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Discussion Starter · #1 ·
I'm picking up a used 383 this coming Fri & am planning a cam change in a few months once everything is driveable. I already have the new cam. I am concerned because this is a regular base circle grind. What's the minimum clearance I need between the camshaft & connecting rods ? Max rpm will be 7500. Thanks. Dave
 

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yep, .050 minimum clearance. Since your cam is already ground, I guess it's just a matter of installing and checking. I bought the Eagle h-beam 3D stroker rods for max clearance since I had already bought my cam too (which is on a 0.980" base circle). I didn't have to grind on anything, but I also have a baby cam that definitely wouldn't support your 7500rpm goals either..
 

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I agree. The best way to be sure is to check it and make sure. You may get lucky....you may not depending on the rods in there. It sounds as if your intending to measure anyways.....but I just wanted to throw that out there. And with plans for 7500 revs.....Id be checking a whole lot more than just this one area, cause the shortblock really has got to be durable to withstand those conditions. In other words, before checking clearance....make sure the current rods are even up for the task first....
 

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Discussion Starter · #6 ·
Thanks for all the advice. This motor will probably never see 7500 rpm but I wanted opinions on what I am up against. Probably more like 6500 to 6800. It has a L/W Scat crank & aftermarket rods w/Wiseco pistons. So I may get lucky on the cam to rod clearances. But I need some info on the parts in this thing & have some work to do. I've heard the engine run & was pleased. Thanks for taking the time to respond to my post. Dave
 

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Dave - Just because it is a 383 does not mean that it has to have a small base circle cam. That requirement is the result of the design of the connecting rods. Rods (typically I beam) designed for 3.75" stroke sbc motors can still use a standard base circle cam (which makes the cam a little stronger and less likely to twist). We have been using the same Summit Proline rods for 14 years in various 383 combinations with hydraulic, solid and roller lifter cams (all standard base circle) with no problems.
 

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Dave - Just because it is a 383 does not mean that it has to have a small base circle cam. That requirement is the result of the design of the connecting rods. Rods (typically I beam) designed for 3.75" stroke sbc motors can still use a standard base circle cam (which makes the cam a little stronger and less likely to twist). We have been using the same Summit Proline rods for 14 years in various 383 combinations with hydraulic, solid and roller lifter cams (all standard base circle) with no problems.

i though most rods if not all rods with capscrews will clear the cam loabs. its only some rod with through bolts and have problems
 

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Discussion Starter · #9 ·
Roger, thanks for your post. That makes me feel better. The cam I'm planning to install in a month or two is only .517"/.541" on the lift. Not real big but a good bit bigger than the one that's in there. I hope to pick up the engine tomorrow or maybe Sat. I've got to change the oil pan, so I'll probably take a peak this weekend & see what rods are in there. I think they have capscrews from what I'm hearing. At that time I'll probably stick a feeler gauge in there between the cam & rods and see what I have clearance wise with the little cam. I believe that I'm getting all the paperwork for the pieces in this engine. Maybe in a year some AFR 195 Eliminators and a real cam ! Thanks again to everyone that posted. Dave
 

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last one I built had about .020, that's fine for me. I don't see the cam or the crank moving around enough to interfere. If somebody changes the cam or re-degrees it they need to be checking. IIRC there's only two rods that are close, can't remember which ones though.
 

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You can use a plastic wire tie for checking clearances, they are alot easier than feeler gauges. This is what I used on my 496 for rod to block clearances etc. Mic the wire ties for thickness and use them.
Jeff
 

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DaveH: Lift or lack of it will not determine clearance between the cam and rods. Most cams are ground so the highest part of the lobe is about .020" under the camshaft bearing diameter. Extra lift comes from grinding the base circle smaller. That is the reason for checking pushrod length after installing a higher lift cam.

A small base circle cam has clearance added between the highest part of the cam and the camshaft bearing diameters. Generally speaking, cams are designed around the high part of the lobe being just slightly under the bearing journal diameter.

Not trying to be a know it all, just trying to be helpful with understanding how things are done and why.
 

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Discussion Starter · #13 ·
Tom, Jeff , & Kirk , thanks for the replies ! I welcome any & all suggestions/inputs as I probably know just enough to be dangerous. Been reading about these type of things for years, but have done very little hands on when it comes to building engines & checking the important issues. Thanks again. Dave
 

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i though most rods if not all rods with capscrews will clear the cam loabs. its only some rod with through bolts and have problems
The key is to be careful of any "all-inclusive" statements or claims (i.e., manufacturer X's rods will work, I beams will work, through bolts will not work...). Verify with the manufacturer before you buy the rods!
 

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There are many factors that determine cam/rod clearance. One rod may work fine in one block with cam "A" and hit big time with a different block with the same cam. Core shift plays a big factor.
Where the cam tunnel starts theres a flat pad. The bearing is supposed to be centered. If it is off center theres more off a chance you will have clearance problems.

Also the LSA and ICL will effect clearance, along with duration and lift.
 
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