Can an XR4 be pumped to a 175 / 200?

[Musclford]

Used to be that I guy told me he had a 90 hp inline, and made it a 115 by changing jets in the carbs.<br /><br />So, if he wasn't blowing smoke up my,, well you know.. <br /><br />I was told when we ordered our NEW XR4 in 88 that it was the same powerhead as a 175/200. 2.4 L I guess, and it had a smaller torpedo. <br /><br />So, what makes a 150 slower than a 200? If they both turn say 5500 RPMs and they both have the same lower unit gear ratio's, are they just able to turn a bigger pitch prop. <br /><br />I know I'm over simplifying this, but maybe someone has a simple answer.<br /><br />Thanks,<br /><br />Phil

 

[KCLOST]

Re: Can an XR4 be pumped to a 175 / 200?

It's the carbs and I believe the lower unit gears are different 135/150-2/1, 175/200-1.87/1....

 

[WillyBWright]

Re: Can an XR4 be pumped to a 175 / 200?

You aren't going to get 115 out of a 90 by changing jets in the carbs. All you're going to do is lean it out and score cylinders if you go smaller, or foul plugs and carbon-up your rings if you go richer. Either of these will result in a LOSS of power, not an increase. The fuel/air mixture is very specific. Just adding more gas doesn't mean you're adding more oxygen. You can do that with a larger throat size on the carbs, or cram more in there with a turbocharger. Or maybe by using an Oxygen tank instead of sucking air out of the atmosphere, but that would open a whole new can of worms.

 

[jimmbo]

Re: Can an XR4 be pumped to a 175 / 200?

difference between inline 6 90hp and inline 6 115hp... Well first the block is different, so are the pistons, carbs, reeds and reed blocks/mainbearing, the throttle linkage has a different throttle cam and finally the exhaust tube/megaphone.<br /><br />As for the XR4 sharing the block of a 175/200 I doubt it very much if they are identical. Displacement yes, porting, carbs, and exhaust unlikely