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RPM Signal

Data Analysis Fundamentals

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Hello, I'm working in a car equipped with Holley Sniper Efi and I'm having some issues with this car and one of my questions is, should the RPM signal be like this? If no, what could be wrong? Its using holley hiper spark distributor. The engine is a Chevy 250 straight 6 Turbo.

Thank you!


Is the engine running smoothly, or misfiring?

Sorry, can't comment of the signal - just want to say cool engine to be experimenting on!

I'm not sure how much experience people have here on the Sniper, but have you tried their forums?

David I don't feel the engine misfiring but it's not smoot, I checked the spark plugs and it look ok, a little rich but ok. I noticed a heavy vibration after 3k rpm I though it could be related with this weird signal.

Gord, I didn't try their forum yet.

Ah, vibration could very well be a big part of the problem - even if not, it HAS to be dealt with before something breaks, like the crankshaft. Actually, it may already have broken, as that can cause heavy vibration and misfiring - I recently had to replace my trusty lawnmower after almost 25 years when it broke it's crank, also with those symptoms.

That engine has a long crankshaft with, IIRC, only 4 main bearings. This could cause a problem with tortion twisting of the crankshaft - especially if not re-balanced for the different masses of the pistons and con' rods. That twist will in turn be passed on to the camshaft which has it's own issues with twist - oh, I believe the oil pump is driven by/drives the distributor via a common gear from the camshaft, so that could also be an issue.

Having a GOOD performance front harmonic balancer/pulley is a CRITICAL part of the build - I assume you have one? If not, and it's the original, not only may it not be able to provide the damping required, but with age the outer damper's mass ring can move on the polymer (rubber interface) and actually be making things even worse.

Yah Gord, that might be the problem. Thank for the advice, I'll check everything out.

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