273 commando Build

-
Newbomb Turk said:
Ok, I’m a bit lost (again lol). That failure looks like detonation. Across from the plug, that’s what it looks like.

Did you post pictures of your plugs? Did you say your compression ratio and cam timing? I apologize if you did.

If you are getting oil in the chambers and you are already on the edge of detonation that will send it right into detonation.
Click to expand...
the first two times the gasket failed it blew out on the lower part of head by spark plugs ... the last two times it blew in to the valley
 
stroker402 said:
I read that felpros have NO need to re torque. just say in
Click to expand...


Yup, that’s what they say. I retorque them because they get loose.

My brother had a 440 in a Dart in 1984ish. It had composite gaskets like that. Blew the gasket.

Almost all the bolts were loose on both heads. Both gaskets were failing. The failing gasket caused the bolts to get loose. It’s a self feeding problem.

That was detonation. My brothers buddy in auto shop put his whiz bang tune up on it.

Once the detonation was gone and the heads retorqued it didn’t fail.
 
stroker402 said:
the first two times the gasket failed it blew out on the lower part of head by spark plugs ... the last two times it blew in to the valley
Click to expand...
champion n9y cold plug timing 16* initial 18 mech 34 total commando engine with domed pistons composite head gaskets 318 compression maybe around 10:1 .. 150 # cyl compression
 
Newbomb Turk said:
Are those pictures in this thread?
Click to expand...
that pic is from the last time it blew gasket 2 cyls into the valley 2 and 8

273 blown head gasket best .jpg


IMG_20241101_145331 my cuda head gasket #8 cyl blown.jpg
 
plugs all looked fine a nice light tan brown color champion n9y .035. the timing mark on the spark plug strap was near the base ring not an the curve point on the strap. timing set at 16 initial 18 in the plate and 34 total.
 
Newbomb Turk said:
Ok, I’m a bit lost (again lol). That failure looks like detonation. Across from the plug, that’s what it looks like.

Did you post pictures of your plugs? Did you say your compression ratio and cam timing? I apologize if you did.

If you are getting oil in the chambers and you are already on the edge of detonation that will send it right into detonation.
Click to expand...
the engine did not have oil in the cyls did not smoke or burn oil . it was a excellent running commando before the gaskets started leaking .
it just did not like the secondaries to be opened ... pedal to the floor ... full power .
 
Just so you know;
The Wallace calculator predicts, with cam of 260/260/106, in at 104, with a true Ica of 54*, points to 150psi at ~8.85Scr.
But, because it's a solid lifter, I have no idea when the intake actually closes.
Probably a couple of degrees earlier
At 52*, 150psi would be ~8.75Scr.

So; if your Scr was a true 10:1, and
the intake actually closed at 52*,
then the Pressure could be as high as ~179psi;
Or if the Leakdown was 16%, then yur back to 150psi. But if your LD was that bad, she'd likely be a bit of an oil-burner, leading to detonation.
If your pistons are at zero deck, and with closed chambers, your Quench equals the gasket thickness....... your gonna need a dash of luck running @.028Q, @179psi, @WOT, on pumpgas, with iron heads.
So;
IMO, you need to get to the bottom of your actual Scr and true-pressure;
or your problems may continue; asin ............
maybe the gauge you used was wrong.

For a given Scr, your 273 total chamber volume would need to be, see below;
with predicted pressure following, using an Ica of 52*
For 10/1, 62.1cc; 179psi
For 9:1, 69.9cc; 156psi
For 8:1, 79.9cc; 133psi
The Wallace is usually pretty close.

The thing that peaked my interest was;
new rings on old pistons, in high-mileage bores.
How sure are you that;
the bores were round and not tapered?
that the ring-lands were sealing?
the pistons aren't rattling up and down because of too much clearance?
You know that the rings have to also seal on the lands right......... and you admitted that the grooves were heavily carboned..........
If cast rings have to follow tapered bores, the lands will not last long, and if simultaneously the rings are rubbing on carbon, even less long.
If the bores are not round, the oil-rings will leave oil behind. Oil in the air-fuel charge leads to detonation. which creates tremendous cylinder pressure.
And honestly, why would you push a 222*@050 cam, that peaks at under 4800 in your 273, and especially in a used-piston 273, past say 5300 which would already be high for those factory heads (and a 4speed)? Why?
Don't answer, I know why; but it's not working very well, is it?
Just saying.

but what's even more intriguing to me,
is that yur gonna try again
with another 273.
And no, I'm not a 273 hater; yur the one killing them.
 
Last edited:
stroker402 said:
plugs all looked fine a nice light tan brown color champion n9y .035. the timing mark on the spark plug strap was near the base ring not an the curve point on the strap. timing set at 16 initial 18 in the plate and 34 total.
Click to expand...


At what rpm is the timing in. There should not be brown on the plug. That’s fat.

Edit: At your compression a 9 is too cold.
 
Newbomb Turk said:
At what rpm is the timing in. There should not be brown on the plug. That’s fat.

Edit: At your compression a 9 is too cold.
Click to expand...
Agree. The 9's are too cold. I converted to Autolites and somehow ended up with a 8 heat range. I always had a rough/rich idle I couldn't tune out. I switched to 12's and it immediately cleared up. They have been in for 10 years now.
 
