RS bumper vs. S bumper

[Lukesportsman]

First, I have no intention on a front mounted oil cooler with this engine. Second, I'm kind of fond of the S bumper in aesthetics. Third, most interested in function though.

Comparing a RS"S" type front bumper with an S bumper with added splitter. Does either give up much in Cd? The S just looks so clean and this why I like it, but does that translate into reality. Was the RS shape to create a high pressure area at the oil cooler? If so, is there more drag? The RS"S" bumper would be the cheaper route since it incorporates a small dam/splitter and the S would require additional components. I must admit that I fell in love with BBI a couple of years ago and maybe this is subconsciously in my decision making.

Or is this just a mute point, and I splitting hairs instead of air? I'm ordering next week so help!

[lateapex911]

Well, it's just an opinion, but I agree with you on the aesthetics...

I would GUESS that the RS bumper came from an S bumper that got modded for a cooler.

I'm working on a splitter for my S bumper myself.

[Avery]

There is a real practical consideration here. The provision for the RS bumper mounted oil cooler is real susceptable to getting bashed by curbs, etc. Since the bumper is fiberglass, you will be constantly fixing that thing. If your not going with a bumper mounted cooler, I'd go with the S bumper style.

[Tyson Schmidt]

The RS bumper will lower the stagnation point, sending more air over the car and less under it. This will lower front lift, and I would guess drag as well.

The RS bumper is the way to go for effectiveness, but I prefer the S bumper on aesthetics. Jack and I both run S bumpers with splitters that are removeable, giving the best of both worlds.

[Randy Webb]

I like the S shape also - that rectangle always looked out of place to me with its square corners.

The aero effects will make little difference except at high speeds -- i.e. highly illegal speeds. It is likely that the S bumper yields a lower Cd, but aerodynamics is widely misunderstood and hard to predict. i.e. you'd need to find a wind tunnel somewhere and know how to use it. If you were really, really crazed about this, you could build models and scale the flow for similar Re numbers - usually with water.

[Lukesportsman]

It'd probably be cheaper to just run top end runs with a VW engine swapped in the rear and compare top speeds with both bumpers.

Thanks really for the response Randy. I just figured with all the club racers out there, it would be a known fact which bumper is advantageous for straight line speeds.

[Randy Webb]

Yup - my comments are more directed to the budding graduate student.

BTW, there is a really nice wind tunnel right in your home town. It belongs to George Bakken, a colleague of mine and prof. at ISU. He forged it himself(!) It's for measuring birds tho - not cars.

[dweymer]

Tyson,
Do you have pics of your or Jacks setup? As I am also considering a new smile.

[Lukesportsman]

Don, look up "Poor man's ground effects".

[Lukesportsman]

This is one that was posted week or so ago.