hi all, i'm gathering the parts to stroke a chevy sb 327 to 383 and trying to decide between 5.7" and 6" rod lengths. aside from all the other considerations i've run across a few references that seem to say that the longer rod would require more metal removal to clear the block than the shorter rod. if there is a difference is it significant, say, on the order of 010" or more? i'm having trouble visualizing how this would work. it seems like the difference in arc wouldn't be that much. but every little bit would help. thanks.
It has more to do with the type of rod you use . An aftermarket rod with cap screws instead of bolts offers way more clearance, especially at the cam.
You won't truly know until you have a rod on a journal in the mock up stage. The type of rod you use makes a big difference as some have a physically larger big end. -Abone.
the block is a small journal '67 657 block. my understanding is that these blocks were cast to accommodate both journal sizes and come with some additional clearance cast in from the foundry to clear 350 rods. so far the plan is to use 6" **** pro series I-beam rods which fwiw are advertise as "stroker" rods and do come with cap screws. i guess i was just hoping, all else being equal, a shorter rod might give a little more clearance. thanks guys.
Friend of mine did a 383 SJ Can’t recall him mentioning rod clearance issues but might could ask. Don’t know the rods used.
Small journal mains are 2.30 lg journal are 2.45 . I have never tried it with an early block but it seems to me it would be a whole lot easier to start with a 350 block.
I understand finding all the parts and pulling it together. If you don't already have most of the parts - really look at the cost of a balanced ***embly from aftermarket, compared to pulling one together. Machining and balancing costs can be significant on a mismatched ***embly. Even if you do piece it together, work with your balancing guy on piston weight. I'd stick with 5.7 rod, pistons are priced better, and have a better compression height for stable ring lands. There's so much info out there on rod length and dyno testing showing it doesn't make enough difference at the power levels we're running. Read thru this, lots of opinions on both sides. https://www.speed-talk.com/forum/viewtopic.php?t=18625 Rod clearance issues are typically at pan rail, bottom of cylinder wall, and in cam / tunnel area. When you get into 415 - 434 strokers they sometimes require small base circle cams. Put the 6" rod money towards better heads and valvetrain. Aftermarket rotating ***emblies will offer rods that clear the block significantly better If ya wanna get wild - I have a 4" stroke Cola crank, been on the shelf for years, needs the rear thrust surface welded up.
You didn't mention if the intended use was street or strip. If a street engine, here is another consideration. I have built several 406s for street use and spent time debating with myself the 5.7" or 6" rod choice. In the case of the 406, the 6" rod put the wrist pin up into the oil ring groove requiring a bridge. The 5.7" rod did not. So I decided to go with the 5.7" for simplicity as the performance difference really didn't matter for the application. On many combinations you will need a bridge in either senerio. This is not to imply that there are big issues related to them. I just prefer not to in a street engine if I have a choice.
LOL I am one of very few that I know that would run aluminum rods on the street. On a 383 normally cam clearance is not an issue and the cam clearance issue would not be with the rods it is with the crank throws. The rod clearance is going to be in the actual crank case, and you will just need to mock it up and spin it. The bottom of the cylinder and the pan rail is where your clearance problems will occur and it is just a matter of mockup and checking clearance. here is something that separates a builder from an amature. A builder may ***emble and dis***emble more than once to make sure that all the clearances are proper. You cannot ***emble an engine with a calculator and a picture. There is too much difference in manufactured components.
Been a million of them built. I'm going to repost an old article on rods so it may make selection easier. I'd reccomend the longer rod and something with cap screws from the bottom. Look for ones that have shoulder clearance rather than a bolt head sticking up to hit the cam.Also, consider weight. Its false economy to buy a heavier piston and rod and then spend far more money getting mallory weight to counter balance it. This is an old article and there may be newer stuff, but when you buy based on initially cheaper costs, it often costs more later on.
