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Mercruiser 420 with a Weiand 177 blower?

bigsbetter

bigsbetter

Active member
I have the opportunity to buy a factory Mercruiser 420 complete engine. They are 9.4-1 compression ratio with factory roller rockers, rectangle port heads. I've been running my little Weiand 177 blower on my stock non mag 454 for over 9 years now with no issues. I want to go faster. My question is, is 9.4 too much compression with the blower? Currently I'm only getting about 4.5 lbs of boost and I run very low timing(28 degrees total).
 
Do the compression ratio vs boost calculator. If its over about 12.4 (thats from memory)to 1 is too much for pump gas. If not you will be fine using 92 0r better octane fuel. sounds like a solid plan though. And increase the timing to 35 total.....
 
Look into the specs of a 525SC. That was basically a 420 with the 177 on top with a dominator carb. Might have had a bit lower CR though. The extra static compression might not be bad though, need less boost to achieve same power.
 
the 525's had less than 8-1 rebuilt a pair a few years ago, I would say give it a try, you could also go with a thicker head gasket to knock it down dome as well..
 
I do believe the 420's and 525 SC also used the same cam. The 525's were around 7.5 compression and used a lot of timing. I've been scared to used to much timing on my cast inerds and cast pistons, so I kept it real low. would I still be able to here it spark knock or ping with all the noise from the headers and blower whine? I'm worried how I will know if I'm near danger once I run it?
 
Hack said:
Out of curiosity, what does your blown 454 push the 251 to?
Click to expand...
Low 70's on a good day.
When I bought the bought 9 or Ten years ago, it was a stock 330 horse 454, it ran about 54 MPH. The same year, Installed the supercharger and nothing else. I used the same carb same stock iron exhaust manifolds and same ignition. It ran high 60's...like 68-69. Ran that for a few years, then got CMi exhaust gained maybe 1 MPH, Then bought new 850 Holley...no real gain, Then I Changed the Cam to the 525SC cam, gained a little more, maybe 1-2 mph. I run it hard too, im surprised it has lasted this long.
 
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bigsbetter said:
Low 70's on a good day. I run it hard too, im surprised it has lasted this long.
Click to expand...
That's good information. :bigthumb:

Bravo 1 holding up without issues?
What grade gasoline on a regular basis: 89, 92, or 93?
How many hours on the engine when you installed the blower?

Thinking about adding some performance to my stock 7.4L/330, so that's why the questions. I'm pushing a smaller/lighter boat have a Persuarder 219.

Tossing around the idea of also picking up a used engine to build next winter.

Sorry for the hijack. :cheers:
 
The engine had fairly low hours when I put the blower on, about 150. now the engine has roughly 300. No issues with the Bravo, I just change the gear oil every few years. I run premium pump gas, mostly 91 octane, sometimes I get fuel on the water and then its not premium, I think 87 or 89 octane. I still don't see any issues. Ive seen people spend a few thousand dollars on new heads and camshafts and intakes and gain 5 or 6 mph. I think a small supercharger is the way to go. You can spend 2500.00 and gain 15 mph in 1 weekend.
 
A couple years ago, I pretty much tried to blow it up so I would have an excuse to build another engine. We ran for about 10 miles down river at 90-100% throttle the whole way. We were running 65-70 most of the way and then 71-72 at WOT for a mile or so at a time. I don't remember if that was before or after I put the different camshaft in it.
 
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