Bandit 1200 with 'busa pistons info and potential upgrade path

[rerb]

My motor currently runs stock bandit rods, stock busa pistons, standard cometic MLS head gasket and copper base gasket. The cylinders were shaved 1 mm. I'm trying to save some money by buying hayabusa turbo pistons instead of mtcs for better internals. (Almost half the price!)

The hayabusa pistons have a wrsitpin center to timing edge distance of 25 +/- 0.2 mm. Wossner K8734DA-4 hayabusa turbo pistons are 26.8mm. 

With gaskets installed, squish band with my setup is 1.0mm on the nose using the solder method. Deck height is ~1.25mm but it was a pain to get consistent and the squish should be the same measurement since the bandit head doesn't have a taper on the sides I measured and the piston shouldn't have "tipped" in the bore during measurment since I measured along the wrist pin axis.

The compression ratio is around 7.9:1 with this setup. (Non shaved cylinders with stock busa pistons is about 7.2 using my non shaved spare cylinders as a guide)

I'm going to order a 80 thou (2mm) sheet of aluminum and if it's nice and flat, use the laser cutter at work to make a cylinder spacer. My theory is raising it 2mm will increase the squish 0.2mm (since the pistons are 1.8mm taller) and bring compression to around 8.8:1 6.72:1 with 2 base gaskets. (Edit: stock busa dish is ~10cc, wossner is 17.8)

Anyone see a problem with my plan or have experience with wossner pistons? I've always used them for 2 stroke rebuilds but never performance bits.

Also its been mentioned before but ill back it up, if anyone's running busa pistons I'd definitely recommend shaving the cylinders 1 mm, makes off boost way better. I gained 50 hp from the same boost after doing that.

 

 

Edited Tuesday at 03:30 PM by rerb

[Gixer1460]

I think sub 9.0:1 CR is waaaay to low for use with E85 which is as close to methanol as anything available and that needs compression and rich AFR. Query - if stock Bus pistons have 'correct' ht for your combination why do 'Bus turbo pistons' not (which should be drop- in's) ? Why are they taller and so, even in a Bus motor, INCREASE the CR not lower it? I'm confused!

If it is, what it is . . . . . i'd be tempted to spacer plate only 1mm and skim pistons 0.5mm and get squish to 0.8 - 0.75mm (unlikely to over rev a blown motor & stretch rods!) and 9.5:1 CR if E85 is in constant use. Hell that CR would even work with regular 98 super unleaded if boost was moderate! 

[rerb]

6 hours ago, Gixer1460 said:

I think sub 9.0:1 CR is waaaay to low for use with E85 which is as close to methanol as anything available and that needs compression and rich AFR. Query - if stock Bus pistons have 'correct' ht for your combination why do 'Bus turbo pistons' not (which should be drop- in's) ? Why are they taller and so, even in a Bus motor, INCREASE the CR not lower it? I'm confused!

If it is, what it is . . . . . i'd be tempted to spacer plate only 1mm and skim pistons 0.5mm and get squish to 0.8 - 0.75mm (unlikely to over rev a blown motor & stretch rods!) and 9.5:1 CR if E85 is in constant use. Hell that CR would even work with regular 98 super unleaded if boost was moderate! 

Wossner says "base plate required" for those pistons, I got the 26.8mm number from emailing them. The bike will run pump gas 95% of the time, but for the standing mile and a half events that I plan to go to, I want it to run way cooler than it does currently on pump, and make more power, which I want to achieve with e85. 

I think 9.5:1ish is a good target for CR, I've had 26 psi down this motor at 9.4:1  on standard 93 (98 for you guys) with the clutch being the weak point but I'll have watermeth and a conservative tune. Only thing stopping me from being full time e85 is that I'll have to get it shipped here by the barrel... 

 

[Arttu]

I have to admit that I couldn't follow all your numbers completely But I guess you are aware that Wossner turbo pistons will result lower compression than stock Busa pistons even when you set the squish / deck height the same? Also I'm wondering how you got 1.0mm squish with 1.25mm deck height (if I understood your description correctly)? Squish should be deck height + gasket thickness.

Otherwise ~9.5:1 compression and 1.0mm squish sound pretty good to me. On pump gas you should be able to run it up to 15 psi, at least. Probably more with water-meth injection. And on E85 it should be good for 30 psi or so.

[clivegto]

Don't know about aftermarket pistons but I have hayabusa mk1 pistons and rods in the Harris with B12 mk1 motor it does have a big valve flowed head though. Now if I remember correctly with a 2mm spacer plate (no base gaskets) I ended up at 8.83:1 with 0.8mm head gasket. 

