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[2006ULTRA]

I decided to do a compression test to try and get a better idea of what my compression ratio might be. When I bought the bike used with 650 miles on it I was told the compression was 10.1. I have poor off idle response and a guy told me that my cams want at least 10.5 to 1 comp. The motor was professionally built etc etc and runs very strong. I just hate the off idle throttle lag.

My tester said 182 front and rear cylinder. I cranked it 3 times with throttle wide open.

I talked to an engine builder from this forum and he said I should be 10.5 to 1 with 182 on the compression tester.

Any thoughts?

[MadCVORG]

Sounds about right if the motor was rebuilt with SE 10.5 pistons.  Got the same comp with my build, using those. What cams were installed? Ddi the shop give you a dyno/AFR graph?  You may wan to try a different tuner to see if he can remap the ECM to improve the throttle response.

[Heatwave]

I decided to do a compression test to try and get a better idea of what my compression ratio might be. When I bought the bike used with 650 miles on it I was told the compression was 10.1. I have poor off idle response and a guy told me that my cams want at least 10.5 to 1 comp. The motor was professionally built etc etc and runs very strong. I just hate the off idle throttle lag.

My tester said 182 front and rear cylinder. I cranked it 3 times with throttle wide open.

I talked to an engine builder from this forum and he said I should be 10.5 to 1 with 182 on the compression tester.

Any thoughts?

I'm not sure what the compression would calculate for your build but for comparison my 110 with headwork and Woods 408-6 cams has 198fr/198rr with 3% leakdown. Stock pistons.

[Sklywag]

My 06 with a built 103 & 10.5:1 pistons with Yuill Bros YB13's  44* intake close cranks 195 in both cylinders.

[2006ULTRA]

The cams they used are in my sig.  From what I understand they have a lot of duration so that is why I'm getting the cranking compression I'm getting.

My heads were decked using stock pistons to raise compression.

[Sklywag]

With a 50* intake closing point you are correct, that brings down the CCC quite a bit. 

[Unbalanced]

Some things you need to know before you can calculate any of this besides winging a guess in the ballpark.

How far down where you pistons in the hole      aka below deck height
How many cc's are the pistons you are using I believe the 10.5's for the 110 are either 11 or 13cc's
What thickness headgasket did you use   stock , SE, or Cometic 30?
How many CC's were the chambers in your heads?

When your bike was tuned did anyone play with the throttleblade persistence  .... This can help with lag on the throttle.

If you have this information you can now get pretty darn close to what your cranking compression should be.

When you do a compression test you need to crank the motor till the gauge stops moving not just 3 times around.   on an 11 you also need to make sure you have the throttle blade held open.

The extra overlap will lower the cranking compression for sure.   

[Unbalanced]

Here are a few examples of the compression and how they change depending on the parameters as well as some change in elevation

[Unbalanced]

some changes

[Unbalanced]

one last one with even more changes like deck height

[Unbalanced]

You can back into your cranking compression to say this might be it, but without the real numbers to fill it in you maybe mistaken.

I would go back and crank it till it stops moving the dial, I would then also do a leakdown test.

Most of the normal build tries I did has your cranking compression much higher than what it is showing on the gauge you are using.   In the past I have tried 3 different gauges and they varied by as much as 10 pounds.   If you opt to hold the start down till the guage stops moving you may also try a 2nd guage.

[2006ULTRA]

Thanks for all the info! 

What is throttleblade persistence?  How do I adjust that?  Can I adjust that with my Thundermax?

[Unbalanced]

2006ultra,

I believe I blew the terminology, it it is called progressivity not persistence just to clarify it.

I haven't kept up with the latest Thundermax units.   On the TTS the functionality is called Throttle Blade Control where you can make the throttle work more like it was cabled as far as removing the stock lag.   You should reach out to Zippers and find out if they have some sort of setting for this functionality in the Thundermax.

FWIW, on your build the cranking compression does seem low if you figure in the 9b, a .030 headgasket, an average of your pistons being .005 in the whole and even a 95 cc chamber on your heads and 11 cc pistons, this combination on the calculator comes out at 10.89 static compression and 9.55 corrected.   Shows the combinaton should be cranking 199.x   This is just that a simulation, but in general they are usually in the ballpark.   lots of presumptions here, but plausible.  If the CC on the head is less the compression should go up more, if the thickness of the headgasket is higher then the compression comes down a littlebit, if the pistons are less in the hole the compression comes up a bit

Also are you sure your compression releases were disengaged when you did the compression test.  If the compression releases are on your cranking around 240            However I think the number will be higher if you let it crank out vs. just 3 revolutions.

For sake of discussion if the compression test is accurate after its all said and done, you may want to be sure the cam is not installed 1 tooth off, I believe the results of 185 compression are just about enough to show this kind of result.    

Here's to hoping you figure it out  

[2006ULTRA]

I think the Thundermax has a feature like you're talking about.  I'll get with them and figure it out.

I probably need to do the compression test again because the TMax doesn't close the compression releases for 2 revolutions so basically I probably got good compression on the 3rd revolution.  I can change this in the settings to zero so I don't have to crank so much.

Thanks for all the help.

[glens]

The only thing that closes the compression releases is some combustion, so far as I know.  They should be just like manual releases in that regard; they just get initially "pushed" by solenoids instead of a finger.

I don't characterize throttle blade progressivity as "lag".  The throttle blade doesn't lag behind the twistrip.  It opens when you roll the grip; at lower engine speeds it just doesn't open as much as you rolled the grip when properly set up.  It's a percentage.  If it's set in the table as 30% somewhere in the 40% throttle column, it will follow your twistgrip immediately, but will only go 3/4 as much as the grip went.  Setting the table to make the throttle blade go to 100% at lower engine speeds is pointless anyway since full usable airflow through the engine then is achieved way below 100% opening.  Any engine speed faster than the last row in the table uses the values from that last row, so by the time the engine gets there, it's like none of the other table even exists.

Think of it like this.  100% of any column heading value in all cells in that column is just like a cable-operated throttle body.  When "properly" set up, the two (ETC/direct) pretty much compare to each other the same as a direct-control slide carb compares to a CV carb.  In the CV you don't have direct control over the actual throttle opening anywhere.  Sure, you control the butterfly, but the vacuum controls the actual throttle opening.

I think what most folks are calling "lag" has got to be the "disconnect" between the throttle blade and the twistgrip while on cruise control and trying to "find" it when resuming manual control, near as I can tell.  That takes a few rides to get used to, but after ~25k miles I have to really think about it to even notice it.