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Discussion Starter #1
Hello,

I have a 14 Gen Coupe 3.8 RSpec. I'm looking to swap my final drive to a 4.18. there might be a forum i missed, but i looked around and haven't seen someone talk about there actual personal experience with it. I was considering a 3.909 as well so if you did that please say how you like it and why you chose it. To be honest my goal currently with the car is to make it beat a 5.0 while staying NA and not completely gutting out my interior. not sure if that's possible but i guess we will see.
 

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Hello,

I have a 14 Gen Coupe 3.8 RSpec. I'm looking to swap my final drive to a 4.18. there might be a forum i missed, but i looked around and haven't seen someone talk about there actual personal experience with it. I was considering a 3.909 as well so if you did that please say how you like it and why you chose it. To be honest my goal currently with the car is to make it beat a 5.0 while staying NA and not completely gutting out my interior. not sure if that's possible but i guess we will see.
I think the 2010 auto 2.0 (maybe 2011 as well) had a 4.xx diff.
 

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I thought the BK1 auto 2.0 had the highest ratio

this is what I found.

bk1 auto 2.0
4.81:1 (which seems wrong to me. Might have been a typo, but I found the same number on more than one site)

bk2 auto 2.0
4.18:1

I have a bk1 auto 2.0. I'll check after work.
 

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shorttrack
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I have a 2014 R-Spec with 3:909.1 with many mods ,running sticky when hot 285 35 19 Potenza RE71 r tires (with nitrous oxide) .Am switching to 305 35 18 ( need more traction on the streets),I flared my rear fender arches with a fender roller tool .Will be going to 4:18.1 Gears for more acceleration out the hole on motor and on N2O .If running small 275 35 19's ,go with the 3:909.1 gear set .
 

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Hello,

I have a 14 Gen Coupe 3.8 RSpec. I'm looking to swap my final drive to a 4.18. there might be a forum i missed, but i looked around and haven't seen someone talk about there actual personal experience with it. I was considering a 3.909 as well so if you did that please say how you like it and why you chose it. To be honest my goal currently with the car is to make it beat a 5.0 while staying NA and not completely gutting out my interior. not sure if that's possible but i guess we will see.
You need to be more specific what you say, "5.0"...yes, I know you are referring to a Mustang but what year and model? If you are talking about an '18 or '19, no 3.8 NA Gen will beat it.
 

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shorttrack
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You need to be more specific what you say, "5.0"...yes, I know you are referring to a Mustang but what year and model? If you are talking about an '18 or '19, no 3.8 NA Gen will beat it.
I agree ,the 5.0 with new 10 speed automatic tranny is a fast @ss a mother F'er .
 

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Discussion Starter #9
I have a 2014(with nitrous oxide) .Am switching to 305 35 18 ( need more traction on the streets),I flared my rear fender arches with a fender roller tool .Will be going to 4:18.1 Gears for more acceleration out the hole on motor and on N2O .If running small 275 35 19's ,go with the 3:909.1 gear set .
I have the hankook ventus v12 evo2 tires with 275/30/19 in the rear. they stick well with the stock power, but i dont know how good they will be with more torque. how many shots of N2O do you run?
 

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Discussion Starter #10
You need to be more specific what you say, "5.0"...yes, I know you are referring to a Mustang but what year and model? If you are talking about an '18 or '19, no 3.8 NA Gen will beat it.
Yeah they are fast, what about '14 '15? or maybe even a '16? I got a friend with a 2010 camaro ss that makes about 500 hp. not sure if thats wheel or crank. I guess my question here is how fast can you make the genesis coupe while staying NA?
 

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I have the hankook ventus v12 evo2 tires with 275/30/19 in the rear. they stick well with the stock power, but i dont know how good they will be with more torque. how many shots of N2O do you run?
You will need something much stickier then the evo2s with shots of N2O. If you are dragging, go with the RE71s. For road handling, go with the Michelin Pilot Sport 4Ss.
 

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Discussion Starter #12
You will need something much stickier then the evo2s with shots of N2O. If you are dragging, go with the RE71s. For road handling, go with the Michelin Pilot Sport 4Ss.
I don't plan on running N2O anytime soon. That would be one of the later mods. Also i don't plan on dragging it, maybe just some highway pulls or from a red light.
 

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Yeah they are fast, what about '14 '15? or maybe even a '16? I got a friend with a 2010 camaro ss that makes about 500 hp. not sure if thats wheel or crank. I guess my question here is how fast can you make the genesis coupe while staying NA?
The 14 5.0 is around 425/400 and the 15/16 5.0s are a tad higher, maybe around 440/425 (I am going off memory). The stock 2010 6.2 Camaro is in the same ballpark, give or take. You would have to absolutely max out the NA 3.8 Genny to try and keep up with the aforementioned Americans (not sure it would truly be possible). If racing on the track or street racing anything, the human behind the wheel plays a big role...
 

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Discussion Starter #14
The 14 5.0 is around 425/400 and the 15/16 5.0s are a tad higher, maybe around 440/425 (I am going off memory). The stock 2010 6.2 Camaro is in the same ballpark, give or take. You would have to absolutely max out the NA 3.8 Genny to try and keep up with the aforementioned Americans (not sure it would truly be possible). If racing on the track or street racing anything, the human behind the wheel plays a big role...
Yeah i won't be able to beat them with power which is why i am trying to get creative.
 

