Topic: Message #1126645

[Snowtoy]

Hello Snowtoy,


Here's my real world.  I will be running 31"  tires, R&P 4.10s.  My RPM in 5th gear is calculated to be approximately 2900 at 80 MPH, right were I want it, which is the beginning of my projected peak torque range for my engine rebuild.

Changing R&Ps to 4.56 will move my RPM in 5th gear to 3200 RPM, which is in middle of peak torque, NOT where I want.

I want the RPM in 5th gear at 80 MPH to be at or near 2900 because if I drop down to 4th gear, at say 70 MPH my RPM will be approximately 3200 right in the middle of my peak torque range - right where I want it.
 
Now I have two gears that I can use to take advantage of my peak torque and pull steep grades or buck head winds while traveling at freeway speeds.

With 4.10s if I need to drop down to 3rd gear, my RPM at 50 MPH will be about 3200 RPM, right in the middle of my peak torque range - right where I want it to be.

It does not matter whether my torque and HP numbers are calculated at brake or at the rear wheels.  Whatever power is produced to my rear tires, and whatever energy is absorbed, I will have my peak torque range right where I want it at the rear tires.

Gnarls.

I understand what you are trying to achieve, I just don't see how a few more ft lbs of torque and a couple of ponies at a lower rpm are going to overcome the 11-12% under gearing you have now.  The .020 bore and O/S head will help, as will the header, but I have yet to see any engine mods to a 22r replace the performance lost when being under geared.

My ultimate plan is to pull a little fiberglass 16' travel trailer, so I was going for all the extra power I could get, within my tight budget, to gain needed extra torque at freeway speeds.

Comments here by some folks suggest changing R&Ps to lower the gearing.  I figure roughly that would be around a $600 investment for absolutely ZERO torque gain.  For $400 more I could have several more  pounds of torque.  When I calculate cost per increase in torque, why would I spend $600 and gain nothing except lowering the peak torque in my RPM range?

Here's how I see it right now.....  I only have Tod's expertise at engbldr, my DD data, speculation, assumptions, and comments from the guys who are running or have run a 261C cam in a 22, but some comments seem to indicate that while it gains peak torque in the lower to mid RPMs, it seems fall off in the upper RPM range, which is understandable. I estimate that 90% of my engine running time will be between 2600 and 3400 RPMs - THAT is the RPM range where I want my power. 

If the 261C cam does not perform well enough, I will look at another cam profile, and possibly some other modifications.  But when it comes time to pull a 16' travel trailer, and it just can't do it reasonably, I'll buy another Tundra.

Gnarls.

With the engine mods you have done/plan to do and 4.56 gears you could likely tow the trailer you are looking at w/pleasurable results, but with your current tires and 4.10's, I don't think you will find it all that enjoyable.


The gains of the 261 from 2800rpm's up are nice, don't care for the drop in numbers between 23-2800rpm's though, maybe along w/better intake/exhaust set-up allows it revs faster so that the lower numbers don't effect the performance.

Do you have the numbers for the stock cam and DT header?