9 replies to this topic

[powerss]

Is this a correction or a change that presents a performance improvement opportunity?

 

 

Spec Miata

1. #10358 (SM Committee) Increase throat depth allowance on 1.8l heads

In section 9.1.7.C.1.f.4, change the maximum throat depth column specification in the table for 1.8l engine as follows:

9mm 12mm

Move the table from section 9.1.7.C.1.f.4, to 9.1.7.C.1.f.3.

[Tom Sager]

It's a conspiracy to once again put the 1.6 back in its' place 

[Dan Tiley]

Yes it's a conspiracy to squash the 1.6L forever!

 

No really, I'll take (part) of the "blame" for this rule change.  I measure the FACTORY plunge cut depth of every port in every cylinder head I build.  Out of 12 heads, I had 4 heads that had at least one port that was cut from the factory greater than 9mm before I had even started cutting!  I even had a couple outliers that were as high as 14mm.  In the SMAC committee we decided that it made sense to open the 1.8L plunge cut depths to the same value as the 1.6L due to the high probability of someone being falsely found non-compliant for running factory equipment.  

 

Here is a sample photo of a factory (unmodified) head with a plunge cut greater than 9mm.  This one happens to be 11mm.  Before this rule change I could not use this head even though it was completely fine in every other way.  

 

[Jim Drago]

Is this a correction or a change that presents a performance improvement opportunity?

 

 

Spec Miata

1. #10358 (SM Committee) Increase throat depth allowance on 1.8l heads

In section 9.1.7.C.1.f.4, change the maximum throat depth column specification in the table for 1.8l engine as follows:

9mm 12mm

Move the table from section 9.1.7.C.1.f.4, to 9.1.7.C.1.f.3.

 

This change was made to include so many of the heads that were non compliant from Mazda. The change replicates the existing rule in the 1.6 heads. 

 

I have many calls about " do I need to send my head back to be updated" ABSOLUTELY NOT! There is no gain going down the 12mm, if anything it is detrimental as it slows the air charge. However it does make many of the heads usable that were not before. Also, the heads are no longer available new, so we only have what is out there right now.

Jim

[Dan Tiley]

This change was made to include so many of the heads that were non compliant from Mazda. The change replicates the existing rule in the 1.6 heads. 

 

I have many calls about " do I need to send my head back to be updated" ABSOLUTELY NOT! There is no gain going down the 12mm, if anything it is detrimental as it slows the air charge. However it does make many of the heads usable that were not before. Also, the heads are no longer available new, so we only have what is out there right now.

Jim

Agreed... I have my custom SERDI tooling is still set to only cut to the 9mm depth, and I've known this change was coming since November  (REF TOPIC: The dreaded tech shed – PASS / FAIL tooling that we can all use and understand).   When you start going deeper you just end up cutting a big pocket in the runner which would actually hurt performance.

[Johnny D]

Any comment on Rob B's rewrite of "Race Starts" ?

J~

[Rob Burgoon]

Any comment on Rob B's rewrite of "Race Starts" ?

J~

 

 

The new version may have been inspired by my letter, but it sure doesn't resemble anything I wrote.

[powerss]

This change was made to include so many of the heads that were non compliant from Mazda. The change replicates the existing rule in the 1.6 heads. 

 

I have many calls about " do I need to send my head back to be updated" ABSOLUTELY NOT! There is no gain going down the 12mm, if anything it is detrimental as it slows the air charge. However it does make many of the heads usable that were not before. Also, the heads are no longer available new, so we only have what is out there right now.

Jim

 

Sorry I asked.

 

 

Thanks Jim that was the answer I was looking for.

 

Steve

[fishguyaz]

if these changes dont effect performance, AND I dont need to spend the $ to replace the head i just bought last year; then why are people complaining?

[Jim Drago]

I killed anything that didn't have to do with the topic. I will start another parity thread for you guys to play with

Jim