This thread is dedicated to performance modifications for the 4.5 and 4.9 liter MPFI Cadillac engines. It is not a fix-it guide for those who blow things in their engines, nor is this a guide to tear down the whole engine. It is simply a guide based on what I've done to my 1991 Seville to make her run better. I will include what I believe has worked well, and what has not.
Exhaust is a big thing for these cars.
For those of you who don't want your Cadillac sounding like a Camaro SS, then don't read any further.
What has been done with my Seville is this: 80 series Camaro style dual output muffler (yeah, riiiight, there's no "muffling" here). It is a single 2-1/2 inch in, dual 2-1/2 inch out muffler that will give your car the dual exhaust look. It is also a serious performance enhancement that you're sure to notice if done right. This setup is best served with nice chrome tips that barely poke from under the rear of the car. Don't make the car look stupid by having the tips stick 12 inches from the rear. Subtle, not overbearing.
Things that are needed: two chrome tips. Turn-downs are nice, but I prefer slanted staight tips from Hooker Headers. Two L-bends for the dual outlets. They are for the Camaro when this particular muffler is being used. They might fit others as well. With the L-bends, you'll have a very even look without the tips pointing in different directions. The aforementioned 80 series Flowmaster Camaro muffler is the next-to-last step. Other mufflers will do just fine, but I prefer this one because of the high flow...And noise...Just whatever you do, make the exhaust a dual outlet. It looks better that way!
Catalytic converters can be dealt with in three ways: keep what you have, gut the one you have (highly illegal!), or purchase a high flow from the local performance shop. These will not be application specific, so you had better know how to clamp these things on and make it fit right.
In some cases, you may want to have an actual cat-back exhaust system done for your car. I prefer to do the above listed steps because it's cheaper and will probably yeild the same results.
The last step is all the little hangers and clamps. Not too much trouble if you know what you're doing.
Air intake never hurts a thing...
Unless the intake opening is about the size of a golf ball. Which is the case for the MPFI 4.x engines. The opening is behind the headlight and draws cooler air, but at what price?
A custom open-element air intake routed to a cooler area is the way to go and has helped not only performance, but also fuel economy. I'll post a write-up on how to make the MPFI air intake later on.
Ignition timing helps!
The factory setting is set to a somewhat conservative 10 degrees BTDC. For better performance and somewhat increased fuel mileage, the timing should be set to about 13 degrees BTDC. 14 might be pushing it. If ping is heard, back timing off until it goes away. This is a free modification and takes about ten minutes.
Premium fuel is needed when the timing is that advanced!
MSD ignition has some useful benifits.
The MSD igntion is actually something that you could skip on. The fuel economy will increase some and it seems to give a smoother ride at lower RPM's, but this device is better suited for when you throw enourmous amounts of fuel at the engine. With a stock fuel pressure regulator (FPR), this device may only help fuel economy. The MSD has also been claimed to drop times by a few tenths, but again, for a stock fuel system, I wouldn't say it does that.
Throttle body spacer...
Not really worth the time to install because from what I've heard, they are better suited for the wet intake manifolds with the TBI fuel systems. I installed mine on a dry system and it might help a little because of the rifling/ribbing of my particular brand (Areomotive I think), but overall, it's something I wouldn't worry about if it was your car.
Casper Electronice throttle enhancer.
I could go either way on this. It is supposed to even out the flat spots in the throttle position sensor (TPS), and from all indications, I would say it does just that. Throttle readings under diagnostic mode shows a jump from 78.5 or so to about 80 at WOT. I really don't know if it's that helpful for shaving off elapsed times with that little bit of change.
Cap and rotor kit from Accel.
This is a give-in. It does help strengthen the spark pulse through the copper cap terminals, and response is noticeably better.
Accel ignition coil.
Either the 'Brute Thunder' or the 'Super Coil' will be good enough. MSD doesn't make one for the Cadillac engines that I'm aware of, so the Accel are the next best option.
MSD heli-coil wires.
