A friend has just fitted dana exhaust to a standard 496HO. The kit came with an adjustable fuel regulator and he has tried lifting fuel pressure to 46lbs from the standard 44lbs but the engine is experiencing detonation at about 4700 rpm. It used to rev to 5000 rpm no worries with standard exhaust. Any ideas?

Opening up any exhaust sometimes will sometimes lean out the engine a little. He needs to bump up the mix a bit. Sorry I can't help more, I'm a carburator guy :-)

Have you done anything else to the engine or ECM besides headers. You should also measure the fuel pressure on the boat running at full rpms and load and make sure the fuel pressure is not dropping under load.

Best Regards,
Ray @ Raylar

I didn't need to change anything else when I put CMIs on my old 496. I also didn't see any performance increase...........

i have had no issues since i installed my cmi etops on my 496ho
but my mechanic did increase the fuel pressure he said to protect the air fuel mix ratio
headers alone really didnt net me any visible gains but i was able to get a labbed 4b 26p on the rev limiter
3/5 mph depending on conditions no more

It's hard to get an improvment from exhaust unless you push the rpms a lot higher. Most stock systems flow pretty well. It's not like they have mufflers and miles of pipe.

Nothing else done. I am going to have a look at the boat tomorrow. The owner rang Dana anhd they have done the job many times with no issues. I am hoping it is as simple as a plug lead on the wrong plug. We will put scanner on and take for a run to check fuel pressure at revs as you suggest.

Thanks Ray. PS As a 496 owner in Australia your posts are an invaluable resource. Keep up the good work! I have spoken to you regarding an upgrade and will do one when funds permit. Cheers CC

It seems the guy who fitted the headers did not open the water taps and the engine was getting hot. Opend the taps and changed plugs and all running ok.

Having said that, the engine only revs to 4700 rpm at 66 mph on a a gps. (Checked it had 100% power on the scanner also).

It is in a Domin8tor.

Absolutely no gain whatsoever for the DANA exhaust and if anything lost a couple of mph!

Then you have experienced what most others experience, no gain. The original exhaust flows pretty good, especially for a stock motor. Too much advertising in the claims of mph gain. When BT says that a pair of CMIs on a 496HO will give you 3-5 mph, I don't know where he gets that from, never seen it myself.

THANK YOU!!