"grumpy I purchased a guys supposedly high performance car engine recently, from a car that got totaled, but the guy I bought the engine from has no history or knowledge of whats been done to the engine.
that engines got good compression, and the cam lobes seem to look un-worn,and the engine looks to be in really good condition and recently rebuilt condition, with no obvious wear and clean oil, but it runs rough, like theres one or more cylinders not firing, Is there a way to tell if the cam in an engine is a 4/7 firing order swap outside of switching wires, to see if the engine runs better that way?
obviousl you could have several issues with the ignition, of fuel or valve train, but assuming its not a mechanical issue, fuel, or ignition related, yes Id check for the firing order because those 4/7 swap cams are fairly common, Id simply swap the #4 and #7 wires on the distributor cap to see if it ran better, or worse, as a first test, but yes you could verify the valve sequence, I had a friend recently install one and spend over 30 minutes checking and re-checking why his engine ran like crap until he remembered to change the firing order, which he had done for decades with the standard 1,8,4,3,6,5,7,2 order and had used without thinking..
If your having doubts ,your making this far FAR more difficult than it needs to be!
you can simply swap the #4 and #7 ignition wires on the distributor cap to see if it runs better or, you can physically check the valves sequence,
swapping to a 4/7 swap cam has zero effect on the order the crank throws push the pistons to top dead center, ....it only effects the order in which the valves allow the cylinders to compress the fuel/air mix, what your doing is swapping the compression stroke, for the exhaust stroke on the two named cylinders 4/7
look you remove the drivers side valve cover, you rotate the engine in its normal clock wise direction until you see the intake valve on cylinder number 1 close and then you rotate the crank just a bit further to TDC , this is cylinder number 1 firing location on the compression stroke , so you know the normal firing order, is 1,8,4,3,6,5,7,2 , so if you rotate the engine until its 180 degrees, further or the #1 cylinders at BDC (BOTTOM DEAD CENTER) #4 will normally be on its compression stroke so as you see the engine damper reach that BDC rotational location both valves should be seated and the intake valve on the second cylinder back on the drivers side should have seated recently if the cams the standard firing order version.
but if its a 4/7 swap cam both valves on that second cylinder back on the drivers side will still have the valves slightly compressed as that piston reaches TDC and the #7 cylinder will have both valves fully seated.
look at the chart below
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that engines got good compression, and the cam lobes seem to look un-worn,and the engine looks to be in really good condition and recently rebuilt condition, with no obvious wear and clean oil, but it runs rough, like theres one or more cylinders not firing, Is there a way to tell if the cam in an engine is a 4/7 firing order swap outside of switching wires, to see if the engine runs better that way?
obviousl you could have several issues with the ignition, of fuel or valve train, but assuming its not a mechanical issue, fuel, or ignition related, yes Id check for the firing order because those 4/7 swap cams are fairly common, Id simply swap the #4 and #7 wires on the distributor cap to see if it ran better, or worse, as a first test, but yes you could verify the valve sequence, I had a friend recently install one and spend over 30 minutes checking and re-checking why his engine ran like crap until he remembered to change the firing order, which he had done for decades with the standard 1,8,4,3,6,5,7,2 order and had used without thinking..
If your having doubts ,your making this far FAR more difficult than it needs to be!
you can simply swap the #4 and #7 ignition wires on the distributor cap to see if it runs better or, you can physically check the valves sequence,
swapping to a 4/7 swap cam has zero effect on the order the crank throws push the pistons to top dead center, ....it only effects the order in which the valves allow the cylinders to compress the fuel/air mix, what your doing is swapping the compression stroke, for the exhaust stroke on the two named cylinders 4/7
look you remove the drivers side valve cover, you rotate the engine in its normal clock wise direction until you see the intake valve on cylinder number 1 close and then you rotate the crank just a bit further to TDC , this is cylinder number 1 firing location on the compression stroke , so you know the normal firing order, is 1,8,4,3,6,5,7,2 , so if you rotate the engine until its 180 degrees, further or the #1 cylinders at BDC (BOTTOM DEAD CENTER) #4 will normally be on its compression stroke so as you see the engine damper reach that BDC rotational location both valves should be seated and the intake valve on the second cylinder back on the drivers side should have seated recently if the cams the standard firing order version.
but if its a 4/7 swap cam both valves on that second cylinder back on the drivers side will still have the valves slightly compressed as that piston reaches TDC and the #7 cylinder will have both valves fully seated.
look at the chart below
RELATED THREADS
viewtopic.php?f=52&t=5508&p=17372#p17372
viewtopic.php?f=52&t=90
viewtopic.php?f=52&t=181
viewtopic.php?f=52&t=196