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Old 09-18-2008, 02:33 PM
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(split off from another thread. )


I have a boat, that is a 94 Model with a Chevy 305 Installed in it. It is a Inboard/Outboard with 4 inch thru hull exhaust. I Upgraded the Intake last winter and the carb from a 2bbl up to a Edelbrock 1409 with a High Rise RPM Airgap Intake.

I am looking for some more low end, I can run this motor no problem up to 5000rpms but its supposed to redline at 4600 RPMS and have changed the props and all to get it down to correct this, which I did. I then lost some Low end torque.

So what I am wondering is if I were to find some Vortec Heads to put on it, what type of difference would this make? I know that right now this engine should be around 220 hp, or maybe 240. Also, would 350 Heads work on a 305 or not. If you can't tell, I am pretty new to this stuff, just like it and want to learn it. So if you could tell me what might give me some boost in power, that would be great. The cams are hard to change on the marine stuff, to make sure that you do not get water inversion through the exhaust. They also say the inconnel valve seats are the best for Marine applications. Any ideas would be greatly apreciated.

Thanks,
Bryan

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Old 09-18-2008, 02:55 PM
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Vortec heads on a 305 would drop the compression ratio due to the larger 64cc chambers which would be a step in the wrong direction. If you want more low end I would suggest a cam swap and a new double roller timing chain. a RV cam with a power band around 1000 to 4500 rpm should suit you nicely.
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Old 09-18-2008, 03:03 PM
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Quote:
Originally Posted by bry21317
(split off from another thread. )


I have a boat, that is a 94 Model with a Chevy 305 Installed in it. It is a Inboard/Outboard with 4 inch thru hull exhaust. I Upgraded the Intake last winter and the carb from a 2bbl up to a Edelbrock 1409 with a High Rise RPM Airgap Intake.

I am looking for some more low end, I can run this motor no problem up to 5000rpms but its supposed to redline at 4600 RPMS and have changed the props and all to get it down to correct this, which I did. I then lost some Low end torque.

So what I am wondering is if I were to find some Vortec Heads to put on it, what type of difference would this make? I know that right now this engine should be around 220 hp, or maybe 240. Also, would 350 Heads work on a 305 or not. If you can't tell, I am pretty new to this stuff, just like it and want to learn it. So if you could tell me what might give me some boost in power, that would be great. The cams are hard to change on the marine stuff, to make sure that you do not get water inversion through the exhaust. They also say the inconnel valve seats are the best for Marine applications. Any ideas would be greatly apreciated.

Thanks,
Bryan
Bryan, let me lay out some math to try to help you with this. The RPM manifold is targeted at a 350 cubic inch motor turning 6,500 rpm's. At 90% volumetric efficiency, this means the motor is ingesting 592 cfm and the volume of the intake is matched to do a good job at this cfm.

Two problems arise in your case:
1. You don't have 350 cubic inches.
2. You're not twistin' the motor to 6,500 rpm's.

A 305 at 4,600 (your stated redline) passes 365 cfm at 90% efficiency and a heck of a lot less than that at lower rpm's. The motor is having trouble creating a vacuum to fill the cylinders with all that manifold volume. (What my friend would call a "weak-suck operation").

Other board members may have an alternate solution, but if it were my boat, I'd call around to the automotive boneyards and find a GM 305 4-bbl intake for it.
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Old 09-18-2008, 03:32 PM
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Here is the Intake that I installed. http://www.professional-products.com...uctSBchevy.php

CROSSWIND® for 23° Heads
1957-’95 Small Block Chevy V8

Polished Satin Real Chrome
52025 52026 52022

The new CrossWind Manifold is a special version of the 52020/52021. While it is the exact same height, it features an open area under the plenum chamber. This provides for a flow of cooling air which keeps the temperature of the air/fuel charge lower thus producing more power and torque. The interior plenum and port design are identical to the 52020/52021 and will provide somewhat better overall power than the 52020/52021 due to the special air gap style design.


I think that I should have gone with this one, which runs at idle-5500rpms instead of the 52025 that I installed that goes from 1500-6500rpms, which I will never hit with this motor.

