With a 10.5:1 piston...


10 replies to this topic
  • jdilpkle

Posted March 20, 2008 - 05:23 PM

#1

Question -
My 14,000 mile L has compression of 145 hot. (spec. 199)
If I get a 10.5:1 piston, will I NEED a cam to really take advantage of the piston swap? I don't want to lose any bottom end. A guy up the street from me who works on bikes as a business in his garage said that the cam would not take away bottom end power with the new piston, but give me more pulling at higher rpm in addition.
Thoughts? :confused:
Thanks in advance.
jdilpkle

  • jscompto

Posted March 20, 2008 - 05:26 PM

#2

I am not for sure what the actual answer is, but i just got a 103mm piston with 10.5:1 compression and also a hotcam. as soon as i get it all back together and working right, i can tell you what the difference is with cam.

  • Denn10

Posted March 20, 2008 - 05:44 PM

#3

high comp piston with stock cam will be an improvement, now with a cam you would get max out of it, so i wouldnt say you HAVE to do them at the same time.

  • xrltim

Posted March 20, 2008 - 06:18 PM

#4

I have the piston you are talking about. My cam is stock and I have an XR's only pipe and K&N jet kit. The bike has way more power than stock, pulls at all rpm's nicely. Correct carburation just as good as a fresh rebuild so make sure you have that right. It wheelies very easily in first and second gears, little clutch in third. I have not yet had any negative effects and I run 87 octane gas. Be sure you get the piston rings on right.

  • martinfan30

Posted March 20, 2008 - 07:49 PM

#5

I have just the hotcam, a FCR 41, E2 exhaust and ground down header welds. The engine has lost no bottom end at all. The mid to top end is really nice. It also rev's up quicker mid to top.

Cant wait to try the hicomp piston.

You will notice good power increase with just the piston. The cam will just make it even better. Try each mod in stages. You will get a better appreciation for the power that each mod brings to the table.

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  • jdilpkle

Posted March 20, 2008 - 08:01 PM

#6

Good idea, since finances are the limiting factor. Piston and a good valve job first, cam maybe later. I wouldn't have to pull the cylinder for the cam upgrade. That sounds like the plan. I wonder how the stock valves will be after 15,000 - 20,000 miles. I guess we'll see.
jdilpkle

  • asf

Posted March 21, 2008 - 02:07 PM

#7

There are tons of cams avaialble. I think the one that you want is the HRC stage one. If you get a cam, get hardened lifters, else you are going to have to open the top end up again too quickly.

  • martinfan30

Posted March 21, 2008 - 02:12 PM

#8

There are tons of cams avaialble. I think the one that you want is the HRC stage one. If you get a cam, get hardened lifters, else you are going to have to open the top end up again too quickly.


The Hotcam stage1 I installed is meant to be used with the stock springs and followers.

Says that right in the instruction manual.

Providing that there is not any bad wear on these parts.

  • asf

Posted March 21, 2008 - 02:57 PM

#9

The Hotcam stage1 I installed is meant to be used with the stock springs and followers.

Says that right in the instruction manual.

Providing that there is not any bad wear on these parts.


I meant to say rockers, long week.

Anyways, I'm pretty sure there is a hardness difference in the Hotcams cam and the stock rockers. (I dont know for sure though, please correct me if I am wrong). If one metal is harder than the other, then the softer will wear very quickly.

  • martinfan30

Posted March 21, 2008 - 03:01 PM

#10

I meant to say rockers, long week.

Anyways, I'm pretty sure there is a hardness difference in the Hotcams cam and the stock rockers. (I dont know for sure though, please correct me if I am wrong). If one metal is harder than the other, then the softer will wear very quickly.



Oh you are right are about hard vs soft. I dont know what degree of hardness the Hotcam is, i'm sure they wouldnt tell to use the stock rockers/followers if there was a wearing issue.

  • Itchykawa

Posted March 21, 2008 - 08:49 PM

#11

I have the piston you are talking about. My cam is stock and I have an XR's only pipe and K&N jet kit. The bike has way more power than stock, pulls at all rpm's nicely. Correct carburation just as good as a fresh rebuild so make sure you have that right. It wheelies very easily in first and second gears, little clutch in third. I have not yet had any negative effects and I run 87 octane gas. Be sure you get the piston rings on right.


What would be "correct carburation" with that setup? Would Dave's mods and 160/58 jets do?





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