- All engines have limited reliability and longevity.

- Stroker engines almost always have better reliability and longevity. This is due to lower inertial loads at equal mean piston speeds, and equal volumetric flow (power). There are a few exceptions when parameters are shifted to fringe magnitudes. Stroker Evo engines are NOT among the exceptions.

Post hoc error is often applied to stroker engines that blow up, but the real issues almost always are:

1) Poor machining
2) Poor assembly
3) Unrealistic operation due to ignorance on engine dynamics

As for "quickest/fastest 4G63s in the world are stock stroke" group - take a closer look at the ruleset of those classes. Study the weight breaks. In other lower classes where stock or stockish gearing is mandatory, consider the effect of extra RPM in light of these gearing limitations. There may be classes where weight breaks come together with gearing limits to create situations conducive of lower displacement higher revving engines. Free of these rules and limitations and assuming you have the money, time, skill, there is no reason to relegate yourself to stock stroke.

 

Destroking the engine while maintaining the same rod length alters the rod/stroke ratio such that the engine becomes more efficient at high rpm. This was clearly the idea behind the Chevy 302 for the old Trans Am races, along with the Muncie M22 close ratio tranny and dual Holley 780cfm crossram setup, where the rpm never dropped below 5000 anywhere on the course.

 

With a stroker motor and a lower rod to stroke ratio, the piston is at TDC for less crank degrees and this is makes a motor less likely to detonate. the rod to stroke ratio on the 4g63 is pretty high and my experience from other cars is that a lower rod to stroke combination is reliable provided the pistons and rods are high quality.

the rod to stroke on my other cars engine has a 1.58 r/s and displaces 1800cc, at the track it spins to 10k and makes 600 whp. on 91 octane is makes over 400 whp on a conservative tune with no signs of detonation on the plug whatsoever.

the merits of running a longer rod at the expense of displacement have long been argued, but it has been shown that the longer rod does not make the engine anymore reliable, all it does is create less hp. of course everything is combination, but moving from 2.0 to 2.2 liters isn't a big deal in my opinion.

Also, if you're really pushing the engine in competition making 500-600 whp, i don't think its wise to run the motor without a decreased teardown time cycle for maintanance. Replacing your soft engine parts, (bearings, rings, gaskets) more often than normal will save your expensive hard parts. Regardless of stroke. On a daily driver making 300-400 whp i don't think this is much of an issue.

 

Do not confuse destroking with overboring. Destroking is a by product of overbore that allows an engine to stay within the legal displacement limit of the class. The target is overbore, not destroke.

 

I totally agree. The flow advantage far outweighs the inefficiencies which range in the low single digit percentages. Unless you run parameters to extremes, there is no contest. This has been, and is currently, demonstrated in all forms of motorsport.

 

RSGuy, what kinda herb is in your avatar???

 

i think the affects of longer rod to stroke in terms of high rpm flow are better utilized on a naturally aspirated engine.

on these turbocharged engines, nothing short of putting a huge turbo is going to make reving out to 9k+ rpm useful, and not even a gt35R is going to cut it, as this is really a mid sized turbocharger, and not the monster that people make it out to be. the torque as a turbo charged 4 cylinder approaching 9k falls off considerably.

also the high rpm flow loss that comes with stroking can be mitigated with headwork. unfortunately, this does not work conversly as headwork does not improve low end performance on a smaller displacement engine.

 

When a new 3.0" stroke, large journal crank is created explicitly to work with an off-the-shelf 4.0" bore, large journal 327 block, it's an example of destroking, not overboring. There isn't anything confusing about that.



A GT35R may not be a 'monster' for a 2.5L engine, but it's a different story for a 1.8L engine. I'm fairly certain the airflow of a typical 2.0L 4G63 at 9000rpm and 90% VE is well within the efficiency range of a GT35R.

A short rod engine exposes shortcomings in a cylinder head more quickly because the onset of port turbulence (which chokes airflow) occurs at lower rpm due to the increased acceleration airmass that corresponds to the increased acceleration of the piston toward and away from TDC. As to why the presence of a turbo would make any difference, I've not seen anything to substantiate that.

As for headwork not making a difference in the low speed performance of a small displacement engine, I certainly improved low speed performance when I recently ported the head in my 2.3L Ford turbo, so I don't see where the laws of physics are suddenly displacement dependent. Any change that improves VE, improves power.

 

A GT35R really isn't a monster even for a 1.8, in drag racing applications a 70 mm inducer garrett has proven itself useful on such small displacement. This particular configuration that comes to mind was run in a SFWD application a few years back netting in excess of 700 whp and consistent low 10 sec time slips. The owner of this car is a gentleman whom is an affilate tuner of Neptune systems named Courtney Green. He has since stepped up his engine program to a GT42R and a 2.0 engine, running in the high 9's. You really have to be running these sorts of turbo sizes to capitalize on such a high redline.

