long or short?

[DangerousDerek]

I am looking at different options for pistons and rods and looking at US stuff.

I see that there are possibilities for 6" rods with a 1.25"ish compression height or a 5.7" rod with a 1.55"ish compression height.

So which one would be better and why?

[Dominic TVRetto]

When i saw the thread title i thought you wanted suggestions for your new hairdo

[phazed]

I don't understand the question, (well I do a bit but have nothing to contribute).

[NZ fan]

I always understood the longer the rod the better. it actually alters the breathing of the engine believe it or not. while the piston still travels the same distance i.e.. the stroke the shorter rod will give a longer dwell at the bottom of the stroke then travel faster mid stroke where the long rod evens this out a bit. also short rods give nasty conrod angularity which scuffs pistons and wastes power etc.

[Boosted LS1]

The rod angle will change but it'll make bugger all difference to your times in the real world. Go with what's the most convenient imo. At the end of the day it's better to start with a bhp requirement and rpm ceiling.

[macdeb]

As I see it, the long rod makes for easier timing as it has a longer dwell at TDC whereas the short rod moves through quicker. Long rod has faster piston speed as opposed to the shorter but the shorter will have more lateral force on bores. Long rods faster piston speed can enhance chamber filling. What build are you thinking? High revving n/a or FI? What cam for either? [power/RPM]

[DangerousDerek]

macdeb said:

As I see it, the long rod makes for easier timing as it has a longer dwell at TDC whereas the short rod moves through quicker. Long rod has faster piston speed as opposed to the shorter but the shorter will have more lateral force on bores. Long rods faster piston speed can enhance chamber filling. What build are you thinking? High revving n/a or FI? What cam for either? [power/RPM]

Be a 4.8 or 5.0 forged, twin GT28's, M248, 22 psi for 600+

[N7GTX]

DangerousDerek said:

macdeb said:

As I see it, the long rod makes for easier timing as it has a longer dwell at TDC whereas the short rod moves through quicker. Long rod has faster piston speed as opposed to the shorter but the shorter will have more lateral force on bores. Long rods faster piston speed can enhance chamber filling. What build are you thinking? High revving n/a or FI? What cam for either? [power/RPM]

Be a 4.8 or 5.0 forged, twin GT28's, M248, 22 psi for 600+

......

[macdeb]

Hmmmm, so steel crank then? I'd prob' go 4.8.
Oh, and different gearbox?

[DangerousDerek]

macdeb said:

Hmmmm, so steel crank then? I'd prob' go 4.8.
Oh, and different gearbox?

Whats up with a tuftrided offset ground crank?

Gearbox will come later (maybe)

[macdeb]

DangerousDerek said:

Gearbox will go sooner (definately)

EFA

[Discopotatoes]

DangerousDerek said:

macdeb said:

Hmmmm, so steel crank then? I'd prob' go 4.8.
Oh, and different gearbox?

Whats up with a tuftrided offset ground crank?

Gearbox will come later (maybe)

Mines a standard 4.6crank no need to offset grind unless you go bigger that 4.8 if you have 96mm bores

[DangerousDerek]

Discopotatoes said:

Mines a standard 4.6crank no need to offset grind unless you go bigger that 4.8 if you have 96mm bores

I have a choice of cranks, 4.6 and offset 3.4" stroke.
Also getting a block relinered so can have the bore to suit pistons once I decide on customs or off the shelf.
Another block is at 96mm already but needs at least one liner.

So I can build a 4.6, 4.8 or a 5.0
I am still researching and open to ideas on pistons and rods

[Mr Haribo]

I thought you could use 4.6L crank and rods and use 4.8L pistons
sounds easy ! but I bet its not ......