Eric's porting options

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#1
This winter I will be sending my cylinder off to Eric Gorr for some work. I want my bike to mirror a KTM 125 in performance. What type of powerband should I select? My bike will also feature a Moto Tassinari Delta Valve, which dirt rider claims will "significantly increase top end". I know it wil either be More Top End/ Overev or Mo Better Everywhere but which will give me the easy to ride, super fast mid and crazy top end power of the KTMs? I don't really like narrow powerbands that are hard to keep on the pipe. But I rarely use or need any serious low end power, I like to rev bikes hard.
 

marcusgunby

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#2
The KTM engine is very hard to beat-its very well designed.A v force works well on the RM as does a Bills pipe-thats all i know about the RM so i let others take over.Erics porting will make a good difference-i would go for the mo power everywhere as the top end/overrev is for top experts and can make you alot slower.
 

RYDMOTO

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#3
Back in'93,i bought a slightly used rm125 which was ported for top end.It was actually hard to ride even though i am no beginer.I talked to eric and he suggested to go for the low end porting.He did say most riders think they ride in the upper ranges when really they don't.My buddies even had a hard time riding it.Once it was ported for low-mid,it was very easy to ride.Just my two cents here......hope its helpful.
 

lawman

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#4
why doncha just ask eric what he thinks? that's what i did when he ported mine; i just told him what i was looking for & he did the rest.
 

EricGorr

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#5
You can spray as much orange paint on your bike as you want but it'll never be a true pumpkin!
The KTM125 has a truely unique exhaust port and crankcase design that the Japanese manufacturers will never copy. And its impossible for any aftermarket tuner to duplicate. My suggestion is if you want KTM power then buy one and be a KTM GUY. But watch a lot of old Schwartzenager movies first so you can get down the lingo!;)
 

Vic

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#6
Originally posted by EricGorr
The KTM125 has a truely unique exhaust port and crankcase design that the Japanese manufacturers will never copy.
Why is that?:think
That they won't copy it, that is.
 

clw

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#7
You're kidding, right!

The Japanese not copy something that works better, that will be a first.
 

marcusgunby

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#8
KTM use the no link shock thats offset which allows the carb a straight shot at the crankcases-no jap bike can do that.
 

clw

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#9
The KTM125 has a truely unique exhaust port and crankcase design that the Japanese manufacturers will never copy.
I was interested in the comments (above) by Eric Gorr about the exhaust port and crankcase design. Then again it all may be affected by the straight thru design. Just curious.
 

marcusgunby

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#10
The powervalve on the KTM exhaust port is very good-it can open the main port, then slightly later open the sub ports(im not sure if it does open in this order)It has no bridge and has a very large area compared to the bore.Stange thing is it seems more reliable than the jap engine with a exhaust bridge-backwards to conventional thinking.It is similar to the KX powervalve with the use of subports but they are much higher in the cylinder.It is unque in design.Eric will be able to give a fuller description as its been a while since i had a KTM cylinder apart.The CR powervalve is very good as it has very few parts and does a good job generally.However it does expose the exhuast port all at once and if the port has been opened up as big as it can go then the engine struggles slightly as the powervalve opens,this could be due to the very large port at relativly lowish revs.Ive seen CR engines produce a Hp or more than the KTM engine and yet not feel that fast on the track.The KTM has a very powerful and torquey engine where as the CR can be a true screamer(its based on a RS engine after all)
 

clw

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#11
Kind of neat to see a Euro company doing so well against the Japanese. Still can't believe they won't react. Maybe they did with the YZ250F.

Interesting to note that except for KTM the other mainstream Euro manufacturers (like TM and Gas Gas) basically copy the Oriental bikes technology. I just can't come to grips with the oddball KTM handling.
 
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