5.7 Volvo Penta GS Intake, Carb, Heads & Cam

TNParrothead

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Hello All, I hate to beat a dead horse, but I am needing some help. I have a 1997 Larson 206 with the 5.7 GS & SX outdrive. It is all stock except for through hull exhaust. I have had the boat about 4 years now. This past summer the intake started leaking a little oil. Ive already pulled the intake and carb. Since I’m already in this far, I’m thinking about replacing the intake and carb. I also have a set of vortec heads that I would like to install and would love to go ahead and do a cam upgrade. I am going to post pics along the way.

1) What Intake and Carb Would You Guys Recommend ?
2) What Cam Would Be A Good Fit ?
3) Do I Need To Have Anything Done To The Heads ?
4) Should I Upgrade The Ignition ?
 

alldodge

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Being its a 97 you should already have vortec heads (I think)

What needs to be done depends on how much power you want to build.
Doing a valve job is easy and doesn't cost much, but if you get into changing cams then your talking full rebuild. Could bore it out and change the crank and make you self a 383.
 

Scott Danforth

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welcome aboard

with some head work, you can change the cam to a comp Cam XM264HR or XM270HR. You need to pull the heads, convert to screw in studs and you need to cut the spring pockets for the bigger cam or run beehive springs.

your carb and ignition are fine. no gains to be had there

however, your best bang for the buck will be to pull the motor, build a 383 stroker.

or....sell your boat and buy the boat you want.
 

aimlow

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You're not gonna get much more horsepower at the same rpms you're running now without more displacement.
HP=Torque X RPM/5252. A 4 bbl. carb and manifold will help power over 3500 rpms.

The last Volvo 350 I took apart was a 2 bbl. Holley, flat tappet cam (even tho it was a 1 piece main seal), non vortec head with center bolt valve cover.
 

jimmbo

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Look carefully at your intake. If your engine has the vortec heads, it likely came with a 4bbl intake with an adapter for the 2bbl Holley. While the 500cfm(378cfm when flowed like a 4bbl) Holley is a wee bit too small for a 5.7 turning 4800 rpm, it doesn't need much more. A small 4bbl(450 - 500 cfm is plenty) would help a bit at top end. I replaced my 2bbl Holley with a Holley 650 Spreadbore 4bbl. It livened up my 5.7 with an additional 500 rpm.
A few more HP can be gained by replacing the stock rocker arms(1.5 : 1) with some 1.6:1 versions. That effectively mimics a slightly longer duration cam.
DSC_0007a.jpg
 

TNParrothead

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A few updates and questions. Again, this is the 5.7 GSPLKD engine non Vortec. I’m wanting to go with the XM270HR cam as recommended. I do have the 4 barrel, but it either needs rebuilt or replaced. Also, I am looking at an intake upgrade. What should be done, if anything, to the Vortec heads I am wanting to use ? They were removed from a 98 Silverado.
 

aimlow

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First, find out what cam and lifters you have now, and compare the specs. Frankly, there's better (and simpler) ways to get power than changing the cam. Dial in the carb, have the distributor curve checked, get a free flowing K&N filter/flame arrestor. Start with the basics.
 

alldodge

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free flowing K&N filter/flame arrestor

Air flow thru a filter is good and the less restriction the better as we all know. There is a whole lot of K&N advertising out there but it has been proved on a Dyno that they are not the best, and in some cases the standard OEM is better. Also not many marine arrestor's are not even filters, there just stacked plates to keep large chunks out

But they can look pretty so that's worth something :)
 

Scott Danforth

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A few updates and questions. Again, this is the 5.7 GSPLKD engine non Vortec. I’m wanting to go with the XM270HR cam as recommended. I do have the 4 barrel, but it either needs rebuilt or replaced. Also, I am looking at an intake upgrade. What should be done, if anything, to the Vortec heads I am wanting to use ? They were removed from a 98 Silverado.

with the motor being a non-vortec, its a left over 1995 or earlier. you may have flat tappets. if so, your limited on the cam. an XM268H is the largest flat tappet you can go. however before you buy anything, you need to verify what you have

how many intake manifold mounting bolts do you have? 8 or 12? if 12, non-vortec heads and you will need to pull the intake to determine which cam you have. only some of the pre '96 boat blocks got rollers.

if the heads are stock vortec heads from a 98 silverado... to expand on post #3

at a minimum, get a valve job, get the press-in studs removed and replaced with ARP screw in studs. get the guides cut for teflon seals, get the spring pockets cut for a higher profile cam.

I would highly recommend SS valves, however if your on a budget, dont worry too much. then again, if you look at your local racing classifieds, you can probably pick up a set of vortec heads with a fresh valve job and all the upgrades done for less than you can modifiy the heads. usually about $400 a pair

If you have a roller cam now, the XM264HR is a reasonable improvement over stock. this cam can be run with 1.6:1 rockers. the 270 is largest cam you can go with wet exhaust as you are then knocking on the point of reversion. recommend sticking with the stock 1.5 or the aftermarket 1.52:1 rocker arms with this cam.

a 2" plenum spacer will help mid-range torque

First, find out what cam and lifters you have now, and compare the specs. Frankly, there's better (and simpler) ways to get power than changing the cam. Dial in the carb, have the distributor curve checked, get a free flowing K&N filter/flame arrestor. Start with the basics.

stock cam is extremely mild. there is a bit of power to be had there. rocker arm ratio change will help.

the specs that GM used for the 260hp 5.7's

202 duration intake
214 duration exhaust
395" lift intake
404" lift exhaust
112 lobe separation.

k&n filter wont help, same spark arrestor is used on BBC's as the SBC's. inlet airflow is not limited

distributor curve is electronic
 

aimlow

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My marine cam specs (merc431-5943) show 200/212 degrees @ 0.050". 110 lobe center. 0'400/0.410 lift. 264 cam is only 212/218, same lobe center (so a little more overlap), but really high lift. In any case, not much difference for the cost (cam, lifters, timing set.....) Retard the existing cam 4 degrees, this will move the peak power up a few hundred rpm's.
The tell on flame arrestors is when you remove them and pickup a couple hundred rpms, as happened on my 302 Fords The K&N's are available with CG approval, and actually filter dirt. The key is a tall enough filter to allow decent airflow, or use a stub stack if you have a Holley. Otherwise, I'm NOT a K&N fan..it's just they have marine approval. NEVER! use them on an engine with hot wire MAF!

