.045 squish, should I be worried

[SB107]

I am getting my build together and currently have 215ccp (12.25 static, 58 intake close), but my squish is set at .045" (0 deck, .045" head gasket).

Should we keep the squish at .045" and 215 ccp, or should we do some modifications (machining pistons) to get the squish closer to .030" while maintaining 12.25:1?

The .030" head gasket gives 12.7:1 compression, 223ccp, but with the tighter squish keep detonation potential lower?

More info: 4.125 bore, 4.625 stroke, 90cc heads, 10cc pistons, tw68 cam, 93 pump tune

[RTMike]

.040 is the max squish that most builders shoot for.to start with what size of head gasket are you using to get .045 and what is  available.

[kd]

I am getting my build together and currently have 215ccp (12.25 static, 58 intake close), but my squish is set at .045" (0 deck).

Should we keep the squish at .045" and 215 ccp, or should we do some modifications (machining pistons) to get the squish closer to .030" while maintaining 12.25:1?

The .030" head gasket gives 12.7:1 compression, 223ccp, but with the tighter squish keep detonation lower?

IMO  Yes   
Yes, at that compression it undoubtedly will have important benefits    

You are about to reap one of the benefits of measuring, measuring, calculating and correcting if necessary before assembling.    Consider that you may be able to reclaim your original compression by instead doing some head work, like a little sinking and / or un-shrouding of the valves to gain compression lowering head displacement (cc's).  Less work with possible gains in your favor.

[SB107]

.040 is the max squish that most builders shoot for.to start with what size of head gasket are you using to get .045 and what is  available.

head gasket is .045

[kd]

I believe you will find that ,045 is the OEM stock gasket size.

[SB107]

I am getting my build together and currently have 215ccp (12.25 static, 58 intake close), but my squish is set at .045" (0 deck).

Should we keep the squish at .045" and 215 ccp, or should we do some modifications (machining pistons) to get the squish closer to .030" while maintaining 12.25:1?

The .030" head gasket gives 12.7:1 compression, 223ccp, but with the tighter squish keep detonation lower?

IMO  Yes   
Yes, at that compression it undoubtedly will have important benefits    

You are about to reap one of the benefits of measuring, measuring, calculating and correcting if necessary before assembling.    Consider that you may be able to reclaim your original compression by instead doing some head work, like a little sinking and / or un-shrouding of the valves to gain compression lowering head displacement (cc's).  Less work with possible gains in your favor.

Heads have already been machined and assembled, they were decked minimally to clean up the hg surface, and came in at 90cc (110 heads).  At this point it would be easier to mill the pistons down to get the lower compression ratio. It looks like there's enough meat on the crown to bring the domes down a few cc (4 according to the calculator).

[kd]

I said that because whoever would be milling the pistons would have to check the cc's as you cut.  It would be tough to pick a number and just shave it off. CCing pistons is not so simple and you will lose your 0 deck (based on if you have flat top pistons of course). Now what do you do?  Do you want to get .030?  Can you get the correct smaller gasket? That's a similar or a more time consuming and maybe more expensive process.  From then on if you need to freshen up a piston you will need to customize the same way.

If you had access to a top head guy they may be able to see a way to massage the chambers in a way that would provide some extra benefits.  To me that would doubly justify the expense.  If you can do the head you will have a consistent cc no matter what you do later.


Added later:

It dawned on me that you said you had only a minimal cut on your heads just for clean up.  To me that means you are likely using domed pistons to achieve your higher compression.  That will change my above opinion about 0 deck so I made an additional comment there.

After typing this I see Mr Sachs chimed in.  You're in good hands now. 

[jsachs1]

I am getting my build together and currently have 215ccp (12.25 static, 58 intake close), but my squish is set at .045" (0 deck, .045" head gasket).

Should we keep the squish at .045" and 215 ccp, or should we do some modifications (machining pistons) to get the squish closer to .030" while maintaining 12.25:1?

The .030" head gasket gives 12.7:1 compression, 223ccp, but with the tighter squish keep detonation potential lower?

