I am hoping some one out there can help me. I just have a bored out 400ex. It is on the first bore of 3 for a 440 kit. Compression is almost 11 to 1 and I am running pump gas. Does any one out there have any suggestions for what grade oil I should run in this thing? I abuse it to know end and I would like it to last as long as possible.

 

Pick your favorite synthetic and change it every 20 hours Max. It being winter time I would go with something in the 0-40 or 10-40 range . Regular oil does not flow as well when cold, and does not protect as well when hot.

 

For the EX, I personally like Honda HP4 oil (without moly), a synth blend. Comes in 20W-50, 10W-40, and 0W-40. See your owners manual, for a table of what weight to use at what temperature. Good article: http://www.thumperfaq.com/oil.htm

What octane is your pump gas? Did you know that the STOCK 400EX (9.1:1 compression) requires 92 octane (air cooled, so it runs hot)! You bumped your compression up, so I would suggest bumping your octane up too. I like Klotz octane booster. http://www.klotzlube.com/Merchant2/m...=ATV_ADDITIVES

 

reconranger I use Marathon octain #93. My owners manual says that in stock trim, I can run 87. I did bump up the compression a little bit, so now I use 93. Unless I am at the dunes, then I burn half 110, and half 93. I guess you could say that would be like running 101 or 102.

 

I use Amsoil in my EX, 10w-40 cooler temps and summer I switch to 20w-50...

 

Where in your manual does it say 87 octane??? I am looking at page 84, and it says 92 octane or higher!

Manuals make mistakes sometimes! The 450R manual says 87 in one place, and 91 or higher in two other places. At 10.5:1 stock compression for the R, you know it has to be 91.

The highest octane pump gas out here, is 91.

 

I'd like to comment on that Thumper FAQ link.

Friction modifiers are NOT found in all automotive oils. Friction modifiers are only found in oils that are listed as "energy conserving oil".I run good ol' automotive 10w-40 in my trike. 10w-40 is NON energy conserving and therefore has no modifiers that harm the wet clutch. You can safely run most any dino automotive oil as long as it's non energy conserving.

There's another link kicking around somewhere showing a study how they found virtually no difference between motor oil and motorcycle specific oil. I'll try to find that link later.

The industry has found that it can make a good deal of money by selling oil marked with their own name. It's interesting looking through the manual for my 20 year old three wheeler. It states to use an oil with a certain weight and service rating....it doesn't say to "Use only Honda oil."

 

I know it is a jump but I have always recomended Belray 80w, it isnt the cheapest but it will protect your engine

 

Oil viscosity is directly proportional to the outside air temp. There are many charts out to show what viscosity to run.
For example: If you ride where the temps are between about 32 to 125 degrees F you should use a 20/50W oil. A 15/40 will take you from about 15 to 125 degrees F.
I live in Cali, so I run a 15/40 in everything I own.