Drivetrain Which First Gear To Go With?

[FastDriver]

I'm currently doing all the reading and searching I can to determine the optimal Gear/Tire/transmission ratios to run in Man o' War (see sig). I anticipate power to be in the high 900s to low 1000s at the wheels. I believe I'll cross the traps in possibly the high 150s, and since my car makes peak power at 6300 RPM, I'd like to cross no higher than ~7000 RPM. Besides, I believe I'll be pushing the hydraulic valve train parts pretty hard any higher, and I have the limiter set to 7200. So, a 3.60 rear gear, and a 28" tire should put me through the traps at 6800 RPM at 157mph (a guess). A 3.70 gear set would be crossing the line at around 7k at the same speed, which leaves too little room to run out the traps; it's an average over the last 66'.

I'm in a grey area regarding which 1-4 gear set to use with the T56. The two options are the 2.71/1.79/1.3/1 gear set, and the 2.98/1.99/1.35/1 gear set. I am simultaneously concerned that I will bog with the 2.71 ratio and that I might blow through either gear set in 1st once the turbo spools.

One advantage with the 2.71 gear set is that if I ever run 1/8 mile, I should be able to finish the 1/8 mile in 3rd gear. It seems like reducing rwtq and extending 1st gear is a good idea, as long as the motor doesn't bog, but as you can see, even with 3.60 gears, the numerically low tranny ratio, and the 28" tires allow me to go ~60mph by 7k RPM (my motor's redline).

Here's the comparison between the two. Ignore the performance figures, as 60' times are manually input and may not be accurate.
2.71 gear set

2.98 gear set

 

[jrichker]

You are running pressurized induction, and a turbo at that, You will have an excess amount of low end torque to try to communicate to the pavement. That means your best results will be with a 2.71 gear set to limit the torque multiplication. With proper traction aids and setup, that should put the torque at the tires in a range for best grip and maximum acceleration. Too much 1st gear will smoke the tires all the way through 1st and into 2nd.

 

[FastDriver]

Well, there are some numerically lower 1st gear ratios that g-force can put in, like the 2.62 and 2.29. If I go with too tall a 1st gear, eventually the car will bog and potentially lose the ability to spool off of the line, even with a 2-step.

I'm in agreement with you about smoking the tires. I'm just concerned that a 331 isn't going to make a ton of torque off of the line.

 

[A5literMan]

You should have plenty of torque IMO. You may potentially have to run a higher launch rpm to get the wheel speed up to keep from bogging but I would run that 2.71 or 2.62 gear. I don't think a bog is likely anyways. Now with a 2.29...I'm less confident. With your suspension/tires I don't think you'll blow the tires off with either of those gear sets but it's just my opinion based on a few racers I know locally.

 

[jrichker]

The turbocharged cars typically have a broad, flat torque curve that starts low and climbs a little until just before peak HP. I haven't seen the dyno sheet from your setup, so I can only guess what the torque curve looks like. Posting your dyno sheet, or a link to where you may have previously posted it would be very helpful.

A wild guess tells me that by 2200-2500 RPM the torque curve looks pretty healthy. Pull up to the starting line, rev to 1800-2100 RPM and let out on the clutch, hard as you floor the accelerator. The rear tires should break loose a little and the RPMs rise into the range where the torque curve looks really good. Then the tires hook hard as the weight shift and traction assist that you have tuned into the suspension begins to work. If you did you suspension & tire tune correctly, you probably will need some wheelie bars to keep things under control.

 

[7991LXnSHO]

I can not answer your question, but have one. Will that tranny support 1000 hp?

 

[FastDriver]

Here's the first dyno. It's unfortunate that I don't seem to have the 2nd dyno which showed the curve from about 3000RPM on up to 7k.

Anyway, the turbo spools around 3300-3500 if memory serves. I'll probably be launching on a 2-step from in neighborhood of $5k RPM. Keep in mind that until now, I have not had a tough enough drive train to set the turbo on kill. I felt like even at the power limit below, I was pretty hard on the TKO (rated at 450 ft-lbs), and the 28 spline 8.8" rear end. I kept it on 275/40/17 MT DRs and fortunately didn't blow anything up.

