How to determine REDLINE?

[jspaeth]

Question for any engine geniuses on the forum....

Is there any way other than trial and error to estimate the SAFE redline of a worked engine?

Example: Stock SR redline is 7400 or so, but if you do head work and valvetrain work, clearly, the car could safely rev hgiher.

So, is it siimply a matter of someone doing the mods, and then trying to rev the engine higher (trial and error), or is there some systematic way to determine the new SAFE limit?

Just interested.....

[g6civcx]

I think your question is loaded.

Do you want to know how high you can rev without blowing anything?

Or do you want to know when your torque drop off is? At some point even though the engine can still safely rev, it makes no torque at all so there's no point in revving that high.

The second question can be determined with a dyno provided you know the answer to the first question. The first question should be directed to your engine builder.

[jspaeth]

Yeah I am interested in the first question.....

What allows a Ferrari to rev higher than a 240 (obviously, the workmanship and quality of the parts)....

So as you add stuff to the engine (head work, valvetrain, possibly bottom end stuff), how does the safe operating limit go up?

Assuming you have the power to pull to redline, if you do cams, springs, reatiners, RAS, valves, valve guides, blah blah blah, can you rev an SR to 8000 (just an example)?

What limits how high you can rev, head parts, or bottom end stuff?

These are questions that interest me, and if someone has a technical answser, that would be awesome.

[tt99ol]

technically both things limit your rev capabilities, ive heard sr bottom ends can do 8000rpm in stock form but the head is your main concern here, solid lifters, stiffer springs, titanium retainers, and solid cams can rev to 9000rpm or higher but then the bottom end cant keep up, the fix is to balance the entire rotating assembly for the rpms you want, once balanced there should be no problems in revving the crap outta the engine
gtautosound.com has a drag sr that revs to 9300rpm, maybe you should email them for a better explanation

[jspaeth]

haha I gotcha man....

So I guess with some head/valvetrain work you can raise the redline a bit, but beyond that, the whole system needs to truly be balanced, clearances checked, tested, etc......

[tt99ol]

yeah to be safe, i mean thats a lot of rpms were talking about, stuff goes wrong real fast, one good detonation and your pocket is empty, the least you can get away with is rocker arm stoppers, stiffer springs, and titanium retainers for 8000rpm but i prefer to be absolutely positive it will not come apart

[liv2drift045]

i know quite a few people who rev to 8k w/ minimal headwork.... but nothing past that

[Koopa Troopa]

Yeah I am interested in the first question.....

What allows a Ferrari to rev higher than a 240 (obviously, the workmanship and quality of the parts)....


The fact that they are a 4.6L V12. Small bore, short stroke and the head is designed to do so.

I will turn my rev limiter up to 9k when I get back..

I rev'd to 8k with my stock head. It was fine.

For an SR to rev high you'll need high duration cams, solid lifters, valve springs and a turbo that won't choke out.

My friend with a fully built SR was revving to 9.5k. He would have went higher but that was when the turbo choked out.

[dopeassjackson]

well if theres no more power up top then theres not much point in reving the crap out of it as long as when you shift you will be just in the bottom of the power band.
when i had my sohc NA i wouldnt rev it out to 6.5 because theres no power up there, i would shift sooner and try to keep it in the power band.

[jspaeth]

I am not talking about "what if there isn't enough power, the turbo chokes" here.....clearly you can get a turbo that can pull all the way through....

KoopaTroopa....good response.....I understand about the shorter stroke effecting the redline....good point on that....

How high would you guess you could rev on stock bottom end, but with cams, springs, retainers, and RAS, but WITHOUT solid lifters?

Just interested that's all

[BoostedCoupe]

This is all good info. I understand what parts you need to rev higher but more of what he is wanting to know is what determines the redline. like when you buy valves, etc. It dosent say hey these valves will allow you to rev 500rpm's more. So how do you find the redline out with out just reving the hell out of it and see if it blows.Or is that the only way trial and error. if so thats one hell of a way to find out.

[jspaeth]

This is all good info. I understand what parts you need to rev higher but more of what he is wanting to know is what determines the redline. like when you buy valves, etc. It dosent say hey these valves will allow you to rev 500rpm's more. So how do you find the redline out with out just reving the hell out of it and see if it blows.Or is that the only way trial and error. if so thats one hell of a way to find out.

well paraphrased....this is EXACTLY what I mean.....if I add X components, how high can I now rev....is it just from other people's trial and error?

