I was talking ot some guys at a machine shop around here and they recomended that i go to a 6 in rod 350 for my engine. What are the advantages and disadvantsges of going to this setup.

Thanks

 

The shop makes more money :).

Seriously, you would end up with a better rod/stroke ratio which would create a better crank/rod angle. This would reduce piston side thrust loading which would minimally reduce piston and cylinder wall friction, and cylinder/piston/ring wear. Although it would be an insignigicant amount, your motor would accererate quicker and may rev a few rpms higher. The biggest benefit would be that you would have to run pistons with the pin higher, reducing piston rock and making the piston lighter.

If you have to buy new rods and pistons anyway, I would go ahead and get the longer rods, the cost difference would be relatively minimal. If you could reuse your existing rods and/or pistons, I don't think it would be worthwhile. Going with longer rods is more of a benefit for street engines when you have also increased the stroke. The longer rod will usually bring the rod/stroke ratio up to a better level.


[Modified by Monty, 10:41 AM 12/19/2001]

 

Another advantage is the crankshaft will turn more degrees of rotation with the piston at or near tdc this will allow more time to make maximum pressure on the power stroke don't need as much spark lead plus all of the things stated above. :cheers:

 

For a 355 I would go with Oliver 6 inch bushed 585 gram and two valve relief pistons. That clear 2.055/1.6 Ask about tight quench in the .044 or less with 10.2 plus or 11ish with thermal coated pistons. They run fine with good heads and cam on 92 octane


[Modified by gkull, 10:32 AM 12/19/2001]

 

the big advantage of longer rods is the reduced weight of the piston. it is a 2 to 1 advantage,for every gram of weight that the longer rod adds there is a 2 grams weight reduction in the piston because of its shorter length.

 

Would you post the gear ratio and engine mods you are planning?Monty has given you good advice on the street motor needing stroked for optimum results.That is a .300 longer rod and it might put you out of your usable range .But posting your gears and heads cam,ect will help alot.The only time I run a .250 long rod on a 454 boat motor is in a jet with a C impeller that will turn 6600 + or a .400 long in a 14.1 454 on Methanol that has heads and prop"gear" to support .The additional dwell time at or near TDC can be of benefit it certain cases. The guys with the TPI motors run a 6.0 rod but it does not hurt their bottom end because of the runner lenght.I like a 383 carbed motor with 6.0 rods and good intake and heads.Or a light car with deep gears and a 377 motor just for the thrill of how it gets on the pipe and goes.Not that will out run a simaler 383.
Post your specs!

 

Although the power benefit to a higher rod to stroke ratio is minimal, so is the cost to increase your rod to stroke ratio, provided you were going to get new rods anyway. But the engine is very obviously a much more sweet-running engine. Have you ever compared a 327 to a 350 in the same car? I have. I liked the torque of the 350, but the 327 was a MUCH sweeter engine. Revved so easy you wouldn't believe it.

Rod/stroke ratio does make much more of a difference than a lot of people would believe. And on a 350, you're not giving up torque either, just improving the engine's internal geometry quite a bit.
I have a problem with engine builders who build monster-stroke engines with crappy 1.40 rod/stroke ratios or worse, thinking that doesn't matter. Sure it does! Tons of torque but lazy revver is what you end up with.

I would have to agree with your shop. A long rod 350 would be a sweetheart of an engine. I would go for it.


[Modified by MoMo, 12:55 AM 12/23/2001]

 

A 6.0 rod in a 350 Chevy will change the torque effectively moving it higher in the rpm range.I know this is not a truck forum HeHe but as an example take two identical 3/4 ton Chevy trucks with 3.40 gear and automatic and a cam of say 204@050.One with 5.7 rods and the other with 6.0.Then load them down weight wise and race em.The 5.7 rod motor will win out.
It is much like the 377 vs 383 controversey.The more oversquare 377 will pull the 383 up high so it's usage or rather advantage would be in a lighter car with 3.73 and lower gears and 4spd.Kind of like I was trying to help a guy that was over camming a 308 geared automatic.I look at what I have and decide on the combo before I even buy the oil.
A 1.6 is a acceptable rod ratio.The 350 is just a stroked 327.I would be curious as to what the rod ratio is on a 5.7 rod 350.I have lost the formula to that and cannot remember or find it.
ya know,Chevy stroked the 427 to 454 and you can certainly tell the additional side load on the pistons in a reasonably fresh 454 compared to a higher mile 427 upon tear down.A member from TX with a 66 or 67 Vette can attest to that.Do any of you remember the truck tall deck 427's? I submit they did this for longetivitey but those trucks had the gear to back it up.
Just tech talk here.Not arguing on anything.