Help Me Pick Gears For My Supercharged 2v

JymboSlice

Member
Dec 9, 2008
385
0
17
Hey, i have a built and supercharged 2v mustang and im in need of gears. I currently have 4.10's but i want to switch it up because my first gear is useless.

So my options are FRPP's 3.73 or 3.55 gears.

Mods are:

Trick flow heads
Stage II comp cams (Between a stage 2 and 2.5 MHS cam)
P51 intake
Full slp exhaust
Built motor
Intercooled Novi 2k ~18-22 psi of boost
Return style fuel system
E85
Stock Tr3650 (Soon to be built when it goes)

Tires are 335/30/18's. I may switch to a 325/50/15, 275/50/15, or 275/60/15 rear tire to go with a 15in wheel. I know that 28" tall tires help the most with the steeper gears.

I do not want to shift into 5th at the end of the quarter mile.

Which one would you choose?

Thanks
 
  • Sponsors(?)


Maxpowers

Member
Sep 9, 2009
859
2
19
Pittsburgh, Pa
I've heard many people complaint about not having a low enough gear with the centri blowers. I would recommend getting a stickier and taller tire to fix the problem.
 

usaf_branham

10 Year Member
Oct 30, 2008
926
134
74
Vegas
if your going to change gears, go with 3.73

I dropped from 4.10 to 3.73 and overall I am happy... The car is alot more 'tame' in terms of driveability. With the 4.10's it was real snappy, just a lil bit of gas would make the car lurch, and 1st gear was pretty much useless...

dont get me wrong, i miss my 4.10's... the car was a blast to drive on the street, but I was runnning out of gear in the quarter. As a matter of fact, I would have been happier with 3.90's for my current setup.
 

trinity_gt

10 Year Member
Jan 31, 2003
3,125
80
99
Canada
I agree with sneaky: We need more info.

I did some back-of-the-napkin calcs. I assumed a 25.9" tire diameter, a trap speed of 115MPH and a redline of 6000RPM. Going through in 4th gear (1:1) would require a theoretical gear ratio of 4.02:1.

3.73s would have you at roughly 5600RPM. 3.90s would be at about 5800.

Don't know if these are close to your requirements but it should give you an idea...
 

Winters98GT

Whoop...whoop-whoop-whoop-whoop...GANGNAM STYLE!!!
Founding Member
Nov 29, 1999
5,520
1,291
224
H Town
Car should make 700rwhp. I'd go with a 28inch tall tire and a 3.55 gear.
 

JymboSlice

Member
Dec 9, 2008
385
0
17
Im shooting for 600 rwhp.. if it makes 700 id be more than pleased. Never drag raced it before, first time i will when i get it all together. Tuner and a bunch of other people said it would be about a 6500-6700 rpm redline as well.

I want to use as close to a 28" tire as possible.

Hope this other info helps, leaning more towards a 3.55 gear ratio. I would hope my trap speed is more than 115mph too.
 

Winters98GT

Whoop...whoop-whoop-whoop-whoop...GANGNAM STYLE!!!
Founding Member
Nov 29, 1999
5,520
1,291
224
H Town
Im shooting for 600 rwhp.. if it makes 700 id be more than pleased. Never drag raced it before, first time i will when i get it all together. Tuner and a bunch of other people said it would be about a 6500-6700 rpm redline as well.

I want to use as close to a 28" tire as possible.

Hope this other info helps, leaning more towards a 3.55 gear ratio. I would hope my trap speed is more than 115mph too.
You're going to trap in the low 130's minimum with that setup. Even in full street weight. 18-22psi is a lot of power through a built motor with heads/cams. Just for perspective, my 402 CI motor will make about 900-925rwhp at 15psi with the same blower you have(maxing out the blower, got sponsored by paxton and it is sitting in my living room). That 281CI with those heads and cam at 4-6psi more should easily make way over 600rwhp. That is 130's for sure. I would guess the car ends up trapping 135mph-140mph.
 

trinity_gt

10 Year Member
Jan 31, 2003
3,125
80
99
Canada
Okay, so now you're on 28" tall tires and, assuming because you still haven't actually specified a redline number, a 7000RPM redline on your "built motor": With a 135MPH trap speed you could have 4.30s in the rear with the engine just touching redline in 4th gear.

You're going to need a tougher gearbox than a '3650...
 

Winters98GT

Whoop...whoop-whoop-whoop-whoop...GANGNAM STYLE!!!
Founding Member
Nov 29, 1999
5,520
1,291
224
H Town
Okay, so now you're on 28" tall tires and, assuming because you still haven't actually specified a redline number, a 7000RPM redline on your "built motor": With a 135MPH trap speed you could have 4.30s in the rear with the engine just touching redline in 4th gear.

