I'm building up a HDPE/TimeAttack/Autocross car and i am open to the bumper cut but can't find anywhere that it has any positive impact.

Even looking at well respected cars it is about a 50/50 thing. What are the thought here?

 

A tiny amount.
The big factor is for Time trial will it bump you up in class?

 

IIRC Emilio stated they haven't found any advantage to the bumper cut/removal other than shedding weight off the back of the car.

 

This is all I recall as well..

I did it to mine because I like how it looks... *shrugs*

 

I'm thinking I won't be doing it for a while

 

Kyle did a couple videos on this using a Miata for the CFD. It's a bit confusing because the numbers don't match in the first and second videos, but I think that's because he refined the CFD model between them.


Briefly, the bumper cut helped a bit, both with and without a flat floor.

 

I believe there was someone on ClubRoadster who did a finite element analysis of a cut rear bumper on an NA and calculated there was a 7 pound decrease of drag at 75 mph, amounting to a 1.4 horsepower improvement. Not a large increase but not much cost, either.

 

+ Adds lightness (any lightness is a good thing in an MX5)
+ Looks cool (unless you "butcher it" or take too much off)
+ Prevents your bumper from burning if your 3" exhaust is too close to the OEM bumper

 

You bump a 7+ month-old thread to add an anecdote from ClubRoadster, without even providing a link to the source? I don't think you thought your cunning plan all the way through.

But hey, that unknown source used the words "finite element analysis", so it must be valid..

 

Indeed. FEA is of course the SW of choice for aero analysis, right?

I should know better than to use use irony ... For clarity, and the person who gave me the negcat, CFD (aka Computational Fluid Dynamics) is the software used for aero analysis, FEA is for stress analysis.

 

It is legal to do this in TT with NASA as long as the bumper cover still covers the main structural element.
From the TT5-6 rules (also applies to TT1-4)
4) Cutting/removal of the rear bumper cover/fascia where it does not cover the rear frame/bumper cross beam

 

There's no way it's that effective. You need to provide your source.

For reference, an APR GT250 wing (same one used in the Singular wing kit) by itself generates approximately 7lbs of drag at 75mph at about 4° angle of attack.

 

So I just searched for over an hour for this 7lb at 75 mph research project. Couldn't find it be did find this
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https://grassrootsmotorsports.com/fo...s/97287/page1/