Well thanks, for all of the responses. First I'm posting this on my son's login, I'm actually Blueraven. Well we took the advice to let it rev out, and I have to say this is the first vehicle I've every own, that seems to have gotten more powerful the more we drive it. This was a local city driver and there might have been a "carbon" issue. I've read many post on that. So let's Rev on!!!!!!

 

Although 6000 rpm is kinda low, it's just about on the money for a stock carb'd 12A rotary, so since peejay's right on this one, it's safe to assume the rest of what he's saying is also accurate...we need to see the dyno graphs you have to support the 7000 rpm peaks because experience has shown me the stock Nikki and exhaust are done by 6400 rpm or so...

Here's a real world graph of an absolutely stock, carb'd 12A at-the-rear-wheels dyno run...



Basically lost here in this corner of the rotary community are peejay's observation on shift times and rpm's. Even if your butt dyno tells you the engine is still pulling strong at 7200 rpm, if your car is basically stock with the stock Nikki and exhaust, you're wasting your time. It's an illusion. You should have shifted at 6400 or 6500 rpm if you want to get lower elapsed times or beat the ricer in the next lane...he already made a real world "test" that led to this old gearhead truth, so that has a basis in reality, as well.

If it's not stock, then that's another ballgame altogether except for peejay's observations regarding the seals...

 

Note that with a PS header/exhaust and a better fuel pump, I *consistently* get better times shifting at an indicated 7700rpm.

I do know that the tach is off, though. It indicates 7700 through the traps in 3rd, trap speed of 86mph... my '80 (same gearing, same tires, accurate tach) also went through the traps at 7700 in 3rd... at 90mph trap speed.

I don't feel comfy taking this engine up that high though. I know it's getting worn, it smokes like a boinger that threw a rod when I let off at 86mph in 3rd... I'd feel a lot safer if I was driving an engine that I've physically inspected its internals.

But damn... 16.05 at 86 with stock carb, stock intake manifold, stock porting, stock gearing (well, stock '80 gearing, the '85 trans is in a bag in the basement), at 2600lb with driver...

 

If the buzzer goes off its time to pay attention.

 

Roger Mandeville - a pro rotary builder told me to watch the power curve. It starts to fall off after a point. 7G or so. Time to shift.

 

Too lazy to post under me Sweetege. so where can i get a scatter shield just for safety and how much are they, or could i make one. thanks

 

The above graph shows that at 7000 rpm, you're only making the same power as at 4300 rpm, which is 10 HP below peak at that point...IOW, you should have already shifted. The car had a fresh set of plugs, NGK, and MSD helicoils only a month old. New cap and rotor.

Time to shift is right about 6500 rpm...you're wasting time after that.

 

I see alot of "advice" here saying one liners like, "Shift it when it beeps!", among other things indicating you should rev your engine really high.
I especially find amusing the bullshit posts about reving an un-pinned engine to 9000.

Just to put it down on the thread, Peejay is very experienced, and I suggest you all take into concideration what he has said.

If you're trusting your tachometer or your buzzer to be accurate at such high numbers, or if you believe that your engine is going to behave just like someone else's, and you destroy your engine because you've been reving the **** outta it, then you deserve what you get. Because you were being stupid!

 

I would not trust the stock tach. I have just heard too many bad things about it. Thats why I installed an aftermarked 2 1/16th inch tach. I also like to have one right in my field of vision when looking forward, so I put it up a little higher. I know its accurate though. I used it on another car, and it was accurate to within 100 rpm I think.

I think shifting at redline is the best thing to do. If you want to get technical, you can shift at probably 6700 rpm for best acceleration. This puts you only a little past peak hp and still high enough that your in the powerband after you shift.

 

If you're really serious, go to your local dragstrip's test and tune nights and *experiment*. The nice thing about the dragstrip is that they give you numbers with highly precise equipment so you can quantify changes. Plus it's legal, and you get to watch other people race and hear evil engines and breathe tire smoke too!

I'm still experimenting... but right now, I know that, with *my* car, with *my* mods, I get the best times shifting at 7700 on *my* tach. Finding what's best for anyone else's car will require going through all the same "work" (ha, ha) that i did for mine.

 

Ahh a dynograph. I stand corrected, even though there is still a crapload of places saying 7k @100hp. Nice to see a stock curve, man 93 ft-lbs! I thought they also had 100ft-lbs @4k at the motor.....are they producing more like 125 ft-lbs? interesting.

 

OK, I can't stand it anymore.

There's a common misunderstanding about shift points. What's usually overlooked, and must be taken into consideration, is the torque multiplication of the transmission. That's why you need to determine your shift points either on a dragstrip or a chassis dyno. A dyno is better since its more accurate.

Here's how this works. I'm going to use numbers that aren't exact, just to make it easier to follow, but its pretty close.

The engine makes 100lbs of torque at the flywheel at 7000rpm. The transmission ratios are 1st=4/1 2nd=3/1 3rd=2/1 and 4th=1/1. That means that at 7000rpm in 1st gear, the output of the transmission is 400lbs of torque. In 2nd it would be 300lbs, etc. The differential then does further multiplication (about 4/1), but since that never changes, we'll ignore that for simplicity's sake at the moment.

So what's this mean? It means that if you only look at an engine dyno graph, you'll shift too early. Here's what happens.

