I think you'd have reversion issues with stock Merc exhaust.

Can you elaborate on this a little more?

I have stock Merc manifolds, but also "Fast Glass" stainless 90*risers. I am rebuilding to 420 specs and was totally planning on using this exhaust set up (for money reasons).

Not sure if this is even the same animal, but the exhaust came with my boat (that had 502's with blowers just prior to me buying it). I actually saw the motors (with this exhaust) in the boat the first time we went to see it.


Any thoughts on that?

I would be deleting a silent choice system, definitely heading DOWNHILL into stainless pipe out to flappers, and exiting nicely above the waterline (pre- stepped hull Fountain).

Sorry to burst in here, but it is relevant to the thread.

I akso have 4 sets of Stainless Marine manifolds/headers.

I built my 330 up to 420 specs but I use large oval port heads. I used the cast crank but changed pistons and had everything balanced I did run the motor over 100 miles WOT and had no problems. I really liked they way it ran compared to the 330 until I built the stroker

If you can buy the 420's cheap enough, then swap them out. If you really want to see some power, take the 420's and put a set of SRP part #212135, 212136, 212137 depending on how much overbore you want, add an edelbrock 454-R tall single plane intake and an 750-900cfm carb, set the timing around 33total and watch it get up and go. I did this to some 420's that I had and it was a different boat. That is using the rectangle heads.

I have had great luck taking a 330, changing to the above mentioned piston, putting a 420 cam, set of ovl port merlin heads, (around $1200 a side from JEGS- if you bolt them on out of the box), edelborck 454-0 intake and 850 carb. This engine has great torque in the midrange. I ran one of these for an entire season at WOT, and never had a problem out of it until I clogged up my water intake and overheated it. This was not design related to the engine.

And for the peanut gallery, I know that you can upgrade the Merlins from the way they come out of the box, but I have never had a problem using them this way unless I had a really wild engine.

Anyway, good luck. I can't tell you about exhaust because every boat I have ever worked on with a 420 in it had GIL/ Mercruiser manifolds on them.

Price for 2 sets, any tails ? I'm having my 420's rebuilt, have stock merc manifolds. Those pre gil/mercruiser exhaust are a joke, if any one is still running these, change the rubber gaskets and remove the stainless tails, make sure the water passages are clear of scale. Mine were nearly blocked at the riser and tail flange. I guess the first owner did very little maintenance to the manifold gaskets, and I'm sure it was the cause of both engine failures. I decided to keep the 420's because of their reputation, but will upgrade to roller cams.

If you are going to upgrade cams, call rmbuilder here on the board. Also 454's like a little more comresion. Take them up to around 9- 9.5:1 so you can still run low octane, but you will love them. Especially since you all ready have the square heads. Intake in those engines was OK too. 750 of maybe a little bigger 4150flange carb and you are golden.

I called him last week after reading numerous threads about his work. Great guy and plan on sending some business his way after I get these things apart, hope they're not too bad. Looking for a better exhaust system for sure, any suggestions anyone?

I have a 27/29 1990 Fever with 454 mags, great engines for those older boats. Had the boat for 4 years and never any problems, turn the keys and go. Plan on selling it after I get our Formula 357 back together, 420's and trs. Hate to do it, but we needed more room. Bought the Formula in August and found the engine problems, so we ran old reliable the rest of the summer. Maybe I can sell the Fountain in the spring, someone will be getting a great boat.
Those 420's should be a nice upgrade for your 29 and not empty your wallet.