is the 727 kit the best bigbore kit out for the raptor, os is there an even better and more reliable one?[img]i/expressions/face-icon-small-happy.gif[/img]

 

i'm not sure if thers something bigger then a 7 and a quater but i'll tell you one thing it won't be more reliable
i think once you go past a 686/690 kit your going for hp not reliablity
jmo

 

I wouldn't say the 727 is the best big bore kit, but if done right you can get just as much reliability out of the 727 as you could the 686. The super high compression levels like 13 -1 plus is where you start losing reliability but in turn produce more HPs.

 

I think velocity is right its just how far on the ragged edge you are willing to go

 

IMO, a 105mm bore will not help you until you are built correctly. I say correctly, because there are 686's out there that will and that can beat 727's out there. Once built to the hilt, the extra 3mm bore will help you get that little bit extra out of the motor.

Regarding reliability. Again, IMO I don't think the 105mm bore is any more unreliable then the 102mm, but head gasket issues come into play more with the larger bore. There are ways to fix that though and it seems that not many are going the correct route to make an ultra reliable head gasket for the 105mm bore. I am finding this out the hard way and am making the necessary changes currently.

Also, just so that you understand. Technically, a 105mm bore (stock is 100mm) with the stock stroke (84mm) is not a true 727cc. It is 728.37765, the 102mm bore being 687.35065....to the best of my calculations.

Lastly, and this is FYI in case you haven't considered it. I would recommend you use an aftermarket rod if your considering building any type of half way serious Rap motor, whether it be a 102 or 105mm bore machine. I have seen 4 rods let go with my own eyes and it ain't pretty when they let lose. One of those 4 was my own on a mild 102mm Rap motor, so beware and consider it. A thrown rod can end up costing you twice as much as the initial build in the first place!

Good luck on your build!

 

Great info swytak..Thanks for the suggestions.

 

I'm confused, I just did the calculations on the 105mm bore and I also came up with 728.37765 ??

 

727 sounds better then 728.

 

Air, who knows. You may be right, but this is how I have always figured it.

Bore x bore x stroke x .003146 divided by 4 (for single cylinder) = CC's


Anybody else have any input on the correct way to calculate this?

 

I have a 727 and have had no problems with it other than its almost too much power. yes I have the 02 pro cut tranny with hinson basket and pressure plate and a carillo rod to be safe but like said before rather do it now than something even worse go wrong. I think that it is the best big bore kit out the 770 is 5mm stroked and I have heard about some problems of them not holding up in the long run. also the bigger valves i have been told makes the head crack easier. not to be mistaken with trinity racing having the one middle valve bigger im talking about all three. like i said the 727 has more than enough power to go around I would recommend it to anyone.