SonOfSand

A 4 mil stock cylinder is very inexpensive and will really fly up choke, I was clocked at 44 mph up choke last labor day, and I weigh 210 lbs.

LOL Yeah, I am sure there are some great dunes in Africa and the middle east. I cant get enough of choke cherry, does your short sand car have a Hayabusa with turbo?

Thanks for confirmation guys. I'm putting them on a HJR 10 mil cub, does anyone know if there is something to be gained by going to big bores?

Little Sahara at Easter time is one hella show! I would come down If I were not 15 minutes from the GREATEST sand on earth! Have Fun, and be safe.

If I am understanding you correctly, yes. Did you click on the picture to enlarge it?

Hey guys, I think these are small bore, just wanted to ask someone that knows. Thanks.

I don't think so. MON is what you need to look at. forget 130

The suspense is killing me, if one of them is a cheetah cub, not on alky nor oof drag pipes I might be back on the Cheetah cub band wagon!! End my suffering Andy! Great discussion so far guys.

I did a lot of reading on this along time ago. 100LL does not have a higher octane rating than race gas, you need to research "motor octane number" (MON), i believe 100LL was 98 or 100, and race was 104. The "MON" number is the best way to compare them.

I think you will probably be fine, I have the same compression and timing have run avagas with great success.

Can you provide a link to your video?

Are you saying the boost ports in the bottom picture of the stock cylinder don't add any power? Where are the boyesen ports? Thanks.

I have 35 mm pwk's (non airstryker), I run 42 pilot, cel 2nd from the top, and a 145 main @ 5000 feet. On 100 LL (avgas) Banshee in my sig.

I would go with a 10 mil serval if my goal was to build a dune/drag bike. lots of power at all rpm, and probably beats most non drag bikes out there.

They look lean in those pictures, might be different in real life. I like more brown on my plugs, are you a drag racer?

"I would try some 280 mains, stock pilots, needles on middle clip" This sounds right on, I ride at St. Anthony which is the same ele as LS, and that is the jetting i ran with mostly bolt on's.

I was told by Kevin @HJR (who designed my engine) not to up my timing past +4 with 180 psi on a fresh build and running straight 100LL. @5000 feet above.

The outer dimensions of the dome must be the same to fit the cool head, do you have the rings and domes?

I dont own a cub, but i think they use the same head as stock cylinders. That is one of the selling points.

If you are building a 421 on a budget then there is only two cylinders to consider really. 1. Cheetah Cub, these are drag cylinders, make the most power, but more difficult to ride in an all purpose application. 2. Serval Cub, these are an all purpose cylinder, with great power at most rpm. I would recommend the serval unless you are only drag racing.

I think those are all good staring points, except the pilot. I am pretty sure it will be rich. I don't own a cub though. I would dial in the pilot first.

I would say you are on the right track, like mentioned above, the porting will make or break the engine. Make sure you have an expert do it. I still have the oem clutch plates in mine, but with stiffer springs, that would work for what you are doing.

Is your stock crank already welded? If not, you would need to split the cases and do that anyway. So if you are going through all the trouble and expense for that, ebay the old crank for 100 bucks or so. New, welded cranks are around 450 i think. So you are only out 350, and you have more power, and no regrets!

Go for the serval.

Ahhh, makes sense, thanks.