Big Dog wrote:


So what your saying is, I can go build a low compression car and pull 134-136 and be safe an not worry about dyno differences. And you can go build a high compression car, throw it on the dyno and tune the heck out of it making over 140. Restrict it back down to say 139.5 and hope you don't get caught with your pants down and then complain that the dyno was reading high.

With our current rule set if this were to happen you'd just get moved to last place. Hell you could dyno 145 and just get moved to last place. then go back to your pits grab your restrictor plates and dyno till you hit 140 and go back racing. I believe we only had a dyno at one of our races this year and I bet it's the same with the other regions. I could have raced all season long with a 145 HP car and never get dyno'd.

OK, I'm getting off my soapbox now. You know how I feel, I said enough.

I'll try to speak to the the concerns Jim & I went through on the phone as he requests. Have a seat, and get comfortable...

I can only speak to the 4 different Dynojets that I have been on & seen other cars on, and none of them were back to back with different Dynojets. Still, I have personally seen well over 200 total 944 dyno runs, and more than 50 in one day with my own car while doing testing for the dyno cap last year.

Most Spec motors dyno in the low 130's. With a careful build, and some tuning, most can get up in the upper 130's. It typically takes a lot of both to get into the 140's, especially a 140 average over 3 runs. This trend was born out at Nationals again this year.

There is more than dyno variation going on here. It is hard to stay in a 140+ HP tune, and easy to fall out of tune, and dyno less on a given day and atmospheric conditions. A dyno can correct for changes in conditions fairly well in a general sense, but it cannot predict how a particular car will fall out of tune relative to current conditions.

When Dave Dirks came down to Mid - Ohio, and the MW guys came up to Miller (speaking in terms of altitude), the cars were seriously out of tune, and down on corrected power. It took about 4-5 clicks of the AFM to get the A/F ratios dialed in. With this, all these cars were able to get back into the mid/upper 130's (dyno corrected), gaining as much as 6-8 HP. This is not dyno variation, this is variation due running rich or lean vs. their baseline from altitude changes - i.e. falling out of tune. To a smaller extent, this happens from day to day - maybe 2-4 HP is lost as the car goes out of tune vs. ideal for current conditions

The key here is that power is lost vs. an "in tune" run. Another key is that it takes all ducks in a row to get a Spec Motor over 140 on a Dynojet on any day. So, if you have an average build, and you don't want to bother with tuning, you are likely safe (if that is good enough for you). I have yet to see a home built motor dyno more than 140 average on any dyno I've been to. If you have a seriously built motor, then it is important to find what your motor is capable of - put it on a dyno with a clean air filter, good plugs, etc., and fuss with A/F ratios (typically best somewhere around 12.5:1) until you get the best out of it. If that stays consistently below 138 HP+TQ/2, you are likely OK. On most days, your tune won't be quite as perfect as it was the day you dialed it in, and you car will dyno less. Maybe 5 HP less. But you will be safe.

On the other hand, if you throw your cold car on the dyno, and pull 3 runs, you can't make much out of that number. You haven't found out what your car is capable of. In that situation, your car could dyno 10HP+ more (presuming it's a strong/seriously built motor to begin with) when warm, and the A/F ratios are dialed in. This is where a lot of "dyno" variation comes in. If you don't dial it in, and find what it's capable of, you run the risk of finding its potential on a different day, in different conditions -m aybe the one you pulled for a compliance dyno.

There is a lot of concern over random "high" numbers. I haven't seen this. The cars that dyno higher are the ones you'd expect, and even then, it's pretty rare to see a car get over 140. It takes effort. There are some situations when good motors dyno lower than expected - they have fallen out of tune, or (rarely) have a part going bad (hint, check the distributor rotor!).

If you find you have a strong motor, and you want to be more sure you are safe, dial it back via a more permanent means. Some guys take off the merged "Hanksville" type collector. For others, it may mean a restrictor plate. Whatever it is, make sure your car is then tuned for that setup, and won't go over when dialed in. There will be some days your car may make somewhat less power, and you'll have to live with that, but you will be safe.

