Chevy 305 compression question

[MDrex]

I have a mostly stock Chevy 305 in my T. It is from a 1980 car. It has 2 2-barrel rochester carbs on a custom intake manifold, Blueracer cam(still not sure on specs) and was told it has flat top pistons. I am under the inpression the head gaskets are stock type and the heads were not shaved.

My question is what is the stock compression on a 1980 305 and what would the compression most likely be with flat top pistons?

 

[Baby Huey]

I have a mostly stock Chevy 305 in my T. It is from a 1980 car. It has 2 2-barrel rochester carbs on a custom intake manifold, Blueracer cam(still not sure on specs) and was told it has flat top pistons. I am under the inpression the head gaskets are stock type and the heads were not shaved.

My question is what is the stock compression on a 1980 305 and what would the compression most likely be with flat top pistons?

These smog motors are kinda hard to track without some ID numbers..Remember Compression Ratio figures in the Combustion area("cc") of the cylinder heads too. So without knowing which heads you have it's just a shot in the dark..
LG3, 76-80,2bbl 8.5:1 Comp.
LG4,80-87, had increased compression (?)
L69,83-88, "High Output" 305, 9.5:1 Comp.
LE9 Truck, 9.5:1 comp.

With todays Fuel, I don't think I would increase the Compression much more than these figures..jus my 2 bits. "BH"
Check out your numbers here: http://www.mortec.com/

 

[donsrods]

I'm running 305 Vortec heads on my 350. It gives a little more compression because of the smaller chambers. Not sure how much more, maybe 1 to 1.5 points.

Don

 

[MDrex]

What are some easy, inexpensive things that I can do to get some more power out of this motor?

 

[Baby Huey]

What are some easy, inexpensive things that I can do to get some more power out of this motor?

You say it already has a cam and two-two barrels...How much MORE ya lookin for ? Whats your plan?
We need a little more info to make more recomendations I guess. I suppose if your lookin for a little more get up and go, you might check and see which ratio rear end gears you now have, maybe a set of lower gears could make it a little more snappy..."BH"

 

[MDrex]

Well, I just asked without really thinking about it. I'm not really at the point to make more power yet. I have to first get the carbs tuned right. It seems that the secondary carb is dumping too much fuel and flooding the engine. The car runs well at part throttle, but if I get on it more than maybe 40% the engine bogs real bad. I'm still in the process of figuring out what is wrong and how to get it running well. My biggest problem is I'm used to fuel injection and tuning with computers, I have no idea how carbs really work and how they are tuned. So right now its just a learning stage for me.

 

[MDrex]

As far as the engine, the code stamped on it is F1105CMJ. From that I got that it was built in Flint on November 05, 1980 and that it is a 305cid from an auto full size vehicle or Camaro.

 

[MDANIELSON55]

Compression Has Nothingto Do With Gas It Is The Pressure The Piston Produces In The Combustion Area A Compression Of 105 And Below Is To Low 130lbs Is Ideal . If U Dont Have The Needed Compression Rerun The Intake And Exhaust Valves . If Ur Comp Is Higher Smile Because Ur Engine Is Gona Run.

 

[Baby Huey]

Well, I just asked without really thinking about it. I'm not really at the point to make more power yet. I have to first get the carbs tuned right. It seems that the secondary carb is dumping too much fuel and flooding the engine. The car runs well at part throttle, but if I get on it more than maybe 40% the engine bogs real bad. I'm still in the process of figuring out what is wrong and how to get it running well. My biggest problem is I'm used to fuel injection and tuning with computers, I have no idea how carbs really work and how they are tuned. So right now its just a learning stage for me.

There ya go ! Ya jus answered your own question...Jerk the intake and carbs off the motor, go buy a fuel injection unit and install it and then hook up yur compter and have a ball ! More power, better gas milage, hi-tech..... "BH"

 

[MDrex]

There ya go ! Ya jus answered your own question...Jerk the intake and carbs off the motor, go buy a fuel injection unit and install it and then hook up yur compter and have a ball ! More power, better gas milage, hi-tech..... "BH"

That would be for a later project. This one I'm keeping simple, cheap and also kind of going for a traditional look I guess. I do want to do an ultra modern rod one day with a hot turbo fuel injected motor, independent coilover suspension, big brakes, modern wheels, carbon fiber and all that good stuff. But for now its just a simple old T.

 

[MDANIELSON55]

JUST BEHIND THE LEFT OR DRIVERS SIDE HEAD WHERE THE HEAD SITS ON THE BLOCK THERE WILL BE A NUMBER STAMPED IN THE BLOCK sorry about the caps get this number and look it up mortec then chevy small block this co. will have every block head serial no hope this helps mike

 

[MDrex]

Thanks, I'll look into that. The number I got was off the passenger side in front of the head.

 

[Photoman]

Well, I just asked without really thinking about it. I'm not really at the point to make more power yet. I have to first get the carbs tuned right. It seems that the secondary carb is dumping too much fuel and flooding the engine. The car runs well at part throttle, but if I get on it more than maybe 40% the engine bogs real bad. I'm still in the process of figuring out what is wrong and how to get it running well. My biggest problem is I'm used to fuel injection and tuning with computers, I have no idea how carbs really work and how they are tuned. So right now its just a learning stage for me.

Good luck with those carbs. The Roch 2GC carbs are VERY difficult to tune. Your best bet is to buy an Edelbrock Performer RPM intake and a 600cfm Edelbrock carb. Will run ~much~ better.