What is your Rev Limit Set at?
 

What is your Rev limiter set at? Please vote!
Built engine?
Engine specs: If so, please post relevant specs (pistons, rods, valvetrain, etc)
Do you track the car? On a 1-10 scale, how much hell do you give it?

I wanted to see what everyone is running for there rev limit. I used to run 7900-8000 RPM limit, and never had any RPM related problems other than valve float. But I want to bump that up some. My last motor I reved it to 8700-8800 about 300 times within 700 miles and it didn't like that, so I'm guessing I need to stay below Formula 1 piston speeds to maintain some level of reliability. The head seems to have been fine though!

For me:

Rods-only engine.
RPM Limit: 8000
Built engine: Rods only
Engine Specs: Rodsy only
Track the car: 9/10, Drag race sometimes, mostly street car
Avg number of times your car sees redline/day: 10

Last engine
RPM Limit: 8800
Built engine: Yes
Engine Specs:Rods, full valvetrain, ported head, cast pistons
Track the car: Drag raced, about 50 passes.
Avg number of times your car sees redline/day: 7/day till I wore the bottom end out after 700 miles/50 passes.



Blank one for convenience.

RPM Limit:
Built engine:
Engine Specs:
Track the car:
Avg number of times your car sees redline/day:

For my new engine, it will have carillo H-beams, FM forged pistons, balanced, ATI Damper, fully built head that's turned 8,800 before without a failure. What RPM limit should I set to keep it reliable? I want to go to about 8,500 but I don't know if there are any miatas running that reliably?

On the block end of things the limiting factor is going to be mean piston speed right?

7000 rpm = 3904 ft/min
7500 rpm = 4183
8000 rpm = 4462
8500 rpm = 4741
9000 rpm = 5020

What do you guys think the safe limit is for stock block and for a forged internals block?

Interesting link: Engines with the fastest piston speeds | HondaSwap

From it, engine 3, Honda B18C5
Bore/Stroke: 3.19" X 3.43" (81mm x 87.2mm, more stroke than a BP!)
Redline: 8400rpm
Piston Speed: 4802 Ft/min
Wikipedia says Redline was 8,400, but fuel cut was 8,500.

RPM Limit: 8500
Built engine: Yes
Engine Specs: Trackspeed VVT motor, supertech valves and pistons, Manley H beams, ACL bearings, BE street/strip pump, 949 damper, stock SOBs, Supertech heavy singles, junk2 throttle body
Track the car: auto-x
Avg number of times your car sees redline/day: depends on the course, I estimate the motor has spent about 5 minutes over 8300 rpms (about 2 of that is on the dyno) in its about 10 hours of run time.

I just finished re-shimming and installing the inner supertech springs. The intake valves all tightened up considerably in that time and I'm going to keep a closer eye on them. A couple other auto-xers have had problems with dropping intake valves with similarly built motors after about the same amount of re-shimming I had to do.

RPM Limit: 7000
Built engine: yes
Engine Specs: 1.6
Track the car: yes. HPDE/TT/20 min. W2W races.
Avg number of times your car sees redline/day: 15 track days/year.


broke throttle shaft 1 month after bumping rev limit to 7400. new chicken limit is 7000, don't need to go through that again.
I'm assuming everyone going past 7200 is running skunk throttle bodies?

Spinning stock head and cams to 8k = pointless.

7500.

BP4W. BP5A ecu. I go hard.

Not so. With a 7.5k revlimit I only get a 34mph wide powerband, spinning to 8.5k I get a 40mph wide powerband. I just run more and more boost the higher the revs get to keep the torque up.

