Another Cam and reversion ? but also risers and exhaust ?
05-16-2013, 08:22 AM
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Another Cam and reversion ? but also risers and exhaust ?
I posted this in another section, but I believe I should have just posted this here.
I did a lot of reading of previous posts and I found a lot of good information, but can't seem to find a definitive answer.
I have a '94 Gen V 454 330 HP with silent choice. I have the center exhaust riser style manifold with a 90 degree riser. I have to swap heads and was going to change cam and modify exhaust while I was doing it.
I was thinking flat tappet, but the extra work for break in with having to swap springs, and then the possibility that it won't end up working has swayed me away and I'm going to go roller.
My research shows that I should be okay with the 731 cam. So my questions are these, and some of the questions depend upon answers from the others....
A. Is it possible to run any other style of Riser? I can't spend a fortune on exhaust, but what about the 420 exhaust?
B. What type of riser would I run if I found some decent aftermarket manifolds? Indmars even.
C. Should I be okay with that cam if I can't change the riser?
C2. Is there a better cam to run?
D.If I'm not okay, what cam would you suggest?
Thanks!
p.s. I found out I may be referencing the wrong cam. Some of my research showed that this cam was the 731 http://www.summitracing.com/parts/crn-139011
However, it appears this cam is actually the 731
http://www.summitracing.com/parts/crn-168731
I was referring to the top cam. Would the bottom cam be better? I was trying to keep some low end for pulling skiier and such.
I did a lot of reading of previous posts and I found a lot of good information, but can't seem to find a definitive answer.
I have a '94 Gen V 454 330 HP with silent choice. I have the center exhaust riser style manifold with a 90 degree riser. I have to swap heads and was going to change cam and modify exhaust while I was doing it.
I was thinking flat tappet, but the extra work for break in with having to swap springs, and then the possibility that it won't end up working has swayed me away and I'm going to go roller.
My research shows that I should be okay with the 731 cam. So my questions are these, and some of the questions depend upon answers from the others....
A. Is it possible to run any other style of Riser? I can't spend a fortune on exhaust, but what about the 420 exhaust?
B. What type of riser would I run if I found some decent aftermarket manifolds? Indmars even.
C. Should I be okay with that cam if I can't change the riser?
C2. Is there a better cam to run?
D.If I'm not okay, what cam would you suggest?
Thanks!
p.s. I found out I may be referencing the wrong cam. Some of my research showed that this cam was the 731 http://www.summitracing.com/parts/crn-139011
However, it appears this cam is actually the 731
http://www.summitracing.com/parts/crn-168731
I was referring to the top cam. Would the bottom cam be better? I was trying to keep some low end for pulling skiier and such.
05-16-2013, 10:37 AM
#5
I echo what the other guys have said about getting a custom cam ground for your application, and Bob is a good guy to talk to on that. Also, if you are serious about making more power, better flowing exhaust will be in order. You may be able to find a set of take-off Merc 496 manifolds and risers - these flow better than the old log style manifolds and eliminate the problematic wet joint in the riser / manifold interface.
If you go with a roller with aggressive ramp speeds and high lift, do not skimp on lifters, pushrods and springs. Valvetrain stability is critical for longevity, and to get this you need to invest in quality parts. I learned this the hard way (as others have), and now I am in the middle of doing it all over again.
If you go with a roller with aggressive ramp speeds and high lift, do not skimp on lifters, pushrods and springs. Valvetrain stability is critical for longevity, and to get this you need to invest in quality parts. I learned this the hard way (as others have), and now I am in the middle of doing it all over again.
05-16-2013, 11:03 AM
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What kind of risers can I run with Silent chioce? Are there any tricks to extend the riser a little in SC applications?
Are 496's that much better than what I have, that woudl be very affordable.
Also, The appeal with someting like the 139011 Cam is that I can find it used and cheap...as I mentioned I was just going to go flat tappet originally, so cost is of concern. That is why I am so curious if that specific cam will work. I really like the specs of the 139011.
Unfortunately, this isn't a crazy go fast application, just trying to pep things up a bit so I can pull skiiers with a boat full of people and beer....and people full of beer haha. Plus, who doesn't want to go as fast as they can?
Are 496's that much better than what I have, that woudl be very affordable.
Also, The appeal with someting like the 139011 Cam is that I can find it used and cheap...as I mentioned I was just going to go flat tappet originally, so cost is of concern. That is why I am so curious if that specific cam will work. I really like the specs of the 139011.
Unfortunately, this isn't a crazy go fast application, just trying to pep things up a bit so I can pull skiiers with a boat full of people and beer....and people full of beer haha. Plus, who doesn't want to go as fast as they can?
05-16-2013, 07:09 PM
#7
What kind of risers can I run with Silent chioce? Are there any tricks to extend the riser a little in SC applications?
Are 496's that much better than what I have, that woudl be very affordable.
Also, The appeal with someting like the 139011 Cam is that I can find it used and cheap...as I mentioned I was just going to go flat tappet originally, so cost is of concern. That is why I am so curious if that specific cam will work. I really like the specs of the 139011.
