Cobra jet rods
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Postmaster
Joined: Oct 2005
Posts: 3,083
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From: Victoria , BC
Cobra jet rods
So I'm looking into some cobra jet rods and I got a question on rod bolt strengths. Would a stock bigger bolt cj rod outlast a standard size but with ARP bolt rod? Or is the cj bigger rod bolts still a weakness due to age and quality? I'm debating on getting some cj rods but I have a set of standrad c3 390 rods in the shop that I'm thinking of putting ARP rod bolts on but they have to be resized as well for an additional cost of 175$. Is it worth it I really dont want a rod to fail cuase I went the wrong route. Also is a cj rod with ARP bolts much more of an advantge over my 390 ones with ARP's.
Basically the other thing is are the rod bolts a real issue in FE's????
Thanks guys...
Basically the other thing is are the rod bolts a real issue in FE's????
Thanks guys...
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
Likes: 423
From: Long Island USA
It has been said that the standard-sized ARP rod bolt is stronger than the larger CJ rod bolt, AND the hole being bigger in the CJ rod actually WEAKENS the big end of the rod.
What RPM are you going to be running, and are you going nitrous, or anything else that would require an incredibly strong rod?
What RPM are you going to be running, and are you going nitrous, or anything else that would require an incredibly strong rod?
Tuned
Joined: Mar 2009
Posts: 360
Likes: 3
From: Napa
The Police Interceptor/ Cobra Jet rod with good bolts is a nice improvement for a mild engine, and came in the '61 375 and 401 hp 390 solid lifter engine, all the 406's, 427 Low Riser and High Riser, various PI engines, and the 428 Cobra Jet. They're fairly light and quite strong, the only one I've ever seen or heard about failing was in a CJ that the oil pump drive failed and the rod melted in half- both sides still bolted together
And you can usually find a decent set for less than $200
And you can usually find a decent set for less than $200
Thread Starter
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Postmaster
Joined: Oct 2005
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From: Victoria , BC
i'm trying to keep it reasonable. Machine shop wants 180$ for resizing and arp bolts are close to 100$ Almost getting into those fancy after market H beam ones for that price. Thats almost the way I'd go for another 100$
Buying used I'd almost certain have to resize them or it seems my shop always seems to find something else I'm not expecting!!!....
Buying used I'd almost certain have to resize them or it seems my shop always seems to find something else I'm not expecting!!!....
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Postmaster
Joined: Oct 2005
Posts: 3,083
Likes: 4
From: Victoria , BC
On another note I'm looking to get 420 hp and 550 lbs of tq.
Build is a .030 428 with trw 10.5:1 forged pistons,edelbrock rpm intake,770 holley truck avenger,headers, crane cam electronic igniton,comp cam 33-248-4 and d2teaa heads with fesh stainles cj valves and the matching cam springs..
Are my power #'s realistic? and how important are the rods with these upgrades? thanks....
Build is a .030 428 with trw 10.5:1 forged pistons,edelbrock rpm intake,770 holley truck avenger,headers, crane cam electronic igniton,comp cam 33-248-4 and d2teaa heads with fesh stainles cj valves and the matching cam springs..
Are my power #'s realistic? and how important are the rods with these upgrades? thanks....
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More Turbo
Joined: Nov 2007
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From: Western Washington
I think I read somewhere too since CJ rods are heavier that the motor has to work harder to turn the rotating assembly...any truth to it?
OJ
OJ
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FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
I'd check the big end and see if they even NEED to be resized. When I did my 390 (twice) I checked, and had my machinist check, the big ends of at least 5 sets of rods of high mileage motors that were still running without knocking, and they were all perfectly fine.
The small (bushing) end, well, that's another story.
The small (bushing) end, well, that's another story.
Posting Guru
Joined: Jul 2003
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Stock 390 or cj rods will be fine for your mild build. When you use 40 plus year old rods, you are wise to use new rod bolts, and have the rods magnafluxed for any cracks and checked both large and small ends. Also have the machine shop check for the proper clearance for your piston pins. Most piston pin rod bushings need to be reamed for the proper clearance. Do it right the first time, and you will have years of happy motoring.
