318 driver - cam change or not?
AJ, your gearing and TM points make a lot of good sense. If at some point, I put in a 2600-2800 stall convertor, would I need to run an additional trans. cooler?"Will I see more rpm at cruising speed or is the increased stall mostly noticed at high-load low speed."
As to the cooler, that is always a good idea, but whether you need it or nor is gonna depend on your final gearing and usage.
The stall speed depends on the input torque, versus the load and if the tires are spinning or not. There will be about three times you will notice it
1) everytime you take off from zero mph, depending on how hard you are taking off
2) everytime the engine rpm has fallen to lower than the stall, as in you are slowing down but the trans has not yet downshifted, and then you get back on the throttle
3) anytime your cruise rpm is lower than the stall, and you begin to accelerate..
Lets look at #3 first.
With a small engine, you are kindof gonna have to make up your mind whether you value low speed performance, versus hiway cruising. For cruising, as you know, the 318 likes; 2.76s to 3.23s at most, depending on your idea of comfortable cruising, and the actual cruising speed. Personally I like to cruise at 65= 2200. My combo is happy there and the pipes are singing a nice tune. With 27" tires and a loc-up trans, this requires a rear gear of 2.60. Your 2.76s and 27s would get you 65=2230 at zero-slip, which is very nice.
After that, every 1% higher gearing will increase the cruise rpm by the same 1% . So, 3.23s are 3.23/2.76= plus 17% ,and your cruise rpm at 65mph will therefore increase by the same 17%, so 2610. This is the penalty you pay for small-engine performance.
However,for performance driving with a small engine, 3.23s are entry level gearing. So you have to be careful in selecting the cam versus your cylinder pressure, cuz you can very quickly make a lazy combo out of it. And this is where the Convertor comes in. It can make or break your combo.
That is to say, if you choose a too-big cam, for it's increased power,that may not begin until well after 3500rpm, that will destroy your power under that 3500rpm. So you likely wouldn't want to be powering thru there, so you might choose a 3500 TC so the engine never gets stuck in that lazy place. But with the entry-level 3.23 gearing yur gonna be in first gear until 50 to 55 mph.Again, that is the penalty for using 3.23s.
But say you choose a faster rate of lift cam than you now have, that might be a size, or a size and a half, bigger at .050 . That's smart shopping. So with this thinking, you will not lose any low-rpm torque compared to what you now have, so a modest TC will work very nicely. The question is, and we already know the answer, do you have adequate torque now? No, you don't, else we wouldn't be having this conversation. But choosing those 3.23s, this will increase that low rpm torque 17% as already figured, over 2.76s. And the modest Tc will allow your small engine to spool up to a higher rpm, where the engine is naturally making more power....... because that is how the formula works; namely;
torque times rpm = power. By the formula, if you increase either the torque, or the rpm, an increase in power has to follow. So increasing from 1750(I'm guessing at your current stall, it could be as high as 2150, IDK) to 2800 is a huge deal. Since we are talking about 3.23s that cruise at 65=2610, there is a 200rpm difference that is sortof on the wrong side of locked-up. This means the TC could be slipping all the time while cruising, so the cooler may be required, and is a good idea.
Anytime the TC is not hydraulically locked, that is to say slipping,it is putting horsepower into the oil,heating it up.
Every time you take off from zero mph, the TC will be heating the oil.
Every time a shift is in progress, the oil will get heated.
All this heating has to be controlled.
If you were the kindof guy that just tools around all evening, you would not need cooling beyond what the factory provides.
If this car was a drag car it would definitely need a cooler.
If you are inbetween, then a cooler is cheap insurance.
On a sidenote, I ran an A904 with the A999 gears and a 2800
several winters with no cooling whatsoever, with several different rear gears, and it didn't seem to gibachit about it.
Now, as to your question;
"Will I see more rpm at cruising speed or is the increased stall mostly noticed at high-load low speed."
Simple answer is yes, and no.
With 3.23s, 65=2610 mathematically.
With a 2800TC there is gonna be 190rpm slippage, mathematically, at 65 mph.
but since you don't have a loc-up, that TC could be slipping either way from it's zero slip rpm.
That is to say;
at 65 mph, the rpm could be anywhere from, I'm guessing 150 rpm less that 2610 to the 2800 stall, depending on the load being presented to the TC. On a hard, level,flat, hiway it could be towards the middle, but climbing a hill or bucking a wind it might be towards the hi side, and with a tailwind towards the low side. On a softer surface who knows.
The increased stall makes the biggest difference at zero mph. From idle of say 700 to 2800 is 2100 rpm, and when you nail it from a stop it's like swinging a big hammer; nothing happens until the hammer hits the target, and then all hell breaks loose. After the hit, at WOT and banging thru the gears, you will never know that 2800 is in there.
