rod length for 3.78 stroke crank

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70b7duster

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parts breakdown so far

-SCAT billet 3.79 stroke crank turned down to 2.100 journal size (use to race midgets/sprint cars, left over part)

-mopar aluminum comando heads w/ w2 intake and exhaust ports cut for 2.08 1.60 valves

-w2 m1 intake ported to the heads

-r3 block 9.6 deck

-mopar 50mm ugl cam

the part im debating on is, a freind is offering me a set of olliver chevy 6.125 rods which mean to run them the deck would need a considerable amount of material removed. OR do i buy longer rods and save the machining costs. SCAT has a 6.200 rod in the 2.100 journal size for around $500 with the arp 2000 7/16 bolt upgrade.

anyone have similar builds they can share their specs on?
 
70b7duster said:
parts breakdown so far

-SCAT billet 3.79 stroke crank turned down to 2.100 journal size (use to race midgets/sprint cars, left over part)

-mopar aluminum comando heads w/ w2 intake and exhaust ports cut for 2.08 1.60 valves

-w2 m1 intake ported to the heads

-r3 block 9.6 deck

-mopar 50mm ugl cam

the part im debating on is, a freind is offering me a set of olliver chevy 6.125 rods which mean to run them the deck would need a considerable amount of material removed. OR do i buy longer rods and save the machining costs. SCAT has a 6.200 rod in the 2.100 journal size for around $500 with the arp 2000 7/16 bolt upgrade.

anyone have similar builds they can share their specs on?
Click to expand...

Presumably, the R block can take a pretty big shave but I would think perhaps you start to sacrifice some strength at the top of the bore if you cut too much. How much do you figure you would have to cut?

I'll bet you could get some Chivvy pistons to work depending on your bore size or get a custom set made to fit the combo.

Also, that crank is still going to rev pretty high, especially with those heads and a stout block like an R block. That's potentially an 8,000 rpm combo with the right cam.

Here's a pretty in-depth discussion on rod length. Click me.
 
the block hasn't been machined yet. But thats the plan to be able to use an off the shelf piston instead of having to buy a custom set. The other thing i was worried about w/ the shorter rod was side loading the piston. looking through past posts it looks like MRL performance has built a similar combo.
 
also knowing shes going to be a high rpm screamer whose w2 rockers would you recomend. the heads are complete less rockers.
 
For a zero deck set up.

Deck height = rod length + piston compression distance + 1/2 stroke.

Piece it together from there. Piston CD would be 1.58"
 
depending on what bore size you will be running but you can get a piston with a 1.45 CH normally on a 4.0 inch stroke with a 6.125 rod but just buy a 6.25 chevy rod with that stroke crank you have and it will work you may have to deck the block or buy a 18* chevy piston with a 1.56 CH. and run a 6.20 rod.
 
...but I would think perhaps you start to sacrifice some strength at the top of the bore if you cut too much...
Click to expand...

Not to mention the shaving of the intake that would accompany the loss in deck height.

Oliver rods are top notch if they're a good price....can you just run a custom piston?
 
I have a K1 3.79 crank with K1 6.125 rods and an off the shelf forged Diamond piston for a 383 Chevy engine with around a 1.56 comp height. I can double check the specs and part # when I get home. The pistons did have the valve reliefs relocated for use in a SB Mopar, Diamond charged an extra $32 for a set of 8 pistons. This was way cheaper than total custom pistons. The piston I'm using has -30cc for an 8.5to1 CR with Edelebrock heads, I'm running boost.
 
OK, I believe I have a 9.585 deck height , I will check.
The pistons are even with the deck, not in the hole.
The rods you are looking to use have a .927 chevy pin?
 
yeah they have a .927 pin size. a member here messaged me and has a set of wiseco pistons for my rod and crank setup.
 
Ok Im running a
3.79 stroke crank
6.125 rods
1.55 Comp Height pistons
9.585 deck height.
Resulting in 387CI 4.030 bore
Pistons are .010 in the hole.
 
Street and some road course to shut up my buddies w/ their 240z's


The car is an original slant six car and was my daily through highschool then I got the grand idea to do a v8 swap and take it apart. Which is how it stayed for 5 years (typical story I know lol).

Had the engine compartment painted the original b7 and put in the 360 reverse manual valve body 727 trans and 8 3/4. Ran it for less than a year, tore it back apart again.

Now has a HDK w/ 13" cobra rotors and calipers, doctor diffs 8 3/4 cobra rotors and calipers, and my family owns a tow yard and a car cleared lein sale w/ 18x9 Saleen wheels (score)

So I'll run this combo until the motor is done and do a t56 swap at the same time.
 

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Sweet!! Can't wait to see some more-since I'm on my phone and can't see the signatures, do you have a build thread?
 
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