turbo pistons

[peter1127]

having trouble finding pistons with low CR for turbocharged GSXR1127.  Looking for 8:1 maybe 8.5:1 compression and 81mm/1216cc.  All pistons I can find are high compression so need a crazy spacerplate to lower compression and squish is gone. Anybody a recommendation?

[Joseph]

Would GSX 1400 which are 81m and i think same diameter wrist pin be any good ? Comp is low at 9.5:1 

[Arttu]

MTC seems to have 81mm turbo pistons with advertised 10:1 compression. Maybe that could be lowered enough by machining some dish on the piston and increasing the squish to upper end of working range?

Busa pistons could be one option too. If I recall correctly what others have told here stock Busa pistons in oil cooled engine result about 9.5 compression when the deck height is adjusted to minimum. So turbo pistons could end to that 8-8.5 range, maybe.

[peter1127]

1 hour ago, Arttu said:

MTC seems to have 81mm turbo pistons with advertised 10:1 compression. Maybe that could be lowered enough by machining some dish on the piston and increasing the squish to upper end of working range?

Busa pistons could be one option too. If I recall correctly what others have told here stock Busa pistons in oil cooled engine result about 9.5 compression when the deck height is adjusted to minimum. So turbo pistons could end to that 8-8.5 range, maybe.

MTC seems good option, not sure how I missed that :-)  Yes I could probably machine a dish  and add a 1mm(?) spacerplate

Edited March 5 by peter1127

[Gixer1460]

MTC used to be the 'go to' in GSX draw through installs as advertised @ sub 8:1 CR - it's the same piston used in turbo GSXR's but with shorter stroke gives 10:1 CR! Wasn't going to say anything as you wanted lower!

[Duckndive]

1 hour ago, Gixer1460 said:

MTC used to be the 'go to' in GSX draw through installs as advertised @ sub 8:1 CR - it's the same piston used in turbo GSXR's but with shorter stroke gives 10:1 CR! Wasn't going to say anything as you wanted lower!

They have different pin heights ...

I,ve built 1230 / 1260 EF motors using stock GSXR pistons and you have to deck the block as they sit 2,mm "ish" in the hole 

[Gixer1460]

that explains a bit ! so if you used gsx pistons in a gsxr you should get a similar low CR?

[Duckndive]

21 minutes ago, Gixer1460 said:

that explains a bit ! so if you used gsx pistons in a gsxr you should get a similar low CR?

other way round they would end up above the deck.....

GSXR pin height is lower than GSX pin height 

i,ll dig some out and do a pic 

Edited March 5 by Duckndive

[Gixer1460]

My Brain hurts ! 

[peter1127]

Ordered the MTC pistons. Will see how much I can safely cut out to lower compression. thanks guys

[Duckndive]

On 3/6/2024 at 9:14 AM, Gixer1460 said:

My Brain hurts ! 

Ok found some slugs to show differences both pistons on same 20mm Pin for comparison "both are stock used from there relevant engines"

 

Air Cooled EF on Left Oil Cooled 1100 K, L or Right 

Oil Boiler "Raised Crown" is 0.75mm "ish" Lower than the air cooled flat top 

Oil Cooled Piston Deck is 2mm Lower than EF Deck...........

However Best to Do your own measurements and sums.... 

Edited March 14 by Duckndive
txt

[peter1127]

Got the MTC 81mm 10:1 pistons. They are much beefier around the wristpin area. They are now boring and honing the cylinder block.  Before I mentiioned I want the CR to be 8:1 - 8.5:1. Reading a bit more in various places  I think its a bit too low for a road bike.  9:1 should give faster  spoolup and better low end while it should enable 15psi on 98 octane resulting in around 270hp. (input welcome)

Played in CAD with the pistons to see what could be done to lower the CR while maintaining squish. Around 4cc should be cut from the piston to achieve 9:1. Thing is, in the middle of the piston is a relatively thin area of 5mm which I think I should leave alone. A bit surprised that turbo/nitrous pistons have  a thin area in the middle. Maybe because they mainly make high compression pistons from this casting? The rest of the piston is 9mm so I could reduce that by milling out a ring 1.5mm deep. Of course I'm first going to verify deck height and actual compression volume before ruining new pistons 

Does that make sense, or does that f@ck up combustion in such way that it would be better to add a spacerplate and accept the larger squish?

 

unmodified MTC 81mm

 

Unmodified MTC 81mm

 

 

Bottom of MTC piston

 

 

Modified MTC

 

Modified 81mm MTC

 

 

Modified 81mm MTC thickness check

Edited March 29 by peter1127

[DAZ]

I'll start by saying I have no knowledge of piston design but when I saw your idea to modify the crown of the pistons I immediately thought of diesel pistons I have seen that shape (ish) maybe this helps maybe not but it is an area to research as regard crown shape an squish perhaps.....

[Arttu]

9:1 compression for 15psi on pump gasoline sounds pretty much right. I had earlier 9.5:1 compression up to 18psi or so. Although I had water injection for charge cooling but I tested it also without water injection and didn't notice any problems.

Your plan for piston dish looks exactly like what I did on my current JE pistons. I think the button in the middle shouldn't hurt combustion chamber efficiency in any way. If I recall correclty the crown in the middle was only 4.5mm thick. It has been fine but I wouldn't like to try any thinner. Ideally you would like to make the dish the same shape than the combustion chamber but that's difficult to make without CNC milling...  

[Fredrik_Steen]

I vote for leve them as they are and send it. If you have the ability lower the ignition 1-2 degrees at peak torque. 

[peter1127]

20 hours ago, Arttu said:

9:1 compression for 15psi on pump gasoline sounds pretty much right. I had earlier 9.5:1 compression up to 18psi or so. Although I had water injection for charge cooling but I tested it also without water injection and didn't notice any problems.

