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S16 Head

Posted: July 14th, 2006, 2:22 pm
by petert
Guy, I take it you're impressed with the S16 head? I assume you know they're basically identical to the 1.9L Mi16 head? Here's some flow figures you'll find interesting. Note these were done at 28". When converted back to 10", your std. head was basically the same as mine. So it's reasonable to assume we can compare other values.

The Citroen head was from a factory car raced at Bathurst in the early '90's. It was later fitted with bigger valves by a friend who now owns it. Surprisingly enough it does not flow any better than your S16 head with OE valves!

The other figures are for various 36.5mm valves with different angles as fitted to an otherwise standard S16 head. I finally settled on 10 deg. heads, making a compromise between mass, flow and compression. The 20 deg. valve would have needed dishing.

Also note how impressive the std. exhaust ports are. They're actually too good. I use a tamer exhaust cam to compensate.

Posted: July 14th, 2006, 2:52 pm
by Guy Croft
hello Peter

I'll take a closer look at that, thanks!

Sorry but I don't know what you mean by 10 deg heads etc, please explain..


Posted: July 14th, 2006, 3:35 pm
by Guy Croft
Here are your Mi16 std 34.5mm and 36.4mm 10 deg overlaid Peter, using conversion factor from 28" - 10" of your readings x 0.598.

Mine are temperature corrected, I assume yours are too. I hope I have presented your data correctly, if not let me know.

You'll have to talk me thru how you see it - your results on mine.

Many thanks for publishing,


Posted: July 15th, 2006, 1:36 am
by petert
See the attached pic. The seat prep. for the flow comparison of the four valves was very minimal and probably doesn't do the valves justice. It would be more interesting to overlay the Citroen head with your S16 head, and the two standard heads. My figures are corrected. I know it's difficult to compare flow figures, but what is interesting, is the % difference between the standard heads and the modified heads. I would have said your S16 is all but identical to the Citroen head. Also attached are the finished long stem valves.

Posted: July 15th, 2006, 7:27 am
by Guy Croft
I think I understand now, Peter: the 10 deg is the angle on the back of the valve?
I am not familiar with the M16 head. Photo would help, showing port design. Could you please id the status of your two heads I have overlaid, in terms & mods? I think one is standard with std valves and one has big valves, but beyond that - meaning probably the big valve unit - any mods?
Mine has OE valves, just a back grind but that only picked up 1cfm or at a couple of lifts points, not worth doing, but having tested one one I though I'd best do them all. I certainly don't think the OE valve shape is right for a comp head.



Posted: July 15th, 2006, 7:53 am
by petert
Yes, 10 deg. is the angle of the back of the valve. The 1.9L Mi16 head and the S16 are almost identical. The main identifying feature is the S16 has 10 exhaust studs, Mi16 has nine. Valve sizes, port size, chamber size, layout etc. they're identical. The S16 does have some deflectors before the intake guides, but if you didn't know what to look for you'd miss them. Just to add more confusion, the 2.0L Mi16 head is the same as the S16.

The std. head with 34.5mm/29.5mm valves, was a 1.9L head, absolutely standard with properly cut seats.

The 36.4mm 10 deg. head was a std. S16 head, with only minimal seat work. The purpose of this head was to test the differences between the four different shape valves.

The factory Citroen head is a fully ported 1.9L head with 36.4mm 10 deg. valves and well cut seats. Perhaps you could overlay this one with yours?

It's interesting how much difference the shape of the valve makes and how important it is to match it to the port. As I said in another post however, I decided to give up a few CFM in return for a lighter valve and more compression (no dishing). For the same length valve, the bigger valves are 5g lighter than OE.

I should have some more results next week for a new head. I'm hoping it will outflow the Citroen head everywhere. The hardest part has been the lift below 0.150".

My wife thinks I'm obsessed with this! I probably am!

