Big Boost

I have a question here on this.

Why would this be better then using a 4g64 crank?

You may have a higher rev limit (10,000rpms), but you are actually losing displacement. This seems to be very similuar to the Jun kit, which is WAY over-priced.

If you wanted that high of a rev limit, wouldn't you be better off with a 2.0?

If you a drag racing that is one thing, but for a street car, wouldn't a 4g64 crank make more sense? You would want all the displacement you can get for the torque.

EFIxMR

iTrader: (10)

I think it all comes down to how much money you want to spend, what your intended purpose for the car is, and what you believe the attributes of a race engine should be.

If your main intention is building a fun street car, the extra expenditure does not justify the cost. Also for a drag car keeping 2.0 would probably be best as the operating range of the engine is in the upper rpm band.

I think the 94mm crank is a good compromise between the torque increase and top end. Boosting low speed engine torque to improve spool, while maintaining top end ability. These characteristics are particularily useful for road race / time attack setups. It is no coincidence that Garage HRS/Cyber EVO and the JUN time attack evo run 94mm cranks. Also, the ND EVO is also running a 94mm crank. I think these cars are good representations of balanced vehicle performance.

In unlimited budget builds if the 4g64 crank (100mm stroke) were superior in this situation it would have been used. However, this 94mm crank solution was specifically engineered and chosen purposely, as with the billet crank they could have chosen any stroke that would reasonably fit into the block. That is not to say that the 94mm crank is without compromise in terms of engine geometry, as it is paired with a standard length 150mm rod for production purposes.

So with that said I'll give my opinion of why I would not want the 4g64 crank or a 100mm stroke under the same usage constraints above.

1. not all 4g64 cranks are created equal, some reportedly are not forged.
2. without gearing changes the 4g64 lowers top speed per gear
3. piston speed
4. rod angle
5. reciprocating weight
6. wrist pin location
7. piston skirt length

After speaking with a reputable machine shop/engineering firm, they report that 4g64 motors are not holding their tolerances and their bearings are showing undesirable wear characteristics. Whether or not others are seeing the same thing I don't know. But my main concern here is longevity. Putting a huge crank (100mm) goes against what I know to be reliable.

If someone has some solid information as to why this is incorrect I'm open to reason.

SuperHatch

iTrader: (23)

Anyone have an opinion on Manley parts?

My G/F works there and can get me all of their stuff cheap, just wondeirng if their stuff is up to the task.

What about Ross pistons?

EFIxMR

iTrader: (10)

Manley Turbo Tuff rods are proven. Full-Race Geoff runs them on his 800 whp engine. I have yet to hear of a rod related failure from Manley, however they are a bit on the heavy side.

ShaunSG

iTrader: (1)

Besides weight breaks and fixed gearing necessitating extra shift, there is no reason an engine needs to operate in the upper RPM band. As long as engine throughput if equal or higher, it doesn't need to run high engine speeds.

Did they have one-off cranks made? Or were they running cranks they sell? Are there no other good time attack 4G63s running larger stroke cranks? Are cars in these unofficial classes subject to teardown for inspection? Are you sure what they say is what they're running? Do you personally know anyone who works in the facility who confirms this?

The limit is not a bearing/journal width because the numbers are very clear that the peak loads are far higher in non-stroked engines. I've posted numbers twice at least before.

The limit may be journal overlap. Larger main journal may not be feasible without extensive re-design. Larger rod journal adds considerable mass and cost to crank, and requires custom rod, again cost and weight. Potential clearance issues too. What are stock main and rod journal sizes? What about on off the shelf stroker cranks?

Limit may be budget. The last few tenths in terms of power is one of the last things to look at on a road course car. After spending on lightening the car and setting up the chassis, there may have been limits. These companies have money but it isn't unlimited. If it was they would be running some international race or series.

If a stroker motor is run at as high an engine speed that a shorter stroke motor already close to or on the limit was run at, then things go bad. It never has to get to that point though because throughput would have been matched and exceeded far earlier.

Looking at the bearings in the housing bores, engine deck up and mains down, where is the wear seen? 12 and 6 o'clock? 4 and 8? Is it wear or load deformation? If it is wear, it certainly is not due to stroke. It is an oiling, contamination, dimensioning, clearance, or tolerance problem.

The required areas of examination are not ones of airflow, component acceleration or speed, power, gearing because they have been thoroughly explored and documented.

It is the other unconsidered factors that need attention, a few of which have been alluded to above in question form.

EFIxMR

iTrader: (10)

Hey Shaun,

I was afraid you'd come into the thread and poke holes into my theories, but like I said previously I come into this conversation with an open and eager mind.

I understand and accept that an engine operating at less speed is more reliable than one spinning at higher. And given the same turbocharger and peripheral components a bigger engine can make more power at a lower operating speed which in turn makes it theoretically more reliable than a smaller engine operating at higher speed. However, at what point does the goal of more displacement begin to compromise engine life due to physical geometric limitations of the engine? Or does it at all?

Does running the wrist pin deep inside the oil control ring pack have zero effect on engine life and specifically oil control?

Are the side loading forces on the cylinder wall from large rod angles neglegible to maintaining bore trueness and ring seal?

