N/A exhaust ports and LCB
Turbo Mini Forums

Im tinkering with my exhaust atm and modifying my LCB a bit to get the whole system higher in the tunnel and had a thought.

Im contemplating cutting the mounting flanges off the LCB, matching them to the head and possibly dowelling them like the inlet, then reweld the pipes on but making a nicer flowing job of it.

What do you think? I know Vizard says a step up in size from head to LCB is OK and possibly a benefit but my LCB is massively bigger than my head ports, not that they are small.

Surely a smooth transition would be better!?

Paul

I seriously doubt it!

why not paul, its not like you dont have the ability.....

I thought a step on outlet from head to manifold on a NA engine helps stop gas reversion, even more beneficial to something using a big dirty camshaft profile?

However I guess there is a sure fire way to find out for definite and that is to give it a try.

Thats my understanding Tom, but, looking at Vizards diagrams you only get reversion on the floor of the port where the gases are slowest so maybe a smooth transition on the roof and sides would be better.

Trouble is, I bet no-one has ever looked into it that closely as its such an awkward job to do

Paul

I seriously doubt it!

It certainly would make sense, I guess the anti-reversion stuff won't really affect power but may well help torque lower down, I'll be interested to see what you find out really.

Tom, Ive sent an email to Maniflow, Ill let you know what they say if they say anything. Ill talk to Swifty too.

Would be interesting to know what any of our resident head modifiers think - Benross, Phil

Paul

I seriously doubt it!

I'd be interested in what Maniflow come back with Paul.

I opened my exhaust manifold to match my head. And that was with one of their large 3 into 1 manifolds(Not LCB). I just matched it to the head. Didn’t think at the time just got the die grinder out.

On the inlet side. My inlet manifold runners are undersize. This was done because the head was original designed for a DCOE. And talking to folk about the IDA I was told to keep them smaller to help with the low speed throttle response.

But this was before I met Carl who will probably say I've been told a load of crap. lol

Si

Edited by Si P on 22nd Sep, 2009.

I drill holes in everything..!

Si, As long as the inlet is only slightly smaller than the head it wont make much difference on IDA or DCOE, but, if you have a whappy cam you wont really need low down throttle responses as you need to keep the revs up.

I read Vizards book on exhaust, manifold and pulse tuning last night aswell as a lot of stuff on the web. Its a very interesting subject actually and if done right can improve power/torque.

Oselli did a reversion baffle which allowed good flow one way (the correct way) but limited back flow, and from what I read from atleast a dozen sources last night from A series to big American muscle cars, my theory is correct - smooth transition on the roof and side walls but mismatched on the floor with the manifold being larger.

Paul

I seriously doubt it!

Ok, so I cut the mounting flanges off the outer 2 port part of the LCB and bolted them to the head.

Although the gasket is matched to the head exactly and the LCB ports are bigger than the gasket, its all in the wrong places when bolted to the head and I also hadnt taken the distortion of the pipework into consideration, I always had to force it to line up the stud holes.

I have anti-reversion steps in the transitions from head to pipe but its in the wrong direction. There is a 2-3mm step on the floors of the ports where the manifold interferes with gas flow in the normal direction.

Some serious work to be done and I think there is a lot of scope for improvement.

Paul

I seriously doubt it!

I think you theory is sound Paul,

When i made my turbo manifold I made my own flanges from 10 or 12mm stainless and ground them out to match the head,

Happily the tube i used matched the flanges very well once i squished them square, once welded on they just needed a tiny bit of fettling in the corners with a dremel.

try to get a nice gentle transition from square to round.

What port shapes are you running with on the exhaust side Paul?

Square, D shape or circular.

I've seen a MED head which ran circular exhaust ports which had a matching circular manifold. This worked very well.

Not stepped at the base of the port though.

Also, where are you going to start the step (or should we now call it an anti reversion step? ARS)

Straight from the exit point of the head or at the edge of the manifold flange into the primary?

When reading up on gas flow speeds through a section. Circular always wins.

Due to the even surface friction. As apposed to square section with a narrowing corner sections. E.g. high friction.

Or am I talking bollocks?

But glad you’re experimenting.

Si

I drill holes in everything..!

I guess that this all comes down to the straight length of manifold after head. In our case (apart from Carl who bends the other way) the bend is close to the head and so a benifit could be possible. On a car where the first bend can be further away from the head then it won't have as much benifit (this is not very common though).

