Race Engine Forum UK

Hello

My project is a PSA engine:
Car: Citroen AX GTI
CC: 1360 cc 8 valves
Stroke X bore : 77 mm X 75 mm
Connecting rod length between the axes: 126,8 mm
Inlet valve diameter: 39,5 mm
Exhaust diameter : 31,4 mm

Modifications:
Pistons: forged bore 75.5 mm
Compression ratio: 11,8
Cam: 315º

And now my big problem:
Cylinder head modification.
I have a flowmeter, and never modify an engine difficult cylinder head so
Original without modification : valve cylinder 1 ...., valve 39.5 mm, 30º seat
Test 2, whihout valve guide, seat 70º-30º-15º
Test 3 , whihout valve guide, seat 70º-30º-15º, and modification pipe and short radius(slight modification).
Any modification in the duct worsens the inlet flow.Pipe with many curves.
Any suggestions for modification this cylinder head?
I lost flow ,from 2mm of lift to 10mm . My camshaft lift max 10.84mm , then do not take advantage flow max of 12 mm lift valve.
I'm lost in this work. I appreciate any help with this cylinder head modification.


Thank you very much.

I will take a good look at this.

Your first graph needs to be reloaded - part of the 'legend' explaining what is on test - is missing.

Please also send all your flow data in original Excel format as an attachment by email to me at:

guy.croft@btconnect.com

G

I cannot overlay my data with yours - your format is totally different to my simple Excel one.

However here is my flow data. It is for the XSI which is similar(maybe identical) to yours. For those Peugeot experts I am useless with Peugeot numbers. All I know for sure is it was the head in the pictures below!

For a start I suggest you regrind the inlet and ex valves and seats to the same angles as I used, shown on test 14. The OE 30 deg angles are hopeless so don't waste time with them. The 70 will go too deep into the insert so the throat should be bore out parallel to give a parallel section and 70 deg section of equal height. The valve angles must be left sharp. I recommend you do the valve/seat ops and then retest to compare before doing anything else.

You should plot bare port flow - no valve fitted - so you can compare behaviour with valve in. You can see mine on the graph and yes in the case of this head - it flows more at high lift with valve fitted than not. This seems a ridiculous thing but it is true and some other designs like the 205 Peugeot can also exhibit that behaviour. There is clearly some turbulence over the short radius which disappears when the valve is fitted. Alteration to the inlet short radius by tiny amounts and testing every time with valve in can get rid of it but it is fantastically difficult to do and not frankly worth wasting time on. You would be as likely to wreck it as make it better. One thing you should be aware of is a porting 'golden' rule:

'' if you enlarge the port and the flow does not go up - the short radius is wrong''
I have shown below the optimum inlet port size.

A head prepped my way with standard valve sizes at 1360 cc is quite capable of over 130bhp on ITBs & injection, I do have full test data but it's confidential.

Leave the short radius and port alone for now. Hope this helps you some.

G

Thank you very much for answering GC.

I used 30 º valve seats because they are the originals.
I am waiting for a cylinder head that I bought. (My bad job in this cylinder head, ruined this cylinder head)

A head prepped my way with standard valve sizes at 1360 cc is quite capable of over 130bhp on ITBs & injection

My calculations and hopes are at 120 hp, with the original intake manifold.
The intake manifold gets me in trouble. Decrease floe in 10% from 3 mm valve lift. ( add pictures another day)

Today add this my bad work:
Thanks

The new cylinder head
Flow data:
Later, install new valve seats 45 º (insufficient money for now)

Now I'm worried about this:

The intake manifold is plastic, impossible to change more than 2 mm (+o-) in the diameter.
The intake manifold does not fit with the cylinder head. INtake manifol original no can not be changed, cylinder head original ... any suggestions to solve this?

A curiosity:

If the inlet manifold restricts the peak flow and can't be modified you really have to try and optimise the flow with valve-in in the mid-range, in other words make the best of what you have. Look at my graph again and you will see what I mean. No point chasing great flow over 10mm valve lift (approx) - too difficult to get the short radius right.

But - I cannot see you making real gains until you change the valve angles. You do not need to fit new inserts, you can regrind the old ones from 30 deg to 45 deg and the valves too.

I hope this guidance makes sense to you.

GC

Hello

After a while,I'm with the project.
New cylinder head, not mod camber, no mod short radius, without valve guide: Flow max oe 10 mm : 76 cfm
Flow max mod 10 mm : 83 cfm
Increase inlet flow in 9% .

What surprised me:
Flow max oe 1 mm : 11 cfm
flow max mod 1 mm: 14cfm
Increase inlet flow in :27%!!!!


Flow max oe 2 mm : 22.6 cfm
Flow max mod 2 mm : 27 cfm
Increase inlet flow in 19 %

Flow max oe 3 mm :32cfm
Flow max mod 3 mm :36 cfm
Increase inlet flow in 12.5 %

When I have time I will put measures exhaust.
We continue to work.Thanks for help, Guy Croft

Nice work - well done.

Always nice when my figures make sense to another engine builder,

G

Hi !

Shame on me , I've just been working on a Peugeot 106 1.6 XSI engine few days ago , but sadly haven't made not a single picture of the project. I've prepared it for my friend for racing purposes ...

But Guy , I'm very pleased to know that I've done it just as I saw now on yours pictures ! Been concentrating on working on the same areas .. though I'm not an expert as you! But it's nice to know that I haven't done a "bad job"..

... I just wasn't 100% sure which valve angles work for this engine.

Kind regards
Damir

Hello.

After a long time. Start the engine. the cylinder head of the photos in this post, installed.
roller dyno test: dates, test: Right now, the unit is one Motronic engine original, modified. No maps for more than 7300 rpm.
We are waiting for a programmable engine control unit.
How do you see the results?
I'm somewhat confused. I am not surprised the power and torque. Is more or less what we expected.But I'm surprised the engine speed of max torque and max power. Cams 314º.
I expected max torque at 5500 rpm + or-
Next job, installing programmable ecu and increase compression ratio. Currently 11.2..

Any tips to increase the rpms of maximum torque?

I don't know near enough about the engine to comment yet. I do not have X-ray eyes!

1) need high quality photo of engine with inlet system and exhaust system. I need to get a clear idea of the layouts and lengths.
2) what is the cam timed at?

Thanks for replying.

Guy Croft wrote:2) what is the cam timed at?

Cam Lift(mm) 7.62mm Inlet/Exhaust
Valve Lift(mm) 10.41mm Inlet
Duration 315 Deg Inlet
Timing 53/82 82/53
Full Lift Inlet 104 Deg ATDC
VC (mm) 0.25mm Inlet /Exhaust
LTDC 4.44mm Inlet

Guy Croft wrote:1) need high quality photo of engine with inlet system and exhaust system. I need to get a clear idea of the layouts and lengths.

This engine runs on GrA category. The engine has to follow the GrA FIA regulations .
It has an FIA homologation. , everything about the motor is regulated.
  The intake manifold and exhaust are origin by regulation
I try to get more photos

exhaust manifold photos

The problem may be the igntion timing - might need more or less advance but apart from that - with the regs - the only thing you can do is try relaxing the cam timing say to 106/108 or 110 inlet FL.

Assuming the intake is not restricted by the throttle body (I have no idea what you are using, all I can see is the intake manifold) it may be the cam timing you are using now (104) does not suit the wave characteristics of the header and inlet manifold runners.

G