Exhaust manifolds

[zefarelly]

I'm designing my own . . .Ive been quoted one price which is quite frankly too much for a few tubes welded together, and no one else has answered emails or their phone, I know where to get it fabricated better and can produce my own drawings no problem.

has anyone ever done this ? I'm using the formulae in A G Bells book as a guide, any tips? as I see it the only problem I have is getting it to fit nicely as the inlet manifolds somewhat restrict access (ford precrossflow head)

thanks

[StephenRae]

I seem to recall that for a 1600 ford running to about 7000revs the optimum length of the primaries was 27" it all gets a bit hazy after that. I must have a book on it somewhere if you are really stuck let me know and I'll see if I can dig it out.

[graham bahr]

most engine seem to favour a primary length of 30inchs give or take a bit, if you cant get the lengths 100% equill dont panic as that tends to give a slightly wider power band as each cylinder will have a slightly different tuned length, the primaries on my beemer certainly aren't all the same length, although they are reasonably close, and im seeing over 100 bhp per litre on an 8valve engine designed back in the 50's, as for pipe diameter you cant go far wrong if its the same or just a little bigger than your exhaust valves.

[zefarelly]

having spent yesterday evening 'swotting I've come to this conclusion

Inlet Valve 41mm, inlet port 35mm

Exhaust Valve 35mm exhauost port 35mm

exhaust tube internal diameter 38mm

Primary length 28" which is based around max power at 7500 (depending where I assume max power the calcs varied from 26-30" so 28" will do !)

I'm going for a 4 into 2 into 1 so my secondary tube Diameter comes out at 48mm then to a 2 1/2" tail (matches the existing system)

making it is another matter ! I'll concentrate on drawing it up first to see that its going to fit ok under the webers and inside the inner wing !

[dtype38]

Hayward and Scott in Basildon Essex to bespoke exhausts to your own design. Not cheap, but that's relative in motorsport. This is what they did for mine:

[Eric Falce]

Falcemob pointed your prob out ot me.I am in the process of having a new system for my Escort.Aparently the best system is 4-2-1,inch and three quater pipes at fifteen inches long into between two and a quater or two and a half inch pipe depending on your state of tune or torque curve you want.I am going for the two and a half inch pipe as I will be fitting a Pinto at a later date.Hope this helps,have been advised by a very knowlegdable fabricator,reckons on a 10% power increase on my existing system!
Eric Falce

[dtype38]

Hi Eric

[zefarelly]

thanks Eric, that exactly what it says in my book . . .15" primaries and 30" overall length, I'm going 1 1/2" ten up to 1 7/8 then 2 1/2" . . .I cant get the ports any bigger !

[1200Datto27]

Dtype,

That's a nice set of pipes, i hate to think what the cost of it would have been.

4-2-1 pipes will strenghten the mid range on andengine, whereas a 4-1 will build more power from my experience. I have two difference exhausts for my car, a 4-2-1 for slower tracks with more tighter corners, and a 4-1 for the flowing tracks that you keep in the higher revs for more. They both have the same pipe diameters, and overall lenghts, but the -2 has a 10% mid range increase, and a 5% power lose over the 4-1. If it didn't cost so much ($500a each) to build and test exhausts, I would play around some more.

[dtype38]

Originally posted by 1200Datto27
Dtype,

That's a nice set of pipes

Well, ah thaank ye verry much good buddy. The version shown is mk4. I am now system mk6 which is yet to be noise tested but hopefully will free up some more hp but still be withing track noise limits. All the systems have used the same manifold set, but I've played around with 6-2-2 and 6-2-1 setups with various silencers and tail boxes trying to get a good balance between keeping back pressure down but still keeping it reasonably quiet (the old Jag engines have bags of mid range torque, so generally speaking, freeing up the exhaust always = more horses at the top end without much sacrifice in the middle)

Your're right that all of this experimentation doesn't come cheaply, but it's still chicken feed compared to playing around trying different engine parts

[zefarelly]

I'm buying a proprietry manifold off the shelf (not too expensive) then I'm going to start playing around with tubes etc and hVE A GO AT MAKING MY OWN, better, cheaper etc

I'm still reading and learning lots of stuff so Its all still a very dark art !

[zefarelly]

manifold has arrived from a well known manufacturer . . . .No1 primary is twice as long as No4 . . .No's 2 and 3 are the sameas each other and somewhere between, the secondaries are fine and the flanges arent anywhere near the ports on the head . . . . that'll teach me to go the cheap route

wheres me grinding goggles, and fetch the welding gear

[Tim Falce]

Originally posted by zefarelly
manifold has arrived from a well known manufacturer . . . .No1 primary is twice as long as No4 . . .No's 2 and 3 are the sameas each other and somewhere between, the secondaries are fine and the flanges arent anywhere near the ports on the head . . . . that'll teach me to go the cheap route

wheres me grinding goggles, and fetch the welding gear

Send it back and get one made, you know it makes sense

[zefarelly]

Originally posted by falcemob
Send it back and get one made, you know it makes sense

probably . . .but I'd like to have a go myself as well

a posh ones on my birthday list . . . .and so is a quaife gearbox !

[1200Datto27]

If it isn't to the agreed upon specs, send it back as faulty goods, and name the buggers!

[StephenRae]

Local exhaust dealers sell 90' and 45' bends, or failing that Tweeks sell them, I think they sell the flanges as well. I have had some success bending tube after filling with sand, but its one of those jobs where you get the hang of it just before you finish....one tip use very dry sand.. oh and make sure you know where the local burns unit is!!