11 replies to this topic

[AW33COM]

There are gazillion posts about what happened lately, but not a single post explaining why the porting (short side radius porting) was done in the first place, what are the advantages, if the porting makes sense with a restrictor plate, does it make sense to search for a "good" head now?, and etc.

I'll submit short explanations for the most common questions that I see.  No politics, just technical stuff:

 

1.  Why port short turn radius?
Amount of air flowing through the port is affected by the angle/curve of that very turn.

2.  What are the advantages?
Intake port has two sections if you will: long turn, and short turn.  Most of the air goes through the long turn, but short turn is also critical (especially if it's not correct).  At high RPMs (race conditions) air going through the short turn will "stop" hugging the wall if the wall is not smooth/wide enough (drop off from the plunge cut, or sharp turn).  Air at high speed will separate itself from the wall as aerodynamics come to play.  This separation restricts air flow into the cylinder.  The advantage is simply more air.

 

More air is one, another important thing is how the air flows.  That's where WET head flow test comes into play.  During this test engine builder uses dye to see how the air/fuel mixture flows, when going to the cylinder.  This is a very important part of performance engine building.  It's possible to port the intake and get little of no performance, due to bad mixing.

3.  Does STR porting make sense with the restrictor plate?
Absolutely.  Use your own brain here.  You have X amount of air going through the plate.  With a sharp turn on the short side radius your car has another invisible restrictor at high RPMs as the air separates, and the intake is chocked.  So, from X amount of air after the plate, you end up with X-1% (I made that up) in your cylinder, as you have 2 restrictors.   Cars with restrictor plates, and correctly ported STR will have advantage over other cars with restrictor plate, and no STR porting.  The restrictor is irrelevant, because the STR choke happens past the restrictor plate.  I hope this is clear.

4.  Does searching for a good flowing head make any sense?
Technical yes, since engine casts are a bit different, but the gain you will find from head to head will be much, much less, than the gain from STR porting.  It makes more sense to look for a good cylinder head as oppose to allow one or two engine builders have the best engine at the races.  Now, anybody can look for a strong cylinder head.  More parity.

5.  Does STR porting show gains on the Dyno test?
Yes.

6.  Can you have a cylinder head that shows no machine work and still have different STR?
Yes.  SCCA/NASA must learn how to test for this one, even if the head seems stock.  
** don't ask about this one **

7.  If the STR porting is so great, how come street cars don't have it?
Street cars do not spend most of their time running at 5000-7000 RPM.  As a matter of a fact, porting the STR will make your low end weaker, but your top end stronger.  Something you don't want on the street, but you need it at the track.

8.  Do you need wet cylinder head flow test in order to see how the air flows?
Not really.  These days, good flow simulation software can do the trick.

9.  Was the porting of the STR an innocent act to file down few sharp pieces after the plunge cut?
No.  STR porting is engine building 101.

 

10.  Was there difference between STR porting jobs in SM? 

Accoriding to the Anoucement, cylinder head STR porting was uneven from cylinderhead to cylinder head.  This could be the sole reason why SM is going to stock heads.  There is no way of balancing the cars if they all have different head jobs.   Even if Dyno shows same max HP for 2 cars, the curves could be different resulting in cars being uneven at different RPM intervals.

 

11. My cylinder head is not blended, not ported, no deburring, but it has a plunge cut, why do I need to change it?

The plunge cut could be done in such a way that it would cut into the STR and modify air flow.  Again, different plunge cuts from different builders, or from the same builder. How do you test/tech them and balance them all? You can't. 

 

12.  Do STR ported 1.6 cars have advantage over 99 STR ported cars with restrictor plates?

NO.   Relatively speaking the same amount of air flows through the air filters (1.6 and plated cars) regardless of STR porting or not. 

 

This write up is not all, but should be good enough to fill the void, and stop people writing non sense.  As you can see opening up cylinder head rules in SPEC racing is tricky.  I have a feeling SCCA/NASA/Mazda had no choice.

 

[Karl]

Nice, but a few questions:

 

4.  Does searching for a good flowing head make any sense?
Technical yes, since engine casts are a bit different, but the gain you will find from head to head will be much, much less, than the gain from STR porting.  It makes more sense to look for a good cylinder head as oppose to allow one or two engine builders have the best engine at the races.  Now, anybody can look for a strong cylinder head.  More parity.

 

What are you saying here?  More parity through parts bin blueprinting (searching and flowing and testing until you find the best one?)  If so, you are just plain wrong.  Many of us embraced the crate motor early on and HAD to depart from it since we saw too much variation.  

