Bbc 454 gen 4 overhaul
11-09-2020 | 12:25 AM
#73
Platinum Member
Joined: Sep 2001
Posts: 5,769
Likes: 151
From: tn
It's your motor, and it's your dollars. .050" is pretty much the line in the sand.
Under .045" quench clearance is a "SQUISH MOTOR". Above .055" is not.
A motor with tight quench clearance is more responsive, has better throttle response, can accept optimal ignition advance curves on lower octane, is much more detonation resistant and can handle more boost than a "non squish" motor of the same compression ratio.
In the 70's everybody put pop-up 11.5:1 pistons in our 350 small smallblocks with open chamber heads. The piston pads were 040 to 060 in the hole and we ran 039 gaskets The. actual CR was usually in the neighborhood of 10.5 to 10.8:1. And on pump gas they rattled like a snare drum, and we had to pull so much timing out that they ran like total crap. When we went to the grudge drags, we cranked the timing up, dumped in race gas, and went fast. Then, we pulled the timing back out and ran a sick rattling pump gas motor til the next weekend. We didn't understand the concept of squish turbulence.
If you build the same motor with zero deck, 039 gaskets, and flat-top pistons, and cut the heads to give you the same 10.5 to 10.8:1 compression, then you will be rewarded with a motor that you can't make rattle on pump gas running full timing advance. It will rev quicker, and go faster on pump gas than the other motor would run on race gas.
We've got a 440 Mopar RB running 11.3:1 with aluminum closed chamber heads (TFS 240s) on 91 octane with 18 degrees initial, and 38 degrees all in at 2900 with 56 degrees with vacuum advance. We can't make it rattle. Runs stronger and harder than any of the motors we built the "old way". The biggest example is the Coronet we ran years ago with a solid roller cam and 11:1 pistons that needed race gas to keep from rattling. The new motor runs more compression, has less duration and overlap (hydraulic flat tappet, no less), runs on pump gas, and is 2 tenths faster in the 1/8th and is a blast to drive.
So, do you NEED to make sure you end up 036-040 squish? No. People run motors every day that dont operate "in squish". In fact, chevy big blocks never came in cars and trucks with tight squish. That was a secret engine-builder trick until the late 1980's.
Now you have 2007 6.2L Yukons and Tahoe with 10.6:1 CR and 410hp running on 91 octane and getting better fuel economy than a 165hp Chevy 305 from 1982. These are not the "direct injected LT motors". They are normal port-injected motors with TIGHT SQUISH CLEARANCE.
But yes, to cut the block you'll have to strip it bare and pay $175 or so.
I won't think less of you if you don't.
But its my position that I would be doing you a disservice by not explaining the benefits..
Under .045" quench clearance is a "SQUISH MOTOR". Above .055" is not.
A motor with tight quench clearance is more responsive, has better throttle response, can accept optimal ignition advance curves on lower octane, is much more detonation resistant and can handle more boost than a "non squish" motor of the same compression ratio.
In the 70's everybody put pop-up 11.5:1 pistons in our 350 small smallblocks with open chamber heads. The piston pads were 040 to 060 in the hole and we ran 039 gaskets The. actual CR was usually in the neighborhood of 10.5 to 10.8:1. And on pump gas they rattled like a snare drum, and we had to pull so much timing out that they ran like total crap. When we went to the grudge drags, we cranked the timing up, dumped in race gas, and went fast. Then, we pulled the timing back out and ran a sick rattling pump gas motor til the next weekend. We didn't understand the concept of squish turbulence.
If you build the same motor with zero deck, 039 gaskets, and flat-top pistons, and cut the heads to give you the same 10.5 to 10.8:1 compression, then you will be rewarded with a motor that you can't make rattle on pump gas running full timing advance. It will rev quicker, and go faster on pump gas than the other motor would run on race gas.
We've got a 440 Mopar RB running 11.3:1 with aluminum closed chamber heads (TFS 240s) on 91 octane with 18 degrees initial, and 38 degrees all in at 2900 with 56 degrees with vacuum advance. We can't make it rattle. Runs stronger and harder than any of the motors we built the "old way". The biggest example is the Coronet we ran years ago with a solid roller cam and 11:1 pistons that needed race gas to keep from rattling. The new motor runs more compression, has less duration and overlap (hydraulic flat tappet, no less), runs on pump gas, and is 2 tenths faster in the 1/8th and is a blast to drive.
