: Compression Ratio

02-19-07, 10:21 AM
Hi. I have a 2003 Cadillac Deville. I'm looking to bump up the compression ratio and rework the ignition timing to raise more power than the measly 275 horses that came from the factory. I know I'm not the only one who has been thinking about this, but has anyone done this? What are your thoughts?What kind of gains would you predict?

02-19-07, 12:27 PM
Welcome to the forum. Before anyone jumps on you, I'd highly recommend you read some of the technical archives from the menu at the top of the page. It will save a lot of time and back-and-forth'ing, not to mention to-and-fro'ing....

Short Answer: Not much. Short of NOs, there just isn't much to do. The PCM computer controls all the engine timing, and is smarter and quicker than you are about what the engine needs to produce maximum power. I do not even know if there are aftermarket H/C pistons, but again, if there were, and you put them in, the PCm would probably go nuts trying to accomodate them.

You're getting 275 'measly' HP out of 279 CU..not all that bad, actually. And probably about 20+ MPG. As the saying goes, "All the low-hanging fruit has been picked."

02-19-07, 12:42 PM
Thanks for your response! :)

To give everyone an idea on where I am coming from, my background is in the 1960s big block engines, where camshaft swaps, upping compression, ignition timing, intake, exhaust, et. al., would yeild big power gains.

I remember reading some years ago about Tim Allen building a N/A 398 hp Deville. I forgot what he did to it.

Forgive my ignorance, because I am new to modern engine building, what is it about these new engines like the Northstar that make performance enhancements so difficult (granted that small displacement doesn't help)? Is the engine computer that restrictive?

Anyways, thanks for the heads up. Now I won't blow all my money on useless equipment. :)

02-19-07, 01:23 PM
The engineers at Cadillac have really squeezed about as much power out of the N* as they can from the factory. True, with less-restrictive exhaust it frees up a few more ponies, but the N* isn't tuneable, so that rules out doing anything with the computer, which controls everything; quite the opposite of your 60's-era big blocks.

02-19-07, 04:21 PM
The Tim Allen DTSi was primarily CAI, Exhaust and a few other aspiration things along with lowering and custom suspension. There may have been a turbo or supercharger involved also.

here's a good article on it

And here's the TAD homepage.

02-19-07, 05:04 PM
No turbo or S/C, just ported & polished heads & 12:1 cr custom pistons. Here's some of the article from Car & Driver. I'd like to see how they did the headers and crossover pipe. Apparently it can be done.

Beitzel, meanwhile, busied himself with the DeVille's Northstar V-8, determined to compromise neither its idle nor its broad power band. He thus opted to retain a stock displacement and to eschew blowers. Instead, the cylinder heads received an expensive five-angle valve job and a thorough porting and polishing. A larger, straighter fresh-air inlet was fitted. Stainless-steel headers preceded a sewer-size Corsa exhaust with a trick crossover. Still, most of the newfound power derived from custom pistons that bumped the compression two points, to 12.0 to 1. The upshot was 398 horsepower at 6400 rpm -- a 98-hp increase.

02-19-07, 05:33 PM

02-19-07, 06:07 PM
Forgive my ignorance, because I am new to modern engine building, what is it about these new engines like the Northstar that make performance enhancements so difficult (granted that small displacement doesn't help)? Is the engine computer that restrictive?

It's not that it's necessarily "restrictive", its just that EPA regs and the CAFE standard have pretty much killed the days of V8 tuning in big American cars - the PCM (Powertrain Control Module) keeps emissions low, gas mileage optimized, and power output smooth and predictable. Gone are the days, at least in states with emission inspections, where you could slap a big ol' Holley or Weber downdraft on your big-block, slip in a radical cam, some H/C pistons and other neat stuff, and get away with it. Try that in NJ now, and you'll have to tow your car from the inspection station... :( And the sad part is, you'll probably be following a dump truck or bus that's spewing out more particulate matter in five miles that your car would in a hundred.

Enjoy what you have, and perhaps think good thoughts that you won't have to spend a half hour with a jar of LAVA soap scrubbing the grease from under your fingernails anymore..

02-19-07, 08:14 PM
I forgot about the emissions laws!

Not having worked on cars that weren't exempt from the emissions laws or equipped with the PCM made me forget about the regulations. :(

Oh well. So much for a Northstar project.

Between us I was now confused for the past three hours as to how in the sam hill I was able to squeeze 450 hp out of a big block. At least I have my sanity back. :)

02-19-07, 08:18 PM
Don't know which Cadillac you have, but if the horsepower quest is still in your veins, resto a mid-'60's Chevelle or GTO, tow it with your Cad, and enjoy. OR, spend your inheritance on a tricked STS-V.

02-19-07, 09:39 PM
Due to some of my past performance experiences, one of the other ways to get noticable performance from an already good engine, is build the automatic transmission. More strength from the engine to the drive wheels is horsepower to the tires. ....Uh, I am not a tranny expert, but I have seen the difference with a performance custom torque converter, servo's, valve body mods, etc.

When it comes to a T-80, my friend can build one, but I am not sure on the computer issues. That's over my head.