Tag Archives: Corsa

2008 Cadillac STS-V Spectre CAI + Corsa 394.3 whp 380.4 lb ft

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Today I headed back to True Street Motorsports in McKinney Texas to get some dyno time in and check my air fuel ratios after the addition of the Corsa axle back exhaust.  Click on the graph to zoom in, then hit back on your browser to get back.

STS-V WHP and Torque vs Engine RPM

Coincidentally, the Spectre Cold Air Intake (CAI) added 19 wheel horsepower (whp) over the baseline pre-Spectre CAI, and the Cora axle-back with the Spectre added another 19 whp for a total of 38 whp.  The Corsa addition opened up a nice 20 ft lb of torque.

A dyno measures horsepower at the wheels, or whp.  This is always less than the manufacturer’s advertised engine horsepower, or hp at the crank of the engine.  WHP is hp after losses through the transmission and drivetrain.  A reasonable figure for these losses on the STS-V’s 6L80e transmission is 20-24%.  On my STS-V, the stock car was rated for 469 crank hp and made 356 whp on the dyno, or  a 24% loss.  if we use 22% as an average then the V originally made 456 hp stock.  The addition of the Spectre got the car to 375 whp or +24 crank hp, and the addition of the Corsa with the Spectre CAI got the STS-V to 394 whp or +49 crank hp.  Overall a nice gain for two easy bolt-ons, and the STS-V is now making 394 whp which at 20-24% losses equates to 492-518 hp at the crank.

Air Fuel Ratios

Part of the point of the visit was to ensure the Air Fuel ratio was in the right range and stayed there throughout the Wide Open Throttle dyno run.    The resulting fuel levels are safe and consistent with commanded.

This graph shows the same info zoomed in a bit and with a detail point showing that the new exhaust at key points actually adds +27 lb ft of torque:

I am close to my power goal of over 400 whp on the dyno at 394 whp.   I want to run a new baseline on the dyno with the car cool and not heat-soaked for comparison.  In fact, our 3rd run was at the same whp as the initial run today, but with the intercooler Intake Air Temp 2s (IAT2) hitting 150F+ due to the stress of repeat dyno runs on the original,  stock intercooler cooling system.    That suggests that the V may put down 400 whp when not heat soaked.

Fun day, and as always the True Street Motorsports team is easy to work with and helpful.

Stock Cadillac STS exhaust flow: 308 CFM

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Found this interesting info graphic from a Corsa performance ad on a Lingenfelter site:

Corsa vs Stock Exhaust for Corsa 14157

 

The graphic shown is for the 14157 system versus the stock 2005 Cadillac STS system. This is particularly interesting for the STS-V since this is the same Corsa system that D3 sells for the STS-V.

The text notes: * Flow bench-tested 42.3 gain in exhaust flow vs. stock muffler.

This I read to mean that the graph is for flow through a single Corsa muffler versus a single stock muffler.  So in other words, the dual Corsa mufflers probably flow around 437 x 2 =874 CFM and the stock mufflers flow around 308 x 2 = 616 CFM.  Recall our target is 2.2 CFM/HP for 0 backpressure, so with a modified STS-V making 500 hp plus S/C load we would need 560 hp of exhaust or 560 x 2.2 = 1232 CFM.

I am guessing that the STS-V stock exhaust flow is similar to the STS stock exhaust flow.

We can see from the numbers then that the stock exhaust flow is insufficient, and that the Corsa’s are an improvement, but there is still some margin for further improvement.

 

Cadillac Muffler/Exhaust selection based on Target HP

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For a zero back-pressure exhaust, it can be shown that one should target 2.2 cfm (cubic feet per minute) of flow through the exhaust per engine horsepower of output.

The Cadillac STS-V has a dual-2.5″ exhaust with dual mufflers.  The stock mufflers probably flow 160-200 CFM each, or 320-400 CFM together.

The stock LC3 engine makes 469 hp through the stock mufflers.  However, this is a supercharged engine so at redline it likely makes 469 +~60 hp = 530 hp or so, and the exhaust needs to be suited to this figure.  Moreover, I would like to tune my STS-V to make 500+ hp not considering the supercharger load, so 560 hp with the charger.  Therefore I am targeting 600 hp with the supercharger load (rounding up).  Therefore the exhaust needs to flow 2.2 cfm/hp x 600 hp = 1,320 CFM.  Each muffler therefore should flow 1320/2 = 660 CFM.

What are some example flow rates for commonly used mufflers on the STS-V?   For 2.5″ mufflers:

Stock:  160-200 CFM x 2 = 320-400 CFM

Borla: 373 CFM x 2 = 746 CFM (at 15 inches of Water)

Corsa: 226 CFM x2 = 452 CFM

Gibson: 267 CFM x 2 = 534 CFM (at 15 inches of water)

Magnaflow 11226 (14326 polished) : 588 CFM x 2 = 1176 CFM (shown on a Dynomax video), at 20 inches of water.

and one that is relatively new but I have not heard tested on the STS-V is the Dynomax VT

Dynomax VT 17956: 841 CFM x 2 = 1684 CFM (shown on a Dynomax video), at 20 inches of water.

The 17956 is not recommended for dual 2.5″ installations.   The difference between the 17956 for single installations or the 17156 for dual appears to be the resistance of the spring for the diverter valve.  This Dynomax muffler has a diverter valve built-in, so at cruise it diverts flow for less noise.  The dual-muffler p/n is 17156.  This muffler is 4.5 in. x 9.75 in. 2.5 in. ID 14 in. Shell Length 19 in. Overall Length.  The Magnaflow 11226 is 4 x 9 x 20 inches.

Dynomax VT video:

I am thinking of either the Magnaflow mufflers, or the Dynomax VT 17156s.  Either should be a better match for the potential of the LC3 S/C V8 than the stock setup.  I had a Corsa cat-back system on my CTS 3.6L and loved it, but they don’t offer a system for the STS-V.