Help picking out a cam...
 

Skipping ad

Given the static floating around about MK cams I'd like to let the OSO brain trust handle this one;)

I plan on swapping out the ZZ502 cam this winter largely because of the 110lsa, idle quality could be better, and I have a Vortech RaceM charger/intercooler that I'd like to use but still have the option of not using it. This boat is largely used for towing tubes and the occasional wakeboarder during the summer, so low end manners are appreciated, with some wide open times in the bay and delta during the fall. It's an all around pleasure cruiser but a little more pep would be nice;).

Thoughts? Leave well enough alone?

Baja 272 Islander
502 crate motor ~500hp
QF850M carb
CMI headers (may switch to SM manifolds)
9.6.1 static comp
Comp cams steel roller rockers and push rods 1.7 ratio
Felpro head gaskets/ARP bolts
Forged internals
Performer RPM Dual plane manifold
Performer RPM oval port heads (fresh rebuild)

Cylinder Head Specifications:
Combustion chamber volume: 110cc
Intake runner volume: 290cc
Exhaust runner volume: 110cc
Intake valve diameter: 2.19"
Exhaust valve diameter: 1.88"
Valve stem diameter: 11/32"
Valve guides: Manganese bronze
Deck thickness: 9/16"
Valve spring diameter: 1.55"
Valve spring maximum lift: .700"
Rocker stud: 7/16"
Guideplate: Hardened steel
Pushrod diameter: 3/8"
Valve angle: 26°
Exhaust port location: Stock
Spark plug fitment: 14mm x 3/4 reach, gasket seat

The current ZZ502 cam has.527 intake / .544 exhaust
Camshaft Duration (@.050 in.): 224° intake / 234° exhaust

It seems like Crane is having the better choice of cams these days so I'm kicking around these options. It seems like the 791 with its 114 Lsa would be a nice upgrade or the 731 that is the same but with 112lsa.
Am I even in the right boat of thinking here?
http://i622.photobucket.com/albums/t...099FDABD6A.png

Actually the 761 looks like a solid choice. I'm trying to keep the existing valve train. I don't know the lifter brand but they are not tied together.

You shouldn't have any issues with idle quality and the current cam you have. The 525 efi cam would work really well with that setup and it responds very well to boost. 236/244 @.050 114 lsa. I have one coming out of a motor in the next week. Johnson lifters as well. Cam does have a flat nose for mark iv block...

can't help much on cam, but I ran a HP500 with a procharger for years, several carbs and EFI, last setup had to go down to a 750 from a 850 to keep from leaning out at WOT, thanks god for widebands. the air was being blown thru so quickly that would not pull fuel, the 750 worked perfectly

thats the one I'd put in.you'll be in the 525hp area n/a and 700hp blown

I like the 525 EFI cam or similar

Since you tow tubers and wake boarders, I'd look into selling the centrifugal, and picking up a 250 blower. Couple that to those oval ports , should make more than enough low end, and good top end as well. Throttle actuation and response down low with a roots is very good.

I'm just thinking of his poor drive.700+hp is not gonna be kind.:D

Very true. Maybe he could stay NA, and just run a low pitch prop for those wakeboarding and tubing days. Then when not playing mastercrafter, he could bolt the big prop back on.

As you know, we have the same combo to the carb aside from cams. Mine has a Isky cam with 525 EFI specs. Based on how the boat runs, I'd say it's in the 530HP range.

Absolutely NO fat kids on the tubes...With 700 hp and supercharger torque you will pop that drive faster than a drunk homecoming queen's cherry.

It's a Gen6 block. Would it still work?

The charger has been sitting on it unused all season for the sake of the stock drive, and that's also why I want the option to not run it. I do plan on upgrading the drive to at least a 1x and keeping it easy on the sticks.

yes

Keep me posted.

What sort of EFI did you run and what happened with it? I plan on going in that direction.

Above, somehow i typed answer out in the quote and dont feel like retyping it lol

picts

Double skis??? I didn't even know that those still existed!!! ;)

It looks like the 525 EFI cam is the hot ticket here. Thanks for the input!

I'm actually thinking of chucking the super charger idea altogether. It's an open bow and once your above 50mph chit goes flying everywhere, the women start screaming, and I either run out of lake or the open waters are too rough to open her up. I just think it's the wrong boat to do it with considering the drive upgrades involved etc. I can get 63 out of her now, and a new cam plus some other tweaks oughta get me in the upper 60s which I think is the limit for this boat without reinventing it.

And greetings from the SF Bay during the fleetweek airshow.

http://i622.photobucket.com/albums/t...A288ED301E.jpg

Blue Angels
http://i622.photobucket.com/albums/t...1563F468A8.jpg

And to think we get a rush. Well we do but... Nice pics.

So I'm getter closer to doing the winter mods, and am wondering how feasible is it to change the cam in the boat? I have plenty of room in front to pull the cam out, but my concern is the timing cover and oil pan joint.

If it was me, I'd pull the engine. Way easier to install and degree the cam.

I'm sure it's possible with it in the boat, but my back hurts just thinking about it.

The timing cover is difficult to get off and even harder to reinstall without removing the pan. I would pull the engine as well unless you like oil in the bilge

I bet in the end pulling it out will be half the work as trying to put it in while in the boat. I don't have a tree to winch it out from but I can probably get a tow truck to boom it out.

Would you all recommend new lifters or springs? I saw a mention of using lifters with a tie bar is recommended with the cam but if it's just marketing I'd rather stay with the Chevy oem units as I know they work and fit.

I don't know the spring rate but the specs list them as good for .700 lift and the 525efi cam shows .610/.632

Do you have a 525EFI cam collecting dust? I'm getting ready to yank the engine.

I've got your previously owned bm250' with carbs and intakes with all the hdw if anyone is looking. Will be going on swap.

I'd love a 250 roots but does it come with spare drives, lol. Square port manifolds?

Ps, I got the flame arrestor - thanks!

put a 168741 in it,stepped nose so easy job.

^^^^^forgot to mention,if you go with a cam with above .580 lift you need to make sure the stock lifter is not making contact with the dog bone that keeps the lifter straight,some cam,s with more lift will work,it depends on the base circle of the cam.with the 168741 you would need to go with a retro fit lifter.

Currently the lifters don't have a tie bar, and when I got new pushrods they were the ones sold for the "retrofit" set up. Bear with me as I barely know what the f*** I'm doing with V8s. I was hoping to not need new lifters as I know that these fit and work and don't want to contend with the issues everyone else is having.

By all means if what you have is working and the rollers feel smooth etc keep them as long as there not a bunch of hours on them. You gotta make that call.

So after some googling, soul searching, reading tea leaves and what not, it looks like the 731 would be a nice fit without having to reinvent the valve train and should slide in with the existing stuff. It's not a huge step up from the ZZ502 cam, but has a better LSA and breaths a tad bit better where I tend to putt around in the midrange anyways.

Any thoughts on that, and anyone have a 731 laying around?:ernaehrung004:

I have a 731 sitting on the shelf, but you cant have it,,,its going in my motor.

For lifters, I got my lifters at walmart.

D**k :duel: Lol!

PM sent

How does the open pressure and spring rate compare between the two.

2 different springs can have the same seat pressure and way different open pressure, which may let the lifter jump over the nose of the cam and bounce a few times on the way closed. Plus the open pressure can be way off if it's checked at 2 different lifts.