For all of you out there who have bit the bullet and got either an FCR or a QuickSilv carb do you feel that porting is a must to recieve a gain in power?-
Eddie

 

From what I've read/heard, head porting isn't necessary unless you're (1) running a high compression piston (11:1 on up) on the stock bore, 406, 416, 426, or 440 bores, (2) along with an aggressive cam, and (3) free-flowing aftermarket exhaust system. To answer your question, with your listed mods I would think either an 39mm FCR or Edelbrock carb might give you a little gain in throttle response and overall power, but porting for the carb alone is not necessary. Further, the money spent on porting could instead be spent on other work, such as a higher compression piston or 416 over-bore (10.8:1 JE Piston) with an XR400 cam.

 

Thanks for your input. I was hopeing to hear something of that nature. I dont know why but I have this wierd thing about porting or boreing my engine. What are your feelings on a 12:1 stock bore piston upgrade?-
Eddie

 

From what I understand, you'll have to run race gas (at least 100 octane) on anything above 11:1, regardless of the bore. I don't know of anyone personally who runs that high of compression piston in the stock bore, but I know of two who run the JE 10.8:1 piston in the stock bore and they get away with 92 octane or the same with a little race gas added. If I were you though, since you're into the motor you might as well bore it out to at least a 416, or go all out with a bore and sleeve to a 440. FYI, I was going to bore mine to 426 but decided against it due to the thinness of the sleeve after boring, so I went to a 416 bore instead. I wanted more horsepower, but also solid reliability without excessive heat. If you do go with a different piston in the stock bore though, I would stick to something around to 11:1 and consider adding a cam such as the one for the XR400. With my 416 bore with JE 10.8:1 piston, XR400 cam and FCR carb, my quad now pulls much harder and build revs much more quickly than stock--this is the route I would suggest to anyone who wants to boost power but still maintain reliability.