Outlaw 24

I was wondering if anyone knows whether or not EMI or IMCO exhaust can be added to a 454 MAG EFI engine without reprogramming the ECU? Arizona Speed and Marine said yes and TEAGUE said no. TEAGUE also said that they sell this type of exhaust all the time and do not reccomend reprogramming. Help!!!!!!!

Dave1972

AS&M wants your $$ to reprogram. Chances are you won't notice much, if any, performance gain with just changing exhaust. This topic has been discussed at length on the board so if you do a search for 454 or 502 EFI/MPI upgrades, you should find many many threads on this. Some have mentioned that the better flowing exhaust will clean up the sooty black on the transom but that's about it. Rumor has it that the gain you find will be based on weight savings and not much else. The stock cast manifolds theoretically will flow fine up to about 450-475 horsepower from what I remember reading on here. The new manifolds look much cooler so it's a give and take. If you are looking for speed results, the best bang for your buck is to have your prop labbed. Houston Prop here on the board does a great job as I have had nothing but complete satisfaction. I've also heard that Matt and Julie at Throttle Up who are also on the board are fantastic as well. My guess is that you can't go wrong with either one.

Outlaw 24

Dave thanks for the reply. My major concern is running into a lean condition with installing the EMI exhaust? Any help would be appreciated.

Dave1972

IF you are running a stock 454 EFI you are not going to run into any problems at all. Mercury programs the motors to run pretty rich and that is why you often times will see the black soot around the back of the transom. I ran a stock 502 EFI for a number of years with IMCO Powerflows with ZERO problems. If you are planning on running in saltwater, the cast aluminum manifolds won't last forever from what I hear. I have always been in freshwater so that is a non-issure for me. You might want to check out Revolution Marine as I think they advertise here on OSO and they have great prices and a superior product. I called them a while back and their customer service was excellent.

Outlaw 24

Thanks Dave. We boat mainly on Southern Lake Michigan and at Hardy Resovoir so the EMI's should have a good life expectancy.

Dave1972

Outlaw,

If you haven't checked Revolution Marine....take a look. I think that you will find them to be less expensive than the Eddie Marine products and they might even perform better.

Grog

Outlaw -

You would be very lucky to get 1-2 mph from exhaust. I put on IMCO Powerflows mostly for looks and weight savings. I wouldn't expect that you would need to reprogram your ECU but to be safe, run with the new exhaust for a few hours then pull a couple of plugs. They will tell you what you need to know.

deboatmon

I believe that the single best reason to change to a high quality exhaust system on a stock engine might very well be the elimination of the cooling water through the riser/manifold joint. You may see very little performance gain on a stock engine and no re-programming should be necessarry for a stock engine.

Stock manifolds and risers can become a serious liability to engine life in a relatively short time.

There are several high quality manifold/riser manufacturers out there. I personally like my Stainless Marine setup very much. I dump water all the way at the very end of through transon risers thus greatly enhancing my chances for a long lived and healthy engine with little or no chance of reversion. My engines are not stock thus these attributes are more valuable to me than on your stock engines. But, the stock riser/manifold joint can be a fatal error.

Dump the stock exhaust. Save your engine and begin the trend toward higher performance.

Pat McPherson

Ken is right on all counts.
I pulled the stock casts stuff off my 1999 7.4MPI.
The joint had been leaking. Rust in some of the exhaust ports.
Installed Stainless Marine, little gain, maybe 100rpm. They look good and don't leak though.
This off season changed out the cam for a little hotter one, and had AZ Speed recalibrate. AZ Speed has the ECU back for another round. I am running a stock calibrated ECU right now and the plugs don't look lean. Gained other 200rpm...