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Hi just wondering how much rpm drop there is between gears when up shifting, for example gears first to second and third with stock 3:46:1 diff?
Thanks I used that calculator and filled all the boxes, I was guessing drop would be 1500 rpm, but it's likely to be 2000 rpm or more.
Reason I ask was I was thinking of the mild 108 LSA cam with dyno results posted this forum recently that reached peak torque at 3600 rpm and what that could mean for gear change rpm.
You asked what was rpm drop per gear. But focusing on just the the engine rpm splits isn't the big picture. The only thing that accelerates your car is torque that the tires sticks to the ground. Rear gear does matter because it changes how much torque the tire puts to the ground.
I'm just thinking out loud, but I suppose if you want to be quick as possible then you've got to try to maximize area under the torque curve (tire torque to ground) inside the mph range of interest. Every time you shift there will be a huge loss of torque to ground, so that's one reason why racers hold gears to as high rpm as possible. If you have a dyno chart of your engine, then you could construct a graph of torque vs. mph (it will stair step because of gear shifts) and tweak variables to see what changes push you in the right direction.
I don't like reving more than is necessary for best times and see it as a bit of a compromise, for example if reving to 6000 instead of 7000 before a gear change nets a similar result then reving to seven is considerably harder on engine (engine revs and wear is not linear)
This is just a theoretical example, but in practice I have seen a number of examples where the difference between a baby cam and one with 10 degrees more duration amounts to about 0.2 or 0.3 seconds in the quarter.
Yes, it's more easy to regret going too big with a cam due to possible drivability issues. That's totally subjective so it's your choice to make and your choice alone.
And you're right, engines wear out faster when they're run harder. You've basically got xxx amount of fuel burn until the short block is done, and you get to decide how that happens. And you can wear out the top end (valvtrain) even quicker depending what you do.
I've tried to find info on the relationship between engine wear and rpm many times all I could find was some obscure info from the Air Force running piston engines, not that it matters if you have the money for it all , still it is of interest.
If you've ever been around large diesel engines then you'll learn that engine wear-out has a pretty darn good correlation to total fuel burn. You can burn the fuel at 1500 Hp for so many hours, or you can burn the fuel at 2000 Hp for fewer hours. This is for engines that run within guidelines. I doubt it holds true for racing since most the problems are related to just plain old **** breaking.
So applying this to your situation, the engine will last a lot longer (hours) sipping fuel while cruising the highway at 2000 rpm than it will guzzling fuel while ripping around Road America at 5000 rpm. Obviously there are other factors but it works pretty good at a high level view.
But that still doesn't answer your question of what's the total fuel burn of an LS engine? Those numbers are probably guarded in the halls of GM and I don't know. You *might* be able to get a feel for it if you find recommended maintenance intervals for police service vehicles and how many hours they recommend engine overhaul. But again, you're still not done backwards engineering it with just that info.
Yes some of those marine engines can nearly double engine life with just a small reduction of WOT at max power (about 15% down from max from memory???)
Rod to stroke ratio also effects engine life as there is more side loading at high rpm with long stroke short rods.
These were said to be from a 383 stroker with only 500 miles on them.
04-09-2020, 06:31 AM
6 speed manual t56 how much RPM drop? 
