SPS

Have you any idea why my 98sc2 would be really doggy until about 3500rpm? At half throttle I can feel it like night and day when I hit 3500 it picks up like I flipped a switch or something. Also only getting 28mpg average. I know I had almost 40mpg in my 92 SL1. Any Ideas why I'm suffering from these issues?

Well, there are 1000 possible answers to this.

1. Didn't you say in another post that you are using the SPS2100P coils in your 98 and getting misfires? That would certainly contribute to both loss of power and loss of fuel efficiency!
2. To some extent, a 16-valve DOHC 1900cc 4-cylinder is going to be much more efficient above 3500 rpm than below 3500 rpm. It is designed that way. (Granted the stock tuning of the Saturn S Series DOHC is such that they gave up some high rpm peak power in order to flatten the torque curve at the bottom a bit. But nevertheless, these engines are way more efficient at higher rpm. Afterall, its not a V8...)
3. Have you made tuning changes that are designed to shift the power curve upward to higher rpm? Bigger exhaust or performance intake/air-cleaner for example? Velocity or volume, choose one, you can't have both.

I took the coils off right away cause of the miss firing. I do have a intake and air-cleaner. Next week I am putting on my exhaust. A new OBX header with a high flow 2 1/2" cat, followed by 2 1/2' piping all the way back to straight through muffler. Is that going to cause issues? And did you have any ideas as to why I'm getting such poor gas mileage?

fastricoh21 wrote:

QUOTE:
Next week I am putting on my exhaust. A new OBX header with a high flow 2 1/2" cat, followed by 2 1/2' piping all the way back to straight through muffler. Is that going to cause issues?

Well it will shift the power curve further upward to higher rpm. Large plumbing allows for a large volume of air but does not maintain velocity of smaller volumes of air. (Think about it: A large pipe gives a small number of molecules a chance to spread out, slow down, and linger at the edges. With a small pipe, there is no room to spread out, so the molecules are forced to stay in line and keep moving forward.) That is the volume versus velocity tradeoff. You can tune it to be efficient at low rpm, or you can tune it to be efficient at high rpm. It's really really hard to do both. (Though that is precisely the point of variable camshaft profiles and variable valvetrain timing systems.)

fastricoh21 wrote:

QUOTE:
And did you have any ideas as to why I'm getting such poor gas mileage?

Certainly could be a maintenance issue. (IE: needs a tuneup or more air pressure in the tires.) But most likely is that you're right foot is too heavy. Stop opening the throttle so far all the time.

Thanks for taking the time to help me. I know my foot is heavy but even on the highway the best I ever got was 39. And I took it really easy when I tested that on a 400 mile trip. Maybe it's just low copression. I have amillion questions on other stuff I hope you don't mind helping.
Again thanks alot! Rick

39 miles per gallon??!!

Dude, that is awesome mileage. It's been awhile, so don't quote me for sure, but I think that the DOHC with a manual trans is only EPA rated at 35 mpg on the highway.

So if you are getting 39, then you are kicking ass.