What do you think is best 6 or 5.7 inch.
I was going to use a forged internal balance crank, forged H beam rods and forged pistons. also I was going to use nitrous oxide and turn the engine 6500-7000 at the most.
Do I want the shorter (5.7'') rod with the speed pro light weight dish pistons or the longer (6'') rod and shorter piston?
I was going to use Mantley or eagle rods and I'm not sure what pistons I'm going to use with the 6'' rods if I use them.

 

Truly trivial difference at our level. That said, for nitrous or forced induction I prefer the shorter rod due to better support for the rings (assuming the piston is designed correctly) and faster acceleration away from TDC (may lower peak cylinder pressure a bit). For any really high revving motor, the longer rod+psiton combinaiton has the potnetial to be lighter, so I prefer it in that setting.

But the differences for something that is not an absolute max effort motor are small. Don't sweat it.

Rich Krause

 

From what I hear, negligible differences. I've been told my 6" H beams will provide a tad more torque because there's longer dwell time at top dead center as the rod traverses the ascending/descending phase of the crank cycle. That makes sense to me but as mentioned, I just don't know if the street racer that's not looking for the last bit of oomph to edge out the car beside him can justify the cost.

That said... it's interesting to note that the LS1's GM builds didn't stay with the 5.7" rod length, but instead went to a 6.1" length..

Taken from an LS1 technical site:
<quote>Rod length is 6.1 in., .400-in more than the LT1/4 rod. The extra rod length reduces rod angularity and piston speed which decreases friction and noise and increases durability. LS1 rods have no balance pads making for less overall mass and allowing the engine to rev quicker. Undoubtedly you're asking, "Hey, wadaya mean 'no balance pads.'? How do they balance the rods, then?"

Well, they don't.</quote>

 

I went with the 6" h-beam rod...From what I've been readin', go with the bigger one.

 

I went for the compromise solution.....5.85 rods

 

You are one of a dying breed, a moderate

Rich Krause

 

5.7 and 6" rods can also affect the Dynamic Compression Ratio a bit... not much. Longer rods drop the DCR 0.03 and short rods raise is 0.03 (relative to displacement, cam selection, yada yada...) but you get the idea.

 

Yup 5.85 here. I did it to bring the ring lands down...A turbo car. If I did a N/a (nitrous)motor I would have gone 6"

 

Lingenfelter also went with 5.85s too. FYI. Good point about the ring lands for blown/turbo applications.

 

Nitrous motors benifit from lower ring lands also....thats why I used the 5.85 . NA only I would 6" for sure.

 

If the pistons are designed to work with a 5.7" rod would using the 5.85's be better or should I just stick with the 5.7's. I plan on using the JE/SRP -31 and it said it was for a 3.75" stroke and 5.7" rods. Would I benifit any by increasing rod length to 5.85"?

 

You can't use these pistons with a 3.875" rode. The crown of the piston would be 5.85"-5.75" = 0.10" to far up the piston bore. Actually, it would be sticking up over the deck surface of the block.

The relevant dimensions are the deck height of the block (distance from the crankshaft centerline to the deck surface of the block) and the compression height of the piston (distance from the center of the pin bore to the flat part of the piston crown) along with the stroke and rod length.

stroke/2+rod length+compression height = deck height of the block (for a "zero deck" setup)

Rich Krause

 

Rich,

I understand, that a 3.875 stroke crank would throw things off, I was asking about a 383 w/3.75" stroke and if there is any advantage with using the 5.85" rods over the 5.7's recomended by the piston manufacturer.

Above people said they used a 5.85" to bring the ring lands down for a forced induction setup. I was just wondering if these pistons with a 5.7" rod have the best posible ring lands or if the 5.85" rods would provide a better/more reliable setup.

I also understand they were comparing 5.85's to 6.0 when they said bringing them down but would raising them on this setup be of any benifit?

 

From what I understand, when you buy the pistons, the rod length has to be known beforehand. How else will they know where to position the wristpin? My motor came with stock 5.7 rods. During my rebuild, I installed some 6" H beams. I couldn't just take a stock piston and put it on the 6" rods because the crown of the piston would protrude from the top of the block by .30 inches right? So if you bought your 383 pistons for a 5.7 rod, you can't just decide to instead buy 5.85 rods and chuck those pistons designed for 5.7 rods on there and expect everything to work correctly. The way your posts read, that's what it appears you're asking. I hope you just mean, "Should I order 5.85 rods and the 383 pistons that are commensurate with those rods?".
Just trying to be clear. A friend of mine is building a 383 LT1 so I'm very interested in this thread.
Thanks,
Dave
BTW- Old best time with prior cam(cc224/236) & home ported heads was 11.1 @ 121 mph

 

Dave,
You are correct, I was asking the first thing, and the second. I knew that a 5.7" is what was recomended but wasn't sure if it was just a recomendation or a requirement. I am new to this and this post got me thinking about the setup I am preparing. I planed on just running the "off the shelf" pistons and using the 3.75" stroke crank and 5.7" rods.

But after reading the stuff above about people liking the 5.85's better for forced induction I was just asking was it is better to run the recommended 5.7's and the "off the shelf pistons", or should I go with the 5.85's and possibly use the same pistons or get customs. Nothing has been ordered yet, I am still in the planning stage.

I was just trying to get the best setup for my build and I was just trying to see what people suggested, sorry for the confusion.