420 hp to 540c.i.d.
 

So if I were to use everything I could off of my 420's (Heads, Intakes, Carbs, etc.) What kind of gains would I see by using a 540 short block to start with. Already have good exhaust (imco powerflows). I guess i'm going for a mild 540 build. Has anyone done this with 420's. Heard they have some pretty good components stock. Thanks for the help, this might be my winter project!

You can make some nice torque using your heads and what not. Should be a mild 525-550hp setup 540.

The easier thing to do, and cheaper, would be to install some small 177 or 250 blowers on your 420's. Its a proven combo, it will get you to 550hp 4-5lbs of boost. Probably gain 10mph in your boat.

Some 540 Shortblocks will run you about 10g or more. Than you are gonna wanna go thru your heads, valve job, springs, etc. Cams, lifters, timing chains, and all the other stuff will add up quick. Probably have 15g out of your pocket fast, just to gain 100hp or so. You can find a pair of used blowers complete ready to bolt on for 3-4k and go. Just a thought.

That was my second option, basically make a 525sc clone out of what I have. If there are any 177's floating around I would be very interested. Thanks for the guidance.

I would consider selling my b&m 250 blowers, low hours, polished intakes and blowers, carbs just rebuilt. They are single 1050 holleys. Still on my boat and work great! To make 5psi on my 454s, the 177 blowers were at 2.15:1 ratio. The 250s do it at 1.5:1, not as much heat.
If you were interested, is sell mine with everything, belts, pulleys, flame arrestors, pretty much everything you need to bolt on. I have more aggrssive cams than the 420s, engines idle all day the way its setup now. :coolcowboy:

177's are at their limit on a big block. 250s are much better for your needs. Either will "work" but you're much better off with the 250's on a 454.

I am very interested in this offer. Would like to know a little bit more about your cams if I were to go that route. Like I said, this would be a winter project. Let's keep in touch about this. Sounds like that setup works well for you!

Pm me your number or email and we can discuss some ideas....

I got some nice hydraulic roller cams that would work nice for you too! Depends though on how long your tailpipes are though. If they are the long TRS style Gils, that pretty much go to the inside of the transom before they end, you should be good. 232/[email protected] .578/.578 lift. A little hotter than the 228/236* 530/551 lift 420 flat tappet cam. But the roller grind itself should pick some power up do to the ramp speeds and frictional loss. Either cam though works well with a blower.

If the engines are low hours, and healthy, I'd bolt the blower on it, and keep the boost 5psi or under, and timing 28-30* total. Upgrade to a better fuel pump and fuel lines. You buy my blowers and they come with six valve Holley Mechanical pumps and #8 lines to carb feeds, all AN nickel finish stuff. Youll be making more power than a stock 525SC, due to the larger blower, and extra compression you have.

Just a guess, but I would think the blower package would add 8-10mph in your boat. Which i assume would put you somewhere in the 80mph range..:coolcowboy:

Blown 311
 

Back around 1990 I was at Trenton Marine talking to Dean Nickerson who was doing business there at that time.He was telling me about the blower installations they were doing on 420's/TRS in Formula 357's and 311's.They would increase prop pitch by 4" with the blower.I didn't ask the blower size but it did not look like the small 177 unit.Claimed it made 530 horsepower,said the 357 did about 72mph and the 311's went close to 80.

I think nickerson used the 250 b&m blowers a lot back in the day. He knows that setup well.