View Full Version : General rev limit questions
One for people to get their teeth into :)
What is the highest RPM people would run on a stock engine? The VVTi goes to 7200rpm but the boggo 2JZ runs to about 6800rpm. I think we have had that discussion before and there are mechanical differences? I think, though, that Chris Wilson once said 7200rpm would be as high as he'd safely push a non-VVTi engine.
So, I know fatigue effects increase massively as revs go up, but what's the real show-stopper limits? Valve bounce, valve float, and a piston plain old falling off? Would higher lift cams exacerbate the valvetrain issues?
Anyone know of engines being run at higher-that-stock limits and if they are still intact?
-Ian
Well it's the valve train mainly AFAIK...if you upgrade just the springs you should be able to sustain more..but if you're also running big power then the rod bolts too that will fail.
I have run the VVTi to 7500 rpm with no issue on stock valve train.
Yep, deffo the rod bolts, that's what I've heard ;)
Terry, can you recall what, if any, differences there were between VVTi and fixed cam engines to allow this higher stock rev limit, or is it just a case of better breather via the VVTi made higher rpms worthwhile? And what lift are you running, do you know?
7500rpm is good :thumbs:
-Ian
The valve train looks the same mate.
For the valvetrain its the maximum valve acceleration that is key, so you might be able to run a higher lift with a wider duration quite safely with enough cover on the stock spring as you are moving the valve and lifter further but over a longer period of time.
For information, force = mass x acceleration. If you know the cam profile well enough to plot lift against time, you can convert that to acceleration against time. If you know the mass of the follower and valve you can work out the force that the spring must excert against it to keep it in contact with the cam lobe to prevent valve float. If you know the load vs. compresion curve for the spring you can check to see if the stock spring is suitable or not. Provided you have the right numbers to plug in, this is a straighforward but valid calc for a simple "static" analysis.
Once you add in the spring dynamics and things like spring surge becomes a factor, things go behind what you can do with Excel.
Simply upping the spring load to keep the lifter in contact with the lobe will increase the contact stress on the lifter and increase the wear rate.
For the bottom end, the limiting factors will be (as mentioned above): Big end bolt preload, little end loading, or connecting rod shoulder loading due to the increased intertia loads at TDC on the exhaust stroke. Stronger rods and bolts will solve this.
What you can't do much about is the affect this increased loading will have on the oil film thickness around the crankpin, so you run the risk of knackering the lubrication.
Other things to consider are: Overspeeding the accessories (different sized pulleys can limit the effects of this, but at the expense of "nomal range" operation), and overspeeding the oil pump (although a bit more oil pressure wouldn't go amiss to help counteract the oil film issue.
Ian, after our chat the other day and reading this, I realised whilst driving today that my car doesn't hit the rev limit until 7500-7600rpm. TBH I always thought this was the stock limit, but you say it is 6800rpm on non-VVTi yes? If this is the case I've no idea why mine revs higher, as it is stock ECU with original emanage :shrug:
Ian, after our chat the other day and reading this, I realised whilst driving today that my car doesn't hit the rev limit until 7500-7600rpm. TBH I always thought this was the stock limit, but you say it is 6800rpm on non-VVTi yes? If this is the case I've no idea why mine revs higher, as it is stock ECU with original emanage :shrug:
Mines the same too. Could it be that speed limit defender also raises/removes rev limit????
Do any Supras have peak power any where over 6000 anyway? My bhp and torque are about 5500 and 5000 revs so no reason to go over about 6300 anyway! You're going back down the power band so why the need to know if it'll rev any higher? Or am I missing something fundamental here?
Due to a bonkers tuning effect, Ian C's car makes peak power at 6300 or something daft like that.
Also if you don't have to make a shift from say 4th to 5th on the drag strip you will reduce your 1/4mile time.
Once people fit cams especially ones like 264's or 272's the peak power moves significantly up the revrange as the engine can still breathe at these high RPM's. Once the cams are not a restriction it's the stock turbo's....unless you don't have them. ;)
.....and the stock rev counter is a long way out up top guys.
