Auto engine marinization

I second Stonebreaker's advice on the roller cam. Anything you can do to cut down on wear is good. Odds are you'll run the boat engine longer and harder than it would typically be expected to do in a car, and anything to reduce friction and wear will really help its longevity.
Some people don't mind the choppy idle as they prefer to run full-out.... in most cases though, I think it pays to do a good job with the build and get a motor that runs nice through the entire range.

 

If you use roller lifters, you must use a roller cam which is hardened. A cam for flat lifters won't last.

 

Stonebreaker, both the 305 & the 400 use cast iron dual plane intakes. The 305 uses a Rochester 2v and the 400 has a Holly 650 cfm 4v

The heads on the 400 came off the OEM 307 (1973) casting # 3973487X
The heads on the 305 are the small chamber 305HO heads

both engines have flat tops

As far as breathing , on the exhause side, both exhaust through the outdrive and below the water line. I kinda thought this would be restrictive and not promote free breathing. But, then again, maybe the water passing by the exhaust creates a vacumn efect and sucks the exhaust out. Or maybe this is just wishfull thinking.

At any rate, full speed rpm on both boats should be 4000 -4500 rpm if everything is right on.

These are boats and based on WOT of about 4300RPM, am I looking for torque of horse power? In other words, I want to put more pitch on my prop,which will produce more speed and will also put more load on the engine. If I do this now, the RPM's will drop and the boat actually goes slower because the motor doesn't make enough power to keep the rpm's at around 4300

Think of it this way, You have a car that has a RPM limiter set at 4300RPM.
Top speed in high gear is 80 mph at 4300 rpm. You want to make this car go 90 at the same 4300 rpm so you put higher rear end gears in. Now you find that the car actually slowed down and the rpm also dropped because the engine doesn't make enough power. You beleave the problem is the cam profile. Would you install a cam that makes more torque or more HP? Remember, 4300rpm is the limit or the transmission will blow. Based on the above whats your suggestion? My thought is the 395 cam. But, what do I know? :?:

 

I agree on the benifits of a roller cam versis a flat tappet. Read my last post, this is the real issue. AND, I absolutely have to have a smooth idle at about 500 - 550 rpm. This is an older electric shift I/O and a rough idle or a high idle will end up blowing the lower unit on the outdrive

 

Interesting, I know what the books say but, you would think that a roller lifter would work on a regular cam. HARDENED STEEL FOR ROLLERS :idea:

 

Bobby,

The different designs of the lifters, roller and flat, really alters the profiles of similar flat tappet and roller cams. I suppose a pure racer might be willing to experiment with roller lifters on a flat tappet cam or vice versa, but it's not a good idea for a daily driver. Here's a good basic article on flat tappets vs roller cams, both the good and bad points. The bad points, from the magazine's point of view, consist mainly of the cost of roller parts.

http://www.chevyhiperformance.com/techarticles/95258_hydraulic_roller_cams/

 

Greetings Stonebreaker,

Read the article, interesting to say the least. But I never had a doupt that the roller cam would be better. Problem is, I am dealing with a SBC 400 that is not machined for rollers. And I don't want to spend big $$$$$ for special rollers or machining.

Some guy on EBAY is selling a book for 20.00 that tells how this can be done on older blocks for cheap. http://cgi.ebay.com/ebaymotors/ws/e...&item=200024750367&ssPageName=ADME:B:EF:US:11

Take a look, what do you think?

Personally, I knida think that the 395 cam is gonna be the best way to go for the 400 block and possably for the 305 block as well. What are your thoughts on this ?

 

Does anyone know what cam this might be? Casting # 1579

 

Bobby,

If you want to stick with a flat tappet, give Crane a call and give them your requirements. I would guess that they probably have a cam that will do what you need. If you need a custom cam, they can do that, too. As long as you use lobes from their cam lobe profile catalog, a custom cam is the same price as a stock profile cam. What you do is call Crane and either give them the cam specs you want, or else give them your requirements and let them suggest a cam profile.