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My outer 2 ports are D shaped, with the curved portion outer most.

Since the curved portion is where Swifty made a large improvement last time the head was in for a fettle I decided this bit and the roof had to be perfectly matched.

On the floor and the inner most wall I have made a 2mm ARS.

When I cam to weld the pipes back on they were totally the wrong shape so spent a lot of time yesterday with hammers and a mandrel to reshape them before reattatching them. Ill get some pics later.

It was JH who had the cylindrical ports. Only thing is without gas he only ran mid to low 13s with a very light car and slicks so Im not so sure that was a good head. I keep telling him he needs a Swifty head.

Paul

I seriously doubt it!

My ARS is at the gasket face.







Believe it or not I have removed around 150g from it.

Paul

I seriously doubt it!

I think the correct term is "anti reversion step edge" or ARSE for short......

Was waiting for that Tom.

Paul

I seriously doubt it!

im quite surprised Paul that you dont use a custom trick lcb already!!

a wire wheel in a drill and i bet you could lose another 50g's of rust too

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John haston did indeed have an MED circular ex port head, it was a special with 33mm ex valves, modified inlet calves i beleive were usedand 35.6 race type inlets all on 6mm stems

at the same time john was having his head cut i was working on one for Ian Jonson, i used 32mm rimflow ex and 35.6mm rimflow inlet , this head in now on the front of my twinnie,

when both heads were complete i had both of them on a flow bench i had on loan at the time,

my first impression of the circular port was it loked small in volume compared to my version,

the tests on the exhausts showed that my head flowed i dentical to the CEP on the outer ends and about 10% more on the middle,

as ive said bewfore iv'e lost misplaced all the flow data i gathered but recall the end ports flowed a max of 125cfm and the same on the middle for the CEP, whereas my middle flowed something like 135 cfm plus ,

this proved to me that with the CEP was restrictive, even though it was using a 33mm valve,

i then measured the cross setion of the aperture below the seat and i found i had slightly less than the CEP 33mm but matched it for flow without the need to offset the guide, saving work,

carl

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So did you look into ARSEs Carl?

Could be interesting with the way your headers point upward

Paul

I seriously doubt it!

i also looked into the Benefits Associated with Nitrous Directional Instability Tracts,

so you could say iv'e looked into Arse Bandits,

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Nice ARSE Paul. lol

Looking at the pics you've posted. You have introduced a raised step rather than a step down into the primary.

I'm still trying to get my head around this theory.

I understand Ben's comments with regards to the straight lengths. And the tight bend on the mini being the usable issue.

Paul could you post some links to the subject matter for me to read up on.

I think John H managed to scrap the MED head in question. I might try and get it off him and have a proper look at it. Just to be nosey.

My head is an old Slark item. The old mans item not his son. Still with the square section exhaust ports or be it very large. Might be worth giving them a tickle to the D profile.

Keep up the good work Paul.

Si

I drill holes in everything..!

Paul I have done a lot of hours on this very topic If you look at the build thread of my Racer you will see pic of the new Exhaust tunnel I have designed.
I done a lot of work on a Software program testing this very theory to my utter amazement the program seen a gain in effective VE of 4.5% with a 2mm step on the top edge and a 4.5mm step on the sides of the outer ex ports nearest the centre branchand botom edge. there was no noticeable gain by stepping the centre branch once over 300 ex duration as long as the primary run ran straight from the flange at least 5cm and the next bend was no more that 38deg and another straight run of over 10cm. there is much bigger gains to be got in primary angles and primary lenght tuning but I would rather not go into that here for obvious reasons.

Si, it steps down after the head so the manifold is bigger than the head on the inner wall and the floor but flush on the outer wall and roof. Google anti reversion dam and lots come up.

Paul, I have been intrigued by your centre pipe in particular and would be very interested to see it verses a LCB in a RR test though I cant see that happening. My centre branch is around 3mm larger on both sides and the floor than the head port in standard form which I am leaving alone, Obviously theres a reason for it and I know it works as it gave a power increase when I fitted it over a normal large bore LCB.

Im pretty sure what Ive done will give some sort of benefit as the transition was very random before. Ive now dowelled it to the head to be sure it stays in the right position. I have used the Maniflow stage 2 extra large bore LCB for this.

Paul

I seriously doubt it!