CYCLONE+PLUS™ for 23° Heads
1957-’95 Small Block Chevy V8

Polished Satin Real Chrome
52010 52011 52014

This is our top-of-the-line medium profile street performance manifold. It is similar to our 52000/52001 Cyclone, although slightly taller, but with several important modifications. First, it has a square bore carb flange instead of a spread bore. The square bore flange permits direct bolt-on of all popular Holley, Edelbrock, Carter, and Demon carburetors. This manifold is also the only SB Chevy manifold available that features a built-in rear water crossover passage. This typically will provide for better overall water flow and cooler engine operating temperatures. It also features nitrous bosses, and rear water ports. This manifold is also supplied with a quality intake gasket set, 12-point stainless steel attachment bolts, stainless washers, and a full complement of aluminum pipe plugs to plug unused tapped holes. We even include a tube of Permatex Ultra-Black silicone sealer for use on the two ends of the manifold where it seals to the block. This manifold will typically produce more power than any similar competitive manifold due to larger ports and runners.


What do you guys think, I have a slight power lacking at the bottom end, when I hit it to get out of the hole. Now on the top end I did gain about 5 MPH on my boat, so I went from 48 up to about 53 with the same prop and everything. So that was a huge improvement, up top, but the bottom suffered. I am thinking if I can get the bottom back up, it will really be a screamer.

Bryan
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Old 09-18-2008, 04:47 PM
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To all: Sorry in advance for this being a marine post

Bryan- I went through this routine w/my boat a few years ago. 20' Stingray with '99 Vortec 305. I installed an edelbrock 2116 intake (0-5500 rpm) and the same edelbrock carb (1409). Also put in a GM 395 cam, which is mildly bigger than stock. 1.52 crane roller rockers, too.

I believe my motor stock was 220 hp, and yours 190 hp. Not sure where mine's at now, but it runs much better and is more efficient as well during normal operation Vs the 2 bbl Holley that used to be on there.

However, I'm chasing a small carb problem with that Edelbrock. I went through all the tuning manuals, played with the timing, etc. The problem: it accelerates terrific, but falls on it's face for a few seconds at about 17 mph. I have narrowed this down to the Secondary air valve flapping open and leaning out the motor for a few seconds. I actually locked out the air valve to test this. I have learned that Edelbrock doesn't have any way to tune the air valve as it's counter-weighted and they don't have any available weights to make it stiffer. I am currently eyeballing a Marine Qjet or a Holley that has various springs to tune the secondary operation.

Anyway, that's my story. If I were to do it again, I would have saved all my pennies and purchased a drop in Vortec 350/383 (or bought a different boat). I'm pretty darn close to have spent that much money on it anyway. But, I enjoyed the wrenching/tuning excerise and am happy with my setup.

You're not going to get blistering hole shot AND blistering top end. You really need to settle for one or the other. I just change props depending on what I want to do on the water that day. For me, a 4 blade 20" stainless for pulling toys, and a Laser 21" (should be 23") for top end.
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Old 09-18-2008, 06:58 PM
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Bryan,
there is another problem with your intake choice in addition to techinspectors correct sizing info.....

there is about a 1/2" deep of the dual plane center wall removed under the carb which means each piston on the intake stroke is trying to pull a vacuum over the entire intake volume, not just half the intake total volume for just 4 of the cylinders....
and each pistons intake stoke vacuum signal is spread out over all 4 barrels of the carb, not just 2

so in addition to "no-suck" your "leaking" vacuum across the divider wall to make things worse!

at launch, at low piston speeds, you have next to no carb signal Hg to make a decent "atomized" mix and no A/F velocity to make motor TQ which is the key to "out of the hole" performance

agree with techinspector, best low end TQ intake for "out of the hole" is a stock 305 4V,
sorry, there is no reasonable fix for your your intake choice to help bottem end
adding HP goodies which requires higher rpms will only mean less low end TQ for out of the hole performance....
(sell your intake on e-bay?)

footnote:
as a "last resort"???
I really don't know if this will work to help enough to even be worth the cost...
the WEIAND version of the air-gap doesn't have the divider wall removed....
it definitely makes more low end TQ than the other air-gap brands....
you could have a machine shop put back the missing divider wall so that it atleast does behave like a true dual plane intake....

Last edited by red65mustang; 09-18-2008 at 07:19 PM.
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Old 09-18-2008, 08:41 PM
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Quote:
Originally Posted by D. Newland
You're not going to get blistering hole shot AND blistering top end. You really need to settle for one or the other. I just change props depending on what I want to do on the water that day. For me, a 4 blade 20" stainless for pulling toys, and a Laser 21" (should be 23") for top end.
Ditto, my 351W direct drive pops out on a plane in no time but tops out at 40 mph. That's a 13x13 prop for you...

