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PostPosted: Tue Jul 27, 2021 9:27 am 
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TBI Slant 6
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Joined: Thu Apr 07, 2016 9:15 am
Posts: 193
Location: Rhode Island
Car Model: 1968 Barracuda - Fastback
I've got a 225 with 198 rods and Wiseco PTS536A45 pistons at 3.445" bore - the head and block were just kissed for gasket sealing...

I'm using AussieSpeed's Big Bore gasket that has a 0.060" thickness on the gasket and 0.070 on the ring.

My piston is projecting 0.007" past the block deck.
Is this Okay?



Everything I've read about the long-rod conversion leads me to believe this should be at zero-deck. But I'm not, and the block has never before been cut. This is not a racer - nor will it see high-RPM. Just making sure the tolerances are in spec before buttoning up the engine.

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PostPosted: Tue Jul 27, 2021 1:00 pm 
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Supercharged
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Location: IRWIN PA
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If it does not hit the chamber of the head and there is .090" clearance in between piston and chamber then I would not worry about it.

If you really want .000 you can have that much milled off the piston tops.

I wonder what doc and others think about this...


Greg

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PostPosted: Tue Jul 27, 2021 1:42 pm 
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Turbo Slant 6

Joined: Thu Jun 07, 2012 4:29 pm
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Location: Houston
Car Model: 68 Valiant
It's unclear...what is the compressed thickness of your gasket? I think you are giving uncompressed measurements which don't mean much.

Does the gasket provide full cylinder clearance, or does any part of it overhang the cylinder at all?

If your piston is .007" out of the deck at TDC, and the gasket is .040-.050" thick (compressed), you'd probably never have a problem. That's especially the case on a low revving Six. I might have a different opinion on an 8000RPM small block.


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PostPosted: Tue Jul 27, 2021 5:06 pm 
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Joined: Tue Oct 29, 2002 8:27 pm
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Location: Salem, OR
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If you only took a clean up scrape off the head and the chamber volume is still in the 50+cc range...if the top ring on the piston is still below the deck
at TDC, you should be OK... that being said I would run the compression ratio calculator to make sure that you have met your target SCR, as a little
bit goes a long way when shooting above 10:1 SCR. If the aussie gasket crushes at .066 things will look pretty good...

That being said, the next big danger will be your chosen cam lift...I can tell you that a head in the mid-40 cc range and a stock piston with a deck height of -.014
needed to have the pistons relieved with a .53 lift cam (that engine went from 12:1 and became an 11.8:1 engine)... you might be OK if you chose the .47-.48 lift range...
but at this time I would install piston #1 and #4, degree the cam then put a 3/8" thick chunk of playdoh on top of each piston, install the head with a clean previously used
head gasket or a piece of thin cardboard and install the head with hand tight head bolts, install lifters, pushrods and rockers for those pistons and roll the crank over by hand twice, if the pistons don't get stuck on the valves and halt the rotation, pull the head and see how deep the impressions are...if paper thin you may need to alter the degree of the cam or relieve the pistons...if the impression is pretty thick (1/16"+) you can proceed with the rest of your assembly.


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PostPosted: Tue Jul 27, 2021 6:00 pm 
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My engine was the same, just a little out of the deck. But mine was a race motor so we cleaned @ .015 off the top of the pistons. That being said if you have a compressed thickness of .040-.045 you will likely be fine. Of more concern is if you use big valves or not? If yes then you will need to check the valves reliefs to see if the valve catches the edge of them. Lift is not much of an issue since the reliefs are plenty deep. My .570 lift, .260 @ .050 cam had plenty of room, but the pockets needed opened up a little to clear edge of the valve. ( They are not quite exactly in the right place) :D

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PostPosted: Thu Jul 29, 2021 6:20 pm 
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I have 0.030" between pistons at TDC and head chamber on 1 engine and around 0.040" on another. Pistons are 0.005" out of hole on one and 0.015" on the other. 6000+ RPM redline and no problems. 0.045" compressed gasket on both. Need to measure piston-valve carefully with the cam you will use and the position you will use it in and have 0.090" or more.

Lou

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PostPosted: Thu Jul 29, 2021 6:20 pm 
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Yes, I have big cams and valve notches on both engines.

Lou

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PostPosted: Sat Aug 07, 2021 7:50 am 
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TBI Slant 6
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Location: Rhode Island
Car Model: 1968 Barracuda - Fastback
Thanks for all the info everyone! Here's where I ended up...

I bought the last two Aussiespeed big-bore cylinder head gaskets (AS0193) in the US (sorry folks) which come in at 0.055" compressed leaving a confirmable safety margin. The pistons do have reliefs for the oversized (Ford 289) valves, and with .476"/.479" valve-lift - I think I'm all set. Final compression here BTW, is 9.8.

Much appreciate all the shared knowledge!!

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PostPosted: Sun Aug 08, 2021 1:44 pm 
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Sounds good. Look forward to hearing how it runs.

Lou

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