Holy ******* ****! You have no idea who you just responded to, do you?! An analogy of suggesting that Scott Dixon attend a competition driving school comes to mind...

 

I just don't see why someone has to go into explaining what an F1 formula motor needs just to choose from a 5.7" or 6.0" rod in a sbc. No hobbyist here is gonna have a need for that much science to build his sbc. More like someone just wants to discredit another hobbyist here by using some technical insignificance that in itself would have insignificance results. Why run your mouth about F1 formula motors when it doesn't help anyone here?
Reality is that no here has the resources in time or money to do back to back dyno tests using different rod lengths. So it's become like esoteric knowledge only some claim they have access to.

Let it go. Try and make friends instead of creating spite.

 

It was brought up by someone else in post #25 as evidence that long rods are desirable in high-rpm race engines. I added info about those old F1 engines to point out that this example doesn't mean what one might think it means. They'd run shorter/lighter/stiffer rods if they could, but they don't fit. That's not a "technical insignificance" - it's really, really important to any discussion of rod:stroke ratios where an F1 engine (or a bike engine) is introduced as evidence that high ratios are better.

Reality is that the testing has been done multiple times, by people in the race-engine industry and even by magazines for us plebeians. The results are conclusive: rod:stroke ratio doesn't make any difference to engine performance, and one should focus on all the other important things such as stroke length, piston design, ring packages, deck height, etc., and just use whatever rod length those specs dictate. BTW, RACER7088 has the experience, resources, and technical expertise to have all the access in the world to this information. He's immersed in the race-engine industry, especially regarding pushrod V8s, and has brought significant innovations to the aftermarket Chevy V8 world. So someone here has the resources, and he just told us the answer to the question.

After the F1 posts, ddahlgren started denigrating that info as contrary to "the math and physics" and authoritatively claimed that aspects of piston speed, acceleration, and valve timing favored longer rods. I actually showed the math and physics, which demonstrated that everything he wrote was the polar opposite of reality: dimensions he asserted did one thing to piston speed and acceleration actually do the exact opposite. And beyond that, the math and physics shows no meaningful differences in piston speed/acceleration in the range of rod lengths we have available for SBC use. So again, as with the F1 engine example, I didn't bring up math and physics but I added important information to the points that others brought up about math and physics.

We should be able to do both: get the answers right and also be friendly. However, on a forum thread that began with a very specific question on a technical topic, it's more important to get the answers correct than to make friends. So if you're saying that the only way to be friendly is to just give in and agree with wrong info that you and ddahlgren keep posting, then I guess we aren't going to be friends. Your egos will have to take a back seat to getting the information right, especially considering the pompous and dismissive attitudes each of you has brought to this thread. I'm not the one intent on continuing an argument that's already been lost. You and ddahlgren have both been corrected by the posting of technical facts several times. Each time you've been proven wrong, you insist on continuing the argument even after you've lost. And to top it off, an actual industry insider and expert just came here to share his knowledge and answer the OP's questions: ddahlgren told him to read a book without pretty pictures and to sharpen his math skills, and you just called his knowledge esoteric and questioned whether he actually has access to the knowledge! Talk about creating spite!

 

Who's name calling claiming pompous and dismissive attitudes? How is that necessary? That again is your technique to degrade and discredit others. An example of your hypocritical attacks which accomplishes nothing more than generate spite and contempt. Who are you to label others that don't even quote you. As there's no need to use quotes when its so obvious how stating the facts inflames you and reveals what you are doing.

 

Fortunately. YOU never do any of ^those^ things....right?


That is quite an interesting piece of advice, coming from you.

I'm with Matt on this one. People come on these forums looking for GOOD advice. They don't want lore or posts that are FOS. Who does? I know b/c I used to be "that guy". When I first joined these forums (and others) I got a load of BULL that was worse than no help, b/c it either slowed down my progression more than "no help at all"....or it actually led me down the wrong path, so I was wasting money going backward. So yeah...the right information matters. MM has presented incredibly good and factual info in this thread; more than anyone else has including you. All you're doing is pot-stirring.

Being a big enough person to accept GOOD information is the other 1/2 of the equation that is critical. LEESVET couldn't accept facts, and he left the forums over it. Go ahead...read the link. The guy could have learned a thing...but he left instead. That is unfortunate. What good did that do him? The forum? For GOOD information to flow, we have to have the facts, and we have to be able to receive them, too.


