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Old 02-10-2012, 01:32 PM
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Right parts for a 350 sbc blower marine engine

I am looking for help to find out right parts and installation instructions for my marine engine.

What happened?

My engine is working in a 1989 Wellcraft Eclipse 197, 3 years in my hands. We have a lot of fun with 100 km/h speed and 5 water-skier at the same time... power without end for my little "fishing boat"

After get out of the water in October 2011 we tested the compression and pressure loss: cylinder 7 and 8 failed. We decompose the engine to grinding all cylinder. Now I want to rebuild a real motor with your help.

Here are the parts I should replace or re-use:

Engine parts:

� 350 GM Block 1995-2000 4 bolt block
� Full Roller rocker arms
� Pistons GM 940036 6106 (zero measure)
� Crankshaft (cast)
� Truck oil pan and splash plate
� Roller Camshaft CRANE 119821
� Cylinder heads SBC Victor jr. Edelbrock 77589 complete 64cc
� Carburetor 750 Mighty Demon 5402010 BM
� Edelbrock Racing air filter with K&N Application
� Weiand 144 (translation: 97% power)
� MSD starter, MSD ignition 6M-2 with Marine Rev Limiter and
Marine Distributor
� EMI Thunder -452 with stainless steel riser
� Corsa with both sides outlets (with slip in silencer)
� Monitor 2 circular cooling (water)
� Oil-cooler (from 502 bb)

The Drive is a almost new Bravo 1 1:1,5 gear ratio.

Wish is as result 400-500 hp, suitable for everyday use, not only exclusive extreme performance. Fuel is 95-98 octane.


With what parts would you rebuild the engine?

What is important to note?

What information do you still need?


Oh, a lot of questions, I know but maybe you can help me
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Old 02-22-2012, 12:41 PM
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Which camshaft for 350 CID engine with Weiand 144 supercharger?

I am looking for a roller camshaft for my marine project (21ft Wellcraft) 350 CID engine (overbore 0.030").

Important: acceptable idle, good performance, fuel min. 95 octane, CR about 8.5:1

Any ideas?

Andreas
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Old 02-22-2012, 12:56 PM
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Just do a careful blueprint job, measure everything, replace the rod bolts use arp, they are highly stressed.
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Old 02-22-2012, 01:45 PM
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here are my heads:

cylinder heads SBC Victor jr. Edelbrock 77589 complete
combustion chamber volume 64cc
intake valve 2.08"
exhaust valve 1.60"
intake runner volume 215cc
exhaust runner volume 85cc
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Old 02-22-2012, 03:01 PM
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@F-BIRD'88

Do you have build engines with these cams, practical knowledge?

Andreas
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Old 02-22-2012, 06:42 PM
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I run an Edelbrock RPM cam lifters,push rods, RPM Heads, and roller rocker arms. Love them. 18k + miles. Purrs like a kitten at idle and pulls hard to as fast as I like. I red line at 5500 but it will go higher.
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Old 02-22-2012, 06:47 PM
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In picture 2 I assume you are showing that the skirt has been broken off the piston. I'd replace all 8 with forged pistons for the boat use. Arp rod bolts min. Consider 4340 rods if you run a lot at high speed.
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Old 02-23-2012, 11:48 AM
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Two threads, same subject, merged.
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Old 02-24-2012, 03:58 PM
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What can I expect as save idle (important for onshore boating) with these cams (without losing high rpm power):
#119821
#119831
#119701
#113821

Crane, Comp Cams, other... your recommendation?

Which cam is the best compromise?
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Old 02-24-2012, 04:32 PM
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With my combination the idle is about 950 in neutral and 750-600 in gear. I guess in a boat you would see little drop at idle. If you use a single carb there is no real need for a very hot cam. The blower will smooth out the cam roughness especially at idle. Assuming you have the dist curved correctly and the carb adjusted right.
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Old 02-24-2012, 04:44 PM
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Hi bentwings, I use only one carb (750 Mighty Demon 5402010 BM).
How "hot" should the camshaft be, which LSA?
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Old 02-24-2012, 10:35 PM
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Of the Crain cams F-bird suggests, For your app....boat off shore, I'd go with the first one...119821. You only have a single 750 and a small blower so there is little point in tuning for high rpm. Excess of 5000. You simply will not be able to provide enough boost to make it worthwhile. These small blowers don't make the low speed punch that a 6-71 will even OD'ing them higher.

A boat starts off with a big load at load at 2500-3000 rpm so you really need the power here. Your boat is no flyweight and not really designed for 100 mph speeds. Pulling 5 skiers is a heck of a load so I'd prop for 5000+ at 70 mph I'd tune for max of 5000 to 5500 WOT no skiers. your motor is gasping at this speed.

F-Bird suggests using very low comp pistons...I agree. You will be running on marina gas which is probably 87 on a good day so essentially as I do run on reg gas. Everything needs to be right however and just because you have low comp does not mean burned pistons are a thing of the past. If you go lean under full power you better have a good paddle.

The heads will be fine...I wish I had them. the 64 cc chamber makes a deep dish piston mandatory. I think there is only one -22 cc piston available unless you go with forged ones.
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Old 02-26-2012, 10:11 AM
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@F-BIRD'88
I think it will be a CR of 8.5:1 with these pistons: Sportsman Racing Products 139632 - SRP Small Block Chevy 350/400 Inverted Dome Top Pistons. More than 5-7 psi are not possible with my little blower.

