Melt down

[Anonymous]

Are you the only one out there John.

Yea , the pickup wires reroute into the controller , which retards the spark , but whichever way you look @ it , the spark is retarted to the rotor arm , as it cannot mechanicaly turn the distributor housing , i confirmed this with a timing light.

When the motor is running with no retard taken out via the controller , the rotor tip is just passed the cap terminal , heading towards the next cylinder in line to fire , i checked it to be around 10/12* crank rotation out of phase , bearing in mind there is around 45* crank rotation between towers , probably less due to the wide tip on the rotor arm , this leaves around 33* crank rotation til the rotor hits the next cylinder , add this to the 12* retard the controller pulls , this leaves 25* of crank rotation before the next cylinder in line , with the pressure in the cylinder i'm sure it misfired to the next terminal , which would have fired it when the piston was around 70* BTDC , now was the intake valve still open on that cylinder? , lookin @ the valve events it puts that intake valve pretty much near the mark , if you add the 23* of total advance it all seems to stack up.

Maybe i'll phase the rotor tip @ the leading edge & not the middle , bearing in mind the width of the tip , might be better off fileing the tip a bit.

[AllKiller]

Adam, again im no expert on this but is it at all possible the controller blipped and caused it....i would err on the electrical side....and Jacobs stuff is just as fallible.
My Jacobs ignition box packed up slowly, making the car run worse and worse above 3 grand until it died some weeks later.

Can you check that at high RPM

[Anonymous]

Good point Steve.

As we all know , @ high RPM everthing starts to go funny , but the box does pull what is indicated on the dial , i've checked it from 0* right through & upto 15* , the misfire is always when i run a bigger shot & pull more timing. , which would make sense , it's all i've got @ the moment , appart from the unusually hot day , also an intake valve slightly letting by which could of been caused when it took a bite on the demon.

[steveo]

blimey Adam you was lucky there was not more damage , was at the top end when you ran a 11.1 seven i think ... sounded like you hit the revlimeter just before the the lights defo would of been a 10.99 or 8 i'm thinking if it wernt so hot that day .. cooler air i'm sure you will see 10.99 or something , did not see the run when it backfired ..as left early , the runs i saw ( pit) sounded strong
was the paint damage just on the underside ???

[Anonymous]

Thanks Steve.

Gotta have the bonnet repainted (blistered top) & the electrics sorted on bulkhead , also gotta get another carb.

Just waiten on parts @ the mo , rod bearings , rings , cam & lifters , bla bla.

Probably a god send , as the top rings were shot , this was due to the nitrous.

Wifey wants a holiday too.

[Anonymous]

After further chats with Adam I think he is onto something here, we checked a standard Mopar vac dizzy and it was in fact firing at the point where the rotor arm had almost passed the tower.
Taking the thinking a bit further with the hammerhead rotor arm on the Msd non vac billet dizzy the Jacobs controller retards the firing which would put the rotor well past the firing tower towards the next tower.
Although Adam did not here any massive detonation there were signs showing on the plugs and the detonation meter was starting to light up at higher revs.
I have always assumed that detonation occurs on the firing cylinder i.e. the firing cylinder fires early when the piston is on the up stroke due to carbon or the plug tip glowing but in Adams case there were no carbon build up and the plugs were 2 clicks colder.
Now this is thinking out of the box a bit but here goes.
We now the problem occurred at higher revs.
The jacobs controller was set to approx 12 degree of retard putting his phased rotor past the firing tower.
He was running a 400 shot of NOS.
One of the intake valves was letting by slightly.
That he had a top end misfire.
The MSD box whacks out a bigger single charge above 3k.

Now if the rotor was phased then the charge would take the least line resistance.
With the firing cylinder on compression and the next cylinder coming up to compression and the rotor approaching the next tower I figure the rotor either dual sparked or single sparked the next cylinder which was on its compression stroke the inlet valve would have just closed depending on his cam
As Dave mentioned earlier the higher the revs the worse the problem.
That would explain the detonation not on the firing cylinder but the next one such that the compressing cylinder was "Pre fired" thus causing the detonation and the misfire.
This "Pre fire" would have repeated itself through the run cycle effecting all the cylinders.
Eventually either a valve had not fully closed due to the cam rev's combination or the cylinder with the slight leak on the inlet valve has let past a jet of pre ignited charge into the inlet manifold igniting the fuel Nos mixture and the rest is history.?

[Anonymous]

Good point regarding the detonation , maybe if i had'nt of pulled that amount of retard to avoid detonation , the motor would'nt of misfired & caused the detonation on the next cylinder , sooooo , me pulling timing caused the detonation , ain't life a bitch.

Only way forward is a crank trigger , which makes light work of phasing (just turn dizzy) , but i need the advance curve when on the road , can't fit the adapt a cap either as it will hit the valve cover (anyone using one on a RB?) , so i reckon the max retard you can pull on a correctly phased cap in in the region of around 20* , that's around a 500/600 shot of gas (roughly speakin) , so fine for most applications.

[Anonymous]

Adam if you had been running a 600 shot I think your carb may have got back to the pit's 5 min before you did

[Anonymous]

Or the motor would of eaten all of it.

[AllKiller]

Dont take so much timing out Adam, i know its advised to do so, but they dont want you lunching your motor.

Mine didnt like it when i pulled out the amount of timing you suggested when running my gas....hence the major backfire and stall on the line and during staging.
Put it back 5 degrees and it was better with the gas, so only took out 5 degrees instead of 10, motor ran a treat....then ran out of Gas

[Pete]

Could not the cylinder have "self-detonated" due to a hot spot and was infact never "triggered" by the inition system in the first place?

[AllKiller]

Have you got shrouded ( recessed) tip plugs ?? that will help the glow plug effect

[Anonymous]

Running NGK 8s , which have the short ground strap , the timing was'nt far away when looking @ the plugs , heat on ground strap was spot on so indicated timing was good also porcelaine looked ok with no signs of detonation, maybe i could of gone to a colder plug & dialed in a little more advance , will try a different plug next time.

Have you checked the rotor phasing Steve? , i don't think you pulled enough timing to cause the problems you had off the line , i think you pulled 2* per 50 shot with no margin for error , bearing in mind you have around 11.5 com ratio , did you puge into the motor? , or did you sort out the purge solinoid?

Don't think there was any pre-ignition goin on , as this would of showed on the plug tips , or what would of been left of em.

Was thinking the pickup wires were getting interference as there not shrouded & run along with the rest of the loom , but alls good running off the bottle.

Tis frustrating trying to chase high end misfires.

[AllKiller]

DYNO TIME ADAM
Perfect touch are near you

[Cannonball]

Running NGK 8s , which have the short ground strap , the timing was'nt far away when looking @ the plugs , heat on ground strap was spot on so indicated timing was good also porcelaine looked ok with no signs of detonation, maybe i could of gone to a colder plug & dialed in a little more advance , will try a different plug next time.

Have you checked the rotor phasing Steve? , i don't think you pulled enough timing to cause the problems you had off the line , i think you pulled 2* per 50 shot with no margin for error , bearing in mind you have around 11.5 com ratio , did you puge into the motor? , or did you sort out the purge solinoid?

Don't think there was any pre-ignition goin on , as this would of showed on the plug tips , or what would of been left of em.

Was thinking the pickup wires were getting interference as there not shrouded & run along with the rest of the loom , but alls good running off the bottle.

Tis frustrating trying to chase high end misfires.

whats the deal purging into the mtr