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 Post subject: Carburetor change in GCR
PostPosted: Mon Apr 09, 2018 5:53 am 
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Location: Philly
I'm surprised that this hasn't gotten more attention.

As I read it, this change/clarification says you now have to have a carburetor made from a list of manufactures and the implication from that is that the carburetors now need to not be modified in any way. The old rule just read "automotive type".

This means no smoothing the chokes to take out any casting imperfections. No replacing the throttle shaft screws. No making the trick removable jet holders in down drafts. No coating or polishing the slides in SUs. No mixing and matching SU float bowls. Are modified emulsion tubes even legal? They're not a "jet". You cant even do that trick where you drill and safety wire the jet cover wing nut on a DCOE!

What is "unmodified" anyway?

This means that someone has to be aware of every "original" aspect of every variation of every model of every manufacturer listed. I couldn't imagine how long the list of DCOE variations is (hundreds, at least). Let alone all of models that would be included in the allowed carburetors. So this rule is for all practical purposes unenforceable. I doubt anyone can even produce a single complete set of specs for even a single DCOE model.

I have little skin in the prod game. I'm a GTL racer. So I'm just pointing this out. I don't really have an opinion if this is a good or bad thing. I'm just pointing out some issues with this change. I think that there are lots of folks that have smoothed chokes, or replaced throttle shaft screws, or whatever, whose cars are now illegal.

And yes, I see that it says "chokes" can be modified. But that's "choke" as in cold start enrichment, not chokes as in Bernoulli effect.

-Kyle


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PostPosted: Mon Apr 09, 2018 6:34 am 
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Posts: 156
Link?

In my quick scan, I am not seeing what you are referencing...

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Bill H
92 Saturn SL2 - SCCA F-Production


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PostPosted: Mon Apr 09, 2018 7:01 am 
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Location: Philly
Argh.

This is my freaking point about the Prod section of the GCR being a mess. How long have you been in prod? And you can't easily find the carburetor section of the prod rules?

9.1.5.E.1.B.1

Page 456 of the March&April GCRs.

-Kyle


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PostPosted: Mon Apr 09, 2018 8:44 am 
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Posts: 156
To be fair:

When you said "change/clarification" in your first post, I thought there was something new in a FasTrack that I missed. I did not check the latest GCR.

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Bill H
92 Saturn SL2 - SCCA F-Production


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PostPosted: Mon Apr 09, 2018 8:53 am 
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Location: Farmington, MI
Kyle, where does it say "Unmodified"??

b. Induction System
1. All inducted air must pass through the venturi(s) of the car’s carburetor(s). On cars where
the use of one (1) 40 DCN, DCNF, IDF carburetor is required, can fit one (1) of the following
permitted optional carburetors:
1. Weber 32 DGV/DGAV/DGEV
2. Weber 32/36 DGV/DGAV/DGEV
3. Weber 32/36 DFV/DFAV/DFEV
4. Weber 34 DAT/DATR/DATRA/DMTR
5. Holley-Weber 5200.
Carburetor jets, jet needles, metering rods and needle valves are unrestricted. Choke mechanisms,
plates, rods, and actuating cables, wires, or hoses can be removed.
Where Weber carburetors are specified, Weber type carburetors can be substituted. The
following are permitted Weber type carburetors:
1. Solex
2. SK
3. Mikuni
4. Delorto
5. Berg
6. PMO
7. EMPI
If the specification line for a car references auto-type carburetor(s), permitted carburetors are:
1. Weber
2. Solex
3. SK
4. Mikuni
5. Delorto
6. Berg
7. PMO
8. EMPI
9. Zenith
10. Stromberg
11. SU
12. Rochester
13. Holley
Note: The orientation of the auto type carburetor(s)-downdraft or sidedraft, must remain as
in the stock induction system.

2. Stock or permitted alternate sidedraft carburetor(s) can use an adaptor plate and/or a spacer
in addition to any stock spacer, between the carburetor(s) and the intake manifold. Material
for the adaptor plate and spacer is unrestricted. No adaptor plate or spacer can serve any
purpose other than to space out and/or mate the carburetor(s) to the permitted intake manifold.
The adapter or spacer cannot create a plenum or change the carburetor(s) orientation.
The maximum thickness for the adapter, spacer, stock spacer or combination of all is 1.25”.
For the purpose of these rules an Isolator is a spacer.
3. Stock or permitted alternate downdraft carburetor(s) can use an adaptor plate and/or a spacer
in addition to any stock spacer, between the carburetor(s) and the intake manifold. Material
for the adaptor plate and spacer is unrestricted. No adaptor plate or spacer can serve any
purpose other than to space out, or mate the carburetor(s) to the permitted intake manifold.
The adapter or spacer cannot change the carburetor(s) orientation. Adaptors and spacers can
have a bore larger than the throttle bore of the stock or permitted alternate carburetor(s). The
9.1.5. Production Category Specifications
GCR - 457
maximum thickness for the adapter, spacer, stock spacer or combination of all is 1.25”. For
the purpose of these rules an Isolator is a spacer.
4. Fuel injection: All inducted air must pass through the throttle body and be subject to control
by the throttle butterfly. The stock throttle body casting/housing must be retained. The bore
size and throttle butterfly dimensions must remain stock. The throttle body can be ported
and polished. The throttle butterfly shaft shall not be relocated. The throttle butterfly and any
throttle butterfly to shaft screws/bolts can be attached to the throttle butterfly shaft by any
means including welding or brazing. Holes or slots can be created in the throttle butterfly for
purposes of idle adjustment only. The number of injectors must remain stock. The mounting
position and the injection point must be stock. Electronic fuel injection may be substituted for
the stock type of fuel injection. In all other respects the fuel injection system is unrestricted.
5. All carburetors must retain the stock method of fuel distribution. Utilization or modification of
a carburetor’s components to effect an annular discharge configuration is prohibited.
6. Air cleaners, velocity stacks, air supply ducts and cold air boxes are unrestricted.