I have no idea why you would see 7500rpm on a stock ECU even with a Blue E-Manage. I know my rev limit was disrupted by a gammy sAFC, which as far as I'm concerned is impossible considering what the AFC does and how it's wired in. Nonetheless I hit between 7000 and 7200rpm on several occasions, according to the peak hold on the sAFC, the AVCr, and the fact I crossed the line at Pod doing 120+mph in 4th gear. I also had a mystery random rev limit in 1st gear only, again, even more impossible. It would cut in anywhere from 6000rpm up.
Then the AFC stopped changing the airflow signal anyway, while still reporting it was, and I entered the 5 months twilight of my overfuelling problem :cry: Upon fitting the E-Manage and having the problem clear up, the stock limiter was back in action and has been ever since, and the phantom 1st gear one has gone.
So it might not be just an overreading rev counter, there may be a similar bit of fruitiness going on for you guys. I've thought about this and can only conclude it can't be done, which is worrying because I know it can :looney:
Onto the other question about why raise the rev limit, yep, the stock engine on stock turbos will run out of puff at about 6000rpm. With 256in264ex cams in it was strong up to the limit, though. Hybrids work better at these higher revs because stockers start to run out of flow capacity (boost drops off or power drops due to overheating the intake air). The single turbo with it's manifold and so forth meant I saw peak power at 6630 rpm! The graph shows the curve juuust starting to tail off but it's so close to the rev limiter it may be an artefact of that :blink: it tails off by all of about 5bhp anyway. So, if the rev limit was at 7200rpm instead, by hook or by crook, the gearing would allow for 200mph+ ;) and there would still be enough power on the curve to get it there. See where I'm going with this? :D
-Ian
See where I'm going with this? :D
-Ian
Yeah you need more power
:p
Yah, 1.8bar, race fuel, buckets of advance, 7500rpm limit - and a spare engine and a flatbed truck. TOTB suicide spec lol
-Ian
Yah, 1.8bar, race fuel, buckets of advance, 7500rpm limit - and a spare engine and a flatbed truck. TOTB suicide spec lol
-Ian
Tut Tut, thought we were building true road cars.....;)
Seriously, just do the bolts :limp:
Don't forget a T76GTS... ;) :p
Don't forget a T76GTS... ;) :p
No Ian's onto GT47's now .........
Full Race will supply a manifold for a GT55....we need to convince Ian.... ;)
.....and the stock rev counter is a long way out up top guys.
I never thought that this may be a problem. How far out do you reckon it could be Tel? And which way?
Full Race will supply a manifold for a GT55....we need to convince Ian.... ;)
And a HUGE hole in the bonnet LOL, go on Chis, see if the E-Manage can control 1600cc injectors ;)
I never thought that this may be a problem. How far out do you reckon it could be Tel? And which way?
Difficult to say CJ, as much as 500 rpm( worse the higher it goes)....... ( it reads high)
If you two have quite finished :rolleyes:
Rod bolts. Must get them done. Sigh, more £'s.
So back on topic then, the general idea at the moment is that 7500rpm is do-able with ARP rod bolts, 7200rpm is do-able on stockers but probably not for very long and maybe not with the power output I have now. The valvetrain will survive and function correctly and only over long long term could fatigue problems arise?
-Ian
Yeah, I've seen it 5-10% off compared to the rpm signal.
It over-reads
The stock set up seemed fine at 7500 rpm, the only reason I am suggesting rod bolts is safety, they are the weakest link.....goodbye ;)
If you two have quite finished :rolleyes:
Rod bolts. Must get them done. Sigh, more £'s.
So back on topic then, the general idea at the moment is that 7500rpm is do-able with ARP rod bolts, 7200rpm is do-able on stockers but probably not for very long and maybe not with the power output I have now. The valvetrain will survive and function correctly and only over long long term could fatigue problems arise?
-Ian
It`s 8000 for Dave H! :clap:
from a thread testing out a w58 box on his NA/T (stock internals GE engine except ARP bolts and HG)
5-speed + 600-700rwhp = ??
