[BLK/RD462TA]

Hi Guys, I've been around but not active on here for some time. I have a 1978 trans am with a 455 with butler 290 cfm 72cc heads with diamond pistons with a 20cc dish. 0 decked with a fel pro 1016 gasket 39cc 4.3000 bore. when I first built the engine it did it on a couple plugs. My car weighs 3,800 lbs and has 3.42 gears. Trans is T350 with ATI 3200 stall converter. total timing was creeping past 34 deg to 36 with offshore dist. Since then I put factory weights in and have 8 deg initial
I cant hear any audible detonation or ping. When i run the numbers on wallace using seat duration dynamic is low like 150 psi but it pumps 180 cold. Cam is it butler custom 236/242- 287 293. 520 540. 112 LS lift with scorpion 1.65 rockers. Static compression around 10.11. I think? I didn't cc everything when assembled. Cam was ground with no advance so I put it in at 112. I'm thinking with the short seat timing i should retard it to 115. I am at sea level and when its hot it bucks the starter a little. There was hardly any aluminum on plug this time going from autolite 3924 to 3923. Also how much bigger duration cam can i put in with my stats. When i use the dynamic calculator @50 the crank pressure looks close but dynamic is 9.0. Im stumped what direction to go. Right now im at 8 deg intial with 20 mech so 28 total. car runs awesome . hope to detune to much but if it keeps motor alive so be it. Thanks

[Scott65]

Have you verified the timing marks are right at true tdc? Your combination as listed shouldn't be detonation prone.

[BLK/RD462TA]

When i first put it together 3 years ago it was on and installed at intake closing 49 deg. I had a timing cover leak and installed a new cloyes double roller. I didn't degree it because of having back issues. I know.. But it pumped 180 cold crank psi. before it was 190 ish hot. I did change the 750 vac for a quickfuel 830ss. It didn't seem to make a difference. only wildcard is not sure if piston dish was 20 or 22 cc. Its been a while and I'm new at this don't know how to post a picture of plug. It was a couple before now its barely one with colder plugs. not sure if I should back timing to 6 initial and 26 total if that'll hurt performance. The dynamic doesn't add up when i use seat to seat intake figures. which converted is 75.5 closing. Or 50 deg @ .050

[BLK/RD462TA]

Its not peppered porcelain. its looks kinda like a spec of solder. I did notice from some older pics of new heads that where spark plug threads protrude in head there was some sharp slivers of aluminum. I should have checked for sharp edges during assembly but i didnt. Wandering if i should inch timing up to see where it pings? I think im close but who knows. Im afraid to hurt it.. maybe I just need to monitor it with timing curves . Im afraid if i retard it more from straight up its gonna be a dog.

[Scott65]

I'm talking about checking your timing marks that you use to set ignition timing. If your balancer has slipped, or if the use of aftermarket parts has some tolerance stack, you may be running very different ignition advance than what you think you are. 20 or 22 cc dish should put you at less than 10.5 compression with the gasket and other parts you listed. That shouldn't be detonation prone if everything is right.

[BLK/RD462TA]

It is a new timing cover aftermarket. this cam has really short seat timing 287 and 293. Guess i should put the deg wheel on it again. tell ya i never heard any ping. It a pain degreeing a cam in car but i guess that would help some. I see what you are talking about Scott. i need to recheck things. Thanks

[Scott65]

What are the details of the ignition system? There are things that can go astray to cause over advanced timing with that as well. But an improper timing mark will make diagnosis difficult to impossible. I'd verify that first.
ETA, some pictures of the plugs, both the 3924 and 3923 would probably shed some light.

[BLK/RD462TA]

Here's a pic before the colder plug. Generally 2 cylinders did this since put together 3 years ago. Of course I don't drive it much and parts change along the way. Basically installed factory pontiac centrifugal dist weights and centerplate. Its better now just didn't know if 6 deg initial and 26 total was too low. I should have took notes all the time but unfortunately I didn't. thanks

[Jay S]

If you could would it be possible to see a closer up picture focused on the spark plug electrode, strap, and maybe a close up of the bottom couple treads on the plug?? Gets too fuzzy when I enlarge the pic.

[steve25]

Ok, first off I have some questions!
So you have a 455 that’s at a 4.300” bore which is .150” over, so is this a factory block?

So that makes your motor 489 cid, not 455 or 462 for that matter!

Next, judging by the long plug in your your running Aluminum heads?

Are you running headers?

You posted that the Fel Pro gasket is 39 CCs, it’s not, it’s 9.4 CCs and it crushes to .039”.

When I run your numbers to calculate compression I come up with 10.7 with factoring in 2 CCs in ring land volume for those big bore pistons.

I don’t see a 10.7 compression being a problem with that Cam, and 180 cold cranking should not be a issue if the timing and jetting are good.

If your stating that the 1016 gasket is at 4.300” then that’s right .

If your 455 is .030” over then your compression is
10.1 to 1 .
My 462 bucked and failed to crank at times also even with a Ford solenoid over riding the GM one and I only had 8.5 compression due to running a Blower.

I finally wired in a ignition kill switch to get the motor rolling first before applying the spark.

Your Plug color looks good though !