RPM Limit: 7400 hard, soft starts at 7200
Built engine: no, stock 90' 1.6
Engine Specs: whatever mazda says they should be :)
Track the car: yes, track only car
Avg number of times your car sees redline/day: 2-3 times per lap, 14 ish laps per session, 10 sesssions a track day= 280-420 times per track day(thats probably on the high end, 200-300 seems more appropriate)

RPM Limit: 8200 soft 8350 hard

Built engine: Yes

Engine Specs: Scat rods, Supertech Pistons, Supertech valves 1mm over, Supertech 63lb dual springs, gates belt and WP, BE billet oil pump gears, balanced rotating assembly, stock flywheel, stock harmonic ballancer(for now), OEM head gasket, ARP hardware everywhere, ACL bearings. Turbo, 262hp last time on the dyno. MS3

Track the car: Nope, drag strip sometimes, daily drive in the summer sometimes.

Avg number of times your car sees redline/day: 5 maybe, a lot of times it's just downshifting. I see it most often drag racing as it is needed with the short gear ratio. I did one autocross and it came in handy then too but it wasn't there long.


Edit* Because Revlimiter: Beautiful gauges with 8200rpm redline.
https://www.miataturbo.net/attachmen...ine=1422395931

I am currently set at my desk. In about an hour I will be set in my NA.

RPM Limit: soft-7000, hard-7200
Built engine: forged Crower rods, Supertech 8.4:1, Boundary pump
Engine Specs: NA8 head, heavily ported, stock valves, stock springs (this week;ST light doubles and titanium retainers waiting to go in), stock hyd lifters
Track the car: yes, please
Avg number of times your car sees redline/day: depends on the medication

And a useful post.

7500 limit
Built: no
Engine: NB1 engine and head. Minor head porting. Stock everything. ~40,000 on this engine.
Track the car: once in a great while
Limit per day: Very often. It's not just a forum name.

7k limit, soft at 6900, spark cut only
Built: No
Engine: 99, stock internals and head (i think), 154k miles
Track: 3 times last year while N/A, not yet since turbo
Rev limit per day: a handful

rev limit: 7200.

Built bottom end (Carillo A-beams, supertechs), ported & polished head, oversized valves, stock cams, stock valve springs.

Why the 7200 limit? No point in going higher than that with the stock cams, and i like reliability. Of course, even with that it broke a throttle body screw at Laguna last September.

--Ian

Wow, you guys are all fairly conservative.

My turbo car: 7200/7400, but it rarely goes to normal rev limiter

My n/a car: 7400/7500, multiple launches on the 2-step, usually shifted when power falls off but has been held on the limiter in autocross

Autocross and road race guys with standard valve components usually ask for 7500. I've seen/heard of a couple broken throttle shafts, but no reports of valve or rod issues. One of our guys has a "stock" 01 we set at 7500 soft, 7700 hard years ago. Had one issue where the cam trigger ring rotated--I can't believe it's just a friction fit (?!) from the factory. I believe he put a couple small tack welds on it after realigning it.

Built heads: 7500+ but up to the owner. SUB and custom cams 8000+. The guys who build those kinds of motors generally do not allow me to disclose any real info about them.

Ok, well I would agree if it keeps you from shifting, it MAY be beneficial. Not sure that widens your powerband exactly. ;)

Stock internals, the usual bolt ons, BP5A cam. Redline has been stock until recently, now now that I've gone MS it is set to 7500rpm. It sees redline almost every shift. Averaging about 35-40 days on track a year.

robert

Interested in this thread. I'll be keeping my stock BP head for the time being so I'm curious what everyone else is running on stock heads. Looks like 7000/7200ish so far.

RPM Limit: 8000
Built engine: yes
Engine Specs: H-beam rods, lightened crank/fly, big valves
Track the car: a little drag
Avg number of times your car sees redline/day: it saw 7k all the time, only 8 on dyno/track. no power up there

going to see if I make more power up top with some DIY porting and SUB conversion, if I can get my head back from the machine shop

RPM Limit: 7200
Built engine: no
Engine Specs:
Track the car: yes
Avg number of times your car sees redline/day: 2-3 times per lap, depending on track. Often when driven on the street, which isn't much.
~1k miles/year

RPM Limit: 7,250
Built engine: No
Engine Specs: Stock VVT long block, unopened, ~86k miles, full bolt ons, ecu
Track the car: Almost exclusively, about 10 days per year. TTD/HPDE4
Avg number of times your car sees redline/day: A couple hundred per track day? Depends on track and conditions. Street use is mostly only to and from track. Power really starts dropping off around 7300, and I like to baby the stock head because I don't have time to fix much stuff these days.

