zooguy

iTrader: (1)

so this is kinda stupid, but what is the difference of a stock 350ci and a 355 ci

what makes a motor a 355 exactly?

i know a 383 is longer rods and a different crank and pistons and more.

but i have no clue on a 355. and when my motor pops i want to have most the stuff to build a 355 for a small shot of juice (200 or less)

97pontta

iTrader: (10)

A .030 over bore (4.030) on the stock stroke makes 355ci.

zooguy

iTrader: (1)

cool thanks

RamAir95TA

iTrader: (2)

A 383 doesn't necessarily have longer rods - you can have a 383 with 5.7" (stock length) rods.

zooguy

iTrader: (1)

how... massive pistons and a different crank?

quik95lt1

iTrader: (7)

gonna drop some simple knowledge real quik................

ok a 383 can be made a few ways but heres the most common.........

crankshaft......a 3.75" stroke vs the stock 3.48" stroke (so your piston is gaining an extra .27" of stroke but its all gained at the bottom of the cylinder wall because we obviously cant stick the piston .25 inches up into the chamber lol

rods. .......a 6" rod is the most common but i can be done with a 5.7" rod...........and heres how........picture having the piston at Top dead center in the bore with a stock 3.48" stroke crank and a stock 5.7" rod.........now put a 3.75" crank with the stock 5.7" rod and leave the piston in the same spot at the top of the cylidner..........what has to happen?? the point where the rod mounts in the piston moves up .27"......so when the piston comes down to BDC it is now .27" lower than before but its in the same positoin when its all the way up........follow?

now a 5.7" rod has its advantages and disadvantages in a 383......
Pro's
5.7" rod is lighter vs a comparable 6" rod because its obviously just smaller
Your piston pin mounting point doesnt wind up in your oil ring groove so it effectivly is a stornger piston in the long run (99% of the time)
Con's
5.7 rod because of its low mounting point in the piston puts alot of strain on the cylinder walls and piston skirts because now when it is that .27" lower the angle on the rod is very aggressive at the bottom of the stroke.......

with a 6" rod they are much easier on the cylidner walls and pistons......but they do tend to get up into the oil ring landing which in 90% of cases is no issue.......


hope that helps


oh and btw to answer your original question is a 355 is simple.........stock stroke 3.48".......with a .030 over bore which is the most common to a rebuild.....4.030 pistons are widely avaliable in large variety of choices.......basically the extra .030" bore x8 gives you around a 5 c.i. gain..........pretty neglegable power wise.....

97 6speed z

Quik95lt1, you got it 90% right in the above post, but ......... why don't we go for 100% right, okay.

1) The "point where the rod mounts to the piston" does NOTmove up by .27" it moves up by .300", (the actual difference between the 5.7" rod length and the 6.0" rod length). To better understand this keep in mind that for a zero decked LT1 block at 9.000", the total of one half (1/2) the stroke plus the rod length plus the piston compression height must equal that 9.000".

For the 5.7" rod 3.750" stroke we have: 5.700" + 1.875" + 1.425" = 9.000"
For the 6.0" rod 3.750" stroke we have: 6.000" + 1.875" + 1.125" = 9.000"
Now if you subtract the 1.425" CH from the 1.125" CH ...... you will see that the change in "attachment point", (i.e. compression height of the piston), actually moves up by .300" and NOT .27". And finally ...........

2) The angle on those shorter 5.7 inch rods is NOT very aggressive at the BOTTOM of the stroke! At the bottom of the stroke the connecting rod centerline is co-incident with the cylinder bore centerline, (i.e. it makes a ZERO degree angle with it). The MAXIMUM piston side loading occurs 1/2 way "down the stroke" between TDC and BDC ........ that's where that shorter 5.7" rod makes a GREATER angle to the bore centerline than a 6.0" rod would make.

Major Edit Here: Quik95lt1, after re-reading the first highlighted quote in your original post above, I now realize that you might (???) have been comparing that .27" "move up" with respect to keeping a 5.7" rod length in both a 3.48" stoke crank and a 3.750" stroke crank, engine application. If that is what you really meant then that "move up" in compression height would STILL only be .135", and NOT .27". Yes, the total amount of piston movement would, of course, be .27" more, but nowhere would any CH, (i.e. "attachment point"), change by .27".

For 5.7" rod with 3.480" crank we have: 5.7" + 1.740" + 1.560" = 9.000"
For 5.7" rod with 3.750" crank we have: 5.7" + 1.875" + 1.425" = 9.000"
And CH difference here is 1.560" - 1.425" = .135"