Posted: July 15th, 2006, 8:21 am
by Guy Croft
Hi Peter

to be honest although the manal suggests you can, I'm not sure how much validity there is comparing heads tested at different pressure regimes. Pick up the flows of my std and your std (with just seat recut) at various lift points and there is a huge difference between yours and mine. If it were not for my having the before and after flow figures for my head I'd be thinking I'd done the seats totally wrong!
If we look at the overlay your std head with std valves appears to be almost as good as my modifed head with std valves, but my own 'before and after' (modifed vs production on same size valves) shows up quite high gains on the ported head - except at very low lift; eg: I have a friend with a bigger flowbench than mine who tests at 25" and gets very different behaviour on Vauxhall XE heads.

Do you have a plot of before and after seat work on he head with std valve sizes?

Thanks for the background on the heads, I'll try and remember it all, but I'm number blind. Yes I saw those port deflectors, thanks.


Posted: July 15th, 2006, 11:03 am
by petert
Sorry, I don't have before/after for a std. head. That head is about as standard as it gets! You're right about comparing figures between flow benches, that's why the % increase is so important. The area under the curve is all but identical for our std. heads. The bottom line is you've done a fantastic job with the OE valves.

Posted: July 15th, 2006, 2:56 pm
by Guy Croft
hi Peter, well, I figure you must be quite expert - for me it's the first S16 I have ever done, and it's very kind of you offer your encouragement, and it's also really great to share results with you.


Posted: July 20th, 2006, 11:32 am
by Peter
Guy, I hope these images may help you with the MI16. (I'm sorry about the size, I'm a work and cannot resize them here.)

The head is a MI16 - XU9J4


@ petert: Glad to see you here - TB_205gti from 205gtidrivers ;)

Posted: July 20th, 2006, 12:16 pm
by Guy Croft
Fantastic photos Peter! I shall study them with interest, now, where is my die grinder?!

(I shall have to be careful - not one but two 'Peters', lots of Peugeot numbers (I'm number-blind) and more expertise than I can shake a stick at!)

Joking apart - It is good to have you here guys, thanks for contributing such interesting material so willingly and in such a concise and well-documented way,


Posted: July 20th, 2006, 1:15 pm
by sumplug
Lovely thread. Well done.
Peugeot 8 valve Heads flow very very well. The stock Car guys and girls are using the 1600 8V engine instead of the old Ford Cross Flow. Seems they looked at every engine out there and found the peugeot engine to be far and away superior to use!!
The 16V Peugeot head looks to be a very nice design. In your opinion Guy, which OEM head is the best out there in terms for flowing for power? Of course, the bottom end its fastened to, makes the decision debateable. So which head on which block?? maybe, this could be given its own title, UNACCEPTABLE!!! :lol:

Posted: July 25th, 2006, 1:27 am
by toby7
Thanks Peter!

Great photos.
Would you at all have a cross section photo of a Peugeot 8v head. XU9JA.

Peter Arnold

Posted: July 25th, 2006, 9:27 am
by petert
........ which OEM head is the best out there in terms for flowing for power? Of course, the bottom end its fastened to, makes the decision debateable. So which head on which block??
There's lots of factors here of course, but I think for a low-mid range (cost) engine, it's hard to beat the 2.0L S16/Mi16 iron block over the 1.9L alloy block, or other 2L blocks. First, consider the basics:

2.0L Iron block
152mm rod length, full floating
oil squirters
factory windage tray
factory trap door sump

1.9L alloy block, wet liners
143mm rod, full floating
oil squirters

The larger bore helps unshroud the valves and you get a better rod/stroke ratio. They both have full floating pistons with oil squirters, where as none of the other blocks do. There is of course an 18Kg weight penality for using the iron block, but this is more than offset with the extra power/torque you'll make. Oil control is also superior in the S16. The alloy blocks suffer badly from oil surge. Of course if you're serious, you'd dry sump both.

If you've got heaps of money, the alloy XU7 block with custom liners and custom forged crank is of course the ultimate.