Think I found why my car's a gutless turd.

[V_TastyTacos_V]

Got a cam lobe go flat, and was pondering what to do next. Before jumping in with a solid roller, I decided to boroscope the cylinders. Looks like the motor was probably rebuilt. Has stock .020" head gaskets, but the pistons are completely flat except for the forward notch. No valve reliefs, and it's easily over .120" down the bore. Using a .060" wire as a gauge, the piston to head gasket clearance is 2.5-3 times it's thickness. Just .150" deck height, .020" head gasket, and 88cc for 906 combustion chamber, I get 7.14:1 compression ratio. Here's looking from the spark plug towards the intake manifold. You can clearly see the head gasket, the silver line, piston bottom.

This is looking forward, you can see the piston forward notch, but can't really tell where the top of the deck is, or what is the combustion chamber. Still, you can tell there's a ton of room. The curved line on top is the exhaust valve.

 

[Aron Gleason]

Interesting find. I read where the pistons i have are about .090 in the hole. I was wanting to go with a solid cam around a 590 lift. Don't know if that cam would work or if it would contact the valves.

 

[RemCharger]

Got a cam lobe go flat, and was pondering what to do next. Before jumping in with a solid roller, I decided to boroscope the cylinders. Looks like the motor was probably rebuilt. Has stock .020" head gaskets, but the pistons are completely flat except for the forward notch. No valve reliefs, and it's easily over .120" down the bore. Using a .060" wire as a gauge, the piston to head gasket clearance is 2.5-3 times it's thickness. Just .150" deck height, .020" head gasket, and 88cc for 906 combustion chamber, I get 7.14:1 compression ratio. Here's looking from the spark plug towards the intake manifold. You can clearly see the head gasket, the silver line, piston bottom.

View attachment 1873756

This is looking forward, you can see the piston forward notch, but can't really tell where the top of the deck is, or what is the combustion chamber. Still, you can tell there's a ton of room. The curved line on top is the exhaust valve.

View attachment 1873757

I can tell you with 99% precision that your car is not a turd due to deck height. It's everything else.

 

[V_TastyTacos_V]

I can tell you with 99% precision that your car is not a turd due to deck height. It's everything else.

So 6.8:1 to 7.1:1 compression is a good starting point for a muscle car?

 

[Aron Gleason]

So 6.8:1 to 7.1:1 compression is a good starting point for a muscle car?

More like 9.5 -10.5

 

[RemCharger]

So 6.8:1 to 7.1:1 compression is a good starting point for a muscle car?

This car ran 12.12 with that same bottom end. In fact, if you sent me your "turd", I'll bet I could do it again.

 

[RemCharger]

Same engine, almost identical car, 12.04
Ported 906,s .528 mopar cam. Big stall.

 

[Aron Gleason]

Same engine, almost identical car, 12.04
Ported 906,s .528 mopar cam. Big stall. View attachment 1873764

About 20 years ago I ran 12.16 @109 with a 284 484 purple shaft cam and with the car not running very good.

 

[RemCharger]

About 20 years ago I ran 12.16 @109 with a 284 484 purple shaft cam and with the car not running very good.

Probably had better than 7.xx :1 compression?

 

[Aron Gleason]

Probably had better than 7.xx :1 compression?

Its supposed to have 10.5 compression

 

[RemCharger]

Got a cam lobe go flat, and was pondering what to do next. Before jumping in with a solid roller, I decided to boroscope the cylinders. Looks like the motor was probably rebuilt. Has stock .020" head gaskets, but the pistons are completely flat except for the forward notch. No valve reliefs, and it's easily over .120" down the bore. Using a .060" wire as a gauge, the piston to head gasket clearance is 2.5-3 times it's thickness. Just .150" deck height, .020" head gasket, and 88cc for 906 combustion chamber, I get 7.14:1 compression ratio. Here's looking from the spark plug towards the intake manifold. You can clearly see the head gasket, the silver line, piston bottom.