Anyway, I think those Professional Products intakes look an awful lot like knockoffs of certain domestic brands. Be careful putting any Vortec or other 350 heads on your 305. Your engine probably has 58 cc chambers. The heads for 350s are often 64cc. That'll drop your compression ratio and probably offset any power gain the better heads would otherwise give you. Even so, a cam swap might be a good idea...
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Old 09-18-2008, 09:11 PM
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All of these suggestions are just "band aid" fixes. None of them will give you more low end power. ESPECIALLY the cam Swap, which will only give you more top end power at the expense of low end torque.

You really need to go with a bigger engine. The marine 5.7 is a direct bolt in & would give you a 35 HP & 50lb ft of torque increase. Any 350 bottom end will bolt up to the 305 top end equipment. But it will need a set of large dished pistons (15cc or larger) & composition head gaskets (.038 or thicker) to give you a workable compression ratio to run on pump gasoline.

Using the 305 heads & induction/exhaust on the 350 bottom end will also give the engine an even lower bottom end torque curve.
This will be at the expense of some top end Horsepower.
Since you requested more torque this shouldn't be a problem.

I would strongly advise against larger intake valves, performance intakes, & performance camshafts as these all increase top end horsepower at the expense of low speed torque.

The best camshaft for this application would be a stock low performance 305 camshaft. The best intake would be a small bore 2 barrel like used on old style 283's
Essentially if you want to increase low end torque you need to do the opposite of what increases high speed horsepower.

Small ports
Small Valves
Small Camshaft profiles
Small Carb

More cubic inches is the most economical & effective way to increase low speed torque.

There is one other alternative that would also help.
It would involve using a 3.75 stroke crankshaft instead of the stock 350's 3.48" stroke creating a 377 cubic inch engine.

Having more stroke will also increase low speed torque.
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Old 09-19-2008, 07:20 AM
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Thanks for all the replies guys. I will have alot to ponder over now. Which type of Intake could I just swap to, to remove the one that I installed, I think this is part of the problem as I went with one as stated that does not create as much vacuum. The boat has wicked midrange tourqe, when on plane from about 2500 rpms up to Wide open it will move fast. The hole shot is not horrible, but it is a little slower than it was with the 2bbl carb and old intake.

I think if I were to put a True Dual Plane intake as you guys stated and go with one that makes power from Idle to 5500 rpms, I think this would help. Do you agree or no?

With the old 2 bbl carb and older stock intake, it had alot of low end, and still had some high end speed. Just not as much as I was looking for. I did not think the tourqe would drop much wiht the 4 bbl, and intake, from speaking with others that had done this same upgrade, but It seems I got the wrong intake for this engine. I really want to do the 350 upgrade one day, but was just doing this in the mean time. As stated above, it might have been easier to have just done the newer engine. I have been thinking of looking for a block to use in the future, to start learning how to build an engine. What type of block should I be looking for to build a good strong 350 or a stroked version to go to either 377 or 383 even down the road. I thought about looking for a block, that I can pick up cheap and then start the learning process and building a decent low end torquey engine. As my outdrive will not really handle the higher RPMS over 5k.

Thanks for all the Input.

Bryan
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Old 09-19-2008, 09:31 AM
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your welcome,

the wicked mid range power is due mostly to the added ignition timing and increased piston speed which means more Hg and velocity...

another small problem,
the camshaft in the motor is designed specific for the original 2V fuel feed curve versus rpms (and ign curve) to make max TQ as it winds up and recovers Hg.....

more band aids:

most stock cammed motors will produce more low end TQ with 2-4*'s additional base timing added (gives you a "jump start" on the timing added)(adding anymore than 5* won't help)(confirm the 3500rpms is less than 38* after increasing the base)....
having more timing sooner (recurve the dist) will likely help gain Hg as it winds up....
because the crummy low rpms mix is soaking the plugs do double check that your ignition system is delivering the absolute strongest spark possible (ex: coils don't just die, they performance degrade over time due to heat)....
a fair chance that the $40? Edelbrock rods and jets tuning kit will help low end and top end (you are mis-matched cam/carb/intake)....
try reducing the plugs gap by .005 (from .045 to .040?),when plugs are wet, the Kv potential needed to start the spark event goes thru the roof so the only micro seconds long spark event life is shorter and later and less hot with a wider gap...
buy a vacuum guage ($35?)!!!! and mount it on the dash so you can tell if any changes did actually help!

please do make any modifications very carefully,,,,boats do have a nasty habit of going "kaboom" due to fuel spills and vapors and a just single spark!!!!

