Cheap Go-fast parts (vortec head swap)

I'm thinking of doing a vortec head swap on my 5.7L merc. I'm not trying to break any speed records or anything, I honestly just like tinkering on engines, and the ol' SBC has a pretty robust aftermarket. I currently top out a 46mph, and I would be tickled pink if I could touch 50mph. The motor has unknown hours, but it has strong compression, and it pulls hard. It maxes out at 4100rpm, and I think I've troubleshot that down to bad timing. Over the winter, I'm thinking about swapping the following parts out:

-Chevy Vortec heads: I have seen rebuilt heads on ebay for ~$300/pair. Not a bad deal.

-Summit racing brand ripoff of the edelbrock airgap aluminum intake manifold: Can I run that with an open cooling system in the ocean? Will the salt water wreck the aluminum? Should I look for a plastic composite intake instead? $169

-1.6 ratio roller rockers: I don't know what my cam lift is, but I would bet a paycheck that 1.6 rockers would still be less than the .525" lift vortec stock springs are rated for. $250

-Mallory Marine optical distributor: My current distributor is cracked, and I'm not in love with points distributors anyways. $350

-Chrome valve covers: they're just cool, and they're like $40 bucks at summit.

Do I need special marine grade head and intake gaskets?

Re: Cheap Go-fast parts (vortec head swap)

If you're just maxing out at 4100rpm, you need to make sure your motor's running @ 100%. You can use a water cuff, and any good auto repair shop can checkout your timing and do an engine analysis for you.

You may actually be a propeller away from your intended speed. I would suggest you contact a good prop shop for their suggestions after your engine is checked out. Good prop shops and boat dealers will often allow you to try two or three different props to check for the best performance. I don't know what the optimal rpm's are, but I would think it should be running 4500-4800 rpm's.

Marine motors appear to be auto engines, however there are differences in metal mixtures and marine engines have high torque/low rpm camshafts. There are also some other changes (from auto parts) to minimize rusting in salt water use. Marine use puts very high stress on engines, as they're designed to run at redlines for hours at a time. In salt water, it's best not to use aftermarket auto engine parts on a boat power plant.

Sometimes you've got to accept that all engines have their limitations. You could easily throw $3K to $5K into the motor--only to get very little increased speed out of it. Your money would be better spent on checking out your present engine and getting it propped right. Then, enjoy what you have.

Re: Cheap Go-fast parts (vortec head swap)

I agree with Bamaman1, your current performance does not seem up to par. If it is only timing, then should be an easy fix and test. If the motor is tired, not worth the upgrade. If something else is causing the performance loss, you'd want to know that before dumping $ in the motor.

OK, some answers:

- Vortec heads are a great head for sbc marine engines. Preferably, you get the ones with the hardened exhaust valve seat.

- If your boat is raw water cooled, yes you want a special "marine" intake that has been treated in the water passage area. I haven't seen any composite carb intakes. If your current carb is a 4brl, it is probably a Q-jet. Trying to stay with it, will limit intake choices or use an adapter which is not prefered. The carb will also need some retuning changing to a vortec.

- The springs are usually not the issue, it is the retainer to valve guide space. If having the heads reworked, just have them make the mod. Your engine, most likely has std hyd lifters, and not the rollers.

- Points in a 1990 mercruiser? Sounds like the distributer was already replaced once??? But maybe not. I'm not 100% sure when the thunderbolt was phased in. You wil need a new coil to match the distributer type. Not familiar with the Mallory.

- There are a number of head gaskets that are fine. Most GM's are stainless steel sandwiched with graphite. You don't want any steel shim, that can rust. There are only a couple of good intake gaskets for the vortec. The GM and one other that escapes me at the moment.

- Valve covers, whatever floats your ... If changing rockers, just make sure they fit the covers.

PS: If already a 4brl 350, then this will add about 30HP. It will add about 2-4mph to wot.

Re: Cheap Go-fast parts (vortec head swap)

you sure your motor is at 100% potential?

for comparison, your boat is about 21' as judging by your signature. i've got a 1990 23' with a 5.7 and it will do 50mph (GPS) with a full tank of gas and 7 people. it is a 350 magnum 270hp but my boat has got to weigh more than yours and the engine is unmodified. turning a 14.75 x 20p solas hr titan prop at 4400 rpm WOT.

i am contemplating vortec heads to get that extra oomph but i think yours should do 50 already.

do you have a whale tail on your outdrive? that will steal 4-5mph from your top speed.

