Compression too high
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HDF Community Team
Joined: Aug 2019
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From: Santa Ana, CA
Compression too high
Well. I've been trying to tune this new motor and can't get it to stop pinging at WOT in 4th and 5th. Did a compression test and it's coming in at 225 psi front and rear. I talked with Hammer a few days ago and Dan said I may need to send the heads back and have a little more material taken off to lower the compression. Hammer said you really want to be below 200 psi to run on pump gas. Anyone have any experience with this?
Last edited by OCSpringer; Jan 25, 2025 at 07:21 PM.
Road Master
Joined: Nov 2023
Posts: 972
Likes: 1,016
From: Knoxville
Nothing first hand but its in my head that 215-220 is cool with 93. On 91 and evos in general Id go with Hammer Dans recommendation.
A thicker gasket (head/base) isnt an option? Assuming you want to keep the quench tight, maybe its not.
Id think an 040 quench would be fine and I would try it. But best advice is not to take my advice.
More experienced hands will chime in and help.
Bummer buts its good to start at the top and wind down; thats how we always tuned timing, bump until it slows, retard and retest.
A thicker gasket (head/base) isnt an option? Assuming you want to keep the quench tight, maybe its not.
Id think an 040 quench would be fine and I would try it. But best advice is not to take my advice.
More experienced hands will chime in and help.
Bummer buts its good to start at the top and wind down; thats how we always tuned timing, bump until it slows, retard and retest.
Grand HDF Member
Joined: Nov 2012
Posts: 4,994
Likes: 2,081
From: Newport,TN area
You might see if @aswracing Aaron could provide some insight as he's done
these types of builds (with HammerPerformance) for many years.
He'll need to know your particular build info for heads/cam/exhaust system...
good luck,
T.
these types of builds (with HammerPerformance) for many years.
He'll need to know your particular build info for heads/cam/exhaust system...
good luck,
T.
Last edited by WKNDS; Jan 26, 2025 at 06:43 AM.
Grand HDF Member
Joined: Sep 2022
Posts: 4,425
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From: Florida
Cams with more duration and lift to bleed off and lower your corrected would work. That said yours truly ran about 230 cold cranks in my shovel on pump 93 in Florida summer heat without pinging. Fire ring, combustion chamber eliminating any area for carbon build up was the key.
I assume these are slightly raised pistons with eyebrows and not flat pistons? The higher you can gain compression with the lowest dome was another key. You don’t want any dome blocking the spark from burning the mix evenly.
Is it EFI or Carbed? What carb? How many fuel circuits? Your probably in the neighborhood of 11.5:1 to 12:1 mechanical, don’t know what it is corrected with the cams you have?
I’ll get flamed for saying this. It’s the kinda snake oil I make fun of, but this one I believe in.. Fitch catalyst. These are like goofy lead pellets you drop in your tank. Laugh all you want but been using them in 12:1 street shovels for 30 years. They “do something” to help it from pinging.
My 93” Shovel made 115 lbs & 105 hp with a super broad high torque curve, 11.87 @ 112mph with a 130 street tire and I weighed 230 and am 6’5” of wind resistance. Cams varied, heads too. I was always looking for more. Don’t know your cams profiles? But in shovel world I ran relatively low durations.. like 260-280 and I ran high lifts 550-610. This bleed off a lot of that mechanical compression. Solid lifter probably come into play at the bottom too, hydraulics could help depending on how stiff they are or are not.
EDIT I missed you can only get 91 octane.. it does make a difference. I’d run additives probably.
I assume these are slightly raised pistons with eyebrows and not flat pistons? The higher you can gain compression with the lowest dome was another key. You don’t want any dome blocking the spark from burning the mix evenly.
Is it EFI or Carbed? What carb? How many fuel circuits? Your probably in the neighborhood of 11.5:1 to 12:1 mechanical, don’t know what it is corrected with the cams you have?
I’ll get flamed for saying this. It’s the kinda snake oil I make fun of, but this one I believe in.. Fitch catalyst. These are like goofy lead pellets you drop in your tank. Laugh all you want but been using them in 12:1 street shovels for 30 years. They “do something” to help it from pinging.
My 93” Shovel made 115 lbs & 105 hp with a super broad high torque curve, 11.87 @ 112mph with a 130 street tire and I weighed 230 and am 6’5” of wind resistance. Cams varied, heads too. I was always looking for more. Don’t know your cams profiles? But in shovel world I ran relatively low durations.. like 260-280 and I ran high lifts 550-610. This bleed off a lot of that mechanical compression. Solid lifter probably come into play at the bottom too, hydraulics could help depending on how stiff they are or are not.
EDIT I missed you can only get 91 octane.. it does make a difference. I’d run additives probably.
Last edited by Rains2much; Jan 26, 2025 at 07:08 AM.
Stellar HDF Member
Joined: May 2007
Posts: 3,256
Likes: 522
From: USA
Hammer has a good rep.
Yet, removing head material raises compression, yes?
As mentioned by Blueridge above, a thicker head gasket is what I would start with.
For a second option, before you disassemble, can you increase your octane level to 93 with a mix of some race fuel (or additive) and retest?
Good luck.
Yet, removing head material raises compression, yes?
As mentioned by Blueridge above, a thicker head gasket is what I would start with.
For a second option, before you disassemble, can you increase your octane level to 93 with a mix of some race fuel (or additive) and retest?
Good luck.
Grand HDF Member
Joined: Sep 2022
Posts: 4,425
Likes: 3,831
From: Florida
Hammer has a good rep.
Yet, removing head material raises compression, yes?
As mentioned by Blueridge above, a thicker head gasket is what I would start with.
For a second option, before you disassemble, can you increase your octane level to 93 with a mix of some race fuel (or additive) and retest?
Good luck.
Yet, removing head material raises compression, yes?
As mentioned by Blueridge above, a thicker head gasket is what I would start with.
For a second option, before you disassemble, can you increase your octane level to 93 with a mix of some race fuel (or additive) and retest?
Good luck.
I think they mean take more out in the chamber roof, not off the surface
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HDF Community Team
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Correct. Expanding the chamber.
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Road Captain
Joined: Feb 2014
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From: Arizona
Well. I've been trying to tune this new motor and can't get it to stop pinging at WOT in 4th and 5th. Did a compression test and it's coming in at 225 psi front and rear. I talked with Hammer a few days ago and Dan said I may need to send the heads back and have a little more material taken off to lower the compression. Hammer said you really want to be below 200 psi to run on pump gas. Anyone have any experience with this?
Thread Starter
|
HDF Community Team
Joined: Aug 2019
Posts: 1,843
Likes: 1,940
From: Santa Ana, CA