High compression
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Road Captain
Joined: Aug 2018
Posts: 594
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From: Stockholm
High compression
Hello, Dyna 2006, bored last winter to 98 ci, Andrews 26. Target Tune. Bike has run about 8.000 miles since build.
Estimated static compression 9.62:1
Corrected compression 9.03:1 or 185.9 psi (Big Boyz)
After build I first measured 190 psi on both, but it was made incorrectly. (Battery was not fully loaded before each test and throttle was closed. Added to that: The manometer showed 8 % too much. But say the 8 % took out the decrease in pressure from closed throttle and not super fresh battery charge, then 190 psi would have been pretty correct.)
Anyway, this autumn I measured again with open throttle, freshly loaded battery before each test and with a manometer checked for tolerance. The test ended up in 197 psi on rear and 203 psi on the front.
This is way beyond the corrected compression of 185.9 psi (Big Boyz Calculator) and 191.5 psi (Hammer Performance Calculator).
So why sooo high? Well I might have have carbon in the combustion chambers…
This is what I think. Bike was not easy to tune and it ran pretty rich during break in and after. Also it had the internal crank ventilation for a short period.
So I assume I have carbon build up.
Ways to go:
1/ Seafoam in tank and Seafoam spray in manifold, then let it soak over the night.
2/ Lift the heads, clean them and the pistons.
What do you all here think about this?
The easy way would be Seafoam treatments the coming spring and then a new compression test.
The hard way is to pull the heads this winter.
Any thoughts about this are much appreciated.
Thanks a lot.
Estimated static compression 9.62:1
Corrected compression 9.03:1 or 185.9 psi (Big Boyz)
After build I first measured 190 psi on both, but it was made incorrectly. (Battery was not fully loaded before each test and throttle was closed. Added to that: The manometer showed 8 % too much. But say the 8 % took out the decrease in pressure from closed throttle and not super fresh battery charge, then 190 psi would have been pretty correct.)
Anyway, this autumn I measured again with open throttle, freshly loaded battery before each test and with a manometer checked for tolerance. The test ended up in 197 psi on rear and 203 psi on the front.
This is way beyond the corrected compression of 185.9 psi (Big Boyz Calculator) and 191.5 psi (Hammer Performance Calculator).
So why sooo high? Well I might have have carbon in the combustion chambers…
This is what I think. Bike was not easy to tune and it ran pretty rich during break in and after. Also it had the internal crank ventilation for a short period.
So I assume I have carbon build up.
Ways to go:
1/ Seafoam in tank and Seafoam spray in manifold, then let it soak over the night.
2/ Lift the heads, clean them and the pistons.
What do you all here think about this?
The easy way would be Seafoam treatments the coming spring and then a new compression test.
The hard way is to pull the heads this winter.
Any thoughts about this are much appreciated.
Thanks a lot.
Last edited by OakMountainRider; Dec 7, 2024 at 05:22 PM.
Thread Starter
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Road Captain
Joined: Aug 2018
Posts: 594
Likes: 93
From: Stockholm
It used to ping, with knockcounts on the PV, but it is tuned out. Also pulled timing 18 %.
Last edited by OakMountainRider; Dec 7, 2024 at 05:28 PM.
Thread Starter
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Road Captain
Joined: Aug 2018
Posts: 594
Likes: 93
From: Stockholm
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,997
Likes: 8,065
From: poway
The cranking pressure on early intake close cams tend to be higher than the what the calculators come up with. You can spend time trying to clean the chambers but the easiest solution is to back off on the timing..
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,168
Likes: 7,676
From: Poolville
I would use either MMO or Sea Foam..If it's running good your splitting hairs and probably going to create more problems.. So do you have a timing advance curve that we can see? Curious about 18% less/pulled.
Last edited by 98hotrodfatboy; Dec 9, 2024 at 07:05 AM.
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Road Captain
Joined: Aug 2018
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From: Stockholm
I have actually scratched my head more than twice wondering why my Cold Cranking Compression is so high. I even sent my manometer to be checked, as I thought it showed too much. It did, but not that much.
Been thinking of Andrews 37, or even 54, to bring the compression down, but have not decided yet. Maybe I just seafoam it this spring.
Anyway, bike runs fine and does not ping anymore, in as the ECM does not count any knocks - this after I Autotuned it several times and pulled timing 18 % from the tune (received from Dynojet when I changed to Andrews 26). Especially it stopped pinging after I removed the DK Custom torque plates in my baffles, which made it ping as soon as I twisted the throttle.
(When I say pinging I refer to knockcounts seen on the Power Vision. I have not heard any sound as my hearing is not so good.)
Last edited by OakMountainRider; Dec 9, 2024 at 09:31 AM.
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Thread Starter
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Road Captain
Joined: Aug 2018
Posts: 594
Likes: 93
From: Stockholm
First, when changing cam from stock to Andrews three years ago, I received a tune from Dynojet.
Then, after the 98 ci bore was installed spring -23, I took it to a tuner who dynoed the bike and I got new VE:s. However bike ran too lean on the rear cylinder and after a longer ride it even smelled as something had burnt. I called the tuner who never read the info about my bike which I mailed him, and from this he did not have sufficient information about it, (on that I missed to inform him verbally when leaving my bike to him.)
My bike is the international version of Dyna 2006, prepared for, but missing the narrow band O2-sensors. Instead it had Autotune Pro with broadband sensors, but still it was running open loop. Anyway, this was not communicated to the tuner and he left the VE:s to be balanced and corrected by a presumed, non-existing closed loop.
After this, I autotuned the VE:s and I tried different time pullings; 6, 12, 18, 24, 30, 36, 42 and even 48 %, to see how the bike reacted, and finally I arrived to what I perceived as being the smooth spot, and that was 18 %.
I have then autotuned the VE:s several times and also installed Target Tune with broadband closed loop.
Bike runs pretty good now, it does not ping anymore. Just worried about the compression being this high.
I will come back to you with the timing tables.
P. S. I don’t blame the tuner, who is a great guy. I should have communicated more thoroughly to him.
Last edited by OakMountainRider; Dec 9, 2024 at 10:57 AM.