[Koopa Troopa]

This is all good info. I understand what parts you need to rev higher but more of what he is wanting to know is what determines the redline. like when you buy valves, etc. It dosent say hey these valves will allow you to rev 500rpm's more. So how do you find the redline out with out just reving the hell out of it and see if it blows.Or is that the only way trial and error. if so thats one hell of a way to find out.

Trial and error.

I am not talking about "what if there isn't enough power, the turbo chokes" here.....clearly you can get a turbo that can pull all the way through....

KoopaTroopa....good response.....I understand about the shorter stroke effecting the redline....good point on that....

How high would you guess you could rev on stock bottom end, but with cams, springs, retainers, and RAS, but WITHOUT solid lifters?

Just interested that's all


If we're talking about an SR I was told 9k and no more by someone very experienced so I'm going to take his word for it. Without solid lifters? I wouldn't go past 8. At that point you have to worry about the lifters not getting oil to them. If you want to build an SR that revs then a solid head is the only way to go. Just remember, the higher the duration the higher the power band will be and the higher RPM you'll be able to operate in.

After that then you have to worry about bearings being able to handle oil pressures and the rotation of the crank. 9k is really all you need though.

[slow40sx]

couldn't u just run it on the dyno and see where ur power band falls off

[RBbugBITme]

I would think there is quite a bit that goes into this and no one on here could difinitively answer that for you. There are tribological effects that will reduce the life of every moving component, the oil's ability to lubricate under increased loads and surface speeds, strength of materials obviously, heat, trans capabilites and I'm sure I'm missing stuff I don't even know about. Plus you really have to pick what kind of life cycle you want to deal with. If you build it to rev to 9k but it can only do it for two or three pulls what good is it to you?
However, usually the only thing I ever see mentioned is mean piston speed at the desired RPM. If you're daily driving this car though, you really don't want to run the car up to 9k unless you have your own towing company.

[nissan240sxkid]

Umm...here is another way to figure out your rev limit....which is kinda the way every one has already said....for one your cam choice because thats one of the first things people do and inexpensive, so you wouldnt get a set of 264 and need the car to rev past 8k there wont be any great power gain there...yes you can do the turbo but the turbo has to have the cams swallow the air into the cylinders at high rpm for big power....with what Koopa Troopa said no more than 9k, 8 would be enough with light modded engine...would still do springs and retainers, better to be safe than dumb...
The solid route is great also that is what I run....also when you are going into the 9k plus the bottom end has to be balanced, factory tolerances are not meant to go 9k plus and you want your rotating assembly to be as light as possible for longevity...When you rev high for a long period of time lets say 9k plus you have to remember that stock water pump will run the risk of cavitating and electrolysis so you might want a bigger pulley as well as oil pump safety ect...

[Koopa Troopa]

couldn't u just run it on the dyno and see where ur power band falls off

That doesn't tell you if your motor can survive operating at those RPM's...

If you're daily driving this car though, you really don't want to run the car up to 9k unless you have your own towing company.

Eh, only reason I left my revlimit at 8k was because I didn't feel like having a car that wasn't tuned from 8-9k RPM's so what was the point in changing it... When I get back I'll change the rev limit to 9 and that's in a car that's my only driver..

SR's like getting the piss beaten out of them.

[slow40sx]

That doesn't tell you if your motor can survive operating at those RPM's...


yeah but it helps u see if its even worth reving up to 9K ur motor might be built to rev to 9K but if ur power is fallin of at 8200 then y rev it all the way to 9 thats wasted time, power, stress on the engine, and not to mention gas

[Koopa Troopa]

I'd like to say your turbo and cams should automatically dictate that but.... :rofl:

[RBbugBITme]

You guys are still talking about tunes and flow capabilities when he is asking about mechanical capabilities.

[nissan240sxkid]

I kinda answered a bit about both flow and mechanical capabilities

[jspaeth]

yeah but it helps u see if its even worth reving up to 9K ur motor might be built to rev to 9K but if ur power is fallin of at 8200 then y rev it all the way to 9 thats wasted time, power, stress on the engine, and not to mention gas

FAIL infinitely....read the thread man, I've said 100 times I am not talking about "what's the point if there's no power"....I am talking about the mechanical ability of the engine to operate at that RPM..