I can not answer your question, but have one. Will that tranny support 1000 hp?

Yes. At least, it should. Guys have broken them with less, and others have made more with them. It's the same gearset used by rockland standard gear's "Tranzilla," which is rated at 1200hp and 1000 ft-lbs of torque. I'm going to drive it however I want to, including powershifting if I get the urge. If it blows up, I may switch over to the T56 Magnum since it's cheaper. Either way, I'll be reporting back.

 

[FastDriver]

Well, gosh! I'm disappointed to report that I was wrong about the 3.60s. It turns out that the only 3.60 gear set available for the Ford 9" is a Richmond Pro Gear that is race only, and apparently not well-suited to the street. Couple that with the fact that Richmond is well known for having whiney gears, and the fact that these particular gears are more than $400, and I'm out! Looks like I'll be going with 3.70s. I'd still prefer a bit lower of a gear, but the next street gear that I could find were 3.50s, which further hurts my SLR, and brings me down a bit too low an RPM at the traps. With the 3.70s, I should be fine, though. I can still hit the 1320' stripe at 162mph. If I ever need to go faster, I'll have to swap the gears out.

On the bright side, bumping up to the 3.70s makes the case even stronger to drop to the 2.71 1st gear. This is probably going to work out for the best since I don't expect to see 160mph with my current turbo. Maybe one day it will go faster, but I always have the option of buying another center section for the strip with a spool and better gearing, or swapping out the 3.70s.

 

[cfauvel]

Well you guys seem to know what you are talking about....would you be so kind as to look at my post and make suggestions? I am not in your league, but would love to hear what you all think.

based on my T5 first gear being 3.35:1, I think the 3.70 or 3.75 rear gear ratio would be too much now....maybe a 3.50 rear gear?

Suggestions for rear diff gears - 1969 Mach 351W 4v

My Mach 1 was born with a 3spd TopLoader and 3.00:1 open diff (not going to lie ...that combo sucked) A while back I swapped in a 1993 or so Tremec T5 (I love it BTW) , but the performance is still pretty low....so this year I am going to get a whole complete center section for my 9" rear...

stangnet.com

 

[limp]

Well you guys seem to know what you are talking about....would you be so kind as to look at my post and make suggestions? I am not in your league, but would love to hear what you all think.

based on my T5 first gear being 3.35:1, I think the 3.70 or 3.75 rear gear ratio would be too much now....maybe a 3.50 rear gear?

Suggestions for rear diff gears - 1969 Mach 351W 4v

My Mach 1 was born with a 3spd TopLoader and 3.00:1 open diff (not going to lie ...that combo sucked) A while back I swapped in a 1993 or so Tremec T5 (I love it BTW) , but the performance is still pretty low....so this year I am going to get a whole complete center section for my 9" rear...

stangnet.com

What do you want to do with your car??
The low first gear in your transmission was designed to accomodate a higher rear end ratio for better fuel mileage..... 2.73 or a 3.08 is the ratio designed for your trans. If you want to go to a lower rear end ratio, say a 3.50 or 3.73 you will be out of first gear quickly...

As I said what are you wanting from your car??

 

[cfauvel]

What do you want to do with your car??
The low first gear in your transmission was designed to accomodate a higher rear end ratio for better fuel mileage..... 2.73 or a 3.08 is the ratio designed for your trans. If you want to go to a lower rear end ratio, say a 3.50 or 3.73 you will be out of first gear quickly...

As I said what are you wanting from your car??

I don't want to hijack this thread, but basically better 0-60 times , something that can beat a Honda Odyssey(super embarrassing) from 0-60 ...not looking for low 1/4 mile speed or high top end....it's a stock show car.

Based on my calculations I'd be at 20mph at 3000 rpm in first gear with a 3.50 in my 9" rear end
18mph with a 3.75

Just looked up my original 3spd toploader's gears and 1st was either 2,42:1 or 2.99:1 (not sure if I had a CLOSE or WIDE)

 

[limp]

There is no thread to hi jack, its 10 years old

 

[cfauvel]

There is no thread to hi jack, its 10 years old

LOL ....didn't notice that.

