Hi guys

Been having a look at getting a 4 2 1 manifold to replace the 8 pipe on my 1988 405 mi16. I've read a couple of reviews from people with 205's that reckon the upgrade will give an extra 7-8bhp but i can't find anyone that does one for a 405.

Anyone fitted one to theirs? does it actually make a difference? where can i get one?

cheers

mike

Miles (PugRacing) makes a 4-2-1 2 piece manifold for the Mi16 & is a member of this forum.

It's pre-drilled to suit either 9 or 10 bolt head variations & only needed a little fettling around the (9 in my case) bolt holes. The rest of it fits very well, clears everything & fits snugly.

You'll need a flange welded to the end to pick up the rest of the exhaust system. Ideally, this would work alot better with GrpN mounts (mine are on order). The 'Y' collector has pulled partly out due to engine flex.

As for any performance gain, I can't say for certain, but they certainly helped in getting my engine to 160hp atw.

I'd say it's not quite that much of a gain. If you get an extra 2-3 bhp that would be a success. If you start tuning the intake, however, such as throttle bodies etc., then the gain with the tuned exhaust will prove to be better - maybe even above 8 bhp ;-)

How do you mean by two peices? As in two peices that are in 4-2-1 (meaning a total of 8-4-2 but used with dual exhausts to give 4-2-1 per pipe) or two peices that are 2-1 (giving 4-2-1 when used with a single exhaust pipe). I'm not sure if that makes sense but having trouble gettnig my head around it

Cheers
Cam

Hi Cam,

Sorry for the confusion but it's actually a 4 piece system but found I couldn't edit my post. It's a 4-2-1 with each primary picking up both exhaust ports per cylinder. Easier to explain with a pic.

Click to view attachment

I See . so what's the advantage of 4-2-1? I thought the 8-4-2-1 design was supposed to have superior flow? Is the advantage in the 4-2-1 design or the fact that it's a manifold designed for tuning compared to a manifold designed for 160bhp?

Cammy, that's the question I struggled to find an answer for. You could have seen a topic on here with that question.
The thing is that I can't accept that Peugeot went for all the hastle with 8 tubes in the manifold and 2 tubes (BTW it's not '8-4-2-1' but 8-2-1 ) in the downpipe just for nothing special - especially thinking of production costs etc. There must be something special about that layout they used.

Maybe it's to avoid losses in power and torque due to the manifold not being equal lengths? The 309 one being equal lengths is said to produce same power but +1 Nm torque up in the high rev range....

indeed. Peter says that the manifold is not worth changing unless it is definately hampering performance (apparently the OEM flows better than a 351?!?!). Would it really be worth going to the hassle and expense of changing it for 1nm of torque (I imagine that could fall within the margin of error of a dyno, I mean that's pretty friggin' specific?).

Also if Peugeot thought so highly of the motor that they threw a magnesium alloy valve cover on there just to finish it off. Would they have gone to the extra trouble and expense to put a worse manifold on there? Just seems questionable to me, but then again I'm not an expert... or even experienced

The std manifold is not really 8-2-1 more 4-2-1 as each cylinder is served by 2 pipes instead of one which the later Iron block engine's went too, I have done a back to back abit in a 205 and found a nice gain in torque than anything else on a std engine