Re: Cheap Go-fast parts (vortec head swap)

Yes you would reach your target of 50 but drop the 1.6 rocker's...vortecs cap out at 470 lift and you do not have a agressive cam profile really not needed...A tbolt v igniton is more than adequate and far less money alum intake's will not survive ocean water plenty of marine intakes around.

Tinker is you must...you will see and feel a improvement but that is a old engine and bolting up another 50 hp could cause strain on the old internals and cause problems such as excessive oil consumption.

Re: Cheap Go-fast parts (vortec head swap)

mine has some factory GM performance bowtie intake, it's a cast iron version of the hi-po bowtie car intake. it's supposedly the only difference between a regular 5.7 and 350 magnum.

if you can find one of those, it might be a worthwhile upgrade.

Re: Cheap Go-fast parts (vortec head swap)

I think my timing is off because I pulled my distributor cap off a while back, and I bet I didn't put it back on at exactly the same spot.

I just bought a nice electronic timing light , so ill shoot the timing and get it back to its correct spec.

What is the correct timing spec for a 260hp 5.7L merc? I'm guessing 30* btdc.

Re: Cheap Go-fast parts (vortec head swap)

jumpjets said:

I'm not in love with points distributors anyways.

Click to expand...

a 1990 5.7 had points?

jumpjets said:

I think my timing is off because I pulled my distributor cap off a while back, and I bet I didn't put it back on at exactly the same spot.

Click to expand...

no need to check timing for removing a distributor cap - it is indexed- so no issue there

I agree with the other on looking at propellers. You have a 4 blade alumimum now- not a speedy wheel
3 blade SS is for top end speed.

A full tune up and a nice stainless prop would probably get you to your 50mph goal.

Re: Cheap Go-fast parts (vortec head swap)

Jumpjets - Your dist cap can only go on one way.....It has notches (or something) on the bottom lip/ rim to line it up on the distributor.

Get a genuine manual for your motor or look up the timming specs.......30* BTDC would be your total advance at a certain RPM

Im thinking more like 8* to 10* at idle 600 to 700 RPM....Also need to put in base timing mode!

Need to check which ignition system you have..... thunderbolt iv or v?

Re: Cheap Go-fast parts (vortec head swap)

I just checked some pics. I do have a Tbolt ignition. I'm pretty sure it's a 4. I just ordered a new cap and rotor. Hopefully between that and sweetening up the timing, I'll get my top end rpm back. I have a new accel coil, and I did a pretty comprehensive tune up last spring.

The only other thing I can think of is a gummed up carb. That just seems so unlikely though due to its stellar cold start and low rpm performance.

Re: Cheap Go-fast parts (vortec head swap)

500dollar744ti said:

mine has some factory GM performance bowtie intake, it's a cast iron version of the hi-po bowtie car intake. it's supposedly the only difference between a regular 5.7 and 350 magnum.

if you can find one of those, it might be a worthwhile upgrade.

Click to expand...

That is a great intake, but won't fit vortec heads.

Re: Cheap Go-fast parts (vortec head swap)

John_S said:

That is a great intake, but won't fit vortec heads.

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awww really? that's a bummer. i can always sell it to help pay for the vortec heads when i get there

then tell me this, my current rating is 270hp from the factory. i want to do vortec heads when i do the risers and manifolds next season, if i use the associated intake, will that put me around 300hp?

Re: Cheap Go-fast parts (vortec head swap)

500dollar744ti said:

awww really? that's a bummer. i can always sell it to help pay for the vortec heads when i get there

then tell me this, my current rating is 270hp from the factory. i want to do vortec heads when i do the risers and manifolds next season, if i use the associated intake, will that put me around 300hp?

Click to expand...

I think 270HP is a crankshaft HP ratings, vs the current rating system of at the prop. The equivelent edelbrock intake would be a RPM or RPM air-gap. Carbed 350 Mags (early 90's) are rated 250HP @ prop according to service manual. A 4brl vortec 350 is about 280HP @ prop. Equivelent to the 350 gen + EFI Merc. You could get to the 300HP @ prop with a cam upgrade.

