super vs turbo

[jayjack]

ok i have a 96 grand merc and i kinda wanted to make it a little funner and i was thinkin froced induction would be the way to go. i kinda want something that wouldn't take much maintenance, and im not sure but i thought superchargers take less work and less maintenance. i also don't want to much boost that i tear up my transmision. what would be a good choice, and how much boost could a stock tranny take and still run fine, and is it possible to help the tranny deal with the extra stress? and which would give better low end, a small turbo or a super?

[UncleBob]

there is a section of automotiveforums that is dedicated to forced induction, under teh catagory "cars in general", that has a sticky about the difference between SC's and TC's

But what you are really asking with the tranny is "how much torque/hp can my stock tranny handle?" and that is a tough question to answer.

As for which is better, SC or TC, that will depend what you want and who you ask. With a small turbo, you will have more punch in the midrange than a SC. But the SC will be more linear. Which is better? Depends. I personally prefer TC for several reasons, not only are they more efficient, hit harder, but they are cheaper if you have some fab skills.

[curtis73]

I'm working on a very similar project for a friend right now. He bought a SC Cobra motor to drop in his Crown Vic. The rumor on the street is that the stock tranny (although easy to beef up) won't take much more than what you have. The big cars got cushy pressures and soft shift points that won't like it. Fortunately its pretty easy to upgrade the trannys, but not cheap.

Ford has a few SC options. The 5.4 lightning engine could work, as would a SC from a Cobra. The aftermarket has SCs for the 4.6 as well. Turbos are fanfriggintastic, but they require serious exhaust and plumbing modifications and rarely are they smog legal (if that's an issue where you live).

SC would be much easier and make great power. Turbos are just as viable, but lots more work.

[jayjack]

thx a ton

[UncleBob]

Originally Posted by curtis73

[turbo systems] rarely are they smog legal (if that's an issue where you live).

doesn't matter if its a turbo or a SC, if it wasn't a stock option, you will have a harder time getting it through emissions (depending on how the laws are in your state)

Some states are very loose in their regulation, and a well tuned SC or TC system would pass with flying colors. Its a complex subject that is not so easily answered.

BUT, if the car had a stock SC option (such as the newer mustangs) then it will automatically legal emissions-wise with the proper stock components that are required....but that is the ONLY way its a sure thing for all states

[INF3RN0666]

Hey unclebob,
I know that the reason behind oxygen sensors is to modify how much fuel is added to the mix based on the oxygen content in the exhaust. So if you add a super charger, then would you need to modify the computer parameters? I would assume that the stock computer parameters would assume that there's a malfunction in the oxygen sensor circuit since you're pushing in a lot more air. Or am I mistaken?

[curtis73]

Very true, I was just thinking that there are many SC kits for that engine that carry a CARB EO number, which means it has been tested and approved as a stock-replacment-level part as far as emissions are concerned.

Of course even a stock SC won't pass a sniffer if its not tuned correctly, but there are no turbo kits for that car that have an EO number.

[UncleBob]

Originally Posted by INF3RN0666

Hey unclebob,
I know that the reason behind oxygen sensors is to modify how much fuel is added to the mix based on the oxygen content in the exhaust. So if you add a super charger, then would you need to modify the computer parameters? I would assume that the stock computer parameters would assume that there's a malfunction in the oxygen sensor circuit since you're pushing in a lot more air. Or am I mistaken?

its a complex issue, because there are so many parameters and different methods of engine management. If its a MAF system, (mass air flow) then it COULD work if the MAF is draw-thru, and the MAF is calibrated for the range you are subjecting it to, AND.....the fuel system can handle the added capacity

Likely? Very unlikely

As soon as you start changing injector sizes, everything gets skewed. The engine management makes assumptions about the system that only have so much range of adjustability. Large changes in injector sizes throws that off outside of acceptable parameters.

You can of course change MAF's to work within that, which also requires calibrating the new MAF to work with whatever injectors your working with. But this is considered a "hackish" way of doing it. It works, but has negative side effects. Same goes with tweaking fuel pressure, such as rising rate FPR.

As far as the O2 sensor goes, that is neither here nor there. The O2 is mostly used (non WB) for partial throttle and idle. TC and SC have little to do with those situations. I should add, O2's aren't aware of the *quanity* of air in the system, only the *percentage* of air (WB or NB) so the fact that you are forcing more air through the system at WOT doesn't matter. But most systems go to open loop at WOT so really, thats immaterial to the situation

I haven't even touched on speed density systems.....like I said, its a complex subject