You're going to need a tougher gearbox than a '3650...
Good post. I think you would know a lot more about the 3650 than I do. I run a stock 6060, and at 800-1000hp(crank), it is now giving me problems after 10k and 30 passes and 100 mexico runs.

I would listen to what the guys have to say about the tranny. I have not calculated your mph at the top of 4th with your gearing(3.55-4.30) at a certain MPH, but if Trinity or yourself could, that would be extremely helpful.

Also remember, if you ever do any street pulls, as fast as your car is, game is over if you run out of gear. I run a [email protected] with my gear in 4th, but my car does 172mph in the same gear, so I am not geared for the 1/4 in anyway. I could probably run a 9.4 with a better gear, but once you get to a certain power level, you want a gear that will run a big MPH if you ever choose to(which I do weekly on the street). Your car is going to be extremely fast, so gear choice isn't going to be as much of a deciding factor IMO
 

trinity_gt

10 Year Member
Jan 31, 2003
3,125
80
99
Canada
I would listen to what the guys have to say about the tranny. I have not calculated your mph at the top of 4th with your gearing(3.55-4.30) at a certain MPH, but if Trinity or yourself could, that would be extremely helpful.
In general, the relationship between speed and RPM for a 4th gear of 1:1 can be summarized as follows:

EngineRPM = (AxleRatio * MPH * 336.135) / TireDiameter

where

- AxleRatio is, well, the ratio of the rear axle (e.g. 4.30)
- MPH is the vehicle speed
- 336.135 is a constant
- TireDiameter is the height of the tire in inches

You can also re-arrange to solve for other terms:

MPH = (EngineRPM * TireDiameter) / (AxleRatio * 336.135)

AxleRatio = (EngineRPM * TireDiameter) / (MPH * 336.135)

Just plug in your numbers as required to get the desired output.

Again, this is for a 1:1 (4th) gear. If you choose another trans ratio you'll need to add a term to the equations.
 

JymboSlice

Member
Dec 9, 2008
385
0
17
Okay, so now you're on 28" tall tires and, assuming because you still haven't actually specified a redline number, a 7000RPM redline on your "built motor": With a 135MPH trap speed you could have 4.30s in the rear with the engine just touching redline in 4th gear.

You're going to need a tougher gearbox than a '3650...
I said in the previous post that it will be a 6500-6700 rpm redline. And the "Built motor" is a MMR street mod 1000 rotating assembly and a teksid block.

I just did your formula and used: (3.73 X 131(Est, according to winters prediction) X 336.135) / tire diameter (28in). I got about 5900 rpm's.

I just plugged a few numbers into the formula, i got all under 6300, realistically. 27" tire-28" tire. all with 3.73 rear gears and i used a higher 135mph trap speed.

but once you get to a certain power level, you want a gear that will run a big MPH if you ever choose to(which I do weekly on the street).

this is what I would like ^. But not on the street, haha. I'm not a big street racer, too afraid of getting caught.

Even with the 3.55's: (3.55 X 135 X 336.135) X 27" = 5966 rpm's. Thats with a smaller tire that i will be running too and a higher trap speed.

I only would like the 3650 to survive my dyno session, i would love to just get this thing running perfectly first then build the trans. 800-1000 flywheel horsepower for 10k miles and about 30 passes is pretty respectable for a stock 6060. I wish ford put that trans into the 2011-13 5.0's.

Thank you for the reply's, very much appreciated!
 

sneaky98gt

10 Year Member
Apr 23, 2008
2,387
144
114
NC State University
I've actually got a racing calculator built in Excel that includes all the gearing stuff. After entering your constants (rear gear, transmission gear, and tire height), you can calculate either the speed at an RPM or the RPM at a speed.

You can also enter your torque data from the dyno chart, gearing info, and shift points, and it'll graph the torque on the wheels (which is exactly correlated to how 'fast' your car is). Plus, you can do this with two different vehicles, making it easy to compare two vehicles.

For example, here's the graph of the torque on the wheels of a new Boss 302 vs. a Terminator (Boss in blue).

coyotevsterminatorwheel.jpg

And you can see why a new Boss runs better than the Terminators do....

If anyone wants that calculator, PM me your email and I'll send it to you (unless someone knows how to post it up here).


And back on topic. Here's a little chart I made with the gears/rpms/speeds.