But COULD jump over to my thread in the older mustang section?

 

[FastDriver]

Hijack away. I was the OP.

 

[cfauvel]

Hijack away. I was the OP.

....so what do you think? 3.25, 3.50, 3.70 or 3.75 given that I have a 1990 T5 with a 3.35 1st gear.

note: my 351w 4v is stock with a .030 oversized rebuild in 1989. so very low on actual HP at the rear wheels.

 

[FastDriver]

What's redline? Any idea what your trap speed is? Ever dyno'd or have an estimate of the power (the actual curve would be more helpful)?

BTW, pick your tire before you pick your gear. Your 2 suggestions are hugely different. The tire size difference would account for 1 step in rear gear (3.55 vs. 3.27, or 4.10s vs. 3.73s).

In what order would you prioritize:
- 1/4 mi performance
- Comfortable highway cruising RPM
- Off the line launch ability?

My vote based on some guesses would be:

So, I prioritized a balance of performance vs. reasonable cruise RPM, assumed a 6000 RPM redline, and your eventual preference of 225/70/14 tires. The column under "RPM input" tells you your speed at redline (6k) in each gear. The red/orange column under "MPH input" shows the RPM in each gear at 75 mph. So, looks like you'd be taching 2,400 on the highway.

Assuming your car makes 300 rwhp or less, you are not close to optimal for 1/4 mi. with this setup, because this setup would be optimal for a car that runs 126mph-ish through the traps. I have no idea where you are, but based on your hypothetical against a Honda Odyssey, you'd probably struggle to break 100mph in the 1/4. So, if you wanted to optimize the launch & the 1/4 over highway cruising, then 4.30s would probably be about right.

When it comes to performance, "don't fear the gear." If you want a nice car that will cruise alright on the highway, maybe a tad high, but will also come off the line nicely and do alright on the 1/4, then 3.73s are my vote.

Answer some of the early questions and we can home in on the right gear for you.

 

[Noobz347]

 

[FastDriver]

Yeah... Just mathematical. Don't do 75mph in 1st gear!

And... sorry @cfauvel , I'm used to thinking in terms of 8.8 gear ratios. But 3.70 vs 3.73s or 3.50 vs. 3.55 are imperceptible differences.

 

[cfauvel]

1. Off the line launch ability.
2. Comfortable highway cruising RPM
3. Beating a Mini-van off the light

Those are my priorities....

I will definitely go back to the 225/70r14 tires in the near future

RWHP of a stock 351w 4v seems to be about 175 if you're lucky (I suspect I'm not lucky )
I think redline for a stock 351w is about 5500 rpm

Indeed in stock form the Mach1 with a 351w ran the 1/4 mile at 86 mph close to 16 seconds.

I don't typically take the car out on 1-75 or the like as the potential for a wreck is pretty high....it is mostly a show car, and the occasional off the line, speed away until the speed limit (or slightly above )

I have a 2005 350z that I love, with a 6 speed manual and the ratios are as follows
1 - 3.79
2 - 2.32
3 - 1.62
4 - 1.27
5 - 1
6 - .79

rear diff ratio 3.45

seeing that what I am used to in the Z has a fist gear effective ratio of 13.0755....I might NOT "fear the gear" and opt for the 3.75 which would get me a 1st gear effective ratio of 12.56....which is STILL lower than the Z, and the Z has less OverDrive.

I "think" my speedo gear in the T5 is a 7 tooth, but don't know for sure...I have to remove the speedo cable and borescope it and hopefully figure out the color of the speedo gear.

Thanks for your time....sorry it is such a low HP engine we are talking about.

 

[FastDriver]

It should be an 8 tooth if it's from a 90 5.0.

Are you trying to keep it original? A 351W at your power level has gobs of potential waiting to be unlocked. The right parts would more than double that power. 300+ at the wheels is a pretty easy. Smoke the mini-van & the 350.

If you're going through the trouble of swapping gears, have you considered adding a trac-loc diff?