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I thought the BK1 auto 2.0 had the highest ratio

this is what I found.

bk1 auto 2.0
4.81:1 (which seems wrong to me. Might have been a typo, but I found the same number on more than one site)

bk2 auto 2.0
4.18:1

I have a bk1 auto 2.0. I'll check after work.
I have to think that the 4.81:1 figure was a typo and someone else quoted the typo.
 

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Yeah i won't be able to beat them with power which is why i am trying to get creative.
I would focus on as much of the safe mods as possible: intake, exhaust (not a muffler delete), manifold riser (will need coolant bypass or new extended hosing), 3.90 or 4.11/18 diff gear and shed some weight (ditch as much exterior metal as possible for carbon fiber, remove the back seat (its really not functional for an adult anyway), forged aluminum rims). When all engine mods are done, you will need a custom tune, not a canned tune. I suggest reaching out to Norman at Alphaspeed for the tune.
 

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Discussion Starter #17
I would focus on as much of the safe mods as possible: intake, exhaust (not a muffler delete), manifold riser (will need coolant bypass or new extended hosing), 3.90 or 4.11/18 diff gear and shed some weight (ditch as much exterior metal as possible for carbon fiber, remove the back seat (its really not functional for an adult anyway), forged aluminum rims). When all engine mods are done, you will need a custom tune, not a canned tune. I suggest reaching out to Norman at Alphaspeed for the tune.
ok, appreciate the help. what is a good sounding exhaust? I have muffler delete and love the way it sounds, but I'm nervous to get an actual exhaust and not enjoy the sound of it. Also I just ordered some ARK headers, ARK down pipes, engine leash, lightweight pulley set, and CNT test pipes. I'm looking to get a manifold spacer next. I assume i will need to upgrade my clutch soon as well so i'm trying to decide which one to get. I've heard clutch masters is good, but i don't know how i feel about paying $1700 for a clutch and flywheel (not exaggerating). Also i noticed that the engine gets hot after a few runs, especially living in SC, the summers get pretty hot. What are some recommendations on keeping the engine as cool as possible? Sorry if i sound like i don't know jack squat, I'm new to modifying cars and racing them.
 

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shorttrack
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I have the hankook ventus v12 evo2 tires with 275/30/19 in the rear. they stick well with the stock power, but i dont know how good they will be with more torque. how many shots of N2O do you run?
On the street I keep the NOS at 75 rwhp ,drag strip-100 rwhp. To really get any power to the ground 275 /30/19 will not work for me .Had to go to a soft RE71r 285/35/19 .Now I will be going to a 18x11 rear rim and a 305/35/18 or size 295/35/18 once I install my 4:18.1 diff .
 

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shorttrack
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I might add while active on the streets I beat some pretty fast OEM offerings such as a 2015 Z28 camaro, 2016/17 shelby 350 . I sprayed them ,but still it is my $38,000 home built Gen Coupe again'st a $60,000 plus Mustang and a $70,000 plus camaro . Cars are getting faster so I must change up a bit .I can only get my 60 foot down .Can't throw anymore Nitrous to the car as I don't want to F-up my engine-YET .
 

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ok, appreciate the help. what is a good sounding exhaust? I have muffler delete and love the way it sounds, but I'm nervous to get an actual exhaust and not enjoy the sound of it. Also I just ordered some ARK headers, ARK down pipes, engine leash, lightweight pulley set, and CNT test pipes. I'm looking to get a manifold spacer next. I assume i will need to upgrade my clutch soon as well so i'm trying to decide which one to get. I've heard clutch masters is good, but i don't know how i feel about paying $1700 for a clutch and flywheel (not exaggerating). Also i noticed that the engine gets hot after a few runs, especially living in SC, the summers get pretty hot. What are some recommendations on keeping the engine as cool as possible? Sorry if i sound like i don't know jack squat, I'm new to modifying cars and racing them.
I personally would go with ARK all the way from front to back (the GRIP) with an x pipe added. Their muffler is truly hard to beat. I had this setup before I went turbo and it ran quite well. You really need the muffler for proper back pressure. Make sure to order the headers with ceramic coating (or get them ceramic coated upon receipt, not powder coated). Then wrap them with titanium heat wrap, and dont skimp on this. Do not use the aluminum crank pulley, leave that stock. Are you talking about the phenolic spacer (helps with cooling) or manifold riser (adds mid range torque)? You may have space issues with both. To add the "power" or in this case torque, you want the riser.

You can shed additional weight by going with a DSS carbon fiber driveshaft although it might be a pricey investment for what you are doing.

For cooling, the VIS carbon fiber hood has great vented cutouts and will assist in cooling the engine bay. along with the titanium wrapping. You can get a mishimoto oil cooler to keep the engine oil cooler. I would also get a Koyorad aluminum racing radiator.

I have the 8AT so I am not the one to ask about the clutch. I do know a quality performance complete clutch setup will not be cheap. Shorttrack can probably give best guidance here.

As shorttrack has done, I have done so many mods on my car I have trouble remembering everything off the top of my head. He is well built 3.8 on NOS with MT, I am a well built boosted 3.8 8AT. Neither of our cars, however, are our dailys...
 
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