[Duckndive]

Curious as to why you decked / shaved the block -1 mm 

As this one of a few I've done was stock everything with just gen1 busa pistons at TDC 

[rerb]

On 1/19/2025 at 2:07 PM, Arttu said:

I have to admit that I couldn't follow all your numbers completely But I guess you are aware that Wossner turbo pistons will result lower compression than stock Busa pistons even when you set the squish / deck height the same? Also I'm wondering how you got 1.0mm squish with 1.25mm deck height (if I understood your description correctly)? Squish should be deck height + gasket thickness.

Otherwise ~9.5:1 compression and 1.0mm squish sound pretty good to me. On pump gas you should be able to run it up to 15 psi, at least. Probably more with water-meth injection. And on E85 it should be good for 30 psi or so.

Yeah, I'm not sure why the discrepancy. I did the solder test a good 4 to 5 times on 2 cylinders and kept getting pretty much exactly 1mm, but my calipers would always read higher on the deck height using the depth gauge. 

I know the wossner kit is "tall deck" but I don't know the dish volume of them, I'll send them another email and ask to verify my numbers. 

 

4 hours ago, Duckndive said:

Curious as to why you decked / shaved the block -1 mm 

As this one of a few I've done was stock everything with just gen1 busa pistons at TDC 

Strange, using bandit rods when I first put mine together I had around 2mm of deck clearance and it was way more sluggish off boost than it is now

[Arttu]

39 minutes ago, rerb said:

Yeah, I'm not sure why the discrepancy. I did the solder test a good 4 to 5 times on 2 cylinders and kept getting pretty much exactly 1mm, but my calipers would always read higher on the deck height using the depth gauge. 

I know the wossner kit is "tall deck" but I don't know the dish volume of them, I'll send them another email and ask to verify my numbers.

Was that deck height measurement with or without head gasket? If the gasket was included then the discrepancy is only 0.25mm which isn't that dramatic.

I'm pretty sure the Wossner turbo pistons have bigger dish volume than the stock ones. That's the main idea of low compression pistons, to get lower compression while maintaining good squish gap.

[rerb]

Just now, Arttu said:

Was that deck height measurement with or without head gasket? If the gasket was included then the discrepancy is only 0.25mm which isn't that dramatic.

I'm pretty sure the Wossner turbo pistons have bigger dish volume than the stock ones. That's the main idea of low compression pistons, to get lower compression while maintaining good squish gap.

That was without the head gasket, I'm pretty sure that it was user error as the edge of the caliper was very small and difficult to hold straight against the deck when measuring. 

I sent wosser another email about the volume, I'm fine with anywhere from ~9-9.5:1 for this build, what I'm mostly trying to get dialed is the squish. I understand that with lower compression I might not get all the benefits from e85, but like I said earlier I'd only be running it for it's cooling properties. I know for a fact that longer stretches of WOT at 21 psi IATs were around the 160 mark and climbing with 50/50 watermeth spray, close to 200 pre spray according to my dual sensor temp gauge (Farenheit). However on the teardown after 3 seasons there's no evidence of detonation at all so so far so good.

Main goal is to break 200+ relatively easily in the 1.5 mile event and not cook the motor

[rerb]

Made a mistake, in a hurry I used 21.5ml as the head volume instead of 29, since the forum post I was viewing was discussing the DOT head (21.5).

the ACTUAL numbers are with 1mm shaved: 7.9:1

stock cylinders: 7.15:1

I updated the main post. I also heard back from wossner, the pistons are 17.8cc vs. the stock busa 10cc.

Unfortunately, this setup is too low (sub 7 CR). I'm looking at their other piston options to try and find one that will fit nicely. If I can't, I'll bite the bullet on a set of MTCs.

Edited Tuesday at 04:07 PM by rerb

[Duckndive]

24 minutes ago, rerb said:

Made a mistake, in a hurry I used 21.5ml as the head volume instead of 29, since the forum post I was viewing was discussing the DOT head (21.5).

the ACTUAL numbers are with 1mm shaved: 7.9:1

stock cylinders: 7.15:1

I updated the main post. I also heard back from wossner, the pistons are 17.8cc vs. the stock busa 10cc.

Unfortunately, this setup is too low (sub 7 CR). I'm looking at their other piston options to try and find one that will fit nicely. If I can't, I'll bite the bullet on a set of MTCs.

Stock 8.48:1 

[rerb]

12 minutes ago, Duckndive said:

Stock 8.48:1 

This is what I was using. The deck clearance is the 1mm i measured with the solder for the head to piston TDC with all gaskets and full torque, with an added mm because It was shaved.

Are you using a copper head gasket? The only MLS I've been able to find are 0.030" compressed

[Duckndive]

 

Gasket was the one i removed "MLS" after it spat it out in a tantrum 

If your gasket is 0.030"   thats 0.762mm

 

Edited Tuesday at 05:22 PM by Duckndive