Howdy folks,

Why is it that you will sometimes hear a recommendation to stay with a relatively mellow gearing if your power-adder is a Turbo? I have no experience with power adders, but it seems to me that a nice set of 4.10s would be ideal when mated with a turbo. The gears for power down low, then the turbo kicks in up top. But reputable folks have recommended just the opposite, gear-wise. In fact, I have heard that our stock ratio is ideal. Why is this, and would this also apply to centrifugal blowers like the Vortech? And is this recommendation specific to drag racing?

I don't want to cripple myself from a dig...the idea of turbo lag and spool-up don't appeal to me, but on the other hand I love the idea of the turbo's efficiency and power. I'm trying to find the ideal balance of gears and power adder to get grunt all the way through the power band. I'm thinking either a Twin-screw with stock 3.55s, a centrifugal with 4.10s, or a Turbo with...?

 

Well, the reason you add gears is to increase acceleration. When you add a turbocharger, you don't need anything else for acceleration. It increases shifting amount...which will get annoying. I would do F/I-friendly N/A mods, it will increase your off-boost power and add even more under boost.

 

Well I guess I am just clueless on turbos then. I mean, I owned a friggin turbo, but that was a long time ago and it wasn't a performance car per se (Saab 9000 Turbo). My memory is: build to a certain RPM before turbo kicks in, then a little bit of lag, and THEN boost. Everything I'm hearing is sounding like it kicks right in from the get-go. Yes, I understand that proper turbo sizing can make the lag almost nonexistent, but you still need to keep your RPM's up for a bit to get boost, right? How is it that the turbo is right there for you from the start?

 

Proper turbocharger sizing, material of the exhaust manifold, design of the exhaust manifold, turbocharger features, driving techniques, etc. all have to do with turbocharger lag and spool characteristics. It is virtually from the get-go...the things I mentioned can get you to spooling around 2000-2500 RPMs and achieving full boost around 3500-4500+ RPMs.

What kind of driving will this be used in? Drag racing? Autocross? Road course? Daily driver? Weekend car?

Might want to learn how to brake-boost.

 

This has been a long standing argument, my personal experience with superchargers/turbochargers/Nitrous Oxide is that boost loves to have a taller gear. Power adders work exeptionally well in a street car when under a load, not at the RPM limit while traveling 140mph. Now taller is relative to what you would use in a N/A situation. No matter how you race or if you drive on the street stock gears under boost should work better than "shorter" gears. If you are a drag racer or road course racer and use between a 3.89 to a 4.56 ratio then in a situation where you add one of the above power adders you would most likely want to go to a "taller" gear. Anything taller than 2.73 you should only be salt flat racing/testing. I have elected to keep the stock gear ratio because I am adding a supercharger and already have nitrous. I may be running times a tenth or two slower than cars with 4.10's or 4.30's but when the boost comes in that will all change.

 

OK, I begin to understand now. It's not just turbos that "like a load", it's any boost application. That's what I'm hearing. So regardless of power adder, sticking with the stock gears is the way to go, it sounds like. Cool. Saves me money and hassle. Now I just have to decide if I'm willing to wait for a decent turbo solution. I'm really running out of patience.

 

It's personal preference. I have 4:10's and a sc and would not go back to 3:55's

 

I got into this topic with a friend since I am, at some point, going to a 4:10. He has a 3:55 and said the he was keeping this since he was going to get a s/c within the year. He has had a number of Stangs both s/c and not. For what its worth.