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Getting reversion and need some advise

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Old 11-13-2016, 10:51 PM
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A 454 will revert less than a 502 if they have all the same equipment.

What initial timing and idle speed are you using ?
why will the 454 have less reversion?i would think the other way around.
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Old 11-14-2016, 03:33 AM
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except for the last part i 100%agree.my thinking is it is cheeper&easier to go with dry pipes than changing cylinder heads.if their is no water in the exhaust water reversion is no more.
The problem I have with this is when you have reversion in the intake. And I don't mean the water kind. But exhaust gases backing up in the intake. The motor becomes extremely prone to detonation because the mixture in the intake is traveling to slow and fuel falls out of suspension then starts puddling. When this occurs the fuel gets heated before it makes its way into the cylinder then we have all sorts of problems...

Anyone ever wonder why some guys get away with running unheard of amounts initial compression with pump gas and get away with it? This is one of the contributing factors...
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Old 11-14-2016, 09:11 AM
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I've had the blower off a few times to deal with the coupler issue, and I haven not seen any noticeable carbon staining of the intake ports, but it's something I'll look at next season.

I do have to ask... the rule of thumb is that it's hard to have too much cylinder head in a blown application... with what has been said on this thread, does this mean that most of this rule is out the window? I've read a lot about this subject (including here on OSO), and talked to very knowledgeable people on this... it seems that most follow this rule. I am not at all doubting that intake reversion is a possibility with a NA engine, but everything I've studied says the opposite when using a positive displacement blower. The rotors are spinning and still moving air at idle.... more than what would be put through with vacuum alone. I've also got good idle vacuum per my gauge so it's not like the intake ports are dead at idle.

I understand that the chosen head is huge compared to the displacement, but changing them out is not an option at this time.
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Old 11-14-2016, 09:42 AM
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I've had the blower off a few times to deal with the coupler issue, and I haven not seen any noticeable carbon staining of the intake ports, but it's something I'll look at next season.

I do have to ask... the rule of thumb is that it's hard to have too much cylinder head in a blown application... with what has been said on this thread, does this mean that most of this rule is out the window? I've read a lot about this subject (including here on OSO), and talked to very knowledgeable people on this... it seems that most follow this rule. I am not at all doubting that intake reversion is a possibility with a NA engine, but everything I've studied says the opposite when using a positive displacement blower. The rotors are spinning and still moving air at idle.... more than what would be put through with vacuum alone. I've also got good idle vacuum per my gauge so it's not like the intake ports are dead at idle.

I understand that the chosen head is huge compared to the displacement, but changing them out is not an option at this time.
Tom, I have personally seen 450" motors go together that spin 8,000rpm with forced induction these motors make upwards of 4,000hp. I can tell you the intake ports are tiny. They end up measuring 350cc volume wise because of the length of the runner but the cross section in the head a small. So, if you cant get enough cylinder head on a blown motor then why in a build where money is no object do they chose such a small head to make 4,000hp. I can tell you why... Cylinder head size doesn't matter if it's N/a or forced induction. The head still needs to be sized to the cubic inch and rpm. The only thing you are doing with the blower is compressing air in the intake. When the valve opens a mixture the is more dense enters the cylinder.
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Old 11-14-2016, 09:48 AM
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Originally Posted by TomZ View Post
I've had the blower off a few times to deal with the coupler issue, and I haven not seen any noticeable carbon staining of the intake ports, but it's something I'll look at next season.

I do have to ask... the rule of thumb is that it's hard to have too much cylinder head in a blown application... with what has been said on this thread, does this mean that most of this rule is out the window? I've read a lot about this subject (including here on OSO), and talked to very knowledgeable people on this... it seems that most follow this rule. I am not at all doubting that intake reversion is a possibility with a NA engine, but everything I've studied says the opposite when using a positive displacement blower. The rotors are spinning and still moving air at idle.... more than what would be put through with vacuum alone. I've also got good idle vacuum per my gauge so it's not like the intake ports are dead at idle.

I understand that the chosen head is huge compared to the displacement, but changing them out is not an option at this time.
tom,it is true that to big on the intake port will not effect a blown engine as much as a n/a engine but it is not the best from a performance aspect.while i agree with bb on the intake reversion thing i would not chit can the heads at this point.dry exhaust is the fix for your water reversion issue but before you do that i would go with less initial timing and see if that helps the reversion problem.
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Old 11-14-2016, 09:58 AM
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Here is a post on another forum from Darin Morgan. One of the best cylinder head guys in the country.

The chamber design and camshaft exhaust duration are two huge factors for both supercharged and Nitrous engines. They are basically the exact opposite of what you would do for an NA engine. In an NA engine the quench/squish area is overwhelmingly important. In a supercharged or nitrous engine its important to get rid of all the squish quench area. The pressure rise and flame travel is so fast they a high squish chamber will end gas detonate even though the squish quench is trying to cool the mixture.

If you design a port for an NA engine that's what works best in both Nitrous and supercharged engines. Some people mistakenly try and make them bigger and the engine never responds properly when you do this. I have done some pretty extensive R&D with supercharged stuff in the last 8 years and have tried many different port designs. I of course tried to get fancy and calculate how much bigger the port "should" be and every single time I enlarged it, the engine lost power. Now, your going to ask me why this happens. On this one, I will have to say that I (as well as everyone else I have asked) dont know. I am sure it has to do with the density and heat of the charge relative to NA but I cant quite put my finger on it. I have asked every single engineer and supercharged engine builder I can because its very perplexing to me but no one knows.
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Old 11-14-2016, 10:55 PM
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Couple things I can do...

1. Play with the timing a little. It's locked at 32, and to get it to idle right I'll probably need a get a custom stop for my distributor. Worth a try though.

2. I have some room to extend the inner pipe on my tips. I can get some 3" pipe with an expanded end to try slipping over the internal pipe end. From there I can play with the length to see what happens.

3. Definitely changing the manifold gaskets.

If I was going to covert to dry tails, can I do it with my existing risers? What about keeping the rubber good? Can I introduce "some" water?

Thanks for all the help everyone.
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Old 11-14-2016, 11:21 PM
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More hp in a given engine size creates heat , and heated lake water outflow and volume. Fairly easy to run what you need through the exhaust to keep the rubber alive and the sound down , and send the rest out a starboard side hull fitting. May pick up a few ponies too, if your moving lots of water.
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Old 11-15-2016, 04:29 PM
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couple of things, anytime you have blower surge can revert bad during that time, during that cycle becomes a vacuum, I see your water dumps at front of tail pipes, can you move to the rear ? may be enough to stop it..of course dry is best
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Old 11-15-2016, 09:23 PM
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couple of things, anytime you have blower surge can revert bad during that time, during that cycle becomes a vacuum, I see your water dumps at front of tail pipes, can you move to the rear ? may be enough to stop it..of course dry is best
Yes, the water dumps right before the tips. I'm not sure how I'd move them to dumping aft of the tips without going through the transom with the pipe. If I extend the inner pipe about 8-inches, I'd be mixing close to the end of the tip, though I'm not sure that I have enough room to have the pipe come all the way through without contact.

I was thinking about welding up the holes on the riser (there are 8... maybe leave the two on top open), add bungs to the outer jacket of the riser, and dump the excess water overboard. Good plan?
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