You guys are still talking about tunes and flow capabilities when he is asking about mechanical capabilities.


Thank you, god, you get it!

[jspaeth]

That doesn't tell you if your motor can survive operating at those RPM's...



Eh, only reason I left my revlimit at 8k was because I didn't feel like having a car that wasn't tuned from 8-9k RPM's so what was the point in changing it... When I get back I'll change the rev limit to 9 and that's in a car that's my only driver..

SR's like getting the piss beaten out of them.


Are you running a stock bottom end? I could see headwork allowing for a small increase (maybe to 8K), but I am surprised that with the stock stroke, you can go to 9K....as someone said, peak piston speed plays a large factor.

Glad to hear it though, after some headwork, maybe I will raise mine to 8K...with cams and a GT2871R, maybe I could use the extra 500 RPMS...I could have sworn I've seen some dynos that pull to redline.....

[nissan240sxkid]

2 simple ways:
Dyno see what your mods do (trial and error) set limiter as needed

Factory limits (systematic) + aftermarket parts new power band (systematic)

Will let you know where to draw the line...

The block with no sleaves will be at a 400 to 500 limit

non sleaved but built will let you rev to whatever but power would still have to be in the 400 to 500 plus limit and head mods

built head motor and sleaves can go 9k plus and 500++++

The limiter should be set on mods, your motor is built so thats good..

[cgtdream]

Talking to an engine builder would help alot, and your heading in the right steps to try and research things out....

Anywho, i wish i could pull up some links for you, but i dont have them...anywho, from what ive learned when it comes to understanding, and raising your redline, is that it centers around when and where you make the most power....doing what most have suggested and getting your car dyno'd is one way, and also, i belive, a flow chart of your cylinder head helps....but what really helps the most, are your goals.....

Just wanting a high reving engine, isnt a goal, and im sure you know that....having a purpose of where you are going helps much.....like building an engine for autocross, or rally....maybe drifting or racing right?

Anywho, have a goal...cause from what i understand, the reason why the redline is where it is on the sr20, is because the turbo cant go higher, and the stock internals will not let it right? and thats good, because a turbo usually makes power in the lower rpm ranges and drops off in the mid to high...right? if im wrong, sorry for the mis-info, but i beleive that turbo cars, usually dont redline any higher, because of effeciency issues....i mean, dont most turbo cars even after adding on larger turbo's usually see a redline btwn 6-8.5k????

sorry but now im curious too as to how turbo cars work when raising the rpm.....so sorry if i sound noobish ^_^

[RBbugBITme]

I was really hoping this would turn into a technical discussion about engine mechanics.... I guess its just not the place for it.

[jspaeth]

^ Yes me too...

People just keep fucking talking about flow potential and turbo efficiency.

FOR THE LAST FUCKING TIME:

This thread is not about powerbands or turbo efficiency or torque or anything to do with the car's performance.

It is only about what can the motor mechanically handle without blowing up.

Jesus Christ





............'s birthday is in 2 days

[Koopa Troopa]

I was really hoping this would turn into a technical discussion about engine mechanics.... I guess its just not the place for it.

There really isn't room for it in this thread as the question is limited to SR engines and we've already discussed why SR's generally can't rev high. We'd be going off topic if we wanted to talk about rolling rockers and pushrods. The only thing keeping anyone from revving high is their tune and flow so yeah, that's why we keep going back to it.

Are you running a stock bottom end? I could see headwork allowing for a small increase (maybe to 8K), but I am surprised that with the stock stroke, you can go to 9K....as someone said, peak piston speed plays a large factor.

Glad to hear it though, after some headwork, maybe I will raise mine to 8K...with cams and a GT2871R, maybe I could use the extra 500 RPMS...I could have sworn I've seen some dynos that pull to redline.....

Only thing not stock are my ARP rod cap bolts... Stock stroke on an SR is perfect. 86mm bore and 86mm stroke. I don't know why people feel the need to change it. I was revving to 8k with a stock motor, not that there was any gain from doing that... I just remember hitting the limiter during gymkhana every now and then...