418 Ls3 cranks slow

[Zachalanche]

My 418 stroker cranks slow. It always has, it cranks even slower when at operating temp. Slow enough that im surprised it starts at all.

My battery tests good

I replaced the starter because i was suspicious that i had over worked the first one years ago, but no change.

Battery voltage drops to 9.5 while cranking cold, and 8.5 when cranking hot, so there seems to be a massive load here if the battery is good.

I measured voltage at the battery and at the starter while cranking, and the voltage drop is not more than 0.1V. There was a bit of variation over a few tests, so i could get am exact voltage drop, but it doesn't appear to be significant.



So whats left to check?

Timing? What should it be at while cranking?

Do LS engines need starter shims?

Anything else? What am i missing here?

Thanks in advance.

[Zachalanche]

here is my crank spark map. interestingly when cold it looks like its 9-11 degrees BTDC. seems reasonable. when at operating temp there are a lot of places where it commands -10 degrees...so 10 ATDC? Except for 200 RPM. so if i happen to be cranking there when hot it wants 2-3 degrees BTDC which maybe is too much advance after a good heat soak. I don't know when or why or who set the table up this way, but it seems weird.


I guess I need to do some logging to see what's going on.

[Jim Streib]

I had to do some digging as I wondered if your battery was no longer under the hood and is it still behind the passenger seat ?.

Maybe check all of your connections and if you have not already, maybe run a dedicated ground from the battery negative terminal that is the same gauge as what is on the starter for power and then run this dedicated ground cable to the block and where it's attached, remove the paint and add a star washer.

I don't know your wiring setup but I've seen too many times too small of a starter cable run or people ground the battery close to where it's mounted but then do nothing to get this ground path past things like rubber motor mounts and such up front.

Jim

[Zachalanche]

thanks for digging in.

Yes the battery is still behind the passenger seat. Everything is clean tight and there are plenty of engine grounds. I even ran a dedicated ground from chassis to the block near the starter (in addition to the already existing block to chassis ground and heads to chassis grounds). The unibody was sand blasted then seam welded, so there should be clean path for current (compared to a rusty old unibody where many of the spotwelds are suspect).

I can go through it all again, but wouldn't I see significant voltage drop at the starter while cranking if there was poor grounding, or undersized wires? I am seeing pretty close to the same voltage (9.5 V cold, 8.5 V hot) at the battery and at the starter.

[Hotwire]

Put a battery charger or jumper cables on it and check voltage/starter rpm. You may have too small of a battery (CCA (Cold Cranking Amps)) for the stroker?

Voltage shouldn't be dropping that low during cranking.

[Jim Streib]

Maybe too, do a voltage drop test between the negative post of the battery and the starter housing ?.

Jim

[Zachalanche]

1000 ca, 800 cca. Ill still give it a try to see what i learn. But it gets costly if i need considerably more ca.

I also read somewhere that it takes roughly as many cranking amps as cubic inches....excluding cases where compression is really high. Not sure if thats true, but if it is 800 ca should be plenty.

[68Formula]

here is my crank spark map. interestingly when cold it looks like its 9-11 degrees BTDC. seems reasonable. when at operating temp there are a lot of places where it commands -10 degrees...so 10 ATDC? Except for 200 RPM. so if i happen to be cranking there when hot it wants 2-3 degrees BTDC which maybe is too much advance after a good heat soak. I don't know when or why or who set the table up this way, but it seems weird.


I guess I need to do some logging to see what's going on.

That's a stock LS3 cranking spark map.

[Steve68]

How big are your battery cables??

and you have a ground from frame to body to engine??

[RivGS+]

Sounds like the starter, not the batt or connection. Is it a factory type or hi torque mini starter?

==my hi torque does the same thing on my 6.2 L9H.

[TANKMASTERJ]

I know I have #2 ought both hot and cold. High compression LS7. A single 1000ca 935cca napa commercial battery cranked it fine cold. Slow while hot. With everything super grounded, clean connections nice custom made copper cables and triple shrinke wrapped ends, so my battery is in the trunk. I made another battery mount and I've got two now same as in my duramax. Ran a separate hot all the way to the firewall to my + bulkhead. Starts fantastic hot or cold
I'm somewhere between 12.5 and 13.-1 compression. Big cam shaved heads,. I went through all that starter, test, blah blah blah. Second battery at 150.00 each versus a ridiculous priced larger cranking amps worked for me.
Jason

[Zachalanche]

Sounds like the starter, not the batt or connection. Is it a factory type or hi torque mini starter?

