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.

Please enjoy...

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.

Spark plugs...

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.

Areomotive FPR...

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

*DISCLAIMER*

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!

That is great Illumina! Thanks! :bouncy:

great thread!!!

The "fine" print is hilarious!! Nice write up BTW. See I told you we need you here.

Thanks for the replies everyone :thumbsup:

I created this thread to point people in the right direction should they feel the need have a little more performance on their 4.x series Cadillac engine without having to explain these things on every thread that asks these questions. This guide shows what works, and what really isn't necessary.

For the custom air intake, I would really like to post some pictures as a step-by-step instruction manual, but I am too lazy to get freakin' batteries for my digi-cam. Once I do (Wal-Mart this weekend), I will upload the pics somewhere so that they are hosted without attachments.

All things aside, there are other things I should discuss, such as chipping the cars and doing a cooler thermostat.

The "chip."

For the performance chip (stay away from Superchip!), I have heard very good reviews from Fastchip for these engines. The main issue with chipping is this: you can do most of the performance modifications a chip can provide on your own. This can be done by bumping the timing as mentioned in my first post. The primary function of aftermarket chips is to curve/advance the timing as stated above.

The chip does however have very good benifits that you cannot easily attain yourself. It will remove the top speed limit of your car, and will also change shift parameters for the 4T60E transmission that the Cadillac MPFI 4.x engines are equipped with. The shift parameters as far as I know can not be changed any other way, so that is certainly something to consider. The chip also has the fuel map changed slightly to create more power. I should also mention that on Caddyinfo.com, there is speculation that the aforementioned Casper throttle enhancer may be better suited for the chip.

For more information on the chip, check the following link out. I have heard nothing but good things about these people and I personally emailed Ed Wright before regarding some ECM work, so they are easy to deal with and will help you out with any questions you may have, be it good or bad news...

The "chiiiip." (http://www.fastchip.com/)

Also for the record, I tried to install a Superchip, but they sent me either a defective chip, or the wrong application all together. It would not allow me to start my car via the Pass-key theft deterrent system. Once I bypassed the system, the car started, but was only running on 4 cylinders, or so it seemed! I tried to contact Superchip several times by phone and email, yet they have never responded after I wasted $200.00 plus change over a year and a half ago on their product. I strongly advise that anyone interested in a Superchip take this into consideration. As of now, I am currently not running my car with any chip.

Cooler thermostats...

A cooler thermostat will help to suppress detonation after you advance your timing. It will also keep your engine generally cooler on a warm day. On some of the aftermarket chips, I have noticed that it is recommended that a cooler t-stat be used.

The stock Cadillac t-stat is either rated at 190 degrees or 195 degrees. I would advise against the 160 degree t-stat as it may cause poor fuel mileage through the engine feedback system. A 180 degree t-stat is the way to go, and any small block Chevy t-stat from Jegs or like performance shops will do the trick.

By chance during your mods, did you have a baseline run? How fast were these cars originally before tweaks? I never ran my 91, wish I did, but then again, I feared lunching the trans (>150K miles)

The ECM won't have an issue with it per se, it will go into closed loop, but it will likely be running a % richer all the time, and these cars run plenty rich now. So you don't for sure want to add to it. I would bet if you can lean it out some at WOT, you would see some benefits down the 1/4mi and SOTP. But Cat Converters may suffer too, they richen it to cool them so they don't melt.

By chance during your mods, did you have a baseline run? How fast were these cars originally before tweaks? I never ran my 91, wish I did, but then again, I feared lunching the trans (>150K miles)

The ECM won't have an issue with it per se, it will go into closed loop, but it will likely be running a % richer all the time, and these cars run plenty rich now. So you don't for sure want to add to it. I would bet if you can lean it out some at WOT, you would see some benefits down the 1/4mi and SOTP. But Cat Converters may suffer too, they richen it to cool them so they don't melt.

