chillz

sorry this is a non thirdgen question, im just very desperate

i recently purchased a 68 firebird with a 350 pontiac block in it. it has msd ignition, msd 8.5 wires, and msd pro billet dist. (with no vacuum advance, mech only)

i went to set the base timing on it, and have come across a very odd problem. it seems to run best at like, 50 deg. BTDC (way beyond the range of the timing tab) it wont even run within the range of the timing tab unless i turn the idle way up, then it runs poorly (and hot)

i used a TDC stopper to verify that the 0 deg. mark on the dampner lines up with the #1 slug (drivers side front) at TDC, and it is right on the nose. i tried two different timing lights incase one of them was faulty.

this makes no sense...??? very confused...any ideas? idle is 800 rpm or so, and the mech advance doesnt start till about 1000

please help!!

-dustin

83CrossfireBomb

did you have the pick up lead attached to the correct plug wire?

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former 305 crossfire fuel injection
350 cubes
hooker headers
750 vac secondary
700r4 with shift kit
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"no man with a good car needs to be justified."

88305tpiT/A

iTrader: (2)

I had a similar problem with my computer controled ignition and it turns out that the aftermarket ignition had to be disconnected to correctly set the timing.
if you can go back to the origional ignition wiring for the distributor and coil, then set the timing, then reconnect your MSD.

chillz

thanks for the resonses. i've been thinking this over and talking with some other folks..

this car has no computer and no vac advance, only mech. this timing has to be accurate (yes i have the pickup on the #1 plug wire).

i did a cranking compression test and i only get 100-110 psi with the butterflies open. i also have no low rpm torque at all, and only 5" of vacuum at idle (.485/.511 lift cam, measured with dial indicator, unsure of duration guessing ~230)

my only conclusion at this point is that this cam isnt degreed properly, giving me very low low rpm compression, thus requiring the 50 deg. btdc. i'm still fishing for any other explanations though... i know for a fact that the guy that put this cam in is a knucklehead...

is there anything else that would cause these symptoms?

TIA!

Pony Killer

Remember the distributor in a pontiac rotates backwards of a chevy, the firing order is still 18436572, but, it rotates counter clocwise, and the #1 plug on it, is where the #8 Plug is on a chevy

chillz

yes, reverse rotation of the chevy..got that. the cyls 1 - 8 are still in the same position though. after speaking with some folks, it seems as if there are some bigger problems with this engine, the guy that built it was a real piece of work. i think ill just drop in a new 400 and be done with it.

Pony Killer

got the cam in wrong>?

Damon

110 cranking compression is not that unusual. 8:1 compression motors of the early-mid 70s vintage often have low compression readings. Stab in a hotter cam and they end up REAL low.

When the cam is too big for the motor you will often find that the ignition wants to be be WAY WAY advanced from where you would normally set it. You can advance it until you're biting your fingernails and sweating with nervousness and it will take even more. Big cams and low compression don't play nice together.

Typical big cam behavior will be just pathetic bottom end torque up to about 2500-3000 RPM after which you'll hit the afterburners and make pretty good progress. It will also idle very rough no matter what you do with the timing and carb.