Lower nitro in big engines?

[Zach Vought]

I'm sure this and been asked many times and discussed thoroughly, I'm just not able to find anything on it. If someone has a link that would be great. If not, here goes.

I am working on getting my .90 bullet together. The last 90 size rigger I had was a Roadrunner with a CMB .91rs that I ran on 65% nitro. My current build will have an older CMB .90 (black case with a gold 2 plug head) not sure of the button volume but I can tell you it does have a new, untouched piston and sleeve. I have been told people are seeing better results with lower nitro fuel in these larger engines. Personally I'm not seeing how that can be the case at all. Any info would be great!

Thanks,

Zach

 

[seaducerpete]

Zach I have tested with both 50% and 60% I actually saw a 2 mph gain on a radar gun with the 50% percent I guess the motor was able to burn the 50% better.ask all the gurus that's what it is all about getting the motor to burn the nitro.

 

[Zach Vought]

Thanks Pete. Kinda hoping they will chime in.

 

[bermudadude]

nitro burns too slow to be effective without destroying what ur using it in. thats why we dont run 100%,that said the smaller the diameter of the piston the more efficient nitro is. this is why one would see less gain increasing nitro content in a large displacement engine.

in a .21 ,every 5% increase you will see the improvement. a .21 with 75% can be heat raced. but at the other end of the size spectrum it starts to become the opposite.

yes 50% for most applications will give best results in a .90

more nitro requires a smaller head bubble but its not that simple and it gets all .0001 here and .0001 there and time ,time ,time, and spare perts ,spare parts ,spare parts, which gets costly in a big block,not to mention a poorly running .90/1.00 gobbles up fuel like u cant imagine.

it can be done.i remember Andy Brown telling me how he and Joe Ingrayo where melting pistons and liners together to set records over a decade ago with cmb's and picco's

with todays metalurgy in the new engines it maybe more doable to experiment but i guess you dont see soo much because of the high cost fuel and also lots of engines will run up into the 90's with 50-60% practically out of the box. and the lacj of a fast heat race hull

 

[Zach Vought]

Would 50% be a minimum or could I get away with 40%? This is mainly a play boat that may see an occasional heat race. As you said, 90 motors EAT UP fuel so my race boats will most likely be of the smaller variety.

 

[Danny King]

I used to run very fast with .67 piccos and CMB 90s on 33% in the 90s. If you start off using 33 or 40 stay with it. Just don't jump back and forth. Things need to be set up differently.

There is no reason to run that high nitro stuff for fun runs.

 

[Rick Reisinger]

I had a Young Blood Glass hydro I ran a OPS .90 on 15% Byron at the Last Hydro Master's I ran in 1999 ...........

I thought Doc was going to Sh!t when I showed what I was running for fule .....

Jim Irwin was pitting with me he laughed all day when he backed me running that boat ....

Yes you have to set up right ---- D-m I wished I still had that boat............ LOL

 

[bermudadude]

40% is prob min u can run in a new engine from cmb because they have been steadily decreasing the head volume over the years

if u buy other engines like ops for example ,they still set thier stuff up to run the average euro way wich is 0%-25% for the sport to average racer. the more "money" guys over thier run 50-60% ,over there nitro is about $1 a percent . almost the same here for me.only reason i gave gas a try but i really dont like it.

back when i first started we used to run 25% all day,i can tell u ,we never had more fun. more nitro seems to have translated into more costs,more setup/test time,MORE MONEY. not really much more speed especially if ur playin around or racing.

mainly id say only mess with gettin an engine to run really eficient on higher nitro if ur running it in a rigger .it pretty much comes out to be a waste of time in other hulls. in my experience

 

[Zach Vought]

The motor I has already been set up to run 65% I'm pretty sure. Might just stick with that.

 

[John Knight]

I ran CMB 90/91's for many years on 50% and competed very well. I tested my engines and boats with 60 and 65% and found no real difference in speed, but found a much easier needle to find and keep in any racing condition.

About 5 years ago I did some testing on some 20 and 45 riggers. Tried 25%, 50% and 65% just to see how much difference with the smaller blocks. Using the 50% as a baseline, the 25% was about 2 mph slower than the 50%, and the 65% was about 2/3 mph more than the 50%. Actual small differences in speed but bigger differences with the needles. MUCH easier to find and keep the 25%, good on the 50% and harder with the 65%. It was what I expected.

 

[Zach Vought]

Thank you guys for the input. Unfortunately I don't know enough about the engine and I didn't measure the gasket thickness when I installed the button to know what the squish is. Nor do I know the button volume :/

 

[charles siler]

The engine analasist guy has tidbit on squashbands and setups on his website that are good and explains alot or pay 150 to 400 to have somone mod and set it up for ya. Ive done all and its time in doing that matters and a few mentors. Most important burn some **** up and practice without the push you me or somone wont take it to the next level later Charlie