460 weak performance
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Cargo Master
Joined: Nov 2009
Posts: 2,364
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From: starship enterprise
460 weak performance
as I have previously mentioned, my 460 is VERY, VERY sick.
The cause isn't found yet, might be pistons, might be cam might be ? However, the engine loses vaccum as the RPM increases, like it has a plugged exhaust. Noone seems to have ever seen these symptoms before and We can't pinpoint the cause. Any suggestions?
The cause isn't found yet, might be pistons, might be cam might be ? However, the engine loses vaccum as the RPM increases, like it has a plugged exhaust. Noone seems to have ever seen these symptoms before and We can't pinpoint the cause. Any suggestions?
Senior User
Joined: Nov 2009
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The best mechanic in town replaced an engine just to have the new one do the same thing. I was walking behind the car, while the owner was watching the mechanic try to figure out the problem, and noticed the exhaust crammed with red clay mud. Pointed it out, and the mechanic unplugged the exhaust, and the car ran fine.
Old School Hot Rodder
Joined: Feb 2006
Posts: 6,472
Likes: 11
From: Exmore, VA
I guess this means you still haven't found the problem. The loosing vacuum as you increase rpm sounds like either exhaust or no spark advance. It's too bad you are around 2000 miles from me as I would really like to look at it for you.
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Cargo Master
Joined: Nov 2009
Posts: 2,364
Likes: 117
From: starship enterprise
The engine does this with the exhaust un corked at the manifolds, so I doubt that the exhaust is plugged. Same symptoms with the exhaust hooked up as with it unhooked. As for the spark advance, this occurs with the timing light going all the way to over 40* at about 2500 rpm with the Mr gasket dizzy recurve kit. Thanks for the input so far this seems to be a never ending battle so far. This is the third time that i've asked about opinions on the problem, and am still looking but with perseverence and peoples input from similar problems, I will find it eventually. The builder is thinking that it might be a bad camshaft, we have verified cam timing, tried different distributors, and so on. I will try some L&L headers and fool with the carb a bit, but I think the engine is going to have to come out and be tore down this winter. Thanks guys, I will keep looking for the problem.
Senior User
Joined: Jul 2010
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Have you cked for vacuum at the pcv? If your loosing it on top of the piston maybe it will show on the bottom through the pcv valve? Also what reading are you getting at idle? is the needle steady?
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Cargo Master
Joined: Nov 2009
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From: starship enterprise
steady needle. by pcv valve I am assuming you mean blow by. I have noticed no blow by what so ever. the idle reading is around 15-18 inches. Sound right?
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Senior User
Joined: Jul 2010
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Yes... i was getting at blow by. Steady needle is good but that reading is low. Stock you should be looking at 20-21. How build is the motor? With a reading that low I would be looking for something close to the 700 hp range? Something is definitely off.
Hotshot
Joined: Dec 2003
Posts: 18,423
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From: iowa
Bobby look were he lives. He is at high altitude. 18 is about as high as you can get at 5000ft.
Have the engine builder check with a dial indicator the ACTUAL valve lift at the exhaust valves (all of them) He could be right in a bad cam and have some of the exhaust valves not opening far enough which would cause similar symptoms as a plugged exhaust.
Have the engine builder check with a dial indicator the ACTUAL valve lift at the exhaust valves (all of them) He could be right in a bad cam and have some of the exhaust valves not opening far enough which would cause similar symptoms as a plugged exhaust.
Old School Hot Rodder
Joined: Feb 2006
Posts: 6,472
Likes: 11
From: Exmore, VA
I don't know about setting up for high altitude, but 40 degrees at 2500 sounds a bit high for me. Have you tried backing the timing off a little to see if it makes a difference? I know back in the 70s we used to set up small block Chevy engines to run 38-42 degrees at around 3000, small block Fords we used 36-40 degrees at 3000.
I second the thought of checking all the exhaust valves for lift, heck, at that point, I would check all the valves and valve timing on each cylinder.
I second the thought of checking all the exhaust valves for lift, heck, at that point, I would check all the valves and valve timing on each cylinder.
Senior User
Joined: Jul 2010
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Bobby look were he lives. He is at high altitude. 18 is about as high as you can get at 5000ft.
Have the engine builder check with a dial indicator the ACTUAL valve lift at the exhaust valves (all of them) He could be right in a bad cam and have some of the exhaust valves not opening far enough which would cause similar symptoms as a plugged exhaust.
Have the engine builder check with a dial indicator the ACTUAL valve lift at the exhaust valves (all of them) He could be right in a bad cam and have some of the exhaust valves not opening far enough which would cause similar symptoms as a plugged exhaust.
Senior User
Joined: Jan 2010
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From: Califorina , Cypress
alot of times things like to cral in to your engine and Die. so far over night i have found rats in my air filer box, and a dead squril thing in my 6 inch pipe exhaust. you never know lol