3.875 x 4.125 sbc, do I want a 6" rod?

[redliner]

Dart block,3.875 x 4.125 bore sbc for my 3200lbs. coupe. lookin to make 600 h.p. on pumpgas. Is a 6" rod the way to go? Over simplified question but can elaborate if need be to get a good answer.... Thanks....

[lefty o]

i thin a 6" would be fine. but get the crank, call and talk to a piston mfgr and go from there.

[wyrmrider]

very popular combination
pick your pistons and rods before spending cash
lighter piston (than with 5.7 rod) is easier to balance and keeps the piston from coming out the bottom of the block
that said
if you can find a shelf combination or a shelf piston for a longer rod use it with the longer rod 6 1/8 6 1/4 whatever depending on your application, longevity vs rpm band- which we do not know- etc
we built lots of motors with 4" strokes and 6" rods
pick a rod that will easily clear cam
does the dart block have a raised cam, big ca, tunnel, larger lifter bores by any chance
roller cam or FT? ours were roller but I have done FT
smaller base circle on ft leads to pointy noses- not good with any rpm or spring pressure
on a roller if using a smaller base circle a design for a Buick base circle should be used as chevy base circle on small base circle billet is nowhere near optimum and gives more side thrust so you have to use a milder grind- BVVC
Mike Jones is go to for Buick Base Circles - I think his Buick Indy engines used them- but It's been awhile

[englertracing]

That's what sprint cars run.
Mostly.

Ones with enormous all pro heads use shorter 5.9" rods
Older smaller heads use 6" rods.

So are you using smallish heads or biggish heads?


TBH I'd be tempted to go for 6.125"

[redliner]

i thin a 6" would be fine. but get the crank, call and talk to a piston mfgr and go from there.

Thanks Lefty!

[redliner]

very popular combination
pick your pistons and rods before spending cash
lighter piston (than with 5.7 rod) is easier to balance and keeps the piston from coming out the bottom of the block
that said
if you can find a shelf combination or a shelf piston for a longer rod use it with the longer rod 6 1/8 6 1/4 whatever depending on your application, longevity vs rpm band- which we do not know- etc
we built lots of motors with 4" strokes and 6" rods
pick a rod that will easily clear cam
does the dart block have a raised cam, big ca, tunnel, larger lifter bores by any chance
roller cam or FT? ours were roller but I have done FT
smaller base circle on ft leads to pointy noses- not good with any rpm or spring pressure
on a roller if using a smaller base circle a design for a Buick base circle should be used as chevy base circle on small base circle billet is nowhere near optimum and gives more side thrust so you have to use a milder grind- BVVC
Mike Jones is go to for Buick Base Circles - I think his Buick Indy engines used them- but It's been awhile

The car is street / strip, solid roller ( .700 ish lift) Rpm range is 7500 max.I was going to go with the SHP block which doesnt have the raised cam tunnel. Thanks for the heads up on alll this info! I was planning to talk to Mike about a cam. I will mention the Buick base circle. Very interesting!!!

[redliner]

That's what sprint cars run.
Mostly.

Ones with enormous all pro heads use shorter 5.9" rods
Older smaller heads use 6" rods.

So are you using smallish heads or biggish heads?


TBH I'd be tempted to go for 6.125"

Thanks Englertracing! I plan on using Speier Racing Heads Profier V2.50PF/23* which are 227 cc, 2.53 csa,323@.700

[RevTheory]

Check this article out- http://www.superchevy.com/how-to/engine ... all-block/

[redliner]

Check this article out- http://www.superchevy.com/how-to/engine ... all-block/

Thanks! Very good article!!!

[77cruiser]

That's what I used in mine 6" Scat Procomp rod Scat forged crank. I'm only at 530 hp but it has a small cam.

[rfoll]

With this kind of build the parts are not going to be inexpensive junk. There is not going to be cost differences between the rods and pistons for each connecting rod choice. It is more likely the 6 inch combo will be more common due to the increased stroke, and the assembly will balance internally. In my 415 I have 6" Compstar H beams, and 4 needed to be clearanced slightly for my standard base circle .640" lift cam.

[steve316]

Run small journal crank and compstar rods and you can run standard base circle cam. You will have a little over .045 rod to cam clearance.

[redliner]

Run small journal crank and compstar rods and you can run standard base circle cam. You will have a little over .045 rod to cam clearance.

Im lookin at .700 lift. Small journal, meaning 350 mains?

[wyrmrider]

Honda rod journal or 283 methinks he meant
do that or get the raised big cam tunnel
the bigger the base circle the better for lots of reasons

[redliner]

Honda rod journal or 283 methinks he meant
do that or get the raised big cam tunnel
the bigger the base circle the better for lots of reasons

I was thinkin SHP block which has standard cam location but can be upgraded to bigger tunnel and .904 lifters at a later date. I am lucky if i get the combo built I have in mind... I must draw the line somewhere....