Topic: Alternative performance pistons & squish

[turboguzzi]

damn, the fix doesnt work for me in both browsers... .bummer

for my own photos i switched to google photos, should stay problem free longer i hope

[livefast_dieold]

Doesn't work for me either... any gentleman kind enough to repost the pics?

[MRieck]

 Personally I'd try to get the smallest chamber possible and use the flattest crown possible to get a workable CR. You can achieve a large squish band with minimal flame front disruption.
 I hate welding chambers as the weld is soft and I have seen Branch heads fail at the fire ring BUT if that is your only choice I'd go for it. I also don't like taking .060 or .070 off the head secondary to cam chain angle but if you want something special that's what you have to do. At least on the SOHC 750 you can shim up the cam towers.
 I would also consider very positive deck height with squish band cut into the chamber.

[gschuld]

Some heads get milled quite a bit

George

[turboguzzi]

ricc, if you read between the lines, there's no off the shelve solution.
cam angle wouldnt worry me that much, can be adjusted through slotted wheel inst it mike? or do you mean something else?

[bwaller]

So true TG. Let your imagination run wild Ric!

[MRieck]

ricc, if you read between the lines, there's no off the shelve solution.
cam angle wouldnt worry me that much, can be adjusted through slotted wheel inst it mike? or do you mean something else?

You can mill and deck so much that the rear part of cam chain (where the tensioner sits) comes very close to the front section of the cam chain. I have seen where the M3 solid 750 tensioner hits only a very, very small part of the tensioner material ( at the very top) because it changes the angle to much. The best solution is to shorten the cam chain to retain the original geometry.

[turboguzzi]

ok, got it, guess you can tell i am no 750 expert ,

[bwaller]

No argument Mike, but you must have to remove alot of material to be able shorten a chain this much? I'm about to go through this so I'll answer my own bloody question soon enough!

[kmb69]

No argument Mike, but you must have to remove alot of material to be able shorten a chain this much? I'm about to go through this so I'll answer my own bloody question soon enough!

Yep, essentially 2 pitches - 7.774mm x 2. No half links available that I am aware of. Ain't happening.

Requires some tensioner modification IMHO.

[gschuld]

If one was inclined to deck the head heavily to reduce chamber volume, it could be combined with extra deep gasket thickness along with 1100f rods(1.5mm longer) bushed to 15mm pin. This would increase overall deck height to account for the reduced thickness at the head correct?  Kind of a contorted fix but it gets the cam chain sprockets center to center distance back in the right range I'd think.

[cbr954]

I milled .060 off of a F2 head and was running the old cycle x version of the M3 tensioner.  Took it out after short amount of miles because of wear and poor alignment, chain was rubbing on metal side of tensioner.  Went back to stock honda tensioner wheel setup been good ever since.

[livefast_dieold]

It's quite uncharted territory, and also an expensive path in case of mistake...

BTW, can someone repost jhno pictures? Thanks!

[MRieck]

No argument Mike, but you must have to remove alot of material to be able shorten a chain this much? I'm about to go through this so I'll answer my own bloody question soon enough!

-.060 off the head and -.025 off the deck will do it Brent.

[kmb69]

No argument Mike, but you must have to remove alot of material to be able shorten a chain this much? I'm about to go through this so I'll answer my own bloody question soon enough!

-.060 off the head and -.025 off the deck will do it Brent.

Sending PM.

[Ilja]

I was reading this topic because I was trying to find out if someone made a bathtub chamber out of an SOHC chamber, combined with flattop pistons. 

I have seen a few times that people say you need to run more ignition advance with higher compression...
The higher the cylinder pressure, the faster the combustion takes place. (faster burn speed)

You actually need to run LESS ignition advance compared to what you would need with lower compression.
If you run more ignition advance, you just create a lot of extra heath without gaining power. The result is the engine overheathing.

You can run more ignition advance at part throttle (via TPS) or past the point where the engine makes maximum torque.

Here's a quick read I found, which explains it in more words.

https://www.innovatemotorsports.com/resources/myths.php

Take care about those nice expensive engines. 

 

[MRieck]

I was reading this topic because I was trying to find out if someone made a bathtub chamber out of an SOHC chamber, combined with flattop pistons. 

I have seen a few times that people say you need to run more ignition advance with higher compression...
The higher the cylinder pressure, the faster the combustion takes place. (faster burn speed)

You actually need to run LESS ignition advance compared to what you would need with lower compression.
If you run more ignition advance, you just create a lot of extra heath without gaining power. The result is the engine overheathing.

You can run more ignition advance at part throttle (via TPS) or past the point where the engine makes maximum torque.

Here's a quick read I found, which explains it in more words.

https://www.innovatemotorsports.com/resources/myths.php

Take care about those nice expensive engines. 

You run to much advance and the engine starts working against itself (charge is lighting off to early). Efficient engines don't require a lot of advance

[Ilja]

I was reading this topic because I was trying to find out if someone made a bathtub chamber out of an SOHC chamber, combined with flattop pistons. 

I have seen a few times that people say you need to run more ignition advance with higher compression...
The higher the cylinder pressure, the faster the combustion takes place. (faster burn speed)

You actually need to run LESS ignition advance compared to what you would need with lower compression.
If you run more ignition advance, you just create a lot of extra heath without gaining power. The result is the engine overheathing.

