Why not mill some of the Dome off the piston, if you use an ultr sonic tester you should be able to safley mill, but I do not know how much you can mill off.

 

Maybe I missed it, but what would the CR be on an AP1 engine w/ AP1 pistons and AP2 rods?

 

Compression ratio with f20 crank and pistons, f22 rods would be 7.735. However this combo will also have a quench pad distance increase of 3.35 mm.

 

This is what I was contemplating doing, If I remember correctly I did the calculations and it was around .096 inch that needed to be milled off of the piston dome in order to bring me to 9:1 compression ratio. However this would decrease the piston dome thickness to around .150 in. . I was going to do some Finite element analysis on the milled piston; however im being lazy and still need to model it before I can do this.

 

 

Even if you can mill down to a 9.75:1 that would be the same a 2mm HG but you would still have all the benifits of the factory quench. If indeed you can mill to 9:1 then that would be amazing.

Do you have any pictures of the underside of the pistons?

Since I did not want to pull the motor I ended up using a porting bit and a light hand slighly mill down my pistons then I finished sanded up to 1000 Grit.

 

Alright ignore my last post, I was at work so I didint have my spreadsheet. Here is the actual data. to lower the compression to 9.5 from 11 using an f20 piston, rods and crank, you need to remove 12.48 Cc's of compression from the piston. Which is equivalent to a bore slice of 2.1mm. When I say bore slice I mean this is the height of a slice of our 87mm bore that would equal -12.48cc compression. The actual amount of material to remove from the piston top is not know because the dome volume is unknown. Also the valve pockets on the piston surface also complicate determining amount to be removed.

Im not sure of the best way to determine the dome volume.

 

interesting

 

The build begins, It was actually quite difficult to find any pistons that were not out of spec, I ended up finding some that were good, However due to the machine shops hone on the cylinders my piston to wall clearance is a little on the big side, at around .002-.0025. I figure it should be ok for an experimental motor, as this motor will only be run for around 1 year before I put my race motor in. Anyway here are some pictures.





New to me Pistons





Freshly honed block, around $150 at the local machine shop



Ap1 crank going in



Assembled block






At this point I notice I have a small problem
looks like the #4 piston is crooked. The donor motor had dropped a valve in that cylinder, and I guess it bent the rod
However thanks to ebay I have a new set on the way , but since I did have to take the pistons back out I decided to send them to the machine shop to mill the domes off I did some rough calculations and I think the compression should be around 9.5:1 after the machine shop is done. The only thing Im concerned about is the piston dome thickness, it should be at about .170 ish after machining. Im not sure if machining the pistons is a good idea, however after talking to my machinist he said he would do it for free so I guess im going to find out the hard way . I figure if it dosen't blow in the first couple of days, it should hold for good, hahaha. And yes just to clear things up a little, I am crazy.

 

[QUOTE=dsddcd,Oct 16 2009, 02:14 PM]
Do you have any pictures of the underside of the pistons?



Here are some pictures of an ap1 piston, Notice the blinging top, I polished it on my new pedestal buffer . its my new favorite tool,