lol i probably am.

 

standard compression ratio in these beasts is 17.5:1. as it's been said, much lower will make for harder starts, inefficient burning of fuel. if you watch all the pulllers with low compression ratio and tons of timing, they're blowing white smoke idling until they bring RPMs up. white smoke = unburnt fuel due to low combustion temperatures. think about how close the piston comes to the surface of the head with a stock gasket, the air gets compressed A LOT and in turn, heats up A LOT. if you put, for example, a .020" gasket it may increase the volume of the cylinder, thus, the potential for a higher volume of air to fill it. but, the piston doesn't come as close to the surface of the head as it did before, leaving some of the air (probably not much) partially compressed and only partially heated for complete, efficient combustion of the fuel. make some sort of sense? i could very well be wrong, but that's how i see it. as for streetability, i'd rather keep my 1/2RPM starts with a stock compression ratio. but, if you're looking to pull or race, the low compression ratio and advanced timing is the way to go.

 

thanks jimbo

 

My new engine is going to be about 15-1, hope it works out ok for street driving.
I am looking for a DD so I can just use this as a toy tho..

 

y not high compression?? i've read somewhere that higher compression is ideal for better terminal efficiency something like 70% is achievable..

 

I would just use a .020 over gasket and leave it at whatever compression ratio that is. FYI my truck hazes now with big injectors and a .020 h/g.

 

that'd be quite a task!

shorter rods, cut the deck height, possibly a new crank with a different rod journal throw and even a new design of the piston bowl or piston altogether. not worth it if you ask me.

 

if you want lower compression and r going with a larger headgasket y not port/polish the head and blend the valves seats into the combustion area? I'm sure there is volume to be had in the head....

 

I'm planning on making big power with it some day, you know with a edit-pump Plus I'm hoping to get a new DD soon.

 

I know with Chevy and their 6.5 are 22-1 ratio. You get over 15 psi boost and things are not good. I have a boat anchor sitting at home because of this.

The differences with running a 20 thousands thicker head gasket is not that much. When you start playing with lower compression ratio pistons, then the fun begins.

 

didn't know the 6.5 had so much compression... no wonder why they "knock" like kids on Halloween. A low compression diesel....just doesn't sound right to me. I'm open to new(to me) ideas though

 

According to my ROUGH math, stock combustion chamber is around 56 ccs and adding .020 over adds 4ccs to that. After doing some late night math that comes out to around .1 compression change. Again, very rough math. Using over all bore volume and known compression ratio of 17.5 to 1 I estimated combustion chamber to be 56 cc's and a .020 x bore area = 4cc's then back track numbers with updated chamber size gives 17.398. But its late and I hate math. Not sure how low you can go before its hard to start, but lower compression would give you more volume to play with in the chamber for a given volume of pressurized air. 7% more volume of combustion chamber volume. Not sure how much that affects cylinder pressures though. I am curious how hard it is to get some of these puller trucks running. Hope this helps a bit.

Aaron

 

So did the 185hp 7.3L IDI and the 125hp Mercedes 3.0L OM617.

High compression ratios, low boost (even though the MB can handle 30psi or so), and inferior indirect injection.

 

The high compression is needed to compensate for the inefficiency of the IDI combustion system. IDI does have some advantages, for instance it is much more tolerant of variances in fuel quality.