545 Comp Ratio Questions

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545 Comp Ratio Questions

Post  wickettoby1 on June 28th 2018, 12:27 pm

In prepping for a 93 octane street 545 build I'm trying to find a shelf piston that will give me as close to a 11:1 comp ratio as possible. I understand that I can call Diamond and have whatever pistons I want made but I just don't think that its necessary for this build. I always have the option of mixing the 93 with E-85 or high octane but id rather not have that be a requirement.

1977 Lincoln 460 Block ( I don't believe the deck height has been altered)
Lunati 4.5 Stroke Crank
SCAT 6.7" Steel Rods
New SCJ Heads (advertised as 72cc comb chamber but I haven't measured them yet)
Felpro 1018 .041 Head Gaskets
Custom ground cam from a vendor here
6500 Max RPM
Ignition and timing might end up computer controlled if I go with EFI.  

The Icon IC861 22cc dish has caught my attention. From what I can find it doesn't seem like anyone makes a shelf dish piston with a SCJ intake valve layout between the 22cc that Icon offers and the 36-38cc that Icon and a plethora of others offer.  

If my math is correct and I use the 22cc dish Icon at .020 in the hole my comp ratio should be approx 11.2:1 and the quench would be about .060. Please correct me it my math is wrong. My other option would be to use a bigger dish piston and deck the block to 10.30.

Here are my questions for the guru's.
On a later 460 block (like my 77) the deck height was supposedly 10.32", how often do you find this # to be true?
How many cc's of dish can I add to the Icon 22cc dish pistons if needed? When I talked to UEM they said the 22cc dish crown was .232" thick and they recommended not going thinner than .200" in a NA application.

Thanks Guys

Justin

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Re: 545 Comp Ratio Questions

Post  dfree383 on June 28th 2018, 1:57 pm

Whats the Application?

That Cam? Specs?
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Re: 545 Comp Ratio Questions

Post  wickettoby1 on June 28th 2018, 2:13 pm

4200 Lb Street Car, TKO600 Trans

No cam specs yet, cam will be tailored to the final engine combination

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Re: 545 Comp Ratio Questions

Post  dfree383 on June 28th 2018, 3:18 pm

At that weight with a manual trans, running pump gas I'd stay closer to 10:1 to be safe.

In other words spend the Little bit extra on reverse domes with the proper -CC and get your quench tight to about .045.

Don't allow slightly lower shelf piston cost to influence you to put together a poor combination.

You also need to get the deck height measured to get the proper quench, don't assume the dimensions old blocks are all over the place
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Re: 545 Comp Ratio Questions

Post  gt350hr on June 29th 2018, 12:50 pm

+1 go for the tighter quench and proper dish volume . No more than 10.7 -1 if you only have 91 octane. 11 REQUIRES 93 octane to be safe. Buy the right part instead of reworking a cheap part to fit.

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Re: 545 Comp Ratio Questions

Post  wickettoby1 on June 29th 2018, 3:05 pm

I don't have a problem with ordering custom pistons, if that's what It takes to maximize the combo that I want to build then that's what will happen. A couple of hundred dollars extra is nothing in the grand scheme of an engine build.

I know quench is important that's why I specifically asked about it.

As far as the fuel goes we have 93 octane at most stations here in MI , in fact some have 94 octane and I also have an ethanol plant less than a mile from my house. I've seriously thought about upping the compression and going with E-85 but that brings with it its own set quirks.

Justin

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Re: 545 Comp Ratio Questions

Post  gt350hr on June 29th 2018, 3:33 pm

Compression certainly makes torque which =s HP too.

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Re: 545 Comp Ratio Questions

Post  dfree383 on June 29th 2018, 4:17 pm

If you have E85 avaliable it’s definetly a good option if you want to run some compression but maximizing for E85 means pump gas is no longer an option
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Re: 545 Comp Ratio Questions

Post  Mark O'Neal on June 30th 2018, 10:05 pm

Your calculations, and your assumptions are correct.

The difference between 10.0:1 and 11.0:1 will not be noticed in a street application...unless the cam requires it.

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Re: 545 Comp Ratio Questions

Post  wickettoby1 on July 1st 2018, 9:52 pm

Hey Mark

Is there a 28cc-33cc reverse dome for an SCJ head available from your resources?

Justin

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