Boss Rods and pistons

[Dennis Thomas]

Planing on upgrading my internals.
Need stronger rods, I’m running an eforcesupercharger. Does 2012-2013 boss 302 rods fit 2009 3v 4.6. And if they come with the pistons. What’s the size difference? Just wondering saw couple for sale

 

[tjm73]

4V pistons are not right for a 3V engine. But any 2015 or newer rod will drop right in. And they are good for 600-700 hp as evidenced by all the supercharged and turbocharged 5.0 DOHC cars making 600-700 hp at the wheels. They are cheap too.

 

[RED09GT]

The Boss pistons have the wrong bore size and the wrong compression height for a mod motor. They are 3.63" vs. 3.552" for the 4.6 and the compression height of the boss piston is 1.169" vs. 1.220"-they would sit 0.051" down from the deck. This would drop the compression ratio but make it much more detonation prone-you need to decrease the quench to force the A/F mix into the combustion chamber to optimize combustion-otherwise you get poor flame propagation and have pockets of A/F that can detonate.

You'd need to sleeve the block and shave the deck to an amount that the chain tensioners would have difficulty making up for the slack so it is not feasible. It is not impossible, just would cost a few grand and create a few headaches just to say it can be done.

If you can get a decent deal, buy the set and sell the pistons to someone building a coyote project.

 

[Forty61]

But any 2015 or newer rod will drop right in. And they are good for 600-700 hp as evidenced by all the supercharged and turbocharged 5.0 DOHC cars making 600-700 hp at the wheels. They are cheap too.

Really? I had not seen or heard that was even an option.. why is it only the 2015 up?

 

[RED09GT]

They basically adopted the Boss design across all the platforms in 2015 but the 2011-2014 are decent as well. The 2015+ ones are cheap straight from your local ford dealer and are the part number that comes up for the 2011-2014 mustang GT's and F150's now.

 

[tjm73]

Really? I had not seen or heard that was even an option.. why is it only the 2015 up?

The earlier rods will work, but the 2015 rods are the same as the BOSS rods. All 5.0 DOHC rods starting in 2015 are effectively BOSS rods. You can buy them brand new from Ford for cheap. Like $31.50 each at Varsity Ford for example. That's $252 for 8 brand new "BOSS" rods that can handle putting 600-700 hp to the wheels.

 

[Pentalab]

I believe 86GT used Boss rods a few years ago on his 2009 bullitt. I think he said the issue was the set of 8 rods were all different weights, not matched for weight. He had to get em all balanced to the lowest common denominator, before using em. Hopefully he will chime in.

 

[tjm73]

Well yeah. Any change like that will require a balance. If you are going this route you are probably putting forged pistons on them and that will definitely require re-balance.

I would assume that to be done regardless.

 

[Doug Huggard]

Or you can get 03/04 cobra rods for just a littlemore and have a bit more room for growth (even though there's a bunch on Gen2 coyote guys making like 850 wheel lol). Just another inexpensive strong option

 

[Doug Huggard]

You can even run 03/04 cobra pistons as well. They're like 18cc dished (9-1 compression on a 3v). No valve relief but if vct is limited, that wont matter. They're 4032 forged so you can run a tighter clearance in a street application. I've seen sets of 8 in good condition for like $300

 

[05sonic4.6]

I used boss rods in my first build. They held up great at 600whp. My machine shop definitely had something to say with how much of a pain balancing everything was. I’ve since upgraded to Manley. Considering used Manley rods routinely go for 350-450. I say spend a little more and get them over the boss. Stronger, better bolts and better overall design (no cracked caps)