Race Engine Forum UK

The head appears to have very high flow (see photos) but when the manifold (in fully prepped state) is bolted on the flow drops like a stone.

This irritating issue tied me in knots for a few hours - though I could laugh about it after, can you figure out what's wrong?



GC

Hello Guy !

Something wrong with the upper wall on the inlet manifold side deep down around the injector holes ? or maybe the upper area of the port entry on the head side as being a bit weird triangle shape (well to me it is unusual !)

Regards !
Damir

Hello Guy,

I think you should try an abrupt section change from round to flat section in the manifold/port floor .
I have seen with this manifolds that the air blocks itself.
look for swirl in the ports,
Did you test with throttle bodys mounted?

Regards, Klaas

No mods are needed, the shapes, sizes etc are perfect. Now of course I know what the problem was..!

Clue: Was the bare port flow of the head actually right?

Not trying to be clever, but it is supposed to be a brain 'teaser'!

GC

As you have filling in the top of the head inlet port, don't you need todo the same with the back of the manifold to correspond ?

Seems like you are using the injector holes in the TBs without filling in the manifold holes.

Sean

Having done a few of those on my flowbench Ive never found the bare port flow to be as high as that! A 1400 cannot possibly need as much lungs as that so Id be confident in my figures.

Did the spark plug get left out.... Ive done that one a few times.

Steven

No air goes thru the injector holes at all, makes no difference to manifold-on flow, although I found this out by blocking and unblocking them. The only effective flow regime is the air coming out of the manifold. That's what the head 'sees', the region filled in has no effect on flow at all.
Yes the flow 'appeared' unusually high though at first I was more 'impressed' than concerned that it might be wrong, human nature? It was what happened when the manifold went on that bothered me, could not get rid of the 'loss'...
The spark plug was in it's proper place..

GC

The manifold creates a sharp lip at the top of the port entrance/injector position which could cause alot of turbulance when compared with the smooth entry created by the plasticine on the bare port measurement.

Therefore it looks like the manifold created a loss because the bare port flow was artificially high?

Ben

guides bores open ?

Hi Gc

Like you already know I have done a porting job on a similiar adapter plate beside the fact that mine is sideraft.
On your adapter plate the round to oval shape seem really perfect and the downdraft head port too.
So its not logic that after assembly the head dont flow correctly!
I am not a pro with all this but do you think this flow lost can be caused by the plate port roof which dont allow the air to correclty follow the head port roof?
Or a too abrupt angle between plate and head which cause alot of turbulances near valve seat area?

Hi Guy!


Me guessing some reasons for the head to decrease in flow from 134.6 bare to 117.4 with manifold:


1: The manifold itself flows only 122 cfm - and might well be the limiting factor for what the head flows - Ok down to 122cfm

GC wrote:

.....The only effective flow regime is the air coming out of the manifold. That's what the head 'sees',......

Clue: Was the bare port flow of the head actually right?

Ok this is wild speculation:

2: Airflow entering port from manifold differ vastly from when head tested bare
When looking at the picture of the bare head flow, the air is not forced in at any specific angle but flows freely - and also helped by clay ram pipes:-)
The manifold itself seems from the pictures to change in shape going from round to oval. Actually the shape seems to diverge in the air direction at the sides of the manifold. This means that the airflow into the port with the manifold fitted - at least in this area - differ significantly from the bare head flow.

3: The airstream from the manifold does not enter the port at the right angle.
The airstream from the manifold is entering the port at a wrong angle (too high/low) and hence the flow through the port and valve throat is disturbed.

BTW - another clue wished for:
Is what we see the end/final flow figures with the manifold fitted?


Best regards

Remi Lovhoiden

Is the fact that you can laugh about it now reason to suspect that you made a silly mistake??? Did you flow the head in the wrong direction Guy???

Scott.

Well, you're all very good at the detective work - so either you were all great at head stuff anyway or the site is having an influence! Very impressed with your logic Remi!

All good points but that head/man combo were as near to perfectly optimised as I can do. No-one's hit it on the cause of the 'flow loss' with manifold fitted yet though.

OK - clue. This is the first time I have used port 4 on that head for dev flow, normally I used port 2 or 3, simply because the head sits balanced on the rig more easily.

GC

Apart from obvious but i doubt youd do it- offset on bore or uncovered part of bore-

does that head have exhaust gas recirculation port and you ar getting a leakage from that making inlet seem better than it is? I normally alloy weld it up on those engines

Very good Steve, yes the exhaust-gas-recirculation port (red, photo) that feeds gas from the ex port to the inlet manifold.

OK, in defence of my own mistake: it's a long time since I even had a head in here with egr ports. And it's the first time I've picked the port set with the gallery in it.

And yes, I went thru every single one of the fault-finding steps outlined by members in this thread (and some besides) and wasted a whole afternoon trying to figure out why the flow was so 'atrocious' with the inlet manifold (that blocks off the egr port that I thought was a coolant gallery..) on!

Final flow (actual!) summary (bpf @10") for interest.
Fully developed in port
(with new GC race guides but so-far unmodified seats)
119.4cfm without man
117.4cfm with modified man

std head flows:
98.6 cfm without man
97.3cfm with man

Guide loss per port
std 7.4cfm
race guide 1.6cfm


GC