Manifold design

[jay28]

Hi all.

I'm going to "try" make my own manifold and twin exhaust system. I just cant afford to buy one at the moment and if I could I dont think I could justifly spending 5 or 600 on just a manifold.

Ive been doing some reading through threads on various sites but there are so many different applications for the L6 thats its a bit confusing for me.

I was thinking of going for a 1 3/4" primary's. 28" equall length, then 2, 3 into 1 collectors 1 3/4 to 2", and continuing the rest of the twin pipes in 2".

All in 316 stainless.

Anyone have any other sugestions apart from buy one

Thanks
Jay

 

[zpuppy]

Ive made my own before Jay, but be warned , NOT EASY . I had access to data and a veeery nice tubing bender, and still managed to cock it up 2 out of 3 times,,and this was on a very forgiving 500 + cubic inch v8 . My advice is ,,keep the runner lengths absolutely equal and curves as gentle as possible. I can't really say more except that there are so many variables,, exhaust pulse timing, cam duration, intake arrangment,,the list goes on . saying all that,,I done it to a 9 litre Ford V8 so who's to say you cant do the same with yours ?? All it takes it patience and a lil bit of sweat ! What you want to achieve is a smooth flow of exhaust gasses at an equal rate out and away from the combustion chambers,,I'm sure there are people on here who could give you data on pipe ID sizes and what they have run with etc !

 

[jay28]

I'm not expecting it to be easy at all........And I understand there is alot of science involved but I'm going to give it a try and see how it works out.

 

[Joe NI]

Good luck with that jay...its goin to be complicated..do you have a pattern to work to or do you have mock it up in the engine bay bit by bit.

 

[JakTheRuby]

Good man for having a go. Whether you manage to do it or not your knowledge and experience gained by having a go will be invaluable. Good luck sir and post up some 'in progress' pics if you get time. It's always good to see this kind of thing (any working of metal is cool).

 

[jay28]

I have a spare head to work off Joe, I can then take clearence measurments off the manifold thats in on the car at the moment. I have no detailed patern to work off, those type of things are usually top secret

My biggest problem is going to be the collectors, cant find anyone in the UK that sell's the 3 into 1.

 

[Joe NI]

My biggest problem is going to be the collectors, cant find anyone in the UK that sell's the 3 into 1.

theres a guy up here my brother knows, works for a metal fab business .... he makes up stainless pipework for turbo conversions/induction kits in his own time, i could prob get his num for you.

 

[jay28]

Yeah would be handy to have Joe cheers,
Getting the flange water jetted tomorrow so should have that next week sometime.
Then order the pipe when I know exactly what diameter I need

 

[z-spec]

I have a spare head to work off Joe, I can then take clearence measurments off the manifold thats in on the car at the moment. I have no detailed patern to work off, those type of things are usually top secret

My biggest problem is going to be the collectors, cant find anyone in the UK that sell's the 3 into 1.

I do not know in the UK , I bought some from Burns in the states .

 

[jay28]

I do not know in the UK , I bought some from Burns in the states .

Ide say I'll have to get mine from the states too, thanks for that.

 

[Nigel Brook]

As you are fabricating the rest of the manifold I would have thought doing the same with the collectors is the least of your problems. Purchased ones are probably going to need modifying anyway.

 

[Rob Gaskin]

As you are fabricating the rest of the manifold I would have thought doing the same with the collectors is the least of your problems. Purchased ones are probably going to need modifying anyway.

I was thinking the same as I read the thread, it will also be more satisfying having made it all yourself.

What you need to get right is the face that mates to the head. With such a long engine it is notoriously difficult to keep a gas-tight seal.

 

[SeanDezart]

Be aware though that your exhaust manifold is as critical for your engine as your tyre choice is for staying on the road !

Great for trying - get it right. That's why Nismo and others ARE £600 !

 

[Ian Patmore]

Jay,
I would consider going 1 5/8" primaries. 1 3/4" is too big in my humble opinion. Skiddell mentioned something in a previous thread. The dia. of the pipes is too big for the exhaust gases and this (off the top of my head) slows the gases down. It is not a case here of bigger is best.

Don't know if it is possible (or even worth trying) but what about getting a MSA header off Mike, and modding to suit....?

 

[SeanDezart]

Jay,

without being bothered to track down all the info myself on your spec....what engine have you (2.8 ?), what is your anticipated bhp output, what carburation have you ?

 

[zpuppy]

Hi Jay ! Im in the process of tracking down a formula I used for calc's on pipe dia and length,,,will post asap !

 

[jay28]

Hi All.

Reason I dont want to make the collectors is Ide need a proper saw to cut them, an angle grinder would be too messy and there would be alot of trial and error, I have pipe benders, tig and everything else I need in the garage apart from the saw.

I'm getting the flange for the manifold cut in 5 separate pieces so there should be no distortion from the heat.

I already have an msa 6-1 manifold, but its carbon, its fine and does the job, I guess im just setting myself a challenge , wether or not it can be done is another story.

Engine spec is 2.8, 86mm flat top pistons, p90 head skimmed 2mm, stage 4 cam, triple dellorto's

Cheers for the advice guys and keep it coming.

 

[SeanDezart]

Engine spec is 2.8, 86mm flat top pistons, p90 head skimmed 2mm, stage 4 cam, triple dellorto's

In that case and contrary to Ian P. I would say that a 1 3/4 primary pipe is better than a 1 5/8.........

 

[jay28]

Also I should add that I picked up a ld28 crank a few weeks ago, I'll eventually get around to doing a stroker and would want this manifold and exhaust system to suit that engine also.

Would a 2" twin system from the manifold back be too big?

Also Sean, the 1 3/4" is that ID ot OD?

Thanks again

 

[SKiddell]

IMHO
The engine spec is on the borderline between the 2 (ohh thats diplomatic)
and its all going to depend on what you intend to do with the car....are you going to drive it around like a loon at 7K in 3rd or is driving pleasure more important?

If you are after out and out power then what compression ratio are you running, what size are the triples, how are they jetted, how well do the ports flow (inlet and exhaust), the cam ...stage 4? from who, what lift, duration etc etc...these things and more will influence header design.

Header design is complex, expensive and time consuming which is why really good race headers form Janan for example can be £1000+ .....but never fear, all of the tricky work has been done for you.......by Nissan, the Nismo headers were excellent value for money and worked very well...they quality was a little poor but hey, just copy those dimensions and you wont go far wrong, why reinvent the wheel with the vain hope of eeking out another 1, 2 or 3 hp oh and dont forget the placement of the final collector it can wake up an engine or consign it to the also ran pile.

Finally you will need to rolling road the car as a header change will radically change the fueling requirements, many people significantly modify a setup (new cam, airbox, headers higher comp ratio etc), scrimp on a rolling road session then wonder why the car has abruptly stopped and the remains of their pistons are rattling around in the sump. Modern cars due to ECU's and oxygen senors recalibrate themselves, constantly optimising the AFR to run just on the lean side to optimise fuel consumption, backing off ignition advance at the slightest sign of knock....... running triples means having to re jet whenever a significant modification is carried out, sometimes even a significant altitude change can mean a re jet.

Would a 2" twin system from the manifold back be too big?

2.5 (min) no centre box and a free flowing slightly staggered back box