Turbo gearing
Turbo gearing I've been noticing that a lot of turbo guys go with a low ((numerical) gearing. Is this to get the car out of the hole without spinning or for top end or something else?
Lot of reasons/thoughts from what I understand. For example, the torque from the turbo setup doesn't require a ton of gear to get the car moving, less gear loads the turbo better, no reason to spin a ton of rpms when the engine makes it's power at lower rpms, etc. More will chime in I'm sure.
I went lower because I don't have overdrive (TH400), and want it to be somewhat decent to drive on the street. I had 3.25's last go around, and have 3.0 this time. I was cutting low 1.3's without too much effort or fancy shocks/springs and on radials, so that's good enough for me.
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Load. Turbos respond to load & having too steep a rear gearing, meanin gear ratio & tire diameter, reduces load on the engine. Running a transbrake helps here but for the street it is good to have the right load to have the turbos respond quickly.
Low to mid 3's usually gets the job done with 29" & shorter rubber.
Low to mid 3's usually gets the job done with 29" & shorter rubber.
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Load. Turbos respond to load & having too steep a rear gearing, meanin gear ratio & tire diameter, reduces load on the engine. Running a transbrake helps here but for the street it is good to have the right load to have the turbos respond quickly.
Low to mid 3's usually gets the job done with 29" & shorter rubber.
Low to mid 3's usually gets the job done with 29" & shorter rubber.
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Go hop on a 12spd. At the same speed, turn the gearing to really low & see how easy it is to pedal. Now go the opposite direction & reduce gearing & see how hard it becomes to pedal. That is load.
The right load on the motor makes the intake pressure change & exhaust gas energy to rise quickly. As the turbo is connected to both the intake & the exhaust, the right balance of the two makes the turbine respond.
The right load on the motor makes the intake pressure change & exhaust gas energy to rise quickly. As the turbo is connected to both the intake & the exhaust, the right balance of the two makes the turbine respond.
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Here's how I understand it.
On the AVG turbo setup... say you made a pass with a 4.10 gear, then a 3.10 gear. When you compared the data logs, you'd notice the engine averaged higher boost in the lower gears with the 3.10 gear.
Boost=power. You want to get into boost as quickly as possible for as long as possible in every gear. That will give the highest average power output over the run.
That doesn't mean I suggest running a super low gear. It's a balancing act. The best gear for an NA setup will not be the best choice with a turbo car. You do want to load the engine more with a turbo setup... But as with everything racing all combo's will be different. Vehicle weight, peak torque rpm, Peak power etc... all come into play.
On the AVG turbo setup... say you made a pass with a 4.10 gear, then a 3.10 gear. When you compared the data logs, you'd notice the engine averaged higher boost in the lower gears with the 3.10 gear.
Boost=power. You want to get into boost as quickly as possible for as long as possible in every gear. That will give the highest average power output over the run.
That doesn't mean I suggest running a super low gear. It's a balancing act. The best gear for an NA setup will not be the best choice with a turbo car. You do want to load the engine more with a turbo setup... But as with everything racing all combo's will be different. Vehicle weight, peak torque rpm, Peak power etc... all come into play.
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Go hop on a 12spd. At the same speed, turn the gearing to really low & see how easy it is to pedal. Now go the opposite direction & reduce gearing & see how hard it becomes to pedal. That is load.
The right load on the motor makes the intake pressure change & exhaust gas energy to rise quickly. As the turbo is connected to both the intake & the exhaust, the right balance of the two makes the turbine respond.
The right load on the motor makes the intake pressure change & exhaust gas energy to rise quickly. As the turbo is connected to both the intake & the exhaust, the right balance of the two makes the turbine respond.
Last edited by gsteele; Nov 18, 2015 at 02:13 PM.
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Here's how I understand it.
On the AVG turbo setup... say you made a pass with a 4.10 gear, then a 3.10 gear. When you compared the data logs, you'd notice the engine averaged higher boost in the lower gears with the 3.10 gear.
Boost=power. You want to get into boost as quickly as possible for as long as possible in every gear. That will give the highest average power output over the run.
That doesn't mean I suggest running a super low gear. It's a balancing act. The best gear for an NA setup will not be the best choice with a turbo car. You do want to load the engine more with a turbo setup... But as with everything racing all combo's will be different. Vehicle weight, peak torque rpm, Peak power etc... all come into play.