7000 rpm, 25.66" tire
Rear gear--------4th Gear Speed------RPM to go 180 mph in 5th
3.27--------------------163-----------------------4780
3.55--------------------151-----------------------5190
3.73--------------------143-----------------------5452
3.90--------------------137-----------------------5700

7000 rpm, 27" tire
Rear Gear-------4th Gear Speed------RPM to go 180 mph in 5th
3.27--------------------172-----------------------4543
3.55--------------------158-----------------------4932
3.73--------------------151-----------------------5182
3.90--------------------144-----------------------5418
4.10--------------------137 -----------------------5696

7000 rpm, 28" tire
Rear Gear------4th Gear Speed------RPM to go 180 mph in 5th
3.27--------------------178-----------------------4380
3.55--------------------164-----------------------4756
3.73--------------------156-----------------------4997
3.90--------------------150-----------------------5225
4.10--------------------142-----------------------5493
4.30--------------------136-----------------------5761


This is assuming the stock 3650 gear ratios. As you can see, it entirely depends on what tire you plan on running on the street vs. at the track, whether you want to shift to 5th or not, how fast you want to go on the street (I assumed 180, although I hope you aren't planning on doing that fast....), etc, etc. BUT, this should give you the info you need.

This also illustrates a good reason why a 6-speed tranny with a gear between 1:1 and OD would be nice. If that were the case, the top of 4th would be good for the track, and the top of 5th would be perfect for some Mexico runs.
 
Thread starter Similar threads Forum Replies Date
Blueharry Need Help picking a New springs and shock! 1996 - 2004 SN95 Mustang -General/Talk- 0
Rynb15 Picked up an 85gt, need help with year of motor in car/firing order 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 4
F Help picking a Mustang(65-69) 1965 - 1973 Classic Mustangs -General/Talk- 14
Bion1985 SN95 Need Help Picking Wheel Spacer Size 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 2
ras50gt Edelbrock Or Vmp Supercharger? Help Me Pick 2005 - 2014 S-197 Mustang -General/Talk- 0
T Help Picking Out A External Fuel Pump Fox 5.0 Mustang Tech 2
C Dream's Finally Here : Help Me Pick My Shelby 2005 - 2014 S-197 Mustang -General/Talk- 3
F Help Picking A Cam 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 8
F Help Me Pick A Nice Car Under 4k 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 36
tannerc91gt Engine Help Me Pick New Valve Springs Fox 5.0 Mustang Tech 2
At1Maverick69 Need help picking Special Production 2
T help me pick a camshaft Fox 5.0 Mustang Tech 2
robertdeuce two new options, help me pick please 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 0
T Help Me Pick My Combo (HCI etc) 1994 - 1995 Specific Tech 7
9 help with picking a clutch Fox 5.0 Mustang Tech 11
robertdeuce help me pick a shifter...with options! 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 47
D help picking exhaust please 2005 - 2014 S-197 Mustang -General/Talk- 17
S Please help me pick 15" wheels for track SN95 4.6L Mustang Tech 5
SaleenGT2001 help me pick rims for my 2011 1996 - 2004 SN95 Mustang -General/Talk- 29
bdazzgt HELP ME PICK the COLOR of my car 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 21
TwoToneHatch Need Help Picking Out Springs! Fox 5.0 Mustang Tech 3
D help picking a roush supercharger... 2005 - 2014 S-197 Mustang -General/Talk- 7
F Help Picking Out Gauges and Instrument Bezel for My '65 Classic Mustang Specific Tech 10
M Need help picking a clutch Fox 5.0 Mustang Tech 1
madspeed picked up a car, help with CODES Fox 5.0 Mustang Tech 1
R Help picking heads Fox 5.0 Mustang Tech 5
R help me pick my cams SN95 4.6L Mustang Tech 7
MY 85 GT Need help picking an amp? Mustang Sound & Shine All 6
G Help me pick my Heads/Cam/Intake combo 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 10
281pony Help me pick my new wheels.. Notch 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 40
Jaym14 Help me pick suspension upgrades 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 6
svtboy91 HELP PICKING A SET OF HEADS Fox 5.0 Mustang Tech 9
T help picking out a cam 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 11
nisreo help me pick a cam Fox 5.0 Mustang Tech 14
9 please look at this pick and help me what the problem is here. 1994 - 1995 Specific Tech 33
CrawlinSlo5.0 Need help picking a carb! Fox 5.0 Mustang Tech 5
03s281sc help me pick a tranny!! SN95 4.6L Mustang Tech 6
Trboh22 Help identifying Engine and picking cam Fox 5.0 Mustang Tech 5
R Some help on picking a color for your car Mustang Sound & Shine All 0
P Help me pick an exhaust 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 44
FrankenStang Help me pick a Co-Admin... 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 35
LaserSVT Help pick my next toy! 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 33
T Help me pick Slicks 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 17
T Help me pick a front suspension setup... Fox 5.0 Mustang Tech 4
P Need Help Picking Long Block Classic Mustang Specific Tech 16
maxine-70 help me pick 351 or 393 Fox 5.0 Mustang Tech 44
TrickFlowd Help me pick out lowering springs... 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 28
89hatchlx Need help with picking aluminum or steel?? Fox 5.0 Mustang Tech 16
B Need help picking out hood 1996 - 2004 SN95 Mustang -General/Talk- 35
glowstang93 Need help picking plates for DD 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 5
Similar threads