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 the 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