FE build advice needed

[wsu0702]

I have been collecting parts for my next build and I would appreciate informed opinions on rotating assembly choice.  So far I have a BBM block, a set of bare BBM heads and a new Blue Thunder 4V Medium riser intake. My application is a split street/strip 69 mustang with a 4 spd and a 3.91 rear.  Should I go with a 4.25 or a 4.375 crank? I still don't know what compression ratio would be best so I will wait on the pistons but I would like to purchase a crank and rods soon.

[blykins]

Were you the one that asked a similar question on the other FE forum?  Still planning on spraying?

[Barry_R]

For most street stuff I prefer the 4.25 and as bi a bore as you are comfortable with.
I like it because it keeps the piston pin out of the ring grooves, and because it eliminates any concerns about cam clearance versus the connecting rods.

[wsu0702]

Were you the one that asked a similar question on the other FE forum?  Still planning on spraying?

Yes.  It's only a small shot nitrous system (75-150HP).  There doesn't seem to be a consensus on which way to go.  Some say 4.375" (your recommendation) and other say 4.25".  I'm just trying to get as much info as I can to make the best choice before spending 2 grand. 

[blykins]

Well, here's how I'm looking at it: 

A 482 with good heads will make at least 550 hp.  Even if you stayed with a 4.250" stroke, made 550 hp, and then sprayed 150 on top of it, I wouldn't feel comfortable with a cast crank in that situation, so you're looking at a steel crank.   If you're gonna pay for a steel crank, you're looking at saving at least a couple hundred bucks by going with an RPM 4.375" crank, even if you have to touch grind the mains/rods.  You're also adding cubic inches, especially if you go past the standard 4.250" bore size. 

The only con is that you have to pay a little extra attention to the rod/cam clearance, depending on the connecting rods that you choose.  Some get close, some don't. 

If you go with a 4.375" stroke, you will need a 6.700" rod and the piston will come out to be ~1.265" with a 10.150" deck height.  You will need to cut the decks on your BBM block.  They come in at around 10.160", but there's enough variance that they need to be trued up.  I usually aim for 10.150".   For 700-750 hp, I'd bypass a Scat rod and use something like a Crower, Callies, Oliver, etc. 

There's nothing wrong with the 4.250" stroke, but if you're aiming for big horsepower with the spray, I see it as an opportunity to save some money and add some displacement with the RPM.  Just my thinking.

[wsu0702]

Thanks Brent.  Can you confirm that the part number listed below is the crank that you are referring to?

RMP Crankshaft P/N DGE-DE4375

Also I have been looking at rods this afternoon and here the ones that I am considering.  I could not find any info on the 6.7" Crower rod.

Callies Ultra H-beam P/N U16230
Oliver Big  Block P/N C6700BB8

[blykins]

Crower rods......SP93417B-8

[scott foxwell]

I don't know enough about available crankshafts to make a recommendation  but I would go with 4.25 stroke and as much bore as you're comfortable with. For the power and rpm you're talking about there is absolutely no need for en expensive billet rod. Like I said before, the Scat forged Pro series rod would be more than enough for what you're doing. Any import H beam will be way more than enough. I have to laugh inside a little hearing RPM crank and Oliver or Crower rod used in the same sentence.
I'll also add that the 4.25 engine will respond better to the spray.
JMO

[scott foxwell]

...

[blykins]

Well, before you laugh a little, just know that all of us use the RPM FE cranks quite frequently.  They are the only ones to make a 3.980" crank with BBC rod journals and are the only ones to make a 4.375" off-the-shelf crankshaft. 

Granted, the journal dimensions usually need to be adjusted, but I have a lot of high horsepower engines out there running those crankshafts. 

[scott foxwell]

Well, before you laugh a little, just know that all of us use the RPM FE cranks quite frequently.  They are the only ones to make a 3.980" crank with BBC rod journals and are the only ones to make a 4.375" off-the-shelf crankshaft. 

Granted, the journal dimensions usually need to be adjusted, but I have a lot of high horsepower engines out there running those crankshafts.

That's fine. The last RPM crank I had never made it past receiving. The minute I looked at the fillet grinding I put it right back in the box and sent it back. Adney Brown will build a 3.98/2.20 crank from a truck forging for a very decent price. Much better crank. I believe CAT and RPM are the same. Really don't care about 4.375.
Lot of people don't realize what less expensive alternatives there are for connecting rods. Just pointing out that if they're willing to use a Chinese crank, there are other far more affordable and perfectly acceptable alternatives.

[blykins]

I feel the same about Eagle.  But the difference is that most of those break, right at the 1/5 journal. 

When you get a few FE's under your belt, you'll be better prepared to give a synopsis on what works and what doesn't. 

[scott foxwell]

I feel the same about Eagle.  But the difference is that most of those break, right at the 1/5 journal. 

When you get a few FE's under your belt, you'll be better prepared to give a synopsis on what works and what doesn't.

Yeah, not a big fan of Eagle stuff either. I have a few FE's under my belt. Last high HP FE I built had an Eagle cast crank. Broke that SOB in many pieces. I warned the customer but...well...you know, the customer is always right.
You should know by now I don't look at labels. A crank is either right, or not. Doesn't matter what it's going in. Every engine has it's idiosyncrasies and quirks and if you just look at as an engine, they all become obvious pretty quickly.

[blykins]

I feel the same about Eagle.  But the difference is that most of those break, right at the 1/5 journal. 

When you get a few FE's under your belt, you'll be better prepared to give a synopsis on what works and what doesn't.

Yeah, not a big fan of Eagle stuff either. I have a few FE's under my belt. Last high HP FE I built had an Eagle cast crank. Broke that SOB in many pieces. I warned the customer but...well...you know, the customer is always right.
You should know by now I don't look at labels. A crank is either right, or not. Doesn't matter what it's going in. Every engine has it's idiosyncrasies and quirks and if you just look at as an engine, they all become obvious pretty quickly.

I agree. 

If you notice, I mentioned that the RPM needs a little grinding work before it's a drop-in.  Nothing wrong with that, as I spend a lot of time fixing a lot of aftermarket parts, including new blocks.   

My point was, when you start using everything that's out there, you get a feel for what's "cheap, Chinese" and what's not.  As you have seen, the Eagle stuff will scatter an engine.  Never have heard of an RPM crank breaking yet, but they do need some detail work out of the box.  Every professional FE builder on this forum has used more than their share of them and they are a viable resource for cranks.   Not every guy wants to stop at 500 cubes and with a 4.375" stroke and a large bore size, the average guy can have a fairly big displacement for an FE without buying a $2000-3000 billet crank. 

[fekbmax]

Crower rods......SP93417B-8

That's a nice rod, just got a set this weekend. nice craftsmanship. i plan on doing the L-19 bolt upgrade since i got such a great deal on the rods.