Maybe I'm uber conservative, because I was actually about to post the opposite seeing all these stock-rod and stock head BP's being revved past 7.

Is it not true that nasty things happen like stretching rods and pounding valve seats when you're consistently over the oem rev limit? Aside from the 2 obvious things like floating valves and most of us not making any power up there..

I don't think I've ever revved any of my engines past 7. Stock, built, bp4w, bp6d, all of them.

...And stock oil pumps fail, and possibly throttle body shafts.

There is a dramatic increase in wear at 8000 rpm versus 7000 rpm. Emilio mentioned in another thread about the BP crankshaft being relatively fine at ~7500 and like a limp noodle at ~8500. This would mean that somewhere between those two values very strange things begin to happen. Paraphrasing what I recall, iirc, that the lifespan of the engine goes from being measured in hours to being measured in minutes when spending a lot of time at 7000 vs. 8000. Since I am not a "racer" I have no desire to rebuild my engine every year, I'll keep the lower limits and try to optimize my performance below them. If I was trying to win the HPDE Championship, I might be willing to push things more.

Yes yes and yes. That was my understanding as well :)

I reved a stock rod 99 engine with stock, but lightened valves to 7,800 for about a year (ran 100 shot nitrous and MS2E), then bumped it to 8,000 and did that for over a year, 11 months of it were turbocharged. So probably about 2 years total on a stock bottom end. Bearings looked perfect. Rods were bent, but that was from nitrous accident at the drag strip. FWIW, I used the same oil pump that came on my '99 until 2013, it's seen 30 PSI boost, 100 shot nitrous at idle, 8,000 RPM for several years, it never failed. But I kept the factory harmonic damper.

I've broken 5 BPs now (bent rods, cracked piston, rings failed, crankshaft keyway damaged from vibrating damper off, bottom end wore slap out), and the only one I would say had a RPM-related failure is my current engine I reved to 8,800 I need to pull it and tear it down, something is worn out in the bottom end, and it vibrates, but it's vibrated since I built it so I suspect it could be my fault anyways and extra RPM didn't help.

I'm not sure I agree with your loic. At all. You say "I blew up......but it was due to" over and over, and I'm really curious how you know that the bent rods were from the boost/nitrous only and not overrevving?
Some parts/engines die slowly and some abruptly, but without a serious professional analysis I don't think anyone can ever make a factual claim such as "it broke from ....."
But just my opinion.

If you told me " I ran this engine for 50k miles, revving to 8 every day, and it's still in the car, and still working fine, and here are pictures (or evidence such as comp and l/d tests) that everything is in fact still peachy" I would be thoroughly impressed.

Mine was at 8000, but had to drop it to 7400 soft 7500 hard after having the issues requiring key cycle to reboot the MS3x.

Engine specs, VVT -01, fully balanced, Belfab Rods, Wiseco pistons 84.5 mm, supertech oversize valves, supertech single springs, hard lifters with manley subs, stock cams BP oil pump, stock damper, light Fidanza flywheel reinforced block.

Max power at 6200 rpm, but there are advantages on some straights to save two gearshifts.

I've posted it before when it happened. My nitrous malfunctioned, it hit 100 shot at idle, blew head gasket, bent rods, motor had a vibration to it afterward. I did a compression test to confirm hg was blown, repaired it, then noticed I still had low compression on 2 cylinders, was 15 lower, one about 30. Dropped a 3/8 extension down the spark plug hole and sure enough, cylinder down 30 PSI, the piston didn't come up as high as the others! So yes, it was confirmed. :)

And so far I can't keep a BP alive for 50K without breaking it, so don't be looking for that post from me anytime soon!

