Wanted: Engine Advice

[Ranman]

After seeing the HM pull his engine, check everything out and clean up his bildge, I've decided to do the same. I'll be pulling my engine within a week or so and am looking for some advice.

There's nothing wrong with the engine at this time, I'm just doing this as a preventative measure to check things out.

My question is since the motor will be out, is there anything I can do to gain some HP? I'm thinking along the lines of a cam, lifters, springs, rockers combo. My engine (pictured in the link below) is a 1997 Merc Mag 350 MPI and was only manufactured for 3 years. Can anyone tell me if I stand to gain anything with above changes? Does anyone know the cam specs, heads or anything about this motor? I will also have to have the ECU re-calibrated for any changes I make. I'd like to see 350hp or so, is this possible? Thanks for the replys.


http://www.donzi.net/hull/DNAC8015J697/EngineCompartment.jpg

[boxy]

Ranman, since less weight means more HP, the first thing I would do is chuck that case of beer overboard... :D

[mattyboy]

Randy,
don't know what your budget is but maybe a set of SM exhaust and risers for a few less lbs and some more hp.

Matt

[Rootsy]

OK Ranman,

how much do you WANT to spend? this will require an ECU modification but here goes my scenario of what to do... basicalllllly this was my first go around with my motor... the biggest chunk of change will be the valvetrain, to the tune of around 700 - 800 bucks for parts... you pretty much do if not exactly have the same shortblock that i have in my boat.

you currently SHOULD have Vortec cylinder heads, which beat almost every production cast iron head out there AND THEN SOME.. you do not need to replace them. But with this scenario you will need to remove them and have the spring pockets and valve guides modified (bout 50 bucks).

You also have a roller camshaft in that motor... with self guiding rocker arms (guide themselves on the tip of the valve stem). you do not need to replace your lifters when you replace the camshaft, that is if you stay roller... you will never see enough rpm to hurt anything...

Your exhaust should support these modifications without much issue but if you want go ahead and do a SM kit or what not. besides they look kick ass...


So... you pull the motor and pull the cylinder heads and disassemble them.. check the valves and if there is no pitting you at least lap them back in, or spend the dough and have them reground... if you want to see a decent increase in flow and some hp and want to spend the money have the seats opened up to 2.02 / 1.600, a quality valve job put on and some SS valves stuck in the holes.. with anything over .480 lift you have to Send the heads out to have the spring pockets opened up and guides cut down for head to retainer clearance as well as to accomodate the valve spring diameter (986 is a 1.44 double w/ damper). Have screw in studs (ARP) put in also... buy some ARP head bolts to put em back on with and torque em in 5 steps to 70 - 75 ft-lb using ARP moly lube under the heads and Loctite paste teflon sealant on the threads... i prefer studs just for torque retention and evenness but they get a bit pricy (130 vs 50 bucks)...

Break out your credit card and order a COMP XM270HR camshaft (bout 280 bucks from MartelBros) (218/224 @.050 - .495/.502 - 112 Degree lobe seperation)- (i run an XM264HR in my motor) You'll need COMP 986 valve springs and the 10* retainers and super locks to go along with em... get a set of hi-energy pushtubes and a timing chain with indexable crank sprocket so you can put the camshaft @ -4* from straight up (comp has a tendancy to grind 2 degrees advanced so you'll actually end up about -2*) this aids HIGH end hp and torque at the expense of torque under 2000 rpm. you;ll need Comp or crane teflon valve guide seals for the new guides, my original (NON Vortec) heads had 11/32 intakes adn 3/8 exhaust valve stem diameters so you have to but 2 sets of damn seals @ 25 bucks / set of 16. the vortecs may NOT have this setup... you'll know when you get em apart and measure stem diameters. Also order PLENTY of valve spring shims so you can set installed heights and valve spring locator cups are a good idea also. You can retain your stock stamped 1.5 ratio rockers or for about 191 bucks you can get a set of comp roller tips, 1.52 ratio should be sufficient... also get as set of poly lock cool nuts for the studs - watch the nut to valve cover clearance though - not sure if they'll fit BUT they should.. regular jam nuts are hard on threads... preload your lifters 1 turn down from zero lash

