Connecting rods
TECH Fanatic
Joined: Aug 2008
Posts: 1,740
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From: Nebraska
pretty much what he just said yes you can use 6" rods with the stock crank but you will have to have a different compression height on th episton to make up for the .3" difference of the rod........pretty simple stuff
i suggest you do some research before diving in too fast....
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12:1 is fine on 93, especially with a healthy cam.
You need pistons with a 1.250 Compression Distance for that rod stroke combo
Most aftermarket pistons are designed for use with a 3.50 inch crank with a 9" compression distance. Using them with a stock crank puts the piston at 8.990 which is totally fine. One just needs to keep this on mind to specify squish clearance, deck height, hg thickness, target compression, PTV clearance, etc.
You need pistons with a 1.250 Compression Distance for that rod stroke combo
Most aftermarket pistons are designed for use with a 3.50 inch crank with a 9" compression distance. Using them with a stock crank puts the piston at 8.990 which is totally fine. One just needs to keep this on mind to specify squish clearance, deck height, hg thickness, target compression, PTV clearance, etc.
12:1 is fine on 93, especially with a healthy cam.
You need pistons with a 1.250 Compression Distance for that rod stroke combo
Most aftermarket pistons are designed for use with a 3.50 inch crank with a 9" compression distance. Using them with a stock crank puts the piston at 8.990 which is totally fine. One just needs to keep this on mind to specify squish clearance, deck height, hg thickness, target compression, PTV clearance, etc.
You need pistons with a 1.250 Compression Distance for that rod stroke combo
Most aftermarket pistons are designed for use with a 3.50 inch crank with a 9" compression distance. Using them with a stock crank puts the piston at 8.990 which is totally fine. One just needs to keep this on mind to specify squish clearance, deck height, hg thickness, target compression, PTV clearance, etc.
I was just doing some research on this actually. According to the guys at Reher-Morrison, on an engine that lives under 9000 RPM there is NO gain. Above that there is something to be said about having a longer rod and it's inherent ability to keep the skirts happy due to less piston rock in the bore, but for a daily driver or a race engine that doesn't go over 9K rpm you won't see any gain. Infact they stress using whatever rod necessary to use your desired compression height and stroke. And these guys build 2500HP motors on a daily basis, so I'd trust them.
I was just doing some research on this actually. According to the guys at Reher-Morrison, on an engine that lives under 9000 RPM there is NO gain. Above that there is something to be said about having a longer rod and it's inherent ability to keep the skirts happy due to less piston rock in the bore, but for a daily driver or a race engine that doesn't go over 9K rpm you won't see any gain. Infact they stress using whatever rod necessary to use your desired compression height and stroke. And these guys build 2500HP motors on a daily basis, so I'd trust them.
heres a pic of the piston out of my 385 with a 6" rod........see how the pin is interfering with the oil ring.......creating the need for a support rail
on a 383+ it is worth the 6" rod for the exact reason stated above.....it makes the angle of the rod less, putting less wear on the cylinder walls and creating less heat and parasitic loss........
just run the 5.7 rod its ur best and easiest bet and there are more pistons avialiable as well off the shelf
yeah I've been doin some research about going 408 and spraying the crap out of it, but the idea is keep it under 7K to keep some sort of durability. The only problem is with durability comes price. Out of curiosity, what was the compression height on those pistons?
Sorry for the hijack
Sorry for the hijack
you can use stock as they have been proven to very good HP levels, or you can upgrade to an h-beam or a nice forged I-beam. Either way your cheapest route would be to reuse the stock if you can. Maybe have them install ARP rod bolts, and resize the big end accordingly, but that will add to the cost. It truly depends on your HP goals.
yeah I've been doin some research about going 408 and spraying the crap out of it, but the idea is keep it under 7K to keep some sort of durability. The only problem is with durability comes price. Out of curiosity, what was the compression height on those pistons?
Sorry for the hijack
Sorry for the hijack
great choice!!!!!!