Welcome to Speedwake.

Never re-use old lifters with a new cam....and put new cam barrings into.

 

Hello;
I am new to this forum, and have read through many old threads on this subject, but I don't think I have found the answer to my questions.
1. If I choose a cam under about 5.75 lift, can I keep the rest of the valve train intact, or at worse, change springs?
2. Is it ok to re-use my roller lifters with a new cam (220 hrs. on engines)
Depending on the answers to these question, I will probably have some more.
Thanks!

Why are you looking at a cam change? A cam change alone with not net you much gain for the trouble and $$$ on a stock MPI.

If you plan on keeping the MPI EFI your choices on a cam must take that in to the equation or you will have trouble. EFI do not take kindly to change without reprogramming the ECM.

I would change the lifters also they are pretty resonable in price. Change valve springs to match your cam. MAKE SURE to check clearances for higher lift cam so nothing binds.

Just my 02. without knowing more of what your trying to accomplish. :yak:

 

Here`s my thoughts :

Gen VI 454 has a roller cam / lifters. I`ve re-used roller lifters plenty of times, no problems.
With the 7.4 MPI that you have, you can go as high as .540" lift and still retain the stock valvetrain and bolt-down rockers. You will need to upgrade the springs to match the cam.
If you are retaining the MPI system, I don`t think you`ll realize as much mph gain as you`d like - for the amount of work of swapping cams.

 

Ok, thanks...I understood that the flat tappets would always need to be changed, but I wasn't sure about my rollers. Also I failed to mention that I am switching to Revolution marine exhaust, and I also was planning on the re-flash. From what I have read, these changes might gain 50-75 h.p.(X2), with an increase of 4-6 mph.

Is the .540 lift the absolute maximum for the non adjustable rockers? I saw that Lunati 54848 has lift of .535/.545, @.50 220/230, LSA 110. Wouldn't that be ok with the revolution exhaust? I know this cam would be at the low end of my horsepower estimate, but if I didn't need to change out the entire valvetrain it would be a considerably less expensive mod.

If I did change the entire valve train would the crane 168731 be a good choice?
If it matters, I care nothing about hole shot.
Then to the re-flash question, I know ASM does this, and I think Crockett does also. Does anyone else, and is one better?
Thanks again!

 

The 731 is an excellent cam for the 454. Crane says that for more than a .570 lift, that you need to use longer lifters. As the 731 is well above this, They say to change. They are concerned that the stock lifters will drop below the dogbones that retain them. That being said, I've seen this cam and more used with the stock lifters with no isssues, but I am NOT recommending that you do it.

If you change to this cam, you probably will need to use adjustable valve train. I've never tried it with the stock system, but as you are changing the cam a lot, I don't see it working correctly. Plus you are probably going to need new pushrods. Only checking is going to answer that one.

Roller lifters can be re used on a new cam, but its not the best idea.

 

Is the .540 lift the absolute maximum for the non adjustable rockers?

If I did change the entire valve train would the crane 168731 be a good choice?

.540" is the recommended max lift with stock non-adj rockers. I ran a .544" lift cam and non-adj rockers with no problems.

The 731 is a great cam choice. I ran a 731 with the stock roller lifters with no problems. I ran it for 2 seasons (about 100 hours) then swapped to a custom grind .619" lift and still retained the same stock lifters with zero problems.

 

you should have no issues re-using the factory roller lifters, but changing to a adj. valve train would be a good idea and maybe stop some issues...Rob

 

you should have no issues re-using the factory roller lifters, but changing to a adj. valve train would be a good idea and maybe stop some issues...Rob

Crane offers screw-in studs that have a smaller shoulder, just for this very thing. They run about $80 per set. They are designed exclusively to be used with the 7.4 non-adj rockers.

 

Well, I guess there are a lot of different opinions here!!
Let's look at this from a different angle. I just got the desktop dyno. I entered eveything from the stock motors. A few of the items I had to guess at because it is set up for cars, not boats. But with the stock cam, I got 417 h.p. I believe that would be pretty close to my stock crankshsft h.p.
Only changing to the Lunati 85848 it came to 471. With the crane 731 it came to 474 h.p. Does all this seem reasonable?? Apparently the motor likes the 110 lsa.
It would appear, to get that last three h.p. I would spend a lot of extra money for adjustable rockers, pushrods, longer lifters etc.
So, unless I entered numbers wrong, or that 110 lsa would cause reversion with the revolution exhaust, would there be any other reason not to choose the Lunati? Wouldn't the lower lift mean longer life between valve jobs?
Are there certain cams that work better for the re-programmers?
Sorry, if these are all stupid questions. Thanks for your help.