But how about if the 2.0 engine is running a huge turbo that only begins to spool at 6k and needs to rev to 9k to be of any use?

I understand that on a stroker motor, a change in final drive can regain lost top speed due to lower engine speed limit, but doesn't that come at the expense of the mechanical torque multiplication applied to the ground afforded by a higher final drive? Also, isn't a motor that is able to maintain its torque at upper ranges, making better use of its gearing, which also allows it to put more torque to the ground?

These are just some potential questions that come to mind when I think of the vehicle operating as a whole, they may totally be off base but I was wondering what your thoughts on that are.

Also, do you see any inherent advantages a billet crank of the same stroke, lets say manufactured from someone like Crower would have over the stock 4g64 crank?

ShaunSG

iTrader: (1)

Andy, no holes have been poked, I am only sharing alternate theory or possibilities. I haven't disproved anything on this thread so far.

On previous threads regarding specific speed, acceleration, volumetric flow, it was different because the claims were very specific. Here they aren't and it is more of a discussion.

Besides plain lacking clearance, it does reach a limit at some point. Not loads at T or BDC but at the sides, especially major thrust in FI applications. The increase in side load from going from 1.7 to 1.5 R/S, all else constant, is less than load increase at T or BDC at normalized flow.

My point is that there is no magic cross over point into bad zones. It is a gradual transition. No one can rightly say that 1.X is good whilst 1.(X-1) is bad, without looking at a whole range of factors (at least 10 off the top of my head right now) and running detailed calculation. All these factors are variable. Some at large cost, others at small costs that we can afford, and yet others for free. All this is with R/S held constant. So in itself the number means almost nothing in longevity or power.

The reasons for not going with longer stroke and the comparisons seen so far are all off. Looking at what is being done with current 2.3 or 2.4 L engines, there is no reason not to run them as unlimited non-n20 drag engines, what more road course engines.

Reason for moving pin up is for maximum rod length with or without stroke increase. It is typically done for endurance more than anything else, and it isn't a something done only with strokers.

Pin can be moved high up enough to cause problems, but a good piston designer given enough detail will not design unsafely.

Rod angle change from typical stroking is 1.5 degrees or less. The side load change from this small angle change is not as trivial, but is it not unmanageable. Given what stock 4G63 blocks are doing bore trueness is not an issue. It almost always never is an issue on cast iron blocks. Few exceptions, and the 4G63 is certainly not one of them. I would worry about the pistons before the block. Piston along with ring seal is the piston designers' domain.

Whatever flow is required by the turbine at 6K on the 2.0, will be met by the stroker at lower RPM.

Yes it does, but where is this important besides saving a shift for ET in drag racing? Area under the curve is still going to the larger displacement engine and will offset this. Additionally, gearing strategy with turbochargers especially large one is significantly different from straight forward NA type torque multiplication, because large turbos require high loads to make boost. Sometimes taller gearing is better.

A motor's ability to maintain torque at upper ranges (% wise) has nothing to do with displacement but valve area and various flow efficiencies - tract and cam traits included.

If you mean a specific engine speed range as upper range, a stroker will maintain torque as well as any non-stroked engine, up to its mechanical limits. It is all in design. Mechanical limits may be lower, but volumetric flow does not suffer within limits discussed in paragraph 1.

Maintain torque in upper ranges means making more power. I'm not sure what you mean by making better use of its gearing. It is geared down more, yes, converting crank power to wheel torque.

Yes, strength and/or weight, efficient oiling passages, better internal balance (even between small segments between counterweights) for minimal torsion/bending forces arising from even its own balanced rotation so bearing loads are kept even and the crankshaft less stressed. Internal balance is separate from simple dynamic balancing and has to be standard met at manufacture.


I hope I'm not misreading anything. It's late. Trying to understand and discuss too.

EFIxMR

iTrader: (10)

Very interesting.

Can you perhaps speculate on why the 94mm stroke comes up so often amongst the japanese engine companies, specifically tomei and jun, and soon cosworth in the US?

From their point of view how would a 94mm crank be useful or advantageous, beside the possibility of profit from selling a $3,000 crank?

At the extreme end of the spectrum i can't help but think of sport bikes which have a reliable 10-13k redline, due to their smaller stroke, lightweight components, and general engine design.

ShaunSG

iTrader: (1)

I have already asked questions about the Japanese 94mm crank situation in a previous post that have gone unanswered. The questions show what I think are potential factors that have not been considered.

Cosworth.. I have no idea. Wild guesses.. market pressure is always a factor, if the customers want RPM and the engine won't give them RPM, but power and width of power instead, will it still sell for a high price? Is it possible to re-educate the customer? Or must it be proven with race wins? Fund a race effort? Is there a recognized class to race in that doesn't run weight breaks? External build tolerances and component selection may not be great. Customer may demand many miles of the engine, want to run high RPM, and still want a displacement bump. Logical thing is to do something a balance of, peppy and safe, or just middle of the road that will sell. Bank on heritage and sell on name and quality.

