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3/8 or 7/16 rod bolts #1674762 09/21/14 03:50 AM 09/21/14 03:50 AM
Joined: May 2014 Posts: 108 Socal L littleVAL OP member
littleVAL OP member L Joined: May 2014 Posts: 108 Socal	I am looking into getting some new rods (small block) and noticed that they are basically the same cost to get 3/8 bolts or 7/16 bolts but it adds almost 150 grams. 503 to 645 grams. So what would you do. I am leaning toward the larger bolts for the strength. I am thinking that it might be harder to balance or even hurt acceleration with the added weight of the rod and balance on the crank. It is basically 5 ounces per rod and probably and equal amount in the crank. So 40 ounces in rods and maybe the same in the crank for balance. Is that about 5 pound out of the crank by going with the smaller bolts. Let me know what you think is my math even correct.

Re: 3/8 or 7/16 rod bolts [Re: littleVAL] #1674763 09/21/14 05:33 AM 09/21/14 05:33 AM
Joined: Jul 2009 Posts: 413 Norway (old world) Oyvind Mopar mopar
Oyvind Mopar mopar Joined: Jul 2009 Posts: 413 Norway (old world)	I would say it depends on the weight of the pistons and your rpms. Heavy pistons need bigger rod bolts. If you go with the Nascar lightweight pistons you can use the smaller rod bolts, as they do in Nascar. Depends on what rod you are talking about, you cannot really compare an Eagle 3/8" SIR to a Carrillo. The rod stretching force increases with the square of the rpms....and are proportional with the weight; thus strength is better than low weight; generally speaking.

Re: 3/8 or 7/16 rod bolts [Re: littleVAL] #1674764 09/21/14 10:32 AM 09/21/14 10:32 AM
Joined: Aug 2003 Posts: 1,314 Charlotte, NC L LSP pro stock
LSP pro stock L Joined: Aug 2003 Posts: 1,314 Charlotte, NC	Much more application info needed.

Re: 3/8 or 7/16 rod bolts [Re: LSP] #1674765 09/21/14 12:15 PM 09/21/14 12:15 PM
Joined: May 2014 Posts: 108 Socal L littleVAL OP member
littleVAL OP member L Joined: May 2014 Posts: 108 Socal	I am trying to get my car on the road again finally after years of sitting. The problem is I would prefer to build a 4.250 stroke and a 4.185 bore motor so need siamese r3 block to do it. I have an R block that needs all the machining etc. So in the interim I would like to use a 74 360 block that I have and build it cheap found a k1 crank and rods for 750 have an old roller and lifters just need pistons and machining. So it will probably have a heavier cheaper piston. In the future I want to sell R block and buy R3.

Re: 3/8 or 7/16 rod bolts [Re: littleVAL] #1674766 09/21/14 12:44 PM 09/21/14 12:44 PM
Joined: Jun 2003 Posts: 52,972 Romeo MI MR_P_BODY Master
MR_P_BODY Master Joined: Jun 2003 Posts: 52,972 Romeo MI	Quote: I am looking into getting some new rods (small block) and noticed that they are basically the same cost to get 3/8 bolts or 7/16 bolts but it adds almost 150 grams. 503 to 645 grams. So what would you do. I am leaning toward the larger bolts for the strength. I am thinking that it might be harder to balance or even hurt acceleration with the added weight of the rod and balance on the crank. It is basically 5 ounces per rod and probably and equal amount in the crank. So 40 ounces in rods and maybe the same in the crank for balance. Is that about 5 pound out of the crank by going with the smaller bolts. Let me know what you think is my math even correct. The crank was designed for a base bob weight(what ever that number is) and in the rough balance is set for that.. so is it even close to the bob weight of the 3/8 version or close to the 7/16 version.. but I dont think you will have a issue with either but it might take turning the weights diameter down or it might need weight.. I dont know but the pistons and pins and rings makes a difference also... I went with 7/16 bolts on all of my junk

Re: 3/8 or 7/16 rod bolts [Re: MR_P_BODY] #1674767 09/21/14 01:21 PM 09/21/14 01:21 PM
Joined: Nov 2009 Posts: 3,082 St. Paul , Mn. tubtar master
tubtar master Joined: Nov 2009 Posts: 3,082 St. Paul , Mn.	Buy the best rod bolts you can afford......not my advice , but it makes sense. You will sacrifice some strength with a 3/8" vs. a 7/16" assuming the same material is used in both. Competition Products lists a bunch of Howard's Limited h.p. / light weight steel rods that typically use the smaller bolts and will hold up to a healthy h.p. number. They are pretty popular for roundy round deals that are limited by rules to certain heads or carbs , and are recommended up to 550 horses. But a 3/8th " bolt of unobtanium is much stronger than a 3/8th" out of 8740.

Re: 3/8 or 7/16 rod bolts [Re: tubtar] #1674768 09/22/14 07:46 PM 09/22/14 07:46 PM
Joined: Jan 2003 Posts: 16,376 D dogdays I Live Here
dogdays I Live Here D Joined: Jan 2003 Posts: 16,376	If you're building a 4.25" stroke engine I say go to the 7/16" bolts, that's what I'd want to see on a bigblock with a 4.25" stroke. Then use the lightest pistons you can find. I don't see where you are finding a 503 gram rod that uses the 2.125" rod journal. Most rods for a stock or 2.100" journal come in at around 600 grams. But for that I think you can find a 2.100" journal rod at 6.125 that uses a 7/16" bolt. For example, Scat. R.

Re: 3/8 or 7/16 rod bolts [Re: dogdays] #1674769 09/23/14 12:01 AM 09/23/14 12:01 AM
Joined: May 2014 Posts: 108 Socal L littleVAL OP member
littleVAL OP member L Joined: May 2014 Posts: 108 Socal	Well I just found out about the new JE SRP pro pistons. So will go with a longer rod that works with an off the shelf chevy piston. It is only 416 grams. They only had one size for that length rod 3/8. Last edited by littleVAL; 09/23/14 08:41 PM.

Re: 3/8 or 7/16 rod bolts [Re: littleVAL] #1674770 09/23/14 08:40 PM 09/23/14 08:40 PM
Joined: May 2014 Posts: 108 Socal L littleVAL OP member
littleVAL OP member L Joined: May 2014 Posts: 108 Socal	Well ordered 4inch crank w/2.100 rod journals for the 360 block. Still cannot believe it was only $500 to my door. While the deals are still there getting the 6.25 rods w/ 3/8 bolts but thought I will upgrade arp2000 bolts to L19

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