258 rods and 242 rods
Posted: December 15th, 2020, 7:01 pm
So I have read and read and read for weeks on end now about rod ratio and different connecting rods and the affects on how the engine performs. The conclusion I have came to is that connecting rod ratio doesn’t matter, but it does matter!
It doesn’t matter on its own, but as a system it does matter.
I have read shorter rods tend to give a broader torque curve along with better vacuum at idle. The can allow more room for timing errors and reduce detonation as long as the quench is there to help. I have read that they don’t flow as well but have a longer dwell time at BDC
Longer rods on the other hand have a longer dwell time at TDC, less room for timing errors, more chance for detonation if there is a timing or injection timing error, and it increases peak torque and horsepower as a system
My conclusion from all my research is that long rods sound ideal for engine longevity but if I wanted to build an 4.6 stroker utilizing a 258 crank and 4.0 block it sounds like the 258 rods would give me a broader torque curve, more room for timing errors while I try to get it right, more vacuum at idle, and better throttle response which sounds ideal to me.
I get that quench, head design, flow, piston design, and camshaft selection play a huge part in all of this but is there anything I’m missing on this topic?
I would really like to keep this from turning into a war of long rod vs short rod but more of facts that maybe I am not seeing. I have done lots of research so far and lots of long life well known engines have rod ratios on both sides of this equation so I’d rather not get into all of that either.
Also I’m more doing this to learn more of the facts before I build my stroker for my her which just cracked a ring so it will be happening sooner rather than later.
Tim
It doesn’t matter on its own, but as a system it does matter.
I have read shorter rods tend to give a broader torque curve along with better vacuum at idle. The can allow more room for timing errors and reduce detonation as long as the quench is there to help. I have read that they don’t flow as well but have a longer dwell time at BDC
Longer rods on the other hand have a longer dwell time at TDC, less room for timing errors, more chance for detonation if there is a timing or injection timing error, and it increases peak torque and horsepower as a system
My conclusion from all my research is that long rods sound ideal for engine longevity but if I wanted to build an 4.6 stroker utilizing a 258 crank and 4.0 block it sounds like the 258 rods would give me a broader torque curve, more room for timing errors while I try to get it right, more vacuum at idle, and better throttle response which sounds ideal to me.
I get that quench, head design, flow, piston design, and camshaft selection play a huge part in all of this but is there anything I’m missing on this topic?
I would really like to keep this from turning into a war of long rod vs short rod but more of facts that maybe I am not seeing. I have done lots of research so far and lots of long life well known engines have rod ratios on both sides of this equation so I’d rather not get into all of that either.
Also I’m more doing this to learn more of the facts before I build my stroker for my her which just cracked a ring so it will be happening sooner rather than later.
Tim