More info: 4.125 bore, 4.625 stroke, 90cc heads, 10cc pistons, tw68 cam, 93 pump tune

Whose pistons, what dome configuration, and where were they bought? I did 2 124" engines using 110" MoCo heads within the last2 months. 8 cc dome CP pistons that I had to alter the domes on. PM me and I can tell you what I removed from the domes to get them to 6 cc. if the pistons are the same.
John

[SB107]

I said that because whoever would be milling the pistons would have to check the cc's as you cut.  It would be tough to pick a number and just shave it off. CCing pistons is not so simple and you will lose your 0 deck (based on if you have flat top pistons of course). Now what do you do?  Do you want to get .030?  Can you get the correct smaller gasket? That's a similar or a more time consuming and maybe more expensive process.  From then on if you need to freshen up a piston you will need to customize the same way.

If you had access to a top head guy they may be able to see a way to massage the chambers in a way that would provide some extra benefits.  To me that would doubly justify the expense.  If you can do the head you will have a consistent cc no matter what you do later.


Added later:

It dawned on me that you said you had only a minimal cut on your heads just for clean up.  To me that means you are likely using domed pistons to achieve your higher compression.  That will change my above opinion about 0 deck so I made an additional comment there.

After typing this I see Mr Sachs chimed in.  You're in good hands now. 

I appreciate your input. The pistons are 10cc domes, so you are correct.

[SB107]

I am getting my build together and currently have 215ccp (12.25 static, 58 intake close), but my squish is set at .045" (0 deck, .045" head gasket).

Should we keep the squish at .045" and 215 ccp, or should we do some modifications (machining pistons) to get the squish closer to .030" while maintaining 12.25:1?

The .030" head gasket gives 12.7:1 compression, 223ccp, but with the tighter squish keep detonation potential lower?

More info: 4.125 bore, 4.625 stroke, 90cc heads, 10cc pistons, tw68 cam, 93 pump tune

Whose pistons, what dome configuration, and where were they bought? I did 2 124" engines using 110" MoCo heads within the last2 months. 8 cc dome CP pistons that I had to alter the domes on. PM me and I can tell you what I removed from the domes to get them to 6 cc. if the pistons are the same.
John

All I know about the pistons (currently not in my possession) is that they are 10cc domes configured for the 110 heads. When I get them back I will PM you. I appreciate your help!

[speedzter]

Can you just add 10 thou' (or so ) to the base gasket ?

[kd]

You lose the .000 deck and increase the quench or squish dimension by that .010 barrel lift.

[FXDBI]

Can you just add 10 thou' (or so ) to the base gasket ?

That doesn't zero the deck height.  Its add cc's to the heads or remove from the pistons to be done right. Bob

[SB107]

Assuming the material density is 2.75g/cm^3 (forged 4032), we would need to remove between 11 and 13.75 grams off the piston dome to get to 5-6cc total dome, which gives 12.06-12.18 compression ratio with .030" squish.

I would be sure to keep pistons weights as identical as possible. I will use an indicator to measure before and after height measurements, so both piston domes are the same height.

[rigidthumper]

Bar hopper build? Use the .030" gasket, precise tune, and retard the cam 4°.

[kd]

Assuming the material density is 2.75g/cm^3 (forged 4032), we would need to remove between 11 and 13.75 grams off the piston dome to get to 5-6cc total dome, which gives 12.06-12.18 compression ratio with .030" squish.

I would be sure to keep pistons weights as identical as possible. I will use an indicator to measure before and after height measurements, so both piston domes are the same height.

SB, you start off by saying "assuming".  Then you give some numbers as a calculation.  It sounds sorta technical but I don't see how it is going to work. Each cut off the dome will be different due to the change in the taper and shape of it. Do you plan on catching the chips and weighing them?  I think you are still best to cc the piston dome and check it as you remove layers. John has offered some info that could help if you PM him.  I just hate to see a pair of pistons go to waste by removing too much or different amounts.

Rigid has a good suggestion too.

[SB107]

Bar hopper build? Use the .030" gasket, precise tune, and retard the cam 4°.

