Realistic Gains on a 2013 GT swapping from 2018 intake to Cobra Jet intake?

[palsmith]

I have a 2013 Brembo GT manual that I have driven and tracked since new. In 2021 I had a timing chain get loose and hurt motor while running at Barber (car had over 100,000 miles and several hundred road course laps). Installed a Frankenstein 3-2-1 long block that included L&M Gen 1 intake / exhaust cams and 2018 intake. I have stock exhaust manifolds and now have GT500 mufflers. Car made 426 rwhp @ 6900 rpm on a conservative tune at Palm Beach Dyno (and made 441 @7150 on E85) with stock GT mufflers. I recently bought a first generation Cobra Jet intake and was planning on getting a JLT intake and VMP twin 69mm throttle body. What is a realistic expectation for horsepower gains and potential torque loss?

 

[Mad Hatter]

To make it worth while you would probably need to have the Cobrajet ported. The castings are truly terrible with lots of rough edges and big gaps compared to the 2018 manifold. A 2018 will probably be slightly better the a unported stock Cobrajet, but check yours to see what it looks like.

Without getting headers, you would limit you power output somewhat as the engine has to breath.. Have to let those big 67mm TBs do their thing! With the 3-2-1 block, headers and the cobrajet setup and the rest of the bolt-ons you have, you could get to 500rwhp. At least that's what several of us have reached with 98 or E85 fuel.

In my case, I could not get gen2 heads for my Boss, so installed Livernois ported heads with the same valve's as the gen 2 etc. Non Boss Gen 1 heads suck.

Edit: Remember the Cobrajet makes great power to 8000rpm and beyond, if you dont plan on going that high maybe the 2018 manifold its a better option. High RPM wins races, but also kills all kinds of things (trannies, for example.)

 

[Wolf]

I know someone who just did this with their boss, 3-2-1 coyote with L&M intake and boss 302r exhaust cams, ported CJ intake and shorty headers (with cats)
Made 474 whp with a lund 91 tune
Definitely something I’d like to do down the road, I’m sure E85 would be right around 500 whp

 

[Mad Hatter]

Not to be too critical. But having the gen 3 block with its 12 to 1 compression is not going to be to happy with 91 octane fuel with a gen 2 head etc.. Am pretty sure a tuner like Shaun at AED would not tune the car for 91. A trip to the track on 91 could be very damaging!