i just bought my series 4 fc and it has been modified, one of these being porting, the engine was previously rebuilt using 3mm seals, i am only going to use this car for track use meaning alot of high reving i was just wondering if it would be worth limiting the revs to like 6000-65000 rpm so the engine life is extended, thanks for any help

 

Well really you should get a dyno sheet and see where your power is made and shift accordingly, which will probably be before redline anyway. I wouldn't install an artificially early redline because you don't want to get forced to shift or throttle off because you run out of revs in a turn or the like.

 

It would help if you knew details about what the redline was designed to be. Of course the less you rev the engine the longer it will last, but your obviously interested in the engine for racing and not for longevity otherwise you'd be driving a diesel Volkswagen or something. There is a certain point where the engine will start to have problems and wear excessively if you exceed it, the redline of course. So you need to find out what that is and you'll only find out from the engine builder.

 

It's been my experience as well as others' that hitting a rev limiter while under power does engine damage.

A 3mm seal engine won't be hurt if you keep it under 8000rpm, assuming iron seals. If it's carbon seals, then the next issue will become the oiling system.

If you're maintaining at least 90psi oil pressure, you should be good to ~9000 sustained and ~9500 momentary. I've seen over 10k on mis-shifts with iron 2mm seals and not much more oiling mods than higher oil pressure.

 

Get it on a dyno. You'll probably take it to at least 9k on the dyno, assuming you don't have a stock ECU. If you do, it won't get that high, but you can get the rev limiter deleted on a stock ECU, which is a good idea for a track car if you want optimum power/speed.

Use a gear calculator to find your RPM drop between shifts and then shift accordingly so that the RPM drop falls within the peak range of your curve.

I'm going to take a guess that you are going to need to shift around 9k if you want to optimize your power. You probably make around 190rwhp. At 6k, that's probably around 150rwhp. The only way to know the correct shift point is getting it on a dyno.

Make sure to watch the temps and that the rest of the car is ready for the track (bearings, brakes, suspension bushings, etc).

 

Question: how often are you expecting to poke redline?

I've adjusted my rev limiter to a touch over 9000, so that I wouldn't need to shift late in the slaloms (i.e. autocross). Briefing entering redline doesn't bother me as much as all the other things that could go wrong when the rev limiter kicks in.

 

lol, yeah i was just gonna say that...

shifting early is ok, especially in endurance racing, but you don't want to bang off the rev limiter for long periods

 

I agree with the others - you really don't want to artificially limit the revs.

What I would suggest is that you go pick up a shift light and mount it on your dash. Set it for just below your desired shift limit. That way you will get a really "in your face" reminder about when it's time to shift. I have one in my track car set to 7800rpm. Usually I will short-shift well below that point - just over 7000 or so, but sometimes I may need to stretch a gear a little.

The other thing you will find is that over time you will become much more familiar with the car and the engine response. When I first picked up my current track car, I was very concerned about the engine life, not breaking anything and trying to "baby" it on the track. After all it was a significant purchase for me. But as I got more comfortable with the car I found out that a) the engine (stock Mazda reman) really loves to rev, and b) things aren't going to blow up if I drive the car hard. Today at the track I was routinely pushing the revs to about 8k in 4th at the end of a straight, rather than trying to grab 5th.

I would worry more about making sure that you have sufficient cooling for the engine (both water and oil) and that the drivetrain is in good shape. A well-built NA rotary engine is probably one of the more reliable things in a track car. ;-)

Good luck,

-bill

 

A motor with a balenced rotating assembly with properly clearenced rotors will run "all day long" at 9k rpms provided the oiling system, as previously noted, is up to par.

FWIW,
Crispy

 

Not with iron 3mm seals it won't. It'll run about ten or fifteen seconds and shortly afterwards it will come apart.

Extended use over 6200rpm will also seriously mess up the rotor housings over time. 3mm iron seals do not like revs! If they are carbons then all is okay.

I built a GSL-SE engine recently, meaning iron 3mm seals. I blocked off the aux ports entirely, theory being that if it doesn't make any high RPM power then I won't be likely to overrev the engine. Of course I still want the engine to breathe so it got a nice bridge port on what was left, but only on the secondary ports because it's still stock seals after all.

 

Info...Explain. I'm very curious. Engineering please not anecdotal evidence. To many variables to point specifically at a seal failure wihout consideration of other failure mechanisms at play. Something to do with higher spring pressure on the 3mm seals coupled with the more abrasive iron seals, than perhaps ceramics? Ditto iron vs. carbon seals?
Similarly whay can a 2mm iron seal engine rev and a 3mm not? Wheres the delta?
TIA,
crispy

 

Anecdotally, I've only ever pulled apart two 3mm seal engines that had decent housings, the rest were chattered out garbage. I have never pulled apart a 2mm seal engine with bad housings.

But you didn't want anecdotes.

The 3mm seals do bounce over 6200rpm. This hammers on the housings and at roughly 8500rpm the forces will crack the apex seals. I've pulled engines apart where the remaining rotor with compression had at least one apex seal that was cracked in half but hadn't left its home yet. The cracking is invariably in the middle, which can be interpreted in two ways: part of the cause could be housing overheating at the spark plugs resulting in the seal cracking itself over the raised area... or it could just be that breaking in the middle is less likely to result in FOD than breaking lengthwise, or at the ends.

The 3mm iron seals are heavier than the 2mms of any flavor.

They also are single-sprung, versus the double-sprung 2mm seals.

 

Great info. Thanks. You describe the effects (housing chatter, etc.) but do you think causes the seal bounce above 6200rpms? Inadequate lubrication, not enough spring pressure,....

I ask because I know of multiple track driven 13BREW's that regularly see in excess of 8k rpms that are built with 3mm seals - everything from 1 piece ceramics to OEM 2 piece seals. Tuned they do last. Longer than 10-15 seconds. Call me a hypocrite as I realize this is anecdotal - I did pull apart a 3mm OEM seal 2 piece bridge port engine over the summer that had two seasons or track abuse that showed hardly any housing wear, some plug hole cracking though.

Is the issue simply the weight of the iron seals? As for the springs the springs I have for a set of 3mm ceramics sitting on my bench are monsters! Although I can see the double springs applying load more equitably along the length of the seal.

Your thoughts,
Crispy

 

Springs have nothing to do with chatter or holding seals against trochoid surface during engine operation. They´re just for start-up. Apex seal moves up and down, but mainly side to side in slot. This is adjusted by pressure difference between two chambers. And since 3 mm vs. 2 mm apex seals have different mass, it seems that heavier seal can´t adjust at high RPMs as good as lighter one. I have to assume, that forced induction engines can do better thanks to higher pressures...

 

^Liborek,
Excellent point. I was not aware that the springs were for startup compressiojn purposes only. I'm thinking the dleta here is the difference between a normally aspirated engine and a forced induction engine. All the engines that came to my mind were turbocharged engines. Would a turbo charged engine see higher combustion pressures though to help with seal performance? And nonetheless where is the seal chatter/bounce occurring...on the intake side not the combustion side which would make sense from a forced induction perspective.
I'm still suprised that the spring "does nothing" during engine operation.
A good discussion
Crispy

 

inadequate lubrication will cause it, on any seal type.

the 3mm iron seal's weight makes the "floating" problem worse, if you've ever held one, they are kind of beefy.

ive run 3mm iron seal engines up to 8k+ before, but i like to keep em around a 7k redline. especially if its got miles on it, or its really old

the 2mm seals will go 9000+ no problem.

ive pulled apart 13B's with bad housings, the chrome doesn't fall off like the 12A's though