350 Map MPI cam spec
 

Can anyone enlighten me what the stock 300HP cam specs are? I know I've seen it posted but can't seem to find it now??? Trying to compare it to XM270HR.

Might be Merc # 86602T01

Thanks,

AB

I haven't been able to cross check your cam part number, but the GM "395" cam was used extensively in the Merc 350s in both pre-Vortec and Vortec head models. This was the cam that was in my motor. Here are the specs.


Dur. @.050"
IN.= 196*
EX.= 206*

Adv. Dur.
IN.= 288
EX.= 308

Lift.
IN.= .431"
EX.= .451"
Lobe Center Line= 109*

Step up to the XM276HR!:p

I cannot say with confidence this is the same cam you have, however, these specs are the "395" cam specs. The part number on the end of this cam will end in 395 (surprise...). I personally measured my cam and came up with the same numbers as listed in several sources.

The 300 HP 350MPI cam was the same cam as the 250 HP 2bbl. and 260 HP 5.7EFI. Induction setup was the only difference in those motors.

Thanks for the info.

As for the XM276HR, called Comp Cams and they say with short risers reversion could be an issue. They claim that the XM270HR its a non issue. Subsequently, for the little hp gain, not worth it to me. Plus, with stock rods, I'm not spinning this over 5k to take the advantages the XM276Hr cam provides. Now, if someone on here documented success I would consider it.

I'm running a Crower 00483LM hyd roller which is 221/230 @ .050" and .525/.545 on a 1.5 rocker. 114LSA. GLM manifolds and stock Merc stainless riser/elbows. No reversion I've noticed and the wide band is still alive. Very similar to the XM276HR. Crower said this cam would work but don't go bigger. Kind of an apples to oranges comparison but it is a reference point.

Did you have to change you valve spring setup or have the ecm tuned?

I had that cam in a 383 with 10:1 compression and short IMCO style stainless risers and had no reversion issues. Things like port velocity, idle speed, and initial advance all have an effect on potentials of reversion. Motor made 437hp @ 5400 RPM and 479 lbf @ 4100 RPM in that motor and idled it a 700-750 rpm. I have since gone to a bigger yet cam from Bob Madera and added 8" to the length of my riser and that cam was 234/242 @ 050 on a 110LSA. At least the HM276HR is on a 112 LSA. Cam is sitting on the shelf collecting dust if you would be interested in it for a reasonable price.

Anyone running the 1.6 rocker comp cam part #35329 these are the stock rocker 383 ? Can you run without a spring change. (Chnage with motor in Boat )

Any increase in HP ? I read that the stock rockers are closer to 1.47, the 1.6 would leave the duration but bump the lift to .459" / .480"

Yes I did change the springs, but the entire motor was rebuilt. Dart heads, Crower dual valve springs, Ferrea valves etc. etc.

Motor started and ran off the stock tune and injectors with the cam, head, compression and displacement change. However that was only a baseline and I tuned the ECM myself.

Yep, it was the "395" cam. I checked the intake and got about [email protected]. The interesting thing is the intake centerline was 104.5. Checked this over and over. The Chain only had .125" of deflection so that setup most have been intended. I called comp cams again, got someone different and asked again about cam choices and reversion. This guy said the same as others. With Vortec Heads and 9.5:1 Compression, XM270HR is the choice. Since i'm not raising the rev limiter, this should be fine. Though the XM276HR sure sounds nice.