.

 

You are. In case you've forgotten, here is your first reply to me in this thread, before I had replied to or referenced you at all:
So you fired the first shot, complete with sarcasm, dismissal, and grammatical tragedies. You chose to enter a respectful discussion I was having with someone else.* You didn't have to post any reply at all. Your choice, your consequence.

*Which is fine as long as you don't act like an asshat.

 

Thanks to everyone who tried to help me. It's been very educational to read through all this. I had no idea it was such a complex topic.

Because you don't know what you don't know till you know it, inspired by some of the lines of reasoning here I found some reading material on rod lengths and researched that. The only thing I found that was not touched on here was piston rock and unsupported ring lands and a claim that, while the pistons are much lighter in some cases, unsupported lands on the street can lead to ring flex and premature wear on the finely finished edges of the ring. Which, in turn, leads to poor oil control.

Thanks again.. Appreciate it.

 

Yes I know a few in both Formula Car and in Pushrod V8 and some F1 engineers are involved in both through NASCAR and PS. Some I knew by chance and through school and through the many seminars I've been to all over and some through other bulletin boards just like this.

Rod length does matter in as far as piston design and ring stacks for certain usage of course. In our "LTx" stroke range and bore to stroke range it has very little to no effect on anything although in many cases long rods are a negative overall to piston and piston top design.

In F1 engines for instance with their very short strokes and very overquare bore to stroke ratios with relatively large valves the longer rods and resulting overly high rod to stroke ratios can be VERY negative.

The smaller you make the stroke on any given engine the harder it is to make compression all else equal.

The higher the rod to stroke ratio becomes the deeper the valve reliefs must be with any given cam profile.

The deeper the valve reliefs are the lower the compression ratio becomes thus lowering hp.

The deeper the valve reliefs are the lower the top ring must drop on the piston thus increasing crevice volume above that top ring.

The lower the top ring drops down on the piston the lower the compression drops to as well from the extra crevice volume lowering hp.

The lower the top ring drops down on the piston the higher crevice volume becomes which also can't burn due to quench thus lower hp.

F1 has cam lobes specially engineered to open and close the valves more in line with piston position so as to reduce the need for huge reliefs but its still a very real problem made worse by the overly long rod to stroke ratio that they are often stuck with.

I many F1 engines yes they would love to lose some rod length if they could since it will help the engine in every conceivable way including rotating and reciprocating mass as well as overall mass and stiffness.

Not exactly hard to figure out if you look past some kind of magical "rod ratio" fetish. Keep in mind ddahlgren I'm not saying you have this fetish just the internet bulletin board world on average it seams.

At least it's not as bad as the "TQ vs. HP" threads of old which are the dumbest threads ever to exist I think.

In general people that are overly concerned about rod to stroke ratio in particular don't seem know almost anything about engines or engine design and certainly have not been around many dynos or racetracks.

It's mostly 99% an internet bulletin board topic when anything and everything else makes way more of a difference like your heads and intakes and valvetrain which all are maybe 100 times as important.

 

Someone else mentioned that so I went into many reasons F1 rods might be longer than the actual engine builders wanted them to be.

I would use a 6 inch rod over a 5.700 myself on many SBC apps as it usually results in a lighter better rotating assembly especially if the crank you got was setup and cammed for the 6 inch rod with narrower and taller counterweights. If the piston gets too short than you can go back to a shorter rod. You also want a piston that really works in the cylinder length your actual block really has both at TDC and BDC. Not all pistons are designed correctly.

 

Good point Hot Rod Roy... AND the offset that the factories both domestic and overseas use make rod ratio even worse on the power stroke and intake stroke as well. The OEMs must not be worried too much about it either! They do it as it makes the piston rock over quieter.

 

PS: During my research I found this. There's some pretty good reading here:

http://garage.grumpysperformance.com...strokers.2378/

 

Confab,

That's what I used to worry about too as far as longer rods and shorter pistons putting the oil rings in the pin bore necessitating the oil support rail to keep it there.

Saying all that, and in too long a sentence probably for the grasmmar *****, it doesn't seem to matter that much in practice or at least the ring and piston companies have made it work very well nowadays.

 

LOL, there've been a few of those around here recently, too! The whole torque thing is the fallacy that never dies...