View attachment 1873756

This is looking forward, you can see the piston forward notch, but can't really tell where the top of the deck is, or what is the combustion chamber. Still, you can tell there's a ton of room. The curved line on top is the exhaust valve.

View attachment 1873757

Tasty Taco when did you cc your heads

 

[V_TastyTacos_V]

Tasty Taco when did you cc your heads

You see what I'm doing. Even if I put a set of 78cc TrickFlows on it, I'm still only at 7.3:1 compression ratio.

 

[RemCharger]

You see what I'm doing. Even if I put a set of 78cc TrickFlows on it, I'm still only at 7.3:1 compression ratio.

No, don't see what you're doing. You don't know any of your specs you're guessing but that's fine. If it was a true. 154 in the hole with a true 88cc head and steel shim you're at 7.9 which is respectable. Make that a 78cc TF and you're at 8.5 even better. That puts you at 2 pts down from the TF dyno mule. Which isn't that great of a hp difference.

Once you understand compression is not the end all of hp, the sooner you'll just bolt some good heads on and enjoy the hp. And run cheap gas doing it.
Or continue your avenue of thought

 

[DanielSlocum]

Isnt it something that the factory over rated their advertised compression ratios on nearly everything? Very decieving and outright dishonest if you ask me.
Doing the math is definetly mandatory when planning an engine build unless you want bone stock.

 

[toolmanmike]

You see what I'm doing. Even if I put a set of 78cc TrickFlows on it, I'm still only at 7.3:1 compression ratio.

And thelack of compression will kill your performance. regardless which cam you use. The bigger the cam, the worse it is. Small chambered heads will increase your compression but usually no more than a half point or two. Flat top engines can run good as long as the pistons are close to TDC.

 

[icetech]

not sure bout the motor.. but i love that scope.. i can't bend mine up like that... very annoying

 

[V_TastyTacos_V]

No, don't see what you're doing. You don't know any of your specs you're guessing but that's fine. If it was a true. 154 in the hole with a true 88cc head and steel shim you're at 7.9 which is respectable. Make that a 78cc TF and you're at 8.5 even better. That puts you at 2 pts down from the TF dyno mule. Which isn't that great of a hp difference.

Once you understand compression is not the end all of hp, the sooner you'll just bolt some good heads on and enjoy the hp. And run cheap gas doing it.
Or continue your avenue of thought

You don't see that I'm using an endoscope to see how far in the hole my pistons are, and using a .060" wire to estimate the measurement? I thought I explained that. Using 2.5D is .150". Do you think 88CC is a poor estimate for a 906 combustion chamber? This is what that comes out to.

 

[V_TastyTacos_V]

not sure bout the motor.. but i love that scope.. i can't bend mine up like that... very annoying

It has two cameras, one forward, and one out the side. There's a mirror attachment to screw on the front, but it doesn't work for ****, so get the two lens version if you're thinking about it.
https://www.amazon.com/dp/B0C9JR3N4W?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

 

[icetech]

It has two cameras, one forward, and one out the side. There's a mirror attachment to screw on the front, but it doesn't work for ****, so get the two lens version if you're thinking about it.
https://www.amazon.com/dp/B0C9JR3N4W?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

yeah, when i got mine i didn't see any of that dual camera stuff... A scope is about my favorite tool now, it comes in soo handy

 

[PRHeads]

That’s got to be the lowest CH 383 piston ever made.

A Silvolite 1271 replacement piston has a CH of 1.848, which would theoretically put them at .0865” down the hole……..which works out to 7.8-7.9cr with a .020” gasket and 88cc heads.
And those aren’t any type of performance parts.

Pistons .150” down the hole in a 383 is not a foundation I’d be building upon.

For reference, the Silvolite replacement 400 piston would be .122” down the hole.

Any idea if the shortblock is supposed to still have the factory pistons in it?