Whats the advantage of low compression?

I don't know which 134 I have, the low compression (6.9:1) or the (7.4:1)
What would be the advantage of having the lower compression ratio?

http://www.jeeptech.com/engine/hurricane134.html

53' cj3b

 

different grade(s) of gas? [like 87 vs. 93]

 

What he said.

Weren't the higher compression engines designed for high alititude operation?

 

Easier to start by hand as well. The MB could be hand cranked if need be.

 

In their origins higher octane fuels weren't available. These ratios were the standard in the industry until the fifties.

 

Lower compression means less power, so there's a price paid for being able to run low octane gas. Both 6.9:1 and 7.4:1 are way low by modern standards.

 

Engines that have lower compression will idle slower (much slower) and lug down to a slower rpm before stalling.

 

And the best one... You can force more air in before detonation occures with a supercharger/turbo/NOS

Everyone else is right though. I just wanted to say that.

 

This is an interesting conversation. Now, I'm wondering how I tell which motor I have. In the day, were the 7.4 motors considered "high" compression? I remember Dad talking about compression braking differences (not necessarily between these two motors), and lugging capacity. I also remember that up until I turned my rig over to a rebuilder (who muffed a few little items) I had a high altitude carb needle hanging by a wire off the carb. Got lost, somewhere. Short of a teardown, any info on bore / stroke combos, or combustion chamber volume? I guess I just answered that question, but still, any way to tell?

 

I think he means 7.4 to 1 compression ratio...not engine displacement

 

i believe he was referring to an f134 with 7.4 to 1 compression ratio.

JB

 

On the older vehicles it was for all the reasons mentioned plus the fact you could get them to run on whatever was available during war time. On late model cars the reason for lower compression ratio is to reduce NOx or nitrogen oxides, a green house gas caused by high combustion temperatures. That was the real reason for the demise of many muscle cars in the early 70's. Nickmil.

 

Just bein' picky... NOx (a collection of the common oxides of nitrogen) is now thought of as a "greenhouse gas" but was targeted initially because it is a major component of photochemical smog. If you've spent time in the LA area in the summer, the brown haze in the atmosphere is due to nitrogen dioxide, one of the NOx compounds. As smog, it's really nasty - in the 70s, when the smog was bad in LA, you could not inhale deeply on hot summer afternoons without coughing. The whole notion of "greenhouse gases" didn't come about until well after the demise of the muscle cars, and usually refers to carbon dioxide (CO2) which was previously thought to be a benign product of combustion.

 

Yer absolutely correct. Just didn't want to get that far into it. Nickmil.