Modifications guidance

[Mohamad]

Hello, I have 2015 gt mustang convertible and recently bought 2018 intake manifold ported, 47lb injectors along with roush air intake and roush axle back. I also bought suspension eibach with sway bars and soon changing my wheels and get wider tires (305’s rear 275 front). First question: Do I keep my throttle body stock? Or shall I get the 85mm bbk. I heard there are alot of issues with throttle bodies. Second question: how much HP on crank and/or whp do you guys think I’m making? An estimate would be fine. Do you think I can beat a shelby gt350R stock with my mods? (Keep in mind my exhaust system is all stock apart from roush axle back). Third Question: am I modding correctly? Will 47lb injectors hurt my engine or a perfect setup with my mods?

Thank you all for reading and answering

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[Ed M]

Are you installing a 12-point cage? Otherwise, no, never.

 

[Schwerin]

You're not even making Gen3 coyote power yet, let alone GT350. Your suspension is also WELL below the 350's. Injectors are pointless with your mods. Same for a throttle body.

Get yourself a full exhaust and proper dyno tune. Then you may be nearly GT350 power numbers. You'll have to shave some weight and do more than just springs/swaybars to handle like the 350.

 

[Mohamad]

You're not even making Gen3 coyote power yet, let alone GT350. Your suspension is also WELL below the 350's. Injectors are pointless with your mods. Same for a throttle body.

Get yourself a full exhaust and proper dyno tune. Then you may be nearly GT350 power numbers. You'll have to shave some weight and do more than just springs/swaybars to handle like the 350.

What if I’m upgrading my gear ratio to 3.73 and changing my tires to 305’s in back and 275’s front that way I’m full modded with stock exhaust, will that do anything? And why would injectors be useless? I’m getting extra air to engine and with injectors it will give that perfect combustion..

 

[Mohamad]

You're not even making Gen3 coyote power yet, let alone GT350. Your suspension is also WELL below the 350's. Injectors are pointless with your mods. Same for a throttle body.

Get yourself a full exhaust and proper dyno tune. Then you may be nearly GT350 power numbers. You'll have to shave some weight and do more than just springs/swaybars to handle like the 350.

Only problem is that I can’t upgrade my exhaust due to being illegal in where I live. Basically loud sounds is illegal and can’t upgrade exhaust

 

[Mohamad]

You're not even making Gen3 coyote power yet, let alone GT350. Your suspension is also WELL below the 350's. Injectors are pointless with your mods. Same for a throttle body.

Get yourself a full exhaust and proper dyno tune. Then you may be nearly GT350 power numbers. You'll have to shave some weight and do more than just springs/swaybars to handle like the 350.

My main goal is to get 3.9 sec 0-60mph

 

[Meatball]

In theory, and only based on a calculation using your stock numbers at 435hp, 3850 lbs (to be generous for a convertible) and a stock 0-60 of 4.7s, you’ll need about 525hp to hit 3.9s. That’s purely by power to weight ratio, which is extremely simplistic, holding everything else constant and ignoring traction issues etc., so may (does) not reflect reality. Coincidentally that’s almost exactly the same power as the GT350.

Unfortunately, I’ll bet you’re nowhere near that now. A full CAI, 87mm TB, higher rpm IM and (conservative) 91octane tune (= PP3 in North America) makes 472-478hp crank. You could free up a bit more with a more aggressive tune for higher octane gas but it’s a long stretch to 525 NA, esp with no other exhaust mods. It’s big $ but you’d (literally) blow past that goal with FI.

The other option is to sell and get a 18+ 10A GT coupe. Those are under 4s stock; not because of power to weight (460-470 crank) but because of the tranny and a power curve perfectly matched to it (flat near the power peak from 5500rpm to 7500, where the engine will live during a drag race).

But again that can be big $ and, if you’re like me, autos are just not as fun even if faster. Consider just enjoying your fast and live-able drop-top car now and don’t worry about chasing a car costing almost twice as much new with an unique and specially developed engine that won’t be matched by a Gen2 with simple bolt-ons.

 

[Mohamad]

In theory, and only based on a calculation using your stock numbers at 435hp, 3850 lbs (to be generous for a convertible) and a stock 0-60 of 4.7s, you’ll need about 525hp to hit 3.9s. That’s purely by power to weight ratio, which is extremely simplistic, holding everything else constant and ignoring traction issues etc., so may (does) not reflect reality. Coincidentally that’s almost exactly the same power as the GT350.

Unfortunately, I’ll bet you’re nowhere near that now. A full CAI, 87mm TB, higher rpm IM and (conservative) 91octane tune (= PP3 in North America) makes 472-478hp crank. You could free up a bit more with a more aggressive tune for higher octane gas but it’s a long stretch to 525 NA, esp with no other exhaust mods. It’s big $ but you’d (literally) blow past that goal with FI.

The other option is to sell and get a 18+ 10A GT coupe. Those are under 4s stock; not because of power to weight (460-470 crank) but because of the tranny and a power curve perfectly matched to it (flat near the power peak from 5500rpm to 7500, where the engine will live during a drag race).

But again that can be big $ and, if you’re like me, autos are just not as fun even if faster. Consider just enjoying your fast and live-able drop-top car now and don’t worry about chasing a car costing almost twice as much new with an unique and specially developed engine that won’t be matched by a Gen2 with simple bolt-ons.

