Hi, I drive a 2006 Monte with the 3.9, early next year I will be performing an LS4 swap, but for now I will be modding the 3.9. My main question is, will headers from a 3800 fit the 3.9? I heard they can with little modifications but I want to be sure before I go buy some.

 

There not a direct bolt on. I don't know what modifications need to be done to make them work if it can even be done.

 

If you're going to be doing an LS4 swap, why not just save your money and mod the LS4 once its in?

 

The 3800 and 3900 are completely different engines. I can't imagine that headers for a 3800 would even be close. Just wait for the LS4 swap. Winter will be here soon anyways.

 

yeah modding the ls4 makes since, I just wanted to make the car alittle more fun to drive in the mean time lol. I'm getting ready to put the SS ground effects on it next week. My car is laser blue metallic and the ground effects will be white. Its gonna look sick, especially when I get the 20 inch chrome Bullitt wheels on!

 

Its always good talking with other Monte owners, our cars are so unique lol, one of the guys at work drives a 2004 ss all red, I think its a dale earnhart edition, i park next to his in the lot sometimes. But you guys are right, in the mean time im just gonna get it looking good. Flowmaster super 44s mufflers with 4 inch exhaust tips is next on the list.

 

The 3900 is actually closer to the 3500 and such engines. Completely different than the 3800.

Save your money, there is hardly an aftermarket for it, however if you are doing the swap, just wait

 

With modifications they could be made to fit, but it kinda depends on your definition of 'little' modifications. Step 1 would be to cut the head mating flanges off the new headers since the ports and bolt locations aren't the same and the V angle that the heads are sitting at is different (the 3800 makes a 90 degree angle between the cylinder centerlines whereas the 3900 makes a 60 degree angle).

Step 2 would be buying or having machined new flanges that mimic the stock exhaust manifold flanges and bolting those to the heads. Step 3 would be modifying the front and rear headers to be get the pipes up to your new flanges so you can weld them on (this could include cutting the current piping short and welding on new primary sections, etc). Step 4 would modifying the crossover pipe since again- the distance between the heads isn't exactly the same due to the V angle, so the crossover length and flange angles will change. How you perform step 3 will determine how much work is needed here. If you left the crossover bolted up in step 3 and only modified the ends of the primaries, you may be able to get away without modifying the crossover. Step 5 would be modifying the downpipe mating flange to correct that angle so the downpipe still fits (of course this also depends how you did step #3; again you could get away without modifying the downpipe if you positioned this correctly before you started welding the primaries back on.


IMO that kind of labor just isn't worth it. Even starting with cheap $200 ebay headers, you'd still have either a ton of money into fab time for a shop (who would prefer to build them from scratch given that alternative)- or if you have the tools/skills, that would be a ton of labor on your part.


I agree with the others, if you honestly believe you're going to do the LS4 swap, then don't put another dime into the 3900. Aftermarket parts sell for a fraction of new, and there is no sense taking a 50% depreciation hit on parts for a few months of use.

If you're that unhappy with the 3900's power level, then why not put all of your available funds towards getting that done rather than spending money on exhaust, ground effects, etc in the interim?

 

The 3.9 has descent power, I'm happy with it right now. I just wanted a little more pep in the meantime. I'm more focused on getting the SS ground effects right now. The 3.9 pulls strong, it hits that 113 speed governor quickly with ease. I'm gonna do the flowmaster mufflers with 4 inch tips because the stock tips are WAY too small.

 

You should talk to Will at overkill. Get a nice tune on the car and it should wake it up plenty until you want to swap.