What should timing advance be on a 5.7L 350 merc (chev/GM)

[Hog Wild]

I have a new 2004 carburated 5.7L 350 Chev. (Indmar/Mercruiser) engine 9.1:1 compression ratio and 89 octane fuel recommended. When around WOT (high RPM) it is at 26 BTDC max. advance. My old engine went to 32 BTDC. Rumor is race car people run as much as 36 BTDC (with a premium fuel). Looking for comments on a recommended BTDC at WOT for a 350. Like which is better 26 or 32 or something in between or doesn't really make that much difference or ??? Talking with dealer/tech's they told me with my warranty I'm free to run either ignition system.? When I asked 26 vs 32 they basically shrugged.

 

[bomar76]

Re: What should timing advance be on a 5.7L 350 merc (chev/GM)

Just for a comparison.....<br />We are running 34 degrees total advance on our 5.7 4 bbl @ 4800 rpm (checked with a light) and burning 93 octane.<br /><br />I know you stated the engine is a 2004, but is it a replacement for a prior year engine?<br />If so, is it Thunderbolt IV or V?<br /><br />What is this engine in?

 

[Hog Wild]

Re: What should timing advance be on a 5.7L 350 merc (chev/GM)

This is in a 1986 Cruisers Inc, 25' weighs 7000 lbs. with everything but people, a heavy beast. top speed 40mph at 4800 rpm, cruise 30mph at 3500 rpm. The 2004 350 is a replacement for the original 1986 5.7L that was Thunderbolt IV. But this was not a long block, it is an all new powerplant, Holley 4 barrel/Vortec intake. I guess does the specific ignition system matter much really. I mean I could theoretically program my own advance curve. The new one is a Delco EST ignition. I find it funny too. It starts the motor at 8 BTDC but then jumps to 18 BTDC when idling at 650rpms (18 seems too high) but then only advances to 26 BTDC at WOT (seems too low). Runs fine. I'm just looking for thoughts/ comparisons and to share the interesting things about ignition. Only thing the manuf. tells me is they set the computer for 8 BTDC in bypass mode then check that it's 26 at WOT. But I'd like to know more / hear more. I've studied the Thunderbolt IV and V advance curves in detail.<br /> http://www.boatfix.com/merc/Bullet/95/95_11.pdf <br />I know nothing about the Delco EST advance curve other then trying to back calculate some numbers. Like it seems to advance about 14 degrees when you pull the jumper off (all at idle) and then advances 8 more degrees when you go from idle to WOT. Is that right for a Delco marine computer even?. I see the computer like:<br /> http://ebasicpower.american-data.ne...er&Product_Code=GLM73190&Category_Code=MER10C <br />Appears to be the same computer for all engines, how can that even be?<br />from:<br /> http://www.marinemechanic.com/site/page229.html <br />ENGINE.. TIMING @.. MAX TIMING<br />CID..... 500 RPM.. @ 4000 RPM<br /><br />181......0............24 <br />250......10...........32 <br />262......2............24<br />305......8............26 <br />350......8............25 <br />454......12...........30 <br />552......12...........30<br /><br />What the above chart is missing is what an engine actually idles at? My GM mechanic friend says it doesn't really matter as long as it idles ok. I set my ignition module at 8 BTDC but that's not what it actually idles at. They do not tell that. Also how can the computer <br />take a 181 engine from 0 BTDC to 24 BTDC (24 deg. advance) but a 350 is 25 - 8 = 17 deg. advance. does it know to advance the different engines different amounts? By the number of cylinders? Curious on any comments / thoughts.

 

[bomar76]

Re: What should timing advance be on a 5.7L 350 merc (chev/GM)

Email me offline.....

 

[Destin]

Re: What should timing advance be on a 5.7L 350 merc (chev/GM)

You have vortec heads on your new engine. They need 4 degrees less advance than the old style heads. 28 degrees is max recommended advance on vortecs, and 32 degrees on older heads. I like the fact that the timing is advanced under light load at low RPM(like old style vacuum advance), it increases gas mileage while trolling. I'm sure there are sensors to retard the spark if it knocks under load. I'd say the timing was right, especially since the WOT advance is what the manufacturer recommends.

 

[navigator336]

Re: What should timing advance be on a 5.7L 350 merc (chev/GM)

If it is an Indmar it should be at 10 BTDC with idle set to 750-850 and done with the timing shunt in place and connected to 12 volts +. If you time it without the shunt you'll be sorry. Your new engine should have come with a manual that lists base timing. The EST module will give you the total advance relative to base timing. I think when I last checked full advance on my Indmars (with the Holley 4150/4160's), total advance was 32, but I don't remember for sure. I can fax you the base timing procedure I got from Indmar tech support if you like.

 

[Hog Wild]

Re: What should timing advance be on a 5.7L 350 merc (chev/GM)

Sorry I have no knock sensor in this system. Pick-up coil drives the ignition module which drives the coil, that's it (almost too simple hunh). Navigator336, I believe I've seen the Indmar directions ("Thanks for the offer") but only curious if it mentions anything about what the timing might be at idle with the shunt and 12+ off as the one I saw from them didn't. <br /><br />The tech. from Indmar that I called told me they go 10 deg. at 750-850. My directions are from Barr by EDM (the motor assembler) and they say (note only mentions the 8 BTDC and nothing else):<br /><br />Carbureted Engine Timing Procedure<br />NOTE: Adjusting engine timing should not be attempted unless you have the proper tools<br />and equipment. An improperly timed engine can be severely damaged. Do not<br />attempt to start the engine unless the boat is in the water or an adequate supply of<br />cooling water is applied directly to the cooling water intake.<br />Carbureted Engines<br />1. Install P/N 801012 timing shunt (plug with looped white wire and black wire shipped<br />with each engine) into the plug on the distributor.<br />2. Attach an appropriate inductive pick-up timing light to the number one cylinder spark<br />plug wire.<br />3. Start engine.<br />4. Connect the loose end of the black wire from the timing shunt to 12 volts<br />positive.<br />5. Adjust the idle to 750-850 RPM by turning the idle stop screw on the<br />carburetor.<br />6. Set timing to 8 degrees BTDC by loosening the distributor hold down bolt and rotating<br />the distributor until the timing pointer indicates 8 degrees BTDC. 7. Disconnect timing shunt<br />from 12 volts and remove plug from distributor. 8. Reset idle to 650 + or - 50 RPM for<br />inboard engines and 1000 RPM for jet engines.

 

[navigator336]

Re: What should timing advance be on a 5.7L 350 merc (chev/GM)

It appears the Barr's procedure is word for word the Indmar one except Indmar says 10 degrees BTDC. I think Barr buys the engines from Indmar, but I'm not sure if there are any differences. I have the spec number on the computer module (a GM part) that Indmar uses - 10482830 -. GM has lots of different part numbers available that work with the EST distributor for a 5.7. The 10482830 is not a common one. Maybe Barr's uses a different one which gives a different advance curve and max advance.

 

[AKJohne]

Old thread... I know.. Hog Wild, what was the upshot on your final TA... ?

 

[southkogs]

I think you'll need a time machine to contact Hog. Please take a moment and read our forum rules.

Closed.