im buildin a 383 stroker, but am wondering what the difference is between a 6" connecting rod and a 5.7". i notice now online that you can buy rotating assemblies that are for strokers and come with the 6" and 5.7" rods. is that true or are the 5.7" rods not going to make it a true "stroker".

im lookin at a scat 9000 with a 6" rod, and the scat technition on the phone said i have to make clearance for the rod by grinding away by the cam bearings, i already know i have to make clearance for the crankshaft.

thanks guys

 

i just found out that i can have my cam custom ground to make clearance for the rod. i phoned comp camps and had them do a custom grind.

 

It's the crank that makes something a "stroker", not the rod. Using a longer rod gives a very slight increase in piston dwell at the top of the stroke and reduced side loading on the cylinder walls. The benefits are minimal in street applications. What is a more important benefit in some applications is that the longer rod allows the counterweights on the crank to be larger to internally balance the rotating assembly without using exotic metals.

I think there was some miscommunication with Scat, there's no way you should be grinding on the "cam bearings".

 

No, that is not true.

STROKE makes a motor a "stroker".

In general, the longer the rods are, the better; up to a point. But there's only just so much space between the crank centerline and the bottom surface of the heads, and all that moving stuff has to fit in there, so the choice of parts to use, i.e. which way you balance all the compromises, is critical.

See this post for the numbers. I put them in there, almost all the way to the bottom.

A 383 is a 400 stroke and a 350 bore. Look back to the history of the 400, and you'll see that the factory used 5.565" rods, because if they used longer ones, the wrist pin would have had to be up higher; which would have hurt the ring sealing; which woudl cause warranty issues. So, to keep the "ideal" ring setup, they used the shorter rod. This incidentally is what made "external" balancing necesary in the 400: whereas in the smaller motors there's enough room between the crank centerline and the bottom of the pistons at BDC to fit a big enough counterweight in all the places that there needs to be one, there's NOT enough space there in the 400, because of the shorter rod.

A longer rod is "better" for 2 reasons. 1, the rod isn't at quite as much of an angle when the piston is exactly ½ way down; and 2, the piston moves slower at TDC and BDC (TDC is the more important one, but both create consequences), at the expense of moving faster at ½ travel. Reason #1 is mostly insignificant, since the difference between normal practical rod lengths in any given motor is only a degree or 2 of rod angularity. But reason #2 STRONGLY affects the way the engine runs: a higher rod-to-stroke ratio makes an engine more "thermally efficient", i.e. converts more of the combustion heat energy into work, and it also changes the interaction of the piston and the intake tract, particularly with respect to cam duration.

You don't "make clearance" by grinding on the cam bearings; you do it by grinding on the RODS to clear the CAM, and on the BLOCK to clear the RODS. The cam bearings aren't in the way of anything. On the other hand, if you buy the right rods, the shape of the rod where it would interfere, is already relieved as much as it can be; so you grind the BLOCK to clear them, and run a small base circle cam so the rods don't hit it (which you should do anyway, to minimize hacking on the rods). Rod length has very little to do with any of that. It's all about the shape of the big end.

 

thanks sofa, the cam im getting ground will have the smaller base circle, and i talked to a machine shop and they say that theres minimal grinding they have to do for rod clearance, and they are very experienced in stroker engines.

this is my first engine build ever, ive got some friends that have experience building motors, but none with experience on 383's and the books i have cant answer all my n00b questions. and its difficult to select the right parts when im in canada and the best parts are online and 1000's of miles away.

ill PM ya if i have any more questions.

EDIT: one question about pushrod length, what is the standard length? and what happens if i go longer (.100"), how does that change my valve lift? is there a website with a calculator like that that asks for pushrod length, rocker ratio and cam specs?

 

Standard length doesn't really matter, you only need to know what the correct length is for your engine. It's not something that can be calculated, it has to be measured. Using the wrong pushrod length at best loses you a small amount of lift, and at worst breaks valvetrain components.

 

Push rod length doesn't affect valve lift; except to the extent that it's so far wrong that it throws the geometry out of whack.

Like he said, there's no "calculation" for it. You put the motor together, get yourself an adjustable push rod, and find the ideal length.

I can just about 100% guarantee that with a small base circle cam, it won't be the "standard" length; it'll be longer.

 

Which rods depends on how you look at a motor. I run 6 inch rods. Does it make much of a difference? No, not much, not for a street motor. But if you're buying new rods anyway, get the longer rods to make your engine more efficient and gain some power. It also makes the engine more octane tolerant.