Inlet manifold matching to match or not to match

Road-race engines and ancillaries - general discussion
Post Reply
Christopher_205Rallye
Posts: 28
Joined: July 7th, 2006, 8:44 am
Location: Copenhagen, Denmark
Contact:
Contact Christopher_205Rallye

Inlet manifold matching to match or not to match

Post by Christopher_205Rallye »

I've read guys article here, but I'm still a little confused here. Down stream matching (inlet is smaller then head port??) how important is it? I have various schools of though here.

1) Its a good thing in general do it. All sharp edges are bad
2) Don't do it especially on the short side. Since the fuel probably is running down this edge at low rpm. This "step" creates much needed turbulance which aids in the mixing of the fuel and air.
3) I think generally Guy thinks this should be done..(but we are talking raod engines here too that don't always run at high rpm)..(correct me if I am wrong here guy:wink: )
4) You don't have a flowbench or a clue. Don't go there


Reason being is last time I had my carbs off I decided to match the inlet to the head since there was at least 2mm. Most of this work was done to "short side radius" of these ports. Since it was this inner curve that showed most mismatch. Roof of upper curve was ok. They basically now match perfect.

It drives much the same (who know maybe some more HP who knows) but it is noticibly harder to start without lots of choke. But when warn runs fine...even at low rpm
Attachments
The TU24 head with OE manifold fitted. No gasket is used. Only instant gasket. Overflow is cleaned of with solvent after from the inside
The TU24 head with OE manifold fitted. No gasket is used. Only instant gasket. Overflow is cleaned of with solvent after from the inside
Picture 067 (Small).jpg (79.78 KiB) Viewed 8711 times
Top
Guy Croft
Site Admin
Posts: 5039
Joined: June 18th, 2006, 9:31 am
Location: Bedford, UK
Contact:
Contact Guy Croft

Post by Guy Croft »

Hi Chris

I cannot give a quantitative answer in this case, only in principle. If the inlet manifold flows the same or more than the port it does not matter, and the step - well it doesn't matter either, the air will just flow straight past it. Well it affect inlet tract pressure wave, well, there are degrees of mismatch but here - not in my experience.

What would be critical with your setup is to examine the behaviour of the head and manifold together, after examining how they behave as separate items. There may well be an issue with the main flow vector of the air into the head. This is a common problem with inlet manifold with acute curves like yours. It may be that in trying to make it better by matching you have made it a bit worse, easily done without a flowbench.

Some guys like to dowel manifolds to heads (see below) but this is a total waste of time unless the head-manifold pair have been flow tested, which they clearly had not in this case. GC extreme limit flow development on this Peugeot 205GTI 8v 1600 head took the flow from an as received, (previously prepared) 100cfm with to 117 cfm with manifold and from 155 bhp to over 170bhp. Plus the head as it came in had inlet valves fitted that were too large for the seats (..a pseudo 'big valve conversion'..) and I actually reduced them in size and reshaped them to get it to fly.

GC
Attachments
Vauxhall 2.3 HSR 16v inlet manifold on bare port flow test.
Vauxhall 2.3 HSR 16v inlet manifold on bare port flow test.
Vaux HS 2.3 flowtest bare & in man_02.JPG (26.11 KiB) Viewed 8701 times
This swept inlet manifold gave almost no loss at all, I was suprised. But it has a generous radius and is very 'roomy'.
This swept inlet manifold gave almost no loss at all, I was suprised. But it has a generous radius and is very 'roomy'.
Vaux HS 2.3 flowtest bare & in man_01.JPG (28.87 KiB) Viewed 8698 times
The manifold flowed far more than the head (even before rework, the head final flow was 116cfm at full lift @ 10", 174bhp), but it still gave a huge loss when bolted on.
The manifold flowed far more than the head (even before rework, the head final flow was 116cfm at full lift @ 10", 174bhp), but it still gave a huge loss when bolted on.
Peugeot in man loss region marked.jpg (110.85 KiB) Viewed 8697 times
1600 cc Peugeot 205 GTI manifold before-and-after rework. Looked OK before, but had a large upstream mismatch and the bumpy internal profile lost 9cfm when fitted up.
1600 cc Peugeot 205 GTI manifold before-and-after rework. Looked OK before, but had a large upstream mismatch and the bumpy internal profile lost 9cfm when fitted up.
Peugeot 205 sidedraft man improved flow.jpg (111.63 KiB) Viewed 8694 times
Peugeot 205 1600 head: The string is in the main flow vector - the route the main airstream wants to take - if the manifold profile disturbs the vector, the flow drops, however much air the manifold flows.
Peugeot 205 1600 head: The string is in the main flow vector - the route the main airstream wants to take - if the manifold profile disturbs the vector, the flow drops, however much air the manifold flows.
2005_1210Image0038.JPG (27.85 KiB) Viewed 8688 times
Last edited by Guy Croft on July 10th, 2006, 10:12 am, edited 2 times in total.
Top
Christopher_205Rallye
Posts: 28
Joined: July 7th, 2006, 8:44 am
Location: Copenhagen, Denmark
Contact:
Contact Christopher_205Rallye