Last edited by red65mustang; 09-19-2008 at 09:49 AM.
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Old 09-19-2008, 09:48 AM
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Thanks again.

I do know about the boats and have been boating for 11 years now, and am very very safe and take every precaution about the kaboom factor! This is the main thing, I make sure that everything is always marine versions and that it is not some junk that was just thrown on in the wrong way.

As to this, the Guy that I had install the intake last time, he adjusted the spark plugs so they were at like .40 or .045 instead of the .060 that was stated in the Service Manual. We also adjusted the Timing so that it is running around 10-12 advanced at idle, which got rid of a slight bog, this was also told to me by Edelbrock, and it did help.

The WOT Timing is running around 32 degrees. So I think the timing is ok, right now. I put on a New Dist Cap, Rotor, NGK YR5 Spark Plugs at the same time.

Now that I have been looking online at some of the intakes, I do see the Missing chunk in the wall on the Intake, that would seperate the 2 planes. Not sure how I missed that when he told me to purchase it.

Also, I have been thinking of trying to swap out the needles and jets from Edelbrock to see how that would help out. Edelbrock told me to try that also down the road, as they stated the 1409 Marine carb comes stock jetted for a 350, that has more power and needs more gas.

Thanks,
Bryan
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Old 09-19-2008, 10:16 AM
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Bryan,
I did a edit add to my last post, don't want you to miss it....

buy a vacuum guage!!!! ($35?) and mount it on the dash so you can tell if any changes are actually making an improvement
and more important,,, to tell you immediately if almost anything is wrong with the motor, EX with just some malfunction animated examples:

http://www.users.bigpond.com/ergoff/vac1.htm

how quickly (and smoothly) does the needle recover to cruise Hg is what your looking for (indicates how quick the TQ is increasing)....
and the carb (usually) wants about .5Hg to 1.5Hg WOT getting out of the hole to make a decent mix/max TQ...

some good news, if your stock gap was .060 that tells you it does have a very high amps strong spark ign system!!!!
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Old 09-19-2008, 10:27 AM
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Barry, if you consider building another motor for the boat, let me help to give you some info to chew on. If you were to build a 355, 400+ ft/lbs of torque would be available through most of the rpm range where you need it in a fairly inexpensive package.
By 1987, Chevy had begun to produce 350's with one-piece rear main seals and hydraulic roller cams. A short block (less heads and intake) of this type would be a good starting point. For instance, I might be thinking something like '89 Caprice.
Here's a photo of the innards of a roller block....
http://www.carcraft.com/techarticles.../photo_02.html
From 1996 through 1999 Chevy produced the best-flowing OEM iron cylinder head they have ever made. It was used on 350 Vortec 5700 truck motors (RPO L31) and should be readily available in boneyards. Look for a sawtooth design cast into the end of the heads and the casting number 12558062 under the valve covers. The heavy duty trucks used a different casting number with Inconel exhaust valve seats installed. If left unmodified, in the opinion of some, this seat will disrupt low lift flow, so unless you want to dink with grinding on the seat and throat of the port, use the 12558062 heads that are induction hardened. Get the rail rockers and the valve covers with the heads and make a deal with the boneyard that you can exchange them if they are found to be cracked upon magnaflux inspection at the machine shop. Disassemble, clean and inspect. If found valid, freshen up the valve job and replace the seals. Toss the springs and retainers that came on the heads and install these springs and retainers from Crane Cams. They should drop in with no machine work and will allow more lift than the stock springs and retainers. Using the stock 1.5 rail rockers will eliminate the expense of machine work to install guide plates for use with aftermarket non-rail rockers. Or, if you feel bucks-up, you can use aftermarket roller rail rockers without guide plates.

http://store.summitracing.com/partde...5&autoview=sku
Fits most 1996-1999 GM Vortec V-8 truck engines. Original
equipment valve locks should be used to obtain the below specifications. Crane number 99097-1 valve locks can be used, however they will reduce the assembly height and travel
by .020” when compared with stock valve locks.
- Recom’d installed spring pressure and height (valve closed)-------------124 lbs.@ 1.750”
- Open checking pressure and height ---------------------------------------------374 lbs.@ 1.150”
- Maximum recommended valve lift and RPM ----------------------------------.550” - 6500 RPM
Stock Chevy roller lifters will tolerate a max of roughly 0.350" lift at the cam (0.525" theoretical valve lift w/1.5 rockers), but you don't need any more lift than that to make a very powerful 355.

