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#1
Johnny D

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#2
Jim Drago

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There was no need for the .040 debur on edge of combustion chamber other than to cover what others were already doing.. Oh well, it is there now.
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#3
Andrew Stowell

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I might be the only one to autocross my spec miata, but if you do, note that they want to delete the section that classifies spec miata in DSP.

 

 

Street Prepared

#16443 Touring Car Clarification

 

he following rule change proposal, effective 1/1/2016, is provided for member review and comment. Delete the following paragraphs from Section 15 Street Prepared introduction:

 

Cars listed as eligible in and prepared to the current Club Racing Improved Touring (IT) rules are permitted to compete in their respective Street Prepared classes. Neither Street Prepared nor Improved Touring cars are permitted to interchange preparation rules. Improved Touring cars may use tires which are eligible under current IT rules even if they are not eligible in Street Prepared.

 

Cars listed as eligible in and prepared to the current Club Racing American Sedan (AS) rules are permitted to compete in Street Prepared class B (BSP). Neither Street Prepared nor American Sedan cars are permitted to interchange preparation rules. American Sedan cars may use tires which are eligible under current AS rules even if they are not eligible in Street Prepared.

 

Cars listed as eligible in and prepared to the current Club Racing Touring category rules are permitted to compete in their respective Street Prepared classes. Neither Street Prepared nor Touring cars are permitted to interchange preparation rules. Touring cars may use tires which are eligible under current Touring rules even if they are not eligible in Street Prepared.

 

Cars eligible for the current Club Racing Spec Miata rules are permitted to compete in Street Prepared class D (DSP), with the additional allowance that they may use any size of any tire which meets the requirements of 15.3 and fits on the Spec Miata compliant wheels and within the compliant bodywork. Spec Miata cars in DSP may not intermix use of the Spec Miata and Street Prepared allowances. The competitor is responsible for being in possession of the Spec Miata rules and for proving that his/her car conforms to the rules.

 

Cars listed as eligible in and prepared to the current Club Racing B-Spec Regulations are permitted to compete in their respective Street Prepared Classes. Neither Street Prepared nor B-Spec cars are permitted to interchange preparation rules. B-Spec cars may use tires which are eligible under current Club Racing B-Spec rules even if they are not eligible in Street Prepared.

 

Note: The SPAC and SEB have become aware of the changes to the scope of modification allowed in Club Racing’s Touring category. The modifications now allowed in Touring represent a significant esclation, well beyond the intent of the allowance for Touring cars to compete in their respective Street Prepared classes. This exemplifies the risk of providing “crossover” allowances such as these, which create dependencies on the GCR and may result in unintended competition impacts. For this reason, the SEB is proposing to remove these allowances from the category.

 

I already wrote a letter. If you autocross, I'd suggest you do the same.

 

The SCCA annoys me with the way they change rules. It feels like if you want a straightforward change that most people want, you ask for year after year, till you're blue in the face, then maybe they'll change it.

 

But if someone on the board find a rule and doesn't know why it's there, "Hey, let's change it right away!"

 

They could at least try to rewrite the section to properly class as many club racing cars as they can. It really annoys me they just want to delete the whole section instead.



#4
OctaneNation

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What's with the change in min head thickness? I couldn't find any background info on this change.



#5
Brandon

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There was word a number of heads were not compliant solely due to exceeding the minimum thickness requirement.

 

A thinner head is ultimately not a "performance improver" (as you apparently lose timing on the cams or something with them being closer to the crank) and in conjunction with the compression numbers spec'ed there's an appropriate check on too much C/R.  Besides, if you're shaving a head and don't perform a proper CC'ing (or accurate C/R calculation) of it afterwards...well...it's on you.


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#6
James York

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 (as you apparently lose timing on the cams or something with them being closer to the crank)

 

Known or unknown impact?


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#7
Jim Drago

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The min thickness rule was implemented in 09 or so due to an advantage gained by cutting the heads very thin and unshrouding the valves. The chambers were starting to look like clover leafs. I don't think there is much difference in this most recent change in min thickness other than it will allow some heads to be saved one more time that would have otherwise been unusable.

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#8
Brandon

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James,

I'm not sure if you edited it or if someone else might have but I appreciate the removal of the 'attack' levied against my knowledge about engine specifics.

