502 MPI Help
 

I am thinking of installing EMI Thunder Exhaust System and a K&M Flame Arrestor on a 1999 27' Fountain with 502 MPI. I was told with these two items I should pick up 2-4 MPH. Has anyone tried this and if so, what were the results. Thanks.

GRS,

Any exhaust is better than the stock pieces. The stock riser/manifold gasket is leak prone. The K&N (IMO K&N=hype) and exhaust are unlikely to gain 2-4 mph. What prop are you running? What RPM at WOT? In the March Powerboat see the tech article on changing outdrive lube. Teague recommends using Amsoil 80-90 synthetic gear lube. This lube has a lower viscosity than the merc gear lube. I run this lube in my XR and it's good for a gain of 1-2 mph. There's alot of viscous drag in an outdrive-even more in the XR with bigger gears. Also, lab your prop. You may want to up pitch 1-2" as well as you'll gain rpm. These two may get you 2-4 mph without the exhaust change. Teague pushes the IMCO powerflow-talk to Dino. The exhaust won't really gain you much though. I've got a 24" LH Hydro 4 blade you could try as well- It's used once, still in original box-unrecognizable from new.

Regards,

Mark

Mark,

Thanks for the input.

Best Regards,
Garry

I did the same upgrades on my 502 carb motor in a 1993 27 fountain and gained 250-300 rpm which equated to 2+ mph gain.

Did the exhaust sound different or louder than standard?

GRS

GRS - the pitch of the exhaust was a little different but not louder, maybe a little tinnier than stock. I think that the exhaust upgrade is definitely worth it and will do it again when I get my new boat.

Re: 502 MPI Help
 

:cool: my buds , is changing out to hedders,air intake, computer on his 502s feb 7 05 ill give you report.

Re: 502 MPI Help
 

did a very similar change on my 1998 27 ft fever, added imco power flows and a air cleaner. on mine i also did the vortec computer swap. mid range was better but not 1 more mph on the top end a lot of monety to spend!!! i feel that adding a whipple would be money spent more wisely...just my .02

Re: 502 MPI Help
 

1999 27 Fountain 502 Mag. Added CMI headers and K&N arrester and gained maybe 2 MPH top end. Better midrange responce.

Looks cool, sounds better, no leaks, and no reversion concerns are the main benefits. If you are looking for more speed this wont do it alone. But it will be required if you want to build power later naturally aspirated.

Re: 502 MPI Help
 

I have a 2001 27 with a 502 MPI. It has a reprogrammed computer, vortech air cleaner, MSD ignition and .045" plug gap, and AMS Oil 80W-90 drive oil. In my opinion the best bang for the buck was to simple switch to the AMS oil in the drive. Gained almost 1 MPH with that alone. Best to date is 69.4 in fresh water with a 1/2 tank of fuel. The MSD makes it much more responsive. I don't think the air cleaner did anything. I am thinking of addind a whipple and getting it over with. Seems to be the most cost effective way to add speed.

Re: 502 MPI Help
 

I think you might well get 2mph. I put on EMI Thunders and modified my intake suppressor on my '99 454 Mag MPI and gained 1-1/2 mph for the exhaust and 1/2mph for the intake, then lost 1/2mph to a drive shower. Those cast iron Merc manifolds are boat anchors! I also installed an adjustable fuel pressure regulator but the fastest boat speed ended up being at the factory pressure setting! :cool:

Re: 502 MPI Help
 

:bunny: up date, on buds 35. adding msd box, 1.8 raito roller rockers, dicthing the the stamped steel ones. this is whalt thier telling him k&n air 8 to 12 hp--roller rockers 25 to 40 hp--haedders 40hp--brainbox,40hp set 5500rpm, fuel pressure set 39lbs. 87oct to 91 oct fuel. going to take it swimming this weakend. will send up date. :drink: :D

Re: 502 MPI Help
 

WOW 113-132 HP gain :eek: :rolleyes: I am sure that it is going to help but I would bet that the biggest increase is going to be seen in raising the rev limit. Keep us posted. :drink: