Missing RPM on 496
 

After getting beat yesterday, I noticed that I'm only revving 4600 on my 496. A Month ago, it was 5100. This time I had less gas and people on board???

Questions.

Could it be that it's 15 degrees warmer out to lose 500 rpm?

What is the easiest way to check a tach for accuracy?

What are normal things to check on a 496/375?? Seems to run great otherwise.

I also took out my muffler-inserts yesterday which was supposed to gain me 200 rpms, that's kinda when I noticed the rpm problem.

I'll probably pull the plugs and check them in the meantime.

Thanks

1995 Mirage 257/496 HO

My big question is not, prop and load and weight... I get that. My question is why am I missing 500 rpm. Throwing a smaller prop on there (which someone recommended) is just a bandaid to some other problem.

If it's the 375 version I was under the impression the max rpm was 4600-4800 or so.... that's what i get out of mine in ideal conditions

I have twin 496HO's, noticed one motor revving much slower than the other, top end was way down, I had a bad plug....

Easiest way to test a tach for accuracy is with an MSD tach generator. they work great.... or send it off to Livorsi.
Where are you located?

I'm in Seattle. I'm going to shoot for the fuel problem or the tach is off. I bought a new fuel/oil separator and a inline filter to replace. I'll try that first.

I just wondered if sears sold some automotive something or other to plug test leads into to compare to tach.

Max RPM on the 375 HP 496MAG is 4,800 RPM. Turbulator removal will not gain you 200 RPM...50 maybe. Check to make sure all your plug wires are fully seated on both the plugs and the coil packs. You are most likely only running on 7 cylinders now. If the wires are all seated properly then check the plugs. There are shop tachs with inductive hookup (place on #1 plug wire) you can use to determine what your true RPM is.

Had the exact same problem. Was only turning 4200 RPM's. Changed fuel filter and spark plugs and got almost 700 more RPM's. Now at 4900. Good Luck!

Thanks. Any plug recommendations?

How did you notice the plug? Was it cracked or fouled out?

had the same exact problem w/ a pair of 496s. fuel pressure was ok.
pulled plugs and fired each one seperately w/ scanner. had 3 not looking good. plugs looked ok upon visual inspection. replace all plugs and bay test. rpm went from 3800 - 4600. Just dont use denso
plugs. I used ac delco # 41-983. good luck

I would also check for guardian problems. If your water pressure drops for more than a few seconds you will get the guardian set which will put you back to %90 power. If it continues to have lower water pressure it will go to even less power. You should see/hear the alarm though when this happens. You can clear it usually by cycling the key a few times.

I have had this problem a few times and ended up getting some harnesses from whipple which prevent the code by showing a higher amount of pressure using a resistor.

As stated above, check your tune. If you have Silent choice check the linkage and make sure its intact. I had a similar problem once, and all it was, is that one of the linkages broke.

What are the gap specs for the 41-983? BTW, Great prices on those plugs from summit racing.....

pretty sure the gap was .060 but specs should be on your flame arrestor cover