Need advice on this Crane 502 Cam
 

I'm planning on doing a mild HP upgrade to my 502 MPI's this winter: Revolution manifolds w/ spacers between the mfld & riser (current Merc mflds are set up w 3" spacers), Arizona Speed's super flow flame arrestor, remap ECU's, pocket port the heads and all new roller valve train (Crane rockers, lifters, rods and springs) w/ the Crane #168731. If anyone wants to weigh in w/ any general advice, have at it, but here's my question: should I be concerned about reversion? The 168731 cam is supposedly more or less the HP500 factory cam (Duration 226/236, .587/.610 lift, 69 deg. of overlap). I can't find the LSA spec -does anyone know it? Are HP500's prone to reversion? Guy I bought the boat from told me the blocks were replaced by Merc due to the origional 502 MPI cam being prone to reversion which is why it has the spacers and resonators in the exh. hoses. I've had no problem but of course have a lot milder cam (211/221 dur, .512 lift)

I'd go with the 168741 instead. It's a little bigger and louder exhaust noise if that won't be an issue. I used the 168731 and I wish I had gone with the 741. The 741 is about the same as what is used in the Merc 525's N.A.

Thanks, but I'm not planning on spending the $ for larger valves and fuel system upgrades, so I've probably got a little more cam than I can use in the 731-

Its a good choice. I used one in my 525SC.

It will make just as much power up to 5000rpms as the 741. The 741 will make more in higher rpm ranges.

Ive used the RM exhaust with milder cams w/o any reversion problems but i think you might be pushing it with that much duration. I would chose a milder cam or a longer riser exhaust. Gotta agree w/ Griff on the 741. good luck.

BTW, lobe separation is 112. You could get it custom ground on 114 to better help prevent reversion.

I'm redoing an HP 500, and I think I'm going to use the 731 also.

What is the effect on performance of 112 versus 114 lobe seperation?

Nothing you will ever notice with ~500hp or less.....:D To really simplfy it, the 112 should have a "peakier" TQ and HP curve, shifted slightly higher in the rpm band.....as Griff suggested, I'd go with the 741 on a 114 as well......:circle:

This is the cam I will use when I up the anti on my 502Mag MPI.

The 500 EFI cam specs as follows:
292*/298* @ .004"
230*/236* @ .050"
.352"/.359" Lobe
.598"/.610" Valve
114* LSA
109* ICL

With the 114°LSA, you will have a better idle with an EFI engine. On a carb engine it probably would not matter.

I made the same choice for the exact same reason. Will you run the engine up to 5700 or will you run at 52-5300. The 731 was a nice improvement over the stock hp500 cam. I think the 741 is too much on that set up.

If I can run 5400 on the top end, I'll be happy. I don't like breakin' stuff when I'm trying to have fun and when you push too hard, somethings' gonna break. I also don't want to spend thousands more on fuel system upgrades etc. chasing a few more MPH. The law of diminishing returns is alive and well in this game-

Just to mix things up a bit (Isky option)

275*/284* @ .007"open & .010"close (they do it different)
228*/238* @ .050"
.325"/.340" Lobe
.585"/.612" Valve (I used 1.8 ratio)
112* LSA
55.5* Overlap


I bought their full retro-roller kit (Cam, springs, pushrods, roller lifters, retainers, keepers, and button for <$750 shipped.

Put it in a 498CI (.070 over stroked 1/4") with 049 mild pocket ported heads with 2.19/1.88 valves and a Edelbrock RPM dual plane with 2" open spacer and dyno'd at 540+hp running just a touch rich. Idle is still a bit lopey but I can't blame it on the cam yet... I still have some carb idle circuit tweaking to do.

Being that this is an EFI engine, the ECU will need to be recalibrated. I suggest that you speak to the guy that will remap your ECU to be sure that there is a proven program.
I suggest Mark at Precision EFI or Tyler Crockett not AZ Speed.
I'm quite sure they will have a program for the Crane 731, 741, Merc 500EFI, as well as their own custom grinds.

