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gekko

Improving performance 5.7 vortec/carb

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gekko

I have a 1999 gekko gts-20 with a 5.7 chev vortec and 600 holley carb. It has a 13 x 13 cvc ss prop and runs 4900rpm. Not sure what speed I'm getting, never calibrated speedos but it gets to 4800/4900 in no time then seems to hit a wall. Seems to me that the camshaft limits my rpm, however according to Pcm, my engine runs the same camshaft as the newer fuel injected 343. Pcm says mine is to run max 4800 and the 343 is to run max 5200. Pcm also said the 343 intake and ignition makes the difference in power, so I asked what about a different intake or larger carb. I was then told that the 600 carb is the best one for my engine! I'm looking for input from those with Malibu boats running the indmar 310hp with 650 holley carb. I'm looking for simple things to change ie. different rocker arm ratio, intake, carb size, flame arrestor, newer style exhaust manifolds. What have you guys tried that worked. Engine is like new so don't want to do anything serious, such as stroker kit. Would like to try simple things first.

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G-Mack

Would that wall be the rev limiter ?

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gekko

Nope, the carb version does not have a rev limiter...only the fuel injection. Anyone know the cam specs for the Indmar 310 hp carb?

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martinarcher

Here's my exhaust project.

I gained 3 mph top speed and wheat i really like it the extra torque for getting out of the hole with my wedge down. Thumbup.gif

I can't remember what it got me in extra RPM's.

What is your goal? Higher top speed? If so I would think about a different prop (higher pitch) if it gets to top RPM in a hurry.

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Steve B.

I just don't think there's any "real" benefit to going over 4900 rpm's in a ski boat. Sure, it's fun or sounds cool, but really, the engine would prefer not to do that for more than a few moments at a time.

That being said, ha. I think the easiest, and best for the engine way is to just reduce friction. Using roller rockers, with the same ratio may be the best investment. Make sure the ignition is true at high rpms, and make sure it's not starving for fuel.

Running an engine hard, with sloppy ignition, half-starving for gas isnt' good at high rpms.

Let us know what you end up doing,

Steve B.

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martinarcher

Agreed. I know you won't find me running my Merc over 4500 RPM for any extended period of time. It spends 99% of it's life between idle and 3k.

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Lakenut

Get rid of the prop! Cvc's are known for coming apart. I switched mine to an oj cnc prop...best thing I have bought for the boat!

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gekko

Get rid of the prop! Cvc's are known for coming apart. I switched mine to an oj cnc prop...best thing I have bought for the boat!

Ok. get rid or the prop, what did you go to for pitch etc. I read on the net that acme and QJ have more surface area and cup than the cvc's do so would I go with 13 x13, acme 13 x 12.625. I would like to hear from guys on here that are running the sportster with the 310 carb engine. See what they run for rpms and get for gps mph.

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dihrdskir

Here's my exhaust project.

I gained 3 mph top speed and wheat i really like it the extra torque for getting out of the hole with my wedge down. Thumbup.gif

I can't remember what it got me in extra RPM's.

What is your goal? Higher top speed? If so I would think about a different prop (higher pitch) if it gets to top RPM in a hurry.

Gotta agree with you Martin. :thumbup: Exhaust is the way to go for easy boilt on HP. Although, I must say that I probably would have gone with the HiTEK option, but either way, replacing log type manifolds with free flowing tubular header style exhaust will reap the best bang for buck. I have been down this road before and the 600 square bore is ideal for this engine. Changing rocker ratio from 1.5 to 1.6 on either inlets or exhaust or both yielded no noticable improvement. Exhaust upgrade, distributor recurve, possibly performer intake and correct propping is the road to VORTEC nirvana without going inside the engine.

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gekko

Gotta agree with you Martin. :thumbup: Exhaust is the way to go for easy boilt on HP. Although, I must say that I probably would have gone with the HiTEK option, but either way, replacing log type manifolds with free flowing tubular header style exhaust will reap the best bang for buck. I have been down this road before and the 600 square bore is ideal for this engine. Changing rocker ratio from 1.5 to 1.6 on either inlets or exhaust or both yielded no noticable improvement. Exhaust upgrade, distributor recurve, possibly performer intake and correct propping is the road to VORTEC nirvana without going inside the engine.

