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Opeler
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21 Posts
Discussion Starter · #1 ·
Hi,

Following my previous topics, I'm still working on determining the "best" combo for my engine. I am on a budget here so no custom 800+ dollar pistons etc.

The ford 2.3 rods (132mm) are 2 mm shorter then the 2.4 rods (134mm)

Since I'm at this point not sure what the current CR is of my engine and I've heard numbers between 9.0:1 and 9.4:1, the result CR will be:
original 9.4:1 will become 8.0:1 (+/-)
original 9.0:1 will become 7.7:1 (+/-)

Since a 305 chevy piston has a compression height of 32.03mm versuz the 2.4's 31.5mm compression height, I can bump up the compression a little by not skimming the pistons which has to be done when using the original rods.
I've also been looking for a matching set of 2.3 pistons but they all have a compression height of 40.386mm which is way to high.

Now my only problem is the piston pin:
Chevy = .927" (23.5458 mm)
Ford = .912" (23.1648 mm)

Is it possible to enlarge the small end of the ford rod to allow the use of 305 pistons?

regards,
John
 

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Old Opeler
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5,564 Posts
0.5mm off

Looks better to use the original Opel 2.4 rods and remove 0.5mm from the top of the piston. When openning up pin holes keep in mind that the original "press fit" must be maintained - or with bushed rods it is imperative to see that the remaining bush is still thick enough .
The difference between 0.906" - 0.912" & 0.927" is not very much.

I got hold of a very nice set of 2.3 Pinto H-beam rods that are fitted with 283 Chevy 2.0" rod bearings.
 

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Opeler
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21 Posts
Discussion Starter · #3 ·
Sorry for not telling that I need a lower compression since I'm building a turbo charged engine. The ford/chevy combo seems to be a good solution to do that (price/quality).
Using forged ford rods and hyperautetic chevy pistons I think that my bottom-end is pretty strong.
 

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Opeler
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21 Posts
Discussion Starter · #4 · (Edited)
GTJim, it seems that the rod you're using is the same rod that I want to use.
- Did it fit to the crankshaft without narrowing the big end diameter using the chevy bearings?
- Which pistons did you use with these rods?
- Are you currently building a 2.4 engine?

The rods that I want to use are 5.205" conrods with a silicon bronze bushing for floating piston pins (0.912") for use with stock pins in aftermarket pistons.
For example this ebay auction: http://cgi.ebay.com/ebaymotors/ws/e...=compare&copagenum=1&coentrypage=search&fvi=1

Since I am not able to find a set of 2.3 pistons with a compression height around 31.5mm (1.24") I am looking at using the chevy 305 pistons but then I need the small end enlarged to .927 (0.015" or 0.381mm) and I don't know if that's possible. Somebody that can help please?
 

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Opeler
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21 Posts
Discussion Starter · #5 ·
I've contacted the ebay seller (AMS RACING) and it's $25.00 extra for the .927 pin hole :D

It seems that this is going to become my new combo. GTJIM, can you give me your thoughts on this?
 

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Old Opeler
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5,564 Posts
Blast!

.. never thought to ask them for rods with a bigger pin hole :eek:
Mine is a 2.2 litre motor and I am still messing about with pistons though I do have a set of 305 ones on hand that look like they can be machined on top to make the deck height correct as they have a dished top. I am going to get one piston right using the cast ones then order as set with .912" pins and the correct deck height. I will see if the pin holes can be taken out to .927" now thanks!
Just going to get the rod journals ground to Chevy small journal specs so I can use Chevy V8 rod bearings and do away with having to use the more expensive Opel ones - or make any changes to the rod width.
Got my rods from AMS Racing too.
 

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Super Moderator
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shockwave said:
Sorry for not telling that I need a lower compression since I'm building a turbo charged engine. The ford/chevy combo seems to be a good solution to do that (price/quality).
Using forged ford rods and hyperautetic chevy pistons I think that my bottom-end is pretty strong.
A small word of warning, hypereutectic pistons are generally stronger than cast pistons, but they are not tolerant of detonation. With a turbo you are of course aware this is possible during tuning to have some detonation present.

Also, the top ring is VERY close to the top of the piston on a 305 Chevy. So the ring will be subject to very high heat (again a problem with turbos). Most special turbo pistons have had the top ring moved substantially down the side of the piston to protect the ring from combustion temperatures.
 

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Opeler
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21 Posts
Discussion Starter · #8 ·
RallyeBob, I understand your concern and know that there is a risk that I "destroy" my pistons with detonation and/or the high heat on the top ring. But I am on a budget.. I mean, I can spend more on pistons but I don't want to spend 1000+ dollar on a set of pistons right now... If I can find a more suitable set for my engine I would like to use that, but right now I haven't found another combo.
 

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Opeler
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Discussion Starter · #9 ·
With an even shorter rod I might be able to use for example ford 2.3 pistons but with the 5.205 rods that's not an option since the CR will become to high.
 

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shockwave said:
RallyeBob, I understand your concern and know that there is a risk that I "destroy" my pistons with detonation and/or the high heat on the top ring.
I understand that you have a budget, but it will cost more if you need to rebuild it twice! Hypereutectic pistons will damage easier than even standard cast pistons if they are subjected to detonation, that is all I was saying.

Have you looked for some forged Chevy 305 pistons? I bought some for my own engine some years ago, I think they were made by Sealed Power or TRW, and were very cheap, about $40 US each.
 
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