The catalytic converter is an enhancement that I cannot mention :shhh: :p

As for the fuel pressure, the integrators show the standard 128 at WOT, which is fine by me. During low RPM operation when closed loop is operating, the higher fuel pressure sends the ECM into that 'lean out' mode and the integrators show around 115 or so, thus leaning out the fuel at low RPM's. I think I have that right...It also seems that it is therefore using less gasoline, making fuel economy a little better when driving below the open loop parameters. When I step on it though, the fuel economy goes right out the door... :bonkers: Does that make any sense?

As for a pre-mod run, no I did not get that chance. I can ballpark for you though that a stock '91 Seville can not run low 15's in the quartermile. The '91 STS ran a 16.6 on the quartermile, so mine was likely a little slower. But then again, who trusts magazine times, right? But again, low 15's was not a time the 4.9 liter enigne powered cars were capable of in stock configuration.

i was just wondering how do your advance the timing i have a 97 N* ETC

Illi's remarks apply only to the pre-Northstar Caddy engines.
This thread is dedicated to performance modifications for the 4.5 and 4.9 liter MPFI Cadillac engines.
Computers control the timing on Northstar engines, they make tens of thousands of decisions per second based on every possible engine management parameter. Trust me, the computer in your Northstar knows better than you or I or anyone how to run that engine.

i was just wondering how do your advance the timing i have a 97 N* ETC

I'm sorry, but you cannot advance the timing on the Northstar cars like you can in the 4.x cars. The Northstar timing controlls are as Jim-Hare has stated: via a very complicated OBD-2 engine management system in which the ignition system is not mechanical like the 4.9 liter and like engines. I don't even think that they make a chip for the OBD-2 Northstar engines, which is any engine made in 1996 and thereafter.

*UPDATE*

Since the time I posted about these mods, I have since blown my MSD ignition ($300.00 loss!) and have been running with the stock HEI. I placed a new Accel cap and rotor kit on along with an Accel Supercoil. It seems that because of this change that the Seville is actually a little more crisp and faster during WOT, though the fuel economy has gone down by close to 10% and part-throttle operation is not as smooth as when the MSD was on there...

So, if you'd like more performance at the cost of a drop in fuel economy, then I advise against the MSD ignition and just beef up the stock HEI system, though I still plan to have my MSD unit repaired so I have the option to use it again.

Curious, with your adjustable fuel press regulator, have you dropped the pressure, say to 35 psi and measured performance? As these cars were often calibrated lean, I am curious if that helps or not.

Maybe do some controlled 50-80 mph acceleration runs in fixed gear and adjust 1psi and retest and see what is best for performance.

great thread idea Illumina! :thumbsup:

Illumina, can you do a step-by-step guide to making your cold ram-air intake? Such as what parts you used, where to get them, etc?

Illumina, pm'd you about this, too. I would be Ohhhhh so obliged if you could supply parts/cost list :) please please please? :halo: it looks soo good.

Hey illumina, do you know if any other adjustable FPR's will fit the 4.9? Such as one of these (http://www.upgrademotoring.com/performance/sard_reg.htm)? I'm not worried about modifying the location of mounting or anything, just if it will work properly...

Ah, I'll enjoy this ONE bit of experience I have over Illumina... Don't bother with the Iridiums...they're just...well...the best I can describe them is in one word..."eh..."

Aeromotive makes an LT1 FPR, and Illumina said that the LT1 FPR would work with very minor mods. It is around $130ish at Summitracing.com

And the Aeromotive one will handle alcohol (aka, E85) if you should ever want to use it.

Here is some info on how to properly tune your engine with a fuel pressure regulator:
http://www.aeromotiveinc.com/largedetail.php?ref=69

Here is a FPR for the LT1 from Aeromotive.

http://www.aeromotiveinc.com/pdetail.php?prod=13

I know the LT1 will fit, but I was asking about that particular one because I've been offered a deal to get the "Sport" SARD regulator for very cheap for my car, and it is brand new. I'm not worried about modifying things to make it fit, that's no big deal.