Post by Christopher_205Rallye »

Thanks for the reply Guy, Appeciated. Just getting my head round the principles.
inlet manifold flows the same or more than the port it does not matter
Very hard for an unexperienced layman like me to know this I suppose. The port is larger then the manifold but obviously has a much larger short side radius then my curvy maifold. Sure its impossible to know without a flow bench...

What would be critical with your setup is to examine the behaviour of the head and manifold together, after examining how they behave as separate items. There may well be an issue with the main flow vector of the air into the head. This is a common problem with inlet manifold with acute curves like yours. It may be that in trying to make it better by matching you have made it a bit worse, easily done without a flowbench.


I like way you use a piece of string in your example..I understand what you mean now

Yes of course you are so right its an dangerous thing on the eye porting without a flowbench. Thats why I only cleaned up the ports in the head and not rework the shape.

On the manifold maybe I went a bit too far...(I must remember to put a superflow on christmas list :roll: ) but of course it must depend n who is using it :?

We all have to learn somewhere :oops: Good thing I have an unmolested inlet and head as spare just in case :wink:

Thanks

Christopher
Top
Guy Croft
Site Admin
Posts: 5039
Joined: June 18th, 2006, 9:31 am
Location: Bedford, UK
Contact:
Contact Guy Croft

Post by Guy Croft »

Hi Chris,

don't feel bad, this website is going to be a learning curve for a lot of people, I hope. Sure it's easy for make to say 'u have to do this & that', but I/you never stop learning... I didn't know any of this 20 years ago. And, in fact it took me 3 weeks to unravel the Peugeot head secrets - when if came in I first thought 'I won't be able to better that'.. but I did and it was useful exp.

GC
Attachments
How it came in, pared back to the limit for an 'oversized valve' and almost a knife edge on the top, narrow and irregular contact face, less than 0.5mm wide in places.
How it came in, pared back to the limit for an 'oversized valve' and almost a knife edge on the top, narrow and irregular contact face, less than 0.5mm wide in places.
Peugeot 205 GTI seat as received.jpg (115.67 KiB) Viewed 8683 times
The valves were too big, after regrinding the seat to establish an accurate contact face of the right diameter I had to do a lot of 'tidying up'.
The valves were too big, after regrinding the seat to establish an accurate contact face of the right diameter I had to do a lot of 'tidying up'.
Peugeot 205 dressing around inseat with dummy valve.jpg (112.52 KiB) Viewed 8680 times
My seat after finishing, compare with as-received below. The flow dropped even with the superior seat work, a sure sign that the short side radius is wrong - it was..
My seat after finishing, compare with as-received below. The flow dropped even with the superior seat work, a sure sign that the short side radius is wrong - it was..
Peugeot 205 GTI - reworked seat.jpg (117.63 KiB) Viewed 8679 times
Top
Christopher_205Rallye
Posts: 28
Joined: July 7th, 2006, 8:44 am
Location: Copenhagen, Denmark
Contact:
Contact Christopher_205Rallye

Post by Christopher_205Rallye »

:D

Yep I am learning.

It's looks fab Guy!! :D I 'm sure it will run as fab too!!

Bit off topic but...

A few pics of my unlcleaned and unmolested spare TU24 head so you have an idea. Looks pretty different to the XU engines.

Better let you get too it :wink:

Many thanks again for the explanations..
Attachments
Inlet valve
Inlet valve
Picture 076 (Small) (Small).jpg (37.55 KiB) Viewed 8673 times
Hard to see much ...inlet port
Hard to see much ...inlet port
Picture 066 (Small).jpg (35.94 KiB) Viewed 8675 times
3 angled inlet seat. Nasty casting imprefections and drop after guide on some ports
3 angled inlet seat. Nasty casting imprefections and drop after guide on some ports
Picture 060 (Small).jpg (55.67 KiB) Viewed 8676 times
75mm Combustion chamber. Inlet valve has a lot of shrouding.. Since the application is planned to be 78.5mm who knows maybe a small gain can be achieved here?
75mm Combustion chamber. Inlet valve has a lot of shrouding.. Since the application is planned to be 78.5mm who knows maybe a small gain can be achieved here?
Picture 059 (Small).jpg (71.32 KiB) Viewed 8675 times
Top
Post Reply

Return to “General Discussions - Road -”

Who is online

Users browsing this forum: No registered users and 19 guests