Next Mod? 300ex with a lot of work done already

[dbc112]

So I have a 300ex motor with a lot of upper end work. The bore was never touched for national specs.

What would you go with? I have a budget of about $400... I have seen some 385 kits...

I already have Top level porting, heavy duty springs and triple angle valve job.... full DG exhaust, 400ex carb (stock jetting) and uni filter.


How can I get the most out of this? I am looking for a screamer. I was also thinking about buying a 400ex engine with 440 kit, but really dont want to go another $1500.. I guess i could sell what I have, but it bolts so nicely to my 250x frame.

Suggestions? what products, companies?

[dbc112]

Ok, spent the better part of the work day reading up and now understand what I have.

Port Job- better air in (approx 15% increase in power)

Web Camshaft- Approx 10% increase

Valve Job- 3 angle allows for better seating of valve after porting job


Next Steps

Increase bore size from stock 74mm to 80mm this will increase CC from stock (not including the above) to approx 329CC


I have a call to GT thunder to see if any stroke work was done. If so,t he CC rating will increase obviously

With everything factored in I gustimate my CC will be the following

329*15% port= additional 49cc

380 (approx adding in above) x 10% cam shaft additional 38cc

380+38= 408 cc


increase of 127cc or 8.4 HP (15cc per 1HP)


With everything else DG exhaust, 400ex carb, and filter I should have adequate breath in and out...

[2muchquad]

i still have my 385 motor,when i sold my quad i put a 250x motor back in it.Those calculations are rather modest.Trying to compute hp per cc based on mods is a excersize in fultility.There are to many variables,hp isnt always made on a linear scale(as far as 2hp for every 20cc gain etc)

[dbc112]

Yeah.. i read that conversion somewhere.. and it is definitely to the wheels etc.