273 commando Build

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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.
 
you guys will have to look up my past posts about the Isky t3 cam I have installed in my 273 .
 
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 .
 
stroker402 said:
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
Click to expand...

When I mention a powerpeak, that is exactly what it says , the rpm at which the power on a dynograph has reached it's highest number.
This has nothing to with the engine's redline
nor to it's shift point.
It's just a powerpeak.
The peak can be long/relatively flat, or it can be short/narrow/ and pronounced.
In a given longblock, in most instances this includes with headers, this peak cannot be moved around much. Yes you can increase/decrease the horsepower number, a little bit, at the peak, with intake carbs spacers and so on, but fundamentally, the rpm of the peak doesn't change much. That will take a different cam, or at least a different LSA..

Your shift point, for a fast trap speed is related to the powerband requirement of the transmission. With a 4 speed this is easy cuz each gear is nearly the same shift split of about 72%. So then whatever rpm you shift at, in the next gear, the rpm will drop to about 72%. and you want the incoming power to be at or near the same as the outgoing power. With a 4-speed, this is gonna be about 400rpm past the peak power, depending on a host of engine parameters. So if your power peaks at 5000, then you might outshift at 5400, and you're looking for the same incoming power at 5400x .72=3900; thus your powerband is from 3900 to 5400. From there you gotta go out and test it. But thru the traps you wanna be very close to, if a lil past, peak power.
If you shift too early, your rpm will fall further down the powercurve, making your engine struggle to get back up on the cam.
If you shift late, you should come in at a higher power, but leave at a lower power. I like this a lil better, cuz this gives the car a lil kick-in-the-azz; but your engine has to survive the extra top-end rpm.
Now, if you have an automatic, that's a whole nuther thing.
So
If your engine is pulling past 5100, with a 222/108 cam, that only means one of maybe three things;
1) the cam you installed does not match the camcard you posted, or
2) the cam has flat-lined early, due to environmental complications, or
3) you haven't actually driven it fast enough to feel it nose-over, cuz until you do, there is not enough time to actually feel it.

The camcard you posted says 44* of overlap. With headers, that should put a nice lil power bulge on the power curve. With headers but a less than stellar exhaust system, or without headers at all; that would mean a long flat power curve/without a powerbulge, like a 340... So yeah, I get it, that you might think it's still pulling at 5800.

I assure you, that I have had bigger cams in much more potent SBM engines than your 273. I even had a cam similar to the one that you posted the camcard for, and while it was a nice hi-torque cam(223/230/110/51overlap), it peaked at around 5000.
Oh sure that lil cam pulled to 7200 as well, but it was way past pulling hard. I just went there cuz she sounded awesome, screaming thru dual 3" cannons, and she was happy about it. The thing is, until it hit mid-Third gear, there was no way to feel the nose-over, cuz at WOT, the tires were still spinning.

I'm glad you like your 222/222/108 cam but 050-wise, let's face it; it's just not that big.
Get yourself a windshield-mounted accelerometer and it will reveal the truth to you.
 
AJ/FormS said:
When I mention a powerpeak, that is exactly what it says , the rpm at which the power on a dynograph has reached it's highest number.
This has nothing to with the engine's redline
nor to it's shift point.
It's just a powerpeak.
The peak can be long/relatively flat, or it can be short/narrow/ and pronounced.
In a given longblock, in most instances this includes with headers, this peak cannot be moved around much. Yes you can increase/decrease the horsepower number, a little bit, at the peak, with intake carbs spacers and so on, but fundamentally, the rpm of the peak doesn't change much. That will take a different cam, or at least a different LSA..

Your shift point, for a fast trap speed is related to the powerband requirement of the transmission. With a 4 speed this is easy cuz each gear is nearly the same shift split of about 72%. So then whatever rpm you shift at, in the next gear, the rpm will drop to about 72%. and you want the incoming power to be at or near the same as the outgoing power. With a 4-speed, this is gonna be about 400rpm past the peak power, depending on a host of engine parameters. So if your power peaks at 5000, then you might outshift at 5400, and you're looking for the same incoming power at 5400x .72=3900; thus your powerband is from 3900 to 5400. From there you gotta go out and test it. But thru the traps you wanna be very close to, if a lil past, peak power.
If you shift too early, your rpm will fall further down the powercurve, making your engine struggle to get back up on the cam.
If you shift late, you should come in at a higher power, but leave at a lower power. I like this a lil better, cuz this gives the car a lil kick-in-the-azz; but your engine has to survive the extra top-end rpm.
Now, if you have an automatic, that's a whole nuther thing.
So
If your engine is pulling past 5100, with a 222/108 cam, that only means one of maybe three things;
1) the cam you installed does not match the camcard you posted, or
2) the cam has flat-lined early, due to environmental complications, or
3) you haven't actually driven it fast enough to feel it nose-over, cuz until you do, there is not enough time to actually feel it.

The camcard you posted says 44* of overlap. With headers, that should put a nice lil power bulge on the power curve. With headers but a less than stellar exhaust system, or without headers at all; that would mean a long flat power curve/without a powerbulge, like a 340... So yeah, I get it, that you might think it's still pulling at 5800.

I assure you, that I have had bigger cams in much more potent SBM engines than your 273. I even had a cam similar to the one that you posted the camcard for, and while it was a nice hi-torque cam(223/230/110/51overlap), it peaked at around 5000.
Oh sure that lil cam pulled to 7200 as well, but it was way past pulling hard. I just went there cuz she sounded awesome, screaming thru dual 3" cannons, and she was happy about it. The thing is, until it hit mid-Third gear, there was no way to feel the nose-over, cuz at WOT, the tires were still spinning.

I'm glad you like your 222/222/108 cam but 050-wise, let's face it; it's just not that big.
Get yourself a windshield-mounted accelerometer and it will reveal the truth to you.
Click to expand...
I under stand ......
why would isky tell me the peak power was at 2000- 6400 ?
I always had the rev limiter at 5900 and bounced off a few times and it felt strong and could not feel a dead spot nose over yet
 
stroker402 said:
I under stand ......
why would isky tell me the peak power was at 2000- 6400 ?
I always had the rev limiter at 5900 and bounced off a few times and it felt strong and could not feel a dead spot nose over yet
Click to expand...
if that cam was suppose to be all done under 4800 why would it still feel strong and still pull to 5800
 
If this isky t3 cam is that small I think I will not used it again in this new engine build . I'm going back to the big erson cam I had in previously.

old erson cam specs 1m286y​

here are the specs on the cam I had in my first 273 with the low compression pistons ........ pretty much the same cam as the d-dart , different number though >>> SOLID 1m286y advertised duration 286* - 510 lift . similar specs to the D-dart 273 I HAVE VIDEOS OF THIS CAM RUNNING IN MY BARRACUDA ... SOUNDS NASTY !

Part No.: E420721

Grind: HI FLOW I M

SOLID

107 Lobe Separation Angle



Overlap: 72.00



Intake Opens: 36.00 Exhaust Closes: 36.00



Intake Closes: 70.00 Exhaust Opens: 70.00



Running Clearance: 0.022 0.022 [Hot]



Valve Lift (Int / Exh): 0.510 0.510



Duration (Int / Exh): 286 286









Checking Figures @ .050" Tappet Rise



Overlap: 28.00



Intake Opens: 14.00 Exhaust Closes: 14.00



Intake Closes: 48.00 Exhaust Opens: 48.00



Duration Intake: 242.0 Duration Exhaust: 242.0



Lobe Lift Intake: 0.340 Lobe Lift Exhaust: 0.340



Intake Center Line: 107



Rocker Arm Ratio: 1.50
 
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