I just wanted to see what the racers thought about rod ratio. Do you have a minimum that you won't go below? Do you have personal knowledge of a long rod car racing that has had above average results attributed to the long rod design? Or do you think it is overrated and the gains from long rods are surpassed by cubic inches gained from long stroke? This is more or less an extension of the 289 vs 302, or 331 vs 347 arguements... Let's talk!
I'll start by saying that I like cubes, but I am more conservative and therefore uncomfortable with pushing the envelope in side loading a block or dropping rod ratio below a generally accepted range. I like the idea of long rods, but think it is far better to use the space for more cubes. From a pure power standpoint anyway. I just ride the fence on the issue of rod angularity. Now that I think about it, I can't even answer my own poll! I think long rods are overrated, but I can't endorse going overboard with stroke length at the cost of side loading and excessive rod angularity. I'm such a puss.
The way I understand it...Too long of a stroke puts too much stress on the rod end at the crank when the rod is laying down because the rod is pushing the pistion into the cylinder wall when it makes it stroke. Going maximum stroke will make power but the shorter stroke is better for cylinder wall life. Sometimes more is not always better
thats just one of those questions that has too many variables. i did talk to an engine builder about that and they said 347. he said it will make more power. it will last amost as long as a 331, as long you run good oil and maintance. ive also heard the stuff about rod angle. so i dont know. the other factor i think would be if your going natual asperated or with a forced induction. if going forced i would lean towards the 331.
a longer rod will give you more piston dwell at TDC and BDC for better cylinder filling and exhaust making more power brad
There's a difference between a "long rod" motor and a stroker. Long rod engines generally use the stock stroke crank with longer than stock rod and a shorter piston. It doesn't displacement. As mentioned by bradleygt it aids cylinder filling, especially with crappy heads. Long rod 289s & 302s were popular 15+ years ago before you could easily buy decent SBF heads and had to run the crappy factory irons. I don't think it's relevent anymore.
We've run stock stroke long rod (6 inch rod) Chevrolet engines on paved short tracks before. As you mentioned, it doesn't change displacement. The engine was still a 358 with or without the longer rod. The wrist pin hole is just in a different place to make up for the longer rod. I know that you can get into a rod long enough that you will start to lose some of the area that you need for your ring pack. Building a long rod stock car engine gave us more snot off of the turns. I think it was explained to me as a better leaverage effect. My 351 Cleveland is being built using a Scat stroker crank for a final displacement of 393 cubes. It is also being built using 6 inch Chevrolet rods. Some of the stoker kit options are for rods even longer than that. My KB pistons are also built with a relocated wrist pin location to make up for the extra rod length.
I understand that a "long rod" engine will technically be stock stroke or destroked. I also understand that any engine has a rod ratio, and that is what matters. Long rod engines can be part of the discussion just as much as strokers and stock engines with rod swaps. I just want to get a feel for what folks believe and more importantly, what they have witnessed. That's a good comment... I have always wanted to build a 383c. 3.75" stroke with a 6" rod. It is my conservative side that wants to keep it 383 rather than 393. That way I have more rod ratio, and at the same time I keep the pistons slightly taller for longer life (in theory). The Cleveland wants to rev, so keeping the stroke a bit shorter is not a problem.
Just for giggles: Does anyone realize that you can use off the shelf 347 pistons and put 351m/400 rods in a 351w? Wonder how that engine would run? Wouldn't cost much to build it that way either. Stock 351w= 1.7 RR This combo= 1.88 RR
So that's a 1.85 RR... What gave you the motivation to do that combo? Do you notice a big difference that you attribute to the rods?
I originally told the speed shop to make it into a 408 but, after taking all of the measurements, I was told that the deck height would not support the 408 configuration and the 393 version would work out for me much better. Don't know why my deck height was any different than any other Cleveland that did get made into a 408.
That's strange... I know at least one guy with a 408c. He loves it, but I am shy of the 9.2 block and 4" stroke. Just seems too tight for me. I really want to do a 383c...
