Max. Boost for stock seals
 

Hi guys,

as I am building my BRN stage 3 twin with WI injection, I was curious what the max. boost pressure would be without blowing my oem Apex seals? Many thanks for your answers.

Cheers,
Simon

I don't think boost pressure has anything to do with seals.
As long as the A/F ratio is good and exhaust temp doesn't get too hot, seals should be good.
I can't remember exactly what pressure BNR can perform up to, but I heard people running around 19 psi.

Boost doesn't matter, it's all in the tune.

Also conservative ignition advance is a must to help prevent damaging apex seals.

Not sure I agree with that. More like it's all in the fuel quality and octane used. And the tune, and the engine build quality.

To answer the OP's question, my brother has been running BNR Stage 3s sequentially for many years with an engine I ported and built for him running OEM two piece apex seals.

He's put it through the ringer, running 14 psi typically but tuning as high as 18 psi on the street with 93 octane and an AEM system injecting wiper fluid. We've also done double duty on the road course (NJMP), with two days of five 30 minute sessions of hot lapping each (both beginner and intermediate groups)...... that's about ten hours of nonstop hard running over a weekend.

Zero problems, runs strong as hell.

Rich or anyone, what do you think is an ideal high boost setting for the bnrs with water/meth injection? I'd leave it on 15 psi for normal street use. But wondering what guys typically run for a high setting on these?

Rich or anyone, what do you think is an ideal high boost setting for the bnrs with water/meth injection? I'd leave it on 15 psi for normal street use. But wondering what guys typically run for a high setting on these? I know some people go to 21-22 for dyno numbers but I am looking for a high setting I could run occasionally

Pretty much what it states in my quote. 18-19, or 1.25ish kg/cm^2 on the PFC commander.

What is the horsepower limit for the stock seals? Is there one?

Or are the housings the weak link? How much HP will the stock studs hold?

I wonder if the coolant seals are also a weak link... Or maybe even the side seals?

here is another, pump gas, stock seals, 6 port irons, and a full bridgeport, T88 turbo, etc.

None of those are "weak links" for making power. Making power is all about an effective tune: the right amount of air, combusting at the right time, with the right amount of fuel. What breaks apex seals is poor porting and detonation. What kills coolant seals is overheating. What kills housings are broken apex seals. What kills side seals is detonation or poor porting.

Water/meth injection is highly recommended as both a cleaner for your internals and to reduce excessive combustion chamber heat which can lead to detonation. Aftermarket apex seals now a days can take a few more detonations than stock seals and tend to not be as damaging to the housing upon failure. The stock seal is going to be your best bet for longevity at near stock power levels.

Matt

There's a theoretical limit to how much pressure (power) any engine block can handle. Just like how every gun has a maximum pressure limit. That's what I'm talking about.

I know there are least 2 more cars from that shop running in the 600+ whp range, up to 1.89kg/cm^2 on pump gas without WI.

:)

the story behind this one is neat, i heard about the car years and years ago, and then i happened to get a JDM Rx7 magazine with the ad in it, so i put up that pic, and the guy from the shop posted the dyno sheet.

its a really small community

ive never seen a combustion pressure or hp number published for a rotary, although some newer SAE papers do.

i have seen the rpm, EGT and limits posted, along with a 3rd thing, i can't recall. the EGT is 1100c, and rpm is high enough i don't recall the exact number, but i've seen dyno sheets past 10,500

I wonder at what point do you need uprated studs, though?

Most everyone on this forum doesn't think like a statistician would do. when you ask a question like how much does a certain engine handle.....I am guessing you want a confidence level of 95% or greater. a lot of these engines putting out over 600WHP are probably anomolies and they don't last long anyway. lasting long to me would be 80K reliable miles. I doubt these 600WHP engines last over 80K miles with a confidence level of 95% or greater. not even close.

so what can a stock engine take with appropriate upgrades to handle all the cooling? no idea. perhaps 300-450WHP is the max with someone driving it like a pansy most of the time.

Boost isn't the issue. However the more power you make, the larger the likelihood of detonation gets. One good knock will break a stock seal and trash the motor. That is why anything approaching 400 hp I recommend upgrading seals. I almost exclusively use RX Parts apex seals as they are super strong, but don't prematurely wear out the rotor housings.

Meth injection adds a huge safety margin at any power level on pump gas. Sure I can retard timing enough and richen the afr to run 30 psi on pump gas, but it just isn't reliable.

Around 500whp and above I strongly recommend studs. I sell a chromoly engine stud kit for $399. Cheaper and stronger than others. Stud install tool is included.

80k miles driving how?

i have a friend with a street car integra and he's pushing 300k on the original everything, and its fine.

we used to race an integra, and we did a few 25 hour races with them. we learned that in order to get the car to even last 20 of the 25 hours we had to start with a new engine, new transmission, fuel pump, alternator, steering rack, tie rods, bushings. we needed to buy new bearings and axles, and then repack them with synthetic grease. obviously brakes are new, and get changed during the race. etc, its about 15k worth of stuff. (for a funny we even had to change the ecu once because the chip fell out) and we still have to limp it across the finish line, as the duct tape and cardboard actually were holding it together.

the shop where we built our car that year has a 900hp drag car, and they rebuild it in the middle of the season, which is a grand total of 7 minutes of run time.

so the mileage isn't the driving factor, its the duty cycle.

Not to mention all the man-hours.

Hours at WOT. Ignoring catastrophic failures, it sort of depends on whether you can afford to lose a few horses due to compression loss. For a race car, that's pretty much a non-starter. For a track day car, it's acceptable. For a street car, it's a non-issue.

I think I saw that on FB haha. Yozo has a big binder full of cool setups and their corresponding dyno charts, really cool stuff.

i'm not sure i understand your point, but in a 25 hour reliability is much much more important than a couple of HP. since everyone is in the same boat, having to run @wot for a day, by far the most important thing is just being able to finish. this is kind of why the miatas do really well, and the daytona prototypes do not. the running joke is that we'll move out of E3, which is all miatas and instead run in ESR, with the daytona prototypes because the sports racer cars hardly ever finish, its an easy podium.

or maybe this story will be more to the point. we ran the LS honda engine, and we freshened it up, and went to the dyno to tune it. we set the AFR to best power, which was like 13.2:1 and then the tuner advanced the timing 3 degrees, which did nothing, so he left it. it was fine on the dyno.

during the 25 hour we blew the head gasket, and on teardown it was really clear that it failed because the engine was detonating. on the street it would have probably been ok, in drag racing it would have detonated, but probably not enough to break anything

with the next engine we tried the 3 degrees advanced tune vs the stock map, and the stock map made more power....

the moral of the story being that the duty cycle on a race car is different, and that detonation is possible on just about any engine.

yeah you might have, and i wanna see that binder!

I wasn't talking about durability in endurance racing, just about engine longevity in general.