mattsmithadelaide
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Mental compression, no power past 4k?
So I sorted out the fireworks display the previous owner had planned for me in the electrics. I take it out for a spin and second gear flat road there is absolutely no power past 4k. I hammers up to 4 grand and then doesn't go anywhere? Checked the compression running 13.0:1 in the cylinders. Would you suggest retarding/advancing the timing? (which one if so) Running higher octane fuel? Or something totally different? Cheers! NB using 32/36 weber carby recently rebuilt. (could be running to rich as it pops?)
post edited by mattsmithadelaide - 2012/12/06 11:29:11
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spigot
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Re:Mental compression, no power past 4k?
2012/12/06 13:57:43
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Wozzah
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Re:Mental compression, no power past 4k?
2012/12/06 18:44:33
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mattsmithadelaide
So I sorted out the fireworks display the previous owner had planned for me in the electrics. I take it out for a spin and second gear flat road there is absolutely no power past 4k. I hammers up to 4 grand and then doesn't go anywhere?
Checked the compression running 13.0:1 in the cylinders.
Would you suggest retarding/advancing the timing? (which one if so)
Running higher octane fuel?
Or something totally different?
Cheers!
NB using 32/36 weber carby recently rebuilt. (could be running to rich as it pops?)
First of all, how did you work out the compression ratio? If it is 13:1 you have no hope running it reliably on pump fuel, period. Retarding the timing may help, but you will need to retard it to a point where it will lose power anyway. Higher octane fuel will help, either ELF, or just run it on E85 (you will need to modify other stuff to do this) Woz
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Gdub
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Re:Mental compression, no power past 4k?
2012/12/06 18:47:07
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I am also keen to understand how you 'checked the compression' and came up with 13:1
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Matt75
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Re:Mental compression, no power past 4k?
2012/12/06 19:30:25
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I had a similar issue and it turned out to be cam timing.
Matt
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mattsmithadelaide
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Re:Mental compression, no power past 4k?
2012/12/07 15:50:38
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Used a compression meter, ran turned the engine over with the accelerator flat to the floor. Read 13 Bar.
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Wozzah
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Re:Mental compression, no power past 4k?
2012/12/07 16:59:34
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mattsmithadelaide
Used a compression meter, ran turned the engine over with the accelerator flat to the floor. Read 13 Bar.
That IS NOT the compression ratio, that is the cranking pressure, and the 2 are not related. 13 bar just means you have 182psi cranking pressure. Cheers Woz
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na.charrett
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Re:Mental compression, no power past 4k?
2012/12/08 22:44:43
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182psi cranking pressure (assuming engine at operating temp and a "dry"compression test) equates to around standard compression or a 9.2 compression ratio as standard is around 175_185 from memory for a HC pinto....
Sounds like your camshaft sproket is one tooth retarded if you are loosing power after 4000 but have very good torque low down... providing you have a standard (non interference) cam- advance the cam timing one tooth and try it. (Of course assuming you have tuned everything else properly - unlike your CR calculation....)
Just my 2.2c worth including GST....
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Matt75
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Re:Mental compression, no power past 4k?
2012/12/09 10:14:43
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as per my previous post i had the exact same issue as Nic described.
Matt
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spigot
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Re:Mental compression, no power past 4k?
2012/12/09 14:34:56
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13 bar is actually 191psi, assuming the gauge is reading correct. At that pressure premium fuel is mandatory.
Generally speaking advancing the cam beefs up bottom end torque and retarding does the opposite.
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Gdub
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Re:Mental compression, no power past 4k?
2012/12/09 19:57:58
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As Wozzah said earlier, there is NO RELATION what so ever between the PSI or BAR reading on a compression test and compression ratio.
All you are being told by that guage reading is that there is nothing wrong with your engine from a compression perspective! Cam timing could be an issue but i would be lining up TDC and checking the relative cam position before i started moving teeth. Otherwise it is nothing but guesswork.
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mattsmithadelaide
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Re:Mental compression, no power past 4k?
2012/12/09 23:45:09
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yeah took it for a spin today, so much low end torque, I put 98 in it and it is ridiculously quick. It seems strange because it says in the manual to check compression by means of a compression test. I must have a bit more of a read! Brakes booster died though. More money. NFI if they can be repaired or replaced
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mattsmithadelaide
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Re:Mental compression, no power past 4k?
2012/12/10 00:31:43
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I will try retarding the camshaft, I brought it forward a tooth as it wasn't idling at all.
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Gdub
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Re:Mental compression, no power past 4k?
2012/12/10 09:19:22
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mattsmithadelaide
yeah took it for a spin today, so much low end torque, I put 98 in it and it is ridiculously quick. It seems strange because it says in the manual to check compression by means of a compression test. I must have a bit more of a read! Brakes booster died though. More money. NFI if they can be repaired or replaced
Nothing wrong with doing a compression test, this will tell you if the cylinders are sealing indicating the condition of the rings, valves & valve seats and compression ring on the head gasket. The point Wozzah and i were making is that compression pressure (e.g. 180psi or 13 bar etc) and compression ratio (e.g. 10:1 etc) are completely unrelated. You cannot determine compression ratio with a compression tester guage.
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mattsmithadelaide
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Re:Mental compression, no power past 4k?
2012/12/10 11:13:01
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okay, sorry about that. Just assumed you took put your reading over environmental pressure to get a ratio.
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