Pat: Do you have a beef w/ AZ Speed? I read nothing but positive comments about them. They do in fact have an ECU remap pgrm. for the 500MPI/ Crane 731 which I plan to have them do (see my original post). Just for yuks, I'll check out Precision and Crockett. Thanks for the input-

I just went through this with my modified 502 MPI's. If you are not going to modify the fuel system, I would stick with the 731. I would use a 114 LCA. Be careful with too much duration or too small of an LCA in these motors. They use a speed-density type EFI system and depend on a strong, stable vacume signal to the MAP sensor to idle correctly.
Also make sure that you do not have one of the 502 MPI's with the factory defect on the #7 fuel rail feed. You can get by with it with a stock motor but once you start making modifications you need to correct this defect or you may ruin a new engine.

My experience with working with AZ Speed on a modified 7.4MPI was not great.
I've gotten great advice and parts from Mark and Tyler. That is where I will go in the future as well.

MJB: Thanks for the advice. I assume you mean LSA, not LCA. Did you experience a problem with a cam w/ 112 LSA? If so, what cam was it? (duration specs?) What's with the Fuel Rail defect? I've never heard of this- I had to change an injector this spring and the fuel rail is basically a triangular shaped pipe w/ 8 injector holes and an inflow fitting- how could there be a defect in the feed to #7? Mine are 2000 model year if that tells you anything-

Yes, I meant LSA- lobe separation angle....not lobe centerline.
Have never used a 112 LSA. I just know that reversion is such a problem that I decided not to take any chances and be conservative with a 114. My cam was custom ground by Cam Motion to match the flow #'s of my ported DART heads. I wound up with 228/233- .592/.600- 114/110. The spread between my I & E is only 5* because the E ports on the DART heads flow much better relative to I flow compared to the stock GM heads. My overall duration was a little lower than I expected because my heads flowed so well. I am very happy with this combination. I wound up with about 540 CHP at about 5400 and she idles like a stocker!
I also started with AZM but was unhappy with their poor customer service. I wound up having my ECM's remapped a second time by Tyler. Much better!!
Do a search on this board. There have been many posts about the #7 fuel rail defect. Not sure, but I think they fixed it by 2000. Mine was 1997 and I had the defect.

Unless they've change their programming go with someone else. My azm mapping was a nightmare. I'm running the 741 and love it. I'm turning about 5400 rpms.

Any signs of reversion? I don't want reversion problems but also don't want to spend the $ on a custom grind if I don't have to. I just e-mailed Crockett with my plans and asked for opinion about 112 vs 114 LSA. Appreciate everyone's feedback on AZM

Call Crockett, he answers the phone a lot more often than he answers e-mails...
You will not have reversion issues with a Crane 731 or a Crane/Merc 500EFI cam...
No need to bash AZSpeed, just take our advise and use Crockett...

Thanks, I'll call him. BTW: I didn't bash AZ Speed at all. I just thanked you guys who strongly recommended I use Crockett-

No, I know you didn't...:cool-smiley-011:
I could though; but there is just too much of that on these sights...:rolleyes:

Aren't they one and the same cam?

Cuda: I've looked a so many cam specs my eyes are going crossed, but I believe there my be a slight, probably insignificant difference between the Crane 731 and the Crane/Merc hp 500 cam

I'm cam shopping also. I asked what cam was used in a 500 EFI, and was told it's a Crane 731.

They are vary close. The lift is the same. In Post #10, I gave you the spec's.
The 500EFI has a 114°LSA and a bit more intake duration.
On an EFI engine, I would use the same one as Merc Racing.
One other thing about the 502Mag vs. the HP500 is the intake valves. The HP500 has 2.25 vs. 2.19...

I know what you mean. My cams were ground on 114* too (or maybe even 115* lobes) and my 565cid NA engines idle like stockers as well and the drivability is incredible. Makes it nice for shifting/manuvering, etc.

Crane has a custom grind # for the Crane 731 except ground @ 114 deg. LSA- #16HR00017. I checked w/ an online dealer called Horsepower Wizard (there's a link on Crane's website)- they quoted me 383.40 for custom grind-

One other thing I just remembered about the Crane 731. There are two different cores and the cheaper one has broken in a few guys marine engines.
I'd check with Tyler Crocket about buying a kit with cam, lifters, valve springs, retainers, locks, roller rockers, conversion studs, ecu remap, and...
It will for sure be a lot easier buy from one source, you will get stuff that works, and I would bet you'd pay the same or less.

If you buy the Crane 731 or any other grind crane make sure to get the copper core not the black core and heres why.....