Which piston-to-wall clearance for forged pistons is necessary, I would take
.004-.005 (SBC -bore 4.000-4.200- .0025-.0035 plus .001-.003 for supercharger)

Which connecting rods can you recommend me?

I have EMI Thunder 452, Corsa switched exhaust, thru the prop (quiet for marinas) or directly out with both sides outlets (+600 rpm full throttle) offshore.

@ bentwings
Not 100 mph, 100 kmh...
We have in Germany 95+ octane... for engine health I will install AFR and EGT gauges.
The old GM cast pistons were not burned at CR 9.2:1. The to small piston-to-wall clearance was the problem (all around 0.002!)


What difference can I expect by replacing the pistons only (CR from 9.2:1 to 8.5:1)? Same boost/cam/prop/exhaust/...
More or less rpm?
More or less hp?
More or less torque?


Andreas
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Old 02-26-2012, 01:41 PM
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Quote:
Originally Posted by andyy
@F-BIRD'88
I think it will be a CR of 8.5:1 with these pistons: Sportsman Racing Products 139632 - SRP Small Block Chevy 350/400 Inverted Dome Top Pistons. More than 5-7 psi are not possible with my little blower.

Which piston-to-wall clearance for forged pistons is necessary, I would take
.004-.005 (SBC -bore 4.000-4.200- .0025-.0035 plus .001-.003 for supercharger)

Which connecting rods can you recommend me?

I have EMI Thunder 452, Corsa switched exhaust, thru the prop (quiet for marinas) or directly out with both sides outlets (+600 rpm full throttle) offshore.

@ bentwings
Not 100 mph, 100 kmh...
We have in Germany 95+ octane... for engine health I will install AFR and EGT gauges.
The old GM cast pistons were not burned at CR 9.2:1. The to small piston-to-wall clearance was the problem (all around 0.002!)


What difference can I expect by replacing the pistons only (CR from 9.2:1 to 8.5:1)? Same boost/cam/prop/exhaust/...
More or less rpm?
More or less hp?
More or less torque?


Andreas
Cast pistons will not hold up to the blower for long. A good quality forged piston is a good investment. I used SpeedPro dished that netted me about 8:1 with my vortec heads. I am running a 142 but the difference for N/A is amazing.
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Old 02-26-2012, 08:58 PM
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Since you have 95 octane gas you have a good start. However.....don't be mislead that this will give license to run high compression. We have flogged this high compression to death for years. It simply does not work. Low compression and more boost is the rule. You are boost limited by the blower size and single carb. 7-8 psi is about all you will get. You can try overdriving the blower the max but I think you will only get max boost at a lower rpm which will be good for your boat.

Turbo and supercharged modern cars also have very sophisticated EFI and extensive intercoolers. This allows optimum tuning at all speeds and provision for boost retards and fuel enrichment as required. We simply can't do this as accurately with a carb. Keep in mind that cars only use max power for short periods of time. You will be able to run high boost for very long times so everything must be right on the money or you will be making like a Trireme. haha

Humor aside.
While you did not burn up a piston you did damage it, and this indicates you were on the very edge of serious problems.

So, new pistons, I'd go for a dished flat top -22 cc forged. You need this for you 64 cc heads to get the comp ratio down. Go to the KB piston site, they have a good ratio calculator. I think there is one hypereutectic available but I'd stay away from that for this boat. Be sure to have plenty of ring end gap. go to the high end of mfg recommendation. A little excess ring gap will not hurt but not enough wil make a big mess.

I don't think an AFR gage will work with a water exhaust. I toasted one 02 sensor getting after the motor before it was warmed up on a humid day. $50 mistake. The EGT might work if you can get the sensor close to the ports. I did look up your manifolds and I'm not really sure just how you can do this.

Hopefully you have a closed cooling system...heat exchanger. A cold water or sea water system will have engine temps all over the place. I had this on my boat and it was nothing but trouble.

I would consider a water/alcohol injector system with a large tank. You can get programmable systems that will provide low W/A at low boost and progressively more as boost increases. You will have to do a search on these. There are about 6 well known systems available. Make sure it has a solenoid check valve and not a spring loaded check valve. Usually a $40-50 option.

As for lowering the comp ratio...replacing pistons...You should not lose any power as you will be able to run a more optimum spark advance and because you will have a better combustion chamber shape more hp potential.....D shape with good "squish" as opposed to the shallow total dish and no "squish". (pictured piston) ...more torque, more power. I'd limit this to 5500 rpm regardless of potential. The blower and carb are the limiters here. the blower will simply create more heat and not make more boost at higher rpm. Hot intake charge= detonation potential.

100 kph = 62 mph so to get to 120 kph (74.5 mph) you will have to get about half again as much power as you had maybe more. Water resistance is very high as you go faster. Your boat is pretty big and heavy so going a lot faster will be tough. However pulling power will be higher and acceleration to speed will be faster.

And just to blow our ranting about high comp ratios...
http://www.edelbrock.com/automotive_...orce_507.shtml

9.5 to 1 and a 2 year warantee.....but this is a car motor not a boat motor.
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