Timing.....again

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firepiper

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So yes I have searched and read several threads about this and I have a mechanical background. Clean, (just splashed), bottom, props are perfect.
I have twin 454's in a 35 downeast style express. I have been chasing a problem of not being able to get the starboard engine to come up as high, (rpms/speed) as the port. So, we checked the timing today.
Idle-700 rpm
Port-21 BTDC
Star-was 18, bumped to match port, 20 BTDC

2500 rpm
Port- 35
Star- 35

Does this seem high? These engines start/run awesome.
Any thoughts?
Thanks
 
The timing advance weights rust and you might need to replace the distributor.At 700 rpm it should be 10 BTDC.
 
Did you check the advance at 3000 RPM? Was that the '35' at 2500 RPM? I expect you have a knock sensor for that much advance.

How about WOT of both engines separately? Did you measure both full throttle opening/position at throttle lever on carb?
 
You list your engine has a Cutler (now Holley?) aftermarket MPI system . I don't know anything about the Cutler or Holley MPI set ups as to what original ignition parts they may retain , but FWIW would only mention my blue 2003 5.7L MPIs do not allow any adjustment of timing by owner, as base as well as advance is completely controlled by the ECM. On my engines, turning the distributor base only adjusts the (distributor) Cam Retard angle and that can only be read via a MEFI diagnostic tool not a timing light.(I check mine a couple times a season to confirm the CR parameter is still within the required 45 +/- 2* spec to keep the ignition pulse arcing to the dist. cap electrodes when the rotor is close to limit heat, ozone and corrosion to those parts.

Jim Pend is correct in that the specs for the original 454ci/350hp engine ignition parts called for 10* BTDC base timing (at 750 RPM)., at least according to the owner's manual for all models that came with my original 1988 Crusaders and I believe that covered at least a few previous years. Specs for WOT were 4200 min and 4400 max RPMs. No spec for total advance but at the 89 octane spec'd in the manual I'd ...think.... it should be "all in " with ~~ 30* at 3000 RPM or a little higher speed with the original setup.

Do you by any chance have any of the installation and maintenance paperwork from the previous owner? I noticed you asked about the Cutler MPI on those engines back in about 2007. No ignition expert here, but 20* BTDC sounds wildly high at 700RPM .

Are you using an advance timing light or just a basic one and counting peaks and valleys on the timing marks? As I recall , and that isn't saying much, the timing marks were spaced so peak to valley was 2* , thus each peak was 4* from it's neighbor, but adjusting an advance timing light to the desired number of degrees BTDC and adjusting the distributor base so the light read 0*BTDC on the timing marks was easier to see correctly.

Could the engines have been rebuilt at some point with different cams? Curious- What were the original points and centrifugal advance distributors (& ballast resistors) replaced with?

I can't picture how a knock sensor would have been installed in or on the old block but that doesn't mean it was not . (I think GM introduced EFI versions of the 454 in 1987 .)
 
advance numbers from GVP. 28* at 3000 RPM for 87 octane, 30* at 3000 for 89 octane and 32* at 3000 for 91 octane.

This was for standard ignition systems. Idle RPM was always left wherever it happened to end up after setting total advance. Could be anywhere from 2* to 20*. Setting timing by total advance made idle timing inconsequential.

I have merc TB ignition. Timing is set by the EMC. Different ECM have different advance curves.

Aftermarket knock sensors can be mounted anywhere on the block or head where there is the right size pipe plug available.
 
Thanks, these engines have been running with this set up for 7 years. I run charters all summer. Haven't had any problems, (KOW), Juust always looking for more efficiency.
These have Accel elec distributors. There is noe tie between the Cutler system and the distributors. That system is fuel only. And no knock sensor.
I'm wondering if the timing markers are correct. Maybe I should check from the flywheel. I'll give that a shot. Thanks
 
35* advance sounds too much. Look it up somewhere to see what your total advance should be. Pull a couple plugs and see what they read. A knock sensor would have told the ECM to either retard timing or richen the fuel mixture if it hears any detonation.

Do you have a timing light that also reads the RPM? If so, take her out and have someone record the advance and RPM as you slowly accelerate. I'm curious what advance you're getting at your normal cruising speed.

Do you ever get any 'run on' when you shut down right after running at cruising speed? Trying to find out how hot your combustion chamber is getting.
 
quote:
Originally posted by firepiper

I'm wondering if the timing markers are correct. Maybe I should check from the flywheel. I'll give that a shot. Thanks

Click to expand...


Those engines would have come with a flywheel timing gauge that could be inserted in the bell housing window when the rubber plug is removed, but I never tried that timing method. The use of the advance timing light is simplest for me since 0* BTDC is so easy to aim for on the timing marker at the pulley end. Just turn the dial (or change digital adjustment on the light until the engine markers line up at 0* and see what the timing light shows your actual timing to be in real numbers.

FWIW, the Crusader techs at the factory told me they only use the 750 RPM idle base timing spec.(10*BTDC for that original engine). If total advance is off at higher revs, that's an indication the advance mechanism needs to be addressed.

I know the very good Delco Voyager EST aftermarket electronic distributor's I had put on my older engines had all-electronic advance, but most other aftermarket "electronic" distributors had no points or condenser but retained the centrifugal mechanic advance. That's probably changed with more recent aftermarket offerings. Any idea how the Accel model you have is set up in that regard?
Regardless , it sounds like the engines are running well now. Just be sure to err on the side of less advance rather than too much to help avoid detonation and piston loss.
 
The Accel distributors have centrifugal (sp) weights. I had them out, checked and lubed two years ago. Thanks.
 
we never exceed 30 at 4000 unless ur running known good high octane race fuel we like the delco est distributors because they idle at 18-20 giving a quiet and smooth idle
 
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