ESE's works engine tuner

[TZ350]

losing 3 or more ponies seems a big effect for just 50 cc's.

I think they and a few friends have fallen down the crevasse between the flywheel and crankcase wall.

[Henk]

Losing three ponies might well be worth it if it puts the ones left over in the right place, there is lots of power and the right power, the bikes wining at Mt Welly don't seem to be HP monsters at the moment. Although it has been said that an RS frame acts as a HP multiplier.
I don't want to ride one of those frames due to the effect it will have on my bank balance.

[wobbly]

CCR is hugely affected by 50cc.
Say the vol with the piston at TDC was 350cc total, this gives a CCR of 1.4.
Add 50cc and the vol becomes 400cc, this gives a CCR of 1.333, thats a night and day difference to a very important design element.

[speedpro]

our foreign correspondent mentioned that CCR was important.

[jasonu]

our foreign correspondent mentioned that CCR was important.

I have all of their albums...

[TZ350]

Chambers is taking a serious look at Ned Kellys 22+ rwhp engine to see if there are any spare horsies hiding in there. The carb is a glued up std GP125 24mm carb and those are the engine mounts to fit a Suzuki GP into an RS frame.

[F5 Dave]

I have all of their albums...

How old are you?

[bucketracer]

our foreign correspondent mentioned that CCR was important.

Yes, he seemed quite sure there was a correct CCR, but it didn't look like he knew what it was, I think he hoped someone like Thomas would fill in the gaps for him.

[ac3_snow]

I think they and a few friends have fallen down the crevasse between the flywheel and crankcase wall.

So can I ask what the ccr was before and after?
Also the reed block modifications you made to your 50 are potentially going to have a similar effect to CCR, or is this a smaller change and which will hopefully have a negligible effect?

[bucketracer]

So can I ask what the ccr was before and after?
Also the reed block modifications you made to your 50 are potentially going to have a similar effect to CCR, or is this a smaller change and which will hopefully have a negligible effect?

The RG50 case reed inlet is similar to previous ideas tried out when building Buckets4Me's 50 ........



And these are the figures (Based on Blairs Book) I got when I checked out TeeZee's engine for him.

Crankcase Compression Ratios Revisited

Primary or crankcase compression ratio is determined by dividing the full crankcase volume including transfers with the piston at TDC by the crankcase clearance volume with the piston at BDC.

For a 125 the ratio will probably be some where between 1.3:1 and 1.5:1, also according to Blair it is very difficult to get a 50 above 1.4:1 and a 500 below 1.55:1.

Pic-01 the good old Suzuki GP125

Pic-02 I found greasing the piston crown and around the piston in the exhaust port then plugging it with paper towels sealed it up OK with out any leaks.

Pic-03 I used anti freeze and a measuring cylinder to measure the crankcase volume. After pouring the anti freeze in through the inlet port and wriggling the engine to get all the air out I found the full crankcase volume with the piston at TDC to be 470cc.

Pic-04 The engine simulation package Mota requires the crankcase clearance volume below the piston crown when the piston is at bottom dead center (BDC), excluding transfer duct volumes. From the bore and stroke and the transfer duct area of the engine being simulated and it works out the full crankcase volume for itself.

Crankcase compression ratio (Primary Compression Ratio).

Terms
Full crankcase Volume = FV
Crankcase Clearance Volume = CCV
Primary Compression Ratio = PCR
Engine Capacity = CC

Formula
FV/CCV = PCR

As
CCV = FV-CC

Then the formula becomes
FV/(FV-CC)=PCR

Then for the GP125 the primary compression ratio is…….

Primary Compression Ratio = PCR

PCR 470/(470-125)=1.36

The Suzuki GP125 has a crankcase compression ratio or primary compression ratio of 1.36:1

I don't expect we will measure the engine again until it is about to come apart.

Primary Compression Ratio or PCR = Crank Case Ratio or CCR

470/(470-125)=1.36 PCR or CCR

Adding 50cc to the above figures..........

(470+50)/((470+50)-125)=1.32

A difference of 0.04 just did not seem that much

[ac3_snow]

yes it does seem like a huge effect from such a small change, I was also amazed at one of wobbly's previous comments about the effect a o.1mm change in transfer heights has on a KT100 (was about 2hp?!)
When working on what seems to be such a fine knife edge I think you guys have done pretty well to get the results you have.
all part of learning, hopefully you can learn back those three horsies!

[bucketracer]

yes it does seem like a huge effect from such a small change,

TeeZee says, he is wondering if he could have made it worse by something else that he has overlooked, but does not know what that could be.

all part of learning, hopefully you can learn back those three horsies!

Yes Hopefully .........

CCR is hugely affected by 50cc.
Say the vol with the piston at TDC was 350cc total, this gives a CCR of 1.4.
Add 50cc and the vol becomes 400cc, this gives a CCR of 1.333, thats a night and day difference to a very important design element.

I thought that my maths might have been wrong, but using the same formula and putting numbers to Wobblys post I get.

For a 100cc engine.

350/(350-100) = 1.40

and adding 50cc to the crank case volume.

400/(400-100) = 1.33

If a huge difference is 0.07 then TeeZee's 0.04 change could be considered fairly large too.

And so maybe those missing ponies are all in that change of crankcase volume.

I am very impressed by what a big effect such a small number can have ...........

[koba]

I am very impressed by what a big effect such a small number can have ...........

Why do you keep thinking of that as "such a small number"?

I think 50cc is a massive number in that context!

I'm no good at maths but isn't that something like a 12.5% change?

What would a that percentage change in any other aspect of the engine do?

[bucketracer]

Why do you keep thinking of that as "such a small number"? I think 50cc is a massive number in that context!

Just hadn't got my head around it.....

350/(350-100) = 1.40
and adding 50cc to the crank case volume.
400/(400-100) = 1.33
1.40-1.33=0.07
(0.07/1.40)*100 = 5% change for Wobblys example.

TeeZees is about 3%

Yes your right 3-5% of anything would be worth having.

[wobbly]

If you look at CCR in the context of what is accepted as being "normal", then the full range is generally accepted as being a low CCR at 1.3 and a very high CCR at 1.4.
This means a difference of 0.1 from "big" to "small", and the 50cc change in the case, represents 1/2 of the engines swept displacement by the piston in a 100cc bucket..
Aprilias latest engines are in the high 1.2s - and a very fast NZ champ 50 quad I built had 1.42, both on the very outer limits.
Changing from 1.4 to 1.3 would need huge jetting changes, like 4 mains, and this then affects the bsfc, and the pumping efficiency,needing a whole new approach to the transfer designs as well.
It goes on and on.
When you consider what happens when you change say the primary com from 13:1 up to 16:1,then this shows the relativity of the difference created.
But again - even the primary com change has huge effects that are not directly related to the numbers.
16:1 would need Avgas to stop deto obviously and this com would give great jump of the turns but would stop any pipe design from overeving.
Thus a high com engine needs a short pipe, or lots of retard, due to all the heat of combustion being released into the piston and the water - not the exhaust, making it appear longer to the engine. etc etc.
Change one element of a 2T and you are then looking at a whole raft of changes needed to optimise that setup,and it will never "work" if just one other element isnt synergistic with the rest.
And remember a general comment I made a while ago, about crap transfer ducting "liking" higher CCR ratios.