rev limits?

[jr1349]

this is a question that was raised by Burns in another thread, but one id also be interested to know the answer.

for my xjr13, the rev limiter kicks in at about redline, and the engine wont pull past 10 grand.

in the past on other sites some legends guys have commented that their limiters come in after 10k, and Pat (I think) has said that his 12 goes past 10k without noticing a limiter.

so the question is, if anyone knows that is, what are, if there are, the different rev limits across the range of fj's?

id be interested to know as its possible that it may be worth my while to go to a higher limit, if it can be done economically, to maximise top end power for the drags.

so, does anyone know?

k

[Burns]

this is a question that was raised by Burns in another thread, but one id also be interested to know the answer.

for my xjr13, the rev limiter kicks in at about redline, and the engine wont pull past 10 grand.

in the past on other sites some legends guys have commented that their limiters come in after 10k, and Pat (I think) has said that his 12 goes past 10k without noticing a limiter.

so the question is, if anyone knows that is, what are, if there are, the different rev limits across the range of fj's?

id be interested to know as its possible that it may be worth my while to go to a higher limit, if it can be done economically, to maximise top end power for the drags.

so, does anyone know?

k

I know that is common to set up some race bikes to wind up well over their max-power rpm.  Those motors make less power at the top of their rev range than they do a bit lower in their "sweet spot" but there are track conditions (especially dirt flat track I'm told) where that is called for.

I'd guess that with the same cam/exhaust etc spinning your motor tighter will probably not make more power. Just a guess though.

[jr1349]

this is a question that was raised by Burns in another thread, but one id also be interested to know the answer.

for my xjr13, the rev limiter kicks in at about redline, and the engine wont pull past 10 grand.

in the past on other sites some legends guys have commented that their limiters come in after 10k, and Pat (I think) has said that his 12 goes past 10k without noticing a limiter.

so the question is, if anyone knows that is, what are, if there are, the different rev limits across the range of fj's?

id be interested to know as its possible that it may be worth my while to go to a higher limit, if it can be done economically, to maximise top end power for the drags.

so, does anyone know?

k

I know that is common to set up some race bikes to wind up well over their max-power rpm.  Those motors make less power at the top of their rev range than they do a bit lower in their "sweet spot" but there are track conditions (especially dirt flat track I'm told) where that is called for.

I'd guess that with the same cam/exhaust etc spinning your motor tighter will probably not make more power. Just a guess though.

only one way to find out, eh Burns?

where your max power is can be changed by tuning, ignition timing, but especially jets in my case, but its more about versatility, if for instance, as seems to be the case with my bike, I keep increasing jets and the peak power keeps going up the rev range, as seems to have happened since I've fitted the pods, then being able to utilise that power, if its likely to be happening beyond my current rev limit, is what I'm thinking about with this enquiry, so I'm interested to know if there are any options in the fj range.

realistically, if for instance I was in a position to be making peak power at 11 or 12k, then I would obviously need a programmable ignition system, or at least be able to somehow reset the limit with my current one, in which case the obvious choice would be a full dyna ignition system including the legends ignition plate, where I could set both initial and total advance at will, as well as both a top end and launch rev limit, and possibly have a gear position setting for nitrous, on top of the fact that the dyna coils provide extra spark.

thinking about it, if I find my power output limited by the rev limiter on my bike, then the dyna 2000 is the logical next step, increased revs, spark and tune ability, whilst maintaining my mandate for an internally stock engine, yeah that'll work, but I haven't finished working with the stock ignition yet, just thinking about other more power alternatives, cost effectiveness is the next question though?

k

[Pat Conlon]

If you have not upgraded your valve springs, be careful of valve float happening north of 10k.

[jr1349]

If you have not upgraded your valve springs, be careful of valve float happening north of 10k.

will do Pat, gotta get there first, cross that bridge when I come to it I reckon

[Burns]

only one way to find out, eh Burns?




yep.  You don't know how much power a motor can make until you blow it up.

[jr1349]

only one way to find out, eh Burns?




yep.  You don't know how much power a motor can make until you blow it up.

personally I've never blown up an engine, you Burns?

[simi_ed]

I've torched a few. I don't recommend it.  It's an expensive PITA, every time!  Single cylinder, 4 cylinder, auto V-6, it's all the same.

My 2¢.

[Burns]

personally I've never blown up an engine, you Burns?
[/quote]

I've tossed a couple of rods in my younger days. One was on a SL125 that I put a 305 Honda piston in. Ran great. Lasted about 10 races.

The "peak" in "peak power" for any motor is the spot just below where it comes unglued. If you are racing (and the rules allow it) you will spend a lot of money finding that spot.  You'll pump it up 'till it breaks then back off to where it lasts long enough to do its job.

If you want to do that with your FJ I suggest you get two - one to ride and one to do the build-and-blow-up boogie

It's a great dance but ya gotta pay the piper. A lot.

