/SC model mopped up at the Runoffs in the T3 class (that class features slightly modified versions of the Honda S2000, Mazda RX-8, Audi TT, Mazdaspeed Miata, Mustang GT, etc.) and the only reason it didn't win was because it was black-flagged for being too loud. When it comes to performance, Chevy knows what they're doing.

[melomood]

thats alot of boost for only 260, im sure the engine cant handle more then that. Like i have said before this car is maxed out in performance.

[Ekora]

damn that's a lot of boost for lil power, even my SOHC make 270whp at 20psi

[rmfa]

I don't think thats saying that the Colbalt SS runs 21lbs of boost. I think that its saying that the TURBO is CAPABLE of running that much.

[knowledge_6]

260hp out of 21psi for maximum power is not that great. It's nothing to brag about at all. 8.5 max psi in the Si puts down 376 at the wheels. It's an amazing machine I agree and is going to be easily the best bang for your buck in that class

someone posted that on that site ; > was it someone from here??

[I Vtec, do you?]

I'm guessing for one, the motor is completely setup to be safe. Look at all these problems people have with 260 WHP on their Greddy kits. Poor tunes and whatnot (obviously because of lack of tuning). How long do you think those guys running 380 WHP will last before shit starts going wrong? I'm guessing not too long.

Not only that, but you can't just measure PSI between two different setups as equal. One turbo boosting at 10 PSI isnt' the same as a different turbo boosting at 10 PSI.

[Asif22]

Size of turbo, tune, and compression ratio all play a big part