Stock 502 - First Upgrades
 

Thinking of purchasing EMI Thunder exhaust manifolds/risers, K&N filter and an adjusted ECM. Any thoughts? Good or bad experiences?

Supercharger is the plan for next year.:confused:

If you purchase the EMI's, I would highly recommend that you go with the stainless steel risers. They are longer and help reduce the possibility of reversion. Some 502's have a bad habit of reversion with these particular headers when used with the standard riser. Email me direct if you have any questions.

502 improvements
 

I installed imco powerflows and have no problems. Where did you find K&N air filter? please let me know what catalog. Thanks

wesley t,
I just bought the K&N filter and the billet aluminum
adapter for my 502 MPI from Rex Marine. They cost $155.00
for both plus shipping. I'll be installing them this week. Did you
see any improvement in performance after adding the Imco exhaust? I had my ECM reprogramed by Energized Fuel Injection
but I haven't tried it out yet. Tim at EFI told me the reprogram should gain around 30 HP.

26ZX
I am on my second ZX, so no smoke blowing from me, known facts only.
I have a 2001 with a OM serial # 502/ OM Bravo I # drive, the last of the heard produced, I added a K&N and a lab prop, that will bring a better return than the stuff you listed above, both gave me almost 500 RPM, factory setup I was stuck at 4700 RPM's, no longer.
In fact I was on the phone with another owner (Frank C) as we read your post. Short of a procharger or whipple, the K&N and Labbed prop are you best bang for the buck for a stock Gen VI 502. The price of the exhaust isn't worth the risk for a maybe 1 MPH gain.
Lastly, on the Donzi BB you will see my scales receipts, my 26ZX with 94 gallons of gas weighs almost 6600 pounds, this hull being able to get 67/68 GPS is incredible, for those who brag, my single engine pig is almost untouchable in the rough water (by other single stock set ups). They fly, I drive by!!!!!! :)
I suggest you try these two bolt ons first.
More Donzi info, and more than you want to know at www.donzi.net
If ya need more info email me and I will call ya.
Bryan

Bryan I put a 502 in my 25ft. BAJA last summer I ran Stainless Marine manifolds with a Victor JR. tall single plane intake and a 1 inch spacer,and a HP950Holley. With a modified 24 Bravo1 prop I turned 5300 rpms and ran 76.2 mph on gps.This year I added a custom ground cam by Bullet Racing Cams and 310 pro 1 aluminum heads.I ran it on Sunday on turned 5800rpms so I just ordered a 26 lab finished prop Hope to have it this weekend.See you at SML poker run in May. Dean

BAJA, sounds sweet!!! We are looking forward to SML, should be a blast!
Bryan

26ZX - you are probably constrained, as we all our, by the limitations of both monies and / or warranty. If your true plan is to put on a supercharger next season, be careful not to through good money after bad.

An expensive labbed prop and a reprogrammed ECM will have to be discarded the following season if you install a supercharger.

Most other upgrades will give you modest or impercievable results.

If you must perform upgrades this year, exhaust and K&N intake are items that will slightly improve performance and can be retainned with the planned upgrade. Remeber motors are air pumps. Air in - air out.

Stainless Marine, cast alum exhaust manifold and ss risers and pipes, used to be a great choice , looked cool and never leaked. However CMI's headers & pipes have come down in price in the past couple of years. These are a full header with polished risers & pipes. A diligent shopper should be able to find a set for $2,400 to $2,600. The aftermarket exhaust systems are a considerable weight savings over factory.

Save your $$$$$$, get a supercharger & new outdrive next season. The wait & expense will be worth the 10 to 15 mph.

I am trying not to lecture. I have made all the bad mistakes. Every time I read a magazine i would buy something that did very little, or caused me to by something else. After two years of dicking around with the little stuff - $200 there, $400 there, $2,000. for this, I would turn around and buy a whole new motor. The recipe comes first, then the baking.

502 upgrades
 

I changed to Hardin Marine flame arresters with K&N filters and Gil Big Guns.
Had to change from 28p to 30p props. 72mph before and 80mph
after. Exhaust is the most
bang for the buck. 33AVS Scarab.

SEE YA, those are impressive numbers, what engines in what boat? Are the engines stock?
If so double impressive.
I agree that mod engines need to breathe, 26ZX modifying his exhaust will be a good call for future "major" upgrades.
Bryan