My car has 25K miles. I've been boosting with APS ST for 5000 miles now. Running strong with no problem, but I want to up the boost to get to 450whp mark safely. So, I want to build up my engine a little. I'm talking bare minimum engine build. Arias 9:1 pistons, Eagle rods and bolts. My question is do I have to overbore the cylinders? I know most of engine rebuild involves overboring 0.2mm, but is it necessary?

 

Well you want the engine's cylinders to be as smooth as possible with little imperfections as possible. If lets say you don't bore and you pull the old pistons and rods, and drop the new ones in, then the old surface may smooth the news pistons and rods. The end result would be increase blow-by, lost compression (lose hps), etc... To be safe, boring is recommended and if you look at it, it is not that much more for this extra precaution. You are spending a few thousands so why not a little 300 more for the bore to do it right the first time?

 

+1 for boring and i would say you might be better with a 8.5:1 than a 9:1 future wise. Good luck and have fun boosting.

 

Due to the nature of stock piston scoring, machining the cylinders is usually recommended to ensure proper piston/wall clearance as well as removing any gaps that could exist between the rings and cylinder walls. For this reason when we build motors (that handle 61psi ) we have found the stock bore with 9.5 compression to suit our needs, but have to take some measure to use them. To run stock bore you must sleve the block, as to alieve the aforementioned issues. Block sleveing also strenthens what can be seen as one ofthe weak points of any motor build, the block itself. We have ran compression ratios in our motors ranging from 8.5 to extremely built-up 10.3. We settled on 9.5 for that it suited our needs for reliability in street cars as well as the extreme power of our race cars. Just about any compression will do and should be determined by the amount of boost and turbo set-up you are running. Good luck with your build, let me know if you have any further questions.

 

Thanks for the advice.. Do you happen to sell built short block just like SGP? I'm thinking about just buying the already built short block and be done with it.. Hicksville... I used to live in Huntington and research at the Cold Spring Harbor Laboratory... I miss Long Island and Manhattan...

 

Yes we do....we sell just about everything and they are all built by proessional motor builder and drag racing champion Vinny Ten. What did you study? My girlfriend just got her PhD in Oncology and is now doing post-doc work at Columbia...C.S.H. looks like a sweet place to work.

 

We consider a .020 overbore a basic requirement of building a shortblock. Each cylinder will be a slightly different diameter, and may have unwanted taper in them. The only way to acheive accurate and consistent piston to wall clearance, is to overbore to the point that proper piston to wall clearance is achieved. Piston to wall clearances vary by piston manufacturer, type of material used, and the size of the piston.

 

It is recomended to overbore, but if your going for the bare minimum build and your doing it yourself, then you can get away without overboring it. But like the pro's say, if your sending the block off to get it done, you might aswell do it.