Recurve dist would be an easy/cheap mod.....wouldn't happen to remember what init/final advance was that you came up with. Already comes with an aluminum dual plane intake, could actually be a performer design. Guess I'll check into exhaust over the winter.

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martinarcher

Gotta agree with you Martin. :thumbup: Exhaust is the way to go for easy boilt on HP. Although, I must say that I probably would have gone with the HiTEK option, but either way, replacing log type manifolds with free flowing tubular header style exhaust will reap the best bang for buck. I have been down this road before and the 600 square bore is ideal for this engine. Changing rocker ratio from 1.5 to 1.6 on either inlets or exhaust or both yielded no noticable improvement. Exhaust upgrade, distributor recurve, possibly performer intake and correct propping is the road to VORTEC nirvana without going inside the engine.

I was between the HiTek's and the Stainless Marine exhaust. If I had a trip planned to Australia I might have had to bring home a pair of those shiny HiTek's. Whistling.gif

I love the Stainless Marine ones and the fact that I could get them within the states and get custom tips made was a huge selling factor. Jerry was super to deal with and really knows his stuff. Lastly, the SM stuff was cheaper with very similar quality and similar performance gains.

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gekko

I was between the HiTek's and the Stainless Marine exhaust. If I had a trip planned to Australia I might have had to bring home a pair of those shiny HiTek's. Whistling.gif

I love the Stainless Marine ones and the fact that I could get them within the states and get custom tips made was a huge selling factor. Jerry was super to deal with and really knows his stuff. Lastly, the SM stuff was cheaper with very similar quality and similar performance gains.

Looked at both exhausts. The ones from Australia look fantastic but expensive.....$2200 actually for stainless in the US.

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dihrdskir

I was between the HiTek's and the Stainless Marine exhaust. If I had a trip planned to Australia I might have had to bring home a pair of those shiny HiTek's. Whistling.gif

I love the Stainless Marine ones and the fact that I could get them within the states and get custom tips made was a huge selling factor. Jerry was super to deal with and really knows his stuff. Lastly, the SM stuff was cheaper with very similar quality and similar performance gains.

When I got mine a few years ago they were also very expensive and I was of the impression that there were dealers in the US where they were available. Since GFC it will be worse for you guys because of the strength of our currency. Yes I agree, performance and quality will be the same, the real gain is going to a tubular header, only the length and diameter of the primary header tube will influence, torque/power characteristics.

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dihrdskir

Looked at both exhausts. The ones from Australia look fantastic but expensive.....$2200 actually for stainless in the US.

Have a look and see whether you can get your hands on some used Monsoon or MCX headers by Indmar or any manufacturer that uses GM vortec as a base and has tubular exhausts eg PCM. They will still be an improvement over log type exhaust manifolds.

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sgt1970-442

Gotta agree with you Martin. :thumbup: Exhaust is the way to go for easy boilt on HP. Although, I must say that I probably would have gone with the HiTEK option, but either way, replacing log type manifolds with free flowing tubular header style exhaust will reap the best bang for buck. I have been down this road before and the 600 square bore is ideal for this engine. Changing rocker ratio from 1.5 to 1.6 on either inlets or exhaust or both yielded no noticable improvement. Exhaust upgrade, distributor recurve, possibly performer intake and correct propping is the road to VORTEC nirvana without going inside the engine.

gotta say switching to 1.6 roller rockers was not a seat of the pants speed upgrade but, your valve train thanks you. the friction on stock rockers is horrible and rollers frees up that excess friction, it also gives you a piece of mind for a few extra 100 rpms. don't waste your time with a different intake. my 99 indmar 310 carb motor came with an aluminum intake that mimicks the edelbrock performer.

best up grades i've done are tuning of the holley carb, patriot aluminum cylinder heads, roller rockers, acme 515 prop, and i bought a set of used etx headers for 700.00

boat is a 99 sunsetter lxi 310 vortec indmar carb engine(sounds like the same engine you have).

