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Discussion Starter #1
Turbo game is new to me, will be shooting for 460ish whp. Now 3.73s would put me at roughly 128 at 6200 but that seems steeper than most of the cars on the site. Is the goal different when the cars turbo? As far as trap/rpm
 

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Turbo cars tend to make alot of low end power. That is why you see all the 3.27 gear ratios. Not such an advantage to tach them up that much many times.
Erich
 

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I have a C4 & I just changed 3.73's back to 3.27's & all I can say is WOW night & day!!
Now it has time to build boost.....Before 1st gear would be up before a got across the intersection! ....Blowing the tires off of course! Now it pulls WAYYYYY longer & harder DR's & I'm sure I'm rolling 10's
 

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I am currently running a 373, but I have not made a pass with the turbo. I had 275/50/15's and 373's on spray with a C4 and my shift light came on at about the 1000' mark. I got a set of 275/60's and I'm going to make some low boost passes to see where I'm at.
 

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Formerly eades5.0
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When I swapped from 3.73 to 3.27 my car felt like it picked up 50rw, this was when my car ran 11's and I drove it daily.

I go 1.4 60's on a DR and a 3.27, leaving on no boost. Power, transmission, and suspension play in also. Point being you can 60' decent on that gear, heck my car should go 1.3's.

I would def NOT run a 3.73 gear in my turbo stang...400rw or 700rw. Just me.
 

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Formerly eades5.0
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I am currently running a 373, but I have not made a pass with the turbo. I had 275/50/15's and 373's on spray with a C4 and my shift light came on at about the 1000' mark. I got a set of 275/60's and I'm going to make some low boost passes to see where I'm at.
3.27 or 3.55 would work great in your car imop.
 

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Discussion Starter #14
lol sup dude met you at keiths shop. Anyways, still dunno where the goal is as far as trap/crossing rpm since im not shooting for redline anymore
 

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Jersey True Street Guy
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I have run both 3.55 and 3.27's in my car. I will echo that a turbo car works better with load on the motor. I have the 27's in the car now even though I don't need the mph. The car builds boost better and goes a pretty high mph. I tested both in a 331/78mm combo also and the car liked the 3.27s then also.

If it is an automatic you really have to watch converter slip. Straight gear ratio based math doesn't apply. You can be losing 3 to as much as 15 % to converter slippage. Most of the transmissions used have a 1:1 final drive ratio but the converter slippage can have a major impact on realistic mph at the top end.

With a 3.27 and the C4 I can drive all over the place on the street and the car feels great.

Turbo cars don't follow the same logic as a NA car. Don't go down the path of that thinking.
 

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Jersey True Street Guy
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Yes, reasonable and in line with what most are using with similar setups.

Mike
 

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If you want the faster quarter mile times possible turbo or otherwise... You want to gear the car to where your crossing the line at around peak HP in your final gear (usually 1:1)

Heck most decent running N/A motors with a lower rear gear will spin tires, so take that and once you have a turbo hit with boost it just keeps spinning and it harder to stop.

The way i look at it is, with the lower gears your motor sort of "outruns" the turbo in a sense. Guys claim all day that higher ratio gears spool the turbo faster but in reality it isnt, with just a simple gear swap...your not bringing any more air or fuel into the motor, meaning your not putting any more energy into the exhaust going into the turbo, so HOW can the turbo spool faster. I dont see it doing that.

What does happen is when you put higher ratio gears in, your loading the car more, so when you romp on it, the higher load causes the RPMs to not climb as fast as the motor is working harder, so when the turbo does spool it will be at a lower RPM, since with lower gears, in that given time from when you romped on it, your RPMS may be a few hundred RPM higher.

So this is where there is the illusion of a faster spool, the turbo still spools the same, its just your bogging your motor down so when it does spool up its at a lower rev.

On the street it can feel like a huge difference, but when i get to thinking, how can a car pull HARDER when your reducing the torque multiplication through the drivetrain by putting a higher gear ratio in. Doesnt make sense. I am thinking the reason the cars feel faster is because your actually able to get traction and better utlilize your gears and such. (a hooking car feels/is quicker then a spinning one)

For example my car when i first put my turbo setup on, it had 3.90s, when i turned the boost up to 12 psi. the car couldnt get traction once the turbo spooled. until 4th gear, then it pulled crazy hard and then hit the rev limiter.

After gear swap I could actually use my gears down lower but it did lose pull on the top end. On the street no doubt the car runs better, its got enough, it helps to stretch the gearing out to actually accelerate the car real fast.
With the lower gears its pulls harder but once you hit your top gear your done.

Now at the track ASSUMING you can spool the turbo off the line, with a 2step or transbrake. Your going to pull off a faster time with the lower gear ratio you can get in the car assuming you have the ability to turn the RPM and not run out of gear.

Theres no magical thing going on causing a turbo car to pull harder with higher ratio gears, what happens with you put higher gears in a N/A car, it slows down, same with the turbo, its just power.... what you are affecting is the spool characteristics and can make the boost more usable.

On a street car, with limited traction on street tires, the higher gears are the ticket, better driving manners and just overall works good and can still bust off awesome times at the track.

If a pure drag car that gets awesome traction and assuming you dont have spool to worry about off the line, gear it as low as you can without running out of gear with your setup and RPM. that will net you the fastest times.


to the OP with mid 400s HP, id say 3.27s or 3.55s if its a street car. Just drive the car with the 3.73s and see how it feels, if its hooks up alright and works for your car, run that for a while. Dont just jump on the turbo high ratio gear bandwagon just because every other guy with a turbo runs em. Set your car up with what it likes.
 
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