Help with Production Limited Prep rules

D

ddewhurst

New member
On the spec line for a limited prep Production car the spec line states:

"Cylinder head prep per IT specifications except that head may be milled to achieve max compression ratio (I.e. no porting, stock valve job, no chamber mods)."

What is your understanding of "Cylinder head prep per IT specifications" ?

What is your understanding of "Stock valve job" ?

Thanks
wink.gif

David
 
Originally posted by ddewhurst:
What is your understanding of "Cylinder head prep per IT specifications" ?
Click to expand...

Port matching, stock valve job, mill to meet CR.

Originally posted by ddewhurst:
What is your understanding of "Stock valve job" ?
Click to expand...

As called out in the FSM. Many (if not most) FSMs call out the specific angles for a valve job, usually with some tolerance.


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George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com
 
David,

What GEorge said is pretty much it. If the FSM calls for a 3-angle valve job, that's what you get. If it calls for a 2-angle, that's what you get. My VW FSM (Bentley) has very detailed diagrams, w/ the angles, and the length of the surface covered by those angles.

As far as porting, you're allowed a 1" port match on the intake and exhaust side.

I'm curious as to why you're asking this. Are you getting rid of the Mazda?

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MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608
 
Geo & Bill, thanks for the info.
smile.gif


Second part of the question which comes from a conversation with a fellow racer. When the Production car "Lmited Prep" spec line has no mention or specification of the cylinder head valves does one then fall back to the PCS spec for valves? D.1.f.4 "Any metal valves meeting the specified head diameter may be used."

***Are you getting rid of the Mazda?***

Bill, shame on you for talking this way. The Mazda & my economic path run parallel. I have only raced onced this year. Kind of hit a wall or needed a stress free summer. Will you be at the Runoffs ? If so I'll see you at the Bergs deal. Do you have any idea how much a paddock on the asphalt costs?

Have Fun
wink.gif

David
 
The other difference is that in IT you can only remove enough material from the head to either reach a 0.5 increase in compression, not to exceed 0.025".

In LP Prod you can take as much off the head as you like as long as you do not exceed the spec line limit of compression for your motor. However that isn't the best way to make power....since pistons are free in LP, the preferred method is to keep the head as close to stock as possible and go with domed pistons to get to your CR limit.

The only area I have ever questioned is the 3-angle valve job (I happen to run the stock Honda configuration).....My shop manual does provide a very detailed description and diagram of the 3-angle valve job. I have been told that any dimension is an absolute minimum (i.e. weight) or an absolute maximum (i.e. track, valve diameter, bore & stroke, etc). So what happens in a 3-angle valve job? Do I use a minimum limit or a maximum for each 'angle' of the valve job? Am I non-compliant if I maximize the 1st & 3rd angle and/or section width, but minimize the 2nd angle and/or section width?
 
Tim, I do appreciate your responses. Back to my second post question. In the PCS spec line for IT cylinder prep if the cylinder head prep spec is for prep of the cast block & nothing on the spec line refers to the valves dose one go back to the PCS rule D.1.a.4 for the valves. "Any metal valves meeting the specified head diameter may be used." If that is a true statement what is the back-up to make it a true statement ?

Greg, on what page are the min/max dimension measurement rules taht you speak of ?

Have Fun
wink.gif

David

ps: It's fun to learn on this site without someone ripping the family THINGS out.
 
David, that's a good point. I'd stay with the the old line" If it doesn't say you can, then you can't". That is for IT as well as production.

I've been told that if I go with the 7mm VW valves instead of the 8mm ones, that I would be illegal. The smaller diameter would flow better, but how much bang for the buck are we actually talking about, with a LP VW head, with 40mm intake and 33mm exhaust valves, .420" lift cam, and 1" IT port/polish.

I don't think the cost of these valves and guides would be worth it.

Just my $0.02 worth



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Tim Linerud
San Francisco Region SCCA
#95 GP Wabbit
http://linerud.myvnc.com/racing/index.html
 
Originally posted by racer_tim:
David, that's a good point. I'd stay with the the old line" If it doesn't say you can, then you can't". That is for IT as well as production.

I've been told that if I go with the 7mm VW valves instead of the 8mm ones, that I would be illegal. The smaller diameter would flow better, but how much bang for the buck are we actually talking about, with a LP VW head, with 40mm intake and 33mm exhaust valves, .420" lift cam, and 1" IT port/polish.

I don't think the cost of these valves and guides would be worth it.

Just my $0.02 worth
Click to expand...

Yes, but if you go with the 8mm guides and valves with turned down stems, that IS legal since valves are "free" in the prod rules. You'll get the same benefit as smaller valve stems and guides.

MC


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Mark Coffin
#14 GP BSI Racing/Airborn Coatings/The Shop VW
Scirocco
Zephyr Race Coaching and Consulting
http://pages.prodigy.net/Scirocco14gp
 
Originally posted by racer14itc:
Yes, but if you go with the 8mm guides and valves with turned down stems, that IS legal since valves are "free" in the prod rules. You'll get the same benefit as smaller valve stems and guides.

MC
Click to expand...


Mark,

With all due respect, I have to disagree. While valves may be free in Prod, the l-p cars say IT prep on the head. The way I read that, is IT prep as it relates to valves. The mod you mention is not legal in IT, so I can't see it being legal on a l-p Prod VW (or any other car).


