Turbo gearing
TECH Enthusiast
Joined: Mar 2013
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Nope, I read it here, right where you typed it. And you're right, it wasn't hard. I do see your point to some degree. Take a naturally aspirated engine and run it on a dyno and get a curve. It would get geared accordingly. Now boost the same engine with 20 psi and get a curve. The curve would be way different and would allow you to get away with less rear gear. Now, the harder the engine has to work, the more heat it's going to build and the more energy will be produced. Heat builds boost, boost builds power. So load does have an effect on building power.
Engine load makes exhaust heat which drives the turbine on the turbo. That's why when you rev a turbo car in neutral it makes little to no boost. There's not much exhaust heat to drive the turbo. Load it up and it'll make boost.
TECH Enthusiast
Joined: Mar 2013
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How long does it take to get to red line in neutral? Not enough time for the turbo to respond. Either way I have already conceded that it takes a load to build boost. My contention is that it has little to nothing to do with an accelerating vehicle. I have always stipulated to no wheel spin so there is always a load and the throttle is wide open.
How long does it take to get to red line in neutral? Not enough time for the turbo to respond. Either way I have already conceded that it takes a load to build boost. My contention is that it has little to nothing to do with an accelerating vehicle. I have always stipulated to no wheel spin so there is always a load and the throttle is wide open.
TECH Enthusiast
Joined: Mar 2013
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Then you understand! If you concede to the fact that load builds boost, boost builds power. Less gear increases load which builds boost. It becomes a factor of leverage as well. A vehicle with less power can use a bigger lever (more rear gear) to get going, whereas a more powerful engine doesn't need as much gear to get going. Look at an NHRA stocker! A 2 barrel 283 in a 67 Camaro can run 11.80s but it's done at 1000 feet. They run massive gears in those cars because they don't have the power to pull themselves and run the number. They rely on the leverage of the gear to get them up and moving, but it doesn't last. A turbo car doesn't have to rely on the gear. The torque does it, which comes from power, which comes from boost. Some turbo guys over on the truck forum run 4.10s, but they're also pulling a 4800 lb vehicle down the track. Before you say they should run a 3.55 and be faster, there's appoint where the leer age thing comes into play. This, in cooperation with the rest of the setup, is called the combination. Some work and some don't.
TECH Enthusiast
Joined: Mar 2013
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How about this? Take a vehicle with 3.0 gears put it on a chassis dyno, get a graph then change the rear gears to 4.56. You get the exact same graph. Gearing does not change the curve. It will change the performance of the vehicle but not the power output of the engine.
I understand what you're saying, I see what you're getting at, and I think we're both debating two different points. My brain is numb. It's been fun, I need a break.
TECH Enthusiast
Joined: Mar 2013
Posts: 503
Likes: 38
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On a 3.5 gear, 28" tire, 7000rpm(I turn less), 0% converter slip(so buffer this some), in your 1:1 gear
7000rpm = 167mph So some converter slip you see 155-160?
You might need more gear just to hit your goals.
Engine size. Scr/dcr. Gearing. All play a role. Too many variables to speak of for a given car. Vehicle weight.traction.etc.
The final gear along w the trans gearing all play a role.
The argument will go on and on with every single person asked will have a different opinion. Even the TQ converter size n build will have a dramatic effect. Stall. Etc.
I'm goin w 3.08 gears in my tt tc78 9:1 408 car. W a th400 n 3600 8.5 converter. The gear is correct for what I'm aiming for for my application. Alot of ppl will disagree with it. But again my goal is different from the next guy.
It's what it boils down to.
The final gear along w the trans gearing all play a role.
The argument will go on and on with every single person asked will have a different opinion. Even the TQ converter size n build will have a dramatic effect. Stall. Etc.
I'm goin w 3.08 gears in my tt tc78 9:1 408 car. W a th400 n 3600 8.5 converter. The gear is correct for what I'm aiming for for my application. Alot of ppl will disagree with it. But again my goal is different from the next guy.
It's what it boils down to.