4-2-1 Manifold for the VX, without cutting the boot

winstar

For the last couple of weeks I’ve been having a look at whether you can package a 4-2-1 manifold in the VX without having to cut the boot up.

So after a couple of attempts I’ve come up with a scheme for the primary runners that will fit in the space available and allow equal length runners of 510+mm in 1.75” pipe, although my target is 550mm as that’s what Clipping point quoted as the length for the Weapon R. The header links 1-2 and 3-4 to make it a sequential design and I’m planning to use 2” for the secondary runners and a terminal diameter of 2.25” or 2.5”, before going into a sports cat. However I have a few things some people may be able to help with:

When measuring the length of the primary runner where do you take the end to be, the end of the thin pipe, the middle of the intersection, the start of the secondary or where the area change occurs? Runner lengths were the bit of the design I was never involved with.

Does any one have a manifold off the car that I or they can measure up? In particular the flange dimension / port locations

What’s standard the wall thickness of stainless tubing? 1.5 mm rings a bell but I’m not sure

What’s the pipe diameters used by the off the shelf back boxes for the NA? As I could make it mate to the standard flange location but don’t want to compromise the design by going less than 2.25”, Although the std and miltek may be out as I may need some of that space for the secondary runners

Does anyone know of a good exhaust fabricator with Mandrel bending in Yorkshire or North West then I can get some quotes from for the work, won’t really need to do any design work, as I’ll do that in CAD/CAE, but may require some fine tuning of dimension as I can’t measure the car accurately enough to just throw it through a CNC bender.

Oh lastly, once one is made it should be easy to make a jig and make more would anyone else be interested in a group buy type of thing, may also make the price a bit Lower. Due my car being off the road while this is developed then I’m prob looking to complete the upfront design work by the end of the summer and get the first one built up and tested in the autumn.

Nearly forogt a picture of the primary runner design so far

Hareng

Just some thoughts.
Are you sure the manifold can be fitted and fed down in the bulk head region?

2 tubes underneath each other reduces ground clearance.

This design would mean a one off exhaust/cr exhaust to be made up.

No provision for a cat unless longer lambda and o2 sensor cabling. MOT

Assuming it bolts in, will there be sufficient clearance on the bulk head and steering rack, the engine rocks a lot.
Leading on to 'give' it will put excess pressure on the weakest link and probably crack the tubes somewhere. Have had many similar designs on other cars one of which was oxy/acet welded no less than 3 times, later mig welded 14 times. Braced and fully welded the pipes to each other inserting 12mm square ms plus plating the bends, weighed a ton. The only thing that stopped it in the end was another lower bracket bolted to the engine. Flexi pipe! I know many reputable companies do not put flexi joints on, but give your engine a rev, watch it rock, something has to move.

Lengths are the total inc bends and where it actually goes to a joint area change.

Made some good exhausts over the years and a nice 70mm downpipe for me ole turboed Sierra v6.

Any info on manifold design and specs? I know the gases effectively pulsate but where do the dimensions come from and how are they worked out?
4:1 gives more poke up the top whereas 4:2:1 gives more mid range sacrificing the top.

winstar

Hareng said:
Just some thoughts.
Are you sure the manifold can be fitted and fed down in the bulk head region?

Well sort of, the clearance between the backface of the flange and the boot on a VX220 is 130 - 140 mm, this design fits in that package altough I suspect when I do the thermal expansion analysis it'll be too tight. But the cad rendering I posted fits into this space, it only hte second iteration and only really for the purpose of illustrating my intended design to get a quote for manufacture.

Hareng said:

2 tubes underneath each other reduces ground clearance.

The ground clearance is dictated by the undertray, the tight bends at the bottom are designed to fit below the subframe cross member and the undertray.

Hareng said:

This design would mean a one off exhaust/cr exhaust to be made up.

No provision for a cat unless longer lambda and o2 sensor cabling. MOT

Assuming it bolts in, will there be sufficient clearance on the bulk head and steering rack, the engine rocks a lot.
Leading on to 'give' it will put excess pressure on the weakest link and probably crack the tubes somewhere. Have had many similar designs on other cars one of which was oxy/acet welded no less than 3 times, later mig welded 14 times. Braced and fully welded the pipes to each other inserting 12mm square ms plus plating the bends, weighed a ton. The only thing that stopped it in the end was another lower bracket bolted to the engine. Flexi pipe! I know many reputable companies do not put flexi joints on, but give your engine a rev, watch it rock, something has to move.

I forgot I hadn't posted the first iteration with the rest of the system on here

Currently I'm looking to join it to the standard backbox flange position, which is just past the cat in VX before the 180 deg bend.

The Lamda postions on the VX can be move to acomodate a relocation of the first lamda and the second location won't change much.

As for durability* I'm intending to fit dual flexi couples in the secondary runners at 90 deg to the engine to take up the movement of the engine, my main concern is that there will be alot of mass only supported by the flange so could have problems with forced vibration as I expect quite a few vibrational modes to fall in the running range, which could require a bracket to the engine.

rabidh

I'd be very interested in how this goes - if it turns out well i'm sure plenty of VXers - me included - would be after one 😉 How were you going to cut out the flanges? do you know someone that will plasma cut? i'd love to get the engine side flange - as well as the manifold/cat-pipe one although i guess you're not making that...

As for the exhaust diameter, there's a thread on vx220.org.uk where Pipo wanted to fit a VXT exhaust onto an NA. Its here:
http://www.vx220.org.uk/forums/index.ph ... hl=exhaust

and has all the measurements of both backboxes. The NA is 46mm internal diameter, the VXT is 50mm - however the same flange will fit both. I'd be tempted to try and make it fit the 50mm turbo one as you could get a nice + cheapish blueflame turbo backbox to finish it off - and there should be less internal restriction.

JohnnyN

I'm sure Vocky will be interested in this!!

vocky

it is quite tight in the vx220 exhaust area, I used a flat cat to allow my weaponR 2-1 section to sit closer to the under tray.

plenty of z22se owners would like something similar for their cars too, astra's, vectra's and zafira's 8)

winstar

vocky said:
it is quite tight in the vx220 exhaust area, I used a flat cat to allow my weaponR 2-1 section to sit closer to the under tray.

plenty of z22se owners would like something similar for their cars too, astra's, vectra's and zafira's 8)

I know it's really tight in there, esspecially if you retain the standard or Miltek backbox.

How long did you manage to make your secondary runners?

One option I'm going to look at is how much extra space for seconaries I can make by using a Larini or Piper style back box.

vocky

flexi's are 100mm, bends look a similar length, so about 210-220mm

Hareng

Sorry, re read the title 😃 VX220

You will be on to a winner if it can be jointed on the two downpipes. This would enable different cars to have the manifold, the only difference is the joint onwards will have to be different, like Vockies piccy.

JohnnyN

Self self self!!

rofl.. rofl.. rofl..