I know that's what finally broke the camels back, but you're missing the point.

My 99 had a 5sp at 300whp. I was "fine" on it for 2 years, after I sold it the kid grenaded it in 1 month. I blew my stock 99 engine at 240wtq from a melted ringland, but after I yanked the rods all 4 were bent.

See where I'm going with this?

Anyways, sorry for off topic. I'll shut up now.

RPM Limit: 7200 hard, 7000 soft
Built engine: No
Engine Specs: BP4W Stock
Track the car: Not yet
Avg number of times your car sees redline/day: Lately only occasionally.

Interesting thing with the soft limit (fuel cut) on MS3. It progressively cuts fuel to the various cylinders (don't remember if it rotates or just kills 1, then 4, then 3; or some such). Regardless, it is truly a soft limit, and if I held it, I'm not sure it would even rev to the hard limit. Last log I have, by the time I feel the falling off of power, I have lifted before I hit 7100 (half way). I think it is a really good cut.

Here is a picture of the soft cut coming in. Got to 7100, and then started down a little. Not bad at all, I don't think.

https://www.miataturbo.net/attachmen...1&d=1422482982

It did flash check engine light, so I think it went either hard cut or AFR cut, but only for a moment as I let off. I did not get a code flash.

Later, I held it, on a slight downhill, and it did go to hard cut.

I voted what I ran my stock '94 BP at:

RPM Limit: 7400
Built engine: All stock internally
Engine Specs: 14psi GT2560R
Track the car: AutoX rarely
Avg number of times your car sees redline/day: zero

I shift when it stops pulling, which with the 2560/BP was well before 7400.

I have the V6 set at 8500rpm but I never get there either.

BP @ 7400rpm: 4127 ft/min
KL @ 8500: 4137 ft/min :party:

6500 soft, 7,000 hard
Built: no
Engine: Stock MSM engine block + internals
Track the car: Several times a year
Limit per day: Not usually.

Since the car is also my DD, it's not worth risking early engine failure to rev it higher, plenty of torque lower for DD (and 3.63 gears to make that wider MPH range) that I only rarely top even 6k on the street. On the track, the reasoning change but the results are the same. Since I drive to and from the track I'd really rather not make a money shift, and grabbing the wrong gear when tired at the end of the weekend from 6,500rpm means i've got a substantial amount of extra time to catch it and abort before I hit really costly rev numbers.

If I was competing I'd have a different opinion, but I'm not.

So yeah, i've left the rev limit at the factory MSM value. Fully aware I could go higher, I just don't feel a need to.

I'll post one just to Give some variety...

RPM Limit: Nasa weekends 6000rpm, street/autocross 7000rpm i bump down the rpm for nasa to kill the peak hp number. in an attempt to be classed lower then TTU.
Built engine: last year no, this year yes. (2015)
Engine Specs: Custom Grind cam 228/237 @.50 .575/.575 lift @112 lsa, Texas speed Cnc ported heads, larger valves "manley" intake and exhaust. double roller timing chain, slp oil pump, Probe pistons, LS2 rods, stock crank.

Track the car: track, street,drift.. it's the car i drive when i feel like doing something stupid.
Avg number of times your car sees redline/day: 90% of it's life.

current state https://fbcdn-sphotos-d-a.akamaihd.n...1bdc51530b946d

Why not reduce timing in the higher rpm range to reduce TQ/HP and keep you under the limit which would give you a broader powerband? (flat HP curve based on regulations)

that is an option. On ls motors the more timing pulled the hotter the engine runs. so i'm trying to avoid that. also my ecu self learns, so it's constantly tuning. so instead of loading different maps sacrificing the tune it's learned, i just knock the main rpm down. i still have 300ft lbs of tq at 2000 rpm so i'm never waiting for the power.

