Next Cadillac update? Intercooler FMHE or Exhaust

I am split on my next Cadillac update.  The choices are to replace the mufflers with performance, high flow mufflers, or to begin to experiment with intercooler cooling system improvements.

For the exhaust I am settled on replacing the stock, low-noise mufflers with Magnaflow 14326 mufflers.  The exhaust system itself is stainless steel, and appears to already be bent properly.  The cost should be around $100 ea x2 for the hardware, plus installation.  I suspect it will free up 10-15 whp.

The intercooler system uses Laminova tubes with a small heat exchanger in front of the car.  I plan to add a 2nd front mounted heat exchanger in serial with the stock heat exchanger.    The original LC3 testing was done assuming harsh heat conditions with high intercooler coolant temps.  Later when required to SAE certify, the engineers also needed to reduce the temperature  for the intercooler coolant; the engine famously went from 440hp with the original assumptions to 469 hp with the cooler assumptions.  So I suspect that anything we can do to reduce the temperature of the intercooler coolant is worthwhile in terms of more hp.

Technically, reducing the intercooler air temp does not add more oxygen to the air, since at that point the mass of air coming into the system out of the supercharger is fixed.  However, what cooler air across the intercooler does do is allow the LC3 engine to run more timing, which it will do automatically, and achieve more power.  Reducing the temperature of the intercooler coolant is one way to achieve cooler intercooler exhaust (IAT2).

Another thumbrule I have read is that Laminova heat exchangers operate best if the area of the heat exchanger is equal to the area of the coolers.    I had to think about that a bit to understand what was meant.    For the Cadillac the area of the Laminova coolers would be 96 square inches.  The area of the stock heat exhanger would be 21×14=294 square inches, which would appear to meet the thumbrule.

It is inviting to do something really revolutionary like put an intercooler reservoir in the spare tire compartment and run hoses the length of the Cadillac, but probably better to stay conservative for a daily driver.

I am happy with my Ambient / IAT / IAT2 measurement capability.  I would like to have a direct measure of intercooler coolant temp before the next changes, but I am unsure how best to achieve and log that.

Cadillac Muffler/Exhaust selection based on Target HP

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.