Sorry for jumping around in this, but I am driving and doing the illegal texting at stop lights, lol!

[BLK/RD462TA]

My mistake. 455 35over. Standard 4.21 stroke. so that would be 4.186 bore. Yes edelbrock d port 290 cfm. yes about the gasket crush .039. originally my timing was creeping with offshore distributor. up to 36 when set at 10. It seems my combo isn't off base.I heard these heads dont what any more than 34 deg total. I also noticed that there might be some aluminum burrs where spark plug enters chamber. problem is when i checked plugs i just scraped it off with fingernail and didnt think much about it untill it reoccurred. Its almost non existent now with colder plug. Could a sharp burr from spark plug threads get hot and melt? Thats my theory cause i shouldnt be detonating.

[steve25]

Possible yes!
For street running there is not any reason to run at maxed out timing off let’s say 34 degrees, so if running 2 degrees less still affords you a livable idle and off idle response then due so.

You will feel far more at ease when your foot in it hard!

PS, you should give a Butter film coating of Antisize on your plugs with Aluminum heads,

[BLK/RD462TA]

Don't get in a accident cause of me bro. It can wait till your stopped. I checked total other day it was at 28 around 3000. I should've revved it past that to see if it creeps past 28. Also starter briefly bucks on a hot summer day and honestly not sure if battery is at full charge cause it sits more than it drives. My numbers match yours for compression. Maybe my whole problem is timing weights creeping past 3000 rpm. I had a coolant leak and while it was drained down I was gonna retard cam timing some .But if you think combo is good I'll recheck dist total again. Car is loud with 3" exhaust and windows down listening for pinging.

[steve25]

It’s very common that light dizzy springs that allow full advance below 2K will allow the timing to slap around and go above where you have it set.
They also fatigue very fast and cause loss of control.
I have some burned up race motor rods from 32 years ago due to spun bearings to prove that, lol!

Also I should have mentioned that Aluminum blasted off of pistons or heads due to detonation shows up on the plugs as purplish shinny balls .

Also in terms of coolant flow I do not like the way the water cross over passages cast into Edelbrock manifolds is far far smaller then the passage in the heads.
I always open them up on a motor that will see any kind of street usage, even if its limited to non highway!

[Jay S]

If the area of question is in the traced circle, that does not look like anything related to preignition to me. Preignition generally is smaller speckles of AL around the porcelain, nothing that big.


FWIW, the plugs heat looks good to me. I came up with 10.25 SCR, the DCR is down in the lower to mid7s, (using the seat timing), the cranking compression looks ok and about what would be expected.

Looking at the cam in the engine to me it appears like a cam that would prefer some advance. Retarding it from where it is at likely will not help anything, and make it run a little worse.

Not sure what that is, something off the threads is as good as guess as any.

[BLK/RD462TA]

I appreciate everyone's advise. You guys are making me feel better about the detonation. I will check my balancer marks and check again to see if my total creeps up past 3000 rpms. Not to drag this thread out too far but what confuses me about the wallace dynamic calculator using seat timing is it says 7.49 dynamic and should crank 149psi. Ok but I'm near 180 cold psi. Guess I'm missing something. I entered 75.5 intake seat timing.

[Elarson]

Regardless of the numbers, any aluminum on the plugs is the engine telling you it's detonating. Take a couple degrees of timing out and let the engine live a long happy life.

Eric

[Jay S]

Originally Posted by BLK/RD462TA

I appreciate everyone's advise. You guys are making me feel better about the detonation. I will check my balancer marks and check again to see if my total creeps up past 3000 rpms. Not to drag this thread out too far but what confuses me about the wallace dynamic calculator using seat timing is it says 7.49 dynamic and should crank 149psi. Ok but I'm near 180 cold psi. Guess I'm missing something. I entered 75.5 intake seat timing.

Your overlooking things like the Wallace DCR calculator doesn’t account for things like the roller cam profile and design, LSA, rocker ratios, head CSA and port velocity. Each one of those can make smaller percentage changes. It also uses some different cranking speed and pressure parameters that create minimum cranking pressure numbers. There are different ways you can calculate V/P index and come up with different cranking pressure.

Would still like to see a super close up pic of the porcelain on the electrode. If your fighting a coolant leak it could be the engine had a hot pocket or temp spike that caused some preignition. May not be anything to do with the tune.

[BLK/RD462TA]

Thanks for everyone's advice. Jay I did have multiple coolant leaks. One was pin hole in heater hose, then heater core leaked, lastly one timing cover bolt wasn't sealing in block. It seemed like every time I took it out which isn't much overflow tank was low. It could have been a hot spot. I think all the leaks are repaired at this point. I also replaced a stuck hydraulic roller lifter on that bank. Its hot here now so I will put fresh plugs in and monitor my timing and new spark plugs and take notes. Unfortunately, Scott I cleaned off the splat on the current colder 3923 autolite plug and didn't get a picture. It was barely on porcelain this time. I think I'm on the edge with timing in summer when its 90ish degree's out. I do have 1.65 rocker arms if that matters.

[steve25]

Actually you may be over scavenging the cylinders with those 1.65 rockers on the Exh side of the motor ?