4-2-1 manifold & 4-1 manifold questions

[kristianbowler]

For some time I have had these questions in my head, but never actually got round to asking them so today is the day!

I know what a 4-2-1 manifold is and a 4-1 manifold is but I'm not exactly sure what the differences/gains is between the two, and which one (if any) is better for performance/flow? and what the point is of upgrading from a 4-1 to a 4-2-1 (I have seen people say this). If anyone could be of help to a manifold noob I'd appreciate it, thanks

(Picture stolen from someone on here)

182 manifold (left)
172 manifold (right)

Thanks

 

[kristianbowler]

Just realised this is in the wrong section, please move! thanks

 

[Skeeter]

I always thought the 421 manifold on the 182 was part of the reason it makes a bit more power than the 172? Hence why the 421 is considered better than the 41

 

[kristianbowler]

I always thought the 421 manifold on the 182 was part of the reason it makes a bit more power than the 172? Hence why the 421 is considered better than the 41

I understand that, I'd like to know how the 4-2-1 makes more power, and why it is considered better over the 4-1

 

[Nyall]

The 4-2-1 mani flows better than the 4-1. I'm no expert, but look at how much twistier the 4-1 manifold's pipes are. The 182 manifold looks more direct, doesn't twist and turn as much, so the exhaust gases flow more freely.

 

[Skeeter]

Manifold design is around how the exhaust gasses interact with each other. Its quite complex and I'm not going to pretend I understand it, but basically gains can be made by adjusting the length of the pipes and the cylinders that are paired up to ensure that the gasses meet each other at the optimum point in the combustion cycle.

If you look at the design the 4-1 just puts all the echaust gasses together, while the 4-2-1 combines cylinders 1 and 4 together, and 2 and 3 together before combining them both later.

Quite how, I don't know, but this obviously has some effect. Probably to do with reducing the effect of gasses meeting from one cylinder that is exhasuting and another that is not which could cause a vacuum.

 

[Jono 69]

Maybe each pipe only has to deal with one cylinders gases at a time? And by having them run into the alternate stroke cylinders pipe first and then into each other, the gases are more efficiently passed through? Just a guess lol

 

[Cup_Phil]

GENERALLY 4-2-1 will produce power lower down, but 4-1 will produce a revvier engine with power up top

But that is a generalisation - as said the length of the headers and the flow rates and the amount of bends etc... will all have an impact on how they perform

On a 1*2 the 182 manifold produces a little bit more torque in the mid range whereas the 172 manifold produces it higher up. The difference on the road really isn't noticeable.

 

[Munson]

Where's Chipipedia when you need him

 

[Nick172Cup]

Where's Chipipedia when you need him

​Lol This tbh.

 

[Djw John]

Speaking from experience you won't notice any difference between them on the road or track.

 

[Munson]

I always lol at that little bit where they smashed it with a club hammer so it would clear the subframe

 

[Djw John]

Lol aye, you can almost hear someone in dieppe realising "merdè, where's my hammer?"

 

[Munson]

My 'ammayreeee?

 

[kristianbowler]

Ah I sort of understand, so there is no real gains from having either one? Apart from what's mentioned

 

[Cup_Phil]

Lol aye, you can almost hear someone in dieppe realising "merdè, where's my hammer?"

The really weird thing is some 182 manifolds don't have that dent in them - mine doesn't
It appears to me some people started complaining about the vibration against ARB, which is actually down to soft/worn or badly fitted engine mounts - and they figured the best fix for it was to whack the manifold with a hammer to make more room lol

 

[2Damnsly Andy]

The really weird thing is some 182 manifolds don't have that dent in them - mine doesn't
It appears to me some people started complaining about the vibration against ARB, which is actually down to soft/worn or badly fitted engine mounts - and they figured the best fix for it was to whack the manifold with a hammer to make more room lol

If in doubt, get the hammer out.

 

[Stuey 172]

4-1 more bhp less torque 4-2-1 more torque less bhp changed my 172 manifold to 4-2-1 and had before and after dyno readings ... Stu

 

[Ph1 Tom]

4-1 more bhp less torque 4-2-1 more torque less bhp changed my 172 manifold to 4-2-1 and had before and after dyno readings ... Stu

Have you got the printout of before and after the 4-2-1?

 

[Greeny.]

Normally noted that the 182 manifold also increases exhaust noise!

 

[domjolly]

As said before 4-2-1 I'd for low down grunt 4-1 for top end, was used to get the fat lumbering 182 moving so it could try and keep up with the 172(specifically the phase 1) lol

 

[ben lee]

the 4-2-1 manifold should smooth out the mid range power and make less power top end over a 4-1. on a standered engine the engine will be minimal.

the length,bore and angles of primary,secondary runners cat and system can be fine tuned to an engine to make the exhaust suck out the combustion chambers and suck in the induction mixture to improve volumetric efficiency. to work better with the cams induction for pulse tuning.

 

[Stuey 172]

No i havent snymore ive had so many bits of paper lol shes running at 200 bhp at the mo and has been for 8 months but im on the verge of supercharging i think