Oh got it. I didn't notice that wasn't a miata engine in that pic. What ECU are you running?

i got a holley hp.efi the thing is sick. i love it.

7300 soft, 7400 hard. All stock internals. Balanced rotating mass. 220/201 Hp/Tq at 10 psi

KMag

We must be doing something wrong. If we ran our HPDE and race cars at the rev limit some of the folks in this thread are posting, we would be blowing up stuff constantly. I wonder how many use the stock tach as their reference. I wonder how many shift within 200rpm of the fuel cute every shift during the 5x 20 minute track sessions (including w2w races) every track day.

In a typical weekend, we might have an 30 minutes to an hour spent within 200rpm of the fuel cut at full load.

In my experience, the life of the stock NB long block that might otherwise last 100 race hours is cut roughly in half when the rev limit is set at 7400. Bump to 7600 and it's cut in half again. Bump to 7800 and it's cut in half again. Bump to 7900, half again. Yes, that's about 6 hrs. That's assuming the TB shaft doesn't let go before then, which it will.

I suppose if it's a street car, autocrosser or infrequent HPDE mobile, it might take a few months to accrue 30 minutes within 200rpm of the limiter at full load, the the reports of service life vs rpm far exceeding ours . I guess we are just a bit more conservative.

Thank you for making me feel sane about my "conservative" limits :party:

I noticed you said stock long lockblock? What do you find is the typical wear points for high rpms Emilio? (Other than the throttle body)Just curious.

I'm actually very surprised and now a little worried at how low everyone is setting their rev limiter.

I thought mine was set at a nice conservative 8200 down from 8400. My soft limiter kicks in at 8000 but I hit that at pretty much every gear change. My peak power is around 7800 (a bit over 175 whp) so I need the revs that high to keep the engine in the power band. I also run stock TB.

So far I've run the engine at 4 events, with 12 or so planned this year before a strip down and rebuild at the end of the year. Most my events are time attack, 5-6 min at pace and around 6 sessions per event. (so around 30mins of total engine wear)

I'd too would be very interested to know the sort of failures people see due to revs. I would expect valve related issues, so damaged valve seats, dropping valves etc. TB has already been discussed... any bottom end damage / extra wear?

I will hook my tach back up to the Traqmate before this weekend and do some analysis afterwards. I guess I could also run MS logs, too.

robert

Ran some very quick numbers from a typical 25 minute session at MSR Cresson:

Average RPM: 3959
Over 6500: 173 seconds
Over 6700: 76 seconds
Over 6900: 20 seconds
Over 7100: 11 seconds

And another set from TWS:

Average RPM: 5601
Over 6500: 176 seconds
Over 6700: 37 seconds
Over 6900: 14 seconds
Over 7100: 8 seconds

This is fairly old data (03/2013) with a very basic motor, just I/H/E type stuff done. I didn't know my tach feed has been dead so long. Kind of sad, considering it is just one wire that needs fixing.

robert

This is MT.net. Not TrackHQ.com

Pretty safe to say there are only a handful of folks who wring out their motors anywhere close to what you folks do in your Miatas. Especially those posting in this thread.

This! With a built engine, what RPM limit would you run?

Stock motor with I/H/E is at stock 7200. Frankly I'm a wuss and rarely, if ever see above 6800.

Building a Forged bottom end and a bp4w with +1 Manley valves and Supertech light double springs.

After reading Emilio's response, I may rethink my planned goal of 7600/7800 soft/hard cut. I'd like for this motor to last. Not trying to win anything, just enjoy trackdays. AFAIK the most wear happens in the valve-train when the revs begin to climb, I'm unsure of the amount of wear the bottom end receives from sustained high revs, aside from oil pump issues. We all have BE pumps by now right?