Be careful with used vortec heads..they are prone to cracking.

Will stock springs work with a comp cam with nearly 0.500 lift?
 

Scott Danforth

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aimlow not a good idea to retard a cam in a marine motor. especially since it changes the piston to valve clearance and marine motors need all the bottom end torque that they can get. what is not covered in the chart below is the effect on reversion. [h=3]How does it affect performance?[/h] Advancing or retarding the cam will move the Torque curve higher or lower in the RPM range. Advance will improve low-end power and throttle response. Retard will improve the power at higher RPM's. See the table below for more information on advancing and retarding a camshaft.
AdvanceRetard
Begins the intake event soonerDelays the intake event
Builds more low-end torqueBuilds more top-end power
Decreases clearance between the piston and the intake valveIncreases clearance between the piston and the intake valve
Increases clearance between the piston and the exhaust valveDecreases clearance between the piston and the exhaust valve
4° of advance will cause the torque to peak about 200 RPM sooner4° of retard will cause the torque to peak about 200 RPM later

no one is questioning whether K&N has marine approval. they do. however they do not improve anything on a stock small block as far as air flow

hot wire MAF need to be cleaned on a regular basis even with paper elements. just more often with a freshly oiled gause/oil filter such as a K&N

NO, stock springs wont work in a vortec head on anything over 0.420" lift. at that point you bind the springs. to go beyond that, you need to cut the spring pockets as stated in post #3 and #12.
 

aimlow

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aimlow not a good idea to retard a cam in a marine motor. especially since it changes the piston to valve clearance and marine motors need all the bottom end torque that they can get.
no one is questioning whether K&N has marine approval. they do. however they do not improve anything on a stock small block as far as air flow

hot wire MAF need to be cleaned on a regular basis even with paper elements. just more often with a freshly oiled gause/oil filter such as a K&N

NO, stock springs wont work in a vortec head on anything over 0.420" lift. at that point you bind the springs. to go beyond that, you need to cut the spring pockets as stated in post #3 and #12.

Not to get into a peeing contest, but SBC valve/piston clearance is not that critical. Retarding/advancing a cam a few degrees is common..been doing it for decades. Look at VVT..they are often 20 degrees or so. Moving the torque point automatically moves the "horsepower" point, since horsepower is a function of torque and rpm.

It's an old wives tale that gas marine and truck engine cams produce and need low end torque..just the opposite. The typical rpm range is higher that a street vehicle, so the cams are actually lumpier...more aggressive. Idle quality is not an issue on marine engines.

Most marine inboards are high rpm breathing limited, especially on exhaust. This is why the split profile cam profiles work so well on them. A taller air filter system will flow more air (and CLEAN air) because the air flow into the venturis is less "turbulent"..most flame arrestors require a sharp 90 degree bend to get the incoming air thru the arrestor and into the venturi. The bigger issue is not the flow thru the flame arrestor, it is the temperature of the incoming air. Cool, dense air always improves power! You'd be surprised at how dirty my air filters got on my boat engines...worse than a street vehicle, and my bilge was clean!

I post nothing which I haven't personally done. Decades of road racing, engine building and tuning, and hands on experience. I'm always open to discussion, though...bench racing.
 

alldodge

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You'd be surprised at how dirty my air filters got on my boat engines...worse than a street vehicle, and my bilge was clean!

Went right over the edge on this one
 

aimlow

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Went right over the edge on this one

I don't drive on dirt roads..truck air filter was changed at 70k or so, but the little restriction gauge had never moved. The boat K&N's had color to them. Mud daubers, boat building dirt, 20+ years of exposure to the atmosphere, and hurricane driven dirt. I've cleaned pine needles out of underneath the gunnels. I was surprised.

Marine engines typically draw air from the bilge, unless they have a dedicated dorade box and sealed engine room. Big diesel sportsfishermen are notorious for restricted air intake.
 

Scott Danforth

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It's an old wives tale that gas marine and truck engine cams produce and need low end torque..just the opposite. The typical rpm range is higher that a street vehicle, so the cams are actually lumpier...more aggressive. Idle quality is not an issue on marine engines.

you obviously never have seen a hull prop curve and the required torque needed to push a boat out of the hole. or the torque curve of a marine motor

idle quality is extremely important in marine motors, especially with any cam change and wet exhaust.
 

alldodge

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Big diesel sportsfishermen are notorious for restricted air intake

Different animal then being discussed in this thread

Let just say we all get to voice our opinions and yours and mine differ, and not just air intakes. Its all good :thumb:
 

aimlow

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you obviously never have seen a hull prop curve and the required torque needed to push a boat out of the hole. or the torque curve of a marine motor

idle quality is extremely important in marine motors, especially with any cam change and wet exhaust.

If 'out of the hole" was that important, a marine cam wouldn't be lumpier. I can easily get 2000 rpms even tied to the dock. It's the part throttle 3500 rpm +/- cruise that's important.

In any case, there's a guy on the Mercruiser forum with Vortec coil bind issues. You have more hands on on that particular issue than I.
 
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