400EX High comp stock piston or 416-need more power

[NKaraidos]

I am trying to decide what to do, either do an XR400 cam with a high compression stock bore or while I'm at it do a 416 kit. Does anyone know how much difference there is going to be from boring or using the stock bore size? What's a good piston to use, don't want to use a WISECO.

[TORO1968]

I'm in the same boat you are... My engine is too new to justify boring it, so I was also wondering if it is worth it to drop in a high compression piston. I know most machine shops like to bore cylinders after measuring the new piston, as the sizes aren't exact sometimes...so with just puttting in a high compression piston, you don't have this luxury. I would hate to spend the money on a new piston only to find it will have tolerance issues.

I was planning on going with a roughly 11:1 JE or Ross piston, HRC cam, Sparks X-6 or HMF Ballance Signature Series pipe, FCR 39mm, CRF cam chain, and who knows what else. I guess if i do all of that i might as well do a 416, port the head, install a heavy duty rod and head studs...dang it, it never ends!

So yeah, anyone have any insight into this? BTW, go with a JE or Ross piston...both are very good. Between the two, I'd choose the Ross since it is a bit lighter.

-Jordan

[NKaraidos]

I don't want to run any race gas.Just fill up and go.

[HondaMan222]

i HAD a 416 piston, JUST the piston, and a stock pipe. me and my friend were toped out and i was barly pulling him, he has the full LRD, and up hills we were dead even! i was just running 92 octane, then it sezed.... i sold that, now on my new one i am saving money to do the 416, i already have a TC cam on the way, and our friend does good porting work. so i want a pump gas bike and thats going to do it.

[JD400exrider]

Originally posted by TORO1968
I'm in the same boat you are... My engine is too new to justify boring it, so I was also wondering if it is worth it to drop in a high compression piston. I know most machine shops like to bore cylinders after measuring the new piston, as the sizes aren't exact sometimes...so with just puttting in a high compression piston, you don't have this luxury. I would hate to spend the money on a new piston only to find it will have tolerance issues.

I was planning on going with a roughly 11:1 JE or Ross piston, HRC cam, Sparks X-6 or HMF Ballance Signature Series pipe, FCR 39mm, CRF cam chain, and who knows what else. I guess if i do all of that i might as well do a 416, port the head, install a heavy duty rod and head studs...dang it, it never ends!

So yeah, anyone have any insight into this? BTW, go with a JE or Ross piston...both are very good. Between the two, I'd choose the Ross since it is a bit lighter.

-Jordan

I think you are on the right track for good power gains. If your doing a 416 with 11:1 compression i would not worry about the heavy duty rod or head studs. Piston, cam, carb, pipe and porting and you have your self a nice ride. Thats what i have and I am pleased with the results. Good Reliable motor.

If your doing the rod then I would spend some coin and stroke it.

[H_W]

Originally posted by NKaraidos
I am trying to decide what to do, either do an XR400 cam with a high compression stock bore or while I'm at it do a 416 kit. Does anyone know how much difference there is going to be from boring or using the stock bore size? What's a good piston to use, don't want to use a WISECO.

Since the stock bore piston and the 416 should be about the same price, I would recommend getting a 416 kit. I would NOT get an xr400 cam. I would get a more aggressive cam like a HRC cam, hotcam stage 2, or one of the engine builder's cams. The xr400 cam is not much different from the stock one. As for the piston, I suggest either the Ross or JE. Most people would recommend getting a 10.8 to 1 compression piston if you want to still run pump gas.

[NKaraidos]

How does your 400ex run compared to a stock motor with a pipe, k&n,rev box ect.

[H_W]

Originally posted by NKaraidos
How does your 400ex run compared to a stock motor with a pipe, k&n,rev box ect.

I am happy with my setup, but if I could do it again I would go with a 416 kit instead of stock bore piston. I would like to have a little more bottom end. I can easily smoke piped 400ex's, z400's and kfx400's. I can outrun stock raptors and banshees. It is close but I can out run them everytime.

[tinner]

Here is what I run....

Stock bore 10.5 JE piston (the machine was so new, I felt guilty punching it out)
GTT cam
GTT race porting
FMF exhaust

Getting it bored out doesn't really cost too much in the whole scheme of things. I just didn't because my machine had very low hours on it when I did the mods. This will run pump gas just fine.