What did you do today? Cobba's rebuild

[cobbadiggabuddyblooo]

Note to self

In a low-compression engine, peak combustion pressures are lower than in a high compression unit.
But percentage-wise, the pressure doesn't drop off as fast as it does in a high compression unit as the power stroke progresses. At the higher rpm a high compression motor is likely to run at, it needs a little more time to blow down the cylinder. This we can do by opening the exhaust valve earlier than with a low compression engine.
This proves possible with little or no penalty because a high compression means more work on the piston at the beginning of the stroke and less towards the end.
So the higher the CR, the wider the LCA can be made by virtue of extended duration by opening the exhaust valve earlier. A rough rule of thumb is to open the exhaust valve 1-2 degrees earlier for every point of compression increase from a previously optimally timed cam. Opening the exhaust valve 2 degrees earlier means the LCA has spread by half a degree.

An increase in low lift flow without a compensating reduction in the overlap area can reduce output right up until very high rpm is reached. The intent here is to restore the overlap triangle, in terms of cfm /degrees, back to its original optimum value.
Sure, it's tempting to analyze thousandths of valve lift and degrees around TDC, but the engine does not recognize valve lift as measured by a dial indicator-only flow capability. This means all overlap characteristics should be related in terms of cfm/degrees not inch/degrees.
Achieving an exceptionally high flow at low lift on the intake can cause the engine to react as if it has 20 or so degrees additional overlap. This often proves way over the top for an engine with previously optimum valve events. An increase in low lift flow is potentially good for added power but, if substantial, usually requires a revision of the valve opening and closure points.

Ultimately what the Kent Yam 9 cams are attempting to do with their 240-240 duration inlet and exhaust is promote more inlet velocity down low .
Larger valves and flowed heads already promoting good velocity and charge down low answers my question on the question 12mths ago about changing the lobe centres to suit my motor.
Remember the Kent yam 9 cams only give you only 2* extra exhaust duration but 11* more inlet than std plus 0.28mm more lift.

Good reference for cam timing (cam science)
http://www.hotrod.com/how-to/engine/cam ... ngle-tech/

[Mincehead]

For a moment there I thought you had written that!

[dandywarhol]

Amazes me that bike engine designers have been so slow to introduce variable valve timing. Just about every car engine has it now.
Maybe it's to do with power to weight ratio and bikes don't really need it (except Harleys)

[cobbadiggabuddyblooo]

No Mince I'm not that good with words... but it took a few goes of reading, playing with the timing disc, looking at piston position, flow chart and slowly piecing it all together to find reasoning.
I understand now why advice for the V2 cams if used in my motor was changed from 108.5 -104 to 113 and 104.. (assymetric cam)
Take note of this Adrian if you choose to use the V2 cams I arranged for you.
I had to fish for the reasoning though...
Exhaust system characteristics really comes into play on the equasion too.
Another reason i want to make a reflective engine/FCR tray not only to keep air temps down but to try to keep the intake velocity up.

[Mincehead]

Boffin!

[cobbadiggabuddyblooo]

Today I finally got around to unwrapping the layers of glad wrap from the motor and tensioning down the head to check the piston / valve clearances once again with the new cams fitted.
Clearances was set using an old compressed Std Yamaha MLS gasket.

Still have plenty of clearance with just over 2mm on the inlet and over 2.5mm at the lowest point on the exhaust.
So next stage is to dial in the cams.
Took a few measurements and it was time to rest the brain so thats tomorrows task.
Too many figures goin around the brain ...


Inlet has 3.1mm lift at TDC which is 0.8 mm more lift than I require.
I'll retard the intake about 8*. This will also give me a little more P / V clearance on the intake valves.



More than ample exhaust clearance to play with so either way I go with is I feel confident I'll have enough clearance .

[Mincehead]

[cobbadiggabuddyblooo]

So with all my homework done from what I've learnt, this is what I'm trying to achieve..
Retarding 8* will widen the angle and reduce my overlap which is what I need to do anyhow.
Should evoke a bit more of that flatter 95Nm + torque curve down in the lower rev range too.
( from 4500 to 6000rpm and continue like before from 6000 to 8000 rpm)
If all works out well with the longer duration and 0.2 mm extra lift than the Kent Yam 9 cams , I should still retain the same torque curve up top and hopefully more.

So I'll take a punt at 115 HP rear wheel with 95Nm + from 4500 to 8000rpm but I'll need to tweet the ignition timing again.
Around 114 intake centre sounded a bit daunting to start especially with the Std trx and Kent cams at 105 but it's all starting to make sense now.
Basically I'm opening the intake valve pretty close to where the Kent opened but gain from the asymmetrical grind and area .The extra duration is used with a later closing intake valve.
Reversion should be managed by the slower closing ramp and a lower area.

