Milling 205 AFR's....
 

I picked up some 205 66 cc AFR second hand with about 200 miles on them and was planning on running them out the box, but now I've read that depending on the cam you run and head gasket you use, you should mill the heads accordingly. I plan on running the GM MLS gasket and currently have a F13/112 cam. I know people are recommend the cometic .040 head gasket, but I've had good luck with the MLS gasket so I'd like to stick with it. How much did you guys with F13 mill yours? I talked to Tony and he told me that he made up a volume chart, I searched and had no luck finding it:confused:

Thanks

If you stick with the GM MLS gasket you will need to mill your heads even more to raise the compression.

Depending on how aggressive of a compression ratio you want you can mill the heads to 59 or 60cc to get a scr of 11.3-4 and a dcr of 8.5-8.6.

This is assuming the cam will fit will that much milling. I'm not sure how to calculate or measure ptv clearance.

If you ended up using the .040 cosmetic's you obviously would not have to mill as much to get the same compression ratio.

I would definitely mill those heads to get the compression up, Especially with the stock MLS gasket.

just got off the phone with AFR, the tech told me that if I run the GM MLS gaskets that he recommends milling the heads to desired CR. He then told me that if I ran cometic .040 head gaskets, that without milling the heads, it would bring my CR to 10.8:1, which is what I'm looking for, so I went ahead and ordered some cometics and we'll see how it works. Also what do you guys think about the FAST 90/90 combo over the LS6/ported TB combo? Is the price difference justify swapping out the intakes?

SCR isn't what you should be concerned about. DCR is more important and a true indication of the actual CR you are running. DCR is determined by the valve events created by the cam you choose and as stated above you should try to aim for 8.5 to 8.6 DCR. This will ensure you have optimum compression for best power along with assurance that you won't ping from too much DCR.
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Using .040" gaskets to raise the compression will help but isn't what you want an .040" gasket for. You want an .040" to tighten up your quench distance. The tighter you can get your quench distance without contact the better. If your pistons are out .004" to .008", common for LS1's and LS6's, you will have a .036" to .032" quench distance. This will help with ping and you can actually run a higher compression with a tight quench than without. For example, if you use the MLS .056" gasket you may not be able to run 8.5 DCR. by making the quench tighter and increasing the DCR you may be able to bump your compression to get a few more HP. Do a search on DCR for more info. What I'm saying is, with 10.8:1 CR you might be leaving a bit on the table that going to maybe 11.3:1 will get you another 5-10hp at least by optimizing your DCR with your cam.

^ Yes I talked to LG last week about my setup and they said that if I use the stock MLS gasket I will lose 5-10 HP than if I used the .040.

Id Mill Them:d

Now that you have the .040 cosmetics you can just mill the heads down to 62cc and get a nice scr and dcr.

scr- 11.33
dcr- 8.51

Not sure what your goals for the car are but it seems you want to run a little on the safe side since you were planning on a 10.8 scr. With the thinner gasket and small mill you will run fine on 93 octane.

How much do you guys recommend milling? Just was worried about piston to valve clearance. Also, I'd like to keep the CR under 11:1.
I was thinking .020"?

Mill the heads to 64 cc for a 11.04 scr.

I milled mine to 64cc with .40 cometic gaskets.

Mill them .018 or 3 cc, don't worry about PTV but you'll need to measure pushrod length.

So milling them to .018 would bring it to 63cc and running the cometics with my cam shouldn't be a problem? Is there any formula you used to get this number?

Experience, nope no formula.

So what values would milling to 59cc chambers give w/ cometic?

For every cc less its about .006 shaved off of the head...If you are looking for 59CC chambers thats about .042 milling...Combine that with cometic gaskets and that yields 11.83 static and 8.87 dynamic...Thats pushing it with pump gas...Probably not recommended...
I would go with a 62 chamber with cometics and that will give you 11.3 and 8.5 which IMO would be perfect...Sounds like the exac set-up I am workin on :secret2:

Kev

Not trying to thread high jack but Kev, is it true about the 59cc heads and the cometic? I am about to run that set up, why you say it's pushing it with pump gas?

Runnning a high DCR can be pretty risky...People will say you can run 93 octane with a DCR lower than 9.0(extreme), while others say 8.5 or lower...DCR is finalized to the cam that you are running...A little further, its determined by both the static measured compression ratio, and the intake valve closing event...
You start running into problems when too high of a compression pressure is present...This yields too high of a peak combustion pressure and thus causes detonation.
To get around this you can run a mix of race gas and pump...This can be very costly especially if its your DD...Plus gas prices are ridiculous now a days...

Kev

Well I've searched around and couldn't seem to come up with a solid answer, so I guess I will take you guys word for it. 62cc it is, hopefully with the cometic's I won't have a piston to valve clearance issues.

What are the numbers (duration) like on the F13?