Kind of a dilemna....
Those 4.11's make you accelerate faster,
but the price you pay is higher RPM....
A SBC in decent shape should have no trouble with 6500, but sooner or later you will wear out the weakest valve spring if they aren't higher strength the faster you go. You can bolt on increase - or secure - your ability to handle 6000-6500 fairly easily. Note this is not to increase performance, but just durability.
- Make sure you have screw in rocker arm studs - they can be threaded and changed to screw in on the engine if not.
- Get the valve springs changed to the strongest you can get without having to machine your heads. (You can change these yourself but they are tough - especially the back few where there's less prying room.)
- Go with some high strength/high speed valve retainers when you do this (steel or titanium).
- Those first three items are skipped if you change heads.
- Change to high strength pushrods.
- Change to aluminum or high strength steel roller-tipped rocker arms.
- Consider installing some type of stud girdle/push rod guides, if you can find one that fits without machining.
- Change your timing chain to an enlarged true roller or a double roller or a gear drive, preferrably a greatly adjustable setup.
- Install a cam bearing thrust collar or button when you change that timing set.
- Go with some reducer or at least deep groove pulleys to both not shed belts and not eat up your water pump, alternator (just had that happen myself
), power steering pump and air conditioning.
- Go with an electric fuel pump or change the fuel pump pusher rod to a strengthened lightweight one.
- Watch your temperature at higher RPM as your water pump may cavitate at that speed and may need a new design, especially if you do not use the water pump reducer pulley.
- Make sure your fan, if it's still mechanical, especially if the fan clutch has been bypassed, is rated for high RPM.
I have the 3.73's in my 12 bolt and have my rev limiter set for 6500. I don't push it beyond 6K intentionally. Today I just verified I got rid of a nuisance oil leak today by running it up to about 115 (gauge) for 10-15 secs and was way under 6K still.
What is your et - about 14.5, 15.5? I'm not a drag fiend, but at that range should only be about 95-100. While you
could switch to the 3.90ish one that's available or even down to 3.70ish or 3.55 one the Dana 44/36 offer, that's a fairly expensive proposition - slightly more
(barely) than those engine upgrades I listed.
A better approach would be to change your tranny. Go to a 4, 5 or even 6 speed manual or OD auto and you get the best of all world's. I favor the Gear Vendors OverDrive to bolt on to my T400 whenever I find my missing pot of gold....one of the Bob's just did it and loved it. It adds gears
in between your regular gears as well - think you'd like
that during a hot quarter run? It's $2.5K, but that rear end gear swap isn't cheap - especially if you don't do it yourself...
Your engine sounds solid and decently powerful, so crippling it's performance with highway gears would be a shame, and just cramming in a bunch of parts to make it survivable at higher RPM seems to beg the question. Your new gears are probably doing great at minimizing your time - it seems a shame to change them.
All of these changes are bucks - but some other tranny swaps aren't that high, depending on what you have now.
:bash 
