Compresion ratio ?

[TrentNell]

What is the lowest you can go on compression without smoking white at idle in summer temps ? And how low is nec when dealing with high boost ( 70-90 psi ) . I am trying to figure out how much to have taken off my pistons when i have them cut. I was thinking 16:1 but heard that for that much boost 14-15:1 would be needed ?

 

[S Phinney]

I think the 15 to 1 would work well for you Trent but I not the expert. Contact Guy or Curtis and they will know for sure.

 

[othrgrl]

I went with about 16:1 and am running over 60 PSI. Talk to Guy, he'll get you set up with what you need.

 

[sweetdiesel]

15.8 to 1 starts great even at some cool nights 8c (with glow plugs)
I think i will go as low as 15:1 next time JMHO




IIRC Frieghttrain was pretty low??

 

[JoshH]

My motor before had close to 15:1 comperssion ratio, and it would smoke when it was cold even with a grid heater and glow plugs. The new motor will be closer to 16:1, and I will be running boost close to what you will be.

 

[03demax]

Talk to JOHNBOY he had issues with coaking in their. He could give you the details. Not sure of the if and whys I just remember him talking about it.

 

[Gasuout]

I hear 15.5 to 1 is the magic # for all around best results .

 

[paint94979]

Simon, I think Freighttrain was around 13:1... isn't that engine still alive?

 

[duratothemax]

My motor before had close to 15:1 comperssion ratio, and it would smoke when it was cold even with a grid heater and glow plugs. The new motor will be closer to 16:1, and I will be running boost close to what you will be.

before or after the rods shortened? :

 

[SmokeShow]

With that much boost (or any given amount of boost), wouldn't the higher CR make more cyl. pressure and thereby be capable of making more power? You just need to know when the block or crank will bow out, right?

 

[TrentNell]

With that much boost (or any given amount of boost), wouldn't the higher CR make more cyl. pressure and thereby be capable of making more power? You just need to know when the block or crank will bow out, right?

yes i have considered that as well , but head gasket problems and injector cups staying sealed are the things i worry about with the cylinder pressure it could generate ? And i am checking into wether i can afford to fire ring or o-ring the heads and block .

 

[juddski88]

for my build, i had plannned to remedy this by using and lly fueling system/heads and o-ringing it....i will still be driving mine year round

 

[Fingers]

The lower reasonable limit also depends on the injectors. Stock injectors will tolerate a lower compression.

My engine is too low at 14.5:1 and stock injectors. It starts fine, but runs rough in cold weather till it warms up some. Depending on how cold it is, I dump a lot of white smoke till warm too. Once warm, everything is fine.

I don't think it will tolerate larger injectors well.

 

[S Phinney]

Not trying to high jack Trents thread but does anyone know the respective cylinder pressure versus compression ratio? Example 16 to 1 produces 400 psi, hypothetically.

 

[05smoker]

14.5 to 1 and no smoke at idle in warm weather.

 

[JoshH]

before or after the rods shortened? :

Assuming I didn't bend them the first day I got it running, it was before they were bent. The outside temps weren't exactly warm though. I think it was probably in the 40s or 50s.

 

[Idaho CTD]

Since you now have a back up truck Trent I would go 15:1. If I was going to DD it, especially at your altitude, I would go 16:1.

 

[TrentNell]

Thanks for the feed back guys :hug: since this is going to be pretty much a race truck i will probably stick with 15:1-15.5:1 and see how it works out .

 

[IdahoRob]

What ever you choose Trent (within reason) tuning can really help. I had the race truck out at the track and it was in the 40's with those huge injectors.

I sat and played with the tuning at idle and cleaned the idle smoke almost completely up with a cold engine.

 

[TrentNell]

What ever you choose Trent (within reason) tuning can really help. I had the race truck out at the track and it was in the 40's with those huge injectors.

I sat and played with the tuning at idle and cleaned the idle smoke almost completely up with a cold engine.

Thanks for the info Rob , that is good to know if i end up having that problem with the lower compression .