THIS IS AN ENGINEERING EXERCISE, NOT A BUILD DIARY.
GEN III based engine.
Trying to go from idle to red line under full throttle milliseconds faster. So we are not "revving to the moon" just revving to 7,500 REALLY FAST. Think super bike throttle response. Let's assume that this is in a stand, so there is no confusion on transmission choices, weight of vehicle or gear ratios. Motor plus flywheel, only accessory drives are water pump, alternator.
Naturally Aspirated
11:1 Compression Ratio
91 octane
7,500 RPM red line
Hydraulic lifters
Aluminum (4 bolt head) block
2 valve heads
Everything else goes.
So - in order to build this there are certain things a person can do in order to achieve faster revs. Lets start out...
1. Shorten stroke - this brings the outermost swing of the crankshaft more in line with the center line of the crankshaft, therefore allowing faster revving at the expense of torque and displacement. This could even be done with the shortest stroke crank available (4.8 crank AFAIK at 83 MM) offset ground to reduce stroke and reciprocating mass simultaneously if using different rods...
2. Lighten/blueprint/balance reciprocating assembly - including (but not limited to) aluminum flywheel, custom flyweight pistons, aluminum or titanium rods...
3. Reduce reciprocating drag - knife edge and polish crankshaft, windage scrapers, synthetic lower viscosity oil...
4. Increase air flow - Higher flow from intake, heads, and exhaust. How much flow (if any amount) is too much considering the red line? In order to increase the flow to the maximum allowed by two valves one needs the largest valves that will fit. The best I have found is the LSX-DR heads 19166979 (
http://www.crateenginedepot.com/stor...P2572C114.aspx) but they are a 6 bolt head. I know that the 4 bolt heads work on the LSX blocks, but do the 6 bolt heads work (even with slight modification) on the 4 bolt block? I read somewhere that these will flow 430+ CFM intake side (at like .8" lift !) and they claim to be good for 900+ NA HP. If they do not work as a 6 bolt head on a 4 bolt block then the next best I see are the LS6 CNC ported 88958665 (
http://www.crateenginedepot.com/stor...-P852C114.aspx) though I may have missed something. They claim these are good for 500+ HP and they will flow 304 at .570 lift. NOW - that being said, the former heads require a minimum 4.125" bore whereas the latter heads will fit a stock bottom end of any GEN III. That being said, the increased bore is a good thing in one respect because it allows not only the largest valves but it also prevents shrouding of said valves. If a person uses Darton sleeves the bore can be increased up to 4.200". This would allow maximum valve diameter and either head (assuming you can in fact use a 6 bolt head on a 4 bolt block) with minimal valve shrouding. ON THE OTHER HAND, the larger bore requires more air all other things being equal. More air means more TIME to fill the chamber, which may in turn mean an incomplete fill for a given time (inefficient) or more time for the increased volume. Then at what point (given a de-stroked motor) is the displacement a limiting factor on the given flow numbers. Also keep in mind that the flow numbers given are peak and an average flow will be considerable less. Additionally, the .8" lift of the DR heads is probably unrealistic. Add to this the chamber differences (50cc for the DR and 65cc for the CNC'd LS6) and we run into changing piston dish to maintain the 11:1 ratio. So the head choice is as clear as mud.
5. Valve train - Assuming that we are using the lightest weight components that we can, then to lighten anything further would be to use smaller valves, allowing weaker springs to limit mechanical losses. Would it make more sense to use the stronger springs to control the valves better? Also, where is the trade off for small, light valves and flow? Roller everything in the valve train? Speaking of which, is it better to use a dog bone timing set or a double roller? I would think that the double roller chain would be the most efficient, but I do not know. Taking the valve train the the extreme I know that some of the piston engine fighter planes from circa WWII even hollowed the camshafts.
6. Under drives - The most aggressive accessory under drives that I know of are 25% - like the ATI 918847. Take this further and put on the smallest alternator available. Is there a MECHANICAL water pump that takes less power to run than others? I have even heard of people under driving their oil pump, though I cannot find that link now...
7. Electronic tuning - I know little to nothing about this, so inform me.
THOUGHTS or SUGGESTIONS?
P.S. - If you do not want to follow the beginning "rules" to this theoretical build, go elsewhere. I don't need to be told that you can make more power with a 14:1 454 LSX.
Also, sorry about being so long-winded.
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Originally Posted by Lincolnman
