Cadillac CTS-V - Compression change in v2

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09-30-2011, 01:16 AM
Im new here but has anybody removed heads and replaced gasket with thinner one to increase compression and responsivness and performance on the V2? It would really help in the lugging department and could possibly help in mileage! It would deff help performance!! Just wondering!

09-30-2011, 01:31 AM
Its only 9:1:1 stock!

09-30-2011, 02:03 AM
Its supercharged, compression is supposed to be lower. You might gain power but your also gonna put more strain on the motor. Id find you power elsewhere there is plenty of stuff to do besides up the compression.

Pulley, cold air intake, heat exchanger, trans tune, stall, port the blower, cam, port the heads etc.

09-30-2011, 08:14 AM
I wasnt asking what else could be done! I ask if anyone had tried this! This isnt my first supercharged car and the compression can be raised without hurting it! Just wondering if anybody has? Ive seen car go as high as 10:5:1 and still run boost. Its all in the tune! The better the car will run without the blower the better it will run with it as long as its safe! If it were 9:8:1 or 10:0:1 it would prolly be so responsive it wouldnt be funny and gain about 100hp Im guessn! Just trying to find someone who has tried it!

09-30-2011, 11:04 AM
You wont gain 100hp from it, The stock gaskets are awsome for the car, so i would not go using an aftermarket on them if you can still use the stock ones. You can have who ever ports your heads shave some off the surface when they clean them up. I try to target a 9.5 cr with the ones i sell here. Unless it is a higher boost car, then i leave it stock.. Cam makes the most change in the lugging...

09-30-2011, 02:35 PM
Wow I guess nobody has tried this.

09-30-2011, 07:10 PM
Be the first! Keep us posted on the results!

In the NA ls series motors it's not uncommon to raise compression by shaving the heads about .03"! But that will decrease your cylinder head deck thickness and make you more prone to pushing water!

09-30-2011, 07:42 PM
anything can be done, and yeah higher compression will help, provided you don't start detonating, etc...A rule of thumb is ~4% more per 1.0:1 increase, but that's simply a guideline; too many variables...I'd say, apples to apples, provided you can get away with it

However, with pressure (boost) comes heat (more chance of detonation, etc.) and of course essentially raises the compression inside the combustion chamber and being the LSA does not use forged components, I don't think I'd want to take the chance and you'd be better off increasing the boost (while cooling it more)...9.1:1 is not real "low" and 6.2L is decent size so it's not like the engine doesn't have any grunt under atmospheric conditions (0 psig)...The thing that helps on these newer engines and why you can get away with higher compression, besides the "tuning parameters" being so variable with ECU and its sensors, is there is a lot of aluminum (heads) that help bleed off compression...Same thing if you go with a larger cam is it will generally help bleed off some of that compression, or let you run higher compressions with crappier gas (octane), within reason.

Sure, with a "tune" you may be able to buy time, but once something goes wrong where you go even slightly lean and add heated air (compressor) above a reasonable ambient temp, let's say...not worth the trouble then, imo to keep a static increase of compression like that, when you're compounding it with the compressor (supercharger)...

Besides, IMO, you're asking for trouble in trying to go with a thinner gasket and running the risk of blowing that gasket and having coolant get into the chambers, etc...A better bet if you're going to do something like this (and don't want to do it the right way with pistons) is to mill the head...But, you need to check clearances and not a bad idea with a thinner gasket too (I don't know how tight the valve to piston clearance is stock on these).

For reference, I run 24 psig or so on a 8.5:1 compression engine, but it's also has a humongous intercooler and is designed to dump fuel to try and keep it cool and the engine is much smaller (2.0) and has forged components. This is on 91 octance...I can hook up the water/meth injection setup I have and maybe go to 26-28 psig, provided I compensate in the fuel and if we were lucky enough to have 93-94 octane here, I could see 30 or so...Now, I were to go up to 9.5:1 comp though, I'd be lucky to run 20 psig under ideal conditions, which is too low for the efficiency of my particular turbo...I know the LSA is supercharged and has really low boost pressure, but you wouldn't want to have to lower or not be able to increase the boost because the static compression is too high, if that makes sense...I don't know the effiency zone of the LSA's blower, but it sounds like people get some pretty good gains by increasing that slightly and much more than raising comp on its own (keeping other same)...

There is a lot more than just 'psi' (boost) of course in determining actual gains, but IMO you may net 20 hp from 1.0:1 increase in compression, yet keeping comp same and raising boost (again cooled properly and increase pertaining fuel) I'd think you could get 3X that easily, staying conservative.

10-01-2011, 06:03 PM
Thanks for the input guys! Not sure I agree with it but thanks its good to here other's thoughts sometimes!

10-01-2011, 08:01 PM
Knowing the combustion chamber volume at TDC and at BDC, you could calculate the new CR with a thinner gasket. I'm not sure how much thinner a gasket you can get, and maybe I'm all wet, but I'd think you're not going to get that much CR increase.

As far as hurting your motor because you exceeded some limit, it ain't gonna happen if lots of other guys are swapping pulleys and all kinds of stuff. A tweak on CR is like pissing in the ocean.