 

Let`s back the hell up for a minute .....

I went back and re-read all the posts, then I realize that you have a 454 Mag. When I read "MPI" I was thinking 7.4 (non-Mag).

I`m not experienced with 454 Mags, do they have a non-adjustable valvetrain ?

 

I`m not experienced with 454 Mags, do they have a non-adjustable valvetrain ?

all Gen 5/6 motors haev non adjustable valve train (at least the black ones do)

 

Well, I guess there are a lot of different opinions here!!
Let's look at this from a different angle. I just got the desktop dyno. I entered eveything from the stock motors. A few of the items I had to guess at because it is set up for cars, not boats. But with the stock cam, I got 417 h.p. I believe that would be pretty close to my stock crankshsft h.p.
Only changing to the Lunati 85848 it came to 471. With the crane 731 it came to 474 h.p. Does all this seem reasonable?? Apparently the motor likes the 110 lsa.
It would appear, to get that last three h.p. I would spend a lot of extra money for adjustable rockers, pushrods, longer lifters etc.
So, unless I entered numbers wrong, or that 110 lsa would cause reversion with the revolution exhaust, would there be any other reason not to choose the Lunati? Wouldn't the lower lift mean longer life between valve jobs?
Are there certain cams that work better for the re-programmers?
Sorry, if these are all stupid questions. Thanks for your help.

110 lsa "may" work. I really like to work with 112, because in almost all aftermarket exhaust cases, you don't have to worry about reversion.

As far as the HP difference between the 2 cam, without seeing the numbers you used, its a guess, but the731 is WAY WAY more cam than the Lunati. your HP at higher rpm 5500+ should be a lot more with the 731. BUT you are usingstock heads, and that is restricting the flow. The cam may be able to get the additional air flow, but the heads can't get get it in/out fast enough without port work. For example, a 731 in a 509 with pretty good aftermarket heads makes in the 540 HP range at 5500.

The best cams for the programers are the ones that they have done a lot of. If they have never done cam xyz, they are guessing. If they have done dozens of cam abc, they are more likely to get it right the first time.

 

I know comp has marine specific cams, just give them a call 800-cam-help....listen to what they have to say weather you use their cam or not....I run them exclusivly for years now, in my boats and my super gas car..Rob

 

Ok, thanks...I understood that the flat tappets would always need to be changed, but I wasn't sure about my rollers. Also I failed to mention that I am switching to Revolution marine exhaust, and I also was planning on the re-flash. From what I have read, these changes might gain 50-75 h.p.(X2), with an increase of 4-6 mph.

Is the .540 lift the absolute maximum for the non adjustable rockers? I saw that Lunati 54848 has lift of .535/.545, @.50 220/230, LSA 110. Wouldn't that be ok with the revolution exhaust? I know this cam would be at the low end of my horsepower estimate, but if I didn't need to change out the entire valvetrain it would be a considerably less expensive mod.

If I did change the entire valve train would the crane 168731 be a good choice?
If it matters, I care nothing about hole shot.
Then to the re-flash question, I know ASM does this, and I think Crockett does also. Does anyone else, and is one better?
Thanks again!

You need to go over changes with whom will do the reprogram of ecm. Even if you dyno tune it when it goes in the boat things change. You will need to go at least 112 maybe 114 LSA with MPI or you will have trouble.

ASM - Crockett and I would consider a call to Mark at Precision Marine for ECM programming. All 3 of these come up on many threads on several of the boards.

Tyler Crockett used a Cam Motion cam for the 502 kit I did and it is on 114 LSA. I also upgrade the heads with 2.250 intake valves and kit is supposed to be good for 500+hp. Used OEM lifters on cam he sent. I can not stress enough to disuss all changes with who will do the programming. Just my .02
Good luck on your project.