View Full Version : 300EX BIG BORE 250SX MOTOR? - Can it be done?!

04-04-2007, 03:07 PM
I have seen this mentioned briefly discussed in threads here and there. Cold hard facts, can it be done? I have purchased a used cylinder,head and camshaft. I am planning on building a motor for my sx and figured if i could get the cylinder and head cheap enough i would see if it can be done. I would like your opinions. I know some guys will say why wouldnt you get a 200x or 350x. I love my sx. Just want a narly motor in it. I know im not the only one.

Some one even mentioned using the 300ex cylinder and piston with the stock 250sx head.

Plan of Attack

supertrapp exhaust system
300ex topend
High comp 300ex piston
WebCam with chrome moly valve springs
oew timing chain
oem valves
oem guides
350x carb
open airbox
K & N filter


04-04-2007, 03:50 PM
not the 300ex but the trx head and cyl combo, also with a few mods (jackshaft assy) you can jsut put the complete trx 300 motor in the sx! I got one and think when my 250 es craps out i might put the top end on .

04-04-2007, 04:27 PM
sykolincoln you are correct. I meant the trx 300. That is what i purchased.

04-04-2007, 04:52 PM
yea do a search for 300sx and should find the thread of the conversion

04-04-2007, 05:36 PM
Yeah but that thread was about putting an etire trx motor into an SX, he is just ging to use the top end.

I would say look at your head bolts on the SX then compare that to the trx cylinder and measure, if the hols line up you might be golden

04-04-2007, 08:54 PM
You will not get more cc's by putting the trx300 cylinder on your sx bottem end because the 300 and 250 have the same bore , the difference is in the stroke

04-04-2007, 09:27 PM
ah yes very true so i wounder if you can just throw the high comp trx piston in the SX ?

04-04-2007, 10:19 PM
no shiz?? didnt even care to look at that! well... damn.... oh well. at least I got extra parts lol.

04-04-2007, 10:42 PM
sh!t i never even thought of that. damn. well the thought was there. Hmm. High comp 300trx piston.......... now thats interesting

04-05-2007, 11:15 AM
you can't use the trx piston in the sx either because the pin hole is alot higher on the trx , i can get a pic of the difference if you would like .

Later jeff

04-05-2007, 03:33 PM
lets see the difference. this is interesting.

04-22-2007, 01:55 AM
i wanna see too.