I'm about to drop for the AP engineering short block special. I am not sure what CR to order the shortblock. I will eventually be going with an FI setup so I will want a final CR of high 8's low 9's maybe. Not looking for 1khp but maybe a max of 750 or so with the majority of driving done 5-600 hp.

I will eventually get some 6.0 heads or the AFR 225's so what should I shoot for on the static CR on the shortblock?

Also any opinions on piston coatings?

TIA

 

On a stock bottom end 6.0L and AFR225s will yield 9.1-9.2:1.

Most forged flatop pistons are -4 to -6 cc with the valve reflief. Puts ya in the sweet spot with 72cc heads using off the shelf parts.

Personally, I like the moly coated skirts.

Phil

 

How many cubes and what power adder are you going to use?

Mark

 

Going with stock cubes and definitely a turbo setup.

Phil can you elaborate a little more on the benefits of coatings? That is one area I am not very familiar with.

 

If one is eventually going to go with lower compression pistons, would it be better to go with stock cc heads like the AFR 205's for a turbo setup rather than something like 72 cc?

 

If you are building a short block then it is not necessary to go with a larger chamber head...

IMO, If its stock cubes I recommend the AFR 205's... 66cc chambers. Last I checked AFR was not offering the 72cc chamber version even though it shows its available on their website. So, that being said a 15cc dished piston, zero deck height, 66cc heads, and a .052 head gasket should put you around 8.77:1.

Couple of real pro's I would chat with prior to commitment are Phil (Road Rebel) on a good cam and Brian Tooley over at TEA on his version of the "225" on a 3.9 bore that he built for Steve Lamar (slamar)... if you are looking for more port volume and/or flow...

Bill

 

Thanks Bill. It will be a stock cubed motor. I believe that the AFR 205s can be ordered with an upgraded spring but I don't think it is a dual spring. Are they reliable or should one upgrade to a dual spring? No more than 7K rpm and not quite sure of the cam lift yet.

 

The (dual) springs that come standard on the AFR205's are a real nice spring. Last I checked the "upgraded" spring AFR was offering was the Comp 921... which is also a dual spring... but keep in mind I have not talked with AFR (Tony Mamo) in awhile so the info I'm providing may be outdated. Cam and spring pairing is vital in building a valvetrain that will acutally work efficiantly and live for any reasonable period of time at RPM's approaching 7kRPM. Don't forget about lifter selection as well. One thing you don't see discussed a whole lot here is cam base circles and how they affect rate of ramp... and how some springs react differently to different rates of ramp. Some springs do not like aggressive ramp rates... and will cause float in the upper RPM's. Lift, duration, centerline, and lobe seperation angle do not complete a cam profile... and therfore a spring that falls within a cam grind profile may not be the spring of choice because of the ramp rate. The cam base circle and its rate of ramp can be important in choosing a cam for a specific application. I'd like to see some discussion from folks who have dealt with this and see what they have to share. As this forced induction section continues to evolve and push the envelope I think and hope you'll see more indepth discussions regarding the "smaller" details that can become very important...

 

True True. I guess the safest thing to do is order the heads with the 921 springs since I don't know which cam I will eventually go with. Right now I have a 224/224 114 and I believe a 560 lift - Need to dig up the specs if I can find them. That is what I will run until I get the funds to forge.

 

 

Bill is it preferable to use the pistons to lower CR rather than big chamber heads? I'm sure there is some quench/squish theories but is one method preferable to the other?

 

The Quench (Squish band on 2 strokes) is important but does not change with the big or small chambers. But, you have to work around what is available. 71-72cc chambers or 66-68 cc chambers are the most common volumes available so when laying out your plan keep that in mind.

Phil