Thread: highest compression ratio on stock rods

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What is the highest compression you can go on stock rods? Just curious. If you *must* know, I'm thinking turning a 305 (cuz I got it) into an ethanol only (or e85) burner. I've got it in my truck and just need to get the pennies together to build the 355. This isn't a question of whether e-85 is a good idea or not, this is just for a possible low buck project to see if I can do it or not. I'll probably ending up making my own alcohol fuel for it. I'm thinking 12-13:1 compression and getting what else I need with ignition timing. Would cast iron heads be ok or would I have to coat them. What carbs would be good to use? I see edelbrock is making a new e-85 carb but with the budget in mind i may hit the swap meet for a used carb that could work. Thanks guys!

I am not 100 percent shure ,but I think most rods fail from the exspansion of the metal ,not the compression.Meaning that they break when pulling the piston down fron top dead center at high rpm ,with a heavy piston.
Usually leaving the piston in the bore and letting the rod beat holes in the block.
I have read that most rods fail because of rpm induced stress from the weight of the piston.Soo to sum it up ,I have no idea how much compression a stock rod will take

im thinking 12 or 13-1 will be too much. about the time you lace into it a few times you'll be mopping up a huge mess. and i think i read you have a 305 and want to make it a 355, that will require a 350 block @ .030 over bore. not even sure they make a 13-1 piston for a 305, and stock oem heads will not be a good choice for that compression. it would run but be very very restricted. probably would hurt the motor eventually also.

You can run up to 12:1 compression on stock rods as long as you use better rod bolts like ARP or other comparable pieces. GM ran 11.25:1 compression on '64-65 327 Corvettes than redlined at 6500 rpm.

If you want to run stock rods, look for a "B" stamp or an "X" stamp on the rod cap. "O" or no mark at all have less nickel in them. Take the time to remove forge flashing off the beams. "Beaming the Rods" is what this commonly referred to. If you wish to go a few bucks more, have them shot peened before reconditioning. This will had some extra strength and I feel you'll be happier. It also takes the sheen off of them. Shiney rods collect more heat than dull ones. Definitely run a good bolt like ARP.

Originally Posted by BigRedTrucker

What is the highest compression you can go on stock rods? Just curious. If you *must* know, I'm thinking turning a 305 (cuz I got it) into an ethanol only (or e85) burner. I've got it in my truck and just need to get the pennies together to build the 355. This isn't a question of whether e-85 is a good idea or not, this is just for a possible low buck project to see if I can do it or not. I'll probably ending up making my own alcohol fuel for it. I'm thinking 12-13:1 compression and getting what else I need with ignition timing. Would cast iron heads be ok or would I have to coat them. What carbs would be good to use? I see edelbrock is making a new e-85 carb but with the budget in mind i may hit the swap meet for a used carb that could work. Thanks guys!

I would not even fart around with stock rods.
By the time you re-size the big hole,small hole,polish,shoot-peen-yes-you have to after you polish the beams,install ARP bolts etc.
I wold look into a set of the Scat I-beams.
We have run these on 1/2 mile stock car engines that turn 7,000 rpm's with zero failures.
If you look you should be able to buy these for less than $200.
Oh,if you are making your own alcohol the ATF might come knocking on your door.
One other thing to remember alcohol is very dry and you must always run upper-end cylinder lube with it.
Also you need to run your valve guides looser at least on the exhaust side.

Eric makes a good point. If you are going to spend a lot of money on stock rods, you would be better off with a set of aftermarket I-beams from Eagle or SCAT. You would be money ahead and have superior parts.

Originally Posted by erik erikson

I would not even fart around with stock rods.
By the time you re-size the big hole,small hole,polish,shoot-peen-yes-you have to after you polish the beams,install ARP bolts etc.
I wold look into a set of the Scat I-beams.
We have run these on 1/2 mile stock car engines that turn 7,000 rpm's with zero failures.
If you look you should be able to buy these for less than $200.
Oh,if you are making your own alcohol the ATF might come knocking on your door.
One other thing to remember alcohol is very dry and you must always run upper-end cylinder lube with it.
Also you need to run your valve guides looser at least on the exhaust side.

Hmm. If I plan on doing it the own alcohol, I may get the license and whatnot. I was kind of making this a cheap project, but few things pan out that way .

i think i read you have a 305 and want to make it a 355, that will require a 350 block @ .030 over bore. not even sure they make a 13-1 piston for a 305, and stock oem heads will not be a good choice for that compression. it would run but be very very restricted. probably would hurt the motor eventually also.

Noooooo. LOL. I have a 305 that I plan to pull out after I build a 350 for it (I've got the block and other stuff). The reason to go with a 305, is cuz I've got it and it wouldn't put a whole lot of power out of it. I could get some of the compression from milling, something to look it once I eventually get the engine out and mic'ed.

Thanks guys for the responses!

BRT....everybody on this post that replied has your best interest at heart. The comment from Erik made me laugh pretty hard. Can you imagine the "Revenuers" blowing down your door? Thanks Erik, that was a visual image that made my day. My reply was meant to help you if you have your own rods, what to look for in a good rod and if you have the belt sander or access to one, you can beam them yourself. Nothing like learning how to do it. You should always have a reputable shop recon the rods when prepped. If you have questions of how to do it without hassle or fear, too many articles on the web and in the newstand rags to help you know when to start, when to finish, and when you have a good piece. Costs nothing but time and keeps your budget for the next build available. Everybody has budget built a motor to keep a good ride under their feet and it can be done affordably. Look for a good rod if you don't already have them and play a bit, it's fun and great therapy. It's not like you're asking for the moon, just a good unit to work with your idea. Thanks Erik, now I can't get that image out of my mind.....

Originally Posted by BigRedTrucker

Hmm. If I plan on doing it the own alcohol, I may get the license and whatnot. I was kind of making this a cheap project, but few things pan out that way .




Noooooo. LOL. I have a 305 that I plan to pull out after I build a 350 for it (I've got the block and other stuff). The reason to go with a 305, is cuz I've got it and it wouldn't put a whole lot of power out of it. I could get some of the compression from milling, something to look it once I eventually get the engine out and mic'ed.

Thanks guys for the responses!

Don't forget you will need a different carb. or you will have to do heavy mods. on the one you have now to make it work right.