Performance manifold

[MINIdriver85]

So...I've read many of you installed Janspeed, GTT, or Milltek manifolds, but all of them are 4-1. What's the difference with 4-2-1 manifolds like the Supersprint ones? From what I know the 4-1 will give the torque and power gains mostly to high rpms while the 4-2-1 are more effective at low/medium rpms, is that true?

[MINI-Morgan]

News to me... I thought it was primary length that effected that but im defiantly no expert on exhausts.

[MINIdriver85]

I may be mistaken...lenght surely affects that...but I thought the 4-1 vs 4-2-1 affected that too. Might be mistaken though, that's why I asked...

[NeuroBeaker]

I'd be interested to know what people's thoughts on this are too. I'm thinking of a new exhaust manifold for the spring and low-mid torque is very important to me in making a decision...

[MINI-Morgan]

Quote: Originally Posted by MINIdriver85 (original)

I may be mistaken...lenght surely affects that...but I thought the 4-1 vs 4-2-1 affected that too. Might be mistaken though, that's why I asked...

Trust me I dont really know either but interested to know the answer I'm sure its not a simple one though as different modified engines will require different flow rates.

[k-huevo]

Here’s some info to consider Intake & Exhaust Systems - Tech - Sport Compact Car Magazine . Keep in mind forced induction is forgiving in some ways making certain aspects of a header’s design less critical. The OEM header design appears to be poor, especially at the crimped merge before the pre-cat, but top end performance can be improved by only replacing the pre-cat with tubing, leaving the un-equal length primaries and crimped merge section intact. Also, the vehicle’s performance management can be tuned for the pipe (and visa-versa), enhancing a header’s design strength beyond the bolt-on level. Not all accepted design characteristics are effective for all vehicles. Our MINI’s have a unique firing order, so although a certain primary paring may be optimum for a Honda’s midrange and rpm bandwidth, it may not carryover to the MINI; I have a 1&3, 2&4 primary paring as an example.

[MINIdriver85]

So if I'm not mistaken it says that 4-1 privilege maximum power gain and 4-2-1 are better for drivability, widening the engine power band, is that right?

[NeuroBeaker]

I think it's saying that 4-1 will give maximum power, but only at maximum revs.

For road driving, I'd say you spend most of the time in mid- to low- revs... so it seems to be saying that a 4-2-1 (or a "Tri-Y") design is better for this. However, this sacrifices some maximum power output when at maximum revs.

It seems to me that a 4-2-1 would give more benefit for my particular style of driving. I do like driving around at high revs, but in a "real world" scenario - I don't spend a lot of time with the engine revved that high.

[MINIdriver85]

Yeah, I like going high on revs too...but realistically, on normal roads...you use mostly mid/low revs...so I think i'll go for the Supersprint manifold which is 4-2-1.

[k-huevo]

We would all like information distilled down into simple, easily understood absolutes, or stereotypical behavioral attributes, but determinations based on parsimonious observations are not always universally valid. Primary paring is not the whole story. Header tube diameter and length play a greater role in the “tune” of a header. A header with a tri-Y design could be a lousy midrange performer if the primaries were too large or merge collectors too abrupt, and by the same token, a 4-1 could have a broad performance range or exceptional midrange sweet spot if designed for it. A “race” header will have different criteria than a “street” header, valve lift (cam profile), displacement, and whether peak torque or hp is targeted. Here is a link to a calculator and to a couple of excellent books about the subject, although the Scientific Design book doesn’t cover forced induction Primary Header Tube Length and Diameter Calculator ; optimum tube length and diameter would surprise you. Keep in mind forced induction forgives many sins in the exhaust and intake path and that’s why many aftermarket headers can limit their designs based on packaging concerns and still be at least marginal performers. Tube length is probably the most critical, but the most limited by packaging considerations.

[alski]

so is their no absolute rule on manifolds as other parameters are more important

or to put it another way, a 911 works even though in theory it should only be a beetle with attitude

[NeuroBeaker]

Oh no, I'm destined to be confused!

Perhaps the safest thing for someone like me to do is to go to a tuner and say "this is the type of performance I want" and trust that they know what they're doing.

[MINIdriver85]

So the matter is highly complex...

[3rdpillar]

perhaps someone who sells these, like one ot the sponsors would shed some light?

[MINIdriver85]

I was hoping for that, but none have come till now...