3.73 on cobra jet - Mustang Evolution

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Old 04-23-2015, 06:13 AM   #1
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3.73 on cobra jet

I hope you don't mind the newbies posts
because sometimes i feel like one like for ever
I have installed a cobra jet intake m on my 2014 gt/cs auto trans
along with its cobra jet cai and dual 65 tb everything's was good
i had a discussion with my tuner over gears recommendation
And i wanted to confirm some details with you guys,
Its all started when i mentioned the 3.73 as a street common
and he said that 3.73 don't seem to fit with the cobra jet or boss intakes
showing me a file on his dyno projectors of someone who installed the cj intake
and had the 3.73 gears on, I've seen the lines going down at 7000 rpms
and losing hp , He said the 3.73 is wasting cj intake hp on both 4th gear and higher rpms,
In the end he told me to either stay with my 3.15 or go with a 3.55
i want confirm these thoughts especially with someone who tried this gears on cj or boss intakes.
Thanks for reading in my bad english
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Old 04-23-2015, 06:45 AM   #2
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3.31's or stay with 3.15's. No more gear than than that. What you should be looking at is a converter.
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Old 04-23-2015, 06:46 AM   #3
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Very interested to know the answer to this as well.

My question to you is will you be using the car at the high Rpm's. Isn't that setup making most it's power all the way to almost 8,000?


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Old 04-23-2015, 07:25 AM   #4
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Op, how have you liked the setup? Keep your gears and do converter if anything.
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Old 04-23-2015, 08:05 AM   #5
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Converter is where you need to be looking. BTW, if someone is dropping HP on a cobrajet pretty much anywhere in the powrband, the tune is off. Second, the car makes plenty of power before 8K, but you do need to rev it to about 7500 or so to really make it a beast. A lot of that has to do with the fall back point post shift though.
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Old 04-23-2015, 08:10 AM   #6
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Converter is where you need to be looking. BTW, if someone is dropping HP on a cobrajet pretty much anywhere in the powrband, the tune is off. Second, the car makes plenty of power before 8K, but you do need to rev it to about 7500 or so to really make it a beast. A lot of that has to do with the fall back point post shift though.

So stock engine safe to rev past 7000?


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Old 04-23-2015, 08:16 AM   #7
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mine went to 7500+ routinely. I also ran amsoil for what thats worth, and my engine / oil pump gears may very well have been knocking on deaths door, but no one ever answered.

I would not be nervous in the slightest about taking this motor to 7500, past that though it does get a little edgy haha, but mine went to 8k a few times for dyno and datalogging and didnt instantly blow apart. These are well put together motors.
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Old 04-23-2015, 08:25 AM   #8
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mine went to 7500+ routinely. I also ran amsoil for what thats worth, and my engine / oil pump gears may very well have been knocking on deaths door, but no one ever answered.

I would not be nervous in the slightest about taking this motor to 7500, past that though it does get a little edgy haha, but mine went to 8k a few times for dyno and datalogging and didnt instantly blow apart. These are well put together motors.

But assuming an individual with this setup had no intention of going past factory redline, would said individual be wasting his or hers money on this setup?


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Old 04-23-2015, 08:25 AM   #9
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I have my shift points at 7600. Anything less is a waste.
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Old 04-23-2015, 08:34 AM   #10
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Originally Posted by Just_Greg View Post
But assuming an individual with this setup had no intention of going past factory redline, would said individual be wasting his or hers money on this setup?


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Yes. The factory redline is only there because thats where the stock IM stops making power, its not from a safety standpoint. When you shift at higher rpms, you fall back at higher rpms, basically just riding out the high rpm benefit of the CJ. If you shift at low rpms, you'll basically see no benefit whatsoever.
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Old 04-23-2015, 08:46 AM   #11
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Thanks for all your help. I've read so many times that people recommend the boss im over the ford racing. So I was wondering why


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Old 04-23-2015, 08:48 AM   #12
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hmmm not sure why, the CJ loses less torque and gains more whp. It can really only be beat by the Boss in terms of cost, and thats just because the Boss will work with your current throttle body and intake. The IM's themselves are not much different in price. I did the math a while back, and assuming you put a CAI and throttle body on when doing your Boss IM (coming from stock) its only like $200-$300 more to just do a CJ from the get go.
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Old 04-23-2015, 09:42 AM   #13
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Thanks for all your help. I've read so many times that people recommend the boss im over the ford racing. So I was wondering why
Because the Boss Intake is cheaper and the CJ Intake hasn't proved to be any better than the Boss Intake at the track.
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Old 04-23-2015, 10:23 AM   #14
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Oh ok thanks both of you for your info


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Old 04-23-2015, 10:26 AM   #15
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Because the Boss Intake is cheaper and the CJ Intake hasn't proved to be any better than the Boss Intake at the track.
hmmm thats not true at all, i dont see any boss manifolds trapping in the mid 120s. Unless you're purely going off ET.
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Old 04-23-2015, 10:49 AM   #16
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hmmm thats not true at all, i dont see any boss manifolds trapping in the mid 120s. Unless you're purely going off ET.
Plenty of guys trapping mid 120's. One guy trapped 125 on the stock intake. Mine traps 122-123.
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Old 04-23-2015, 10:57 AM   #17
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All motor, no power adders. I'm willing to give some to the boss, but not the stock intake...
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Old 04-23-2015, 11:10 AM   #18
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My mistake. It was 124.46 trap speed. On the stock intake manifold. Built by JPC and driven by Justin Burcham owner of JPC Racing.

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Old 04-23-2015, 11:38 PM   #19
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3.31's or stay with 3.15's. No more gear than than that. What you should be looking at is a converter.
Good, i had the same thoughts with the 3.31's too
Very much appreciated.
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Old 04-23-2015, 11:43 PM   #20
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Op, how have you liked the setup? Keep your gears and do converter if anything.
Well first i had problems with the 65 tb
the car would just die after passing each road bump
or after revving the engine a little bit, with the rpm going down to 1000
and close to that rpm i felt the car was vulnerable to die
i got it fixed with a better throttle body tune letting more air in
below the 1000rpm, the car now runs fine without any issues.

On the setup
I noticed a big difference on 120-140 miles
but when rolling on low miles i get hard competitors
from gt's with better gears keeping up with me
until i reach my 4th gear then its a goodbye. lol

---------- Post added at 10:43 PM ---------- Previous post was at 10:43 PM ----------

I'm still waiting more replies
Thanks everyone for the feedback.
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