Lets assume that shifting to the next higher gear drops your revs 2000rpm. So if we shift at 7000rpm in first gear, while we are putting 400lbs of torque to the differential, we drop to 5000rpm. Even if the engine made 100lbs of torque at 5000rpm, we would still be dropping the torque being applied to the differential from 400lbs to 300lbs. Since the engine doesn't actually make 100lbs at 5K, it's even worse.

So you need to shift to the next gear at an rpm that results in the same torque as before the shift, at the output of the transmission, not at the flywheel. That means going past the peak torque in any given gear in order to maintain the lower gear as long as possible.

Let's say you go to 8000rpm in 1st and the engine torque falls off to 50lbs. 50lbs X 4 =200 out of the transmission. If we drop to 6000rpm by shifting to 2nd, and the torque at that rpm is 66lbs, at 3/1 ratio we end up with 200lbs out the transmission. So you have to find where on the dyno sheet the new torque equals the old torque when going to the new gear.

Most dyno pulls are done in a single gear, which doesn't tell you the actual torque that you will get when you shift to the next higher gear. However, if you know your transmission's ratios, you can do the math to figure it out.

All this explains why the Honda S2000 can go from 0-60 in 5sec. with very low torque. Its able to hold the lower gear up to 9000rpm.

This isn't obvious or easy. The best thing to do is get a dyno run in all gears. That will then give you accurate information on your shift points. And chances are, it'll be a different rpm for each gear because of the different ratios in the transmission.

Don't believe me? Don't care. I have 24 SCCA class wins and three consecutive SCCA road racing championships. I've seen it on the dyno and I've seen it on the race track.

BTW MAR3, there's something wrong with your dyno sheet. The relationship between torque and HP is purely mathmatical. The torque curve and the HP curve MUST cross at 5252rpm. It impossible for it to be at any other rpm. Your's appears to cross at 4800rpm.

 

none of this changes the fact that S1-S4 engines redline at 7k, and i trust mazda on where the engine will start breaking.

i shift at 6000-6500. i want my engine to see a quarter mil.

 

Correct. I'm talking about racing use. I expect to do a complete rebuild every 2-3 years. For a street car, obey the buzzer/redline. The earlier you shift, the longer your engine will last.

However, on that subject, and still within the context of a racecar, I've been told by several shop owners that make a living working on rotaries AND race them, that a stock 12A can live with an 8000rpm shift point. I.E. They won't destroy themselves, won't break apex seals, won't tear up the rotor housings. They will wear out faster, that's a given. I don't normally spin mine that fast. But there have been times during a race when a shift wasn't convenient and I've gone that high. I have consistently shifted at 7600 in races for the last two years and my engine still runs at the front of the group. YMMV.

 

as io said in my first post im in australia , and i dont know if our sa's are different to yours but my car goes 7k first gear just over 8 k (100-120kmsp/h) in second gear 3rd gear about 7k Max then from there i dont know i dont boot it that much over 160-170 km's i race my car on the track and off the track and ive punched mine off red lin just showing people with my after market taco that my car can go to 9.5/10k with out blowing and people are amazed, the car has had that happen to it for 3 years and still running strong although i have driven other rx7 12as that haven no punch over 6 u wanna rev it further to get it higher in the next gear :d cheers

 

oh yes my car does have a few mods like full exhast, removed air pumps, bigger jets on carby large headors etc

 

I had a first gen with a streetported 13b, RB exhaust, RB holley/intake, lt weight flywheel etc. I would rev it EVERYDAY to 10,000 Rpm. The engine lasted 121,000 miles. I took it apart, relaxed apex seal springs. Rotor housings were fine, no chater marks..NOTHING. All new seals/springs put it back in, added a 9 inch Camden Blower and Nos. Sold the car 4 years ago and the guy is still driving it with the same motor just no Nos.

 

85 hp! How do you handle all that power?

 

BTW I wouldn't recomend this.

 

Well I've taken it to 10K before, just kept pulling it felt like just finally shifted. I won't do it again now after reading this, but damn the car just keeps feeling like it's pulling hard. Nonstop.

 

85hp is stock amount at the rear wheels for a 1st gen. With a few easy mods you can bring that up to 100hp. Expect up to 110hp with a rb exhaust. Also, when you do any exhaust work, you raise the rpm at which max power is made. With a RB exhaust, I would expect it to be at about 6500 to 7000 rpm.

 

Yes, that point got argued to death in the DoO board recently. Until you pointed it out, I hadn't even noticed the curve crossing point...this one's like it should be but I can't explain the other one, I didn't run the dyno, I supplied the car, money and time...I'll peg Chris on it in the South Forum Board...



This one had the modded air cleaner, explaining the mighty jump in power...

 

gotta love that beeper don't ya!!!!!!!!

 

I am sorry for the Necro-Bump, but I couldn't help it

Research takes me strange places sometimes.

 

Yeah,.those comments didn't age well, did they?

I still stand firm on my statements re: the stock 12A powerband.

One thing I didn't touch on, uh, 20 FREAKING YEARS AGO, is that best shiftpoints are such that the horsepower before the shift equals the horsepower after the shift. So if the engine makes peak power at 6000, you want your shift to bracket that. Shifting at 7700 meant that the engine dropped to about 4600 on the 1-2 shift, where the engine is probably making about 83hp. If the engine made 100ish HP at 6000 and tapered to 83hp by 7700, this makes perfect sense, and is on brand for how rotary power curves tend to plateau and come down gently rather than simply fall off after peak.

About fifteen years ago, I had a half bridge deturboed Turbo II engine. Peak power was something like 175whp at 7000. I got my best tines shifting at 9400 because I didn't dare rev that engine any higher.