Rebuild 3.4L engine. Increase displacement
01-12-2019, 07:41 PM
#1
Addict
Rennlist Member
Rennlist Member
Thread Starter
Rebuild 3.4L engine. Increase displacement
The engine is at the shop ready for a rebuild. I don’t want to end up with the same displacement. Since I am having it bored and sleeved, I have plenty of options regarding the bore and stroke.
Present configuration is 96 bore x 78 stroke, thus 3387cc.
Options are: piston = 99.1 or 100, or 102. Rod = 76.4, 78, 81.5 or 83
I’m most interested in torque as I want a street machine and don’t want to go all of the way to a 3.8 as that would require ECU mapping.
Looks like I have 2 viable options:
If I go to 100 x 76.4, it is 3600 (basic 996)
If I go to 100 x 78, it’ 3675 (MY Selection)
What do you see as the Pros and Cons for them? Is there another combo that would be better?
Present configuration is 96 bore x 78 stroke, thus 3387cc.
Options are: piston = 99.1 or 100, or 102. Rod = 76.4, 78, 81.5 or 83
I’m most interested in torque as I want a street machine and don’t want to go all of the way to a 3.8 as that would require ECU mapping.
Looks like I have 2 viable options:
If I go to 100 x 76.4, it is 3600 (basic 996)
If I go to 100 x 78, it’ 3675 (MY Selection)
What do you see as the Pros and Cons for them? Is there another combo that would be better?
01-13-2019, 12:46 PM
#3
Instructor
What does the shop recommend based on their experience? Is 93 octane readily available and are you willing to feed it to your car? Previous mods? 3.4s are high compression engines before modification, changing the bore and especially the stroke affects compression ratio. Without proper tuning you risk driving a hand grenade and are missing out on cheap horsepower.
Rods don't determine stroke, the distance between the centerlines of the main journals and the rod journals on the crankshaft (times 2) determines stroke. Crankshafts with longer than stock strokes might require shorter rods so you don't push the pistons into the head / valves.
Rods don't determine stroke, the distance between the centerlines of the main journals and the rod journals on the crankshaft (times 2) determines stroke. Crankshafts with longer than stock strokes might require shorter rods so you don't push the pistons into the head / valves.
01-13-2019, 06:14 PM
#5
Instructor
What does the shop recommend based on their experience? Is 93 octane readily available and are you willing to feed it to your car? Previous mods? 3.4s are high compression engines before modification, changing the bore and especially the stroke affects compression ratio. Without proper tuning you risk driving a hand grenade and are missing out on cheap horsepower.
Rods don't determine stroke, the distance between the centerlines of the main journals and the rod journals on the crankshaft (times 2) determines stroke. Crankshafts with longer than stock strokes might require shorter rods so you don't push the pistons into the head / valves.
Rods don't determine stroke, the distance between the centerlines of the main journals and the rod journals on the crankshaft (times 2) determines stroke. Crankshafts with longer than stock strokes might require shorter rods so you don't push the pistons into the head / valves.
01-15-2019, 01:14 PM
#6
Instructor
Dyno charts indicate a Cobb flash and protune is the cheapest HP per HP available for pcars. Stock settings are conservative and not designed to adapt to major mods. Spending 10-15K+ on a rebuild but leaving out the 1K flash seems folly IMO.