Raising compression

Hello Ford lovers.I have done my math and came with 8.6 scr.
I have a box beside my bed with new speedpro forged flattops that have 2.7cc valve relives and a
set of arp´s for my rods.
New headgaskets 0.045" but it seems that I have to cut my heads to get the chambers around
48cc to get the scr up to about 10.5.
How much is safe to cut?
I have 2 options on cams as well:comp 282s or comp 280B-6.Or maybe custom?
I think it is the low dcr from low scr and way to big cam now that is killing my performance.Like you said.
What do you think?
Have a nice day/Gresse

what size are the chambers and how far in the hole are the pistons? Those #'s don't add up for me.

I agree with Brian, Whats your deck height set at?

Deck is standard 0.015 I think.
Gasket 0.039
Dish Standard 12cc I think
Chambers 55cc
I get it to 8.6
Gresse

If the main reason for tearing into this engine is to raise compression and the pistons are going to be replaced, I'd take it one step further by replacing the crank & rods with a 302. That will increase displacement and help raise compression.

As far as deck clearance goes, don't guess, measure it. Piston to head clearance is critical with quench type heads. The Power SqueezeYou should be shooting for a .035-.045" distance max. So if the pistons are .015 in the hole you should be looking for a .030 thick head gasket. If you want to run a .045" gasket, the block should be decked .015-.020.

That should get you pretty close to 10.5:1. If you still need more, then you can cut the heads.

Do you have 2.7cc valve relieves or 12cc?

Plus there is a lot of "I think" in there, you need to really measure anything that has not been. A stright endge and a feeler gauge at TDC is better than nothing, and recommend you do at least the 4 corner holes because rarely is a deck that hasnt been squared decked even close.

However, with 12 cc I get 8.6 too, with 2.7 I get 9.71 SCR, even thats a smidge low

However, DCR isnt the only number, as you rev higher the motor gets closer to 100% VE, and even exceeds it. That means it will be filling the cylinder well above the DCR number and even exceed the SCR

If it were be, I'd go with the 2.7's, be sure to degree the cam and have it installed no later than 106 ICL, you could even run it at 104 if you have P/V clearance, and maybe find a .020-.022 head gasket

However, dont guess at the cam installation, the deck clearance, the valve clearance, , the cc'd of the heads, or if the deck if straight. Once we have the info, even if its ugly, we can deal with it. If you dont check it, all the math and money is a waste

There also may be another option, if you order a custom grind from Comp you may be able to find a cam with steeper ramps (less adv, more .050 duration) if you do that, you will need less SCR for the same DCR

You have too much cam and too little compression. You need to zero deck the block - .015 is too far down for most common head gaskets. If you're running stock rods, you need to measure the deck. On the 302 here, it was anywhere from .009 to .018. If you go to zero and run a flat top with 3cc of valve relief, you're at 10:1 with a regular Felpro gasket. That's a minimum for the listed cam and will not be a problem on 91 pump gas. Zero deck with a set of flat tops will help a considerable amount.

Are you sure on the 55cc - most 289 heads come in at 58cc. If you end up with more than 5cc out of the pistons and/or the heads come in at 58, you could use a smaller cam. With 5cc reliefs and 58cc chamber, about 230 on the intake.

I think you are a tad fat on the jetting.

Thank you very much.Sorry for the " I think". I havent tear it down yet but when I do I will get all the measurement right.
Questions are just so I can do a little math and hopefully learn something.
My new pistons in a box are 2.7cc.Will go in this winter.
Just a little curious how much is safe to cut the heads,if I have to.
I think your right about the jetting.It feels stronger now and its real cold outside.
Thanks again for all the help and tips you give me./Gresse

I think the general rule is that you can cut around .030 before you need to get the intake cut too to match. Im not positive on that either.

Depends - the first order of business IMHO would be to mock up the engine with the new pistons, finished rods and finished crank. Then measure the deck in each hole on both banks. You'll need a deck bridge, dial indicator and degree wheel to do that accurately. Then the shop can use those numbers to cut the block. Do that first, not the heads. Then measure the chamber cc, then plan any further cuts. Figure about .006 per cc on those heads, more or less. On my new 351C, we cut the block .016, then the heads .012.