[jr1349]

I've tossed a couple of rods in my younger days. One was on a SL125 that I put a 305 Honda piston in. Ran great. Lasted about 10 races.

The "peak" in "peak power" for any motor is the spot just below where it comes unglued. If you are racing (and the rules allow it) you will spend a lot of money finding that spot.  You'll pump it up 'till it breaks then back off to where it lasts long enough to do its job.

If you want to do that with your FJ I suggest you get two - one to ride and one to do the build-and-blow-up boogie

It's a great dance but ya gotta pay the piper. A lot.

in my experience there are two ways to blow up engines, ignorance, and incompetence, I suffer from neither afflictions and I go my own way, based on my personal knowledge and experiences, I realise that many don't go their own way, but follow trends (well when it comes to mechanical stuff anyway), that aint me, if I were to suffer a blow up, so be it, I would learn from that experience, and move on.

unfortunately Mr Burns I don't find you to be of particular expertise, clearly that's not your opinion, we are simply going to have to disagree on that.

I started this topic to see if there was much of a knowledge base about rev limiters with the fj/xjr engine format, seeing as there has been little comeback on the topic, I see no reason to indulge you further.

k

[Burns]

I take no offense and certainly do not hold myself out as a master mechanic of anything close to it. But I've been around folks who push their machinery to the limit (the XS650 crowd) and I respect such folk greatly. They tell me every motor HAS a limit (XS650 cases break just North of 70 hp e.g.).  So, like you say, we'll just agree to disagree on that one.

Best of luck on your project(s) and Happy Riding.

[Firehawk068]

I am no expert when it comes to the programming included in the FJ ignition control box, but I do believe I have verified on a few occasions that my 1990 has a rev-limit somewhere around 11,200 rpms.......................at least according to the stock FJ tach.....................
I don't recommend running the engine up that high, nor did I do so intentionally.......................Lets just say that I got a little overzealous with the acceleration a few times getting on the freeway, back when I lived in Phoenix (It had more power before I moved to Denver), and was not watching the tach until it reached the rev limiter.
It takes a tad longer to reach, say....................10,000 rpms up here, so I am more aware of how long it takes to get there.............

Having done a bit of research on engine theory, and design however.....................I believe the peak horsepower,(and more toward your interest) the RPM at which it occurs, is more a factor of intake/exhaust port size/shape, camshaft lobe size/profile/timing, than it has to do with jet sizing or fuel intake.....................Valve size also starts to enter the mix when you start increasing the port sizes, and the camshaft lobe sizes/duration..........
Airflow is the limiting factor when it comes to horsepower...............and I'm pretty sure, at 36mm, the carbs are about the max size our stock FJ/XJR engines will accept, given the port configuration, valve size, and camshaft profiles.........................Some have used 38's successfully, but they have also increased the displacement beyond 1249cc..........................Granted, you need to start adding more fuel if you are increasing the airflow.................
You are not going to change the rpm at which your engine makes peak HP just by tweaking the jet sizes or needle position..............You will be able to maximize the AMOUNT of horsepower at any given rpm by choosing the right settings.................but not the rpm which it occurs.............
When I lived in Phoenix, I had my FJ on a dyno once.................It made peak HP at 8,600 rpms...............Does it make horsepower north of that? Sure.................just not as much.........

If you really want to increase airflow through an engine, and make big HP........................Add a turbocharger..............................Small engines CAN make big HP........
If you want to blow your mind, look up the BMW Formula-1 racing engines from the mid-80s...............
They used production car engine blocks that were "Well Seasoned", and made close to 1,400 HP from a 1500cc 4-cylinder in "Qualifying" trim...................They ran close to 80psi of boost!  

[jr1349]

fella's, this aint my first rodeo.

interesting to know that you've found a rev limit at 11,2 Firehawk, of course, the accuracy of the tacho is relevant, I wonder if the engine actually can rev faster than the tach can read when tuned with all the bolt-ons, from what I've read the legends engines that use fj ignitions found a rev limiter at about 10,2, and from what I can gather their category sealed dyna ignition units are about the same.

which brings me to my next point, ahh the turbo era, imagine where engine technology might be today if turbo's weren't banned in F1 20 odd yrs ago, of course they are back now, but in a whole other capacity, all they would have had to do was limit boost to equalise the competition back then, instead they decided on a 3L V10 engine format of completely exotic engineering, instead of, as you say Firehawk, with some production based components like the bmw engine block, interestingly, Jack Brabham's repco sohc V8 that won one of his teams championships in the late 60's, was based on a buick engine block, and the same casting was used for Holden (GMH) V8 engine blocks down here in oz, obviously, the casting aside, the engineering between the two applications is poles apart.

but like some other particularly well designed production engines, our fj/xjr engines are particularly robust in design, not without weaknesses of course, but still, as a base to work on, particularly for its age and price, an excellent piece of kit to work on, and work hard, just ask the legends guys, I cant even remember the last time I heard of one our fj/xjr engines having a major failure out of the blue.

