snowrunner

Looking for input, have 2 rebuilds with 15 hrs. Both run great up to 4200, when the SB motor runs out of power snd RPM. The SB engine can drag it to 4400 or so.

New plugs, new injectors (Smitty Tuned on the water). Compression is 160-155. New distributors at rebuild. Wires are new 8 mm GM perf from Crate motor. 39 psi on rail under load. Timing at 8 deg. Moved rails from engine to engine

During tuning we didn’t have any codes, no knock. The only ignition part not new is the coil, but this doesn’t seem like a coil type issue.

Is there something I ‘m missing? Want to heck it out before its put away for winter.

regards.

SB

iTrader: (1)

New cams degreed in ?
New valvesorings just out in or did someone do all the actual trsting and measurements ?
Exhaust have mufflers ?

In boat tuning with wideband ? Assuming yes but checking
wot verified ? Assuming yes but checking

snowrunner

Tyler Crocket built the heads.
no mufflers, Hardin Manifolds
wideband
boat ran 78 after new distributors last year ( ign modules were junk). Running around 70 now.

The issue started before injectors, changed them all after one stuck open.

i rarely run full out, so not clear when it started

articfriends

iTrader: (1)

After providing a "scaled" tune for the 48 lb injectors I provided and hearing boat doesnt "pull" on top, snowrunner verified timing, fuel pressure, changed filters, etc. Still having the issue, I became concerned the scaled tune may just simply be too rich and the port motor which isnt pulling as well as the stbd motor may possibly be loaded harder than the stbd and running in a higher map setting, possibly getting into the 10s in afrs or something. I DID flow these new injectors against some good stock ones and used that data to scale the tune, Sooo, I offered to come down and scan/tune boat with AFR meters on water. I found the light throttle 50, 60, 70 map areas under 2200 were in low 11s and tps accell was still too rich, rescaled these to clean it up BUT the afrs in midrange and wot are pretty much where they belong in low to mid 12s. I did some touch up work to those areas and pushed some more timing in mid range with no sign of KR.
So, the wot AFRs are in 11.9 to 12.4 area, its got as much timing as Id dare to put in with 87 octane, NO KR, tps, ect, iat, look fine. The ONLY anomaly I DID see is the lower rpming motor is running in general in a slightly higher map cell and running .3 to .4/.5 richer than "good" motor, of course if its got a problem thats exactly what it will do. Not uncommon too though to see one motor in a twin at 12. and one at 12,4 at wot. On my dyno going from 11.8 to 12.2 to 12.5 barely changes power a measurable amount, to NOT rpm from tune, it would have to be burn down lean or pig rich, I was HOPING it was signifigantly off and some clean up would fix it but unfortunately NOT, injectors been swapped from side to side with no changes also.
Snowrunner, what valve springs are on your heads?

SB

iTrader: (1)

Engine hydrolock ?

snowrunner

Thx Smitty!

Running Isky springs, crane rockers, Johnson 2126BBRB lifters. Stock 500 EFI For everything else.

snowrunner

No Hydrolock.

Compression good all cylinders within 5 psi.

cut filter, no debris. May be able to bend a rod, but should make noise or cause debris.

articfriends

iTrader: (1)

Those plugs are pretty black BUT motor was idling and running fairly rich down low so the color is deceiving. IF you had new plugs in and were driving it today, they would be much cleaner overall. At one point you changed them and made no difference, correct?

snowrunner

I changed them after the original injector failed, then again after the new injectors.

Made a difference after the stock injector failure, though changing them after new injectors but really didn’t change anything. They look the same now as the set that came out when the injectors went installed.

I keep leaning toward a SP wire with a weak connection or resistance issue issue a peak power and full load? Looking at the wires, these were not new with the rebuild - but have max of 75 hrs and were from my 502 MPI.

1MOSES1

Have you looked at plugs recently to see what they look like? Looks like it’s burning oil. When you did top end, was the intake shield re-installed? Any grey smoke when you run?

does the engine break up at top end? Usually that’s an ignition or wire problem.