cool little write up and you can't beat the dr atv bore kit for the price. Can you run that piston with the china head he sells? What cam you putting in?

 

this is the cam I will be putting in. http://www.hondatrailbikes.com/catalog/product_info.php?cPath=52_53&products_id=626

I picked one up on Ebay for $18 shipped that is brand new.

I guess the head would depend on which one you are talking about. Do you have a link to the one you are referring to?

The piston has a little dome on it so you get an increase in compression. But, if you get a head that has a bigger combustion chamber you may be back to stock compression again. You might lose a little bottom end but w/ bigger valves you should have a good top end.

And this thing runs great w/ 93 octane. Doesn't really like 87 or 89 so I would guess the compression to be in the range of 10.5:1 -11:1

I know there are other factors to consider when figuring compression but seems like anything below 11:1 doesn't need race gas.

I tried it w/o a base gasket when I first put it in. It put out 4.51hp like that w/o the carb tuned. It had a 85 jet in then and was running too rich. But, I found that the silicone I had used blocked off the oil hole and the top end was w/o oil. I guess if you could find a thinner head or base gasket for it you would see a little more hp but I don't know that you would notice it except for on the dyno.

 

can't beat that price you got that tb cam for. I have the same one in my bike and I like it over the stocker. This is the head, after reading some info on it I guess you can.

http://www.dratv.com/necoto.html

 

I hadn't even seen that head up there b/4. Will probably lose a little compression but the top end should be great. And the best thing is it will take the cam I am getting. Well, I wonder how much money is in my Paypal account?

I'll probably have to get a bigger carb too though.

If I would have known that I would have gotten the 88 kit for the 70 and that head. $220 + $20 oil pump + carb?$ Why didn't you show me that b/4 I put this engine together?

 

Ive been using Dr.Atv parts on and off for a couple of years now and always quality parts at great prices..... Hey Mello good bang for your buck Id say!!

 

Yeah, I don't care if there is not even a name on the box or parts. If it is cheap I will at least try it. You see so many people saying that the top names are the best b/c they are the most expensive. Fact of the matter is most won't try these no name parts b/c they are scared someone will rag them for it. But, that's another topic.

I have been ripping on this thing off and on all day today. Been doing some wheelies, circles, high speed cornering, and stoppies. I am very surprised at how responsive this thing is. Probably b/c I tapered the intake port on the head to match the intake. I figured that would give me some good fuel/air velocity.

 

does the xr70 head have 20mm x 23mm valves? Mello your bike looks fun with that disc set up and street tires. You might want to pick up the 20mm sheng wey carb dr atv has for around 26 bucks. I prefer that carb over my mikuni and is perfect for the cheapskates like you and me.

 

Most of the Preformance Parts that Dr.Atv carries are Dragon racing those are great good pistons Cylinders cams.... ect ect stuff works great im always happy with the Preformance you get

 

does the xr70 head have 20mm x 23mm valves? Mello your bike looks fun with that disc set up and street tires. You might want to pick up the 20mm sheng wey carb dr atv has for around 26 bucks. I prefer that carb over my mikuni and is perfect for the cheapskates like you and me.

I am pretty sure that is the valve size the old tb race head had.

I think it is 22/19 on a stock 70 and 19/16 on a stock 50. If I am wrong, someone will jump in and let me know I am sure.

The reason I stuck w/ the 18mm carb is I wanted some good throttle response down low and it doesn't really need a great top end for stunting. If I decide to change the head on it I may go a bit bigger. I will see what happens when I put the TB cam in it. It shouldn't lose any of the grunt down low but it might give me a little higher peak hp.

And those disc brakes are almost too good. I have no problems getting the back wheel off the ground. W/ the stock drums on the front I was having to squeeze the crap out of them and couldn't get used to them. I can meter these a lot better.

 

Here are some pics of me playing around today. My camera is really slow. I should have pics of me w/ one hander stoppies and my leg over the bars but the camera is acting really weird. One time it has a 1 sec. delay and the next it's like 3 sec. Doesn't really show anything about the engine. Just me having fun.

 

Kane, I think this would solve the problem of some of the lost compression if you were to go w/ that head and the 88 kit for a 50 instead of the 70. http://www.dratv.com/cohega54bofi.html

I am going to measure the thickness of the head gasket that comes w/ the kit to see how much thinner this would be. This might be my deciding factor. If I can keep my compression about the same I will get it for sure.

 

I run the dratv 85cc kit/51mm stock head piston with that small dome.., with a TB crank, 24mm carb and the dratv race head linked in this thread.



I'm guessing the compression is somewhere around stock-- runs fine on 87 octane.



Before I put the head on it, I was running the same piston on a stock head stroker that would ping on 87 octane. It liked 110 octane. My wallet didn't.



This 104cc budget motor rips forsure.

 

Here's the dyno sheets. Hopefully you will be able to read them. Had to take pics of them.

The first is the basic kit w/ the 18mm tuned as good as I could get it. If I could find a 78mj I could pick up a little but I am happy w/ it. Dynoed in 2nd gear. (4.1hp)

The second one is the basic kit w/ no base gasket and the carb had not been tuned, dynoed in 3rd gear. (4.66hp)

I measured the head gasket today and it is .8mm so the .38 copper gasket from dratv would give me a bit more power. Maybe get me close to the 4.66hp I had w/o the base gasket. I can't wait to get the new gasket and the cam.

 

good work mello, what coil and plug you using? Also dr atv processes and ships his orders as fast as anyone.

 

Still running a stock plug and the coil is just some chinese coil that came w/ my loncin motor I had.