I installed a 383into my demon I don't have any specs on the motor I do know it sounds like it has a noticeable cam once the engine has run for about 20-30minutes it turns over very slow I installed a high torc starter with no change I unplug the coil wire no change the motor sound and runs great once it starts and it's operating temp is 160-185 even on hot days, any ideas? Thanks

Pulling the coil wire tells you it ain't from excessive initial or too high of DCR. Bad batt cell. heat soak in the starter. bad starter. poor cable connection. too high of eng drag when hot. cables to small (critical if trunk mounted batt). You've eliminated some of these. I'd clean EVERY connection/terminal starting at the batt positive post to its' cable & so on & the ground side also, starter to block, block to firewall, firewall (frame) to batt neg cable, both ends of that cable. Pull the plugs (do it quick while it is hot) & check turning torque on the crank bolt (1&1/4" socket/ft lb torque wrench).

Thanks I will try the cable cleaning first since I've already changed starters three times I think I can eliminate that, the eng drag your talking about is what scares me what is the cause of that? The eng I bought like it is supposedly good I dropped the pan and it looked like it was built recently(very clean)the pistons were clean and have.030 on them

Grounds grounds grounds.
the motor must be grounded well to the body and directly to the battery!

at least one ground back of motor to firewall (two may be better). then a bigger ground front of motor to the frame and battery

My battery is in the trunk so I split this heavy ground off and run a #8 ground wire to the battery where it goes to the negative post and is again split to the body. The battery also has a heavy ground to the body.

You can never have enough grounds. unibody front to back creates too much resistance to to be a good ground by itself.

Then if you have the battery in the trunk you should have at least a #8 wire (6 or 4 is better) from the alternator to the battery .
Doubled #10 will work. too much voltage drop going that far on a single #10.

If the battery is in the trunk should have a #1 or bigger wire from the battery to the starter and 4 or 6 up to the starter relay.

Also your amp gauge may be week bypass it by putting both wires on one terminal and getting a volt gauge.


what voltage is your battery at after the 1/2 hour drive??

If alt main wire goes in through dash and back out check both contacts at the bulkhead connectors and the amp gauge.

Thanks yes my batt is trunk mounted I did run a heavy cable positive side all the way to the starter but the neg I only ran to the rear frame rail and then from the front rail to the engine block I will run one from the batt to the engine block and see if that works the motor is mounted with a engine plate (aluminum)

let us know grounds grounds grounds!

I chased that problem for a while, it was the battery

You could put the battery tray back in up front & the original batt to relay/batt to block cables & a known good battery & rerouting/jumping the relay as needed then when it's hot & slow cranking see if it will crank normal from/with the battery up front which would tell you that it ain't the engines' drag nor the starter & that it's either the batt or the cables. With the headers being fenderwell & 3 different starters I would not be thinking the starter. Holler how it goes

Ran a heavy cable from neg bett term to starter bolt no help, I switched batts and that was no help, getting a 14.6 reading at batt while at idle,moved timing to 10degrees from 12 no help ,water temp is never over 185 :-(

I will try moving the batt to the front, I'm really running out of options the motor really seems to run great just doesn't want to turn over when warmed up hate to pull it out but... Have you heard of using a batt that is 16volts for starting that also has a 12volt post for running? Someone mentioned that also someone said I should add a retard box to my msd box to make it start easier?

Check your voltage at the start relay!

Then on both sides of the amp gauge

I would bypass the amp gauge by putting both wires on one terminal

Have you tried starting it (rolling it over) by jumping the starter relay??

check bulkhead connectors.

If it has 13 or more volts at the starter relay battery in the trunk is not your problem.

Start retard is not needed unless it is kicking back on the starter when trying to start.

I assume boosting it helps??

Did you try boosting it with positive to big nut on relay and negative to the block.

If the motor is getting real hard to turn over it could be for 1 of two reasons
1. pistons are forged and not enough clearance so they are tight hot

2. It has a turned bearing.

3 Overly tight pistons has caused a rod bearing to fail and turn.

Thanks again,I will try testing voltages at relay, and boosting it at relay, if it has any of the tight motor problems would it still run so good once it starts?

Yes on the pistons being tight and somewhat on a turned bearing if it's a bearing it will get worse.

I little starter switch to use at the relay to roll it over eliminates all the under dash stuff.

I had a problem like yours once and it was loose wires at the starter.

Once the main live from trunk and once the step up plug on the mini stater (that black plug is bolted to starter under cap I eliminated it.

Ok ,I'm ready to rule out grounds I have run Heavy cable from the batt to the starter bolts from the rear of the head to a large fender bolt from the front frame rail to the front of the head plus the three smaller grounds that were already there I took the bulkhead main wiring harness plugs apart and cleaned them ,once warmed up it still doesn't want to turn over, but runs and sounds great once I get it to start,I tried to start it at the relay but it was the same as with the key,maybe it's time for a timing retard box? HELP

If it has good grounds and 13 V at the starter relay look for loose bad connections.

as I stated above.

If you pulled the coil wire and it still rolls slow it's not timing.

you can have sufficient voltage, but you need amperage.... test for amps. we had a car in the shop the other day, 12.8 volts, but only 7 amps..... get an amp clamp and test.

Ok someone stopped by and listened to it and when i told them the history ,they said to try to advance the timing to 32 degrees, once this was done the motor woke up and starts good, they said someone had degreed the cam? anyway problem seems to be solved:-)