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2.5l rods by larry mimbs
Started on: 12-19-2013 05:52 PM
Replies: 6 (186 views)
Last post by: trotterlg on 12-27-2013 01:25 AM
larry mimbs
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Report this Post12-19-2013 05:52 PM Click Here to See the Profile for larry mimbsClick Here to Email larry mimbsSend a Private Message to larry mimbsEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have seen numerous comments about the quality of the 2.5 l connecting rods. Who has actually had problems with the rods, and what were the problems? I am not a fan of the cast "armasteel" connecting rods, but Pontiac and Buick both used them in a lot of engines.
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KurtAKX
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Report this Post12-20-2013 12:36 AM Click Here to See the Profile for KurtAKXSend a Private Message to KurtAKXEdit/Delete MessageReply w/QuoteDirect Link to This Post
I've popped a few rods through 2.5 blocks. If you get a 1984-86 rod and a 1987-88 rod in hand and compare them. You'll see that they improved the beam, and the later rod directly interchanges to the early engine
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larry mimbs
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Report this Post12-20-2013 05:00 PM Click Here to See the Profile for larry mimbsClick Here to Email larry mimbsSend a Private Message to larry mimbsEdit/Delete MessageReply w/QuoteDirect Link to This Post
Could you tell exactly what failed on the rods that "popped thru the side of the block". Rod beam failure, bolt failure, bearing failure? Thanks.
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Report this Post12-24-2013 01:11 AM Click Here to See the Profile for KurtAKXSend a Private Message to KurtAKXEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by larry mimbs:

Could you tell exactly what failed on the rods that "popped thru the side of the block". Rod beam failure, bolt failure, bearing failure? Thanks.


Yes; something broke.

Seriously, there's not much left to go on when one of these lets go, but in the most recent one I believe a bolt let go. Consequently I now use ARP rod bolts and resize the big end of all my 2.5 rods.
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larry mimbs
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Report this Post12-24-2013 03:22 PM Click Here to See the Profile for larry mimbsClick Here to Email larry mimbsSend a Private Message to larry mimbsEdit/Delete MessageReply w/QuoteDirect Link to This Post
I believe these are the same rods used in the Pontiac 301 v8. Did they have problems with the rods? I'm not sure about horsepower, but they had a turbo version which would have loaded the rods pretty well. Is it possible that the low final drive gear (4.10) made over-revs more common?
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Report this Post12-26-2013 11:59 PM Click Here to See the Profile for KurtAKXSend a Private Message to KurtAKXEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by larry mimbs:

I believe these are the same rods used in the Pontiac 301 v8. Did they have problems with the rods? I'm not sure about horsepower, but they had a turbo version which would have loaded the rods pretty well. Is it possible that the low final drive gear (4.10) made over-revs more common?


You can hope, wish, conjecture, speculate, and second-guess all you want but the fact is and will remain that the stock rods are not a good choice for performance. The 301 turbo did not really "load" the rods, it only made something like 200 hp- figure the BMEP for that. Would a 4.10 car spend more time at revs- sure, bit plenty of 2.5s have been exploded while connected to 2.84 autos- ive done it.
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trotterlg
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Report this Post12-27-2013 01:25 AM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
When you blow up a rod it is very hard to tell which came first in the failures that happen (bolts, caps, rods, wrist pins, pistons). I think the old style were breaking in half at some point and punching a hole in the block and causing an oil fire. Not sure the new ones had less failures or just less exciting ones. Larry
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