Car rules and preparation for a "Street" Class car

[Jackal]

Hi All,

I'm starting this thread for interpretation of the Street Class rules.  Although limited,  there may be some questions about what may or may not be permitted. 

Hopefully this thread can be collectively used for folks to prepare their cars effectively for the Street class only. No Touring, Prepared, Modified chat here please.

[Jackal]

I'll start.

I have the 2006 Z4MC and I would like to remain in BS as this particular M car is omitted from Touring classes and skips straight to Prepared.

MY question is in regards to Exhaust bypass cutouts.  As per the rules for Street Class Exhausts....

"Any part of the exhaust system beyond (downstream from) the last catalytic
converter, if so equipped, may be substituted or removed provided the
system exits the car in the original location and meets the requirements of
Section 3.3.3.B.16, Section 3.5 and Appendix I where applicable. Vehicles
equipped with exhausts that exit in multiple locations may change to a single
outlet in any of the original locations. Stainless steel heat exchangers
are permitted only if the physical dimensions and configuration remain
unchanged."

Realizing that the cutouts will have their own challenges with sound limitations, does this rule look like cutouts may be a legal modification?  I like the idea of getting the power from the bypass, and if I have a variable switch for it,  I should be able to ensure I'm under the sound limits as well.  I just want to be sure I'm within the letter of the law.

[Jackal]

My Second question is a bit funny. 

I love the look of the Z4M with a GT style wing on the back of it.  Staying within BS won't allow it.  However,  if I were to remove the actual wing itself but leave the uprights on the car, would that still qualify as a BS car?

[Mkelder]

I'd say no to exhaust modifications you're looking at. You have to run the tailpipe to one of the holes in the rear bumper after the cat anyway. Or are you thinking muffler on one side outlet and muffler-less on the other side? I think the added weight and complication wouldn't be worth it and even that might be a no no.

The rules are basically saying you can replace the "cat-back" portion of system all you want and can goto a single outlet if original was a dual outlet.

I don't think anyone would protest having the uprights left for the wing but if you trophy anything can be picked apart that isn't OEM or specific in the rules as it is allowed.

[Jackal]

I'd say no to exhaust modifications you're looking at. You have to run the tailpipe to one of the holes in the rear bumper after the cat anyway. Or are you thinking muffler on one side outlet and muffler-less on the other side? I think the added weight and complication wouldn't be worth it and even that might be a no no.

The rules are basically saying you can replace the "cat-back" portion of system all you want and can goto a single outlet if original was a dual outlet.

I don't think anyone would protest having the uprights left for the wing but if trophy anything can be picked apart that isn't OEM.

Basically my idea would be to have the stock exhaust fully intact,  but right at the X pipe (well after the CAT), run two exhaust cutouts that allow the exhaust to bypass completely the stock hardware. My confusion was generated from the ability to "remove" any component.  With a cutout half engaged, half the exhaust has the potential to exit from the stock location.

[sti-tom]

The performance gain would be negligible for autox, So I would just run it closed for events which should definitely be legal and enjoy it open the rest of the time. I thought S2000 guys used to just disconnect their catbacks all together.

[nnywg]

I always say build the car you want to drive every day, and worry about the RAW scores if that matters to you.  Unless you're holding the top of your class or top times of the day, it just doesn't make sense to try mods that conform to the rules IMO.

[Jackal]

The performance gain would be negligible for autox, So I would just run it closed for events which should definitely be legal and enjoy it open the rest of the time. I thought S2000 guys used to just disconnect their catbacks all together.

There's not a lot I can do to squeeze more power out of the car.

In BS I can't use underdrive pully's, or replace headers.  The exhaust mod is about the only power adding mod allowed.

I always say build the car you want to drive every day, and worry about the RAW scores if that matters to you.  Unless you're holding the top of your class or top times of the day, it just doesn't make sense to try mods that conform to the rules IMO.

Eventually I'll be building her for BSP,  where I can have the aero, pully's, headers.....

[MurrayPeterson]

The performance gain would be negligible for autox, So I would just run it closed for events which should definitely be legal and enjoy it open the rest of the time. I thought S2000 guys used to just disconnect their catbacks all together.

To meet rules, you need at least a straight pipe to guide the bypassed exhaust to one of the original openings.  And you will certainly need a muffler on this straight pipe to meet sound.

BTW, it is illegal (and extremely unsafe) in any class to have exhaust released underneath the car.  You wouldn't pass tech if you tried that.

[MurrayPeterson]

Eventually I'll be building her for BSP,  where I can have the aero, pully's, headers.....

BSP does not allow wings, just spoilers without endplates.  To get a wing, you need to move up to SM.

[Stuart]

BTW, it is illegal (and extremely unsafe) in any class to have exhaust released underneath the car.  You wouldn't pass tech if you tried that.

There are a few classes that do allow this but they generally are ones that are a dumping ground for roadcourse cars.  For example Spec Miata's can terminate at the rear axle, then again we cannot run with windows legally so it does help to minimize the safety concern.

[Jackal]

The performance gain would be negligible for autox, So I would just run it closed for events which should definitely be legal and enjoy it open the rest of the time. I thought S2000 guys used to just disconnect their catbacks all together.

To meet rules, you need at least a straight pipe to guide the bypassed exhaust to one of the original openings.  And you will certainly need a muffler on this straight pipe to meet sound.

BTW, it is illegal (and extremely unsafe) in any class to have exhaust released underneath the car.  You wouldn't pass tech if you tried that.

Deuce! and Double Deuce!!  Time to erase that idea and start coming up with others.

[Jackal]

Eventually I'll be building her for BSP,  where I can have the aero, pully's, headers.....

BSP does not allow wings, just spoilers without endplates.  To get a wing, you need to move up to SM.

Hmmm  SM does give me a reason to get that supercharger I've been pining for.

[Mkelder]

As I've learned after the fact like many before me...Street prepared/Street Mod are the cut your fender for stupid wide tires class that tricks people into thinking it is the add power to my car class. It takes a very high level of car preparedness to hope to pax well in those and higher classes.

Tires first, then power unless your going to ignore pax like me and then I'd say add all the power you can and have fun!

[Jackal]

As I've learned after the fact like many before me...Street prepared/Street Mod are the cut your fender for stupid wide tires class that tricks people into thinking it is the add power to my car class. It takes a very high level of car preparedness to hope to pax well in those and higher classes.

Tires first, then power unless your going to ignore pax like me and then I'd say add all the power you can and have fun!

I've made that mistake before on the 135 and ended up in STU for wheels only.  I've done alright in SM with a Subaru way back when as well,  but that one I just blindly wandered into a class without thought.

My goal with this car will be gradual mods and likely an eventual settling in SM,  by way of BS and BSP.  Next year I'd like to compete in BS and put at least a full year to that class.