East Tennessee Region SCCA

So, does anyone know the details on the dust up about heads in Spec Miata?

I've been getting e-mail from Mazda Motorsports about it, but I'm not involved so I don't know what they're talking about. Just curious.

Other internet rumors....said it was vague rules, will be corrected for next season, those heads will returned to the owners and also will be legal for next year.

The issue for Spec Miata heads are the specific GCR rules regarding 'plunge cut' machining below each valve seat. These rules were 'clarified' a few years ago, with these 2 paragraphs focused on the plunge cut:

3. The throat area of the port consists of the 90 degree angle at the very bottom of the cast steel valve seat as it transitions to the aluminum casting below. It is permitted to plunge cut the throats in order to correct for core shift that is commonly found in many cylinder heads. This cut cannot extend further than the specified number below from the bottom of the ferrous valve seat. There can be no tooling or machine marks in the head below this point. The area under the seat where the plunge cut ends and the casting resumes cannot be blended by hand, machined, or chemically processed to create a smooth transition. The 90 degree bend at the bottom of the valve seat and the aluminum directly below it will be measured with a gauge and must conform to the maximum diameters and depths listed below.
Engine Maximum Intake Throat Diameter Maximum ExhaustThroat Diameter Maximum Throat Depth
(inches) (inches) (from bottom of ferrous valve seat (millimeters)
1.6L 1.095 0.948 12
1.8L 1.178 1.020 12

4. No aluminum in the bowl area (other than that specified for the plunge cut) or the ports may be removed, added, or manipulated for any reason. It is understood that heads may look slightly different from bowl to bowl due to casting irregularities. 3. The throat area of the port consists of the 90 degree angle at the very bottom of the cast steel valve seat as it transitions to the aluminum casting below. It is permitted to plunge cut the throats in order to correct for core shift that is commonly found in many cylinder heads. This cut cannot extend further than the specified number below from the bottom of the ferrous valve seat. There can be no tooling or machine marks in the head below this point. The area under the seat where the plunge cut ends and the casting resumes cannot be blended by hand, machined, or chemically processed to create a smooth transition. The 90 degree bend at the bottom of the valve seat and the aluminum directly below it will be measured with a gauge and must conform to the maximum diameters and depths listed below.
Engine Maximum Intake Throat Diameter Maximum ExhaustThroat Diameter Maximum Throat Depth
(inches) (inches) (from bottom of ferrous valve seat (millimeters)
1.6L 1.095 0.948 12
1.8L 1.178 1.020 12

4. No aluminum in the bowl area (other than that specified for the plunge cut) or the ports may be removed, added, or manipulated for any reason. It is understood that heads may look slightly different from bowl to bowl due to casting irregularities. No material may be removed or added from the short turn radius in the port.

At the Runoffs a competitor filed a protest against 9 of the top 10 qualifiers (the protestor was one of the top 10), based on the last sentence in section 4 above. Teardown for the protest occurred after the SM race, and 8 of the 9 protested engines were found to be illegal; 6 of these cars were the top 6 finishers on track so they were penalized to the rear of the field & finisher #7 became the champion (but did not have to go to impound for teardown because only the top 6 finishers are impounded).

The basic dispute is over the smoothing the sharp edge near the intake/exhaust ports created by machining the plunge cut. Several major SM engine builders were involved in creating the rules and they contend that a deburring operation is implicitly allowed to 'clean up' the sharp edges; however, the last sentence in section 4 specifically states that 'no material may be removed or added from the short turn radius in the port' and those penalized were judged to be in violation of that sentence - apparently the violators did not do a blatant 'smoothing or blending' as prohibited in #3, but did do enough cleanup that material was removed in the short turn radius area. Word is that smoothing the flow in this short turn radius delivers some torque improvement at mid-range RPM which would be a significant advantage in accelerating a Spec Miata out of corners.

Looks like Mazda is concerned about the negative publicity from having 6 top finishers penalized, and
there are statements going around that as many as 750 heads may now be 'illegal'. However, many regional Spec Miata racers are being very vocal that they should not have to pay for 'pro head machining' to be competitive regionally. So, it will be very interesting to see if the 'rules clarification' that is definitely coming in the near future makes the illegal heads ok and therefore raises the $$ bar for many SM racers - or whether the powers that be will try to reign in the rising costs of competing in SM.

Dick Hancock
#39 ITA '92 Miata

What kind of power is it worth?

thrdeye wrote:What kind of power is it worth?

.25687 horse powers.

I mean.. it does help coming out of the corners.

John Brown wrote:

thrdeye wrote:What kind of power is it worth?

.25687 horse powers.

I think that's what my car makes.

JB, you running a spec mistake engine?

Sent from my SPH-L710 using Tapatalk

Meant Miata.

Sent from my SPH-L710 using Tapatalk

Over the last few years the '99 & up NB's in Spec Miata have gone from low 120's hp at the rear wheels to around 130 - combination of head work & adjustable fuel pressure allowances. SM's have to use a stock intake between MAF & throttle body, no porting work allowed, stock exhaust manifold, stock ECU, etc - 1.8's have to use a specified restrictor plate. Word is that the next round of research & improvements with make the VVT motors the 'have to have'

Dick

I thought I read that the protest was based on qualifying … and the protester was qualifier #12 … and that the protest was followed up on after the race, rather after qualifying

Of course JB has a cheater SM head!

I'm surprised VVT hasn't been the 'have to have' engine for years now. They've been so dominate in NASA that they've penalized them quite a bit. All that power under the curve!

integra55 wrote:I thought I read that the protest was based on qualifying … and the protester was qualifier #12 … and that the protest was followed up on after the race, rather after qualifying

The name on the protest was Will Schrader - 9th place qualifier. Schrader is from Oregon, and word is that a group of Pacific NW racers put up the $14k bond needed for 9 teardowns. There wasn't enough time (less than 1 day) between final qualifying and the race so scrutineers did some paint markings on bolts after qualifying to 'seal' the engines until teardown. Erik Stearns was the 12th place qualifier who finished 7th on track and moved into 1st after the penalties - he was never called to impound and therefore had no post race inspection for compliance...

Dick

I think its great to see this.. I wish the same "OLD" tactics happened at SOLO Nats !

I like to see racers have some balls! and not just take what given to em....

DickCDawg wrote:

integra55 wrote:I thought I read that the protest was based on qualifying … and the protester was qualifier #12 … and that the protest was followed up on after the race, rather after qualifying

The name on the protest was Will Schrader - 9th place qualifier. Schrader is from Oregon, and word is that a group of Pacific NW racers put up the $14k bond needed for 9 teardowns. There wasn't enough time (less than 1 day) between final qualifying and the race so scrutineers did some paint markings on bolts after qualifying to 'seal' the engines until teardown. Erik Stearns was the 12th place qualifier who finished 7th on track and moved into 1st after the penalties - he was never called to impound and therefore had no post race inspection for compliance...

Dick

ok … sorta what I'd heard … if the 7th place finisher had finished higher, would he have been part of the protest, (since he wasn't named in the original protest) … i.e. would he have been torn down ?

disclaimer: no dog in the fight … really just curious