Hello all, New here.
Does anyone have any sugestions as to what rear end gears i should run in a 86 mustang dedicated to drag racing.
It has a 331 stroker, stock heads with bigger valve,1.6 roller rockers, victor junior intake, holley 750 douple pumper, msd ignition, 1 5/8 headman headers, powerglide trans and 373 gears.
The guy i bought the long block from said it dynoed at 437 hp and 467 tourqe?
My question is what size gears do you think i should be running.
I have not raced it in the 1/4 yet but in the 1/8th it has run consistant 8.5.
I have not realy paid attention to my trap RPM.
All help and sugestions would be appreciated.
Well, we need to know what RPM you are making power at. Dyno sheet would be best, but a SOTP feel of when your car stops pulling should tell you the max RPM you can get useable power out of.
With that Known, and your current trap RPM we can get a good educated answer.
Also, are you strictly sticking to 1/8th, or will you be running a 1/4. If so which one will you do most?
How are you on traction right now? You don't want to go low enough to have traction issues and hurt your 60' time.
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2006 Mustang GT in Torch Red
C&L Intake, Evolution Performance Tune, Borla Axle Backs, Hurst Shifter, 4.10's, JBA Long Tubes, Prothane Engine Mounts, Steeda UDPs, FRPP Charge Motion Delete Plates
Hey Guys,
Sorry for not responding to your replys. I have been out of town working.
I really have not paid attention to my trap RPM'S.
I am running 1.8 60' times.
Tires 26-10-15
dyno sheet said 6500 rpm
Stall speed 3500
i will mainly be running 1/4 mile, i have been testing on 1/8th mile because i can not hook up at 1/4 mile track on test and tune nights.
I appreciate the replys.
I would suggest starting with a 4:10 with those tires, and since you don't know your trap rpm. If you could find that out, we could fine tune the combo. You might need a 4:30, or maybe a 3:90. But 4:10 to start with.
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Thanks for the responses, I know im not maxed out at the trap, I think im somewhere around 5200 rpm. I will be out of town the next few weeks and am planing on taking it back to the 1/4 mile track to practice when i get back. I will repost then with trap RPM speed an ET.Again Thanks
Let me guess you go to lakeland dragstrip since you can't hook at bithlo right? Lol yeah it's pretty bad because of all the street cars that run out there.
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Single Cam Hatch
VTEC - All the lag of a turbo............None of the boost
If its Fast and reliable, it ain't cheap.
If its Cheap and reliable, it ain't fast.
If its Fast and cheap, it ain't reliable.
Even though I don't run an automatic, the same principles apply when considering traction and gear ratios, which is based on suspension. I run the Hotchkis suspension with 80/20 front shocks. If the car is used only on the strip 90/10 ratio will provide the best transfer rate to the rear, but are not the way to go if the car is street driven period.
There also quarter mile estimation software programs that will give you a ball park figure on trap speed, horsepower, and vehicle weight. I mention trap speed, because it will give you fairly accurate horsepower estimation if the vehicle weight is accurate.
Once you know the strap speed recorded on your time slip, you can use the following formula to get an approximation of the proper gear needed to maximize the car's ET.
MPH = (tire radius x RPM) / (168 x gear ratio)
Extrapolating the formula to determine gear ratio is as follows:
Gear ratio = (tire radius x RPM) / (MPH x 168)
Example 1:
Tire radius = 26/2
Trap speed RPM = 5500
Current Gear Ratio = 3.73
MPH = (13 x 5500) / (168 x 3.73) = 114.10 mph
Example 2:
Tire radius = 13
Trap speed RPM = 6000
¼ mile trap speed = 110 mph
Gear ratio = (13 x 6000) / (110 x 168) = 4.22
In this case the suggested gear ratio would be 4.10:1
Just for your info, most experts will state that dyno numbers are more realistic when comparing baseline runs against new additional performance enhancements; meaning as an example, did you get a 40 horsepower increase with the new after market performance heads? In fact, the horsepower ratings and quarter mile performance can be totally meaningless. As a prime example, my 1988 mustang was running 11.80’s at 118 mph, when atmospheric conditions were idea at the track altitude of 5800 ft. However, after switching to E85 and increasing the fuel delivery system to handle 1100 horsepower, the speed shop dyno readings were given as 240 hp, and 270 ft lbs of torque, and adjusted for sea level.
Prior to the changes, the car was not capable of pulling the front wheels off the ground, but now it can easily pull the front wheels in both first and second gear. In fact, I cannot apply the new nitrous system in the first two gears, because of how fast the car revs. You’ve already been given some good advice by other club members. I just that I would add my two cents worth of info and I hope it helps.
Good info ubie . Yeah bithlo is real hit and miss, I like to go there early and towards the fall-winter, when its summer that track jus turns to crap since it gets real greasy combined with the street cars tearing it all up. I suggest with what the dyno is saying I'd go with a 4.10 if you're goin to juice it one day if or 4.30's if you're goin to stay all motor.
__________________
Single Cam Hatch
VTEC - All the lag of a turbo............None of the boost
If its Fast and reliable, it ain't cheap.
If its Cheap and reliable, it ain't fast.
If its Fast and cheap, it ain't reliable.
Thanks for all of the advise. Next time out i will pay attention to everything you all sujested and hopefully can get this thing running low elevens like i should be. Again thanks for the help and will post my findings.
Thanks
Chris
Hi Chris,
I'm also new to this forum, and being the old gizzer that I am, I don't understand all of the lingo; such as bithlo. I do wish to pass as much knowledge to Ford drag racing enthusiast as possible. It doesn't make a lot of sense to re-invent the wheel. However, your main objective should be having fun and learning from what works for your car, and making incremental improvements. This will give you an idea of what works for your application and what doesn't. If you watch NHRA, then you know that the fastest ET doesn't mean you will win the round. So, the bottom line is to enjoy the adventure of legal drag racing, because many factors can determine the outcome of a race. And that is why, the race is run.
Ubie
For the rest of you Ford motor heads, being very new to this forum, I would appreciate someone giving me info on some of the lingo that is used in this forum. It's probably obvious that if I've been developing my Mustang over the past twenty years that I'm behind the times on the jargon that are clear to many of you. Also, I'm not clear on what specs are meaningful that many of you used as an indicator of performance changes based on your current ET's. In any event, the modifications to my '88 Mustang is so extensive that it would not be practical to provide all of the changes done over the past 20 years. So any info that will be beneficial to this forum would be helpful.
Best gears for drag racing a 1986 Mustang? 
. Yeah bithlo is real hit and miss, I like to go there early and towards the fall-winter, when its summer that track jus turns to crap since it gets real greasy combined with the street cars tearing it all up. I suggest with what the dyno is saying I'd go with a 4.10 if you're goin to juice it one day if or 4.30's if you're goin to stay all motor.
