dclintonh

what is needed to switch my os18cvrx to 30%?

about to need a new gallon and figured why not.

thanks

bluecaka69

youll need to run richer cause 30 burns hotter then 20

mozzzy_2000

and you may need to add a shim but that will depend on what the engine is originally configured for. I think you'll have to shim the infinity .27, not sure about the OS. Also when you do change just go easy for a couple of tanks as the engines adjust to the increased compression.

el_tonto

You might also need to go to a colder glow plug, because higher nitro % might ignite too early. A colder plug will delay ignition a little, preventing pre-ignition/knocking. Shimming in order to lower the compression will achieve this also.

ehroof

you dont need the shim, just a cooler plug like an os a5, the a3 is too hot for 30%

mozzzy_2000

Thats if its factory shimmed to 30% in the first place. I find most .21 engines seem to be factory shimmed for 25%, not sure about .18s though to be honest. Some big blocks are factory shimmed for 30% but if the OS18 is not you may indeed need to add a shim. I think his original question also included the infinity .27 and for that you would definately shim for 30%. You would also use a colder plug as suggested

ehroof

the original question is an os .18 cvrx, i own 3 of them, have the manual and it is made to run on 20-30% fuel without shims. i run one of mine only on 30%

dclintonh

#8 plug be ok?

ehroof

yeah, try a #8 and see how it runs

arlo1

How much of a difference do you think it made to run 30% vs 20% and how much more do you go through? It seems that I can burn a tank pretty fast!