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454 Engine Rebuild

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Old 04-20-2016, 06:14 AM
  #11
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Originally Posted by Sonic30ss View Post
Interested in this- debating/researching this choice now
Okay, I PM'd him to see this thread, but in the meantime I found one of his posts in my notes:

Note: The boat I believe is a 26' Powerquest . Single engine, Bravo drive.

Originally Posted by apollard View Post
That would be me. I don't consider 51-5200 high rpm. Engine is a 0.030 over 454, iron 781 heads with some mild work (valves and removed the hump that is in half the runners. that's it - not even port matched). Off the shelf ISKY cam 221/231 @0.050, .565 lift, 114 LSA, 114 ICL. Mercruiser 496 exhaust and risers. Stock HP 500 carb (holley 800 dp).

Hardly what anyone would call great heads, excellent cam or good exhaust. What i would call a good budget build, nothing above average but better than stock Merc (except exhaust).

I've run and tuned both the Air Gap and the Victor Jr. No dyno sheets, but more in boat data than you can shake a stick at - AFRs on both banks, vac, fuel pressure differential (from which I can calculate fuel flow), RPM, advance all mapped.

The Victor Jr was faster by 2 MPH - and I saw none of the poor throttle response, etc you state. Planing time is exactly the same (I timed it). And I think there is more there with some fine tuning. 30 lb-ft in a boat is nothing, under acceleration your prop slip is covering for any loss (think high stall converter). Under steady state cruise, the lb-ft is the same at the same rpm - then, fuel flow tells the story as to which is better.

I was able to go down in jet size (primary & secondary) when i put the Vic Jr on due to improved fuel distribution. Fuel flow is lower at 3, 4, and 5000 rpm. So, more efficient due to all cylinders being equal afr - which almost always equals more power. So, I doubt I am losing 30 lb-ft at 3500.

Search here if you want the details of the poor distribution I experienced with the air gap - both in other threads and earlier in this one.

I'm not saying dual planes won't work, but saying they will only work well above 5000 and with above average parts is not correct IME. Your experience is different. That's fine. But don't tell the OP there is no other way. There is.

Last edited by SB; 04-20-2016 at 06:17 AM.
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Old 04-20-2016, 06:16 AM
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What I couldn't find, but I totally remember, is that his 800cfm carb (HP500) is still a little undersized. He measured vacuum just under the throttle blades and top rpm and it was near 2"HG.

Nothing beats good data, and he compiled a ton of it.
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Old 04-20-2016, 07:25 AM
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Yep, that would be me - again.

Basically the info on the Performer Air Gap RPM to the Victor Jr is in the post above. Victor has much better fuel distribution than the RPM in my experience. I want to make clear I am talking boats here. I've used the Performer RPM on other engines on the street with no issues. But, they are not 100% loaded all the time. This was my intro into "Boat Engines ARE Different".

The entire reason for trying the Victor was HUGE problem getting the fuel distribution right with the Performer RPM- I had some cylinders sooting the plugs badly yet other plugs on the same banks were looking lean. On the widebands, the AFR would do weird things from cruise to WOT. I tried spacers, staggered jets, different carb, changed O2 sensors (thinking it was BS data), etc, etc. I found one other discussion about this on another forum, he even had it on the dyno and saw the same thing on the EGTs.

Then I put the Victor Jr on and it evened out AFR side to side and cylinder to cylinder. I changed nothing other than the intake and the carb jets. Both the plugs and the widebands agree the Victor is better in my boat.

More to the point, the GPS agrees it is faster - on a build that turns 5200.

SB is also correct, I pull almost 2" (depends on load) below the HP 500 carb. I never see less than 1.75" vacuum under it at WOT. I see less than 5 inches of water above the carb, so it isn't a restriction in the flame arrestor. I could use a bigger carb, but this isn't an all out build, so a $1000 carb for a couple of MPH isn't worth it.
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Old 04-20-2016, 10:01 AM
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I would gladly pay $1000 for a couple MPH especially something as simple as a carb swap LOL.
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Old 04-20-2016, 03:41 PM
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Originally Posted by apollard View Post
Yep, that would be me - again.

Basically the info on the Performer Air Gap RPM to the Victor Jr is in the post above. Victor has much better fuel distribution than the RPM in my experience. I want to make clear I am talking boats here. I've used the Performer RPM on other engines on the street with no issues. But, they are not 100% loaded all the time. This was my intro into "Boat Engines ARE Different".

The entire reason for trying the Victor was HUGE problem getting the fuel distribution right with the Performer RPM- I had some cylinders sooting the plugs badly yet other plugs on the same banks were looking lean. On the widebands, the AFR would do weird things from cruise to WOT. I tried spacers, staggered jets, different carb, changed O2 sensors (thinking it was BS data), etc, etc. I found one other discussion about this on another forum, he even had it on the dyno and saw the same thing on the EGTs.

Then I put the Victor Jr on and it evened out AFR side to side and cylinder to cylinder. I changed nothing other than the intake and the carb jets. Both the plugs and the widebands agree the Victor is better in my boat.

More to the point, the GPS agrees it is faster - on a build that turns 5200.

SB is also correct, I pull almost 2" (depends on load) below the HP 500 carb. I never see less than 1.75" vacuum under it at WOT. I see less than 5 inches of water above the carb, so it isn't a restriction in the flame arrestor. I could use a bigger carb, but this isn't an all out build, so a $1000 carb for a couple of MPH isn't worth it.
Thank you very much for the info. Decision made!
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