Main Caps and Harmonics

[jsawduste]

While searching through the archives here I came across an interesting thread.
http://www.jeepstrokers.com/forum/viewt ... &hilit=ATI

With all the talk lately on harmonics I`ve been particularly interested in this subject as I prepare for my next build.

A build which will focus on exploiting the Edlebrock head. The plan is to use a 12 cwt crank and a 98 XJ block.

The crank is chosen for the mass, inertia and what I believe to be better capable of controlling the harmonics these engine exhibit. This will be a trail, rock, generally duty engine.

The 98 block offers the extra ribbing, higher nickel, dowels in the deck. I am fine with the pin and spring.

SIXPAK posted a picture of failed 4.0 main caps on a drag race engine using a 4 cwt crank/cap.


A bit further down in that thread SIXPAK mentions

Was using the factory main girdle at the time. The caps are the factory 4.0 and they are not solid. New block MAY get the early solid 258 caps.

SIXPAK further goes on to state

Main studs will be in this time without the main girdle. Over the years I've raced these motors I've never used the girdle and have had no issues

Then he mentions

The 12 cw crank I removed to install the 4 cwt had eight years of racing on it and it's going back in.

These statements bring several questions and also confirm a couple thoughts.

1. Are the 4.0 main caps actually hollow and the 258 solid ? Or are the 4 cwt (regardless of whether it is a 4.2 or a 4.0) caps hollow and the 12 cwt caps solid ?

2. The extra clamping force of main studs outweigh the benefit of the girdle

3. SIXPAK`s comments would lead you to believe the extra mass of the 12 cwt crank moves the harmonic frequency to a different threshold that is better suited for his application. An argument I`ve been preaching also.

I`ll have the 12cwt engine to exchange parts from and an align hone is SOP anyway. Obviously the main caps are something I`d like to learn more about.

Fragmented post but lets get the ball rolling.

[jsawduste]

A little bit of Google Fu and I think I understand the "hollow" main cap comments. Not the cap is actually hollow but the material in the center is removed.

Hollow 4.0`s


Solid 4.2`s

[gradon]

Interesting. Guess a line bore is needed if you use the 4.2's caps.

[mountaineerjeff]

Maybe it's just because it's against everything I do in the other motors I build, or maybe it's just because I'm stubborn but I just can't see the 12w crank being a better choice than the 4w. I'm considering going even farther and having the 4w knife edged and lightened.

[jsawduste]

Jeff, you have to understand that your desires are quite different then mine.

Your looking for a "high performance" I-6 with plenty of HP/RPM and ability to reliably run with potential spray.

My desire is a SOLID platform which to build a moderately powerful, relatively low RPM engine that will pull from damn near zero rpm and level off in the low 5,000`s. My personal stroker does this right now. It has been dyno-ed several times (one of the earlier pulls is published here on strokers) and from that published baseline I`ve further tuned the engine almost to my satisfaction. The last upgrade will be the addition of JTEC and ECM reprogramming from Ryan Hogan. That engine was built 8 years ago. My customer engines are built similar and thus far they have worked pretty well. This typical type engine build with a tweaked SBEC controller is around 300 hp/325 tq. on the dyno.

However a new player has entered the market. That being the Edlebrock head. In order to optimize that head it is going to require a quite a bit different build approach. Add some new knowledge, improved part availability and a tuner that is capable of putting it all together I`d be a fool not to invest/research and take advantage of the better scenario.

My goal and expectation is not lose any low speed tractability while achieving ~ 20-25% increase in peak numbers. Number which may be conservative at this point but should be easily obtainable. IF we take advantage of a number of different inadequacy's that are currently typical of stroker builds. I have a lot to learn yet.

Frankly for your desires your getting into areas that I can only offer somewhat educated comments and no practical experience.

[mountaineerjeff]

I don't think we are as different as you let on. The edelbrock head release was in fact the same point of motivation for me to put the coals to my build again. And your estimate of 375 is exactly what I'm shooting for, it may be conservative, but I hate being one of those guys that have huge bench racing numbers and can't come up with anything.

So I still gonna back to my original statement, I don't see why you would go with a heavier crank. I've seen heavier rotational weight help 4cylinders and I've heard of their effect on 60ft times on a drag car, but you aren't building either. I've never been in a situation where I was like "I'd give up efficiency,reliability, and horsepower just so my i6 will have enough off idle torque" it's not like we have an anemic 4banger that's gonna stall out at red lights.

With what you described as your goal, you'd think a lighter crank would be even better way to turn a 25% increase into a 30% one.

On a slight subject change, have you had any contact with edelbrock? Or are you just going by the same mass info the rest of us are?

[jeepxj3]

This typical type engine build with a tweaked SBEC controller is around 300 hp/325 tq. on the dyno.

Is that on a chassis dyno? rear wheel hp/tq?

[jsawduste]

I don't think we are as different as you let on. The edelbrock head release was in fact the same point of motivation for me to put the coals to my build again. And your estimate of 375 is exactly what I'm shooting for, it may be conservative, but I hate being one of those guys that have huge bench racing numbers and can't come up with anything.

So I still gonna back to my original statement, I don't see why you would go with a heavier crank. I've seen heavier rotational weight help 4cylinders and I've heard of their effect on 60ft times on a drag car, but you aren't building either. I've never been in a situation where I was like "I'd give up efficiency,reliability, and horsepower just so my i6 will have enough off idle torque" it's not like we have an anemic 4banger that's gonna stall out at red lights. With what you described as your goal, you'd think a lighter crank would be even better way to turn a 25% increase into a 30% one.