but what I've noticed since fitting the pods and jetting up is that peak power is going higher up the rev range (from about 8k with the airbox and now about 9K with the pods, and I've only just started tuning them really), and envisage that its possible that I may find that my peak power may actually end up being limited by my 9.5-10k rev limiter, and if so, then id be interested in what options may be available for me to do something about this, hence my enquiry of this thread.

whatever the tuning limitations of my engine in its current state are, I will find them, the technicalities of what should or should not be possible I have no interest in discussing, I've proven to myself many times over the years that a lot of what people tend to believe is only true within certain limited parameters, and that if one simply goes their own way, you find out what is actually possible, so I tend not to very impressed by fear mongering about blow ups, if you know how to run engines safely, blow ups simply don't occur, providing you take the relevant precautions.

I'm not saying I know better than everybody, I have, however, proven over the years that I do know better than many who claim to know a lot though, especially those armed with only hearsay, and not direct personal experience with the hardware and parameters at hand.

personally id be more interested in nitrous than turbo's, if I was going that way, possibly instead of a dyna ignition too as I think they cost about the same, its a bolt on that you don't need to modify your engine for, only tune for, yet delivers similar results, if you know what your doing.

interestingly, I read an article in a local bike mag about a bloke who has a 250hp turbo'd zx12r, or had one 10 years ago, turns out this bike was featured in the very first issue of the mag, so the mag chased this bloke up for their 10th anniversary edition, expecting the bike to no longer be, instead they found the bike rebuilt and making 500hp now, and without nitrous, which is very surprising to me because the only other bloke I've heard of trying to make 500hp out of a street bike was in a similar article I read in a pommie magazine featuring Guy Martin's (of IOM fame) pet project gixxer 11, who was making about 300hp or so but was saying he needed nitrous to make the 500 he was chasing, of course a year or two later I read the zx12r article, sure, neither of these bikes are low budget projects, but its interesting to me how a bloke down here is oz just decided he wanted his 250hp zx12r to do 400kmh, figured he'd need 400hp to do it, but ended up with 500hp, and without nitrous, and these engines aren't much smaller than the 1.5L F1 engines of the turbo era, which made up to 1500hp in qualifying trim, now I'm not thinking anywhere near along the lines of any of these situations, but this does highlight what is possible when one does not take direction, and thinks outside the box.

I'm just gonna tune my engine my way, and see where I end up, hell I'm only trying to get the thing into the tens at the drags, and I was only 0.06s off it with the airbox fitted.
interestingly, with the airbox peak power was about 7.5-8k, I would rev it to 9k in some gears but not in others, whatever seemed to work best, but with a 120 main jet the thing would flood and stall at 7.5k, like it was hitting the limiter hard, I tried to tune around it but didn't manage to change it, so I went down to 117.5 jet, and she pulled straight through to rev limiter at 10 or so k, making the best peak power it ever had with the airbox fitted, so I'm interested to see how much fuel I can give it now, with the pods, and how much quicker it will go, if at all, when I've maximised the tune up with the current engine hardware.

it is what it is gents, this thread was about rev limiters, and nothing else.

k

[ribbert]

in my experience there are two ways to blow up engines, ignorance, and incompetence, I suffer from neither afflictions and I go my own way, based on my personal knowledge and experiences, I realise that many don't go their own way, but follow trends (well when it comes to mechanical stuff anyway), that aint me, if I were to suffer a blow up, so be it, I would learn from that experience, and move on.
k

That is not only a contradiction but as Otto Von Bismarck said. "A fool learns from his own mistakes, a wise man from the mistakes of others" You could save yourself a lot of money, time and heartbreak learning from the experience of others.

I'm not saying I know better than everybody, I have, however, proven over the years that I do know better than many who claim to know a lot though........

Err, I think you might be.

However, on the subject of your original post, does the FJ have a rev limiter, I have just read Firehawks post and don't believe it necessarily suggests the existence of one. I don't know whether they do or they don't, but I suspect not. The absence of answers to your query probably stems from the fact that no one sees any point in revving the shit out of an engine beyond it max power and beyond it's design parameters.

In my opinion, the FJ's are a relatively innefficient engine and not capable of over revving themselves to destruction easily, unlike more modern machines and I think it's likely that what Firehawk experienced was the engine reaching the limits of it's efficiency.
Rev limiters were introduced as engines became more efficient and easily capable of revving themselves beyond their mechanical limits (OHV and hydraulic lifter engines were sort of self governing) and if fitted, kick in just above redline, not 2000 rpm higher.

I have seen inside the engine of a fairly new (at the time) Porsche, without a rev limiter, blow up on a single flat shift.

Noel

I would not be surprised, given their age, if the FJ,s didn't have them.

[Burns]

you are clearly far more knowledgable than me in this area (your et's speak for themselves) but your statement " if you know how to run engines safely, blow ups simply don't occur" is a bit of a stretch.  We've all seen pro-built engines come apart just after the Christmas tree said "go".