I love your thinking, but I’m curious how is a gen 3 mustang (460hp) and my gen2 is 435 hp which is 25hp difference but gen3 can do a 3.9 sec stock. So I thought by just changing my stock manifold to 2018 manifold ported can achieve atleast 4.1-4.3 giving the fact my car is a convertible. I’m trying to find a way to go Full NA without exhaust mods since my city is similar to California with all the mods restriction.

That’s why I’m ready to do these simple bolts on mods like manifold upgrade, gear ratio upgrade from 3.55 to 3.73, suspension and sway bars, (shocks in future), 305’s 275’s tires, injectors LU47, (i was going to do throttle bodies but I heard they had issues with throttle bodies upgrade did a research on it and heard different reviews), (different LOK 8.8 in future).

I’m trying to challenge myself getting NA no exhaust system by being near shelby gt350R or same speed.

 

[Mohamad]

In theory, and only based on a calculation using your stock numbers at 435hp, 3850 lbs (to be generous for a convertible) and a stock 0-60 of 4.7s, you’ll need about 525hp to hit 3.9s. That’s purely by power to weight ratio, which is extremely simplistic, holding everything else constant and ignoring traction issues etc., so may (does) not reflect reality. Coincidentally that’s almost exactly the same power as the GT350.

Unfortunately, I’ll bet you’re nowhere near that now. A full CAI, 87mm TB, higher rpm IM and (conservative) 91octane tune (= PP3 in North America) makes 472-478hp crank. You could free up a bit more with a more aggressive tune for higher octane gas but it’s a long stretch to 525 NA, esp with no other exhaust mods. It’s big $ but you’d (literally) blow past that goal with FI.

The other option is to sell and get a 18+ 10A GT coupe. Those are under 4s stock; not because of power to weight (460-470 crank) but because of the tranny and a power curve perfectly matched to it (flat near the power peak from 5500rpm to 7500, where the engine will live during a drag race).

But again that can be big $ and, if you’re like me, autos are just not as fun even if faster. Consider just enjoying your fast and live-able drop-top car now and don’t worry about chasing a car costing almost twice as much new with an unique and specially developed engine that won’t be matched by a Gen2 with simple bolt-ons.

And for wait reduction, I’m removing my spare tire in the trunk only keep all factors the same

 

[Meatball]

And for wait reduction, I’m removing my spare tire in the trunk only keep all factors the same

The Gen3 hits 60 under 4s stock only with the 10 speed, because of the 10 speed. The manual is faster in the quarter than a Gen2, all other things being equal, commensurate with its 25-35 hp power increase, although to 60 that advantage is reduced by overly tall gearing.

The injectors won’t help at all unless you’re pushing a lot more air through (=FI). A better use of your money is a CAI, but that only adds a little. Honestly, you just aren’t going to reach a GT350 without mods that make it silly not to go FI instead. If that’s too expensive, don’t worry about it - enjoy your car now. If you’re obsessed with matching the Shelby, FI or selling and getting another cheaper car (eg 03-04 cobra, if available over there) that can be modded for those speeds is the only way. Making a 15-17 GT convertible that fast while staying NA with no substantial exhaust mods is just impractical. Enjoy your car for what it is!

 

[Mohamad]

The Gen3 hits 60 under 4s stock only with the 10 speed, because of the 10 speed. The manual is faster in the quarter than a Gen2, all other things being equal, commensurate with its 25-35 hp power increase, although to 60 that advantage is reduced by overly tall gearing.

The injectors won’t help at all unless you’re pushing a lot more air through (=FI). A better use of your money is a CAI, but that only adds a little. Honestly, you just aren’t going to reach a GT350 without mods that make it silly not to go FI instead. If that’s too expensive, don’t worry about it - enjoy your car now. If you’re obsessed with matching the Shelby, FI or selling and getting another cheaper car (eg 03-04 cobra, if available over there) that can be modded for those speeds is the only way. Making a 15-17 GT convertible that fast while staying NA with no substantial exhaust mods is just impractical. Enjoy your car for what it is!

I have got roush axle back and CAI already installed. Getting 2018 intake manifold 47LU injectors vmp tune 3.73 gear ratio new wheels and tires suspension and sway bars eibach.

Next: shocks, 8.8 differential LOK, and long future headers.
If I get headers and exhaust system I can reach a 3.9-4.1?

I understand impractically impossible without headers but if I had headers on will I still be able to reach 3.9-4.1? If it still be impossible then whatever lol. Forced Induction is a bit expensive where I live + taxes make it even more
Impossible. Mustangs in Dubai costs 2.5x mustangs in america. Which makes it equivalent to a shelby gt500 2020($77k) in america for a mustang GT in dubai and still be a bit more expensive in Dubai lol

 

[bluebeastsrt]

My main goal is to get 3.9 sec 0-60mph

If your main goal is 0-60. Get a drag radial or similar soft compound tire.

 

[Mohamad]

If your main goal is 0-60. Get a drag radial or similar soft compound tire.

That would definitely help get me 0-60 in fastest way but unfortunately I’m a street performance guy not a fan of tracks

 

[Bran2TheDon]

Did you make a bet with a 350 owner that you could beat him and you come to the forum to ask for input?

 

[Mohamad]

Did you make a bet with a 350 owner that you could beat him and you come to the forum to ask for input?

Not with a 350 nope, with a 2015 hellcat actually

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