On a slight subject change, have you had any contact with edelbrock? Or are you just going by the same mass info the rest of us are?

Random picture playing on smaller rocks. Tires are 37`s for perspective. Clutch fully engaged, no stalling.


How am I giving up efficiency ? The engine is doing what I want it to do. Gas mileage or emissions is of no concern, nor are they adversely effected. No power is being lost. The extra 20 lbs of mass perhaps ? But then that would be offset by the lighter weight of the head, would it not ?

IMHO the heavier crank is more reliable. So again where is reliability compromised ?

The horsepower is still there, it just takes a little longer for it to be delivered to the rear wheels. And the opposite is true, it takes longer for the engine to slow down. That is one of the effects of inertia.

I have access to another 12 cwt crank. One 12 cwt has proven itself in the vehicle pictured above. That engine has seen plenty of time running at 5500 rpm. So why not use it ? If I didn`t have a 12 then a 4 would go in and I expect it would also perform adequately but perhaps not as efficiently as defined by my usage.

Have had several conversations with both Blakely and Hooker the last being in and around the first of the year. These conversations revolved around several design parameters and availability as a head was trying to be obtained for a KOH 4500 class rig.

[mountaineerjeff]

Gas mileage is a direct result of efficiency. So if you understand the drop in gas mileage then you understand that the motor isn't going to be as efficient.
As far as power goes, any loss in rotational weight shows a gain in HP. Now sure, the motor isn't technically making anymore power, it's just not wasting as much to turn heavy components.
To make it easier to understand let's say one weighed 1,000 lbs and the other only 5lbs. As long as we assume that they are the same strength then the light one will obviously dyno higher numbers.

You said a "solid" rig was your goal, and I took that as meaning well rounded. The only pro to more weight is the stored.energy, I've just personally never been in a situation where a 400+tq 4.6+ motor didn't have enough power on tap to need that. But that could just be a lack of experience on my end, so even if that was the case and you are 100% correct about needing the inertia then just get a flywheel ring, that's exactly what they are designed for.

[jsawduste]

I am sorry Jeff but I do not agree with your comments. The extra energy required to spin the heavier crankshaft is stored as inertia.

If you put a light crank and a heavy crank on the dyno both would have the same power. The difference would be the light FW would attain the peak number sooner because it overcame the inertia of the heavier crank quicker. Conversely when the load was removed the light FW would spin down faster as it has less stored inertia.

Efficiency can be measured in a number of ways. The common perception is MPG or emissions. My definition is that of low speed tractability and reliability. Yours may be expressed in a 0-60 time or feet per second. All in the eye of the beholder isn`t it ?

[mountaineerjeff]

It's simple physics. Inertia is the objects resistance to acceleration. If you have a resistance to acceleration then you're going to have less of it. Everyone knows a car accelerates faster with a lighter wheel and tire combination. The same goes all the way down the drivetrain. It is very common knowledge that lighter rotational weight nets more power at the dyno.

Let me put it a different way. Heavy parts with lots of inertia don't make the power they are storing, it has to come from somewhere. So during the entire dyno run, while your engine is accelerating the inertia will be taking some of the energy that should be making it to the dyno, then storing it. For what? Then you get to 5krpm let off and it stays at 5krpm for just a little bit longer? That doesn't equate to more power at the end.

Maybe I'm just doing a bad job explaining this

[mountaineerjeff]

Also, engine efficiency is not in the eye of the beholder. It's a defined term.

http://en.m.wikipedia.org/wiki/Engine_efficiency

[jsawduste]

It`s Newton's first law of motion.

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction

I can understand your comments on horsepower. Horsepower defined is an amount of work done in a given time. The problem is that the formula doesn`t reflect Newton's law. Again, while it may take longer for a heavy FW to spool up that doesn't mean the engine has less HP. Once both engines are at a given RPM they will have the same HP for that moment. Where things get muddy is defining peak HP vs a rising rate HP. In this instance you are correct in that if you measured HP on a graph as the engine accelerates the heavy engine will show less HP because it has to fight Newton's law and is not following the def of HP comparatively with the light engine. Hence your comments about a light engine accelerating faster, it will. However, once both engines reach there peak the HP it will be the same no matter how much weight it is throwing around.

You said it yourself with the inertia ring on a 4 cylinder. Isn't that the same as a heavier counter weighted crankshaft ? They both do the same thing (see Newton's law) although I will concede that the FW ring would offer more inertia as it`s mass (if that mass was of the same weight) is further away from the crank centerline.

Don`t be fooled into thinking my stroker is nothing but a slow speed freight train. While it pulls very well from the very bottom the HP peaks are at approx. 5,000 rpm and it is still making decent power at 5500 where the rev limiter kicks in. In fact there is a noticeable increase in pull at around 2300 or so where the engine gets up on the cam. It has been known to put more then one SBC on the trailer.

I run 224 @.050 and .480 lift with a 113 LSA advertised duration of 274 advanced 4*. A fairly healthy cam compared to stock cam with a typical sub 200 ish @ .050 and a sub .424 ish lift with a LSA of 112.

At the same time, isn`t the Edlebrock head a measure of gaining efficiency with it`s improved performance ? Be it power, mileage or whatever. This what it`s all about isn't it ? The difference is how we wish to define efficiency on the personal scale.

If you improve you 0-60 time that means your rig has improved it`s efficiency within that category that you have defined. Maybe you did it with sticker tires. The engine didn`t put out more power you simply made the traction more efficient by transferring that power to the ground.

Let`s build a campfire, pull up a couple chairs and crack a couple.