lumpy, you're right and you're not the first person to tell me that i'm nutz. if i had any sense i'd get a crate motor and be done with it for a lot less money. for some reason i've got it in my head to try and maintain the look of the 327's with the sealed valve covers, oil fill tube with the pcv valve and the breather at the back of the block. indy, just got through talking to my machinist and he said basically the same thing you did about the shorter rods. the reason i mentioned the **** rods is because they're part of a rotating ***embly i'm looking at. like you say, it comes balanced and machined with matched parts. jmountain, this will be a very mild build for a car that mainly goes to shows, club meets and the occasional cruise. the 327 in it now has been there since 1968 and is getting kind of tired though it still runs well and doesn't smoke or use oil. since i want to rebuild anyway i thought a stroker would be fun and give it a little more kick in the a$$. budget, here's a long thread about these blocks that will give a lot more info than i can. all this brings me back to my original question, can i expect to see a significant difference in clearance between the 5.7" and the 6" rods. thanks for all the input guys. https://www.corvetteforum.com/forum...3892657-block-a-small-journal-or-large-2.html lots of good stuff here and i'm sure elsewhere. http://www.camaros.org/index.shtml
I have a 383 with 6” rods in my ‘40 with years of dependable street/strip use. I used the **** 7/16 cap screw rods and they cleared fine. The oil ring in the wrist pin hole hasn’t been a problem. (On mine anyways). There are a couple cam lobes that are close but no additional clearancing was needed. I used a big zip tie for a go/no-go gauge when I built mine. I prefer the 6” rod but either will work fine. I would though as others have said just use a large journal block rather than the 327 block. You used to be able to buy factory roller blocks machined and ready to go from summit with all the stroker clearances already done. I’ve used them and they were actually pretty darn good.
As said above, a grinder will fix any clearance issues. Just don't get carried away and hit water. https://k1technologies.com/blog/how-to-clearance-your-block-for-a-stroker-crankshaft
I see now, but what is being said is a small journal crank and caps can be bored to a large journal. Ya had me scratching my head for a bit
Considering you can usually get a good SBC 350 block core by asking nicely, I don't understand why one would want to undertake the extra work to make a large journal block out of a small journal 327. I was just at an auction this past weekend where 4 bolt main 350 blocks were selling for $5. There is also a ton of good info in that article on rods. If the info there is above your pay-grade, there's no shame in that. But then it's all the more reason to buy a complete stroker rotating ***embly from a company like Eagle or **** since the homework has already been done for you, instead of trying to piecemeal the whole thing together, hoping it will work as good as the setup you could have bought for marginally more money that is already engineered to fit together.
joe, i agree, not only are 350 blocks cheap but i could probably buy a nice crate motor cheaper than i could build it. problem is, i'm trying to maintain the stock look of the 327 with the oil fill tube/pcv valve, the vent tube at the back of the block and most importantly, the sealed valve covers. and yes, i know this is crazy. this whole thread started because **** was putting together a rotating ***embly for me and asked me if i wanted 5.7" or 6" rods and i realized i hadn't though about it. for my application there doesn't seem to be any serious reason to choose between the two other than one might give me a little more clearance between the rod and the block. that's what i'm trying to find out.
You're right, if the road draft tube provision is that important to you, then yes, I understand what you're saying. You know, you can run smooth valve covers without a road draft tube provision in the block though.
joe, the plan is to put this build in an mostly original '67 corvette and it needs to retain the stock appearance.
If the main saddles and caps are machined as your reference link you posted, the only additional cost to used a large journal crank would be the line bore. Which might be a good idea on a 50+ year old block anyways when stroking it. Plus side vs align boring a large journal block is you can still run a standard timing chain set with a small journal block. When a shop does a align bore/ etc, they remove some material from the caps or mains (as I understand it) the offset the bore to make it right. But seems you won’t have to have that done (offset).
I wouldn't make any big decisions on the block one way or the other until you have a crank and rod in there mocked up. Even if you start with a stock stroke crank and stock rod, you can see where the pan rail and cylinder base clearance is now and make some fairly solid decisions based on current vs. future clearance. My 422W Ferd needed a fair bit of grinding on both the cylinder base and the pan rail to get .050" of clearance, but I did get away with cam clearance. YMMV.
Gotcha. We're all working within our own constraints one way or another. In that context, the extra work involved in machining a small journal block into a large journal block makes sense. For those of us here, like myself, that are building custom cars or hot rods without a consideration as to whether it looks factory or not, a different decision could be had.
thanks guys, at this point everything relies on the rod selection. can't order the rotating ***embly until i decide on the rod length. and of course those parts will have to back ordered for 6 weeks and my local machine shop is also 6 weeks behind. so i'm potentially 3 months away from finding out what kind of clearance the block is going to need.
The Jalopy Journal
