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-   -   con rod research (https://www.miataturbo.net/engine-performance-56/con-rod-research-55901/)

Techsalvager 02-26-2011 09:31 PM

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.

falcon 02-26-2011 09:39 PM

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?

Techsalvager 02-26-2011 09:47 PM

heh didn't notice that. fixed. Not looking for a longer rod.

Savington 02-28-2011 02:47 AM


Originally Posted by falcon (Post 694887)
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.

JKav 02-28-2011 04:46 AM


Originally Posted by Savington (Post 695244)
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.

Techsalvager 02-28-2011 09:08 AM

b16a rods are 1-2mm longer from the specs I've seen with the same big end size

leatherface24 02-28-2011 09:53 AM

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

Techsalvager 03-01-2011 11:09 PM

BMW M20B27 stock con rods
BE dia 48mm
PE dia 22mm
CTC 130mm

Techsalvager 03-08-2011 02:35 PM

anyone aware of a con rod with a 140mm ctc and a 48mm big end?

Savington 03-08-2011 03:36 PM


Originally Posted by JKav (Post 695257)
+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.

Techsalvager 03-08-2011 05:34 PM

I think I may found some, I Got to check the M42\44 motors from bmw

shuiend 03-08-2011 05:43 PM

I know MarkP talked about using Honda rods and pistons back in the day.

JasonC SBB 03-08-2011 07:29 PM


Originally Posted by Savington (Post 695244)
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?

Techsalvager 03-08-2011 07:41 PM

m42\44 140mm ctc
big end 48mm
pin end 22mm

Techsalvager 04-18-2011 07:00 PM

BMW con rod, miata crank

http://img9.imageshack.us/img9/2940/dscn2433q.jpg
By techsalvager at 2011-04-18
http://img705.imageshack.us/img705/783/dscn2434x.jpg
By techsalvager at 2011-04-18

Savington 04-18-2011 10:56 PM

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?

y8s 04-18-2011 11:29 PM

I dunno but if those rods are from an i6, it's "buy two sets, get one free" for the miata.

Techsalvager 04-19-2011 03:46 AM


Originally Posted by Savington (Post 715996)
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

viperormiata 04-19-2011 05:00 AM


Originally Posted by Techsalvager (Post 716083)
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.

Techsalvager 04-19-2011 05:59 AM

stock piston, bmw rod
http://img833.imageshack.us/img833/4060/dscn2403g.jpg

Uploaded with ImageShack.us

note bmw rod uses bigger wrist pin

Alta_Racer 04-19-2011 08:53 AM

It's common to bush rods for a performance build, easily done and you can get it to the size required. The rod "looks" heavy, did you weigh it? How is the side clearance when you had it on the crank?

PatrickB 04-19-2011 09:35 AM

following..

shlammed 04-19-2011 10:02 AM

you could have the rod bushed differently.... but you mentioned that it is shorter than stock BP

edit: aaaaaaaand i didnt see page 2.

ianferrell 04-19-2011 10:09 AM

BTW, a little quick math says that 400hp on 6 cyl isn't that impressive...
i.e. 400 / 6 = 66.66 hp/rod
66.66 * 4 = 266
So that's the ball park of power per rod that kills miata rods, having 2 more cylinders helps spread the load a bit :) Your buddy needs to turn the boost up some more, imo :)

Techsalvager 04-19-2011 11:20 AM


Originally Posted by shlammed (Post 716150)
you could have the rod bushed differently.... but you mentioned that it is shorter than stock BP

edit: aaaaaaaand i didnt see page 2.

This is why I am also doing piston research between 78mm to 81,5mm pistons.

Of course a 1.8l person can research for their own setup as well for pistons

viperormiata 04-19-2011 04:04 PM


Originally Posted by ianferrell (Post 716154)
BTW, a little quick math says that 400hp on 6 cyl isn't that impressive...
i.e. 400 / 6 = 66.66 hp/rod
66.66 * 4 = 266
So that's the ball park of power per rod that kills miata rods, having 2 more cylinders helps spread the load a bit :) Your buddy needs to turn the boost up some more, imo :)

I was just using him as a quick example. That was that power was made using a Holset hx35 (can't remember exhaust housing size) and a unported intake manifold. With a bit more work he pulled a 6.9 @ 103. Plus you have to remember that this is a OEM rod that you can find for DIRT cheap.

Now, he is using a Borg Warner S376 and is aiming for a low 6 in the 1/8th. Should be on 30-40psi. AAAAAAAAAAAAAAAAAND he will still be using the same bottom end with the same stock E-car rods.

dgmorr 04-19-2011 04:50 PM


Originally Posted by viperormiata (Post 716094)
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.

The M20 was never underrated with regard to how much the bottom end can take. It is the single cam, low cfm head, and 12 valves that make NA expensive and typically advised against.

viperormiata 04-22-2011 05:31 AM

Just got all 6 rods for free from 325e m20(thank you e30 buddies)

I'll hold on to them and see what happens with this thread. I'm all about experimenting :giggle:

Techsalvager 04-25-2011 09:15 PM


Originally Posted by Alta_Racer (Post 716123)
It's common to bush rods for a performance build, easily done and you can get it to the size required. The rod "looks" heavy, did you weigh it? How is the side clearance when you had it on the crank?

It was weighed and is indeed heavier than stock but should take more power than stock rods can before giving, side clearnance is same as stock.

Techsalvager 04-25-2011 09:25 PM


Originally Posted by viperormiata (Post 717531)
Just got all 6 rods for free from 325e m20(thank you e30 buddies)

I'll hold on to them and see what happens with this thread. I'm all about experimenting :giggle:

What bottom end work did you do to your 1.6 to make it into a 1.7? just bore up?


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