 

But to answer the question (now deleted), I'm not an engine builder but can quickly grasp the concepts associated with various recommendations (lift, duration, overlap, timing in general) and it was explained on our call that month how cams being 'closer' to the crank can affect camshaft timing (retarded I believe - aka no performance advantage).  I agreed with what the other experienced builders on the committee were explaining and agreed reducing the minimum head thickness would not be a performance advantage while allowing a greater number of heads to be used which would otherwise be unusable.

 

I might be giving away 'internal deliberations and/or debate' of the SMAC but in this case I think it's allowable.   :burst:

 

Thanks,

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#9
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Brandon, I'm not an engine builder either and I do understand the item similar to you.


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#10
OctaneNation

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it was explained on our call that month how cams being 'closer' to the crank can affect camshaft timing (retarded I believe - aka no performance advantage).  I agreed with what the other experienced builders on the committee were explaining and agreed reducing the minimum head thickness would not be a performance advantage while allowing a greater number of heads to be used which would otherwise be unusable.

Cam timing definitely gets retarded when milling a head. This moves the power band up in the RPM range, so I'm curious how it was deemed 'no performance advantage'. See end of page of http://www.solomiata.com/cams.html

 

But if an engine was already at the max CR with a cylinder head the only way to salvage the head without exceeding CR would be to use another block that hasn't been cut.



#11
chris haldeman

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Octane. Wouldnt you think a head gasket with added thickness too make compression would be smarter? Gaskets are open and often shims are juggled around too get proper compression.
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#12
Brandon

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Cam timing definitely gets retarded when milling a head. This moves the power band up in the RPM range, so I'm curious how it was deemed 'no performance advantage'. See end of page of http://www.solomiata.com/cams.html

 

But if an engine was already at the max CR with a cylinder head the only way to salvage the head without exceeding CR would be to use another block that hasn't been cut.

 

"No performance advantage" was due to their being a max compression rating for all engines - that's the 'check' for having a head at the min thickness and still permitting the block to be decked.

As Chris notes, head gaskets and shims and such are allowed to reduce the CR to the level the builder desires.

 

Regarding the retarding of timing and it being a performance advantage: that is an accurate statement but as I understand it there's nothing we can 'tech' to prevent this from being done so it wasn't addressed.

 

Again, I'm not a builder so I'm having to take the word from those on the SMAC who are builders to comment accordingly.


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#13
38bfast

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just for reference brining the cams closer to the crank alters timing in a less than desirable performance.


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#14
Jamz14

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just for reference brining the cams closer to the crank alters timing in a less than desirable performance.

Why? And can it not be corrected with additional advancing of the timing?


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#15
Steve Scheifler

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Mechanical timing (valves open relative to piston stroke) is different than ignition timing (spark relative to pistons).

Better or worse depends on various factors but Ralph is saying that in our case generally worse. If the power band shifts to a higher RPM where the engine is already flow limited, then I may loose more torque/power at the lower end than I gain at the top for less total useable power.
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#16
Jamz14

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Mechanical timing (valves open relative to piston stroke) is different than ignition timing (spark relative to pistons).

Better or worse depends on various factors but Ralph is saying that in our case generally worse. If the power band shifts to a higher RPM where the engine is already flow limited, then I may loose more torque/power at the lower end than I gain at the top for less total useable power.

Thanks Steve. Couldn't the mechanical timing be modified by one tooth on the cam gears to adjust for this? Is shaving thousandths of an inch really enough to modify the mechanical timing that much?


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#17
Jamz14

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Hmmmmm. I always become a bit suspicious when the mechanics fall quiet.


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#18
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Hmmmmm. I always become a bit suspicious when the mechanics fall quiet.

I hate to go there, but Ralph, Jim and Steve concur. Info from 3 out of 3 mechanics is not good enough??? 


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#19
chris haldeman

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I'll answer so your not scared :-)
No matter how you get too legal compression the cam timing will be the same. Aka deck head,deck block, adjust gasket thickness ect. Honestly there is no need for a min. Head thickness anymore. Years ago before the piston part numbers were spec'd people built 1.6 cars with auto pistons that were lower compression then decked the head a lot too get too legal compression. The gain was unshrouded valves and retarded timing. Both good for the 1.6 but useless on the restrictor plate motors. Now pistons are spelled out in rules and that can no longer be done. The 1.6 auto pistons were lighter and ran a thinner oil ring also providing a gain
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#20
Mike Collins

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The automatic 1.6 rods are lighter too....


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