Correct. I really did not Change much in these builds. However, one thing that was hurting me possibly was the previous valve job. The guy who did my heads, had told me the valves were sunk into the heads quite a bit. Enough that he suggested replacing all the valve seats. I agreed.

I was told by a couple other cylinder head guys, that that situation I had is no good for airflow. I've also learned that a quality valve job can be more beneficial than porting and polishing the ports. Basically the valve area is a major restriction in flow, and working on that area can show substantial increases.

Another area is obviously the blower change. I would imagine that going from 86% overdriven, to 7% under driven, is like adding a intercooler in a way. At 7% under, I'm probably not making a bunch of heat from the blower itself. While there will also be heat from compressing air in itself, at least I'm not superheating it. Therefore, if I installed a intercooler right now, and did not change pulleys , I don't think I would gain much of anything power wise. I don't think at the speed I'm turning the blower, or the amount of boost I am running warrants it. Jim valako I believe did something similar as I am talking about with a chiller, and came out with a result that agrees with my theory. Now, not to say adding a chiller and a couple more psi, wouldn't help me out, but I'm more than happy where I am power wise now , and definitely don't want to be tearing drives up!

Also, I had a single 1050 on the 250 blower. As its very hard to overcarb a roots blower setup, I think the dual 850 carbs are a bit help. If the roots blower starves for air on top, it just won't work to its full potential .

I also had my timing at 30*, and a rich fuel mixture on the 250 setup. I didn't have access to a dyno when I bolted the 250's on, so I played it safe. Or at least thought I was. Hindsight I should have ran a bit more timing, but nothing broke, so I guess it was ok.

Last year my best was 84mph on gps with the old setup. I am guessing, with my new setup, I am probably up about 100hp per side. Can I hit 90, not so sure, but it would be nice. I'll never be the fastest nor am I trying to set any specific goals, reliability is what I'm hoping for, a speed increase would just be a bonus!

In the end, I think I did the engines a favor by going to a larger blower with dual carbs, some nice headwork, upgrading the rods/lifters/pistons.

I will say, these engines ran very well with the smaller blowers, for what they are. Never hurt them, and they made good power. The cam and head combo I think is the key with these.

Those are stout numbers and the motors look amazing! Gotta get some pics up when they are in the engine bay. Congrats.

Nice job, nice results and Kudos to those who helped from here on OSO and yourself who listened , learned and put good advice to work for you. This is the great positive side of OSO and the help of those good guys who reside and contribute unselfishly here on OSO.
That Fountain should respond nicely to the extra power, so be safe, have fun and enjoy your season!

Best Regards,
Ray @ Raylar

Thanks Ray. This kind of stuff was what these forums are about. You are also a great asset to guys on here.

So the 420's worked out well for you. Good numbers. I sure hope you have access to good fuel all the time. 35* and no chiller is a tiny bit scary. I would really suggest installing a knock meter on those and watching it real close when ya give er. Long WOT pulls might build some heat under the blowers.

Good luck, the old fountain should scoot pretty good with those puppies strapped in the back.

You Bring up a good point. I have some questions about timing.

From all the old tech info Ive read, regarding marine supercharged apps, such as the old weiand and B&M catalogs, they normally suggest 30-32* of timing.

But then when I look at the merc racing supercharged stuff in this manual i have....

525SC: 177 blower at 2:1 ratio, 5.5PSI, 35* total timing
600SC: 420 blower at .93:1 Ratio, 6psi, 33* total timing
800SC: 420 blower at 1.17:1 ratio, 8psi, 28* total timing

Granted they are 7.5:1 with iron heads, no chillers, and 143* water stats. They did live a long time though. Im guessing the 800sc only ran 28* total due to the longer crank stroke, and added boost.

My question is, why don't you see more boost retard functions on marine setups?

While EGT's may come down on the dyno with added timing, what happens when the throttle is pinned for say 5 miles in a boat??

As for fuel, I was always told by guys like Eddie young, and Kris Vogt, that if your tuning with a 02 sensor, you want to see AFR numbers in the low 11's to keep things safe on a marine supercharged deal.

I'd like to have some 02 bungs welded in my tails, and do some tuning on the water. While I chose to dyno it, it was more or less to get a rough idea of what kind of power I am actually making, vs. what speeds I am running. Since there just really are'nt alot of older 38 straight bottoms with #4 drives around to compare to. I'd like to do the 02 sensors also to monitor all other throttle positions not just WOT. Since a lean spot at 4000RPM cruise can put holes in pistons just as well.

My guess is the richer low 11 afr's help give a safety margin for poor gas quality, and maybe the additional fuel in the roots blower helps cool the intake charge?

At the end of the day i'd rather have a boat that can run 87mph all day long, than one that does 89 for a minute before it starts to detonate

What static CR are you running? My 509 is 8.2 to 1 with aluminum heads and a chiller. I still only run a max of 32* with 7lbs of boost on 91 octane.

I think that safety can be had around 12 to one AFR so long as its not detonating. With mine being efi, its actually tuned to run around 13.2 to 1 and 36* of timing at 0 boost and drops to 11.5 to 1 and 32* at 7psi. Of course, I do have a pair of knock sensors keeping deto in check. If I didn't, there would be a deto display on my dash board. That's for sure. I do have a wide band sensor in the collector and a read out on the dash just to keep an eye on things.

Mild thunder, you've inspired me. I too have IV 454s and have been looking at purchasing some 502s to repower but your VERY impressive numbers have me reconsidering (not that I'm brave enough to buy/run blowers) Congratulations on a very sweet build x2!

Congrats on the new Mills! Dean's the man!!

Really cool MT, great job. I agree with airpacker on a/f numbers and timing. My engines always look nice inside after a season of 11.7-11.9 af. I try to stay under 12 at wot. That 35* would not be something I'd try in a boat with significant boost and long hard runs. How much less power was made at 32*?