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Old 02-26-2011, 10:31 PM   #1
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Default con rod research

Well since I started looking at different pistons I decided to do some research to find a con rod with near same sizes as ours or the pistons I may use and stock big end \ length

I've found the
A20\B20 honda rods use same size big and small diameter and is longer by 5mm

CA18DET rods have same big and little end and length as stock con rods.

I will update this as I find more info.

Last edited by Techsalvager; 02-26-2011 at 10:47 PM.
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Old 02-26-2011, 10:39 PM   #2
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The real question is,... why?

There is no reason to get a longer rod. Are you going to make 5mm shorter custom pistons? You're trying to solve a problem that does not exist.

How can CA18DET PISTONS be the same length as CON RODS?
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Old 02-26-2011, 10:47 PM   #3
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heh didn't notice that. fixed. Not looking for a longer rod.
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Old 02-28-2011, 03:47 AM   #4
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Quote:
Originally Posted by falcon View Post
The real question is,... why?

There is no reason to get a longer rod.
Plenty of reasons to lengthen the rods with a stock crank. Less piston speed, more RPM capabilities, and better rod reliability to name a few. Longer rods let you shift the wrist pin up in the piston and improve the rod ratio of the motor. 5mm is a bit excessive since you'll interfere significantly with the oil control ring, but 3-4mm is doable and has been done.
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Old 02-28-2011, 05:46 AM   #5
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Quote:
Originally Posted by Savington View Post
Plenty of reasons to lengthen the rods with a stock crank. Less piston speed, more RPM capabilities, and better rod reliability to name a few. Longer rods let you shift the wrist pin up in the piston and improve the rod ratio of the motor. 5mm is a bit excessive since you'll interfere significantly with the oil control ring, but 3-4mm is doable and has been done.
+1. Longer rods have nice cascade effect. Who has done it on a BP?

OP, sometimes the rod width can be narrowed a hair at the bigend but not always.

Custom pistons will be needed, not a big deal.
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Old 02-28-2011, 10:08 AM   #6
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b16a rods are 1-2mm longer from the specs I've seen with the same big end size
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Old 02-28-2011, 10:53 AM   #7
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There is a rather long thread on this topic where some dude used honda rods in his BP block. I will not search for it as I am lazy
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Old 03-02-2011, 12:09 AM   #8
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BMW M20B27 stock con rods
BE dia 48mm
PE dia 22mm
CTC 130mm
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Old 03-08-2011, 03:35 PM   #9
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anyone aware of a con rod with a 140mm ctc and a 48mm big end?
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Old 03-08-2011, 04:36 PM   #10
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Quote:
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+1. Longer rods have nice cascade effect. Who has done it on a BP?

OP, sometimes the rod width can be narrowed a hair at the bigend but not always.

Custom pistons will be needed, not a big deal.
I know Bike In Dirt from M.net has done it as well (Cali track junkie, N/A motor with ~175whp). If I ever get around to building an ethanol-specific 11:1 bottom end, it will be a longrod motor.

The only complication is that the wrist pin gets elevated into the oil control ring, which requires a bit of trickery to make work, but it's doable.
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Old 03-08-2011, 06:34 PM   #11
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I think I may found some, I Got to check the M42\44 motors from bmw
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Old 03-08-2011, 06:43 PM   #12
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I know MarkP talked about using Honda rods and pistons back in the day.
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Old 03-08-2011, 08:29 PM   #13
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Quote:
Originally Posted by Savington View Post
Plenty of reasons to lengthen the rods with a stock crank. Less piston speed, more RPM capabilities, and better rod reliability to name a few. Longer rods let you shift the wrist pin up in the piston and improve the rod ratio of the motor. 5mm is a bit excessive since you'll interfere significantly with the oil control ring, but 3-4mm is doable and has been done.
Would said 3 mm add'l length show noticeable benefits?
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Old 03-08-2011, 08:41 PM   #14
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m42\44 140mm ctc
big end 48mm
pin end 22mm
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Old 04-18-2011, 08:00 PM   #15
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BMW con rod, miata crank


By techsalvager at 2011-04-18

By techsalvager at 2011-04-18
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Old 04-18-2011, 11:56 PM   #16
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You can't elevate the wrist pin 7mm in the piston (8mm once you account for the additional wrist pin diameter). What's your plan for that?
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Old 04-19-2011, 12:29 AM   #17
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I dunno but if those rods are from an i6, it's "buy two sets, get one free" for the miata.
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Old 04-19-2011, 04:46 AM   #18
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Quote:
Originally Posted by Savington View Post
You can't elevate the wrist pin 7mm in the piston (8mm once you account for the additional wrist pin diameter). What's your plan for that?
Those bmw rods in the picture are out of a 325e e30
They are 130mm CTC, which is shorter than stock rods
If you get the rods out of a 325i e30 they are 135mm CTC

I don't plan to do anything with them, just documenting that they do indeed fit on the crank with no issues
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Old 04-19-2011, 06:00 AM   #19
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Quote:
Originally Posted by Techsalvager View Post
Those bmw rods in the picture are out of a 325e e30
A friend of mine uses a E-car bottom end with a I-car head. 400hp/480tq @ 25psi on the stock E-car bottom end. Those rods are super tough. Good find, the M20 is a seriously underrated motor.
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Old 04-19-2011, 06:59 AM   #20
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stock piston, bmw rod


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note bmw rod uses bigger wrist pin
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