Manifold quandary

[Rich 378]

So I have the 1320 manifold. It whistles a bit. It's certainly not the worst example, but I'd rather it didn't as it doesn't sound great. I've had a quote for rewelding the flex joints, going to be £192 plus gaskets, which is near enough £220.

The the issue is, get it rewelded, which may or may not solve the issue, or get something new and try to flog the old one to someone unfussy?

[Tareim 343]

didn't someone have this issue previously and it turned out to be the flexi pipe that caused the issue? so changing that will resolve it, there are several manifolds out there that don't have any flexi sections at all (such as the JDL manifold) so just replace it with a bit of pipe and you'll be sorted

[surrey86 352]

Might be a complete pain in the arse to fit without the flexi sections though. Only reason I can think of for them is for dealing with sub-optimal manufacturing tolerances.

[Kodename47 446]

1 hour ago, maurice said:

Might be a complete pain in the arse to fit without the flexi sections though. Only reason I can think of for them is for dealing with sub-optimal manufacturing tolerances.

Or flex in the block or exhaust system? Probably not a bad idea to give it some give to prevent stress on the manifold. The OEM has the flexi sections. Could be tollerance based but may not be. It would be cheaper for them not to, but then It has a heavy cat hanging on it so I'd guess it's more to prevent failures.

[DanJ 374]

The flex is to cope with differential thermal expansion as the manifold grows in size as it heats up. If there's no flex then something else has to got to deform to account for the change in size.

[Rich 378]

14 hours ago, Tareim said:

didn't someone have this issue previously and it turned out to be the flexi pipe that caused the issue? so changing that will resolve it, there are several manifolds out there that don't have any flexi sections at all (such as the JDL manifold) so just replace it with a bit of pipe and you'll be sorted

Not many (any?) are completely rigid. They tend to have at least some play in there, either via flex joints or slip joints. Getting the flex replaced isn't the problem in and of itself, it's that it will cost a significant chunk of change and I may still be left with a crap manifold.

[Rich 378]

11 hours ago, DanJ said:

The flex is to cope with differential thermal expansion as the manifold grows in size as it heats up. If there's no flex then something else has to got to deform to account for the change in size.

 

This is my understanding too - there will be differential expansion of the engine block and the manifold runners, so without flex or slip joints the manifold will crack.

[Tareim 343]

6 minutes ago, Rich said:

Not many (any?) are completely rigid. They tend to have at least some play in there, either via flex joints or slip joints. Getting the flex replaced isn't the problem in and of itself, it's that it will cost a significant chunk of change and I may still be left with a crap manifold.

There are a few without anything, and replacing the flexi with a straight bit a pipe (provided the welds are good) should prevent any gaps for it to whistle

[rob275 1817]

Mine also. 

[Deacon 1357]

My JDL manifold, all the ACE manifolds and also the HKS ones also don't use slip-joints or flexi-sections.

[Church 209]

rob: i'm curious, of what make is yours? Looks unfamiliar.

[Kodename47 446]

Just now, Church said:

rob: i'm curious, of what make is yours? Looks unfamiliar.

CGR Exhausts'

[rob275 1817]

As @knightryder said, it's a custom CGR system.

[DanJ 374]

11 hours ago, DanJ said: The flex is to cope with differential thermal expansion as the manifold grows in size as it heats up. If there's no flex then something else has to got to deform to account for the change in size.

 

This is my understanding too - there will be differential expansion of the engine block and the manifold runners, so without flex or slip joints the manifold will crack.

 

It increases the risk of cracking, but a well made manifold should be fine. Something, somewhere will bend/deflect to account for the changes in size.

[Bfranklyn86 52]

Are there any draw backs to the flex joints? Like weight added, or turbulence created. Seems like a good safety measure.

[Church 209]

Costs to add it in / complication of header construction with arguable need. Also making construction more complified not only can solve some problems/failure points, but add some new ones. Keep It Simple Stupid principle :). Most very first aftermarket headers for our hars had flexi or slip on joints, but many made later on - didn't, including headers from several top vendors. I guess by failure rate by statistics was too low to justify costs of adding them. This is no overengineered mercedess from middle of 20th century :).