I know you weren't happy with the Comp cam you bought previously, but Crane's always done good by us. As a general observation, Crane tends to put a little more advance in their cams than Comp does, which results in more midrange for the Crane cams but at a cost of some top end compared to Comp.

 

It's been my experience with SBC's that the cam gets less radical as the cube's go up. I swapped a cam from a early z28 301/2 into a 383, and the cammy idle went away, and the idle vac went up. Therefore I'd go with a milder cam in the 305 if you want a smooth idle. I've had good luck with Crane, both with their advice and with their cams, and FWIW, I'd spend the $ on roller just for the longevity. Boat motors run at much higher cruise rpms than car/truck engines, and most of the flat tappet cams I've seen in marine motors had at least one worn lobe.

 

Has anyone marinized a ZZ383 crate motor?

I am replacing my 350 MAG MPI, which has only 100 hours on it but also has a cracked block. WITH Its forged crank and almost 400 ft. lbs of torque at 1500 rpm the ZZ383 looks like a good candidate. In particular, I believe that it has the same cam (GM 846 or Crane 109831) as the old Mercury Racing Scorpion 377. With six more cubic inches than the Scorpion and the same marine cam (see the Crane web site http://www.cranecams.com/index.php?...CHEVROLET&Year=2002&Engine_Size=305-350 C.I.), there shouldn’t be any water reversion, but… ?

The 350 MAG has Vortec heads and the same block as the ZZ4 and other GM crate motors so my manifolds should bolt right up to the Fastburn heads on the ZZ383. Wouldn’t everything else bolt on as well?

The biggest problem is the computer, which is a Mercury Marine ECM-5550202. I would like to keep it for the SmartCraft features. Some companies say they can remap it but I would rather do it myself. Would it be possible to do that using one of the tools that are available for cars? Alternately, would it be possible to keep the 555 for its SmartCraft features but disable its ignition and fuel outputs so they could be controlled by an automotive ECM?

The MAG 350 throttle body is about 2 7/8” in diameter and looks like it has enough flow capacity, but obviously the wet exhaust will have more back pressure than dry headers. How much power should I expect and do I need bigger fuel injectors, etc.?

It is my intention to set the rev-limiter at 6000 RPM but not run it over 5000 for any length of time. With the right prop the boat should go about 100 mph at 5000 rpm. It will have a fresh water cooling system that is supposed to be able to handle up to 500 hp. Any help would be greatly appreciated.

 

I don't see why the computer would be a problem. The Ramjet 350 crate motor uses a marine computer. I'd have to look on the GMPP site to make sure, but I think it's either the MEFI 3 or the MEFI 4. Email Bryan Herter at programmer@pcmforless.com and see what he says - that guy can tune anything. He started on LT1's but has done everything from t-types to c6 vettes. He's pretty reasonable, and doesn't encrypt his tuning, so he can set it up for a good conservative tune to start with, and then you can tweak it to your heart's content.

As far as the 846 cam goes, with that much torque that low, there can't be much reversion going on. That cam's a little choppy in a 350, but I've heard it in several 383's and it's hard to tell there's a hotrod cam in there. I ran its little brother, the 845, in my 350 LT1, and you had to really listen to tell there was a cam in the engine.

Fuel injectors: are you running throttle body injection or mpfi? If mpfi, I'd suggest running either the 36 pounders or the 42 pounders. The 36ers are a little easier to tune, and should be plenty for anything under 6000 rpm (I run 30 pounders to 6400 rpm in my 355 LT1).

 

Does anyone have a realistic number for fuel burn of a 350 producing 100hp?

This would assume a 350 set up for low speed and moderatly low power for cruising.

FAST FRED

 

Should be around .55 BSFC. .55 x 100 / 6.75 (pounds of fuel per gallon) = about 8 gallons per hour.

 

The computor does not look like a MEFI and it says Motorola on it. There are some old posts on Speedwake that said no one could remap the Motorola ECM used in small block Mercruisers. I assume that by now it is possible but it's still a mystery to me.

Also, does anyone know the size of the injectors in a 2002 350 MAG MPI Bravo or the part number?