APEX SEALS

bldn10

bldn10

New member
I know this has been discussed before but not in awhile and the top RX-7s seem to be going faster and faster.

Am I correct that there are 3 choices: stock iron, carbon (Racing Beat), and ceramic?

The first 2 are priced about the same and I am not seeing why the carbons would be any better than the stock - no?

The ceramics are close to $2000 at the current sale price from Mazda. Is anyone here using them? A guy at Mazda yesterday told me that "they are good for 17 hp." That is mind-boggling to me because that would mean north of 190 rwhp. Any truth to that?
 
That's news to me. gulp.

The steel ones do a better job sealing at lower revs, and are reported to aid torque. I also hear that they transfer heat better. Not sure from where to where, and what it is worth, if anything, in power.

The carbon ones are reported to seal better at high revs, as thier low weight means they can follow the contours of the chamber better, so therefore make more top end power.
They are also reported to 'vaporise' or disintegrate when thay fail, saving the engine internals. Hard to believe that one. Pretty much any damage done to the side plates or outer housings makes them junk, so they would have to be very "kind" on the way out, LOL

Now, if they are indeed worth that much power in a ceramic form, on a 13B, I imagine the cost of racing has just gone up. For a 12A guy, I imagine that might be a 12 Hp jump. 12/17Hp = $2000? Somebody will think thats a great deal. Which means you will have to as well.

As for legality, they are clearly legal, as the rule satates "Alternate rotor seals and springs ARE permitted".

gulp.

Still, it would help the ITA guys tremendously.

I would love to hear the opinion of known builders such as Mike VanSteenberg, and the gentleman at Mazdatrix.
 
I have had 13B motors with both steel and ceramic. The claim that ceramic will give you 12-17 hp is uh, overstated. Maybe 5. The advantage with ceramic is you can rev the piss out of it without ruining the motor - if done occassionally. I.e. I would carry third gear up to 9500 rpm (sometimes 10K!) down no name straight at LRP and be able to duck under guys as they started braking. I'd carry the gear, late brake and have a ton of torque in 3rd to get up the hill. That's a great way to pass there, but the faster way is to carry 4th and just hang on. (4:66 rear - no can do with 5:12)

I'd do the same thing at NHIS going into the bowl - carry third longer down the hill. It will put a whipping on your motor doing that but its definitely helpful to pass guys as they will brake a little sooner than you and you'll be able to slow down a tad quicker without rowing the gears.

My ceramic motor was faster, but no 12 hp.

PS - I did blow up my ceramic motor by missing a shift to 4th at Pocono. The MONEY SHIFT - second blew that awesome motor up good. I had it repaired with steel seals - not as fast, but $2K cheaper. And I learned to row the gears a little better under braking. :eclipsee_steering:

If you want the championship in ITS - go ceramic.
 
I'm definitely NOT in the know (and have had no success yet in generating respectable power). I'm running steel. Chris Ludwig has carbon, and should have first-hand experience with the comparison. I've heard exactly what Jake said - carbon give a little better top end.

I THINK that ceramic only gives a real boost for higher output and/or higher revving configurations than IT trim - Prod or GT. Ported engines and well over 9K RPM.
 
Jake hit the nail on the head. It breaks down like this.

Stock or any cast iron/ferrous metal (RA, Atkins...eek!, PTS, etc) will seal better at low revs that carbon. Low revs being a relative term and IMO a rev range that you will never see with an IT engine. At somewhere north of 7000 rpm the ferrous seal tends to skip along the rotor housing because their inertia is greater and they can't change directions as well. This is not only bad for power but it will also ruin a housing. Higher spring pressures could counteract this but that increases drag which robs power, creates heat in the seal, and wears the rotor housing more quickly.

Carbon seals are a one piece design. Most ferrous seals are two or three piece. Ceramic can be had in either one or two piece. The multi-piece design is largely responsible for the better sealing at low revs. Carbon seals will make significantly less cranking compression than any of the multi-piece seals. A new, well sealed engine with ferrous seals should make 120+psi compression while a carbon sealed engine may only see 90. Starting fluid becomes your best friend with a cold engine. The chief advantage of carbon is their light weight. If you've ever held them they literally weigh nothing. Because of the low inertia they follow the contours of the rotor housings better and hold a seal better in the useable rev range and don't require high spring pressures to do so. The stock Mazda seal uses two springs, the carbon seals use one. They are also easier on rotor housings than any of the other seals. When they break bad things do happen. Unforturnatley I have first hand knowledge. My guess is that even if the seal itself doesn't damage anything there is still a steel spring behind the seal that will wipe out the rotor and housing if given the chance. IMO, for most people's budget the carbon seal is the one to have for an IT engine. The only down side is lower cranking compression that may create cold starting issues. Once the engine is warm you just hit the starter and go. And even cold they'll pop right off with a squirt of starting fluid.

