S3 cylinder head

[motopsycho87]

Hi all, can anyone tell me if the squish on the S3 head inserts is different between all of them of the same? I'm looking to buy the S3 head as I like the idea of changing compression ratio to alter the power band (I use my bike as SM and for enduro), I know I'm going to have to machine it for correct squish, but is the only difference in the chambers or squish height as well? Cheers

 

[dANbOT]

I have an S3 head. The higher compression inserts certainly have less squish clearance, I got my squish down to about 1.6 with a thin base gasket and the AA insert (highest comp) Runs great @ 3000 - 7000 feet on 91, any lower and you will surely need better fuel.
I believe the coolant flow is improved as well, I rarely boil over any more.

 

[Moto7man]

Jakobi has an extensive thread with photos on the squish for the S3 heads. More comprehensive than anything else on the web.

 

[motopsycho87]

I've had a hunt through the post but can't find a list of squish clearances or anything... Am I being blind?

 

[dANbOT]

For what it's worth, here's what I was told as I ordered my S3 kit:
-The shape, and volume of all 3 inserts combustion chambers are identical, except for the depth they reach down into the cylinder (affecting both squish, and compression ratio.
I can't confirm this, but I CAN tell you that the squish is reduced with each step to higher compression, and otherwise they look the same.

If your a perfectionist, and want to achieve 1mm of squish, you would need to have some work done to balance squish, and comp ratio on the S3. Additionally, if you cannot use the higher comp inserts due to elevation your probably going to be close to OEM squish measurement. (mine was over 2mm in stock form). At this point, you may as well just send out your OEM head for machining, to achieve what your looking for.

If however 1.5mm or so is acceptable to you, the S3 will work great. I have zero complaints, and my 300 runs noticeably stronger than stock with the "AA" insert at 3000 feet +. I also feel it runs cooler, but there's too many variables to be sure.
Again, with the "AA" insert, a thin base gasket, and a Wossner piston, squish on my 2014 300 ended up at 1.6mm

 

[motopsycho87]

Sounds like there is no point at all then, I was hoping the squish would be the same on all and just different dome volume, but there's no point if I'm going to have to machine each insert after machining the head. Nice thought anyway!

 

[dANbOT]

You bet, I can see that.
It worked well for me, since I needed to replace a cracked OEM head anyways, and got my squish to a reasonable gap without sending parts off for machining.
Don't take my word as gospel either though... my findings were only what I was told by the vendor, and visual observations as I experimented with the 3 inserts.

 

[motopsycho87]

Any chance you could measure ny of your inserts or just a picture from the side next to eachother?

 

[Jakobi]

I have S3 inserts here for both 250 and 300cc capacities. They both fit in the same 'outer' body.

I could cc them but it probably won't happen for a week. I'm sure I have notes in my build thread, as I did it then too.

As above, the concept of 3 different inserts offering 3 different compression ratios sounds great in theory, and would be in practice if they offered 3 x volumes, but then you'd have no method of adjusting the squish clearance other than the base gaskets, as the outer edge of the insert has to match the depth of the outer head as well.

In a perfect world they'd have a range of inserts with different offsets/depths to set squish, and various volumes. Too much work on their end for what it's worth.. so end of the day the performance gain lies with a well modified stock head.

FWW, I used an S3 on a 250cc. High High (black) insert, and had volume machined out of it for use with a 0.5mm base gasket. 1.25mm squish with 14:1 uccr. Was well through the roof before machining.

 

[dANbOT]

Any chance you could measure ny of your inserts or just a picture from the side next to eachother?

Here ya go:

-silver is low compression
-red is medium compression
Measurements are the amount protruding down into the cyl.

 

[(F5)]

Good grief I'd forgotten what it was like to read analog verniers.

 

[motopsycho87]

It's a shame the squish depth is different, then you could just machine the head and fit different inserts for different characteristics, never mind hey thank you for the pictures!

 

[(F5)]

Well you could machine the squish area all the same, then the head to get down to 1mm, then the inserts you could play with volume and reduction of squish area.

 

[Jakobi]

Well you could machine the squish area all the same, then the head to get down to 1mm, then the inserts you could play with volume and reduction of squish area.

Except the inserts and head join together to form the mating surface on the 2 O-rings, so you would have to machine each insert and the outer head itself to get the squish clearance down. End result a modified S3 head that only uses modified inserts.

Do S3 machine custom inserts? Very possible. I know another brand of after market head did/does offer the service. You could always do this after market too, but you'd be working with squish band angles, widths, volumes, etc. A bit more work than modifying a stock head.

 

[motopsycho87]

Actually sounds quite plausible! So skim the head to the lowest compression head, then skim the squashes to match the first.

Are the combustion chamber volumes actually different between them then, or just the squish? As surely I'd just be machining them all the same in the end?

 

[Jakobi]

Chamber volumes are the same.

The compression increase just occurs by reducing trapped volume as the insert closes the squish up (sits deeper into the cylinder).

 

[motopsycho87]

Wow that's rubbish, so what compression do you get if you go for 1mm squish as it should be?

 

[Jakobi]

Depends on how many base gaskets you need, which head insert you need, etc. Based on variables for your particular engine..

I have notes somewhere from when I ran an S3 black insert on a stock 2010 300cc barrel. Can't recall the exact setup and figures though.

 

[motopsycho87]

I've got 1.5mm base gaskets. So if I were to get the S3, I would need to;

measure piston to TDC gap, lets just say 4mm

machine each insert for 3mm stepped section

skim head to suit

then ideally measure the volume of my current head, and machine the bowls of each insert 1cc less, so i effectively have 4 different compression ratios to play with?

 

[memphis2857]

I think Jacobi did something similar with his S3. The problem you will run into is machining the head itself AND the inserts because each price accounts for a portion of the mating surface.


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