 

7.  If the STR porting is so great, how come street cars don't have it?
Street cars do not spend most of their time running at 5000-7000 RPM.  As a matter of a fact, porting the STR will make your low end weaker, but your top end stronger.  Something you don't want on the street, but you need it at the track.

 

I find this misleading.  Our dyno testing, which typically looks at 2000 RPM and above, showed NO loss with STR blending.  The curves simply continued to diverge, but there was no crossover as you suggest.  Mazda don't blend because its an extra cost, but you can speculate that they understood the problem, because the NB casting is clearly better and more consistent post machine work.

 

6.  Can you have a cylinder head that shows no machine work and still have different STR?
Yes.  SCCA/NASA must learn how to test for this one, even if the head seems stock.  
** don't ask about this one   **

 

This is EXACTLY what we need to be talking about.  Why learn to test for it?  ALLOW IT and the complaints go away.  Which takes me to this....

 

10.  Was there difference between STR porting jobs in SM? 

Accoriding to the Anoucement, cylinder had STR porting was uneven from cylinderhead to cylinder head.  This could be the sole reason why SM is going to stock heads.  There is no way of balancing the cars if they all have different head jobs.   Even if Dyno shows same max HP for 2 cars, the curves could be different resulting in cars being uneven at different RPM intervals. 

 

Again, misleading.  First, the differences will go away if this modification becomes legal.  Some just pushed a little more than others as they passed more and more inspections, the newer guys on the block might not have been so comfortable going that far.  Second, leaving all else the same in a head, there are no meaningful torque curve changes that STR modifications (removal of material in varying amounts) will produce.  Meaningful for me is 3 ft*lbs or more from 3500 to 5000.    

 

I stand by this:  The STR blending is the cheapest and easiest way to power parity.  I wish the suggested penalty weights for the cars with the modification would stay around for at least a couple of years AND be allowed at the 2015 Runoffs.  The data would be very valuable to the masses who look on.

[Karl]

I wrote up a big post on 6 above, but I'd rather see all of you ask about these secrets and then post "the word on the street"

 

Don't fear the pithy replies here and by all means if someone is telling you behind the scenes that what you read here is BS, ask for clarification.  Honest, open debate is good, poisoning the well behind the scenes serves only those who do so.

[Steve Scheifler]

Yea, I don't get the "don't ask" note after 6, and most of the above is fine but totally generic web search results and not quantifiable in our context without direct testing.

But Karl, you can bring me over to your side easily with some facts. The key being, IMO, quantifying:

- the differences in power between stock heads
- the gains from re-plunge only on a "bad" head and a "good" head
- the additional gains on each with your proposed rules applied by someone with all the tools of the trade at their disposal to optimize the work (and ability to use them)
- the additional gains by someone following a written how-to guide but no access to a flow bench or other optimization options

With that, an informed decision could be made AND justified.

[scott sanda]

   

 

I stand by this:  The STR blending is the cheapest and easiest way to power parity.  I wish the suggested penalty weights for the cars with the modification would stay around for at least a couple of years AND be allowed at the 2015 Runoffs.  The data would be very valuable to the masses who look on.

 

When the head is ported by an engine builder, with access to flow bench and dyno, to a level no non professional builder can ever acheive.

 

There, I fixed your statement for you.

[AW33COM]

Karl, I was not taking any sides in the post, and I don't disagree with you.  If the porting is the same from car to car, then all is great.  Problem is 80% of the cars have unspec porting, and there are only 2 ways to fix it:  either re-port them, or buy them stock. 

[pat slattery]

Karl I am assuming to talking about EDM process on heads.  We have that problem with engine builders using this and with it done well it is very hard to tell.

[chris haldeman]

Please??? Only an idiot would want too change the current rule

[Andrew Charbonneau]

Please??? Only an idiot would want too change the current rule

I want change guess im an idiot

[chris haldeman]

Andrew you don't want change too the current rule!!! Like most you just think you do :/)

[FTodaro]

This is a problem that in my view will me impossible to police. Plunge cut heads will have variances and so will stock heads, they will not look the same from head to head either. There will be no template  to follow only individual judgment. The problem will be the same plunge cut or stock.

[greengreengreen]

I can teach all about EDM (Electro Discharge Machining).  We have one of the most advanced machines in the country.  If someone will send me a message regarding the quickest way of adding pictures I can give the 101 201 and 301 of EDM.

 

Also of interest would be the process used for applying texture to a metal surface.  Think about the texture to the panels inside your car.  We are the primary refurb facility for the Toyota plant.  It could be done to ports as well.

 

If there is interest I can start a new thread.