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Restrictor Plate sizing for 2020

Xavier C.

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Based on the all the data I have accrued over the years, I've been seeing some trends. Primarily in the world of nb1 versus of nb2.

Before, the logic of the nb1 vs nb2 was the nb1 had more power less, torque whereas the nb2 was the opposite. However, it has become obvious that the nb2 has become a more favored car because (overall data), the nb2's are making more power AND more torque. I am taking feedback at the idea of giving the nb1 a MINOR bump in power. My intent is to do some testing to see what a "not-overdog-creating-change" would be. I will be testing a 39mm, 40mm, and so on. 

I am looking for constructive feedback on this topic. I am not looking for "magic motor" scenarios (we all have at least one in our regions). These are trends based on years of dyno runs at championship events, east and west coast pulls.

Edit: the idea of making the nb2's smaller may be of discussion also. From what I've heard, the na's are almost unable to reach the 99's. 

Thank you for your feedback.


Edited by Xavier C.
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I mean, in our region the NB's and 1.6's are pretty much crushing the NA8 cars we have. Though our sample size leaves a lot (all?) open for driver mod and car prep. So shuffling the top dogs isn't a concern or mine.

My vote is still drop NA8's back do
wn to 2350. Then enforce a LOW horsepower cap so us guys without pro motor budgets can still be competitive on horsepower tracks... (but yes, I know that's a pipe dream and a total departure, but what was this class supposed to be about again?)

In the greater picture, would this change be in combination with or as a break from "the other club"? I still think equal rules allowing crossover between clubs should be Paramount (and hopefully they'll come to their senses on tires and ditch the moneypit hoohoos, Hell... I'd vote the whole class run on 200tw tires). Not that we have a lot of crossover guys in our region, but we're working on it...

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Thank you for your input. Your comment is spot in regarding driver mod and prep. In this area outliers will always exist and it's an incredible balancing act. The SMAC was spot on with the changes they set forth with the na6. 

The na8 discussion is interesting. It would seem your region and the West coast favor the na's. Hence the reason for the edit. Regarding your comment about the dyno, I get it but there is already a racing class revolving around power:weight. 

Regarding working with the scca. Communications with the smac have improved. I understand the weight of these decisions and do not take it lightly. NASA has years of dyno plots that I have shared with the competitors who competed at those events and the trend is clear.

As far as tires I agree with you there. But I'll admit I'm biased in favor of Toyo so I won't comment much further on that. 


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I don’t know how this doesn’t ultimately come down to dyno. There are so many variables with regard to build, driver, track, prep, etc. Track times are subject to the balance of torque vs horsepower, e.g. VIR vs summit point, etc.
With all of the variables, your plan of adjusting restrictor size seems the most expedient.

How about checking with Drago our Rossini or other builders? They could probably offer excellent perspective, not only from a performance aspect, but also a cost to be competitive perspective on each version. 

Edited by dadasracecar
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To be perfectly honest, lots of us are on tight budgets and NA8's are cheaper because they're underdogs, so that's why we run them... I hear you on there already being a dyno class... but I don't quite think it's a proper analogy. SE30 seems to do well with it. Keep our engine rules but cap HP at a reasonable number not too far off from a VERY good junkyard motor. I'm just frustrated at the never ending engine builder arms race as the builders find new creative ways to squeeze more hp out of these things and leave us junkyard takeout guys further in the dust. 

sorry, I know you weren't looking for my opinion to completely change a huge part of our entire class, carry on. ? 

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Xav, I have always found you to be a very fair guy, both on the tack and off.  I have no idea how many people frequent here so maybe this should be posted on FB and MR.com???I have a few points of view I would like to share with you as follows:


First as proved at Mid ohio your dyno methods are not fool proof, I did nothing to defeat your dyno test and my car was easily as strong as the car that won the race. So basing decisions off dyno results IMO are not the best way, none of us race on dyno's we all race on the track and in the tech shed!


Second we currently have most of the talented drivers racing in vvt's IMO there is two reasons for this.  First if your building a new car and money is not and issue which for most front runners in the class it clearly is not, why wouldn't you build the newest model available at the time of build?  Second the last two national races are on tracks that clearly favor the vvt, both Mid ohio nasa 2019, and Vir scca 2019 championships races are vvt tracks in most competitors minds.


