Stroker S2

[aronmatic2]

Very nice to see ,its installed.

[Pat D]

Finally had windscreen and rear window put back in

[Pat D]

Finally have the head back with some extra work done.

[[sTeeWie]]

Clean work!!!
The carbon in the entrances fits very well to the outside colour

[Pat D]

So, the latest update on the engine goes like this...

First some blueprint figures:

Bore- 82.5mm

Stroke- 95.5mm

Piston- 3.244"

Piston to wall clearance- .004"

MLS gasket compressed thickness- 1.61mm

Piston deck height- 10thou or .254mm below deck

Combustion chamber volume- 45cc

Piston dish volume- 15cc

Compression ratio as is 8.28:1

My desired compression ratio I asked for when ordering the JE pistons was 8.5:1CR. To achieve this I'd have to have the piston at least 4thou or .1mm above the deck to give a comp ratio of 8.48:1 and my piston to head clearance would be 1.51mm, minus piston rock which hasn't been measured yet. I have been advised that this could be 20to 30 thou/0.51mm to 0.76mm. So if get say 0.6mm rock at TDC I would minus that from the gasket thickness and then minus another 0.1mm for my piston that will be sitting above the deck.

1.61-.6 = 1.01mm
1.01- .1 = .91mm

So now my piston would have 0.91mm head clearance with piston rock included, which is quite close, as I've been told that 40thou or 1.02mm is usually desired. My issue is if the measured piston rock is going to be more than 0.6mm, say 30thou or 0.762mm I would be coming too close as I would now have 0.85mm piston to head clearance. To be safe I would need to have the piston at deck level when at TDC, but this would drop my compression ratio to 8.42:1.

If anything I would've wanted the comp to be higher so it wouldn't be a slug to drive off boost. I don't know what it would be like as I haven't driven an S2 with similar comp ratio figures. I will be using E85 and a higher comp ratio would've worked out a well. I'm almost at the point where I want to get another set of pistons and bump it up to 8.8:1, but this is way too expensive for me and I would have to put the project aside for a while unfortunately

[Tonks4x4]

Sell your pistons to fund a new set £???

[Pat D]

Sell your pistons to fund a new set £???

I'll let you know, I may machine these ones down.

[Pat D]

[JP]

You can rebush the rods and offset drill them to raise the pistons. But in all honesty if the head work has been done right I wouldn't worry about it. I'm running 7.8:1 compression ratio on my stroker as wishing to stick with normal super unleaded whilst pushing the limit of a 3586 and it's throttle response and driveability is such that if I change gear at 7000rpm in first it's revving up so quick it bounces of the limiter at 8200rpm.

[Pat D]

Raising the piston isn't the issue though, I can skim the deck down instead. The problem is the comp ratio I get when I'm at the safest minimum clearance from the head. I called JE today to get some figures on how they designed my piston, all was good until he said a 1.1mm gasket was part of the equation. So I ended up with 16cc's in my piston dish, we all know that a 1.1mm gasket doesn't exist so in the end when pretty much the only gasket available is the 1.6mm MLS is used, I end up with 8.2:1. 034 are dealing JE's screw up as JE were the ones that came up with the gasket thickness.

I'm sure the 7.8:1CR you have is fine with boost, but what about off boost? I will be using E85, so if anything a higher than 8.5:1CR would've been welcomed in my situation, not the other way around.

[JP]

I'd say that's 034's **** up. JE default to 1.1gasket unless specified differently by customer. Also before the ok is given to go ahead with production you get the specs and have to sign off against them.

Like I said if the head has been ported correct with appropriate airspeeds car drives no different on/off boost it will just mean peak boost comes in a little later. On average every 0.1 compression drop looses 50-60rpm spool.

Hth

[Pat D]

Cheers for the info. Regardless of who's fault, it's up to 034 to get it sorted for me. For the amount of money I've spent just on machining and assembling the head and bottom end, I'm not going to to settle for a near enough good enough result. Imagine if a customer was running 8.2:1CR pistons and wanted an upgrade to 8.5:1CR pistons and ended up like me. That's my view on it.

[AndyP]

Have you measured the deck height of your block?

The 3 that I've measured have all been more than the quoted 236mm, which will make your CR even lower.

[Pat D]

Have you measured the deck height of your block?

The 3 that I've measured have all been more than the quoted 236mm, which will make your CR even lower.

My deck is 236.25mm. The piston rock was measured today and the most rock noted was a total of 15 thou. So half that figure gives me my absolute piston height of 7.5 thou/0.19mm. Which is somewhat good news as I was expecting rock to be a lot more than that. The pistons are currently 0.25mm below and to get 8.5:1CR I'll have to shave 0.65mm off the deck to have the pistons 0.4mm above the deck at TDC and I'll have 1.01 piston to head clearance/squish. Only prob is the little block of metal that has been screwed to the side of the block for water sealing would have to modified as the head of the bolts holding it would be too close to getting skimmed themselves.

[JP]

As you are decking the block anyway I would remove that adapter block and tig it with dissimilar which is what we do on all the I5 and 1.8t diesel block conversions.

Just out of interest how did you measure deck height? As the mains caps are not 100% split central to crank giving varied results.

Best way to measure is fit the crank. Put it to tdc and use a depth gauge to measure from the deck to the big end journal.

Then take that measurement add the stroke of the crank to it. Then use a micrometer for the big end journal size and add half of that to your existing total. It should come out closer to 236.5mm which is the official production deck height.