Hi all - so im trying to get some usable numbers for folks (like me) who have little idea what they are talking about when it comes to cams! Since there are some incredibly bright folks around here I thought Id post what ive researched and see if any of you can chime in and confirm/correct me and my results -

I am in the process of camming an otherwise stock 6.2 for a customer. I have found through many hours of research that merc used the ramjet cam in many of there 90s-2000s 6.2 motors so ordered one. So I searched online for a overlap calculator and found a very nice one here (no affiliation) and here (again - no affiliation) - the numbers add up on both.

• https://mgispeedware.com/camshaft-calculator/ (this one is great cos you can enter 4 profiles and compare!)
• Camshaft Overlap Calculator - Wallace Racing (very basic)

So I compared these two cams for my example:

• Ramjet cam (PN 14097395) - great cam option for the 6.2, tremendous torque, works on stock heads, great price and OEM made
• Comp XM270HR requires machining, springs, more expensive.

The comp cam shows -4 degrees of overlap despite having a larger LSA and shorter duration numbers VS the ramjet - longer adv duration and tighter lsa but -19 degree overlap.. is lower better, and what is the safe threshold? Im sure the IVC and EXC play a role in reversion but I am not skilled enough to even begin a conversation on where the safe threshold is-

Please excuse my lack of expertise if I have missed anything critical or come across misleading but I really think some overlap numbers would really help us in cam selection options - would be wonderful if vizard could/would chime in on this

Here are my results:

Comp XM270HR: -3 degrees overlap






GM Ramjet cam - 19 degrees overlap

Where'd ya get the Ramjet cam info as far as that's what Mercury used?
Seen your other thread. I guess you degreed the current one?
What year is the 6.2 you are working on?
Not disputing anything, just FWIW, the lift specs are off with it compared to this manual 31 snip I posted in this thread here: 2006 mercruiser 6.2 engine specs
I'm not sure what year 6.2's the manual covers.

The '395' cam was used on a bazillion marine small block motors. It is mild. Don't expect a screamer motor with that cam. Not saying its a bad cam but don't expect big numbers from it. It will also fall on it's face around 4400 rpm. If you want to bring a little more life into the motor something closer to the 270 would be appropriate. If you want a rock solid basic cam the 395 is a good choice.

2001 boat- No screamer here - this is a 40ft twin 383 fishing cruiser, low down torque is key and the 395 cam is a torque monster, 444ft lbs at 3000.. I was mostly interested in the overlap calculations - hard to believe the GM cam has less overlap despite a tighter lsa - which is what most ppl tend to quote ito marine cam selection and reversion - i would say cruising rpms are around 3200-3500, and the 395 cam fits nice, i was more concerned with reversion..

https://www.offshoreonly.com/forums/...0-a-print.html

I found more references to the ramjet being the merc cam - found it elsewhere too, ppdiesel or somewhere.. I basically used the comp cam to compare the overlap as a factor in making a safe choice.. fwiw i also bought a CRANE 2032 cam Hydraulic Roller P/N - 104224 which was cited as the merc 6.2 cam elsewhere. Its closer to the comp 270 cam but for the size and use of the boat i opted for the ramjet cam instead.. i dont think the customer would care much for anything over 4k..

and fwiw - this one came with a kellog crank-

Is this 6.2 (377 cid) fuel injected ? If so, it will need reprogramming for many of the more typical marine sbc performance cams that would be good for 383’s. GMHot Cam, Comp Cams Extreme Marine 218/224 at .050”, etc/etc

What kind of exhaust ?

runs through regular dry joint manifolds, then thru the chambered inboard exhaust and out the back via flappers.. this ramjet is a mild cam - im hoping the stock ECU will work ok with it- im specifically trying to avoind any kind of programming and im not building a race boat! This is a heavy cruiser-

Okay, so I’m lost. The stck 300hp 350mpi/ 320h 6.2 mpi cam is the vortec truck 196/206 109 lsa cam right ? The svorpian 6.2 and merc reman 383 used bigger cams , right ? Didn’t you ask about bigger cams ? Sorry for being confused with your wants and needs. Straihten me out, thanks

Nope - ive been trying to get specs for the motors, stock basically.. I guess I wasnt aware the scorpion variants sued bigger cams - im also trying to get some overlap numbers down so people who are looking for marine style cams can perhaps get a hook.. thats part of what I wanted to find out - a: stock cam specs (as confirmed there are various ones - i thought there was one or 2 with slight variances), and b: get some overlap numbers down ito reversion because alot of ppl drop LSA like it solves reversion but unless ive made a mistake or the 2 calculators are inaccurate, lsa alone has little to no bearing with overlap I referenced bigger cams because it was suggested they might have been stock cams-

Okay, well I'm a pretty good source of cam info. If you look back under my name, I've done most cams in .004, .006, overlap at such, .050", overlap at such, and ,200" durations...most marine performancer bbc cams and some sbc cams, but know them pretty well too.

I understand overlap well too. BTDC and ATDC. The one we are more concerned with is exhaust ATDC as that's when the piston is going down and doesn't care where the air comes from - intake or exhaust.

Crane used to state Overlap at .050" passed +8 degrees probably needs dry exhaust. That's a pretty good spot to ponder. Also, all the crane blu motors with crane cams, had the cams installed + 5 degrees. So, 114LSA cam was installed 109ICL/119ECl.

Enough of that.



If you are not going to program the motor, then don't touch the cam. All These mercruiser (black and race blue) motors are speed density.

Good info thanks SB! so looking at the graphs i posted - the overlap numbers - are they the numbers you specify @ 50? or are they perhaps calculated differently? I want to know at what point reversion becomes an issue - i might want to build some hotter engines for my boats (and friends) and would like a scientific based approach I have a few good cams here and would like to punch numbers in so I can get some idea of what might cause issues -