Bill K... roller rocker question....
02-11-2009, 05:34 PM
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You were stating no loss of reliabilty etc. If you are increasing the amount that you are flexing the spring from where it was desgined, you are decreasing it's lifespan. You shouldn't have a piston clearance problem, since those are flat top pistons. Since this is also not a carbed engine you are going to have a leaning problem and since the only way you are going to see the HP gain is to rev it more, I am saying this is just like pissing in the wind, but some guys have to learn the hard way.
we have guys asking questions like this all the time on this board using research from a street engine or a small block or something that is irrevelvant to what we do in the marine environment.
What we were saying is that the HP gain you are talking about 415-435 is not going to Net anything except wasted money, shorter lifespan on a valvetrain that no one knows the hours on, and a potential problem. Your not going to gain anything except a conversation and a little speed when you are out of gas at the end of the day and headed for the pump.
Good luck anyway though since you seem to be convinced.
Don't forget to check your springs to make sure that they are not in a bind from opening a little further than they were installed to do.
we have guys asking questions like this all the time on this board using research from a street engine or a small block or something that is irrevelvant to what we do in the marine environment.
What we were saying is that the HP gain you are talking about 415-435 is not going to Net anything except wasted money, shorter lifespan on a valvetrain that no one knows the hours on, and a potential problem. Your not going to gain anything except a conversation and a little speed when you are out of gas at the end of the day and headed for the pump.
Good luck anyway though since you seem to be convinced.
Don't forget to check your springs to make sure that they are not in a bind from opening a little further than they were installed to do.
as for the potential coil bind , ill make sure i consult the instruction manual that came with my feeler gage set so that i know how to use them properly... wouldn't want to make a mistake there either... more rocket science and all...
and for making up my mind... thats an easy one. ill just wait to hear what bill has to say about it ... you know... someone that actually knows what he is talking about.
02-11-2009, 05:47 PM
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youre right. more than a few hundred motors across my dyno when i had my shop ( albeit none of them 502 mag mpi ) have left me with no experience in this area at all. i guess i just don't have a clue how any of this works. and valve springs operate and rated rated on a cyclic rate... the number of times they operate... not how far. as long as they strain within their elastic limit, it will be that cycle life that dictates their reliability. there will be no leaning problem since the total percentage charge delta will be well within the safe area of the existing stock fuel map... in fact it will be probably a bit closer to " best" than it is now...
as for the potential coil bind , ill make sure i consult the instruction manual that came with my feeler gage set so that i know how to use them properly... wouldn't want to make a mistake there either... more rocket science and all...
and for making up my mind... thats an easy one. ill just wait to hear what bill has to say about it ... you know... someone that actually knows what he is talking about.
as for the potential coil bind , ill make sure i consult the instruction manual that came with my feeler gage set so that i know how to use them properly... wouldn't want to make a mistake there either... more rocket science and all...
and for making up my mind... thats an easy one. ill just wait to hear what bill has to say about it ... you know... someone that actually knows what he is talking about.
Actually the rocket science is thinking that 25hp a side is going to make a difference in that bucket your driving. Let me know when those majic rocker arms get it to the 65mph club.
Thanks for the insults, I'll remember to put you on my mailing list.
02-11-2009, 06:07 PM
#13
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did i just read this right ????
02-11-2009, 06:22 PM
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02-11-2009, 06:55 PM
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Steve,
Never tried it ..... you would gain a little lift on the cam and a little less friction on the valve tip so you would have to pick up something but you would need to tune the engine for the extra lift to take advantage of it. A .610 lift cam would become .645 lift. Depending on which springs you have, they may or may not be an issue.
Never tried it ..... you would gain a little lift on the cam and a little less friction on the valve tip so you would have to pick up something but you would need to tune the engine for the extra lift to take advantage of it. A .610 lift cam would become .645 lift. Depending on which springs you have, they may or may not be an issue.
02-12-2009, 05:04 PM
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I am currently running 1.8 rollers on twin 454 carb motors. My first experience with them are on a carbed 454 with a little cam. The single engine setup gained 400 rpm so a size up in prop was an improvement in speed. My current setup is twins in my powerquest, And I gained 500 rpm out of the two. I firmly believe in this WITH A CARB, The one thing people don't realize is the increased ramp speeds on the cam opening. Yeah it is slight, But if you have your boat tuned right you will notice it! I can't say about MPI, But add headers and remapp the ecu and you would have a nice gain IMO.
02-12-2009, 08:56 PM
#18
I have always been a believer in looking for a few more HP here or there.....15hp here......then another 15hp there now adds up to 30hp. It all adds up. So,....is it worth it??? I guess that question is up to the person doing it. Lay the pro's & con's on the table, but I am a little hesitant to blame a guy for wanting to try. Have fun Steve 
By the way, maybe we should do something that would REMOVE 15hp from our engines.....after all, it "won't make any difference"....right????
By the way, maybe we should do something that would REMOVE 15hp from our engines.....after all, it "won't make any difference"....right????
Last edited by KAAMA; 02-12-2009 at 09:02 PM.
02-15-2009, 11:16 AM
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02-24-2009, 08:02 AM
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One of the reasons why the 502MPI only makes 415hp is because the cam takes forever to open the valves (Large seat duration, normal .050" duration, and puny .200" duration) and it does so to a palty lift of around .510" added with Open chamber Rectangular port heads with big valves to .500" lift ? Come on !
For those replacing camshafts, you can get a cam to provide the desired lift with the stock 1.7 ratio. Thus why not many people using 1.8's.
Small blocks going from 1.5 to 1.6 and making good extra power ? Well, a few reasons for this. One, you are starting from a super low ratio anyway (1.5 to 1.6 is larger % gain then 1.7 to 1.8) .
Going with higher ratio's on HR cams I have seen the fuss points in valvetrain lower in rpm. Say your typical 5800-5900 fuss point on most BBC HR cam engines. Switch to 1.8's and these now had a fuss point around 5600 rpm.
Also, on aft heads (not done it on factory heads with factory valvetrain) switching to 1.8's I've run into pushrod to head and pushrod to guideplate interference.
For those replacing camshafts, you can get a cam to provide the desired lift with the stock 1.7 ratio. Thus why not many people using 1.8's.
Small blocks going from 1.5 to 1.6 and making good extra power ? Well, a few reasons for this. One, you are starting from a super low ratio anyway (1.5 to 1.6 is larger % gain then 1.7 to 1.8) .
Going with higher ratio's on HR cams I have seen the fuss points in valvetrain lower in rpm. Say your typical 5800-5900 fuss point on most BBC HR cam engines. Switch to 1.8's and these now had a fuss point around 5600 rpm.
Also, on aft heads (not done it on factory heads with factory valvetrain) switching to 1.8's I've run into pushrod to head and pushrod to guideplate interference.