Your plan for piston dish looks exactly like what I did on my current JE pistons. I think the button in the middle shouldn't hurt combustion chamber efficiency in any way. If I recall correclty the crown in the middle was only 4.5mm thick. It has been fine but I wouldn't like to try any thinner. Ideally you would like to make the dish the same shape than the combustion chamber but that's difficult to make without CNC milling...  

good info thanks! 

[peter1127]

17 hours ago, Fredrik_Steen said:

I vote for leve them as they are and send it. If you have the ability lower the ignition 1-2 degrees at peak torque. 

On the dyno that probably will be ok. On flyers it’s not. Been there repaired that. 

[Fredrik_Steen]

5 hours ago, peter1127 said:

On the dyno that probably will be ok. On flyers it’s not. Been there repaired that. 

What was the failure and root cause?

[peter1127]

Had 13.5:1 1277 wiseco’s, still thought it was too slow and went the turbo route. Didn’t want to buy new pistons so did machine them to approx 10:1 and thought this would be ok up to 10psi.  I turned it up a bit more  past 15psi  and that did held up for a little while until  all 4 pistons gave up during a flier.  Ringlands broken and it smoked like a mf. Bottom end was fine, head not so much and of course barrels and pistons were gone. Detonation due to too much boost for this setup. Did fix it with new again modified wisecos and thicker spacer plate at 8.5:1 and drove that for years without problems with 15 psi.

Past and now I run 98 octane pump fuel , stock plugs, no intercooler, stock  cams at stock timing, 4 degrees ignition retard and a proper oil cooler. Before I had a td04-16t and now a td05h-16g

 It’s hard to compare setups, but I think that 15 psi on stock cr is pushing it. 

[Blower1]

Old boost calculation formula: (boost (bar) x compression ratio) + compression ratio = 16 or less is safe.
Above 16 needs intercooler and/or lower compression ratio.

[Fredrik_Steen]

11 hours ago, peter1127 said:

Had 13.5:1 1277 wiseco’s, still thought it was too slow and went the turbo route. Didn’t want to buy new pistons so did machine them to approx 10:1 and thought this would be ok up to 10psi.  I turned it up a bit more  past 15psi  and that did held up for a little while until  all 4 pistons gave up during a flier.  Ringlands broken and it smoked like a mf. Bottom end was fine, head not so much and of course barrels and pistons were gone. Detonation due to too much boost for this setup. Did fix it with new again modified wisecos and thicker spacer plate at 8.5:1 and drove that for years without problems with 15 psi.

Past and now I run 98 octane pump fuel , stock plugs, no intercooler, stock  cams at stock timing, 4 degrees ignition retard and a proper oil cooler. Before I had a td04-16t and now a td05h-16g

 It’s hard to compare setups, but I think that 15 psi on stock cr is pushing it. 

What do you think was the root cause for the failed ringlands? 

[Reinhoud]

On 3/29/2024 at 9:38 PM, peter1127 said:

Got the MTC 81mm 10:1 pistons. They are much beefier around the wristpin area. They are now boring and honing the cylinder block.  Before I mentiioned I want the CR to be 8:1 - 8.5:1. Reading a bit more in various places  I think its a bit too low for a road bike.  9:1 should give faster  spoolup and better low end while it should enable 15psi on 98 octane resulting in around 270hp. (input welcome)

Played in CAD with the pistons to see what could be done to lower the CR while maintaining squish. Around 4cc should be cut from the piston to achieve 9:1. Thing is, in the middle of the piston is a relatively thin area of 5mm which I think I should leave alone. A bit surprised that turbo/nitrous pistons have  a thin area in the middle. Maybe because they mainly make high compression pistons from this casting? The rest of the piston is 9mm so I could reduce that by milling out a ring 1.5mm deep. Of course I'm first going to verify deck height and actual compression volume before ruining new pistons 

Does that make sense, or does that f@ck up combustion in such way that it would be better to add a spacerplate and accept the larger squish?

 

unmodified MTC 81mm

 

Unmodified MTC 81mm

 

 

Bottom of MTC piston

 

 

Modified MTC

 

Modified 81mm MTC

 

 

Modified 81mm MTC thickness check

Not much experience;

 

What I noticed, the sort of turbo, as in, how fast it spools up, determines a lot if you get detonation or not.

AFAIK, there are a few guys here who have EFI who have no problems with detonation.

In hindside, I'm not sure that they don't have problems with detonation because of the EFI, or the sort of turbo..

[peter1127]

1 hour ago, Fredrik_Steen said:

What do you think was the root cause for the failed ringlands? 

detonation due to overdoing it

[peter1127]

5 hours ago, Blower1 said:

Old boost calculation formula: (boost (bar) x compression ratio) + compression ratio = 16 or less is safe.
Above 16 needs intercooler and/or lower compression ratio.

According to this 15psi at 9:1 is not safe (18) and maximum cr for 15psi is 8:1. Sounds conservative but indeed it’s safe. 

[peter1127]

21 minutes ago, Reinhoud said:

Not much experience;

 

What I noticed, the sort of turbo, as in, how fast it spools up, determines a lot if you get detonation or not.

AFAIK, there are a few guys here who have EFI who have no problems with detonation.

In hindside, I'm not sure that they don't have problems with detonation because of the EFI, or the sort of turbo..

I don’t think the speed in which it spools up results in problems. Afaik detonation when turbocharged  occurs around peak torque, or at prolonged high rpm when everything gets ff hot. Both have nothing to do with spooling up. 
I can imagine a poorly chosen turbo heats up air more which doesn’t help.

efi and carbs both are fine as long as afr is correct.  You can run into fuel starvation with carbs when you turn down the pressure  too much to prevent flooding. Then again there are multiple ways to f up efi too :-)