Unfortunately, this isn't a crazy go fast application, just trying to pep things up a bit so I can pull skiiers with a boat full of people and beer....and people full of beer haha. Plus, who doesn't want to go as fast as they can?
Are 496's that much better than what I have, that woudl be very affordable.
Also, The appeal with someting like the 139011 Cam is that I can find it used and cheap...as I mentioned I was just going to go flat tappet originally, so cost is of concern. That is why I am so curious if that specific cam will work. I really like the specs of the 139011.
Unfortunately, this isn't a crazy go fast application, just trying to pep things up a bit so I can pull skiiers with a boat full of people and beer....and people full of beer haha. Plus, who doesn't want to go as fast as they can?
That was before the SECOND rebuild - now I am putting together a billet cam, Morel lifters, Manton pushrods, AFR heads, etc. Scared the wife will find out and try to match my spending at shoe and furniture stores. 
05-16-2013, 07:15 PM
#8
Back to your question - You would have to run a shorter riser with most of the Corsa Captains Call systems or the Merc Silent choice, unless you can get someone to modify the lower leg to offset the diverters further back, and that will depend on how much distance you have to the transom. I was lucky enough to score a set of diverters that will go in place of the collectors on my Lightning headers. I recently sold a real nice set of Gil manifolds that had diverters built right into the risers. They were really nice, and I have not seen another set like them.
Another option might be to ditch the Y-pipe and diverters and go to a set of switchable muffler tips thru the transom. Several sets of those in the Swap Shop.
The Merc 496 is based on the newer GM platform, and from what I understand does not have a forged crank. Kind of limited on any serious performance due to this. Most of those are EFI as well.
Another option might be to ditch the Y-pipe and diverters and go to a set of switchable muffler tips thru the transom. Several sets of those in the Swap Shop.
The Merc 496 is based on the newer GM platform, and from what I understand does not have a forged crank. Kind of limited on any serious performance due to this. Most of those are EFI as well.
05-17-2013, 05:55 AM
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I think he is referring to the 496 manifolds. Someone mentioned that he look for a set of those. If budget is a concern I would highly recommend you look at the prices of a roller cam conversion. Just the lifters will run you $550-600. Even if you find a used cam it will be around 300. Then you need springs retainers and locks. Most recommend tool room steel and they are not cheap, then the price to have the heads rebuilt. I just got done doing all of this and I was shocked when I realized how much I spent on just valve train. Nothing cheap about marine valve train.
I've done two motors for two boats in the last year. The first one I wanted a blower, but when n/a. The second I went blower and from experience the n/a setup was a lot of money for not much gain. I gained 4 mph for a lot of work and money. Should have thrown a 177 or 250 on it and been done. Lesson learned.
I've done two motors for two boats in the last year. The first one I wanted a blower, but when n/a. The second I went blower and from experience the n/a setup was a lot of money for not much gain. I gained 4 mph for a lot of work and money. Should have thrown a 177 or 250 on it and been done. Lesson learned.
Last edited by cp5899; 05-17-2013 at 05:58 AM.
05-17-2013, 08:41 AM
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Well, as I mentioned, I'm having to get new heads anyway, which will have all new springs and hardware to support whichever cam I choose. Since I have to tear this far down anyway and spend money on heads, I decided to go ahead and do the cam so it's all done.
So, it seems I can find some Gill manifolds at a decent price, then there's the 496's, would the merc 420 manifodls come in behind both of those? Would I have to use my stock riser with any of those aforementioned maniolfds? Or can I use the larger ID risers usually had by those chioces and just hopefully modify them to fit my SC?
Is there a certain distance from water outlet to exhuast opening that has been found through experience, to be a minimum to work with the 011 cam?
.....Now that I'm thinking about it, I could do some calculations with some estimated temps and thus estimating mass flow/volume flow of exhaust assuming inlet flow at a low VE due to closed throttle, Which can then be calclulated into a velocity, and then caclulate overlap time at idle at 700, 800, 900, 1000 rpm with adjusted exhaust and intake flow and velocity to get a ballpark as to length of time, and thus, riser outlet length to avoid reversion...hmm....we'll see how ambitious I get.
So, it seems I can find some Gill manifolds at a decent price, then there's the 496's, would the merc 420 manifodls come in behind both of those? Would I have to use my stock riser with any of those aforementioned maniolfds? Or can I use the larger ID risers usually had by those chioces and just hopefully modify them to fit my SC?
Is there a certain distance from water outlet to exhuast opening that has been found through experience, to be a minimum to work with the 011 cam?
.....Now that I'm thinking about it, I could do some calculations with some estimated temps and thus estimating mass flow/volume flow of exhaust assuming inlet flow at a low VE due to closed throttle, Which can then be calclulated into a velocity, and then caclulate overlap time at idle at 700, 800, 900, 1000 rpm with adjusted exhaust and intake flow and velocity to get a ballpark as to length of time, and thus, riser outlet length to avoid reversion...hmm....we'll see how ambitious I get.