Bar hopper, 150mi max per day. Now, the exhaust is being tuned to work with the cam timing, would retarding the cam 4° affect much in terms of the step length calculations? Thanks man

[SB107]

Assuming the material density is 2.75g/cm^3 (forged 4032), we would need to remove between 11 and 13.75 grams off the piston dome to get to 5-6cc total dome, which gives 12.06-12.18 compression ratio with .030" squish.

I would be sure to keep pistons weights as identical as possible. I will use an indicator to measure before and after height measurements, so both piston domes are the same height.

SB, you start off by saying "assuming".  Then you give some numbers as a calculation.  It sounds sorta technical but I don't see how it is going to work. Each cut off the dome will be different due to the change in the taper and shape of it. Do you plan on catching the chips and weighing them?  I think you are still best to cc the piston dome and check it as you remove layers. John has offered some info that could help if you PM him.  I just hate to see a pair of pistons go to waste by removing too much or different amounts.

Rigid has a good suggestion too.

I said assuming because forged 4032 ranges from 2.7-2.8 g/cc, so I just took the mean density and ran with it. If we know density we can figure out how much volume we have to remove by removing so much weight. We would weigh the pistons and see how much weight is removed after each pass, so take Pre-machined weight - post machined weight.

I agree about the piston dome volume though, I will look into the methods of doing so. I apologize if I sound stubborn, I just like learning and having constructive conversation. I really do appreciate any input on the subject.

[rigidthumper]

Some "accommodations" must be made @ this level- guys do it all the time, with the understanding that it's "break, fix, enjoy, repeat".
You will never get stock like reliability/manners from a high compression build, nor should you expect it- but that doesn't mean you shouldn't  have fun, either.
Retarding that cam 4° @ 12.68 static CR should bring the CCP to just under 220. Livable for a hotrod build, IMO.
ACR's/dual manual releases mandatory.

[No Cents]

  knowing that your heads are 90cc's...you know your bore and stroke measurements...why not just buy some CP pistons that will give you exactly what you are shooting for? Randy at Hyperformance might even have what you need in stock...if not he can have a set made for you to get your compression where you want it. He got me +4cc domed pistons for my 124" that is using a set of 110 heads.
  John Sachs could possibly look at the domed pistons you have and he might be able to machine the domes down enough to get you where you want to be. You have to examine the piston first to see if enough material is able to be machined off them. You don't want to weaken over the pistons pin hole too much.

[SB107]

  knowing that your heads are 90cc's...you know your bore and stroke measurements...why not just buy some CP pistons that will give you exactly what you are shooting for? Randy at Hyperformance might even have what you need in stock...if not he can have a set made for you to get your compression where you want it. He got me +4cc domed pistons for my 124" that is using a set of 110 heads.
  John Sachs could possibly look at the domed pistons you have and he might be able to machine the domes down enough to get you where you want to be. You have to examine the piston first to see if enough material is able to be machined off them. You don't want to weaken over the pistons pin hole too much.

I am trying to avoid buying another set of pistons at the moment. I already have these bought, so it would be cheaper and more time efficient for me to chuck them up in a mill and start shaving the crowns.
We will check the crown thickness prior to machining. If we cant machine them, then I will buy a new set of pistons, just trying to avoid the extra cost at the moment.

[SB107]

Some "accommodations" must be made @ this level- guys do it all the time, with the understanding that it's "break, fix, enjoy, repeat".
You will never get stock like reliability/manners from a high compression build, nor should you expect it- but that doesn't mean you shouldn't  have fun, either.
Retarding that cam 4° @ 12.68 static CR should bring the CCP to just under 220. Livable for a hotrod build, IMO.
ACR's/dual manual releases mandatory.

Heads have ACR's, might have manuals put in just in case. Thanks

[kd]

  knowing that your heads are 90cc's...you know your bore and stroke measurements...why not just buy some CP pistons that will give you exactly what you are shooting for? Randy at Hyperformance might even have what you need in stock...if not he can have a set made for you to get your compression where you want it. He got me +4cc domed pistons for my 124" that is using a set of 110 heads.
  John Sachs could possibly look at the domed pistons you have and he might be able to machine the domes down enough to get you where you want to be. You have to examine the piston first to see if enough material is able to be machined off them. You don't want to weaken over the pistons pin hole too much.