Re: Cheap Go-fast parts (vortec head swap)

John_S said:

I think 270HP is a crankshaft HP ratings, vs the current rating system of at the prop. The equivelent edelbrock intake would be a RPM or RPM air-gap. Carbed 350 Mags (early 90's) are rated 250HP @ prop according to service manual. A 4brl vortec 350 is about 280HP @ prop. Equivelent to the 350 gen + EFI Merc. You could get to the 300HP @ prop with a cam upgrade.

Click to expand...

Ayuh,.... Agreed, But,.... It usually takes a swap to quench pistons to get the full benefits of the Vortec heads...

Re: Cheap Go-fast parts (vortec head swap)

I would like to verify my timing is correct. Does anyone have a downloadable service manual for a 1990 5.7L V8? I can't find any on google, just outdrive manuals.

Re: Cheap Go-fast parts (vortec head swap)

Bond-o said:

Ayuh,.... Agreed, But,.... It usually takes a swap to quench pistons to get the full benefits of the Vortec heads...

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Yes, the HP I refer to above, is with normal production type quench or lack of. I made the assuption that the OP was not interested in pulling the engine to do pistons or other machine work that would be required to get a good quench. Cam might be doable in the boat, but even if you had to lift motor, doesn't require full teardown. Anyway, what my thought process was.

Re: Cheap Go-fast parts (vortec head swap)

jumpjets said:

I would like to verify my timing is correct. Does anyone have a downloadable service manual for a 1990 5.7L V8? I can't find any on google, just outdrive manuals.

Click to expand...

the manuals are here in the mercruiser forum at the top, in the thread "adults only"

mine is a 1990 and advance is 8* BTDC, as stated right on the engine cover with serial number and all that. it's thunderbolt-iv ignition.

Re: Cheap Go-fast parts (vortec head swap)

500dollar744ti said:

the manuals are here in the mercruiser forum at the top, in the thread "adults only"

mine is a 1990 and advance is 8* BTDC, as stated right on the engine cover with serial number and all that. it's thunderbolt-iv ignition.

Click to expand...

Thanks. I used the boatinfo.com manual. very nice.

I pulled apart the distributor, and it was a little messy. The cap had a huge crack in it, and the rotor was slightly loose. I replaced the cap and rotor, and tried to clean out all the loose debris inside.



This sensor looks like it has seen better days. I might get a new one. I'm assuming that rusty thing is supposed to be a magnet?

With everything back together, I shot the timing at idle, 1500, and 2500 rpm. Apparently, the initial timing I've been running has been 10* at idle, 17* at 1500rpm, and 27* at 2500rpm and higher. I haven't heard any knocking, so I'm wondering if that higher timing was done on purpose by the previous owner for a little extra performance.



I retarded the timing to 8* at idle per the chart from the service manual. It showed 14* at 1500rpm, and 24* at 2500rpm. That is right in the zone according to the chart.

HOWEVER.... There is a note on that chart that says it doesn't account for the initial 8* BTDC. Does that mean that my timing light should be showing me 16* at idle, 22* at 1500rpm, and 32* at 2500rpm? Those seem more aggressive, like a common automobile.

I'll run the boat tomorrow, and see if I got my top end rpm back. I might even adjust the timing on the water to find the sweet spot.

Re: Cheap Go-fast parts (vortec head swap)

I got everything figured out!!!!!!

I took my timing light, gps, and a wrench out on the water today, and dialed in my timing. started with the timing light showing 8*BTDC at idle, and made a high speed pass. The engine topped out at 4050rpm.

Next, I dialed in 12*BTDC at idle, and made another pass. I got a very marginal difference, of about 4100rpm total. I tried 14* at idle next, and got no real improvement.

Finally, I dialed in 16*BTDC at idle, and checked to see that I had 24* at 1500, and 32* at 2500+rpm. I made a WOT pass with great results. I got 4400rpm on my tach and on my digital timing light tach. I saw 49mph on my GPS, and I learned what high speed chine walk is. No fun. I was worried about knock, but I ran with the engine cover off, and I never heard anything of the sort, even with 32* total timing on 87 octane. I probably could have gone for another degree or two of total timing, but then I'd be wandering into premium fuel territory.

I made several more passes, and my average was 48mph. Not too bad. Now I'm wondering about my flame arrestor. It's very small, and at WOT I can hear a very distinct "sucking" sound from it. I think I need a bigger air cleaner.

Re: Cheap Go-fast parts (vortec head swap)

Sounds like your electronic advance is not working correctly. With an 8-10 initial, you should be getting 30-34 total advance at 4000rpm.