Ghost, if the price is right and you want to tinker with all of that, without having any serious leaks, then give it a shot. But remember this: the Aeromotive is boost referenced, i.e., if you also do any forced induction, then make sure you get thr right regulator.

Happy fueling that 4.9 liter :thumbsup:

Tom, I haven't had any time, but I will tinker with the fuel pressure and adjust accordingly to see what can be done. I'll post the results.

Also, the P/N 13106 Aeromotive is the one that fits our engines. That's the one that I have on there now.

I'm not that familiar with MSD ignition systems...nor am I in a position to buy one right now lol..but just wondering. Does it allow you to fine-tune the timing on each cylinder?

I'm not that familiar with MSD ignition systems...nor am I in a position to buy one right now lol..but just wondering. Does it allow you to fine-tune the timing on each cylinder?

The "7 series" MSD ignitions allow fine tuning for each cylinder. The "6 series" that I used does not.

I have read that around 0.88v is optimal power for most cars. so for tuning, you can run WOT with the diag display on O2 volts and read it.

It isn't super accurate, as it isn't a wideband O2, but it does give some reasonable reliability for this type tuning.

Really have to dial it in with some controlled acceleration runs and run 3 runs to be consistent, then change fuel at WOT, then run again. Hell on the car, but it would give good data. Takes lots of time.

Ghost, if the price is right and you want to tinker with all of that, without having any serious leaks, then give it a shot. But remember this: the Aeromotive is boost referenced, i.e., if you also do any forced induction, then make sure you get thr right regulator.

Happy fueling that 4.9 liter :thumbsup:

Tom, I haven't had any time, but I will tinker with the fuel pressure and adjust accordingly to see what can be done. I'll post the results.

I have read that around 0.88v is optimal power for most cars. so for tuning, you can run WOT with the diag display on O2 volts and read it.

It isn't super accurate, as it isn't a wideband O2, but it does give some reasonable reliability for this type tuning.

Really have to dial it in with some controlled acceleration runs and run 3 runs to be consistent, then change fuel at WOT, then run again. Hell on the car, but it would give good data. Takes lots of time.

Hey, I make my car go through Hell every day! :D Or at least on some days...

I have a road that I can likely get away with doing that...But what you are saying is that I should adjust fuel pressure accordingly and find the best / optimal pressure by doing the runs, right?

As for the o2 sensor, is it possible to connect a voltmeter inline with it to help get the most accurate readings?

I did just that on my Cutlass, it worked well. Just make sure it is a digital volt meter, I used a Fluke 87 from work, the analog ones aren't high enough impedance and will load down the O2. And make sure you don't put voltage on the O2, I have heard they get cranky when you do and blow. I don't buy it really, but that is what THEY say. I have played with mine, and the PCM gives a .45v reference to it anyway. I was trying a voltage divider and later a op amp to try to shift the voltage down 0.1v to try to richen cruise. And nothing would work, as there is only a REFERENCE VOLTAGE there, no current can be sourced from it, any load at all will drop the voltage and make it think it was lean and it would compensate by richening it up.

Try a run where there is no shift, and you are at peak acceleration before you hit the stopwatch. Say 45-75 in second gear. Start your run so that you are already at WOT in second when you cross 45 (or whatever speed works). You don't want traction to be a variable, and you don't want trans shifts to be a variable either. I find my runs in 2nd gear from 35 to 85 work for my data logging runs (not timing it, just looking at airflow data and such).

One could get creative and connect a LT1 or Vortec MAF to a RS232 port and calculate airflow (I have charts of what these 2 MAF's output) and start doing what it takes to peak it, that might show some good results too. It won't show rich/lean improvements, but it will show other airflow changes like air box, K&N, etc.

Hey, I make my car go through Hell every day! :D Or at least on some days...