[Mincehead]

Mate, have you seen any Ivan Teague cams with lift and duration similar to a 1999 R1`s cams I believe?

[cobbadiggabuddyblooo]

Yes Thighe cams are local here in Brisbane. A couple of times I've sent them all the specs , flow charts , and all the info he'd need to tune the cam to compliment the motor.
But I never got a reply after 3 e mails and giving him all the info requested from their site. Called a couple of times and no reply from messages sent.

The I tracked down Ulf Penner in Germany and Huby supplied the cams he had designed for the trx in much the same tune as mine.
He saved me time and money too with dyno results from a range of exhaust systems , hence why I sold the Over system I had hanging in the garage and never used and stuck with the Alrapovic.
I figured the way I'm tuning the cams should compliment the Akra system too with their conical headers keeping good velocity spread over a wider range and the longer headers giving me the gains in the mid range.
I probably could have obtained a magical 120 HP if I used the Over system and more overlap and lost some mid range but it's not about how long my dick is but how well I can use it..
The lighter Pistons an rods will easily take running up to 10,000 Rpm and the Over system would be perfect ( and the SP 6 speed if It was fitted) for this but the 5 speed gearbox supports the use of the choice I've taken.
I believe Brett ( quick draw ) has those R1 style cams from Ivan Thighe in his trx.

[cobbadiggabuddyblooo]

Looking at R6-R1 cam timing they seem to run more inlet duration than exhaust or close to similar duration on their race spec cams much like Mik has gone for with the Kent D 1580 with 253* inlet and exhaust.
This May suit a 4 cylinder bike with a smaller bore and different rod ratio than a trx so I'd question if you would gain more with a longer duration exhaust.
I'm sure that's why the trx is set that way from Std where the R6- R1 is opposite and has a longer duration intake from std..

I may be wrong but if you look at the V2 specs they follow the same trend with 7* more exhaust duration..
Don't get me wrong, I'm sure you'll still find improvements. I'm only making assumptions based on what I've learnt so far.
I'm starting to think the reason Kent and others may regrind a lot of their cams with the same duration and lift specs is due to costs and can be marketed over a range of motorcycles. Good business sense..
Dare I say the intake length comes into play here too Mince on the R6/R1 would promote the use of a longer duration cam especially with the higher rod ratio on an R1 which doesn't favour good velocity down low with carbies.

[Mincehead]

Yes he's local here in Brisbane. A couple of times I've sent him all the specs , flow charts , and all the info he'd need to tune the cam to compliment the motor.
But I never got a reply after 3 e mails and giving him all the info requested from their site. Called a couple of times and no reply from messages sent.
The I tracked down Ulf Penner in Germany and Huby supplied the cams he had designed for the trx in much the same tune as mine.
He saved me time and money too with dyno results from a range of exhaust systems , hence why I sold the Over system I had hanging in the garage and never used and stuck with the Alrapovic.
I figured the way I'm tuning the cams should compliment the Akra system too with their conical headers keeping good velocity spread over a wider range and the longer headers giving me the gains in the mid range.
I probably could have obtained a magical 120 HP if I used the Over system but lost some mid range but it's not about how long my dick is but how well I can use it..
I believe Brett ( quick draw ) has those R1 style cams from Ivan Thighe in his trx.

That`s the guy, Brett, couldn`t remember him. I do know the Teague cams aint cheap!
Oh and Kent?
They`ve been in business a very long time mate, gotta be doing something right eh.

[cobbadiggabuddyblooo]

Yes and I'm not knocking them as such but they are a good for what you pay.
£200 gives you good improvements over the std cam profile.
I was chuffed with what I got with the Yam 9's from Kent but.
Spode I just wanted to go to the next level.
I'm sure if I told them exactly what I have and flashed more cash, they could have accommodated my needs.
All a part of this good learning curve for me.

[cobbadiggabuddyblooo]

Here is a handy hint if dialing in the cams.
I measures the distance across the sprocket from the outer edge of 1 bolt hole to the other. ( no.1 )
I measured the hole size. ( no.2 )
Deducting the hole size ( no.2 ) from the length ( no.1 )
Now you have the diameter of the circle that would pass through the bolt hole centres. ( no.3 )

Next you need half of ( no.3 ) and work out the circumference of this circle that will pass through both bolt centres.

I then divided the circumference by 360 ( there is 360* in a circle ) and this gave me 1 degree of the circumference .
Now I needed to move the inlet cam by 12 crank degrees which is 6 cam degrees.
6 x 1* worked out just over 2.2 mm that I needed to remove from the bolt hole.
Worked perfectly.

[Mincehead]

Hahahahaha, good job, well worked out. I would have used a dial guage or a DTI.