strokers, pistons speeds, rev limits and rotating weights

[trinydex]

talk about these please


The prevailing consensus in the race engine industry is that durability takes a real dive above piston speeds of 25 m/sec, and piston ring sealing efficiency takes a dump around 30 m/sec.Â*

For any 100mm stroke crank, 25 m/sec works out to 7500rpm.Â* Unless one has deep pockets, a lift, engine building equipment/skills, and access to spares, adhering to that figure is wise advice.Â* Spinning any motor faster than necessary is the quickest way to kill it, and high rpm coupled with the short rod/stroke ratio (1.5:1) of conventional 100mm 4G63 strokers doesn't make a recipe for either efficient high rpm operation or longevity.


The 2.2L uses a 94mm stroke, which gives a piston speed of 25 m/sec right around 8000rpm, which is ~500rpm higher than a 100mm stroker.


Good info Ted! I assume those speed specifications on durability take into account having light weight pistons and rods and that a stock 4g64 would really be in sad shap if you reved it to 7500 very often due to the heavier stock parts correct?

Keith



Yes, that is definitely a safe assumption.

[ryan0]

my stroker stops at 7300 for these very reasons.

[Team_swiff]

i wanna stroke my car!!!!! need that gain... O0

[Terry S]

...someone should calculate this out for the new AMS 2.3RR kit..

Terry S

[faruk]

I notice the jap kits do not go over 2.2 L....thoughts?

[GokuSSJ4]

my stroker stops at 7300 for these very reasons.


do you have a stroker on your evo? who built it for you?

[trinydex]

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.

[trinydex]

Quote:
Originally Posted by Ted B
In general, the direct issues associated with high mean piston speed include material limitations (due to stress and fatigue),

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


Quote:
friction and heat, ring flutter, and lubrication efficiency.

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


Quote:
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.

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.


Quote:
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).

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.

[rtype02]

I think 7300 sounds very fair on a 100mm stroke. What I like to do to keep the odds in my favor are:

*nitriding / cross drilling the crankshaft
*high performance coated bearings
*better oil flow including upping oil pressure
*better rod bolts (arp L19's)

But IMO anything past 7000 rpm is fairly risky in teh 4g63 stroked...