Xu5ja Upgrade Question

[ifcho 0]

Hi,

 

I have bought a cam from newman, the third one on this picture:

 

So now I'm not sure whether I need some uprated springs. I have spoken to QEP and they offered me a set of springs + retainers but I'm wondering.

Do you think this cam can work with the standard valvetrain?

Also I'm thinking of a xu10j2 head. Not that much about the bigger valves, but because of the fact that it has round ports vs. the square ones on the xu9 head.

I'm planning on running the engine with bike bodies, so I think that the round ports will be much better than the transition from round to square if I'm left with the original head, what do you think?

I have also heard that xu10j2 are running cams with quite high lift, so the valvetrain from that head could be sufficient for my needs?

 

Also, what compression do you think will be suitable for this cam. I have never understood why a higher CR is required for lairier cams, but I know it is so. I was thinking of aroun 10.5:1 but may go as far as 11:1 (i want to run on regular fuel, without any additives).

 

And finally, I'll be bying a new set of pistons/shells/rings/liners and from Mahle the price at which I get them is around 300 euro (full set).

However, a wiseco/je piston set would get me back around 600 euro (double) so I cannot decide which would be the better choice.

 

Has anyone run such cam? Does it need machining the pistons to allow some valve clearence? The engine is 1.6 XU5

 

Sorry for all the questions. They are buggering me for quite some time, and I thought I could ask here

Edited January 24, 2008 by ifcho

[ifcho 0]

anyone

[petert 601]

I doubt the std. springs will handle that much lift. I would fit doubles for sure. With installations like that you simply have to measure and check for spring bind. You'll definitely need 11:1. The compression stroke doesn't start until the inlet valve closes. The inlet valve closes later on bigger cams, therefor less time to build up cylinder pressure.

[ifcho 0]

Yes, I think I'm going to order the springs these days (they ain't exactly cheap ).

Thanks for the explanataion for the compression, I understand now.

Do you think I should stick with the xu5j head with the square inlets, or go for a xu10j2 head with round inlets. I think that the transition from round trottle bodies to square ports won't be very good for airflow..