On the AVG turbo setup... say you made a pass with a 4.10 gear, then a 3.10 gear. When you compared the data logs, you'd notice the engine averaged higher boost in the lower gears with the 3.10 gear.
Boost=power. You want to get into boost as quickly as possible for as long as possible in every gear. That will give the highest average power output over the run.
That doesn't mean I suggest running a super low gear. It's a balancing act. The best gear for an NA setup will not be the best choice with a turbo car. You do want to load the engine more with a turbo setup... But as with everything racing all combo's will be different. Vehicle weight, peak torque rpm, Peak power etc... all come into play.
What you are calling load is a illustration of the fact that to maintain a certain speed or acceleration and you drop a gear or two you have to increase the torque. Lets say you have two cars one with a 4.56 rear and one with a 3.00 rear gear. Let's say they are identical and have the same engine and transmission(automatics) and are both turbo charged and are not traction limited so they have some huge slicks. Which car is going to accelerate the quickest? The one with the 4.56 gear. Now depending on the set up, the 4.56 gear car may not get to max boost in first gear but it will get to full boost as soon as the 3.00 gear car with regard to time.
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You're comparing apples and oranges with this example. A certain setup might require a 4.56 (not usually. More seen in 1/8th mile setups) and another a 3.00. Turbo setups rely on torque which is a horsepower at a lower rpm. No need to scream Roma to make power. If you see someone running a 4.10 with a turbo, first gear in the trans is typically very high (low numerically). The 4.10 is in an effort to achieve a certain finish line rpm to optimize the power of the engine. Plus, as Forcefed86 said, boost is power. So your 4.56 example of not getting to max boost in first gear is leaving you short on power. You'd basically be relying on n/a power (which is nowhere near boosted power) until the engine was being loaded.
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Frankly- on top of everything mentioned above- turbo cars are simply freaking faster
Lets say you had an NA car trapping mid 160's @6800 max RPM with a TH400 and a 28 inch tall tire. You would need a lower gear to make it to the end of the track anyways.
The lower gear also allows more time in gear, which makes traction easier to come by.
Lets say you had an NA car trapping mid 160's @6800 max RPM with a TH400 and a 28 inch tall tire. You would need a lower gear to make it to the end of the track anyways.
The lower gear also allows more time in gear, which makes traction easier to come by.
When I first put my setup together, I still had my 4.57 gear in the 9 inch, it went 6.35@109 at the track. Only thing I changed was I switched to my 3.50 gear, and the next time out it went 6.05@115. Car achieved more boost in high gear also. Sixty foot dropped from 1.45 to 1.36. Both runs the car dead hooked and did not spin. Just wanted to add some real world results to this thread instead of a bunch of in theory.
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When I first put my setup together, I still had my 4.57 gear in the 9 inch, it went 6.35@109 at the track. Only thing I changed was I switched to my 3.50 gear, and the next time out it went 6.05@115. Car achieved more boost in high gear also. Sixty foot dropped from 1.45 to 1.36. Both runs the car dead hooked and did not spin. Just wanted to add some real world results to this thread instead of a bunch of in theory.
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When I first put my setup together, I still had my 4.57 gear in the 9 inch, it went 6.35@109 at the track. Only thing I changed was I switched to my 3.50 gear, and the next time out it went 6.05@115. Car achieved more boost in high gear also. Sixty foot dropped from 1.45 to 1.36. Both runs the car dead hooked and did not spin. Just wanted to add some real world results to this thread instead of a bunch of in theory.
I appreciate your real world experience as it lends great credibility to the discussion, but I am not speaking from a theoretical basis. I have quite a bit of real world experience. I never made the mistake of running too steep of gear. I spent a lot of time hanging out with turbo Buick guys back in the 90's. One guy in particular was very knowledgable & showed me the ropes. He ran a mid-8second car back then so when he talked I listened. Then I followed his advice.
I have never ran more than 3.50 gears in a turbo set-up. My last car had 3.27's running a 29" tire. I would blink the 6200rpm pill at 1200'. & run through the traps at 130mph.
Last edited by gtfoxy; Nov 18, 2015 at 03:17 PM.
