In Aug I am building a 686. I was planning on using the 11/1 compression piston but got to thinking, and listening. So how much more would like a 13/1 add over an 11/1? And would it also be feesable(sp?) to do for anything other than drags? I want to be satisfied with it when I get done and don't want to question if I had only done this or that then maybe I wouldn't have just lost. Every once in a blue moon I will do a little slow ridding, like going to a sand bar with my wife on the back, would I still be able to do this?

Thanks in advance for any help.

 

is it gonna be worth it to you to run race gas all of the time?

 

Yes he would have to run race gas all the time, For drag race it would be feasible and you would have ton of power on the low end. I think you would lose some on the top end since it high on compression. Correct if I am wrong on this guys.

Would you be doing anything else beside drag race or your wife in the back, like trail ridings,etc?

Just asking.....

Bill

 

Ward,

You may want to consider going with a 12:1 comp and using a bit more cam. This would allow to have the best of both worlds, bottom and top.

I believe my 727 will be coming with 12:1 and yes, I am using a bigger cam(trinity cam grind #737) and all 3 intake valves will be 2mm over size as well. This should give me good bottom and awesome mid-top end too.

Are you having a reputable builder build your 686 or are you just gonna have it bored, buy the cam, valve springs, piston, gaskets etc. and do it yourself?

What about head work?



Swy



Edit: Just to let you know, I was recommended to use VP MS-103 fuel for this set-up. Only 103 octane and does contain more lead then alot of fuels, but no need for 110 or anything too crazy.

 

Ward- I have the 11-1 with pro-port. Drops it down a bit to 10.5-1 or so. I am thinking of going to 13-1 now. No cost difference. My 686 now is a sweet riding machine. I probably should not fix what aint broke. I want to step up 1 level over the 696/697 web cam also. All the DS's guys around me are switching over to alky and nipping at my tires. Can't have that. I will not run alky, i am waiting from them to go boom any day now. Race gas over super unleaded will not be more than a few hundred dollars a year difference. If you are not around a lot of fast machines stay go with the 11-1, very few can out run that combo now. I like for my quad to back up my mouth so i believe a change is needed for me. So far the only thing that has outrun mine is a DS760, a DS720 or nos,a alky 673 rapor (high comp, high cam) and a 686 raptor with a cam from hell. Not bad for a machine on pump gas. And none of those were all that bad.

Back to your question on difference, my guess would be a 7 percent hp improvement over the 11-1, probably 2 to 3 hp. You should feel it.

 

First off thanks for the help.

derekhonda I have good access to race gas so it wouldn't be that much of a problem. And it would be worth it if I won the races that I wouldn't have on pump gas.

desracers I seldomly ride my wife and if I do it is for a very short time. What about mx, I ride a track every now and then? I drag about 20% of the time, sand 20%, trail ride just to get from one place to another, mx about 5%, and the rest are dirt and sand pits. So from what you are saying I would have more topend with an 11/1 over the 13/1.

swytak that would be another good option. I haven't decided on the cam grind yet, because I am not sure what I am going to do with the head. I am probably gpoing to get fussed at for saying this but, I work with a guy that has built and race almost every motor you could think of except the 660. He is going to do all the machine work. He also wants me to let him do a P&P on the head. Now remeber that ALL of this is going to be done for FREE. I am still kind of skeptical on letting him have the head. I want to send it to Trinity but I could use the $400 for something else, like a-arms. Sorry for rambling. could you recomend a good cam grind to go with the 12/1?

14mins I thought about alky but scrapped that because of to many ifs. There are not that many super fast around me but I go to LA Dunes as often as possible and there are some fast ones there. I am also starting 300' drags and some shees are running 4.0. I would also like to go to badass's territory without getting my feelings hurt to bad. Have you decided on a cam to use with the 13/1?

THANKS AGAIN FOR ALL THE HELP!!

 

Ward660R

What I have been told and read that the Raptor can handle the MX at ease as long you have a good shocks on it. It would make the riding easier due to all the bump amd whoop sections.

For the compression far I use on my experience. the higher the compression when at full throttle at speed you will feel it stop short, that you think there is more. The riding you mention to me and do fun, I would go with 13 to 1 along with the cam. Call Trinity and see what they got to say about it.
For me I would go to 11 to 1 because I do the desert racing and it would be more reliable in the long run.

The main thing is just have fun.