I chose the 8.5 mm wires because of my igntion setup. However, the 8 mm set of wires will do just fine. The wires will help the energy from the spark transfer much better and cleaner.
Be warned though, you'll have to get the custom set and cut the wires yourself due to lack of application.
I would also avoid the Accel wires because of the higher resistance than the MSD. In fact, just stick with the MSD wires and be cool with that.
Accel 7-pin ignition module.
Put it like this, either the GM brand or Accel will do just fine. I chose the Accel because of the higher RPM capacities and the MSD ignition. But really, we're talking about the 4.x series Cadillac engines: high RPM's aren't what they're known for.
AC Delco rapid fires are by far the best choice. Stock .060 gap seems to work fine, though I haven't really experimented with the gap. For 9.5:1 compression ratio, I understand that said gap is the most optimal.
Other plugs such as the Bosch plat-4's are junk. They shroud the spark! Plat-2's might be better, but I would just suggest the single tipped plugs.
Iradiums are something I have yet to look into.
This is the Areomotive FPR for the Chevy LT-1 engines. It will easily adapt to the fuel rail on the Cadillac 4.x engines. In fact, it's almost a direct fit! (Slight modification is needed.)
I could go either way on this one. On one point, it will screw with your ECM and the integrators will lean out the fuel delivery due to it being in closed loop mode. On another point, during open loop mode (above 3000 RPM's), the FPR will help out some if set just right. I have mine at 3 PSI above stock right now.
A set of 19 lbs. injectors over the stock 18 lbs. injectors will likely yeild the same results...
This is the thing the MSD would be needed for, but with the closed loop system at lower RPM's, I really don't know if it would help that much.
So far, we have the following items with grades of approval:
MSD ignition (mine is/was a digital-6...Long story for why it was...). A 6A will do just fine for your application if you choose to purchase an ignition. I wouldn't recommend getting the digital-6 because of the expense and reliability. Fuel mileage will improve no matter what, but to get the most out of this, fuel enhancements are the best thing or the MSD ignition. Grade = B
MSD wires along with the Accel cap and rotor kit and Accel coil help tremendously. Just try it and see for yourself. Either a GM ignition module or the Accel will help add to the fury, but don't expect seconds to be shaved here. Do the AC Delco plugs too! Grade = A+
Exhaust is the single best mod for you 4.x Cadillac engine. Do it right and you will not be sorry! Grade = A+
Ignition timing could be compared to the exhaust. Do it!!! Grade = A+
Custom air intake. For this to work properly, it must be routed to a cooler area. A short ram intake will be better than stock, but drwas too much heat. Keep it cool. Grade A+ for cool air, B- for short ram.
Throttle body spacer. Don't waste the cash for this. Grade = D
Casper throttle enhancer. See above...Might be somewhat better than the above, but probably not worth the cash. I also hear somewhere that a home-made job of some sort can yeild the same results. Grade = C-
Adjustable FPR. It will play with you ECM and drive you nuts at times. I like the high end it seems to give though. Best served with the MSD ignition. Grade = B
Should you purchase said performance items and said performance items do not show signifigant improvements or even minimal improvements to said car (Cadillac 4.x engine), Illumina and his subsidiaries are not to be held responsible for such purchases.
Illumina also claims special performance enhancement rights to the 4.1, 4.5, and 4.9 liter Cadillac engines. Should someone attempt to enhance said engines and said engines do not show signifigant improvements or even minimal improvements in performance, Illumina and his subsidiaries are not to be held responsible for such actions.
Illumina has a wide range of mechanical knowledge for said Cadillac engines. Should someone attempt to tinker with, or otherwise disrupt the balance of power in said Cadillac engines without the consent of Illumina, Illumina and his subsidiaries are not to be held responsible for such actions. Even with Illumina's consent, user acknowledges that said work on said Cadillac engines are at the risk of said user and Illumina and his subsidiaries are not to be held responsible for said mechanical actions.
Illumina and his subsidiaries hope that said enhancements and purchases help the purchaser of said items.
Now go out and enjoy your Cadillac 4.x series MPFI engine!