gps shows 49mph at 5000rpm and the holeshot is awesome with the acme 515 prop.

as others have said, long periods of high rpms are not good. i am normally between idle and 3200rpm 98% of the time.

hope this helps

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gekko

gotta say switching to 1.6 roller rockers was not a seat of the pants speed upgrade but, your valve train thanks you. the friction on stock rockers is horrible and rollers frees up that excess friction, it also gives you a piece of mind for a few extra 100 rpms. don't waste your time with a different intake. my 99 indmar 310 carb motor came with an aluminum intake that mimicks the edelbrock performer.

best up grades i've done are tuning of the holley carb, patriot aluminum cylinder heads, roller rockers, acme 515 prop, and i bought a set of used etx headers for 700.00

boat is a 99 sunsetter lxi 310 vortec indmar carb engine(sounds like the same engine you have).

gps shows 49mph at 5000rpm and the holeshot is awesome with the acme 515 prop.

as others have said, long periods of high rpms are not good. i am normally between idle and 3200rpm 98% of the time.

hope this helps

What rolller rockers did you go with? Did you do one thing at a timek heads, rockers, prop, carb tuning. Indmar 310 comes with 650 spreadbore and my PCM has a 600 straigntbore. When you say tune the carb did you jet up or down? Isn't max hp on the 310 vortec 4800? not 5000? Did you try any other props ie. pitch?

Edited by gekko

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sgt1970-442

sorry i haven't replied sooner, i was up north deer hunting.

as for the rockers, i went with scorpions. heads and rockers were done at the same time. etx were the first change. the heads and rockers were next and then i played with a make shift adapter for an o2 sensor to get air/fuel ratio. thats when i started to tune the carb, different jets and jet extensions also adjusting float levels.(jetting up or down will depend on several different things so its tough to say what your motor will like) also made a 3/8" thick plastic spacer plate for under the carb. indmar uses a holley 600cfm carb.

about the rpms, 4800 is a conservative suggestion by the manufacturer. with freeing up the valve train its not hard to go a couple hundred extra rpms, just don't hold it at 5000 all the way acrossed the lake. i built and race a big block olds motor that runs 6200rpms in the 1/4 mile, i've also built sbc motors that are close to 8100rpms at the end of the 1/4 mile. you need to ask yourself what you want to do with your boat. we are a ski family only so prop and torque are whats most important to me.

my next upgrade will be a custom grind erson cam and valve springs

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gekko

By going with a makeshift o2 sensor I take it you are referring to an air fuel ratio gauge. What did you find was optimum 12.3? Where and how did you end up mounting it? Also what is your base timing and max timing specs? For now going to stick with stock exhaust manifolds....they are like new, will keep looking for a good used hiperfomance ones.

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sgt1970-442

14.7 is the optimal ratio you can get. i got 14.1

12.3 would be way rich.

for the o2 sensor, i took a piece of 3" schedule 40 pipe (outside diameter will be 3 1/2" to fit inside the exhaust hose) and drilled and tapped it for the o2 sensor. i mounted it temporarily and checked each side. you need to get the engine up to about 130* and the weather needs to be about the same conditions as it will be on the lake. you can only do this as a dry test. i removed the raw water impeller and did my tests. it will take several times to get this done with jet changes and letting the engine down. also did a vacuum test and had to change the power valve in the carb.

factory stock base timing is 6* btdc, mine is set at 8* btdc

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Woodski

If I recall my calculations correctly, and you can easily do them yourself, a 350 CID engine requires 600 cfm @ 5,000 rpm so the carb is pretty close to the limit. The smaller cfm does provide better response than a larger one. There are other components in the system that will limit the boat to approx 4800 rpm +/- 200 or so. Those would include ignition timing (11 degrees helps v. the standard 8 deg to give you a full advance of 33 [email protected],000rpm), less restrictive spark arrestor, less restrictive exhaust system. If you stay with the 600 carb, you can do the traditional blueprinting to improve the flow at higher cfm's and running rich will certainly limit the power at the upper end of the flow curve. There are subtle intake manifold changes you can make, but the standard GM marine manifold is pretty much the same as the Edelbrock Performer RPM that is good to 6500 rpm, so that is probably not the culprit and the GM marine cam is good for up to 6000 rpm, so that is not the issue unless something is wrong. On the boat side, the hull could be the limiter and many props do hit the wall at 5k +/-, 4 blades certainly do in the testing I have done. I had CVP that did not, it was good to 5500 but I reworked it, dings and bent blades will lessen the performance of a prop particuarly at higher speeds.

