[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

[T-bucket23]

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.

[F-BIRD'88]

The lower compression ratio will allow more boost and some more spark advance.
and makes more power. The increased spark advance lower exhaust temps when under boost ( extended WOT) a lot easier on the exhaust valves.

The lower the cr the better. 7.5 to 8:1 allows a lot of boost and timing.

9.2:1 requires very modest boost and timing on pump gas.

The actual real octane of the fuel used is the limiting factor.

Lower compression ratio and more boost makes the most of the blower on pump gas.

blower boost-timing:
what you can get away with on the street-strip for short WOT bursts will burn up the motor on the water. ( extended WOT under full boost)

The only thing that will brake a cast piston ( or any piston) is detonation-preignition from excessive boost and lean jetting and excessive timing and garbage fuel. Cast pistons are no problem, incorrect tuneup is the problem.

forged piston to wall clearance. go to the big end of the recomedned wall clearance. You do not need to add beyind this. You want generous but not excessive. The piston manufaturer can advise.
Piston rind end gap needs to be generous. ( cold water, cold block hot pistons )

the edelbrock heads require VTP clearance verification with any piston.

Don;t bother with the smaller crane cam. get one of the larger ones I listed.
Call them for tech advise. These crane hyd roller cams are sweet in a boat with the blower.

the exhaust looks good. I have never used them but they look like a step up from the good Mercruiser magnum manifolds and should work very well.

What is the blower pulley drive ratio you are using now?

[bentwings]

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.

[andyy]

@Chet
I flirt with these pistons: Sportsman Racing Products 139632 - SRP Small Block Chevy 350/400 Inverted Dome Top Pistons


@F-BIRD'88
piston ring end gap - my engine has a half closed cooling system (thermostat 160 deg.)
VTP (ventil-to-piston?) clearance - Edelbrock 77589 valve spring max. lift is 0.650"
blower pulley drive ratio - 1.97:1 - 5 psi boost at full throttle (on gauge)

Which cam would be your favorit?
Is this cam an option or to hot? http://www.edelbrock.com/automotive_...orce_507.shtml


@bentwings
AFR/EGT - I use a connecting piece (e**y 310137061646) between manifold and riser (there is it dry)


Andreas

[bentwings]

I use the flat tappet version of that cam and love it. It's what I'd use were I to do another motor for myself. I use the entire Edelbrock valve train. 18k miles and no probems.

VTP= valve to piston clearance.

I use Innovate Motorsports AFR and software. It's good but there are many others. I like this one as it is real time and very fast and plays into a laptop pretty easily. they hve more extensive data recording too. More expensive too.

[andyy]

about cam selection:

CompCam
- 08-418--8 (LSA 112)
- 08-301--8 (LSA 113)
- 08-305--8 (LSA 114)

as I said, idle is important to maneuver in the harbor
and for low speed through the small rivers and from 3.000 rpm
to max. 5.500-5.700 rpm for high speed.
Higher LSA = better idle (during larger vacuum)?

Andreas

[T-bucket23]

Originally Posted by F-BIRD'88

The only thing that will brake a cast piston ( or any piston) is detonation-preignition from excessive boost and lean jetting and excessive timing and garbage fuel. Cast pistons are no problem, incorrect tuneup is the problem.

?

This is true but the forged pistons are more forgiving. It would be foolish to build a blower motor and intentionally put in cast pistons was my point.
With a blower engine it is all about the tune up for sure.

[andyy]

following parts I suggest:

Crank:
Eagle Specialty Products 435334805700 - Eagle Forged 4340 Steel Crankshafts

Pistons (bore 4.030):
Sportsman Racing Products 139632 - SRP Small Block Chevy 350/400 Inverted Dome Top Pistons

Rings:
Sportsman Racing Products S100S8-40305 - JE Pistons Pro Seal Premium Sportsman Series Piston Rings

Cam:
CompCam
- 08-418--8 (LSA 112)?
- 08-301--8 (LSA 113)?
- 08-305--8 (LSA 114)?

Piston to cylinder wall clearance?
Ring end gaps?
Lifters?



Best regards, Andreas

[andyy]

Which spark plugs are recommended for mild blower use, engine thermostat 180 deg.

Brand, heat value?


Andreas

[F-BIRD'88]

Any all of the comp cams you listed are fine.
They are all very similar. Pick one.
Excellent low speed and idling, no water reversion, peak power just under 6000 rpm.

The edelbrock cam is too hot. The WOT peak power rpm point will be higher than you want. (6000+ rpm) May cause water reversion with the wet marine manifolds. May require and manifold water cutoff control valve to avoid water reversion at idle and engine shut down.

A 224+/- in-234+/- ex 112-114 LSA ish cam is just right.
its your goldie locks cam.




VTP valve to piston clearance must be checked.

You want th spark plug slightly cooler than for normal N/A use.
gap at .035".

Lower the compression ratio and run more boost and timing to go faster.

[andyy]

Thanks, F-BIRD'88.
My favorite is the 113 LSA.

Can I check (calculate) the VTP before buying parts?

Can you tell me a heat value?


Andreas

[F-BIRD'88]

Originally Posted by andyy

Thanks, F-BIRD'88.
My favorite is the 113 LSA.

Can I check (calculate) the VTP before buying parts?

Can you tell me a heat value?


Andreas

No you must verify the VTP clearance. Large valves, valve guide C/L.
Do not assume anything with these edelbrock heads.
CCheck it.

if a champion RC12YC is normal for N/A or that head use a Champion RC9yc or RC10YC
or similar NGK, Autolite.

A dyno test tune up will save you a lot of time and hassle and get it right the first time.

You want 7.5:1 cr.

European 95 octane is no better than our 91-92 R+M/2 rated fuel.

if you want to run high boost and high compression and decent timing to make power you will want to blend in 110+octane unleaded race gas with your best pump gas. Much cheaper than busted parts.

[F-BIRD'88]

VTP clearance. you must verify radial and depth VTP clearance
Use clay/modeling putty. Do not guess, do not assume .with those heads.

[andyy]

about wrist pin style, can I use this piston SRP-139632 (pin diameter 0.927) with this Eagle connecting rod ESP-5700BLW with pin end bore diameter 0.927 as full floating pin?

Andreas