Long Rod 306 - Ford Muscle Forums : Ford Muscle Cars Tech Forum

Stangboy69 · 04-02-2007, 12:24 AM

Has anyone had any experience running a long rod 306? eg. 5.4" rod, 3" crank. I've heard this setup revs real easy and makes big power up top due to the rod/stroke ratio. I'd love to try it out in a '65 or '66 coupe. Has anyone tried this setup?

mikemustang289 · 04-02-2007, 01:53 AM

It's not going to make "that much" of a difference, especially if the rest of the combo isn't well put together. The whole rod/stroke ratio debate has been discussed at length many times. What I have gathered is that it's not worth the effort, or should I say expense, if you already have 5.090 rods. Spend the money on the right heads and cam combo.

ckelly · 04-02-2007, 07:09 AM

What he said - an engineering exercise and a way to spend money.

thekingofazle · 04-02-2007, 09:35 AM

I don't remember if tony ran a 306, I think he did. In fact I think his handle was tony306

But I haven't seen him around in a while.

From what I understand - long rod motors were developed when head technology was pretty poor - the longer dwell time near TDC and BDC promoted better cylinder filling. With new heads, the need is eliminated.

blkfrd · 04-02-2007, 10:19 AM

Do it!

Longer rod advantages:

Less piston friction

Reduced reciprocating weight (don't use a heavy rod...use a good aftermarket I beam rod unless your hard set on H beams)

Less rod stress. Piston weighs less and better rod/stroke geometry slows the piston acceleration down at TDC and BDC a tad to reduce G forces

Slight piston dwell advantage (the other advantages are the main reason for doing a long rod motor). Going from a 5.09 rod to a 5.40 rod will only make a small difference in piston motion. .010 to .015 at most. I wrote an Microsoft Excel progam to look at this a few years ago.

KB makes a forged piston for a long rod 306 and there are probably other manufacturers as well.

If I were building a 306, i'd definitely build a long rod engine...it probably won't cost that much more if any.

woody1 · 04-02-2007, 11:22 AM

useless, rs ratio = useless. Put a good head on it

ckelly · 04-02-2007, 11:37 AM

Get an estimate on balancing too - with different rods and a short piston, balancing could easily cost double what the pistons cost. I still think the gains do not in any way justify the expense. You can roughly figger $350 for rods, $250 for hyper pistons and $200 to balance plus heavy metal at $40+ a slug. Estimate two slugs to balance and you're near $900 to pick up maybe a few HP and reduce sidewall loading a hair. Running 500 miles at WOT - worth it. Running 5 miles to the Sonic - not.

BrianS · 04-02-2007, 03:12 PM

Why would you need to rebalance with heavy metal? A longer rod uses a shorter and lighter piston. The longer rod should only weigh slightly more, if any, than the stock length rod.