SB

This is true.

SB

Kinda, but more importantly overlap duration and more so overlap after tdc.
lsa effects this, so doesn’t duration, and so doesn’t if cam installed advanced or etc.

That cam has so little at .050” duration and overlap at .050” dur after tdc, even with 109lsa, it’s no biggie.

prohan007

Thanks for the insight.

bajaman

what a great question and series of responses! THIS is what forums are all about!

Wally

We are all here to support the same love of boating and to help each other out.

prohan007

Update:

I checked the timing and all appeared to be spot on.
I pulled one of the old cams from my old VP 5.7GSi engines and brought it to Isky Racing Cams (who are just around the corner). Richard (the owner) reported back that the cam was almost identical to the Mercurser cams that are reportedly in the new engines.
I pulled the spark plugs and performed a cold compression check on the cylinders, here are the results:

SB Engine (New)
#1 - 173
#3 - 171
#5 - 168
#7 - 182
#2 - 176
#4 - 168
#6 - 175
#8 - 154

I'm also having a slight overheating issue on this engine, the normal operating temperature is 175° but it was running at 180°-185°.
I swapped out the thermostat and it actually made it worse. Now running at 190°-198°.
I checked the raw water impeller and it looks great.
The coolant in the reservoir may have dropped by 3/8" but it's hard to tell TBH. The oil appears clean.
I'm in the process of swapping out the circulation pump to see if that's the issue, I did reuse the pumps from the old engines as they were only a tear old.

Any input is appreciated.

Wally

Id hook up a vac gauge and see what the needle tells ya....if that doesnt point in some direction id probably do an oil sample test at the same time to see if that tells you anything about bearings etc....
If neither of those pan out then id be diving deeper into each section of the motor....carb/fuel......ign.....cooling...one at a time bit by bit maybe swapping parts between both engines until the problem follows to the other engine....

Wally

The cyl #8 is a little low compared to the others....maybe you have a stuck ring?

prohan007

Sorry, I forgot to mention, the TB has a heavy coating of oil that has to come from the valve cover vent hose. Would seem to indicate blowby don't you think?

mcollinstn

For "fresh" motors, I'm not impressed with the compression test results.
was the compression test done after you had run it a few hours to seat the rings?
was the throttle plate fully open when you ran the compression test?
If yes to both questions, then you need to do a leakdown test to determine WHERE the weak cylinders are leaking.
One big issue on assembly-line rebuilds is "where" the cam is installed/degreed.
If your old motors had the cams "more advanced" then there will be a difference in Los end torque.
But another thing - if your electronics includeva knock detector, then there is a chance that the new motor has some "mechNical noise" that is causing the ecu to pull out ignition timing under heavy load.
If you have a scantool, you can warch and see if thats happening.
if you dint have a scanner, get a knock sensor (in your hand) and plug it into the harness instead of the one in the motor. (Some actually have two. But I'm not familiar with your setup).