Even if the compressor of the GT35R could flow the cfm for 9k+, the engine @ 30+ psi of boost has too much exhaust flow restriction to support that kind of rpm. Under those conditions even a P trim T4 isn't going to cut it, to make a 9k+ plus redline effective you need something like a GTS or GTQ turbine.

Also why strokers don't flow as well under high rpm there are a multitude of theories. In my opinion one of the better theories that doesn't involve any fancy terminology is the fact that the combustion mixture has to travel a farther path due to increased stroke. That and the fact that pistons speeds are raised means that the mixture has less time to do so.

Reviewing some of the stroked dyno graphs posted by members can be a little disappointing, as their engines torque fall short pretty quickly, but most of them are still running the stock intake manifold and would definately benefit from a large plenum manifold like the AMS. That and stepping up the ex a/r size will reap a significant increase in high rpm ability.

As to why longer rods are more effective in n/a applications relates back to my first point of exhaust pressure. when a turbocharged engine's exhaust pressure vs intake manifold pressure strays too high the engine is not going to make more power by reving it farther. the mechanical advantage flow wise given by a longer rod does not outwiegh this limitation of exhaust choke.

my background is in naturally aspirated high output, low displacement engines (honda k-series 237 whp on 91 octane)... in this world picking up 1 or 2 ft/lbs of torque at redline is the difference between making more hp and reving your motor out needlessly. In this application the mechanical advantage of a longer rod might prove useful.

In short, to make horsepower at high rpm 9k+ you need to maintain a balanced pressure ratio between the compressor and turbine. this is accomplished by running a big turbine and big compressor, with the supporting head components. A long rod isn't going to do squat if your turbo can't support high rpm.

And as for why you picked up low end on your ford engine, my assumption is that it was never meant for high specific output and the ports were sized too small from the factory and acted as a restriction even under low rpm.

On the 4g63 the ports are already pretty big, and porting them bigger surely isn't going to increase the low end as you are increasing port volume and slowing the velocity of the intake when the engine is breathing without the assitance of boost.

 

Please take a close look at the displacement limit for the class. When you go overbore or stock bore in combination with whatever stroke (whether it is stock or custom crank) to arrive at, or just under, a displacement limit, the destroking was never a target. It never is. If it is, it never makes more power or lasts longer - throughput normalized.

You are in fact confusing the reasons for desiring to run maximum permissible bore (whether a stock bore, or whatever overbore) with minimum stroke.

Please list a prominent racing class (accessible info) that purposely destrokes and reduces displacement on its engines in order to go faster and live longer. I will happily update my current understanding of racing history and engine dynamics.

The same claims have been made in Cup racing and it was only by teams who wanted to explain why their engines were turning significantly more RPM than competitors through cheated up induction systems. Their excuse was that they were running a smaller engine (no lower cubic inch limit). To stop all the BS, a lower cubic inch limit was imposed and that is the rule that is still followed today.

 

You have to consider the magnitude of actual change. There is very little dwell time change with changes in rod ratio. It is in the lower single digit percentages for stock 4G63 to 2.4L stroker 4G63.

To crutch a head with a long rod takes:

1) A heavily taxed head to begin with (right at or just over the limit)
2) A very large change in rod length. Small changes just don't do anything.

Virtually all 4G63s in steet use do not have heavily taxed heads, neither does stroking them change rod ratio a whole lot.

All this talk about crutching heads arose decades ago when domestic heads were junk and and you have many block height options with those engines that allow you to run a very wide range of rod ratios especially if the class displacement limit was small.

Things are very different today - especially with modern multivalve high performance heads and not many options on block height.

 

I think what's key to making a stroker motor last is proper assembly, quality internals, proper engine calibration, realistic hp and rpm levels for hardware limitations, motor building tricks that come with experience, and maintanance. Not very much different than what goes into a normal good engine build.

 

I'm not confusing anything. I reiterated the story behind the Chevy 302, nothing more. Chevy could have created a longer stroke crank to fit the smaller bore 283/307 block, but they didn't. And interestingly enough, Ford's engine in the series had the very same internal dimensions. Go figure.

 

Concur

 

To go up on stroke, they would have to go down on bore in order to stay within displacement limits. Going down on bore would compromise valve area, hence power. You are confused. Target was bore. Stroke requirements were secondary.


Here's a question for you...

2.0 L I4 racing class
Displacement limit is 2000cc
No engine speed limit
20 min road course sprint race
Maximum bore that bore spacing safely permits is 80mm

What bore would you decide to run? What stroke crank would you manufacture?