No 'magic', just sound guidelines.

 

8500rpm is my limit

 

If this is your dynochart:

https://www.evolutionm.net/forums/sh...d.php?t=235300

You're losing power rapidly after ~7200rpm, and if you take the time to calculate optimum shiftpoints, you'll very likely find that spinning to 8500 rpm makes you go slower. Not to mention that it's needlessly harder on the motor.

FYI

 

I'm wondering what those guidelines are based on. What happens beyond those speeds and why? Who are these people in the race industry who have set these guidelines and what do they say they're based on?

 

Shaun, if you have something to say, then why not just say it?

 

I have questions and I just asked them in the last two posts. I have asked these questions elsewhere and have received no good answers either. I have read some good books and papers but never seen anything regarding this in detail. I've heard good people talk at length on a range of topics, but never anything about this specifically or in ways you mention, so I'm wondering how or where you got this race industry consensus. What are the factors as you understand it?

 

I've had the opportunity to talk about this (and other things) casually with several interesting persons, including a Ford Zetec engineer (F1), a BMW engineer (associated with the McLaren V12), and a few others.

In general, the direct issues associated with high mean piston speed include material limitations (due to stress and fatigue), friction and heat, ring flutter, and lubrication efficiency. I recall a Ford SVT engineer (U.S.) mentioning that in his experience, the rate of reciprocating parts failures tends to increase exponentially above piston speeds of ~4000fpm. The majority of decent, respectable experienced opinions on the subject I encounter usually concur with the figures I quoted as reasonable guidelines (or are even more conservative).

Of course, there are indirect issues that often inhibit the need for extreme mean piston speeds, such as the difference between piston speed and flame front speed (especially with short rod/stroke ratios), which makes combustion less efficient, as well as VE issues. As a result, it's often of no benefit to generate such high piston speeds, simply because VE vs. rpm characteristics seldom warrant it (especially in street driven applications).

I don't think anyone will disagree that the quickest, easiest way to accelerate wear and reduce longevity of an engine is to spin it. For an engine that is expected to endure many miles of street service, it's an important consideration.

 

It is acceleration that stresses and fatigues, not speed. You can have similar speeds at different accelerations.

The first two I understand, but with lubrication efficiency, what happens? With greater piston speed isn't hydrodynamic lubrication better?

That's because that happens to be the point at which forces grew large enough to start fatiguing the component. The forces from the very start rise exponentially so failures should too, except for strength overkill for the lower forces in the lower engine speed range.

The reason the guidelines are vague and have a large range to them is because they are trying to approximate component mass, component strength, forces magnitude and vectors, and number of cycles. It can't be done easily, especially not when you get to setups that are not common. 10 years ago the blanket guidelines for mean piston speeds were extremely low although the same materials and technology for components were available. So I don't take these guidelines seriously. It's all in the details. Now you have F1 all around 26 m/s mean pistons speeds and a few years ago 25m/s with all their exotic materials, at the same time you have few year old cup engines breaking into upper 27m/s without exotic materials, and now with gearing rule still running just under 27m/s. And this is all wide open, near constant redline operation, up against a huge aero load, for hours at a time. Then you have IHRA big blocks breaking 30m/s, 32m/s.. and although it is drag racing, they aren't going to go there if their rings aren't sealing well.

Your experience with people in the industry is the opposite of mine. I've never heard blanket guidelines from good people in the industry. Maybe just one... but then what's happening in real life proves it wrong.

 

LMAO don't take it serious I bet you will when your piston comes out the side of your block. If the 4g64 can handle 8500 rpm reliably why did mitsu put the stock rev limiter at 6300 could it be because that is actually a safe rpm for this engine?

 

u can go 8k if u want to get this with 4g64 crank
http://club3g.com/forum/showpost.php...&postcount=706

 

Of course you can.


I honestly didn't get the impression that excessive piston speeds (or rpm in general) improves lubrication, nor would I feel that is a reliable assumption.



It is all in the details, and how critical those details can be. This is why such race engines have improved only through years of testing very specific combinations and components, are disassembled with great frequency, take greater steps to reduce rotational and valvetrain mass/stress, and only need last from rebuild to rebuild.

This is hardly representative of real-world street engine expectations.


I haven't encountered so much as one person in the industry that advocated revving any engine higher than necessary to obtain expected power while maintaining best possible reliability.

Real life for 95% in this forum more often than not consists of extracting best power from an engine that is expected to be reliable for many thousands of miles over a wide variety of conditions, and whose powerbands scarecely warrant excessive piston speeds regardless. This being the case, there is not one good reason to test the limits of reliability any more than necessary.

Again, the easiest and quickest way to kill an engine is to spin it - needlessly.

 

Shaun in having talked with many race engine builders (nascar, IRL and F1) none of them would give me straigth answer but all implied at 25m/s internals and lifetime was hinted simply because of the strain on the material (f1 motors normally won't exceed 24m/s)...when 30m/s came up they would all hint at the rings and ringlands...flutter and cracking the lands.
No one would give a complete answer but would only point me in the right direction...doesn't help as I don't have a spintron to use yet...mostly seem like limits of keeping the motor together.

 

thats my chart that was before the cams and head work, but i understand what you saying about staying at the right shift point.

 

Post a new chart, and I'll calculate the optimum shift points.

 

Cool as soon as shes on the dyno again i'll give you a shout.