Cam question: More or less LSA for low compression engine?
 

I am considering a cam change because the engine is coming out anyway to explore my oil pump issue, and there have been some long term durability questions raised about my custom grind cam that was based on a Merc billet core.

That being said, I am considering a few directions here. Engine is a 489 with GM 088 casting heads with 1.88/2.25 valves, Isky 8005SP springs, and some mild pocket porting and bowl work. Compression is the big factor on this engine, as even with the block being square decked, with the 119 cc chambers the best we could do is around 8.6:1 CR. My current cam has these specs: 222 / 232* @ .050, .575 / .578, 114* LSA

Option one - GM ZZ502 cam. 224 / 234* @ .050, .527 / .544, 110* LSA Pro's - can be picked up for reasonable $$, and would work fine with the GM dogbone lifters that are in there, and it should be easy on valvetrain component life I have seen a few posts of people having good luck with these in boats with the proper exhaust. I am running Lightning headers, so reversion would probably not be a problem. Con's - lift is kind of wimpy, and I am concerned about the overlap with the low compression on this motor.

Option two - Merc HP 500 carb cam; 222* / 230* @ .050, .576 / .598, 110* LSA - this would have the same issues with overlap and tight LSA as the ZZ502 cam, but with considerably more lift. I would have to upgrade to a good set of lifters (Morel?) with this cam, which means considerably more $$.

Option three - Crane 731 cam; 226* / 234* @ .050, .587 / .610, 112* LSA - Similar specs to the Merc HP 500 cam, but wider LSA at 112*. This might help me to keep my dynamic CR up a little higher. This would also require the lifter upgrade.

Also considering one of Bob M's cams that a member has up for sale, but it was optimized for a 502 with AFR 305 heads, so not sure if it would run as well on my engine. And before everyone asks, I have talked to Bob and am considering having him grind a cam for me. I sent him my specs via email but have not heard back from him yet - I am sure he is a very busy guy and will get back to me soon. I'm not in a real big hurry - pretty much written off this season anyway, although it would be good to get it running and tested a little bit before the cover goes on for the winter.

Another option to consider might be an HP500 EFI cam.

So I guess the gist of my question here after writing this novel: Should I be looking for a cam with more lift but less overlap & wider LSA to try to keep my dynamic CR higher for better performance, or does this go out the window?

I'll hang up and listen now. :cool:

I doubt there is enough difference between those cams to even notice. The 110 ls will give you a slightly rougher idle stronger bottom and midrange. The 114 will extend the power band maybe 200 rpm if you can get there. Just an opinion.

more lsa...

I would get the Crane 731. I used it in my 525SC.

If your going to buy a new cam I would just save yourself the headache and call Bob. There are a couple of hp 500 cams for sale in the swap section but the guy want $300 for it. For a bit more you can have a custom cam from Bob. Nothing wrong with a 731 but its an old design, when going with Bob your going to get the most modern lobe profiles plus customer service that no one will be able to match. Plus the price between the 731 and a Marine Kinetics cam will be the same.

You may also get good results by simply running 1.8 rockers. I called Bob on my Reed cams and he told me to run 1.8's on the intake. Bob will only sell you a cam if you need one.

What exhaust are you running?:party-smiley-004:

BigJim, I am running Lightning headers, with Corsa muffled exhaust tips.

contact Bob @ marine kinectics.....nuff said.

other way to go since motor is coming out; up the CR, either with pistons or aftermarket heads. of course, that is a leetle more dinero than a new cam...

Wish I could! It's hard to justify putting the money that I have already spent into this 25 year old tub. You can only polish a turd so much, they say. ;)

Sent you a PM.

Got it, BBC - thanks. I'm mulling over my options right now. Anyone have a killer deal on a set of Morel 4603 lifters for a great price? :D

Cool, just let me know, I've had it for about 8 months and always said I'd keep it unless I could help someone else out who had a similar set-up, you kinda fit that bill. If it's not the right piece for you, no problem and good luck with your project!