325 +/- wheel horsepower?

**makenzie71** · 07-31-2017

I'm looking at picking up a BMW 5409 with a tanked engine and I have access to a 2003 GTP that's all smashed up...and my desire to make weird **** work is driving me nuts!

Basic idea is to adapt the 3.8 to the BMW 420G 6-speed tranny so I can leave the driveline alone. If I can't pull that off then I'll source a T5 and adapt the drieshaft. The rest is tedious boring stuff with making mounts and plumbing systems and wiring.

What I want to know, though, is what would it take to push the 3.8 up to 325whp? We're talking a 100~120hp boost over stock. Will the stock bottom end be up for that? Can I get it by just cranking up the boost (smaller pulley)? What am I in for here? This is going to be what makes the project a consideration.

**SgtMarshal** · 07-31-2017

you need to increase the exhaust flow out or you will grenade the bottom end. most people run speed daddy headers from ebay. I run an XP cam, and it works well, with some head work, E85, and an intercooler or methanol injection you should be able to hit about 350 hp at the wheels with the smaller pulley of course.

**makenzie71** · 07-31-2017

Considering the project everything past the exhaust ports will have to be custom...I'll be able to make the primaries whatever size needed.

**Fivefingerdeathpunch** · 07-31-2017

I would run some stock camaro 3.8 exhaust manifolds, then make it into a custom exhaust.

You will have to swap camshafts if you want to make anywhere near 300-325whp without trying to jam a stupid amount of boost out of the GEN 3 blower. At the speed it work take to spin the supercharger that fast you'd be creating so much heat that it's very hard to make a lot of power without lots of E85. An intercooler would be a must there as well.

I'd do a mild cam, a 3.0-3.2ish size pulley with a good tune on 93 pump gas and you should be atleast in the 280-300hp range with lots of torque down low.

**blueguy91** · 07-31-2017

These aren't horsepower motors; they're torque based. No need to rev the crap out of it either, however I'd tell you ten out of ten times to just run the T5 from an FBody, fab up mounts, and find a driveshaft that'll work. Would be easier I'd think than trying to fit a Bimmer tranny to the old V6.

**sparkydog** · 07-31-2017

Originally Posted by Fivefingerdeathpunch

I would run some stock camaro 3.8 exhaust manifolds, then make it into a custom exhaust.

And if the OP takes this advice - you have two different styles of GM RWD 3.8 exhaust manifolds. The most common has a quasi-center dump and then there's a version that was on like 99-01 (approx) that has a rear dump.

**Toys4life C5** · 07-31-2017

Originally Posted by makenzie71

I'm looking at picking up a BMW 5409 with a tanked engine and I have access to a 2003 GTP that's all smashed up...and my desire to make weird **** work is driving me nuts!

Basic idea is to adapt the 3.8 to the BMW 420G 6-speed tranny so I can leave the driveline alone. If I can't pull that off then I'll source a T5 and adapt the drieshaft. The rest is tedious boring stuff with making mounts and plumbing systems and wiring.

What I want to know, though, is what would it take to push the 3.8 up to 325whp? We're talking a 100~120hp boost over stock. Will the stock bottom end be up for that? Can I get it by just cranking up the boost (smaller pulley)? What am I in for here? This is going to be what makes the project a consideration.

I have about 310 whp - here is proof. https://www.youtube.com/watch?v=XcFNm7F7GwU&t=3s

Ingredients.
1. 3800 series II stock
2. VS or XP cam
3. better front manifold as stock is very restrictive.
4. 60lb injectors
5. E85 fuel
6. Deatschwerks E85 rated fuel pump
7. some tuning on HP tuners.

Have fun!

**GTPpower** · 07-31-2017

Cam and intercooler will get you there. You could get by on a cam alone if you run better fuel.

**madhavok09** · 08-12-2017

Originally Posted by Toys4life C5

I have about 310 whp - here is proof. https://www.youtube.com/watch?v=XcFNm7F7GwU&t=3s

Ingredients.
1. 3800 series II stock
2. VS or XP cam
3. better front manifold as stock is very restrictive.
4. 60lb injectors
5. E85 fuel
6. Deatschwerks E85 rated fuel pump
7. some tuning on HP tuners.

Have fun!

What else needs to happen to be able to run E85? I may be looking to switch to that on my '07 GT if I can find somewhere around me that has it.

**Toys4life C5** · 08-13-2017

Originally Posted by madhavok09

What else needs to happen to be able to run E85? I may be looking to switch to that on my '07 GT if I can find somewhere around me that has it.

1. Some tuning with HP tuners. I have a 97 PCM so it may be different than an 07. Easy way is to lie to PCM as to injector size (tell them they are 30%+- smaller than they really) which leads to the 30% more fuel E-85 requires. Timing needs to be increased then quite a bit under high load/WOT areas for the E-85.
2. Research as many threads as you can find on the subject.

**madhavok09** · 08-14-2017

Originally Posted by Toys4life C5

1. Some tuning with HP tuners. I have a 97 PCM so it may be different than an 07. Easy way is to lie to PCM as to injector size (tell them they are 30%+- smaller than they really) which leads to the 30% more fuel E-85 requires. Timing needs to be increased then quite a bit under high load/WOT areas for the E-85.
2. Research as many threads as you can find on the subject.

I've been looking into it. Buy the sad part is I can't seem to find E85 near me at this time. It is something I may still look to do, but I'd just need to find a gas station. Thanks for the input.

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