Building a 6.4 Cummins the CORRECT way

adamsmarshall

adamsmarshall

Drilling Crooked Holes
Joined
Oct 12, 2008
Messages
1,915
Ok, so there have been a ton of threads about the 6.4 and although relatively informative for the most part, they tend to trail off into the somewhat vague area of leaving people to either go to particular shops that build them on a regular basis, or go off of the general 0.060"-0.080" off the deck and run with it using the 5.9 crank in a 6.7.

My question here for those with information pertaining to the OTHER ways of going about it, would you mind sharing what you have?

The original plan for my build was a built 6.7 with billet rods, massively ported head, etc etc etc. My donor block came from a truck with a stuck EGR and gummed up the entire thing, and I mean ALL of it. Upon teardown it was discovered that when it gummed up, it decided to take out a rod bearing and FUBAR'd the crank journal. SO, the decision was made to destroke it with a 5.9 crank and go about our rat killing.

So I ask you, if running longer rods, as opposed to decking the block, what is the general (or exact if known and willing to share) length of rod needed? I've heard 205-207 mm thrown out there, but it was never expanded on further.

I've already spoken with a couple manufacturers of billet rods and gotten quotes, and from current perspective between cost and increased longevity of the build, this is looking to be the best/smartest way to go.

Now to add to this, like before, while mentioned vaguely, the subject of ideal piston design whether stock, stock marine, modified stock, custom. What is the most ideal if anyone cares to share for a 200% over injector, 194/220 cam and a highly worked over head with oversized valves and lots of porting?

Thanks to anyone willing to share ANY information on making this happen.
 
adamsmarshall said:
Ok, so there have been a ton of threads about the 6.4 and although relatively informative for the most part, they tend to trail off into the somewhat vague area of leaving people to either go to particular shops that build them on a regular basis, or go off of the general 0.060"-0.080" off the deck and run with it using the 5.9 crank in a 6.7.

My question here for those with information pertaining to the OTHER ways of going about it, would you mind sharing what you have?

The original plan for my build was a built 6.7 with billet rods, massively ported head, etc etc etc. My donor block came from a truck with a stuck EGR and gummed up the entire thing, and I mean ALL of it. Upon teardown it was discovered that when it gummed up, it decided to take out a rod bearing and FUBAR'd the crank journal. SO, the decision was made to destroke it with a 5.9 crank and go about our rat killing.

So I ask you, if running longer rods, as opposed to decking the block, what is the general (or exact if known and willing to share) length of rod needed? I've heard 205-207 mm thrown out there, but it was never expanded on further.

I've already spoken with a couple manufacturers of billet rods and gotten quotes, and from current perspective between cost and increased longevity of the build, this is looking to be the best/smartest way to go.

Now to add to this, like before, while mentioned vaguely, the subject of ideal piston design whether stock, stock marine, modified stock, custom. What is the most ideal if anyone cares to share for a 200% over injector, 194/220 cam and a highly worked over head with oversized valves and lots of porting?

Thanks to anyone willing to share ANY information on making this happen.
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Someone might know the exact length or at least what they have done, but this is how I would approach it. First is to take the current crank or the 5.9 crank, and install it. Install the stock rod and piston for number 1 cylinder in the block. Find top dead center, and measure your piston protrusion. Once you have this number you can mathematically calculate any combination for this block. I don't like using the book numbers because there is a tolerance, and the block could be anywhere in that tolerance. And also the block could have been machined before.

Now depending on what your doing with the truck, for example drag racing, or pulling, can determine what you want to do for rod length and piston. I usually start with the piston, and work back to the rod. Your application is going to determine what kind of piston. From what you have told me, I would consider at the very least a modified stock piston. If this is purely racing, then I would use a forged/billet custom piston. I would also consider your valve clearances and calculate weather or not you need more valve relief, or if you might consider a cam change this year, and you do not want to pull the motor down to cut pistons. Once you know that then you need to figure out the compression height of the piston. Once you have that number you will have the rod length. Now if you use a custom piston you can specify the compression height. In this case you may want to balance the rod length, and compression height. As far as getting too far in left field with length is hard to do.
 
Good luck getting any exact measurements from the places that build these all the time. I tried getting help and specs for the 6.4 build I was gonna do and all I got was, there's a bunch of ways to do it, but never any solid numbers to build off of. So I decided to just run a 6.7 and have a different taste in my mouth for a few places.

Good luck with the build though.
 
I kicked this idea around for my next build but decided it wasnt worth the extra money.

However eric staab ^^^^ just gave the most common sense approach to determine what you should do. If low compression is ok for the build you dont need machining. Stock 6.7 block, and pistons. 5.9 crank and rods will put you around 13.75 : 1 compression ratio.
 
EricStaab said:
Someone might know the exact length or at least what they have done, but this is how I would approach it. First is to take the current crank or the 5.9 crank, and install it. Install the stock rod and piston for number 1 cylinder in the block. Find top dead center, and measure your piston protrusion. Once you have this number you can mathematically calculate any combination for this block. I don't like using the book numbers because there is a tolerance, and the block could be anywhere in that tolerance. And also the block could have been machined before.

Now depending on what your doing with the truck, for example drag racing, or pulling, can determine what you want to do for rod length and piston. I usually start with the piston, and work back to the rod. Your application is going to determine what kind of piston. From what you have told me, I would consider at the very least a modified stock piston. If this is purely racing, then I would use a forged/billet custom piston. I would also consider your valve clearances and calculate weather or not you need more valve relief, or if you might consider a cam change this year, and you do not want to pull the motor down to cut pistons. Once you know that then you need to figure out the compression height of the piston. Once you have that number you will have the rod length. Now if you use a custom piston you can specify the compression height. In this case you may want to balance the rod length, and compression height. As far as getting too far in left field with length is hard to do.
Click to expand...

Thank you Eric!

DIESEL_POWER said:
We have billet pistons built specific for this. no need to get different rods.
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Yeah I messaged you and got a quote on them the other day, I'm leaning towards rods right now though as that's $600 more vs almost $2k
 
Charger said:
Are you a vendor on here now?
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While I understand why you made this comment, lets for once please for f*ck sake keep this on subject and make a useful thread out of it rather than a few of you comparing cock size with Wade...
 
FYI , Wiseco here soon or already a line of pistons for both 12 and 24 valve along with pistons for stroker application.
 
MAXTORQ said:
FYI , Wiseco here soon or already a line of pistons for both 12 and 24 valve along with pistons for stroker application.
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To my knowledge the stroker piston from Wiseco is for a 5.9 block with 6.7 crank. PM Smokem for Wiseco forged pistons
 
It will see the street, however it'll be VERY few and far between.

The plan is to run a coated modified stock or marine piston more than likely.
 
97crewcab said:
To my knowledge the stroker piston from Wiseco is for a 5.9 block with 6.7 crank. PM Smokem for Wiseco forged pistons
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Yes I understand this. Spoke with Jeff and Ron at Wiseco and they are looking into 6.7 as well.
 
Blue grass diesel offers offset wrist pin pistons to make a 6.4 with factory length rods and no decking.
 
As much as I like the idea of an offset wrist pin piston, I like the idea of longer rods better.

You end up with better rod angle/ratio than you do with modified pistons. Less rod angle = better potential longevity
 
If you want to keep it simple, have rods made 194mm long. This will keep piston protrusion the same as stock 6.7 specs. If you wish to raise compression, make the rods longer than 194mm, and machine the top of the piston down the same amount, reducing the cc of the bowl the correct amount to get your desired compression ratio.
 
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