since i put the nitrous on my ds i have been thinking about a higher compression piston. mine is the lower compression tvi 720, the thing works great for me but i run between 180 -190 most days. when i go ride with friends most are welcome to ride my quad, but having watched the bigger riders they seem to not do as well on my ds, as me. well i was talking to john at nx and discussing compression with the nitrous, and it was a very informative conversation. he was telling me that the compression effects the reving ability, higher is harder to rev, which sounds right when you think about it. thus with the lower compression you can rev faster, but the trade is less torque, which is where the nitrous comes in to play, it will bring back the torque. i've seen several discussions on this and have been watching, and sometimes i get caught up in the numbers thing myself, such as a 760 must be faster than a 720, or a 14-1 must be better than a 11-1. anyway after riding the half mr hp 730 it was interesting to feel the difference of the two engines. mine you rev to 6-7000 off the line and hang on and keep it pinned the hole race, short shift and your done. the high compression you start about the same place and it pulls different, it didn't feel as abrupt off the line, but comparing in race result they were the same, it didn't seem to require as much swingarm to keep the front down. just interesting. again just some info. well thought i would share some of this, since there has been a lot of discussion on compression ratio. the reason for the call was to find out about fine tuning the nitrous system.

 

Hi Bill,
It sure was fun riding with you, Jeep, Marky, and Big Slim at Florence .It was a real kick watching you spank the hill on my full dress heavyweight stock looking 730.I have several more rides on it ,about 20 gallons worth, and it seems to be pulling harder the more I ride it.With equal rider weight You would probably still beat me with the juice but Holy Smokes when you hit the button your bike rips!!! Monday it goes back to Chuck for the new clutch, valve adjustment check, and minor tunning.August 1st I'm taking it to Kentucky for
dyno runs and serious tunning.
[img]i/expressions/face-icon-small-cool.gif[/img] look forword to seeing you again in the sandbox, Ron

 

yeah after riding that thing i've been thinking more more about that high compression, it was fun working those 450's.

 

Bill, When preacher built my motor, I told him to do it "HIS" way and I also told him I want torqe and he knows all I do is run the hills. In our conversation, He told me 15-16:1 would be optimum, I said holy moly!!! I have .045k piston wall clearance also, thats why I went w/ the juice. I know people have said high compression doesnt take well to the juice, Well Ive rode my bike with the nos, and let me tell you, It hits rediculously hard...222 with HP research also told me my bike would probably take good to the n20, He was right.

It takes 114 octane to get my bike to purr like a kitten, But when I put 105 octane it knocked a bit, So to sum it all up, I have alot of compression and it takes well to the nos. The only way to find out is real time testing with your bike... Example, I took my ds out to try the chart recomended 17 hp shot, And rolling slow in 5th gear and hitting the button WOT @ 3k rpm w/ tall gearing that I run, The front end came up and it instantly was Almost out of controll and reved all out... This was on hard packed dirt. JUst put it this way, IT WORKS DARN WELL. I think you should try the high comp 105.5mm.

 

i will be doing the higher compression but it was a interesting conversation, it just seems to show two different paths. and i know that hit you are talking about it's pretty cool.[img]i/expressions/face-icon-small-smile.gif[/img]

 

it's a trade off. the higher the compression the less amount of NOS you easily can run.

if you put an 8:1 piston in and run 80-100 shot of NOS you'll put lengths on the same bike with a 14:1 piston with only a very small shot of NOS.

The RWHP you get is usually less than the stated HP of the NOS jets.

you need to set the HP level on and off NOS that's suits your style. if you want more peak HP on NOS, you need a little less power off the NOS. if you aren't willing to have weaker off NOS power, then your peak power on NOS will be limited.

West coast Jeff with the 830 is running a small shot of NOS. Even with the alcohol, he had trouble burning up plugs with bigger shots without lowering compression. You might ask him about it.

FYI, when people see a blue bottle they expect a lot from the bike. You'd get more respect from the motor work alone then running a bottle setup only to add 10RWHP.

I've lost count of the number of raptor and DS people I've come across that had problems with medium or higher shots of NOS with high compression.

 

How long would a motor last under 80-100hp shots?, Not long.IMO



GREAT EXAMPLE, Jeffinrivercity Runs a small shot of nos and he has not been outran by any other 4 strokes at HIS hill, And he gets the utmost respect for even the blue bottle. He even beat the turbo ds from what I understand that went up there recently...


Scooby, the last 760 w/ 25 shot at Dumont I left him by 7-8 lengths, and I was on all motor... I am useing the nos based off my power curve on dyno sheet. My hp peaks from 6k to 9k. Straight accross on the hp line from 6-9k. Torq starts peaks @ around 5500-6k...EDIT 5K.

I WILL get a solid 17-20hp on the dyno more out of my bike which will be significant for what "I" DO. The point is that my motor has the same performance that it did before, now I have added a little more. Im not looking to be the fastest in the world, But I do my fair share of torturing around my way.


Another example, A yfz gained almost half the hill w/ only a 20 shot at Sand MT Utah. Pretty impressive to me!!!!


BTW- Ive talked to Jeff extensively about the nos set up. He helped me diagnose the jetting.




Sandman, I have heard many opinions about high comp motor on nos, You should try it and then see for yourself.

 

i guess my interest was where the line of most good was done, i know you will feel the result of nitrous on a high compression piston. there seems to be a thought of the resistance and there is a place where the nitrous helps more, with less compression. like scobby said bigger shots.