Third, I know of many front runners that will be building new 1999-2000 model cars for 2020, why because it will give them the best chance to win at Road America where the vvt falls flat on its face in 4th and 5th gears once it reaches 6500 rpm and having longer straights favor the 1999-00 in that rpm range.


What will you do once you have taken away from the vvt and all the most talented guy now have 1999 cars and are all winning in the 1999 then will we be discussing taking something away from them?  The vvt is winning because the talent that is driving them, not because of the car itself.  If you put all those same drivers in a 1999 and rerun the scca runoffs the same 7-8 guys will still be at the front of that group, I guarantee you that.


Currenty and for the last few years we have had the absolute best and tightest racing we have ever had in SM since I began in 2010. why even monkey with that? we have the least amount of people discussing parity then we ever have in history yet you seem to believe we need a parity adjustment.  

In the name of transparency. I own a 2000, a 2002vvt, and a 1.6... I can race any car I want to and all are prepped to the max. all dyno at the top of the charts on the ESR dyno, all at completely legal.  Why do I have 3? for one thing I'm nutts! but I also wanted to have the best car for the track that I am going to be racing at.  


If Nasa and scca are really interested in true parity we need to mandate one model engine, and one subframe model for all model cars and have competitors to swap wire harness and engines and subframes so this constant juggling will go away.  and before people scream bloody murder this was done with SRF and it sure looks to me their numbers of participation have only grown since they forced a big $$ upgrade on competitors. 


Flame away, and no the 94-97 does not need any help it as fast as any other car out there, but nobody that has the talent to win the championships has one or is prepping one, end of discussion!



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  • 1 month later...



Agreed the Toyo RR should be the race tire. Great sponsors are tough to get and Toyo has been fantastic with their timely contingency for the competitors and they appear to be great to NASA as well. There are other power/weight categories which give compensation for higher tread wear vs stickier tires so for those who cant spend the money for the race tire they can still compete in the other categories.  

You may have dyno sheets showing that the NB2 has some slight advantage. If warranted as per your concern, then the change should happen.

In our region I do not see a distinct advantage, maybe all our drivers just need to be better.



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  • 2 weeks later...
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Hi Xav, 

I'd like to add a few comments in the hope that they will be constructive and helpful.

If we want to equalize the cars, I'd suggest having one year as a control to the experiment. I think that car should be the NB1. Because so much time and attention was paid to correcting it when it was the overdog, its performance should be the benchmark for the class. Adjust the others to be equal with the NB1 to avoid the see-saw adjustment phenomenon Kwebb mentioned in his fifth paragraph. 

If the NB2 is now looking like the car to have because it is a VVT engine, then adjust its restrictor plate or its weight, but not both. For the record, I don't think we should add weight to them. They're already the heaviest in class. Adding more weight will be a detriment to tire wear during a given race, and could be rightly construed as unfair. That points to the restrictor plate, which I think is probably the way to go in correcting any discrepancies in performance. Test to verify. 

The NA 1.6 got some boosts in recent years, and it seems to be a capable car in good hands. I don't know of any 1.6 owners clamoring for more allowances that will increase performance. 

I'm going to respectfully disagree that the NA8 does not need any help. I think you and I have discussed this previously online, maybe at Mazdaracers, or maybe even by phone. I owned an NA8 when we added 50 pounds and removed the restrictor plate. Now, as then, I don't think it made an improvement in the car's performance, if that was the point. I agree with infamousjim that the car should be allowed to go back to 2,350 pounds, and continue without a restrictor plate. Full disclosure: I no longer own an NA8. 

My concern for the well being of the NA8 also stems from the fact that it uses hydraulic lifters, which "lay down" a bit as oil gets hot — and it does — which decreases valve lift and overall performance. Yes, the NA6 also uses hydraulic lifters, but it also benefits from a much lower minimum weight. 

As for the VVT cars, tech inspectors need to be vigilant in looking for piggyback VVT controllers, which are inexpensive, easy to conceal and sold where people shop for Spec Miata parts. 



Edited by Brett B.
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