There are many choices for pistons. Here is an example of a 12cc dish hypereutectic piston with 5/64ths rings that would make about 9.6:1 static compression ratio with the 64cc Vortec heads.
http://kb-silvolite.com/performance....tails&P_id=155

Mated with a tight 0.035" to 0.045" squish (quench), this combo should run on most any marina fuel and make excellent power and torque when mated with the proper camshaft. The stack on this particular combo will be found by adding up all the components. Half the stroke is 1.740", the rod is 5.700" and the piston compression height of the KB I listed is 1.561". Added up, this gives you a stack of 9.001". So, cutting the block decks to 9.001" will result in a piston deck height of 0.000" and allow a standard gasket of around 0.040" to set the squish (quench). Speaking of the cam, do not choose the cam yourself. Call up your favorite cam grinder, give the tech all your specs, tell him what you want the motor to do and let him spec out the cam for you.

When push comes to shove, I don't think there will be a ton of difference in the manifold selection, although you will need to use a dedicated Vortec head specific manifold. If I were to build it, I would probably use a Edelbrock Performer Air Gap Vortec, while others on this board might opt for the Edelbrock Performer RPM Air Gap Vortec.

Although the math would indicate a 600/650 cfm carb, I think you would see better power with a 750 cfm vacuum secondaries carb. At least that's the way I see it on my software dyno.

In my opinion, if you instead opted for a stroker 383, you'd need more head than the L31. I'd be considering the Airflow Research aluminum heads in that case. For instance, here's a dyno build at AFR....
RPM Torque H.P.
2500 457 231
3000 467 273
3500 483 322
4000 511 389
4500 517 443
5000 504 480
5500 481 503
6000 439 502
Dyno Test Criteria:
383ci Stroker SBC
AFR Street 195cc Cylinder Heads
9.5:1 static compression ratio
Holley 0-4779 750 cfm
MSD Distributor 36° Timing
Comp Cams 12-433-8 Hyd Roller Cam
1 3/4" Headers
93 Octane Pump Gas
Engine built and dyno tested by American Speed ultilizing an Edelbrock RPM Performer Manifold.

Last edited by techinspector1; 09-19-2008 at 01:29 PM.
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Old 09-19-2008, 11:04 AM
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I'll throw my 2 pennies in the ring. Alot of this has been already discussed so forgive the repetition.

That intake is just not going to make you happy on an I/O boat. It is designed for top end power and it kills low end torque. The 600 carb is a great choice.

If you want to change cams, keep it mild. In fact, keep it an I/O marine cam if you're not sure. Through-hull exhausts are very sensitive to exhaust reversion caused by bigger cams. I never thought it could be, but it really is. You also want to keep the cam small to promote low end torque. You also need to make sure that the torque peak happens close to the same RPM where you can sustain plane. That not only puts the fat part of the torque curve right in your hole shot, but it makes sure you're never lugging the engine. Anytime you have lots of throttle and the RPMs are below the torque peak its terrible for fuel economy and hard on the engine.

The problem is that your 305 is basically a copy of a smogger engine minus the smog equipment. There is little there to inspire good performance. A switch to better heads is the real answer, but there are very few options for a 305 that will work well. You can't practically do aluminum, so that leaves you with factory iron options and there just really aren't many. The obvious but expensive answer is a 350. You can get a Marine Vortec longblock for $1200 delivered, no core.

I recently built a vortec 350 for my 19' I/O. I kept the stock Mercruiser cam, put roller rockers on it, aftermarket GLM divided exhaust manifolds and risers, and a Performer intake with a Holley 670 cfm carb. It was a 290 hp motor, so I'm assuming I have 300 with the upgrades. It was about a $3000 repower, but it was worth it. Tons of torque down low and 300+ hp at 5000 rpm. It moves my 2700-lb boat at 60 mph and pops two skiers out of the water like corks.

Keep this in mind: an increase of 1 mph requires about 15 hp. But torque is what gets you out of the hole.
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Old 09-19-2008, 12:42 PM
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I'd stick with the 2 BBL setup & tune the 2 BBL to make the most of it in the higher rev ranges.
You could replace the timing set with a high quality true roller setup to gain a couple of lost HP & TQ. Timing set chains on chevys stretch terribly and don't last much more than 20% of the life of the engine.
"Bolt on" modifications that increase real world low speed torque are non-existant.
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