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Ted Russell

1974 FP Fiat 124 Spider


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PostPosted: Mon Apr 09, 2018 9:03 am 
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Location: Farmington, MI
Is this just more a debate about Motorcycle type VS Automobile type carbs?

I did find the not to be Modified in Level 2.

Section: 9.1.51E.B is for Level 1

Level 2 now has the must not be modified wording

b. Induction System
1. All inducted air must pass through the venturi(s) of the cars carburetor(s). All single carbureted
cars may fit a permitted optional carburetor. Permitted optional carburetors are:
1. Weber 32 DGV/DGAV/DGEV
2. Weber 32/36 DGV/DGAV/DGEV
3. Weber 32/36 DFV/DFAV/DFEV
4. Weber 34 DAT/DATR/DATRA/DMTR
5. Holley-Weber 5200

"The stock or permitted alternate carburetor must not be modified."

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Ted Russell

1974 FP Fiat 124 Spider


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PostPosted: Mon Apr 09, 2018 9:35 am 
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Location: Philly
Again, this goes the the idea that the GCR, especially in the Prod rules, is very hard to understand.

The "unmodified" part comes from the idea/rule that "if it doesn't say you can, you can't". It doesn't say you can modify the carburetor. So you can't. Previously, when it just said "automotive type", there was no datum to call it modified from. Now, so I'm told, with this datum now specified (the list of allowed carbs), the "if it doesn't say you can, you can't" rule applies to prod carburetors.

My information here is from both current and past PAC members.

Don't shoot the messenger. Prod cars have been my favorite cars in Club Racing since my childhood (loong ago). I'd like to see prod continue. This is the kind of thing that needs to be addressed for that to happen.

-Kyle


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PostPosted: Tue Apr 17, 2018 7:38 am 
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Joined: Wed Oct 28, 2009 9:24 am
Posts: 807
9.1.5. Production Category Specifications
GCR - 456
E. Authorized Modifications
1. Drive Train Level 1
a. Drive Train Component Modification
1. Stock and permitted alternate components of the drive train can be modified by any mechanical
or chemical means. Modification of a drive train component does not permit relocation of
that component.
2. No material or mechanical extension can be added to any stock or alternate component, unless
specifically authorized by these rules. Repairs to a stock or alternate component are permitted,
provided the repair serves no prohibited function.
3. Stock and permitted alternate components of the drive train can have thermal barrier and friction
altering coatings applied.


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PostPosted: Tue Apr 17, 2018 3:11 pm 
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Posts: 55
Location: palm bay, florida
Definition of drive train is rotating parts from the flywheel to the drive wheels. I can't picture the carb as a rotating part.

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Fast Family Racing
GP Nissan 210


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PostPosted: Wed Apr 18, 2018 12:08 pm 
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Joined: Wed Oct 28, 2009 9:24 am
Posts: 807
jerry larson wrote:
Definition of drive train is rotating parts from the flywheel to the drive wheels. I can't picture the carb as a rotating part.


That's true per the "technical glossary" - but looking at how the rule book is organized, Drive Train is the the heading where we find the carburetors and the entire "Power Train", to wit:

9.1.5. Production Category Specifications
GCR - 456
E. Authorized Modifications
1. Drive Train Level 1
a. Drive Train Component Modification
1. Stock and permitted alternate components of the drive train can be modified by any mechanical
or chemical means. Modification of a drive train component does not permit relocation of
that component.
2. No material or mechanical extension can be added to any stock or alternate component, unless
specifically authorized by these rules. Repairs to a stock or alternate component are permitted,
provided the repair serves no prohibited function.
3. Stock and permitted alternate components of the drive train can have thermal barrier and friction
altering coatings applied.
b. Induction System

Kind of makes Kyle's more general point about ambiguity in the rule book. This section of the rules plainly covers the entire powertrain not just post flywheel. So I think that the bold italic underline words should be Power Train not Drive Train.

Assuming so, Level 1 carburetors MAY be modified in ways not specifically excluded.


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