2270 Deck Height and CR, Pistons sitting proud of the deck, how many shims is too many shims? Options

[vjb206]

Hey folks! I have the bottom-end of my 2270 assembled and spinning freely. Thanks to all who helped me get to this point!

(IMG:http://www.914world.com/bbs2/uploads_offsite/media.giphy.com-23760-1708984357.1.gif)

To quickly recap: I bought the 2257 kit from AA Pistons (78mm stroke, 5.158" rods, etc.). And when I threw a P&C on for a test-fit last weekend, I immediately noticed the piston sitting proud of the deck height at TDC (negative deck) by about 2mm.

(IMG:http://www.914world.com/bbs2/uploads_offsite/media.giphy.com-23760-1708984358.2.gif)

Before I overreact, or buy the wrong stuff, I thought I'd ping the community...

1. Is this normal for a stroker set-up?
2. Can you stack multiple shims when getting up into the .06 >> .09 range?
3. (If no-stack) What's the best place to have custom shims cut?
4. I recall Jake saying using large shims requires lots of advance, anyone have experience here? What am I looking to adjust for upon start-up?

Once I figure out whether or not this is normal (I.E. verifying that I don't have to backtrack), I'll get into the CR questions (just waiting on clear plastic from Amazon so that I can measure my CC volume this weekend) (IMG:style_emoticons/default/biggrin.gif)

Thanks!

[Jack Standz]

Did some measurements this weekend!

(IMG:http://www.914world.com/bbs2/uploads_offsite/media.giphy.com-23760-1709694116.1.gif)
My combustion chambers are 60ccs. Measured with fluid as well as called the manufacturer. Double confirmed.

(IMG:http://www.914world.com/bbs2/uploads_offsite/media.giphy.com-23760-1709694117.2.gif)
Deck height is -0.090. Got that with a dial indicator.

@cgnj LMK if this is in your range if you recall...

@VaccaRabite great to know re: CR range (and thank you for the details, really)

So here's what I'm thinking, would love opinions...
• Base shim of 0.090
• Copper head shim of 0.08
That'll get an 8.6 CR

...a 0.060 copper shim would have gotten me to an 8.9CR. I would have run with that prior to reading this thread, but maybe not?

You need a base shim of 0.135 and NO fire ring (Head shim) at all to achieve .045 deck height. This is for forged pistons.

Base shim of 0.130 for cast stuff.

Few use a head shim (fire ring) today due to what Superhawk referred too.

If you create a deck height clearance LARGER than .060 you eliminate the quench action which VASTLY increases the tendency to detonate and reduces your compression ratio.
Bad in two ways...

Less power AND an increased requirement for higher octane fuel.

Might want to check the deck height for all cylinders, don't assume they're the same.

In addition, you might want to skip the copper head gasket, unless you're racing the car and will re-torque the heads regularly. And using your numbers, you're aiming for zero deck height? If you use a head gasket and zero deck height and you've measured even a little off (again, check the deck heightfor all cylinders), you might end up hitting the piston crown on the head gasket, if it encroaches into the cylinder. Might get away with it, might not. Better to figure it out now before the mock-up. No matter what, plan to mock things up a bunch of times before the final assembly.

[vjb206]

If I'm 90 under and get a 90 shim I'll be at 0. Then the head gasket = my deck height. based on the thread above, I might not want to go that route in the end (still doing some reading per @superhawk's recco).

Can / should multiple cyl base shims be stacked to achieve desired deck height (rather than doing a cyl shim + head gasket)?

Did some measurements this weekend!

(IMG:http://www.914world.com/bbs2/uploads_offsite/media.giphy.com-23760-1709694116.1.gif)
My combustion chambers are 60ccs. Measured with fluid as well as called the manufacturer. Double confirmed.

(IMG:http://www.914world.com/bbs2/uploads_offsite/media.giphy.com-23760-1709694117.2.gif)
Deck height is -0.090. Got that with a dial indicator.

@cgnj LMK if this is in your range if you recall...

@VaccaRabite great to know re: CR range (and thank you for the details, really)

So here's what I'm thinking, would love opinions...
• Base shim of 0.090
• Copper head shim of 0.08
That'll get an 8.6 CR

...a 0.060 copper shim would have gotten me to an 8.9CR. I would have run with that prior to reading this thread, but maybe not?

You need a base shim of 0.135 and NO fire ring (Head shim) at all to achieve .045 deck height. This is for forged pistons.

Base shim of 0.130 for cast stuff.

Few use a head shim (fire ring) today due to what Superhawk referred too.

If you create a deck height clearance LARGER than .060 you eliminate the quench action which VASTLY increases the tendency to detonate and reduces your compression ratio.
Bad in two ways...

Less power AND an increased requirement for higher octane fuel.

Might want to check the deck height for all cylinders, don't assume they're the same.

In addition, you might want to skip the copper head gasket, unless you're racing the car and will re-torque the heads regularly. And using your numbers, you're aiming for zero deck height? If you use a head gasket and zero deck height and you've measured even a little off (again, check the deck heightfor all cylinders), you might end up hitting the piston crown on the head gasket, if it encroaches into the cylinder. Might get away with it, might not. Better to figure it out now before the mock-up. No matter what, plan to mock things up a bunch of times before the final assembly.

[Superhawk996]

Can / should multiple cyl base shims be stacked to achieve desired deck height (rather than doing a cyl shim + head gasket)?

Can they be stacked - yes

Should multiple shims be stacked - no.

Each time you add a head gasket or stack shims you are creating potential leak paths by adding unnecessary interfaces between parts.

[vjb206]

Just going to do some more reading before pulling the trigger on the Type 4 store .150 Blanch Ground Cylinder Shims. Soon. This will get me me an 8.9 : 1 CR. Type 4 Store 2270 page says, "Target compression ratio is 9.0:1 using pump 91 octane or 9.5:1 using pump 93 octane (R+M)/2." So that's just giving me pause that perhaps I need .140. Either way, single shim. No fire ring. I'm in NJ (no altitude, and not mountain climbs) and will run 93 octane at all times.

Also will measure my valve pockets, and factor that into the CR calculations / internal debate.

While I'm mulling that over the plan is to take apart my feeler gauge to set the deck height approximating a big .150 shim. While the deck is mocked up, I'll start playing with the valvetrain geometry. I have an adjustable pushrod so I can start to get the feel. This is the 1s time I'm doing this so I want to have time to explore....

Thanks again for all who have weighed in!

Can / should multiple cyl base shims be stacked to achieve desired deck height (rather than doing a cyl shim + head gasket)?

Can they be stacked - yes

Should multiple shims be stacked - no.

Each time you add a head gasket or stack shims you are creating potential leak paths by adding unnecessary interfaces between parts.