I am trying to avoid buying another set of pistons at the moment. I already have these bought, so it would be cheaper and more time efficient for me to chuck them up in a mill and start shaving the crowns.
We will check the crown thickness prior to machining. If we cant machine them, then I will buy a new set of pistons, just trying to avoid the extra cost at the moment.

What Ray is saying makes sense too.  If you are paying for the machine work that's added expense.  You may / probably can sell yours to pay for the others.  I'd look into it at least. The 4.125 bore is pretty common so they may be readily available.  You'll then know what you need for future replacements also.  To me it sounds more like a KISS solution.

[SB107]

  knowing that your heads are 90cc's...you know your bore and stroke measurements...why not just buy some CP pistons that will give you exactly what you are shooting for? Randy at Hyperformance might even have what you need in stock...if not he can have a set made for you to get your compression where you want it. He got me +4cc domed pistons for my 124" that is using a set of 110 heads.
  John Sachs could possibly look at the domed pistons you have and he might be able to machine the domes down enough to get you where you want to be. You have to examine the piston first to see if enough material is able to be machined off them. You don't want to weaken over the pistons pin hole too much.

I am trying to avoid buying another set of pistons at the moment. I already have these bought, so it would be cheaper and more time efficient for me to chuck them up in a mill and start shaving the crowns.
We will check the crown thickness prior to machining. If we cant machine them, then I will buy a new set of pistons, just trying to avoid the extra cost at the moment.

What Ray is saying makes sense too.  If you are paying for the machine work that's added expense.  You may / probably can sell yours to pay for the others.  I'd look into it at least. The 4.125 bore is pretty common so they may be readily available.  You'll then know what you need for future replacements also.  To me it sounds more like a KISS solution.

The pistons are going to be machined for no cost by my headwork guy. He will then re-check compression to ensure we can set squish at .030-.035 and keep the compression closer to 12.2:1. Thanks for your input, you guys have been a huge help!

[No Cents]

  deleted
never mind.

[Ohio HD]

Maybe go with new cams? Set your squish at 0.030", Cycle Rama 660 will drop the compression to about 206ccp.



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[1workinman]

  knowing that your heads are 90cc's...you know your bore and stroke measurements...why not just buy some CP pistons that will give you exactly what you are shooting for? Randy at Hyperformance might even have what you need in stock...if not he can have a set made for you to get your compression where you want it. He got me +4cc domed pistons for my 124" that is using a set of 110 heads.
  John Sachs could possibly look at the domed pistons you have and he might be able to machine the domes down enough to get you where you want to be. You have to examine the piston first to see if enough material is able to be machined off them. You don't want to weaken over the pistons pin hole too much.

I am trying to avoid buying another set of pistons at the moment. I already have these bought, so it would be cheaper and more time efficient for me to chuck them up in a mill and start shaving the crowns.
We will check the crown thickness prior to machining. If we cant machine them, then I will buy a new set of pistons, just trying to avoid the extra cost at the moment.

What Ray is saying makes sense too.  If you are paying for the machine work that's added expense.  You may / probably can sell yours to pay for the others.  I'd look into it at least. The 4.125 bore is pretty common so they may be readily available.  You'll then know what you need for future replacements also.  To me it sounds more like a KISS solution.

The pistons are going to be machined for no cost by my headwork guy. He will then re-check compression to ensure we can set squish at .030-.035 and keep the compression closer to 12.2:1. Thanks for your input, you guys have been a huge help!

My 143 is set to the 12.2 and I was a tad worried at first but a really good tune and some oil and ward cooing fans really make a difference . Of course a good tune . I check the oil temps and use that to show what to do and not as far as stop and go traffic ambient temp ect . At 12.2 depending on your cam timing really makes a difference . A light that shines brighter may not last as long not that I care lol

[SB107]

We shaved the pistons and dropped it to 12:1 with .030 squish.

We are going to run a dual 10 row oil cooler setup to drop engine temps. Being a larger displacement with healthy ccp I want to keep the temps in check.

[kd]