==my hi torque does the same thing on my 6.2 L9H.

factory type starter

[Zachalanche]

I know I have #2 ought both hot and cold. High compression LS7. A single 1000ca 935cca napa commercial battery cranked it fine cold. Slow while hot. With everything super grounded, clean connections nice custom made copper cables and triple shrinke wrapped ends, so my battery is in the trunk. I made another battery mount and I've got two now same as in my duramax. Ran a separate hot all the way to the firewall to my + bulkhead. Starts fantastic hot or cold
I'm somewhere between 12.5 and 13.-1 compression. Big cam shaved heads,. I went through all that starter, test, blah blah blah. Second battery at 150.00 each versus a ridiculous priced larger cranking amps worked for me.
Jason

my compression is around 10.5. I hope i don't have to run 2 batteries.

[Zachalanche]

So I did a bit of experimenting today.

Also it should be noted that despite my efforts to get the car as warm as I could, I don't think i was able to achieve the same level of heat soak that occurs during normal driving. I say this because through all of my testing I never had the super slow crank that I have experienced if i drive the car somewhere, then try to stop and start it.

I no longer have room in my engine bay for a battery, so I improvised using a battery from another car so that I could easily switch back and forth between the front and rear mount or use both. The image below is the reason I didn't drive the car prior to testing. I also didn't want to connect the negative cable to the block with everything in the engine bay at 200+ degrees.


Here is a rough schematic of my dual battery arrangement. I included the location of the ECM, which is mounted behind the firewall near the cowl, because that is where voltage is being measured.


First i warmed up the car until coolant temps were around 210. Then I let it sit for roughly 10 min and Coolant temp increased to 217. temps varied throughout testing, but were always over 205.

with the rear battery only connected, I am cranking at around 60 RPM, and voltage is in the low 8s (after an initial dip into the mid 7s) while cranking, total crank time is about 1.3 seconds (from start of crank to 1000rpm) which sounds short but seems long.


Using only the front battery, I am cranking at around 70-80 RPM, and voltage is in the mid 9s (after an initial dip into the mid 8s) while cranking, total crank time is about 1 second (from start of crank to 1000rpm)


Using both batteries, I am cranking at around 85 RPM, and voltage is in the mid 10s (after an initial dip into the high 9s) while cranking, total crank time is about 1 second (from start of crank to 1000rpm)


I also tried playing with the crank spark table. first, I tried 5 degree advance (across the board at the higher temps), and the hot start condition was way worse, but it eventually fired. Then i tried -10 degree at the lower crank speeds (50 and 0) and the engine would not start at all. after this, I set it back to factory.

So, it appears that (as many of you have hypothesized) I do actually have too much voltage drop. Connections are as clean as they can be, but I am running 2Ga cable, so it could be upsized. Interestingly, for this test, the front battery was rated at lower cranking amps (875 instead of 1000 at the rear), and the positive side cable was 4 ga, and it still outperformed the rear mounted battery. So My next step probably needs to be upsizing the positive cable.

[dhutton]

I use fifth and sixth gen Camaro positive cables in all my builds. Heavy gauge flexible cable. Cut it to length and crimp on a lug connector.

https://www.ebay.com/itm/28434800082...temCondition=4

Don

[Zachalanche]

I use fifth and sixth gen Camaro positive cables in all my builds. Heavy gauge flexible cable. Cut it to length and crimp on a lug connector.

https://www.ebay.com/itm/28434800082...temCondition=4

Don

Interesting. I didn't know those Camaros mounted the battery in the back. do you know what size the cable is? I was considering buying some 2/0 welding cable.

[Hotwire]

If you don't use the Camaro cables, whatever you purchase make sure it's multi stranded copper, not copper coated aluminum. The greater the number of strands the more current it can flow with less voltage drop.

Have you checked the voltage drop across the solenoid?

[dhutton]

Interesting. I didn't know those Camaros mounted the battery in the back. do you know what size the cable is? I was considering buying some 2/0 welding cable.

I can’t say with certainty but I am confident it’s all you will need.

Don

[Zachalanche]

Have you checked the voltage drop across the solenoid?

I have not. I'll check that next.

[Zachalanche]

I can’t say with certainty but I am confident it’s all you will need.

Don

I would just hate to find out it's the same size I already have after I buy it because that might also mean the problem is elsewhere. Sure, I could just buy something else so that I know what I was getting, but it would be nice to know what the late model Camaros use just for comparison. If I learned that they are using 4/0 I would know I was way off. (i assume it's not actually this extreme)

After a bunch of internet searching, I found one comment on a Camaro forum where someone thought it was 2AWG, but they didn't seem certain on that. other than that, the sizing of this Camaro cable seems to be a well-kept secret.