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gekko

If I recall my calculations correctly, and you can easily do them yourself, a 350 CID engine requires 600 cfm @ 5,000 rpm so the carb is pretty close to the limit. The smaller cfm does provide better response than a larger one. There are other components in the system that will limit the boat to approx 4800 rpm +/- 200 or so. Those would include ignition timing (11 degrees helps v. the standard 8 deg to give you a full advance of 33 [email protected],000rpm), less restrictive spark arrestor, less restrictive exhaust system. If you stay with the 600 carb, you can do the traditional blueprinting to improve the flow at higher cfm's and running rich will certainly limit the power at the upper end of the flow curve. There are subtle intake manifold changes you can make, but the standard GM marine manifold is pretty much the same as the Edelbrock Performer RPM that is good to 6500 rpm, so that is probably not the culprit and the GM marine cam is good for up to 6000 rpm, so that is not the issue unless something is wrong. On the boat side, the hull could be the limiter and many props do hit the wall at 5k +/-, 4 blades certainly do in the testing I have done. I had CVP that did not, it was good to 5500 but I reworked it, dings and bent blades will lessen the performance of a prop particuarly at higher speeds.

Good info......what would you recommend for a prop upgrade....presently running as I said a 13x13 cvp....rev 4900....how about a 13x13 acme...don't mind if it brings the rpm down to 4700. Will check initial timing and total advance this coming summer. Would running without the engine cover, with flame arrestor on, and then wfo with it off tell me if it is restrictive? Have access to a 780 holley but my aluminum intake has both the straignt/spreadbore pattern on it. A buddy fixed a 74 vet with a 454 and tried both a 650 holley and a qjet....picked up over 1/2 sec in the quarter with the qjet.....Perhaps I'll try one of them also this summer. Not going to change exhaust manifolds...too much money.

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Malibudude

Agreed. I know you won't find me running my Merc over 4500 RPM for any extended period of time. It spends 99% of it's life between idle and 3k.

I know yours is a Merc but after talking to Larry at Indmar running these engines at wot for 15min a month or so is good for it, These engines are built to run wot all day. While I don't abuse it I'm not afraid to run her either. Part of his reasoning is due to the fact these engines are required to run much cooler that autos and therefore tend to have more built-up of carbon and these engines idle much more than a car does. For gas consumption I usually cruise 25ish seems to give me the best mpg.

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Woodski

I have changed my prop from the CVP 13x13 M to an Acme (but a modified one at that) and it works well. The 515 is the recommended swap for lower altitudes, you can also run one with a little less pitch (don't remember the #) but the 515 should give you the closest result to what you indicate you want. Bill Weeks at Acme is very helpful and can steer you to a good replacement. I added cup to mine to get what I wanted (more cup/less pitch than the 515). I have no issue running mine up past 5000rpm, as noted, a SBC does it all the time but of course it rarely goes there for either slalom or barefooting. As for testing the spark arrestor, you can do that test a couple of ways. Simply try with and without as one test, remember, cooler ambient temps will have an effect on the test. You can also run the test by simply cracking the engine cover a small amount, simply stick a short 2x4 or 4x4 under the enging cover to allow some air to enter the compartment, so yes you are on the right track with that. Measure the differences and decide what you want to do. As noted, I ended up making my own spark arrestor that upped the top end by 200 rpm. I also plumbed cool air directly to the spark arrestor. Exhaust manifolds do make a difference, Martin can also chime in on that as he did them also.

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