Chevrolet Corvette Stingray C7 Forum - View Single Post

ALLTRBO · 07-22-2010, 10:24 PM

This is part of a conversation on the 60V6 forums (not in the build thread) when asked why I'm going with a destroker 3.2 rather than the 3500 block that it's based off of. Here are the main reasons...

*Less torque: With equivalent components (top end/cam/etc) a smaller displacement will usually make almost as much power but at a higher rpm. The torque, however, has a higher percentage difference. Look at the stock (late) 3100 vs. 3400 hp and torque for examples. The 3400 has 10 more hp (185 vs 175) but 15-20 more lb/ft. Though the 3400 has 6.9% more displacement (3350cc/3135cc), it has only 5.7% more hp, but 7.7% more torque.
They are, of course, identical other than the bore and slightly bigger TB on the 3400. So to make an even comparison put the 3400 TB on the 3100 and it might gain ~5 hp, bringing the hp advantage of the 3400 to only ~2.8%, but not really changing the peak torque. I've seen several examples of this, stock and modified, some to a more extreme degree...
I want less off boost torque to go easier on the tranny between shifts. It isn't much of a difference, but every bit adds up. Shock loading is what kills trannies, not really horsepower. However, I still want the reasonable off-boost torque of a V6 over a blatty l4 so I wouldn't go that route (been there done that with my Talon... no thanks).

*Rod/Stroke ratio: The 3100/3400 is 1.72:1, the 3500 is 1.79:1, and the "3200" will be 1.96:1
A higher rod/stroke ratio allows more resistance to detonation, which will allow me to run a bit more boost on the same octane (possibly making up for that slight hp drop without retaining that off-boost torque). In addition, the maximum piston speeds are slower.

*Less rotating mass: There will be less shock loading on the tranny between shifts, again. It isn't a lot of a difference, but every bit adds up. It will also use up less hp to turn the crankshaft, mainly at high rpm. Not only because the crankshaft is lighter, but also because the rod journals and the lighter counterweights take away weight from the outside diameter of the rotation, where it counts most.

*Rod availability: Using the 76mm crank and the 3400 pistons (.100 over) will allow me to use 5.85" SBC rods (slightly machined of course) for the perfect piston height vs. quench clearance vs. head gasket thickness, and very stout 5.85" SBC rods are somewhat easy to find, hence easier and cheaper than custom options that will handle ~650 hp.

*Crank strength: This one probably doesn't differ as compared to the forged 3500 crank, but comparing to the 3400 steel crank, there is more overlap between rod journals with the 2.8 crank. Many say that it doesn't matter because no one has ever broken a 3400 crank, but I don't think anyone has ever pushed ~650hp through one either (correct me if I'm wrong).

*RPM capability: All of the above adds up to a rotating assembly that'll probably beg for 7500 rpm with a few valvetrain mods and mild turbo cam upgrade, and intake and head porting (I'm talking about you, Ben. [IMG]http://60degree*******/forum/images/smilies/icon_wink.gif[/IMG] ). Maybe even 8000rpm. My heart skips a few beats at the thought of a jet-like spooling and screaming 7500-8000 rpm 60V6. The 282 doesn't care to shift above 7k from what I hear, but I think that's covered by an aluminum flywheel and lighter rotating assembly, along with my friend Will (aka: "The Dark Side of Will" on RFT and "Will" on PFF) with his awesomz 282 rebuild skillz, heh.

I could also add some panzy-arse reason like the extra gas mileage it could theoretically get, but this car isn't being built for economy, though it'll still be good enough. [IMG]http://60degree*******/forum/images/smilies/smile.gif[/IMG]

07-22-2010, 10:24 PM	#5
ALLTRBO Drives: V8 up front and 7-spd out back FTW Join Date: Apr 2010 Location: MD Posts: 746	This is part of a conversation on the 60V6 forums (not in the build thread) when asked why I'm going with a destroker 3.2 rather than the 3500 block that it's based off of. Here are the main reasons... Less torque: With equivalent components (top end/cam/etc) a smaller displacement will usually make almost as much power but at a higher rpm. The torque, however, has a higher percentage difference. Look at the stock (late) 3100 vs. 3400 hp and torque for examples. The 3400 has 10 more hp (185 vs 175) but 15-20 more lb/ft. Though the 3400 has 6.9% more displacement (3350cc/3135cc), it has only 5.7% more hp, but 7.7% more torque. They are, of course, identical other than the bore and slightly bigger TB on the 3400. So to make an even comparison put the 3400 TB on the 3100 and it might gain ~5 hp, bringing the hp advantage of the 3400 to only ~2.8%, but not really changing the peak torque. I've seen several examples of this, stock and modified, some to a more extreme degree... I want less off boost torque to go easier on the tranny between shifts. It isn't much of a difference, but every bit adds up.* Shock loading is what kills trannies, not really horsepower. However, I still want the reasonable off-boost torque of a V6 over a blatty l4 so I wouldn't go that route (been there done that with my Talon... no thanks). Rod/Stroke ratio: The 3100/3400 is 1.72:1, the 3500 is 1.79:1, and the "3200" will be 1.96:1 A higher rod/stroke ratio allows more resistance to detonation, which will allow me to run a bit more boost on the same octane (possibly making up for that slight hp drop without retaining that off-boost torque). In addition, the maximum piston speeds are slower. Less rotating mass: There will be less shock loading on the tranny between shifts, again. It isn't a lot of a difference, but every bit adds up. It will also use up less hp to turn the crankshaft, mainly at high rpm. Not only because the crankshaft is lighter, but also because the rod journals and the lighter counterweights take away weight from the outside diameter of the rotation, where it counts most. Rod availability: Using the 76mm crank and the 3400 pistons (.100 over) will allow me to use 5.85" SBC rods (slightly machined of course) for the perfect piston height vs. quench clearance vs. head gasket thickness, and very stout 5.85" SBC rods are somewhat easy to find, hence easier and cheaper than custom options that will handle ~650 hp. Crank strength: This one probably doesn't differ as compared to the forged 3500 crank, but comparing to the 3400 steel crank, there is more overlap between rod journals with the 2.8 crank. Many say that it doesn't matter because no one has ever broken a 3400 crank, but I don't think anyone has ever pushed ~650hp through one either (correct me if I'm wrong). RPM capability: All of the above adds up to a rotating assembly that'll probably beg* for 7500 rpm with a few valvetrain mods and mild turbo cam upgrade, and intake and head porting (I'm talking about you, Ben. [IMG]http://60degree*****/forum/images/smilies/icon_wink.gif[/IMG] ). Maybe even 8000rpm. My heart skips a few beats at the thought of a jet-like spooling and screaming 7500-8000 rpm 60V6. The 282 doesn't care to shift above 7k from what I hear, but I think that's covered by an aluminum flywheel and lighter rotating assembly, along with my friend Will (aka: "The Dark Side of Will" on RFT and "Will" on PFF) with his awesomz 282 rebuild skillz, heh. I could also add some panzy-arse reason like the extra gas mileage it could theoretically get, but this car isn't being built for economy, though it'll still be good enough. [IMG]http://60degree*****/forum/images/smilies/smile.gif[/IMG]