What is the difference between the weight of the pistons and the weight of the rod??? I mean if the rod is longer it will be heavier as the piston... does it have to do for the piston being the farthest weight? and thus if eliminated it will be better? I always thought that using a shorter rod yielded a more free reving engine...

 

The added length of a rod is not that much.

Now a shorter piston is also more likely to have a short skirt which will have less friction, but can rock more in the bore.

Let me show you some examples......

A Keith Black KB100 is 505g and is for a 5.7" rod in a 383.

A Keith Black kb122 is 425g and is for a 6" rod in a 383.

These are both flat top pistons, but vary in compression height for their respective applications.]

Now a Eagle H-Beam rod in 5.7" is 640g, while a 6.0" is 655g.

Now first you see that the Piston saved you 80g and the rod cost you 15g. You get a net savings of 65g.

On top of that on a high reving engine a lighter piston will not put as much force on a crank throw or a connecting rod due to the fact that it's mass is lower. F=MA as A increases F will increase, the only way to lower F is to slow down the engine or put a lighter piston/pin combo out there. I'm going to make that piston lighter before I slow the engine revs down.

That's my thoughts on it.

On a flat top piston you can get to about 1.000" compression height in a domestic V8 before it starts becoming a engineering challenge. Which is a 6.25" rod on a 3.500" stroke in a 9.000 deck height block.

Bret

 

And why have I heard that 5.7" rods are freeer revving engines?

What is the advantage then of a 5.7 rod? It seems to me now that the 5.7 rod is useless.. I have heard it makes the most power....

The 6.0 rod/piston is lighter and puts less stress on the engines sidewalls... So why are 5.7rod / piston combo then?

 

Why doesn't everyone have a Rolex watch? 18"+ diamater wheels on every vehicle they own?

Money. There's a heck of a lot of used 5.7" rods laying around waiting to be used and not everyone building motors buys Eagle/Oliver/Callies/JE ect. ect. ect.

 

Back to the original question.....

Putting the piston further in the hole vs. going dished. I'd ASK them why they recommend that. I would wonder if it would have something to do with keeping the top ring down near the water jacket at TDC (so it runs cooler).

Sound weird? Well, I'll throw this one at you just to chew on. GM typically does a fairly good job of preserving the quench characteristics of their 2-valve motors. But if you look at a stock set of Buick Grand National 3.8 Turbo motor pistons you'll find that they sit WAY down in the hole- .055-.065" if memory serves. Why did they do that instead of just dishing the piston out more???

I suspect there's more to this issue than we are getting at in this thread.

 

There is a limit to the ammount of dish you can run in a piston without compromising piston strength.. Actually I feel that my 31cc dish pistons are at the borderline of dish vs strength that is acceptable in SC motor...

 

Well, I didn't have the chance to call Ross today, so I will report back after I talk to them as far as trying to verify what I heard.
Interesting about the turbo Buick. What I was trying to get at may relate to the Buick. Is there so much turbulence under boost that squish doesn't matter? That's all I can think of, and it seems wrong to me. Be interesting what they say...

As far as rod length goes, I have been using 5.7" because I think they help with detonation - by moving away from TDC faster peak cylinder pressure should be lower, and hopefully this help keeps detonation at bay. As StrokerAce says, there are advantages to a long rod. I see these primarily as beneficial in high rev motors though and I like a low revving setup. But I am strongly considering going a little longer, as long as it doesn't crowd the rings together too much or interfere with the strength of the crown. Remember: I am running 14lbs of boost plus a 300hp nitrous shot, so strength of the piston is paramount.

Mike: I am currently using JE and they haven't broken, so I will likely stay with them. Maybe Wiseco "wised" up . But it was my own fault for not rounding things off. I got in a hurry I guess and just forgot.

Rich Krause

 

Personally, with a oem block, used on the street, with F.I., I see zero advantage to 'getting fancy' with longer rods, which will do little more than sacrifice piston durability. Sure, it's feasible, but what is the point? You won't see or feel enuf extra power on the street to be concerned with. Also, lightest piston vs. durabilty may not be a good trade off on the street.

As for quench; in conversation with SRP, I was informed of testing that used no quench in the short block with promising results. This testing however, if I'm correct, was at boost levels of 25-30#.

Also, somewhere, don't recall source so take this with a grain of salt, but something closer to ideal has the piston crown with recess mirroring the chamber, in lieu of a flat crown with large chamber. But, then again, this may fall under the same scrutiny of whether or not the difference will be noticed on the street.

YMMV

 

Actually, don't 6 inch rods do more to reduce detonation. I have seen blower cars run 6 inch rods mainly to reduce detonation.

I think they do more to help avoid detonation than 5.7's If I understand correctly.