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MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608
 
When the spec line for a LP car states:

"Cylinder head prep to IT specifications except that the head may be milled to achieve max. compression ratio(I.e.no porting, stock valve job, no chamber mods)."

The rule dose not spec Cylinder head assemble or complete cylinder head.

I understand this spec line information to mean "bare cast head prep" (the rule written words reference is to machining/preparing the bare cast head) per rule ITCS D.1.l. this rule states nothing about valves. I find no other written spec for the IT "cast head prep".

Is this understanding of the rule correct ?

If this understanding of the rule is correct dose one then go to the PCS valve rule ? Any valve meeting the specified (stock) head diameter may be used with the FSM grind.

Have Fiun
wink.gif

David
 
Originally posted by Bill Miller:

Mark,

With all due respect, I have to disagree. While valves may be free in Prod, the l-p cars say IT prep on the head. The way I read that, is IT prep as it relates to valves. The mod you mention is not legal in IT, so I can't see it being legal on a l-p Prod VW (or any other car).
Click to expand...

Just my interpretation of course. In the ITCS, the rules do NOT have a separate clause allowing any valve w/ same head diameter, but the PCS does. If I were building a limited prep car (and I'm contemplating it) I would have no problem using valves of a different design than stock.

Rick Haynes recently said it best when he said, and I'm paraphrasing here, "some folks read the rules disadvantageously to themselves. That's why some folks win and some folks lose." My own personal philosophy is that if I can point to a rule or clause in the rules that permits me to do something, then I feel comfortable in doing it. If it's a loophole that the rulesmakers never intended, then it will be closed and I'll have to deal with it then. E.g. the thermal barrier ("plating or painting") rule in IT.

MC

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Mark Coffin
#14 GP BSI Racing/Airborn Coatings/The Shop VW
Scirocco
Zephyr Race Coaching and Consulting
http://pages.prodigy.net/Scirocco14gp
 
Let me get this straight. The Production rules say that you can use any valve. The Limited Prep rules say that you must use the IT-prep head rules.

I just don't see how you can make the argument that valve size is free within the confines of IT head prep.

What consitutes the head? The whole, fully assembled unit. The ITCS doesn't seperate each into it's own section.

The ITCS rules with regard to head prep are located at ITCS - page 11 D.1.L and ITCS page 12, D.1.P.

Guess what the latter says? "All engine components not otherwise listed in these rules shall meet specifications for stock parts. Where factory specification are absent or unclear, e.g., cylinder head thickness and/or combustion chamber deapth, etc., the Club may establish an acceptable dimention and/or allowable tolerance..."

You can't cherry pick from both rule sets unless I am missing something specific.

AB

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Andy Bettencourt
ITS RX-7 & Spec Miata 1.6 (ITA project)
New England Region R188967
www.flatout-motorsports.com
 
Andy, Mark, Bill, following is the specification from a LP spec line in the PCS.

"Cylinder head prep to IT specifications except that the head may be milled to achieve max. compression ratio(I.e.no porting, stock valve job, no chamber mods)."

The rule dose not spec Cylinder head assemble or complete cylinder head.

I understand this spec line information to mean "bare cast head prep" (the rule written words reference is to machining/preparing the bare cast head) per rule ITCS D.1.l. this rule states nothing about valves. I find no other written spec for the IT "cast head prep".

Have Fun
wink.gif

David
 
Andy,

By that logic, and OHC car could not legally install a different cam with alternate lift & duration, since the cam is installed in the head, but a pushrod motor could since the cam is in the block.....

I'm with Mark & David on this one, in that the head prep is refering to a bare head assembly. Valves are 'free' in Prod, but the size is still specified in the PCS.

[This message has been edited by Greg Gauper (edited August 25, 2004).]
 
Tim,

Yes I know it is defined (it's actually page 10, not page 9). I was trying to make a point about Andy's argument which (I am assuming) he interpetted to mean that since the valves are part of the head and the head is to be prepped to IT rules that you have to run stock valves in spite of the fact that D.1.f.4 (page 11) states any valve may be used. I was merely stating that by Andy's reasoning, you couldn't change the cam in an OHC motor either because it's part of the head assembly and IT prep rules don't specifically permit an alternate cam. I myself do not agree with this interpretation.

And I still stand by the interpretation that the cylinder head prep rules as they pertain to limited prep production cars refers to the bare cast head prep. Further, it states any valves meeting the specified head diameter may be used, any valve springs, any valve guides, and any cam (meeting the LP specs for maximum lift), so Mark's idea is legal.

[This message has been edited by Greg Gauper (edited August 25, 2004).]
 
Mark and Greg, maybe this discussion needs to be on the prod site instead of the IT site.

Mark, I have heartburn with stating that valves are "free" in Limited Prep, that you can "turn down the stems". I don't think that this goes with the intent of the Limited Prep head prep per "IT" specs.

Yes, the head is different than the valves, but which rule takes priority?

I take "IT head prep" to mean that you can't do more to the valves than a stock valve job.

Tim
 
Great thread guys! Keep going.

Right now I am leaning towards the logic of the valves not falling under the IT head prep rules as the cam example sets a precedence.

But.....at first I assumed the opposite. Great out of the box thinking.

I am though unfamiliar wiht Prod rules Is it fair to say that a prod car can run non stock valve sizes that are listed on the spec line, and a cam that is non stock but meets specs and so on?

If so, the LP rules appear to limit valve size to stock, while allowing other specified changes.

I suspect this is a letter of the rule legal mod.

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Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]
 
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