I have a road that I can likely get away with doing that...But what you are saying is that I should adjust fuel pressure accordingly and find the best / optimal pressure by doing the runs, right?

As for the o2 sensor, is it possible to connect a voltmeter inline with it to help get the most accurate readings?

I could always run in manual 2nd / 3rd for a run to avoid shifting...

But I am having trouble understanding something: the higher the voltage, the richer the mixture? Please explain this to me...

He said the opposite I think...


I was trying a voltage divider and later a op amp to try to shift the voltage down 0.1v to try to richen cruise

The more oxygen the sensor picks up, the lower the voltage will be. So if there is high voltage, that means there is less oxygen in the exhaust, so the ECM commands a lean mixture such that not as much of the oxygen gets burned up.

Higher voltage = Richer (commanding LEAN is the result)
Lower voltage = Leaner (commanding RICH is the result)

So if I dropped cruise O2 voltages by 0.1v, the PCM would command it to richen to come back to 0.45v.

If you watch the BLM values in the PCM, and then disconnect a vacuum line, the BLM climbs. Integrator does momentarily till BLM climbs, and Integrator returns to 128ish. The Integrator is the high res computer representation of the O2 readings. Much easier to read. BUT, it is disabled at WOT (not technically, it goes to a fixed value is BLM is averaging 128 or LESS, if higher, it should pickup the BLM value), so you have to read the O2 off the FDC display in diagnostic mode.

it is now 4 years later.

updates to this great thread?

it is now 4 years later.

updates to this great thread?

Hehehehe...

Sorry, I've been very busy with about 2,000 other projects, and an even bigger one is coming up pretty soon (not car related).

That said, as far as bolt on mods that can be bought off of the shelf and will readily fit, what I've listed here is pretty much it. I still plan to make a picture instruction post regarding a nice clean air intake, and the tranny thread will be posted real soon too (still waiting for my LSD!!!).

So please hang in there, I have not forgotten this performance business, I just have other priorities at hand right now. :cool:

Knowing GM, they typically run fairly rich at WOT, this is where you often find lots of power @ WOT. If you can lean it out at WOT somehow, then you can likely find on the order of 10-15 hp. That coupled with illuminas's mods might really perk things up.

Why does GM err on the rich side? Cat Converters, they melt if they get to hot, most GM tunes try not to let the cats exceed 800-830C. I have seen performance cars like CTS-V in the 900-950C range, so it does sound like converter technology is changing to allow hotter exhausts. So anytime you lean out WOT you are putting some risk of the converters melting. This is not to scare you, if you tune for WOT power around 13.2-13.3:1, I have NOT heard of people having issues. An engine misfire causes far more damage than a WOT run running @ 13.3:1....

I had always wanted to get another exhaust pipe for my 91 Deville (that is a sweet one factory isn't it guys??) and tack weld it to the stock pipe and make a dual exhaust option. It might work. But probably more gains for a good muffler design would do more. That large pipe is a nice size for a 4.9L, so the real issue is probably the muffler anyway.

One of these days if I can get a 90 4.5L car or a 91-95 4.9L car I will do what I can to dissassemble the PCM code and make a true custom tune. I just need the car to start working on, which I don't have at the moment (I do have access to a 90 4.5L, but is isn't mine and it is trying to be sold, so I can't really hack at it too much right now, but if I can get the base code read I might have something to work with, I hope to get the reader today....) and I need the time, the tools for code hacking are the easy part.... Hacking isn't always fun either....

Oh, a performance mod worth noting, for economy and performance is a Wideband O2 that replaces the Narrowband O2 with a wideband controller that has a Narrowband output for the PCM. I hope to do one soon on my LT1. You can setup for leaner cruise for better economy, or richer cruise for power (this will kill mpg) or whatever you want...

Did the FastChips chip do anything at all other than remove speed limiter, that is all it looks like it does.

If anyone has one that they can have read and send me the .bin, I would like to examine and see if they did more than that.