Hey Guys! I want to increase the performance of my '92 DeVille 4.9 and I'm on an extremely small budget. Over the course of the day googling, my research has given me this list of relatively cheap things to increase perfomance:
1. Adjusting the timing on the distributor from 10 to 13-14.
2. Replacing the stock muffler with a Performance one.
3. Replacing the air filter with a performance air filter OR a cold air intake.
4. Adding a Throttle Body Spacer.
My questions are:
Which of these things, if any, are worth doing?
What effect will each of these things, or all of them, have on the car in terms of HP, torque, gas mileage, noise, etc.?
(Emissions don't matter. I already removed the catalytic converter and bypassed the egr valve, if it makes any difference.)
Also, are there any additional things I can do to increase performance that were not previously mentioned(inexpensively)?
Put the EGR back together right away. You're probably thinking "But putting exhaust gases back into the intake is a bad thing" and you'd be right BUT the fuel mapping programmed into the computer accounts for that exhaust gas displacing oxygen in the combustion chamber and fuels accordingly. Without EGR, what would otherwise be unreactive exhaust gases is now fresh air instead. Extra fuel would need to be added to go with the extra air. The system can compensate over time(to a point), but you still run the risk of going lean while the engine is cold and at wide open throttle when the system is not reading the oxygen sensors. Add this risk plus the extra ignition lead and you've got yourself a recipe for ventilated pistons.
1 and 2 on your list are the only things worth doing if you want more mojo. Bear in mind you will have to run the highest octane available at the pump. 91 to 93 depending on your location (dont get crazy and buy race gas, it contains lead and will wreck the oxygen sensors)
One thing that you dont hear much about is the cam sensor inside the distributor - it controls fuel timing and when you turn the distributor, you are also advancing the injector timing. I dont know if a few degrees makes a difference in the fueling but my motor seems happiest at about 12 or 13... You will notice a big difference going from 10 to 12 but after that, the 'law of diminishing returns' sets in and adding more doesnt help all that much. Remember that when you advance the distributor, you are adding 2 degrees of lead to the entire advance curve which is preprogrammed into the computer. You can't modify it at all. There is a point around 44mph in 4th gear where the computer is adding the most ignition lead. It's around 50degrees total advance which is damn near unheard of in the performance world but they did this to make the archaic engine design pass ever stricter emissions and mileage standards. The point is, whatever you add to the distributor is applied at this ~50 degree advance which is already pushing the limits by itself. Everywhere else besides this high advance cruise condition is improved though. So listen carefully for any sort of metallic 'pinging' sounds coming from the engine in 4th gear cruise.
I dont recommend gutting the converter for 2 reasons: A) once you put an aftermarket muffler on there (flowmaster especially), it sounds like ****ing hell when you get on it. Like fire crackers going off in the trunk. I found this out the hard way. Nobody talks about it, but the cat has a large effect on the sound.
And B) You wont find it written on ANY aftermarket muffler package EVER, but simply put, back-pressure is good for torque. When you reduce backpressure, you essentially move your engine's 'torque peak' to a higher point in the rpm band. In a street driver, your peak torque ends up at an rpm that your engine will rarely ever see in daily driving. These motors dont rev high, and they dont flow much to begin with, so increasing the exhaust system's flow capabilities will not net you much hp. In my opinion, the only reason you see a benefit from a performance muffler on these cars is because they were designed to be quiet as number one priority. Notice just how big and heavy the stock muffler is....
In your case, since you already gutted the cat, I dont recommend changing that muffler but if you must do it, try to get one that contains both baffles and fiberglass packing. This will help suppress the awful banging that you will hear through a chambered muffler such as a Flowmaster. In my case, I first added the flowmaster 80 series and the sound was nice and smooth with a good low rumble to it but then I got greedy and gutted the cat and all hell broke loose. Performance also dropped through the floor. My remedy was to replace the cat with a 1 3/4(backpressure!) magnaflow glass pack.
For the same reason as mentioned in the exhaust system, doing anything to the intake will net you zip. The motor itself cannot out-flow the stock intake.
A TB spacer will do nothing also, mostly because the engine is multiport fueled rather than throttle body injected. Adding length to the intake tract is only beneficial if it is done for each individual cylinder rather than the entire shared manifold volume. See the Allante's 4.5L - that's how it's done!
The irony is that on these cars, the most noticeable increase in power that you can have is the one that costs $0.00
Wow, thanks for all the info! I actually got the idea of advancing the timing from an older post of yours. I only bypassed the EGR because it broke and was going to cost $80 to fix, but it sounds like if I want to advance the timing I should fix it though... Is there any way to adjust the fuel mapping or increase the fuel?
I always put 93 octane in the tank, so that won't be a problem. I'll set it to 12 first and take it from there. If I read other posts right, I just stick a paper clip in the A and B terminals of the ALDL connector, and then the timing can be set without computer interference?
"Nice and smooth with a good low rumble": That's the noise I would like! After I do the timing I'll look into a muffler, but I don't think I'll get as much as I thought out of it. I might do it just for the sound, but I definitely don't want the firecracker noise. Do you have any recommendations for the muffler?
I'm going to forget about the tb spacer, but unfortunately I already bought an airaid filter before I saw your post. It was $70 at advanced auto, but I got it off there website with a code for $40... hopefully it does something haha.
There are some crude haphazard ways of increasing the fuel, but not in any way that will be optimized for your conditions in the way that the factory programs are designed for the stock motor. All of which will decrease mileage and cause carbon buildup over time which further increases the risk of detonation. When you mess with your car, you have to be willing to accept the risk that it might mess with you!
Yes, just jump the A and B and the computer will stop adjusting the timing.
The sound is a matter of personal taste and the bitch of it all is that you cant know what a particular combo will sound like untill you have purchased and installed it. Being that you have no cat converter, you are in uncharted territory. All I can tell you from my experience is that a Flowmaster 80 series (camaro/firebird) sounds like hell with no converter. You dont have much to choose from if you want dual exhaust. I would stay away from fully chambered mufflers in your case. Also like I said, you may notice a loss of acceleration after replacing the stock muffler. I would really consider reinstalling the convertor. Generic ones can be under $75... Factory replacements cost a mint.
Then of course you have all the clowns who say "a Cadillac shouldnt sound like that"
If your $40 filter is washable, it will pay for itself over time being that a one time use filter is around $10-$15... Just dont expect any performance out of it.
The best thing for performance is to make sure eveything is tuned up and working properly. EGR and cat won't affect performance unless something is wrong with them. Sometimes EGR being disabled can be worse for performance and mileage.
The computer expects the timing to be set properly, you can adjust it a bit but go too far and it will start affecting other engine systems.
It won't do much for perfomance but I always like the look of the dual tail pipe mufflers on those cars.