987 Exaust Manifold on 986 3.4L
 

i know i have heard of this being done. does anyone know if i can just swap out headers to use the 987 version, or would i need to install the other components as well?

Hi Kevin,

I have not done this yet but as I recall (??) a 987 header can be used with minor modifications but it is not plug and play. Another option is to use a 996 header and reverse the bends. Tholyoak used both methods I think.

i think you are in for the whole shooting match. from what i recall the 987 headers take the exhaust a different route than a 986. check with che; last time i talked with him he was working on an inexpensive 987 option.

Although the 987 headers will lined up ok at the flange, they proceed to route the exhaust along the outside of the subframe and chassis - which is very different from that of the 986.

Johnny - how sure of this are you?

I am most concerned with the flange location & whether i clear the tranny mounts. Everything else is basically fluff.....

First and foremost, my information is based on retro fitting 987 headers on a 3.2 986 boxster. With that said, I can't say for sure how this application would work on a 3.4 conversion. But, in any case, back when I was considering a turbo system for my vehicle, one of the issues that I was faced with, was the necessity of swapping out headers in order to make the "plumping" work. Basically, I was considering TPC's system - whereby they require the use of 987 headers because they route the exhaust in such a way that it accommodates their turbo design. With that said, it's my understanding that the 987 headers are a direct bolt on to the M96 engine.

so you were able to put 987 headers on a 986 boxster & have the OUTLET flange on the header line up w/ the rest of the 986 system? i know they will bolt to the head. my concern is whether they line up w/ everything else. thx again.

No. As I said, the 987 headers will presumably bolt to the head, but they will not line up with the rest of the 986 exhaust system. Therefore, the remaining plumbing has to be altered because the 987 headers take a different route.

got it! when you said they 'line up at the flange', i though outlet flange instead of inlet. thx for your help; it all makes sense now.

You have to use the entire 987 system. You also have to extend the 02 sensor wires. Other than that it bolts up nicely. Keep in mind though that 3.4L 987's have larger exhaust ports than 996 3.4L engines. While not a huge problem, it does cause you to loose some potential power.

thx for the info. sounds like you use that on your 3.4L. do you run the stock 996 ECU program? any piggyback computers?

How were you able to bolt it up on a 986 ?

Insite, the 987 manifolds route outside of the suspension uprights & the outlet is close to the brake caliper. I have heard this requires rerouting a brake hose etc. I believe the main benefit is keeping the heat further from the engine. If I had a non-precat Box I would be investing in a good set of 986 headers with the ideal tube size for me & have them ceramic coated inside & out. (This is the reason I am open to buying a 98-99 model now)

i am pretty sure the headers i'm using are sized right for my 3.4L. i am, however, obviously down on power compared w/ 996C2's and Cayman S's (they pull my on the back straight at road atlanta). since my headers are cheap ebay headers, they were my first suspect. i ran some calculations, though, and i'll be damned if they aren't a GREAT design for the 3.4L.

i just ordered a wideband o2 sensor so i can check to be sure the 996 tune is working right w/ my setup. with my intake & exhaust, this thing should be breathing very, very well.

What is the diameter of the primaries ?

I concur. Especially in view of the fact that both the 986 and 987 headers utilize 400 cell pre-cats .

42mm if i remember correctly

That's the size of my NHP manifold with sport cats at the inlet.

That's small. I run 2.25 inches from the flange, through the primaries - all the way to the catback. The catback has 3 inch inlets and 3.5 outlets.

Not the Hemi 'Cuda, the Boxster.