Stock engine, valve sets take a beating if it spends much time past about 7600. The NB1 has less seat pressure than the NB2 so it suffers worse. Main bearings also take a beating at those revs. Engine still runs, just doesn't make any power. So it's clear, I consider the useful life of an engine also defined by still being capable of making the power it's designed to.

Plenty of high mileage HPDE NB's running aroundon their original engine that runs smooth, don't burn any oil and have ~160psi in all cylinders. To me, that is not "still healthy". This is key to interpreting my previous post. Does it still have ~210psi and <5% leakdown?

Past 7600, rod like to stretch which leads to rod bearing wear and eventually failures. Stock BP crank flexes a lot, thus broken oil pump on high power or high rpm builds. It becomes critical at around 8500rpm. Cracked main caps, spun mains, bent rods, broken oil pumps there.

When spun to an appropriate rpm for the build, the engine should still be making within a few % of it's original power 50-100 hrs later. The BP's were not designed for high rpm so getting anything to last for 100hrs when being spun to 8k constantly is nearly impossible. 8krpm/100hrs is a $10~12k long block.

Emilio,

For a stock crank, stock main caps, Forged rods, forged pistons, ACL bearings, Harmonic balancer, oil pump, ARP hardware, and everything you sell for the head to build it, what RPM limit would you say would last 100hrs? Or 50 hours? Can a stock forged crank built engine every last 100hrs at 8K?

RPM Limit: 7400rpm
Built engine: Stock head and bottom end
Engine Specs: MSM BP4W
Track the car: Autocross, HPDE's coming and then more
Avg number of times your car sees redline/day: >25

Assuming light or heavy double springs, O/C that will never let oil go above 250°, cooling that will never let it go above 210°, O/P never below 45psi at full load, OEM width valve seats My guess would be 50hrs at full power. Gradually declining after that. at 100hrs it would still be good enough for HPDE but might have lost enough compression, mostly from valve seat wear, to not be effective as a race engine.

Personally, I have never seen a BP that frequently sees 8000rpm last 100hrs without enough degradation to be deemed ready for rebuild long before that. It's not a high RPM motor. Spin a BP to say, 7600 with all those goodies and 100 or even 150hrs is possible. Drop to about 7300-7400 rpm with all that and I think 200hrs would be a reasonable expectation. Again, that's based on my experience. Others seem to have different results.

Has Andrew chimed in? He does a lot of ail analysis and actually assembles some engines. While he's built fewer engines than our shop, he's far more hands on than I am.

7500 hard limit, I can't recall the soft limit
Built: no
Engine: Stock NB2, 106,000 miles.
Track the car: only autocross, and haven't made it to more than three a year for the past two years.
How often hit rev limit?: very rarely, but I do go above 7k all the time.

Hmm. My stock NB2 only has ~165psi in all the cylinders. Maybe that's why it seems down on power. That thing hits 7k or whatever the stock fuel cut is pretty often. Probably two - four times a day. It has 80k miles i think. Purrs like a kitten, starts every day, and doesn't burn a drop of oil.

Thats how I felt reading that too. When I had my turbo Miata it was 7000 soft 7200 hard.

All you other guys are nuts lol :party:

^^^^^ ditto.
built 1.6 @18psi. W2W 20 min. sessions /hpde/etc. went from 7200 to 7400 and promptly broke throttle shaft. I'm staying at 7000 rpm, thank you very much.
I've got the shift beeper the S2K nuts use, so every shift on the track is at 7000rpm.

Ok so I'm actually kinda surprised at the poll results. 80% of the miata people here who voted (currently 46) are at or below 7,500, with a solid 40% of all voters below 7,200.

I guess my question is, what is the weak link? If higher revs are bad/wearing things out too fast, what specifically is wearing out?

My guess is the bearings wear out from the crank flexing around too much. If this is true, I wonder what could be done to help? Higher oil pressure, better oil, better bearings, different ($$$) crankshaft?

1 month after raising limit from 7000 to 7400, i broke a throttle shaft. I dont believe in coincidence.