Like Jim, I don't think we should crucify those who dyno over any more than we do those who go under in weight. We all make judgements on how close we want to run things, and sometimes, on a given day, we are wrong, and pay the consequences. The goal of the dyno rule is not that no on ever falls out. It's to put a ceiling on motor development, while not catching the average guy out. SE30's National championship participation was decimated this year by the appearance of "legal" 170 RWHP cars. We were the second largest class. I think we are on the right track!

Eric, thank you for that. I believe it helps understand what we all are dealing with. IF the dyno variation is minimal, your "blueprint" for how to tune a car is perfect.

Only more data will confirm that the dyno's have good consistency from dyno to dyno. If they do, great. If it is shown they do not, I have every confidence that the appropriate fix will be found.

Regarding the Spec E30's, from what I have been able to read on their forum, and by talking with drivers, the upset was the way their dyno rule was done and when it was done.

Our class had our own version of that bloodbath some years ago over chips and headers and it was ugly. A number of guys took their cars and left NASA and never came back. So. Cal. was particularly hurt by that mess. The good news is that the newer attitude of having open discussion, gathering feedback, and considering racers opinions in rule changes makes for a MUCH different dynamic, a dynamic that needs to continue.

Jim Foxx

Sterling Doc wrote:


I'm not calling anyone a cheater or trying to crucify them either. But if you don't take a stand and DQ the person that goes over you will have motor development going on. I'd much rather choke a motor down than try to build up to the HP limit. You said most motors make low 130's and if you put it on a dyno and tune it up once, should make mid 130's. Certain days it will make more and others less. Now this is suppose to be low cost racing but if you have to spend hours on the dyno and big money to build a "PRO" motor where's the low cost? For those building "home" motors your increasing their cost to keep up with the HP. By letting the person that goes over the HP cap and do so without a DQ, your sending the OK to them and everyone else to get the most HP they can and choke it down right to the limit. This increases the cost, encourages them to try to develop the engine more, increases the chance that people will cheat to get that last few HP and increases negativity to the series by perceived and real cheaters.

If you knew that you would get a DQ for going over the HP limit would you
A Do nothing and hope you don't go over.
B Dial it down so you don't go over.
My guess is most would choose B. If you make people fearful that they will be DQ'd, then they won't be pushing to the limit quite so hard. Add to that knowing the dyno variances could be against you, and people will back down from that limit. Which would better help to make more cars equal in terms of HP/TQ since most run in the mid 130's.

Ken, at least there is now a mechanism to rein in very high performing motors in, and narrow the gap. Even in series with sealed, single source, Spec motors (i.e. SCCA's Formula Enterprise), there is a few HP variation.

A couple of years ago, we had no idea how to narrow the gap between the high 120 cars, and the lower 140's cars. Now, we know that $100 of dyno time can get most cars into the lower/mid 130's, and we have a means to bring down the 140's cars into the upper/mid 130's. That's progress. I think that's about as close as we can hope to regulate a couple hundred 30 year old cars from across the country. Yes, we need more dynos, and more data from across the country. That will come over time, and hopefully more dynos at NASA. I also think you will find that we have less HP spread than other Spec classes. While we may not get perfection, I hope we can settle on merely being the best

I hear you on the DQ vs. move to last issue. We are the only class that does this. We were also the first (but no longer the only) Spec class to adopt a dyno standard. So we hedged our bets, and made it a bit softer. If it seems there is a problem with people ignoring the rule, because it's teeth are too dull, we can get the grinder out next year and make it hurt more. Let's see how this plays out.

Same with the dyno variation thing. Let's see how this plays out a bit. If we have large numbers of cars getting "moved to last" using our current process (like Jim's example of the scales that put everyone on a magical diet), then we'll see about what to do. If few cars dyno over, then the solution would be to leave more headroom, and the rule is probably working like it should.

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As far as the SE30 story, the dyno rule was put in place last minute because of the low turnout. Despite more cars nationwide, and a lot more out west, SE30 registration never reached 1/3 of what ours was at the same time, before the new rule was put in place, and the rule was a reaction to that poor turnout. In the end, the late rule change finished things off with the few who did sign up. I'm not trying to give my SE30 brethren a hard time - they were placed in a tough spot at difficult time. They probably wish they'd pushed a rule through last winter as planned, before the really big HP showed up, or waited until next year once it did. I just think it's important that we learn what we can from what happened.