AJ/FormS said:
Just so you know;
The Wallace calculator predicts, with cam of 260/260/106, in at 104, with a true Ica of 54*, points to 150psi at ~8.85Scr.
But, because it's a solid lifter, I have no idea when the intake actually closes.
Probably a couple of degrees earlier
At 52*, 150psi would be ~8.75Scr.

So; if your Scr was a true 10:1, and
the intake actually closed at 52*,
then the Pressure could be as high as ~179psi;
Or if the Leakdown was 16%, then yur back to 150psi. But if your LD was that bad, she'd likely be a bit of an oil-burner, leading to detonation.
If your pistons are at zero deck, and with closed chambers, your Quench equals the gasket thickness....... your gonna need a dash of luck running @.028Q, @179psi, @WOT, on pumpgas, with iron heads.
So;
IMO, you need to get to the bottom of your actual Scr and true-pressure;
or your problems may continue; asin ............
maybe the gauge you used was wrong.

For a given Scr, your 273 total chamber volume would need to be, see below;
with predicted pressure following, using an Ica of 52*
For 10/1, 62.1cc; 179psi
For 9:1, 69.9cc; 156psi
For 8:1, 79.9cc; 133psi
The Wallace is usually pretty close.

The thing that peaked my interest was;
new rings on old pistons, in high-mileage bores.
How sure are you that;
the bores were round and not tapered?
that the ring-lands were sealing?
the pistons aren't rattling up and down because of too much clearance?
You know that the rings have to also seal on the lands right......... and you admitted that the grooves were heavily carboned..........
If cast rings have to follow tapered bores, the lands will not last long, and if simultaneously the rings are rubbing on carbon, even less long.
If the bores are not round, the oil-rings will leave oil behind. Oil in the air-fuel charge leads to detonation. which creates tremendous cylinder pressure.
And honestly, why would you push a 222*@050 cam, that peaks at under 4800 in your 273, and especially in a used-piston 273, past say 5300 which would already be high for those factory heads (and a 4speed)? Why?
Don't answer, I know why; but it's not working very well, is it?
Just saying.

but what's even more intriguing to me,
is that yur gonna try again
with another 273.
And no, I'm not a 273 hater; yur the one killing them.
Click to expand...
when did compression checks it was always a tad over 150# with stock domed pistons and composite 318 head gaskets at3.90 bore fire ring. I believe compressed gasket was approx .039. I thought compression would be more that 8.8
 
AJ/FormS said:
Just so you know;
The Wallace calculator predicts, with cam of 260/260/106, in at 104, with a true Ica of 54*, points to 150psi at ~8.85Scr.
But, because it's a solid lifter, I have no idea when the intake actually closes.
Probably a couple of degrees earlier
At 52*, 150psi would be ~8.75Scr.

So; if your Scr was a true 10:1, and
the intake actually closed at 52*,
then the Pressure could be as high as ~179psi;
Or if the Leakdown was 16%, then yur back to 150psi. But if your LD was that bad, she'd likely be a bit of an oil-burner, leading to detonation.
If your pistons are at zero deck, and with closed chambers, your Quench equals the gasket thickness....... your gonna need a dash of luck running @.028Q, @179psi, @WOT, on pumpgas, with iron heads.
So;
IMO, you need to get to the bottom of your actual Scr and true-pressure;
or your problems may continue; asin ............
maybe the gauge you used was wrong.

For a given Scr, your 273 total chamber volume would need to be, see below;
with predicted pressure following, using an Ica of 52*
For 10/1, 62.1cc; 179psi
For 9:1, 69.9cc; 156psi
For 8:1, 79.9cc; 133psi
The Wallace is usually pretty close.

The thing that peaked my interest was;
new rings on old pistons, in high-mileage bores.
How sure are you that;
the bores were round and not tapered?
that the ring-lands were sealing?
the pistons aren't rattling up and down because of too much clearance?
You know that the rings have to also seal on the lands right......... and you admitted that the grooves were heavily carboned..........
If cast rings have to follow tapered bores, the lands will not last long, and if simultaneously the rings are rubbing on carbon, even less long.
If the bores are not round, the oil-rings will leave oil behind. Oil in the air-fuel charge leads to detonation. which creates tremendous cylinder pressure.
And honestly, why would you push a 222*@050 cam, that peaks at under 4800 in your 273, and especially in a used-piston 273, past say 5300 which would already be high for those factory heads (and a 4speed)? Why?
Don't answer, I know why; but it's not working very well, is it?
Just saying.

but what's even more intriguing to me,
is that yur gonna try again
with another 273.
And no, I'm not a 273 hater; yur the one killing them.
Click to expand...
another thing isky told me was this t3 cam was good from 2000 to 6400 peak power. the engine seemed really happy around 5800 and was still climbing .. I never took it above 5800.
from what you are telling me this t3 cam was all done pulling under 4800 is not even close . I can assure you of that lol
 
I never received a call back from ARP fasteners today either and they were sort handed and need more help he told me.. what gives ???
 
Newbomb Turk said:
Yeah, that’s fat. Light tan is fat.
Click to expand...
Newbomb Turk said:
Yeah, that’s fat. Light tan is fat.
Click to expand...

spark-plug-lean-rich-optimal.jpg

click on pic to see all three type conditions.. mine never ever looked like the middle pic or the one on the right pic . all mine looked like the lean pic by reference . this pic is not my plugs just a reference .
 
You must log in or register to reply here.
-

Back
Top