Manifold / TB rule revisions

[Greg Amy]

I'm confused by all this Intake manifold/throttle body revisions to the ST rules...

Specifically what regs are you referring to?

If you swap engines, you can use the intake that was on the engine you installed or the car you installed it into.

- GA

[Z3_GoCar]

Specifically what regs are you referring to?

If you swap engines, you can use the intake that was on the engine you installed or the car you installed it into.

- GA

It's under the section just added last month 9.1.4.G.1.e.1:

1. Regardless of the intake chosen, the total number of throttle bodies must remain the same.

The same as.... the chassis, the motor, or??? My chassis has two different generation motors installed in it along with about seven different motors, one of those has a two barrel throttle body, five have a single barrel (some are cable operated and some are electro-servo,) and one has six throttle bodies. All of these motors are in my dealer sourced shop manual, and are USDM.

Any insight into what this means? Thanks Greg.

James

[Greg Amy]

The same as.... the chassis, the motor, or???

Good point. The rule stems from someone - a BMW driver, of course, trying to install a 4-choke ITB intake onto an otherwise-STU compliant engine, that would have provided a distinct competitive advantage. I'll bring this to Eric Heinrich's attention, he can explain more.

If we need to, we'll adjust the verbiage.

- GA

[Knestis]

The "writing a rule to prevent something specific" trap. I believe that's Ad Hoc committee standard error 37.1...?



K

[Greg Amy]

Aye-yup.

[JS154]

Good point. The rule stems from someone - a BMW driver, of course, trying to install a 4-choke ITB intake onto an otherwise-STU compliant engine, that would have provided a distinct competitive advantage. I'll bring this to Eric Heinrich's attention, he can explain more.

If we need to, we'll adjust the verbiage.

- GA

The advantage comes from part throttle driveability, every builder I've spoken with agrees that moving a single TB further away from the head can make the same power as ITB's.

Regardless, the point of the rule wording was because initially it was completely in conflict with it self - originally the rule said you had to keep the original intake manifold unless you changed it in which case you had to keep the original intake manifold. I"ll take a closer look tonight at the wording and what's being asked here and post my thoughts.

One thought I have had is, given the FI car's continuing dominance inspite of weight and restrictor adjustments, I think N/A cars should have more freedom to play with the intake manifold than they do, but I'm pretty sure that idea would be DOA.

[Chip42]

I'm with Eric, and have been on record thinking the same (and more) for well over a year.

in a displacement to weight class with street car origins, using street car parts is a very good way to separate the haves from the have-nots. FI will overcome a lot of those issues and, especially with the more modern turbos, sacrifice a touch of peak hp for huge gains in area under the curve over a NA sibling, even with small restrictors. couple that with a huge industry-wide shift (more true in smaller STL type engines but still) toward low end torque and efficiency over performance, and you get a similar enhancement to the NA cars but a lot less peak power potential in most cars than in a few exceptions. yes, hp/L numbers have been on the rise, but once the rules are factored in a lot of that dies off in lost "gains" and you're often times left with a relatively shitty (for racing) intake and head designed to get 11ty MPG on 7-11's 87 octane. NA generally can't compete with FI under that basic premise. open the rules and let the displacement be the driving force like it's supposed to be (at least more so), and fields will be a lot more diverse, and yes, maybe more expensive. and the gap to FI should shrink.

[JS154]

I'm with Eric, and have been on record thinking the same (and more) for well over a year.

in a displacement to weight class with street car origins, using street car parts is a very good way to separate the haves from the have-nots. FI will overcome a lot of those issues and, especially with the more modern turbos, sacrifice a touch of peak hp for huge gains in area under the curve over a NA sibling, even with small restrictors. couple that with a huge industry-wide shift (more true in smaller STL type engines but still) toward low end torque and efficiency over performance, and you get a similar enhancement to the NA cars but a lot less peak power potential in most cars than in a few exceptions. yes, hp/L numbers have been on the rise, but once the rules are factored in a lot of that dies off in lost "gains" and you're often times left with a relatively shitty (for racing) intake and head designed to get 11ty MPG on 7-11's 87 octane. NA generally can't compete with FI under that basic premise. open the rules and let the displacement be the driving force like it's supposed to be (at least more so), and fields will be a lot more diverse, and yes, maybe more expensive. and the gap to FI should shrink.

Chip..

submit a letter. otherwise it's just an idea that's on some forum somewhere.

www.crbscca.com

[Matt93SE]

I pretty much agree with both guys above-- I've been bitching about the stock IM for quite a while now..

for my 240, it was either go FI with a JDM engine, or go slow forever on the stock intake manifold. The old SpeedVision guys were making ~220whp with that engine built to their specs, which was about same as the current STU specs. Sorry, I need another 50hp to be able to even think about keeping up in a 2.4L.

... So I went to an EP rotary.. It's cheaper there. (yes, I'm going to keep fooling myself with that until I blow up my first engine..)

[dhrmx5]

[QUOTE=Z3_GoCar;346701]It's under the section just added last month 9.1.4.G.1.e.1:

1. Regardless of the intake chosen, the total number of throttle bodies must remain the same.

The same as.... the chassis, the motor, or??? My chassis has two different generation motors installed in it along with about seven different motors, one of those has a two barrel throttle body, five have a single barrel (some are cable operated and some are electro-servo,) and one has six throttle bodies. All of these motors are in my dealer sourced shop manual, and are USDM.

Any insight into what this means? Thanks Greg.

James[/QUOTE

This rule was specificaly written to ALLOW the use of either the intake and TB from the installed engine OR the intake and TB from the chassis. This was to facilitate the install of RWD/FWD engines in either RWD or FWD chassis.(example: B18 GSR engine in S2000 for STL) The manifolds frequently prevent the install because most FWD manifolds would point at the firewall.

With this rule you could install a 2.3L MZR engine in a 06+ MX5 and build a competetive car for STU. Conversly, it would allow the install of a 2.0L MZR into a Mazda3s for STL.

To prevent the use of the BMW ITB setup that came in some of the 3 series, Z4s, etc from being used with the approved engines in STL and STU we made the rule reflect that the number of TBs had to remain the same as the INSTALLED engine came with.

So far that is the only conflict we can think of that needed resolving.

The rule was made confusing because the words "for the installed engine" got left off. We don't care if the TB has one or twenty venturis, as long as it is stock and unmodified.