I finally got my 720 going and I hate to say this, but for the amount of money dropped in it I feel that the power increase is mild. Is it me? I know 4 Strokes aren't as responsive as 2 strokes when it comes to modding it but I was expecting a whole lot more torque and "oommmphhhh".

Anyway my main gripe is this, the piston I noticed at the top is flatter than my existing Ron Wood Racing 11:5.1 piston. When I I had the crank turned over to TDC the pistons edge doesn't come up to the full height (or flush) to it's opening of the cylinder. It's actually recessed a bit (maybe a hair more than 16th of an inch). Correct me if I'm wrong but doesn't that hurt power (loss of compression)?

I called Gary and mentioned if he has another piston. He told me that he has a 13:1 piston. I told him i was expecting more snap, he replied if I had bigger valves and that my 44mm lectron wasn hampering my DS which personally that is the first I have heard of it. When I was getting the kit he said stay away from the 46 and that the 44mm is good, now he is telling me it's my desirwhats NOT giving ed "snap" on the bike. I really dislike the accessibility of the TM45 and it's proven that the HV46 outperforms it (which I will get in the future).

What concerns me is that he needed to machine the head so the piston clears it. I was wondering if running someone else's piston would work or I'm better going to TVI and just get a piston from them? I also read in these forums of someone with a TVI 720 that realized he was at 9:5.1. I would be happy at 11:5.1 at this point of the game.

 

ever look at a piston from powroll, the 10.8 in my honda 440, is flater than the one in the 720. but anyways i raced those higher compression piston 720's i wouldn't change. buy nitrous that will give you some snap you will feel. 650 and you'll have adjustable power. ever wonder why powroll, yamaha, sparks and seems lots of other people put big dual carbs on there big bores.

 

Hey Sandman,

Somehow I knew you'd have some sort of input on this (that wasn't meant to be an offense). I don't know, maybe I did something wrong on my DS. I'm going to check the valve clearances once again maybe they are too tight and I need to adjust them (I need to order some shims). I'm not trying to trash TVI at all. I always state facts and events that have happened to me.

I know when I installed the RWR 11:5.1 piston there was a difference in response. It pulled a lot harder all the way around.

Who knows I might be at the right compression, but I find it odd how the the piston sits at TDC when the RWR one I had sat MUCH higer. A friend is going to borrow a compression tester to see where its at.

All I want to know if there is an alternative to the piston I have now. I was told I might have lost compression from TVI machining that part of the head.

 

I don't belive your piston is holding you back alot if you were trying to run race gas maybe. but if you dont have good head porting big valves and good cams you can put all you want in that piston hole and you still won't have d%#K .To have a fast bike its a complete package. If you want a fast trail rider then the 44 or the 46 will work if you want to be faaassssttttt then you might want to look into dual carbs. Now if you want to be the "man" Fuel injection can't be beat.But why would you build 720 and not do a complete package??????? [img]i/expressions/face-icon-small-confused.gif[/img]

 

Where did they cut the head???

Can you tell how much they removed???

Have any pics of the combustion chamber???

I can't understand why they would have to machine material from the head for clearance when MrHp's 14:1 stock bore piston fits. Sounds to me like someone made a boo-boo with the design of the piston on TVI's 720 and instead of trashing them they cobble them in there. I would rather they machined the piston for clearance, machining the head is too permanent.

JMO

 

AZ,

I got everything on the DS except for large valves. I got the cams, headporting and big bore from Gary. I figured while it was apart I can do everything now. At the time I just didn't have enough $$$ and getting larger valves would just mean removal of the head to get it done. Like I said all this at once I thought I was going to feel a MASSIVE difference.

Don't get me wrong it's been like 8-9 months since I rode my DS before all this and it defintely feels strong, espeically in the midrange. I have heard numerous reports running too high octane gas hurts performance.

I do not want dual carbs. The idea is nice but I don't think I will like the effort it will do on my thumb. I had a TM45 and I absolutely hated it. Aceess to the needle is a pain and when I installed the accelertor pump, thumb effort was terrible. Drag racing isn't my #1 priorty with this machine tho I do it more on my DS than I do on my Raptor. I like to do a lot of jumping and I actually ride the DS on an MX track. I just want the maximum gust out of my quad for all the trouble it put me in.

 

Entomber any thing is going to seem slow after your t-rex. [img]i/expressions/face-icon-small-wink.gif[/img]

 

i think azsand put it right i've lined up with his 760, he handed me my a@# nicest guy you could lose to, but it wasn't the piston. it was the package deal, all i'm saying is you keep going on about the piston, it's not the piston, if the other one was that much better i'd have it. raced garys high comp 720 i won everytime, sandbombers i would pull out of the hole every time and he would track me down, wasn't the piston it was the gearing. i guess i just see you causing yourself pain over what some piston top looks like, i was looking in the back of dirtwheels and there was the powroll piston for the yamaha 450 flat as a pancake. just use the thing and learn the right set up for what you got, i could beat stage two's with stock and 686's with stage two, it's all set up. somebody on a drunk 760 told me last year enjoy the ride or it's not fun thanks azsand[img]i/expressions/face-icon-small-smile.gif[/img] oh maybe you need to rev the engine more also 720's like to rev, hope that helps.

 

AZsand your right.... that little thing for what it is, is rediculous. My stage III buddy was astonished. He has reminded me it is too radical for my kid. Thankfully he isn't a WIDE open rider. I have to get on him to crack the throttle.

I don't know guys... I spoke to someone else who felt the same way as me. I'm worried of putting in another piston and because I didn't use TVI's I might end up doing damage.

The part of the head he mills (I'm assuming) or machines off is off on the right. It's kind of a small angled peice. I wish I had the head off to take a picture of it.

 

Entomber, from what I understand if you were at 9.5 to 1 and went to 11.5 you would gain approx 4 hp and that is not going to be the magic bullet you are looking for. By all means run a compression check and get with these guys to decide which fuel to run. If you are running on MX tracks and want all around perf the 44 doesn't sound bad at all. Check your jetting carefully. What gearing and tires are you running, you have to put that power to the ground. If you can go 75-80 and don't need to then maybe think about gearing down. Get the best tires you can afford. Want to see what your DS can do? get it out on some pavement and open it up, oh and when you are going up against your buddies at least get some compareable tires to what they are running.