While the heads are off you might as well put em back on with a set of .015 steel shim head gaskets (available from Felpro or Merc or your GM dealer in SS for abotu 20/ea) to pop your compression up to 9.39:1 and it'll help your quench setup. stock gaskets are like 0.028 composite yielding 9.12:1 roughly. I have a spreadsheet with all fo the math for working this crap out if you want it... basically with the .015 shims it puts you right at a .040 cold quench distance but you have -13 cc dished pistons @ -.025 from the deck so it helps but not as much as with a flat top D-dish "quench" piston. you should be able to get away with regular as long as you don't go nuts on the ignition timing.. which btw you'll set at 32* TOTAL btdc for those vortecs

you'll need a 1 piece pan gasket and timing chain cover... the cover is plastic on the vortec motor and only usable once... 50 bucks for a new one from the local chevy dealer. while you have the pan off you might as well install a new HV oil pump and ARP driveshaft... plus whatever gaskets you will need to put the intake back on plus a thermostat housing gasket from merc...

The distributor gear and camshaft compatibility will be nothing to worry bout... your distributor has an iron gear on it and comp's roller cams have a cast iron austempered gear so no wear issues as with a steel core.

you'll be looking at the far side of 350 crank hp and somewhere around 415 ft-lb of torque in the 3500 rpm range and pushing 380 or so ft-lb @ 5000 rpm where the camshaft will make peak HP...

hmmm i think i've done this before or something... :rolleyes:

[Fish boy]

Boxy,
which one, the main, the back up, or the backup/backup case?

[BUIZILLA]

Good advice Rootsy...very good.

J

hmmmm, were '87 engines Vortec roller motors???

[MOP]

Damn Rootsy what an EXCELLENT POST!! I am going to print that sucker. Now its up to Ranman I know he "A Thinken!"

[Tony]

Jamie, you engineers are some pieces of work!
About the only things I understood in your post were:

"cold quench" - Bud Light works for me.
"locate cups" - when the beer is in a keg.
"jam nuts" - I've done that...it hurts like hell.

[tailwind]

Rootsy, what a great piece of work, all hats off in a genuine salute!

Those mods should really trick it out.

questions:

Would they be applicable to my 91 King Cobra with spitfire elect ign?
Presuming an eng in solid cond. what would be parts costs, labor etc?
Let me bring the boat to you for the mod - how much for a turnkey?
What mph increase could you guarantee for your mods? Running 64 gps now.

Many thanks again
Randy

[Kirk]

Rootsy...

Nice Set up!!

Any pic's of your set up. I will be powering a 73 ski sporter 350 chev. and want 300 plus hp. What do you suggest for MODS.

Thanks,

KJ

[MOP]

I can almost feel the butt pucker from nailing it the first time after the mods :D :D :D

[Kirk]

Ya the butt should pucker and the ears will be enjoying the decibels

[MOP]

Another thought back awhile there were some 300+ marine crate motors out there for under 4k with a warantee. Anybody remember who had them, that would be a drop it and piece of mind and a ton less time and work that worth something.

[fasttrucker]

Iam in the middle of cam,heads,ect. On my 502.project.I called and the block is being honed to seat the new heads.Also replacing the bearing in the crank.New timing gear too.If you are keeping the boat,when you have it apart,replace as much as you can like rootsy is the man. biggrin.

[BUIZILLA]

fasttrucker:
I called and the block is being honed to seat the new heads. biggrin. :confused:

[BigGrizzly]

Rootsy gave sound advice. Or you can buy that similar setup for $4500 with a carb. I know an engine builder who does this to new crate motors. He keeps a couple in stock because it is a hot seller on this lake.

[Rootsy]

hmmmm lets hope they are using a diamond stone and a dab of spit for that hone job... wouldn't want em to leave any grit-n-oil in the metal from an arkansas stone :D wink