So, do you NEED to make sure you end up 036-040 squish? No. People run motors every day that dont operate "in squish". In fact, chevy big blocks never came in cars and trucks with tight squish. That was a secret engine-builder trick until the late 1980's.
Now you have 2007 6.2L Yukons and Tahoe with 10.6:1 CR and 410hp running on 91 octane and getting better fuel economy than a 165hp Chevy 305 from 1982. These are not the "direct injected LT motors". They are normal port-injected motors with TIGHT SQUISH CLEARANCE.
But yes, to cut the block you'll have to strip it bare and pay $175 or so.
I won't think less of you if you don't.
But its my position that I would be doing you a disservice by not explaining the benefits..
11-09-2020 | 01:03 AM
#74
Charter Member # 55
Joined: Oct 2000
Posts: 20,272
Likes: 2,513
From: Omaha/LOTO
Run the retrofit cam which is the same specs as the 731 except made for MarkIV/Gen V. https://www.summitracing.com/parts/crn-139011
Then use this timing chain set up or similar. It has a thin bearing on the block side of the upper sprocket. https://www.summitracing.com/parts/crn-13977-1
Then use a cam button like this or similar. https://www.summitracing.com/parts/crn-99165-1
I'm pretty sure these are the exact parts I used when I swapped to roller cam in my 525SC.
Then use this timing chain set up or similar. It has a thin bearing on the block side of the upper sprocket. https://www.summitracing.com/parts/crn-13977-1
Then use a cam button like this or similar. https://www.summitracing.com/parts/crn-99165-1
I'm pretty sure these are the exact parts I used when I swapped to roller cam in my 525SC.
11-09-2020 | 05:27 AM
#75
Registered
Joined: Jul 2009
Posts: 8,527
Likes: 706
From: Taunton Ma
It's your motor, and it's your dollars. .050" is pretty much the line in the sand.
Under .045" quench clearance is a "SQUISH MOTOR". Above .055" is not.
A motor with tight quench clearance is more responsive, has better throttle response, can accept optimal ignition advance curves on lower octane, is much more detonation resistant and can handle more boost than a "non squish" motor of the same compression ratio.
In the 70's everybody put pop-up 11.5:1 pistons in our 350 small smallblocks with open chamber heads. The piston pads were 040 to 060 in the hole and we ran 039 gaskets The. actual CR was usually in the neighborhood of 10.5 to 10.8:1. And on pump gas they rattled like a snare drum, and we had to pull so much timing out that they ran like total crap. When we went to the grudge drags, we cranked the timing up, dumped in race gas, and went fast. Then, we pulled the timing back out and ran a sick rattling pump gas motor til the next weekend. We didn't understand the concept of squish turbulence.
If you build the same motor with zero deck, 039 gaskets, and flat-top pistons, and cut the heads to give you the same 10.5 to 10.8:1 compression, then you will be rewarded with a motor that you can't make rattle on pump gas running full timing advance. It will rev quicker, and go faster on pump gas than the other motor would run on race gas.
We've got a 440 Mopar RB running 11.3:1 with aluminum closed chamber heads (TFS 240s) on 91 octane with 18 degrees initial, and 38 degrees all in at 2900 with 56 degrees with vacuum advance. We can't make it rattle. Runs stronger and harder than any of the motors we built the "old way". The biggest example is the Coronet we ran years ago with a solid roller cam and 11:1 pistons that needed race gas to keep from rattling. The new motor runs more compression, has less duration and overlap (hydraulic flat tappet, no less), runs on pump gas, and is 2 tenths faster in the 1/8th and is a blast to drive.
So, do you NEED to make sure you end up 036-040 squish? No. People run motors every day that dont operate "in squish". In fact, chevy big blocks never came in cars and trucks with tight squish. That was a secret engine-builder trick until the late 1980's.
Now you have 2007 6.2L Yukons and Tahoe with 10.6:1 CR and 410hp running on 91 octane and getting better fuel economy than a 165hp Chevy 305 from 1982. These are not the "direct injected LT motors". They are normal port-injected motors with TIGHT SQUISH CLEARANCE.
