Stainless Marine manifolds on a stock 350 Mag MPI
 

I know there won't be a big gain but is there anything there? Will a set of SM manifolds and a K&N arrestor give me a couple mph on a stock 350? They weight savings alone is nice but is there any real hp/speed gains?

Thanks

Re: Stainless Marine manifolds on a stock 350 Mag MPI
 

Don't know about Stainless's specs, but EMI drops weight by about 60-70 lbs on a 350, and claim approx 10% hp increase. I assume Stainless is about the same specs. I replaced my stock Mercs mainfolds on a past boat with a 454, dropped around 70 lbs. The boat planed off a bit easier, and probably picked up 1-2 mph, and 50-150 rpm's depending on conditions (water conditions, temp, how many on board, etc).

I'd say that if your manifolds are due, definitely look at Stainless, EMI, etc. But if this is strictly a performance upgrade w/o adding anything else (aka blower which requires more exhaust flow), then the $$ invested may not equal a sizable return, especially if you can't do the job yourself and are paying for shop labor rates. I only did mine because they needed replacement. Hope this helps.

Re: Stainless Marine manifolds on a stock 350 Mag MPI
 

When using the Stainless Marine stuff, make sure to check ALL of the water fittings to be sure that they aren't seated against the inner manifold of the water jacket.

We put a set on a 509 in a 29' Profile many years ago and had severe flow problems. Couldn't figure it out for the longest time. Actually detonated and blew the first engine due to overheating. It was my friend's boat and he wasn't smart enough to not run it when it wasn't working. The second motor did the same thing until the people at stainless marine said "sometimes the fittings are too long and bottom out against the inner maniflod". This after MANY phone calls with them and purchasing several accessories that were supposed to fix the problem. It never even occurred to me that a fitting that was sent with a several thousand dollar manifold system wouldn't fit right.

The Stainless Marine stuff is probably high quality, and it worked fine for the Profile after finding the problem. Just make sure to look over EVERYTHING before firing it up!

Re: Stainless Marine manifolds on a stock 350 Mag MPI
 

Heres the good the bad and the ugly.......
not trying to push one product or another but my manifolds need changing on my twin smallblock (carb) 29 Fever.....heres what Ive found.
The Feb 2003 issue of Family and Performance Boating Magazine (FPBM) tested a 21 Eliminator stock sbc (carb) changed the manifolds at the dock to GLMs, went out 1.5hrs later and ran 2mph faster.......the aluminum versions can be had for like .......cheap.
The Nov issue of FPBM .....the guy had a 22 Scarab with a tired stock 350......rebuilt the motor completly to stock specs and added a set of Stainless Marine manifolds......picked up 2mph......they attributed the 2mph to the rebuilt engine.........said nothing about the pipes.......they listed the price for the manifolds at $2195, including tips......OUCH!!!!!!.......I know they sell blems on ebay for a ''buy it now" price of $1720
Revolution Marine claims 2-3 mph gains on a P29 Scarab 350 mpi's with much better midrange and sound, which goes along with their tri Y design as seen in their cutaway on their website........all aluminum construction.....the black ones list at $949 and about $70 for brackets........a dealer quoted me $1150 for the fully polished version plus brackets........I did see a set of fully polished big block manifolds and they were REALLY nice.......tons of bling.
I dont know anything about the Eddies or Gills.................doug

Re: Stainless Marine manifolds on a stock 350 Mag MPI
 

That's what I kind of figured. I had a chance to buy a brand new set for $900 that's why I was considering it.

Re: Stainless Marine manifolds on a stock 350 Mag MPI
 

I picked up about 2 mph on my boat with a 350 Mag MPI, but I have a Procharger also. Depending on the age of your boat, for $900 I'm buy them just to have a spare. Sooner or later, you'll need them.