You can run more ignition advance at part throttle (via TPS) or past the point where the engine makes maximum torque.

Here's a quick read I found, which explains it in more words.

https://www.innovatemotorsports.com/resources/myths.php

Take care about those nice expensive engines. 

You run to much advance and the engine starts working against itself (charge is lighting off to early). Efficient engines don't require a lot of advance

Exactly, and they become hot as hell if you do that especially with high compression stuff. Leads to pre-ignition followed by a holed piston.

People also twin sparked some engine's back in the 70ies... this also makes it possible to run less advance and therefore increasing efficiency and reducing detonation / pre-ignition threshold. 
But for the CB head it's not possible I think...

[Captain]

 Ignition.................... Is a much more complex subject than is being talked about here (so far in this thread)
   
 The answer lies with 3D and the mapping for all throttle positions not just 100% (full) which is what you conventional old school 2D is factored on.   There is much to be gained using this technology and I have successfully implemented it and the part throttle torque increases are not to be dismissed. 
 It's all about burn speed and the slowing of same when at part throttle and to make the connection to this so it's clear to all, you increase ignition advance in these part throttle conditions (by surprisingly large amounts at times)  in order to have max cylinder pressure peaking at 15-20 degree's ATDC.  If you don't you are effectively retarded and this results in greater waste heat and increased fuel consumption. There are more but these are the main ones.

 If this is to much to understand consider this.................. Every single current automotive manufacturer is fitted with 3D ignition mapping for a NA or Turbo gasoline engine.

 Captain

[MRieck]

Ignition.................... Is a much more complex subject than is being talked about here (so far in this thread)
   
 The answer lies with 3D and the mapping for all throttle positions not just 100% (full) which is what you conventional old school 2D is factored on.   There is much to be gained using this technology and I have successfully implemented it and the part throttle torque increases are not to be dismissed. 
 It's all about burn speed and the slowing of same when at part throttle and to make the connection to this so it's clear to all, you increase ignition advance in these part throttle conditions (by surprisingly large amounts at times)  in order to have max cylinder pressure peaking at 15-20 degree's ATDC.  If you don't you are effectively retarded and this results in greater waste heat and increased fuel consumption. There are more but these are the main ones.

 If this is to much to understand consider this.................. Every single current automotive manufacturer is fitted with 3D ignition mapping for a NA or Turbo gasoline engine.

 Captain

.....and fuel injection with all the sensors to support the system. Sound a bit pompous with the "if this is to much to understand". I bought a Hayabusa instead.

[PeWe]

Retarding curve at higher rpms (after torque peak) will improve?

[Captain]

Retarding curve at higher rpms (after torque peak) will improve?

No, it’s the other way around. Torque peak is where maximum cylinder pressure occurs and so has the fastest burn speed.
At anything less then the burn speed slows and so more lead is needed to achieve the same finishing point of max pressure (15-20 degree ATDC)
 This is most pronounced during part throttle events and in particular very low openings. This is sometimes hard to get ones head around but never the less is factual. Of course there is also RPM to consider and so this is factored in as well and is the reason we have higher numbers at higher RPM.  After years of knowing nothing but 2D which is what all bikes had up to around the EFI era became common place. Many don't realise that the reason EFI became a practical solution was because the ECU's became powerful enough to crunch the numbers in real time, this then enabled 3D ignition to be addressed additionally as the calculations required were now available as 6they could be "piggy backed" onto the  EFI calculations. In our case we run carbs and just utilised the 3D ignition function and the results were instant. 
  So all of what I'm talking about has real benefits when applied to these "Old School" engines and is a reality as I've been through it, tested it and now would never build another race bike without it.

 Captain

 Captain   

[simon#42]

Retarding curve at higher rpms (after torque peak) will improve?

No, it’s the other way around. Torque peak is where maximum cylinder pressure occurs and so has the fastest burn speed.
At anything less then the burn speed slows and so more lead is needed to achieve the same finishing point of max pressure (15-20 degree ATDC)
 This is most pronounced during part throttle events and in particular very low openings. This is sometimes hard to get ones head around but never the less is factual. Of course there is also RPM to consider and so this is factored in as well and is the reason we have higher numbers at higher RPM.  After years of knowing nothing but 2D which is what all bikes had up to around the EFI era became common place. Many don't realise that the reason EFI became a practical solution was because the ECU's became powerful enough to crunch the numbers in real time, this then enabled 3D ignition to be addressed additionally as the calculations required were now available as 6they could be "piggy backed" onto the  EFI calculations. In our case we run carbs and just utilised the 3D ignition function and the results were instant. 
  So all of what I'm talking about has real benefits when applied to these "Old School" engines and is a reality as I've been through it, tested it and now would never build another race bike without it.

 Captain

 Captain

not quite as simple as just adding lead , what you need is a high octane fuel that will resist detonation but still have a fast burn speed .high lead content in fuel is great for valves and valve seats but is not good for burn speed . motogp engines make 280hp without any lead at all

[Captain]

  The “Lead” I mention is.....as in ignition lead, amount of ignition advance.
Not lead fuel additive.

Captain

[simon#42]

sorry captain i miss understood that , not the first time that has happened .