Gearing or Power, lesser of two evils?

Joined
Jun 12, 2005
Messages
80
Location
SW
I am contemplating putting a turbo the size of my head on the car. Some thing that just came up, I also have the option of putting in 4.44 gearing on both ends as I am AWD. So on my balanced, 2.0L, 8500 rpm motor, I can do either 600hp with 3.9 gearing or keeping my 450hp turbo and adding 4.44 final drive. I suspect the 4.44 would be quicker as the 600 hp turbo will only net 500 or so on pump fuel. The difference on my car would be 400 rpm or so. So on the highway at 70 mph I would spin 3500 rpm instead of 3100 rpm. The question is, assuming proper oil and oil temps is maintained etc.. is spinning the motor harder on the bearings or is cramming more power out of each power stroke harder on the bearings? Hopefully this is not a "taste great" "less filling" kind of topic.
 
Joined
Feb 9, 2005
Messages
2,199
Location
Arizona
Given the assumptions you listed, there's no problem at all spinning the motor a little faster. Putting more stress on the motor with higher output will shorten its life. How much depends a lot upon how often you use that extra output.
 
Joined
Dec 21, 2003
Messages
12,385
Location
Northern CA
quote:
Originally posted by jdmboy: The question is, assuming proper oil and oil temps is maintained etc.. is spinning the motor harder on the bearings or is cramming more power out of each power stroke harder on the bearings? Hopefully this is not a "taste great" "less filling" kind of topic.
If you gear it like dump truck, it will be turning faster all the time on the highway. If you cram more power into each stroke, the extra stress will only be there when you are using the power. Unless drag racing is big thing for you and you are after the last few miliseconds in a 1/4 miles, use that lever in the middle of the car to select another gear ratio when you want to spin the engine faster.
 

jdmboy

Thread starter
Joined
Jun 12, 2005
Messages
80
Location
SW
No, not at all. The 4.44 gearing nets faster acceleration is every gear. The effect of gears is to multiply toruqe, and in this case a 12% increase. That is in effect in every gear. Get through the gears faster, get to boost sooner, get through the rpm range sooner and get to the next gear quicker. All about 12% faster. An additional 30 Ft torque at the wheels through gearing is definitly noticable. The issue is acceleration. From a start, getting up to highway speeds, I have to go through 3 maybe 4 gears. The acceleration can be had through gearing or through more power. Believe me, every time you have to accelerate in my car, you will accelerate with the all the force you can. The turbo whine, the air sucking soung, the thrust into your seat, it is very intoxicating. So, it is not so much an issue of down shifting down shift when I am on the highway, is is for the actual acceleration within each gear as I am in each gear. The down side, if there is one, is that when I am cruising on the highway at 70mph, I will be 400 or so rpm higher after I have enjoyed the acceleration. I am going to put the pedal to the floor regardless. I can go faster through gearing or more power. The question is, If I choose gearing, is the resultant cruising at 400 rpm higher on the way to work harder harder then putting the pedal to the floor with yet more power per litre harder. On one side, I will stress the engine more with more power with a bigger turbo and on the optother side the engine load actually decreases through gearing but the effect on bearings is unknown to me. I would thing rings would give out before bearings but that is wht I am asking.
 
Joined
Feb 9, 2005
Messages
2,199
Location
Arizona
Changing to a lower gear ratio will reduce stress levels on all components of the drivetrain except the axles when compared to increasing engine output. There will be no adverse impact on the bearings from the engine running at slightly higher rpm. Don't worry about the rpm (except for possibly fuel economy and engine noise, both of which I assume are not very big factors to you). The lower gearing will let your car last longer and still thrill you like you want without any downside.
 
Joined
Dec 21, 2003
Messages
12,385
Location
Northern CA
quote:
Originally posted by jdmboy: No, not at all. The 4.44 gearing nets faster acceleration is every gear. The effect of gears is to multiply toruqe, and in this case a 12% increase.
Then run one gear lower and get a 25% to 35% increase instead. [LOL!] [LOL!] [LOL!]
 

jdmboy

Thread starter
Joined
Jun 12, 2005
Messages
80
Location
SW
Hmmm, I see. Ok then, once I wind out first gear, and shift into second on the way to third, how do I do that? I am already there and I am talking about making acceleration in a particular gear faster while winding it up. I am talking about accelerating through a gear not cruising and then down shifting. 2 different things. [Smile] bulwnkl, that is what I am thinking as well. Noise and mpg is not an issue. Engine is buttery smooth and I have 6 rolls or Dynamat Extreme in the car.
 
Joined
Jun 15, 2003
Messages
36,725
Location
ME
Do you think you'll get meaningful boost in 1st? Or will it just be all wheelspin? I vote for keeping the taller gears for a while.
 

jdmboy

Thread starter
Joined
Jun 12, 2005
Messages
80
Location
SW
Good point. I can get 21 Pounds in first now. I use AVC-R which allows me to control wastegate duty or boost by gear and RPM actually. It is AWD with sticky 235 ultra high performance summer tires. wheel spin is almost impossible. Slight but then instant grab. Even then I do not launch as the driveline shock is incredibly harsh on the drive line. I walk it out of the hole then pass them like the millenium falcon jumping to light speed. [Wink]
 
Joined
Oct 22, 2003
Messages
13,132
Location
By Detroit
It seems to me that a lower (higher number) rear end is only beneficial off the line. Otherwise, as said above, you can select a gear that gets the RPMs up.
 
Top