Hi all,

I am just about ready to weld the 'log' onto my inlet manifold
but need some opinions from the house please.
As it is ATM the runners are poking into the plenum around 4-5mm.
Do you all think this will be fine,or should i shape the ends of the runners
to match the inside of the tube?

I will try and post a pic now to show you all what i mean.

Andy.
[img]]http://locostbuilders.co.uk/upload/8inside.JPG[/img]


HMM. That didnt work,i must learn.

[Edited on 15/8/11 by lotusmadandy]

[Edited on 15/8/11 by lotusmadandy]

Hope that helps

It does indeed.

Much obliged sir

Andy

I'm sure I read a thread on here some time ago where the concensus was that having them poke through a few mm is the best way, I shall go look for it!

You should buy some nice trumpets and insert from the inside, then weld the to the runners

It will deffo work like that. Trumpets will make it better though.

Thanks guys.

I agree that trumpets would be the best option but the problem is
that they will be bigger than the holes in the plenum,so it won't fit over
the top of them.
I think i will just leave it as is and weld it up.

Andy

What he said but I dont see an easy way of attaching bellmouths inside the plenum.

It might be worth looking on ebay for some rubber bike TB trumpets that fit. If you let the runners poke through a bit you might just be able to put / glue / sikaflex them on before you weld on the plenum end caps. If you see what I mean....

Indeed Wasa,

The only way i could fit steel trumpets,is by cutting the
plenum and i dont fancy that very much.


Sebastiaan,

I do see what you mean and you may just be onto something
there.I am intending to make the plenum double ended with a blanking plate,
so the throttle body can go on either end.It is made from a 4" tube so if both ends are
open it should be easy to fit them.

Andy

Hi,

Dont mean to hyjack but I have a quesiton as I am going to be doning the same fabrication in the next month or so.

Why are trumpets better than straigh tubes? Shape is better for air flow? Lips are rounded increasing air flow?

Thanks

Biz.

I will be using a sausage filter so have the luxury of using pre fab trumpets if they are THAT much better.

Maybe i should have mentioned, i will be fitting a turbo
as well. I dont know if it will make any difference to
the flow into the headers?

Andy

No difference. The trumpets increase airflow on boosted and N/A engines equally.

Cool. Thanks Sebastiaan.

Andy

ram pipe flow

This is a fairly accurate guide of what trumpets can do to airflow.

Sikaflex is not fuel resistant, ask me how I know.

im no expert here but it doesnt look right to me

if the inlet is at one end, wont the pressure difference between the trumpets be all over the place, you could solve this by making it conical in shape so that as the pressure dropped across the trumpets the cubic capacity also dropped increasing the pressure?

there must be a fomula for this, but like i say im no expert and i could be talking bollocks

Mike - don't think so, providing the plenum volume is big enough. I think that ideally the plenum volume is such that the inlets don't really "see" the fact that they're in an enclosed chamber at all. (Yeah, I know it's a *bit* more complicated than that...)

The OEM plenum on my Alfa engine is a constant size all the way along, so it'll definately work as is. ISTR that it's best to have narrowing plenums for FI engines though.

quote:

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Originally posted by MikeFellows
im no expert here but it doesnt look right to me

if the inlet is at one end, wont the pressure difference between the trumpets be all over the place, you could solve this by making it conical in shape so that as the pressure dropped across the trumpets the cubic capacity also dropped increasing the pressure?

there must be a fomula for this, but like i say im no expert and i could be talking nutsack

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quote:

---

Originally posted by atomic

Mike, are indeed correct. The fixed diameter plenum will work but is not the most efficient design.

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Thanks for all the info fella's.

I have been busy with a file creating nice radius on the inlet runners,to try and smooth
out the air flow.I am going to go with the plenum shape as it is,it will be a very
similar size to a griffin manifold.Ad to this the turbo boost that will be blowing through
and it should be fine as it is.

Andy

quote:

---

Originally posted by lotusmadandy
Hi all,

I am just about ready to weld the 'log' onto my inlet manifold
but need some opinions from the house please.
As it is ATM the runners are poking into the plenum around 4-5mm.
Do you all think this will be fine,or should i shape the ends of the runners
to match the inside of the tube?

I will try and post a pic now to show you all what i mean.

Andy.
[img]]http://locostbuilders.co.uk/upload/8inside.JPG[/img]


HMM. That didnt work,i must learn.

[Edited on 15/8/11 by lotusmadandy]

[Edited on 15/8/11 by lotusmadandy]

---

where does the throttle body go? was wandering as didnt know if that effected how efficent the setup was as no1 would see the air first and 4 last if it was on the end

Beaver,

How efficient the plenum is going to be,i dont know.What i do know is
that there are a lot of cars with that type of plenum fitted as standard and
they seem to work ok.The thrittle body
fits on the end of the plenum,griffin style.

Dale,

I will be in touch with you when i come to fitting my MS1.
To start with i am thinking of having an MS2 Daughter board fitted
and you will be my first port of call.I will no doubt be in need of tuning advice
to get the motor up and running anyway

Cheers,

Andy

[Edited on 19/8/11 by lotusmadandy]

Better if you can weld some wedges in, so oval where the TB sits, tappering down to the last cylinder

quote:

---

Originally posted by beaver34
where does the throttle body go? was wandering as didnt know if that effected how efficent the setup was as no1 would see the air first and 4 last if it was on the end

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