Cosworth's standards for durability are higher than most. In order to meet these standards, the system and not just the component has to be engineered. The component prices especially crank and piston go up. Are they then to sell pistons and rods a long with crank? Does that even help if build process is not controlled by them? So take it further and build the shortblock? With the system properly speced and properly built the costs are much higher. Will the customer pay? Will he follow the engine speed limits set?

Like I said before, there is a range. Some companies go 2.1, 2.2, others 2.3, 2.4. They all have different standards, depth of analysis, intended application. All these arguments have to go the other way too.. why do you not destroke 4G63s to 1.6 and reap all the supposed benefits of short stroke?

When is Cosworth going to start selling the crank? If Cosworth was the company you alluded to earlier experiencing wear on the bearings then more details are needed on it. I'm not sure who at Cosworth you might be communicating with, but I firmly still stand by loads not being the cause of bearing wear, only bearing flaking/cracking/deformation. You can't push through hydrodynamic oil wedge to arrive at journal to bearing contact to cause wear. The loads will damage what is below the oil wedge (bearing) before it pushes through the wedge. Wear factors were listed in earlier post. Far out possibility (is it even possible?) is that the flakes fold up and pass through the wedge.

Sport bike engines have very short service life, compared to car engines.


====

Over the past few months I have provided, at different times, at least a few solid numbers from calculations on the stroker issue, that illustrate my points. I would like to get some back from the short stroke guys... their numbers to their points. The concepts are all there, but which ones are the larger factors need to tbe shown in numbers.

It would also be nice to hear officially from any company on what is wrong with >94mm strokers. It has all been short and vague hints so far with nothing explicitly mentioned.

Also look at current >94mm strokers and the applications they are running. Are they not working? Are there no >94mm stroker good time attack 4G63s?

EFIxMR

iTrader: (10)

well RC developments is running a 101mm stroke billet crank. From what im reading it looks like they are getting some solid performance out of their car... low 10's ET, 200 mph top speed.

in comparison ND's evo runs a 94mm crank i believe they have run high 9's, and also a 200 mph top speed.

Back to the issue of 4g64 cranks... After reading some dsm boards, there are reports of peoples stroker motors bore going out of tolerance within a short period of time. But at the same time I think these guys are still spinning their motors to 8000 rpm.

On the question of Cosworth, I think I'd better give them another ring, and ask them some better questions thats developed from this thread, as to not falsely put words into their mouths as I am definately not their trained representative. I do remember clearly though that they told me that the piston speed of the 4g64 crank inside a 4g63 block has piston speeds that were greater than a formula 1 engine. But that does come down to a problem of lack of restriant from the driver.

With that said at high hp levels it is hard for a driver to maintain a rev limit that isn't enforced by the ECU due to how fast the engine can tach out. While the most reasonable thing to do would be to lower the ECU rpm cut, with how fast engine speed is increasing, bouncing off the limiter which pretty much results in a loss of momentum can be a performance handicap.

jj_008

iTrader: (8)

IMHO, the main reason the 100mm crank is used is for cost. It's cheap and proven to hold some HP, but, as stated above, the piston speeds get really high at 8000rpm. I also don't like how deep the wrist pin is in the piston, but I haven't heard of one failing either.

I believe this is why Japanese companies came out w/ the 94mm crank. Lower pistons speeds, better pistons, yet still gives a decent increase in displacement. You know companies like Jun, Tomei, and the Cyberevo are turning close to 8500-9000rpm w/ these kits.

ShaunSG

iTrader: (1)

ETs vary with track, weather, setup.

Top speeds are in no way related to displacement, only power. Similar or greater power can be made at similar or larger valve areas, with shorter stroke, less diplacement, but lower service life. Top speed also varies with aero setup.

Does ND run in some drag class? Do both RC and ND cars weigh the same? Same aero?

This is what I mean by short and vague...
What is the tolerance they seek and what wear are they seeing?
When they say short period of time what do they mean?
What application and what MEP at what RPM?

A 2.3-2.4 stroker turning 8000 RPM is like a 2.0 turning 9200-9600 and still sideloads are ~15% higher even at the lower RPM.

As I said before, a systems issue cannot be confused with a single specific issue. To make certain it is a single specific issue, it has to be first confirmed that all other factors are right. This is difficult. Crossover into "unacceptable" is not sudden.

ok

Yes, it is all to do with right application. Piston speed is a rough indicator of component acceleration. Component acceleration is what matters. IHRA big blocks run mean piston speeds that short stroke drag engines can only dream of. They are able to do this because their stroke is long and mean piston speed held constant, component acceleration is lower.

A Honda S2000 engine has mean piston speed similar to some 2004/2005 F1 V10 engines, but only about half the acceleration because of roughly half the RPM and a much larger stroke, vs F1.

Yes and this problem is experienced by any hard accelerating engine, stroker or not.

ShaunSG

iTrader: (1)

Piston speed or acceleration is controlled by the driver. Spec realistically for application, stick to it, and all will be fine.

Ever wonder what the service life of the Jun, Tomei, Cyberevo engines is ?

EFIxMR

iTrader: (10)

I think the service intervals on those cars 94mm stroke or not is still pretty low. Its always cheaper to replace the soft parts than the hard ones.