Basically, ceramics are the best of both worlds. Very light weight, more detonation resistant than either carbon or ferrous, and available in a multi-piece design that can give excellent sealing at low cranking speeds. The downside is obviously the price. Saying the ceramic seals are worth X amount of HP at any rpm would have to be bunk IMO. There is a gentleman that frequents nopistons.com who campaigns a GT3 car in Cen-Div who uses both ceramic and carbon with no reported difference in power. There is a company called NRS that produces a ceramic seal. They're priced at around $1000 per set. They have a good reputation among the rotary internet community. I have no direct experience with them however.


This is what a housing that has experienced chatter looks like.

jaime_rebuild10.jpg
 
Great writeup Chris! Thanks!

Looks like I won't be spending the big bucks soon :), but alas the hondas are safe too...:(
 
I don't get over to this forum very often --

Chris Ludwig gave a good write-up -- all true.

Steel will outlast carbon, but we have seen carbon engines run multi seasons with no problem.
Chatter on the housing from higher revs IS the problem with the steels.

If the engine inhales bad things, it really does not matter what seals you have, and they all seem to do about the same damage (bad) from inhaling small nuts, washers, bolts, rocks, etc.

In spite of what MANY people say, I have seen no definite power increase from ceramic versus carbon - but yes, there may be a few hp increase. The power band on my E/P 13B street port is 7800 to 10,000. Yes, I am shifting at 10k on about every shift - so I am running my engines VERY hard.

I prefer the one-piece ceramics. I spent a lot of time talking with Francesco Ianetti on the one-piece versus two-piece. I found NO hp difference between them. He is still amazed at that. The two-piece are a ROYAL P.I.T.A. to install.
I have gone through a fair number of engines in the last few years -- trying many experimental things (only a few worked). Then I changed over to a dog box, and the driver had a lot more trouble adapting to it than I thought I would. Missed shifts, so engine goes to 15-17,000. They do NOT like that.

Here is the main point that I believe in, and tell my customers:
-- IF you can afford it, buy the ceramics. They will pay for themselves eventually!!!
Consider them an INVESTMENT.

I am STILL using most of the initial six I purchased in 2002 to BEGIN my E/P motor program. I do not want to admit how many engines they have been in. I also have a set of the two-piece. Between the two sets, I have at least (no joke) 500 engine dyno pulls -- and it may be a lot more than that. 30? race weekends. But the main point is the engine damage they have survived.
The MASSIVE over-revs are one thing, however the melted rotor housings were the really amazing thing. A cone broke the nose, and a piece of sheet metal put a small hole in the radiator. Lost ALL the water, heat of the battle, etc. The rotor housing around the spark plugs (BOTH housings) was MELTED away -- the end of the lead plugs were hanging in the breeze!!! From the rotor side, you were looking INSIDE the water jacket, and the steel/chrome/aluminum was smeared ALL the way around the rotor housing.
---- CERAMIC SEALS WERE FINE !!! --

End of testimonial

Dave Lemon,
#99 E/P RX7 Convertible
Owner, Mazdatrix
 
Dave, please post more. :)

Interesting that you'd mention losing all the coolant and melting an engine. I had the same thing happen this past summer. One good ping wiped out 3 carbon seals, new rotor housing, and a rotor. Amazing that the ceramic would with stand that kind of heat.
 
Thanks for your valuable input, Dave. And you too, Chris.

The question I have about the carbons is that everything I see in writing says that their value only comes into play at RPMs higher than I run most of the time. Based on a dyno chart I am now trying to shift under 8000, although I certainly go over that sometimes. One vendor says this: "These Race Apex Seals are specifically designed to replace the stock cast iron seals in engines operating near, or above, 8,500 RPM." Dave, your own site states as follows: "The carbon apex seals ... seal better above 8k rpm due to their lighter weight. They do NOT last very long (20k miles on the high side), and do NOT seal well at low rpm's (like starting and at idle)."

So, do carbons confer a benefit in the 7-8000 range that offsets their shorter life?

The low down on the ceramics seems to be that you should buy them for longevity not power (unless you are willing to spend anything for those last few hp) - right? Of course, you would have to use them 7 or 8 times for them to pay for themselves, and that is probably an entire career for most racers. I can't see it.
 
I have used the 2 and 3 piece steels and the 1 piece carbons. I rebuild my own engines and have 1st hand experience that you can break the carbon seals without making a mark on the rotor or side housings. The caveat and the caution is that my breakage (I believe) has been due to detonation (lost only the middle 1/3 of the seal). The carbons are very fragile and don't like the shock wave of a ping even more so than the steels. I think the carbons or any one piece requires a more thorough break in. They are more susceptible to catching a leading edge because of the way they sit in the rotor groove. The carbons have no corner seal and therefore must be clearanced precisely for best compression.

Don't try to use your stock apex springs with the carbons, they won't work without cutting them down.

My 2 cents.

Jamie
 
You must log in or register to reply here.
Back
Top