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I put the stock 5-speed back in my car today since we don't have any drag events for a couple weeks. I'm gonna do some tuning with it, since it's much easier to tune with this rather than the auto and loose converter (plus the auto gets really hot after a few consecutive pulls). I have a clutchmasters stage 4 clutch, the pedal pressure is a bit more stiff than I like, but it is holding well so far. I went out and did a few pulls with the boost at 25 psi, which should be well over 600 rwhp. The car does seem to accelerate harder with the manual trans vs the auto. I've already found a few flaws in my tuning, this should be good.... get the tuning dialled in and then crank up the boost. We'll see what the W58 will take.
ps: I'm running a trans blanket just in case....
So far so good.....
We went out and did some tonite today, man the 5-speed rocks for tuning! The big turbo definitely needed tuning, as it went way lean on top compared to the PT72 on the same tune. All was good, a/f in the mid 11's until around 6200 and then the a/f slowly went lean until near redline it was 13:1!!! If I would have heard my buddy yell I definitely would have let off the throttle.... thx to race gas for not letting the motor blow.
We added a ton of fuel up top and then did some fine tuning at base boost of 23 psi. Then we turned the boost up incrementally and tuned each boost level until we were up to 30 psi. The car hauls butt at upper boost levels. The GT42 really wakes up at high boost.
disclaimer: All tuning was done by trained professionals on a closed course... I was looking through the datalogs and the car goes from 80 to 130 mph in almost exactly 3 seconds.
Quote:
Originally Posted by DaveH
the car goes from 80 to 130 mph in almost exactly 3 seconds.
Dave, is that in 4th gear? Also what diff ratio have you in?
That was 3rd gear, once the car makes serious boost (~5200 rpm) to the end of the run (~8000 rpm), I have a TT auto diff (3.77:1). I did one pull through 3rd and then 4th gear, it goes through 4th gear about as quick as it goes through 3rd.
Full thread here...http://www.clubna-t.com/forums/showthread.php?t=399
Now you're going to tell me how that relates to this thread.
Now you're going to tell me how that relates to this thread.
We`ll take this in easy stages for you Alex..
original post asked....
`General rev limit questions
One for people to get their teeth into
What is the highest RPM people would run on a stock engine?`
my post was merely to ascertain that 8000rpm is `do-able` on a stock motor...ok?
Now what part don`t you understand??
Well....9000 is do-able but how long will it last? And you're talking about an NA head...which for all I know has different springs/shims and valves in it...
yes, i know what you mean, but i still reckon Toyota were being ultra conservative with their rev limit
Well I shan't run 30psi or 8000rpm thanks ;)
-Ian
I am running an AEM with standard engine and my rev limit is set to 7500rpm, not had any issues as yet and its been like that for well over a year maybe two now.
:)
A few Q's:
Rods:
These ARP rod bolts: Do you do torque them up any tighter than stock?
If the answer is no, then athough the bolts themselves probably won't fail, without a higher torque they won't impart any more preload to the big end, so they won't be any better than stockers for stopping the con rod cap separating. What are they made of? What are the stock bolts made of?
If the answer is yes, then what does it do for the roundness of the big end bearing bore? They are only truly round when done up to the stock torque.
Valvetrain:
How does anyone actually know that the stock valvetrain is good for anything higher than stock RPMs? What is this being based on? AFAIK we don't know that the springs for the VVTi are actually the same as the stock ones, even though they may look the same. Has anyone actualy tested the spring rates? Has anyone stripped a head after sustained running at high rpm?
If anyone thinks that an OEM is "over conservative" with anything, I suggest that they run their modification at full chat for 500 or 600 hours and see what falls off first. Chances are if won't be an OEM part. :(
Yah, 1.8bar, race fuel, buckets of advance, 7500rpm limit - and a spare engine and a flatbed truck. TOTB suicide spec lol
-Ian
Good luck Ian :bang: :D
Piston speed guys comes into play aswell ... I think about 4500fpm for a tund motor is the limit .... dont quote me on that,lol
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