marlinspike

I guess I'm looking at fabrik8 on this one. Would lowering a car 1.5" reduce the drag factors?

I read someone postulating that it would alter frontal area is why I pulled out frontal area specifically, but I don't really see how that would happen.

shawn22

Yes.

You're cutting off part of the tire from the front. Although its a minor change.

marlinspike

How about lift? Going from 8" of clearance to 6.5" make a substantial difference in lift?

Fabrik8

The much larger difference is actually the change in airflow under the car and not the frontal area. You're not really changing the frontal area at all, except for the small amount of tire section that's now in the wheelwell (which is negligible). Changing the amount of air under the car can have huge effects though. You can change lift or downforce, or change drag. You'd be surprised how much drag can be created by the really rough underfloor of a car. Choke the airflow from under the car, and a lot of drag (and sometimes lift) can be reduced. That's hard to predict though, because a lot of this also depends on how air enters the underfloor area (for example if there is a splitter or skirt or whatever) so it's pretty hard to make assumptions. A lot of this is speed dependent too, because boundary layer effects that exist at one speed might not be the same at another speed range. You could have clean airflow all the way under the car at one speed, and the boundary layer could stall flow under the car at another speed. So you could have lower drag at one range of speed and more drag at another range of speed. Generally though the less air under the car, the better for drag.

Air under the car can definitely be a good thing for drag and downforce, but usually when the underfloor is flat (like some race series that allow a flat undertray). Then the air under the car can be used along with the air flowing over the car to create downforce. NASCAR doesn't allow a flat floor, and they can't add much for aero devices, so usually they add a skirt to block air from under the car (and a splitter of sorts to add some front-end downforce). So there are different approaches to address undercar flow depending on what you're trying to actually do. On a street car you can't do too much because you still need enough suspension travel for street driving, so you can't leave 1/2" between a front lip and the ground. I can't remember where I was actually going with that train of thought.




My point here is that yes, changing ride height changes things, but the interactions are very complex and hard to make blanket assumptions about.


The total drag of a car is the Cd (coeff of drag) x frontal area. So when lowering, you won't really do anything to change the frontal area, but you will change the Cd.



Just as a side note, I really hate when car manufacturers say "look how slippery our car is, the Cd is only ____". That's cool and all, but when you're talking about some huge sedan with a huge frontal area, the overall drag is still huge. So you can have a lower Cd than a Honda Insight, but much higher drag if your frontal area is larger than an Insight. People don't seem to realize that a lot of times, and it seems to be a marketing half-truth that you see thrown around a lot in advertising.

Fabrik8

Oh, so the question was whether it changes frontal area or Cd. It changes Cd, frontal area will be almost identical.

marlinspike

So what should I do first, bored out throttle body/lower intake manifold opening and swaintech thermal coating on intake parts, or H&R springs+Kmac camber adjustment kit?

Fabrik8

What do you want first, more power or a different stance?

Stance is easy, I want to see you make some serious power from that engine in spite of that weird-ass intake manifold setup. That's a challenge.

You know what I'd do, but you're strangely attached to that K-Jetronic (or whatever it is) mechanical fuel injection setup so your options are limited.

marlinspike

Yeah, I like the K-jet. I like that when I open my hood it still looks pretty much like it always did. I was calling different cam shops to see if anybody had any profile cards for this engine, and one guy who did said if I have cams and an exhaust I'll see decent gains if I bore out the throttle body, so I guess I'm going there first.

BTW, I'll just ask here because I'm sure you know the answer
See the sleeve on this oil filter?


The MB branded filters used to look like that too, but they went to full length sleeves a few years ago. Any idea what it's for? I feel like all it could do is reduce flow and I should go aftermarket to get the shorter (more original) sleeve. Thoughts?

Fabrik8

The longer filter is usually to get more filter surface area to increase flow and reduce pressure drop usually. I'm guessing the blue sleeve is to keep the pleated filter element from ballooning out and blocking flow against the filter housing. It could also be to keep the pleated element from getting damaged during shipping or installation, but that's less likely. The blue sleeve is most likely still less restrictive than the pleated element underneath it, so I wouldn't worry about flow. Besides, there are usually much bigger flow restrictions, like fuel lines and pressure regulators. MB probably changed flow media to something stiffer but lower flow, so they don't need the sleeve but do need to make the filter longer to keep the flow adequate (or maybe even better)...

I'd find out which one flows better before switching from one to the other, but I'm sure either one will work perfectly fine.

marlinspike

Sorry, I think we have a miscommunication, but your explanation still helped me out. MB didn't change the filter length, they just changed the sleeve length from covering only the center to covering the entire filter.