But yes, to cut the block you'll have to strip it bare and pay $175 or so.
I won't think less of you if you don't.
But its my position that I would be doing you a disservice by not explaining the benefits..
Under .045" quench clearance is a "SQUISH MOTOR". Above .055" is not.
A motor with tight quench clearance is more responsive, has better throttle response, can accept optimal ignition advance curves on lower octane, is much more detonation resistant and can handle more boost than a "non squish" motor of the same compression ratio.
In the 70's everybody put pop-up 11.5:1 pistons in our 350 small smallblocks with open chamber heads. The piston pads were 040 to 060 in the hole and we ran 039 gaskets The. actual CR was usually in the neighborhood of 10.5 to 10.8:1. And on pump gas they rattled like a snare drum, and we had to pull so much timing out that they ran like total crap. When we went to the grudge drags, we cranked the timing up, dumped in race gas, and went fast. Then, we pulled the timing back out and ran a sick rattling pump gas motor til the next weekend. We didn't understand the concept of squish turbulence.
If you build the same motor with zero deck, 039 gaskets, and flat-top pistons, and cut the heads to give you the same 10.5 to 10.8:1 compression, then you will be rewarded with a motor that you can't make rattle on pump gas running full timing advance. It will rev quicker, and go faster on pump gas than the other motor would run on race gas.
We've got a 440 Mopar RB running 11.3:1 with aluminum closed chamber heads (TFS 240s) on 91 octane with 18 degrees initial, and 38 degrees all in at 2900 with 56 degrees with vacuum advance. We can't make it rattle. Runs stronger and harder than any of the motors we built the "old way". The biggest example is the Coronet we ran years ago with a solid roller cam and 11:1 pistons that needed race gas to keep from rattling. The new motor runs more compression, has less duration and overlap (hydraulic flat tappet, no less), runs on pump gas, and is 2 tenths faster in the 1/8th and is a blast to drive.
So, do you NEED to make sure you end up 036-040 squish? No. People run motors every day that dont operate "in squish". In fact, chevy big blocks never came in cars and trucks with tight squish. That was a secret engine-builder trick until the late 1980's.
Now you have 2007 6.2L Yukons and Tahoe with 10.6:1 CR and 410hp running on 91 octane and getting better fuel economy than a 165hp Chevy 305 from 1982. These are not the "direct injected LT motors". They are normal port-injected motors with TIGHT SQUISH CLEARANCE.
But yes, to cut the block you'll have to strip it bare and pay $175 or so.
I won't think less of you if you don't.
But its my position that I would be doing you a disservice by not explaining the benefits..
ever had the heads off a 1075? Flat top pistons are .120 in the hole.
11-09-2020 | 06:44 AM
#76
Registered
Joined: Jan 2003
Posts: 6,023
Likes: 1,522
From: Grand Rapids, MI
11-09-2020 | 07:32 AM
#77
Platinum Member
Joined: Sep 2001
Posts: 5,769
Likes: 151
From: tn
And, no. I've not had heads off a 1075sci. I've had bore scopes in them and they do run flat-tops. And while I don't doubt what you say, the Diamond piston website shows the 1075sci stack up with stroke, rod length, and piston compression height to be
(4.375 ÷ 2) = 2.187 (stroke by half)
+ 6.635 (rod length)
+ 1.380 (piston compression ht)
= 10.202"
That's on a GM tall deck, which is a 10.200" block. For the pistons to be down 120 the deck ht would have to be 10.320
11-09-2020 | 08:08 AM
#78
Registered
Joined: Oct 2010
Posts: 1,621
Likes: 402
From: Cheboygan, MI
Take a look at the Daytona Sensors ignition. I swapped from the MSD 6M to Daytona Sensors. The difference is incredible, very useful feature set as well. I run 93 octane, but when I can't, I can flip a switch and pull 4 degrees out to run 90 octane marina gas. Idle control with timing is amazing.
11-09-2020 | 07:11 PM
#79
Thread Starter
Registered
Joined: Sep 2020
Posts: 216
Likes: 15
From: Kentucky
Build
Ok so we got cam and gear train figured out now do do i buy flat top or keep what I have and build from them secondly if u guys do say flat top do I install 1 in the same hole and remeasure the piston height then have cut ???????
