Posted By: mac56
Preferred rod, compression height combo - 01/09/12 10:33 PM
With a 400 block 4.150 stroke and chev rods which combination do you like?
Preferred rod, compression height combo
Posted By: Bob_Coomer
Re: Preferred rod, compression height combo - 01/09/12 10:45 PM
Good question..
My current new engine project is this.. 400 block, 4.15 crank etc..
I have the 6.535 or therebouts rod length. It has the small wrist pin .990, and has the Chevy 2.2 rod journal...
This lightens things up a bit.
Looks like the low deck Chrysler block has a 9.98 deck height.
So we come up with the following..
Compression height would be the deck height minus half the crank stroke, minus the rod length... this would be
9.980
-2.075
-6.535
-----------
1.34 compression height would be zero deck.
This is nice and light, not so short that the wrist pin is in the oil ring pack.. Which is in the 1.3- 1.32 range...
This avoids the oil support rails etc. The 572 Hemi I built 2 years ago had a short piston (Wiesco) 4.5 stroke, 4.5 bore and a 7.1 rod.. Pistons were short 1.32 or so and needed the oil support rail.
My current new engine project is this.. 400 block, 4.15 crank etc..
I have the 6.535 or therebouts rod length. It has the small wrist pin .990, and has the Chevy 2.2 rod journal...
This lightens things up a bit.
Looks like the low deck Chrysler block has a 9.98 deck height.
So we come up with the following..
Compression height would be the deck height minus half the crank stroke, minus the rod length... this would be
9.980
-2.075
-6.535
-----------
1.34 compression height would be zero deck.
This is nice and light, not so short that the wrist pin is in the oil ring pack.. Which is in the 1.3- 1.32 range...
This avoids the oil support rails etc. The 572 Hemi I built 2 years ago had a short piston (Wiesco) 4.5 stroke, 4.5 bore and a 7.1 rod.. Pistons were short 1.32 or so and needed the oil support rail.
Posted By: mac56
Re: Preferred rod, compression height combo - 01/09/12 11:56 PM
I have to order a custom piston and will need new rods so that is where the question comes from. I would prefer not to have the pin into the oil ring.
Posted By: Jeepmon
Re: Preferred rod, compression height combo - 01/10/12 12:06 AM
400 block... 6.760 rod... 4.150 stroke... 4.375 bore = 500 CID
(edited... oops had a typo)
(edited... oops had a typo)
Posted By: go green
Re: Preferred rod, compression height combo - 01/10/12 12:33 AM
Quote:
I have to order a custom piston and will need new rods so that is where the question comes from. I would prefer not to have the pin into the oil ring.
Just run buttons and they support the oil ring . easy
Posted By: 64Post
Re: Preferred rod, compression height combo - 01/10/12 02:56 AM
6.535" Chevy rod... 
Posted By: Cab_Burge
Re: Preferred rod, compression height combo - 01/10/12 04:12 AM
Quote:I like long rods in my 400 block strokers, 6.8 or 6.7, that is with the BB Chevy 2.200 rod journal sizes, BB Chevy type long rods with .990 pins and 2.200 rod sizes
With a 400 block 4.150 stroke and chev rods which combination do you like?
Both my low compression street motor and higher compression bracket motor, 4.300 stroke, 4.375 bore with 6.800 long H beam steel BB Chevy type rods and the new bracket motor, 4.35 bore with 4.250 long stroke with 6.7 long BB Chevy type rods both have the wrist pins on the oil ring, SO WHAT 
The pistons sure are light 
Posted By: ahy
Re: Preferred rod, compression height combo - 01/10/12 04:35 AM
With the Chevy style rod might as well run the 6.5x" rod and 1.3x" Ch piston. My 400 stroker (4.15 x 4.375) has standard BB rods with 6.76x length. 1.13" ish CH which means oil support rails. Benefits of the longer rod are a bit less side loading on the bores and some slight breathing improvements with standard port heads - plus a super light piston. Drawbacks are piston rock with the short piston and potential shorter life due to rock. No problems with the oil support rail yet with 9k miles.
Posted By: Al_Alguire
Re: Preferred rod, compression height combo - 01/10/12 07:09 AM
Well based on your info I would decide on what CD on the piston works best for you and order a rod accordingly. Many variables there like cylinder head choice, for instance a valve relief on a B1 type head on a small bore like that is going to get into the top ring quick. What type and size ring are you going to run, is it a true NA set up or will it be sprayed are all questions that matter. An aluminum rod can be had in any size you like. Best to design the piston to optimize it for it's intended purpose and then get a rod that fits, than try to build a piston based on a rod choice. Just my
Posted By: mac56
Re: Preferred rod, compression height combo - 01/10/12 11:24 AM
Quote:
Well based on your info I would decide on what CD on the piston works best for you and order a rod accordingly. Many variables there like cylinder head choice, for instance a valve relief on a B1 type head on a small bore like that is going to get into the top ring quick. What type and size ring are you going to run, is it a true NA set up or will it be sprayed are all questions that matter. An aluminum rod can be had in any size you like. Best to design the piston to optimize it for it's intended purpose and then get a rod that fits, than try to build a piston based on a rod choice. Just my
Yes Al it is naturally aspirated and will have B1 valve reliefs on 4.380 bore so the rings may end up down a little farther. It will probably have a standard 1/16 ring pack.I was thinking of staying with the 1.48 I use now and a 6.385 rod.