NHGuy

So, what 's the consensus. Do I want them for my new cam?
I'm planning on doing a Comp 12-236-3 hydraulic flat tappet cam with springs, lifters, keepers and retainers. I have non vortec 64cc heads and don't know what pistons are in there. I think they are slightly dished because I got 180 psi when I did a compression test a couple of years back. Flat tops would maybe go too high on the compression with my small chamber heads. So I'm thinking the dynamic compression will be safe.
My ignition is TB IV and has no knock sensing system. I do understand ping and detonation, will be careful about it.
My nephew is a master tech, maybe I ought to borrow his bore scope and view the piston tops.
Any thoughts are welcome, keep me from doing any dumb stuff guys.
As far as I can tell from the head part # the engine has the internals of a 1990 crate motor. How do I learn the compression height and piston volume to get my actual compression? Would that require removing the heads & measuring or is there a look up available. I haven't seen one yet, and I have looked.

ACrooks69

iTrader: (1)

Well I can tell you from modifying my old 1991 Searay Merc 5.7, those centerbolt heads are a big limiting factor. I ran the 260H and it was about the perfect cam for it, The newer cam you have speced will also be fine. I shouldn't worry about anti pump up lifters, you really aren't spinning the motor high enough to need them. You are going to be looking at about 5000-5100 rpm. You likely have between 9 and 9.3:1. My stock motor also had 180psi cranking. You may want to consider doing something to the heads (porting at some point), . You will definitely wan to get a nice intake like a Edelbrock performer or professional products 52001. The pro products with work with the standard intake flange and the 87-95 flange. Let me know if you have any other questions, I'd be happy to help.

I also wouldn't be worried about compression on that crate motor. You have the luxury of nearly unlimited cooling and a cool operating temp and you are not going to really be pushing the limits of the engine, just the flow of the heads. You may also find your cranking compression down a hair due to the added compression. You may also want to consider the 212/218 extreme marine cam since the rest of your engine is stock. You can always step up to a bigger cam if you decide to go with better heads.

NHGuy

Yeah, true that on the porting. I know it won't do a ton, but it's unused potential til I go do it. Whenever the heads come off I I'll port match & smooth them...unless the "finance department" allows me a head upgrade.
My logic does not immediately "get" why the cranking compression won't rise a bit. The new cam has longer duration and higher lift. When I think about it some more I realize the lessened cranking compression would be from the intake valve being open farther past BDC which aids in filling at higher RPM, when the intake air/fuel mixture has more velocity.
So I might need an extra puff to light it off in the morning which is fine. It's good to know what could happen though.
Have any of you done this cam or similar? What kind of total advance works best? Does it call for a spark plug heat change?

ACrooks69

iTrader: (1)

I've had flat tappet and hyd rollers all in this range. You are going to want about 34 degrees total timing, which should put you around6-6 degrees of total timing. f you can find yourself a v6-24 module you can kick it up to 10-12. Everything will run better if you can get your initial up to that 10-12 but you can do that unless you can limit your total timing. Maybe a switch to an MSD marine ready to run dist, Then you can run 12-14 and limit you total to where ever you want. Very easy to hook up as well. Your std heat range plug is fine. What intake are you running? I can't stress enough how a better intake will improve your bottom end. Seeing your location, it looks like you are in salt water. Are you closed cooled or are you running salt. I realize that will impact your ability to run aluminum parts.

A word of advise for future planning. If you end up going any further in you buildup, you are going to WANT to add an oil cooler if you haven't done so.

NHGuy

This is the first engine upgrade, the intake is an OE iron piece. I run in freshwater so I have kept an eye out for a good alloy intake. I'm kind of taken by the concept of an air gap. To do that I'd need to get an electric choke since I have a divorced heat coil on there currently. That's not a problem though, I have the best guy for carb stuff. He has all the right stuff for Qjets at very good prices.
I also wonder about the coolant passage and whether to leave it blocked.
Intakes are such a crapshoot, the manufacturers claim one thing and some users say the opposite. Example, with Edelbrock intakes I'd think boat guys would go for the Performer intake since they are defined as for most torque.
But many claim the RPM is the one to use. And I crack up when I read about Performer RPM intakes. Aren't they either Performer or RPM? But not both? I guess if your motor has the juice you probably ought to go for the RPM to get the most top speed, and if you do a lot of tow sports or have a heavy boat maybe a torque manifold like a Performer or equivalent. Maybe sometime I will do an intake. But for now I am doing the cam,lifters and springs so I can see the difference they make.

ACrooks69

iTrader: (1)

When it comes to the intake, it really depends on you total engine combination. It all has to do with the intake port velocity. In your application, the added plenum from an RPM intake may kill the low speed air movement and make the hole shot sluggish. Better flowing heads with good flow velocities can tolerate a bigger intake on the low end and have benefits on the top end. You do not need a RPM intake and you really do not need an air gap. Since there really isn’t air movement over the motor in an engine compartment like there is in a car, you will see little benefit. You do not want to block any coolant passage in the intake. If you continue to use the divorced choke, you do not want to block the exhaust cross over either.

Since you said it was a crate motor, are the valve covers center-bolt or perimeter bolt? I have a performer intake for the perimeter bolt heads and do not need it any more.

NHGuy

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NHGuy

It's an OE Mercruiser motor, but when you look up the head part #s it's a crate motor.
I have center bolt valve covers, and I just re read the Edelbrock stuff. Performer is good for the rpms than I will use, so you're right. RPM isn't the ticket.

jamie 10017

I cannot stress enough that if you install a camshaft is to degree the cam or get someone to degree it for you. You can buy all kinds of timing chain sets that claim 2 degrees or 4 or what ever. I will tell you from experience they are all over the place as far as getting the cam in where the manufacture wants it . Without a degree wheel you don't know where your cam is in at (Centerline) retarded or advanced, As little a 2 degrees with change the power band of a camshaft beyond belief. Don't just guess at a cam or go with what your buddy told you, get with a good cam grinder and let them help you pick out or even grind one for you its a lot of time and money to put a cam in and not be happy with the end results. A Q-jet and a Edelbrock performer will work just fine for what you are doing. Also a word of advice ...to small a cam is better than to big..... so do yourself a favor get with a cam grinder or engine builder to help with your project.

jamie 10017

Yes there are Performer and Performer RPM intakes and a Performer RPM air-gap