Decking, quench, and compression ratio help for 4.1?

[Sleeper]

Trying to figure some stuff out and need some help. I'm building a 4.1 stroker.
I have a stock 4.1 (291) block that I have had bored 4.005". 40 over
Standard deck height of 4.1 is 9.560
I'm going to be using
4” forged Ross pistons. Compression height on piston is 1.225"
3.625 stroke Buick Motorsports Steel Forged crank
Carrillo 6.350 rods
Champion CNC ported Irons 46cc
The friend/board member who I bought the rotating assembly parts from, had it in a block that was decked to 9.3875, and I'm pretty sure he said it was close to zero decked, and ran Cometic HG (not sure if they were 0.57”, or 0.67”) He said he had around 9.3:1 comp with GN1's,

My problem is I have a heck of a lot of piston low in the hole with the STD 9.560 deck height. (It looks like I'm running 0.1725 in the hole.)
I was planning on running Felpro 1000's (.039)
Any idea of what CR I would run if I use it as is?
Is that much quench just asking for detonation trouble?
If I have to, can a standard 4.1 (291) block be safely decked that much?

Thanks

 

[bison]

Trying to figure some stuff out and need some help. I'm building a 4.1 stroker.
I have a stock 4.1 (291) block that I have had bored 4.005". 40 over
Standard deck height of 4.1 is 9.560
I'm going to be using
4” forged Ross pistons. Compression height on piston is 1.225"
3.625 stroke Buick Motorsports Steel Forged crank
Carrillo 6.350 rods
Champion CNC ported Irons 46cc
The friend/board member who I bought the rotating assembly parts from, had it in a block that was decked to 9.3875, and I'm pretty sure he said it was close to zero decked, and ran Cometic HG (not sure if they were 0.57”, or 0.67”) He said he had around 9.3:1 comp with GN1's,

My problem is I have a heck of a lot of piston low in the hole with the STD 9.560 deck height. (It looks like I'm running 0.1725 in the hole.)
I was planning on running Felpro 1000's (.039)
Any idea of what CR I would run if I use it as is?
Is that much quench just asking for detonation trouble?
If I have to, can a standard 4.1 (291) block be safely decked that much?

Thanks

Without the piston dish we can't calculate compression. If your pistons are that far down they are the wrong ones. Your CR will be too low

 

[TurboBob]

...... (It looks like I'm running 0.1725 in the hole.)...................
If I have to, can a standard 4.1 (291) block be safely decked that much?

Thanks

No way..... something is definitely wrong with that combination. Stop putting stuff together and figure out whats wrong.

The way it is it will never run decently, let alone be fast....

did you mock it up and measure the "down in the hole", or are you just calculating it?

Bob

 

[Jerryl]

Any idea of what CR I would run if I use it as is?
Is that much quench just asking for detonation trouble?
If I have to, can a standard 4.1 (291) block be safely decked that much?

Thanks

Try this;
Engine Compression Ratio (CR) Calculator

And X2 what Bison and Bob said. :wink:

 

[LOT]

Felpro 1000

Trying to figure some stuff out and need some help. I'm building a 4.1 stroker.
I have a stock 4.1 (291) block that I have had bored 4.005". 40 over
Standard deck height of 4.1 is 9.560
I'm going to be using
4” forged Ross pistons. Compression height on piston is 1.225"
3.625 stroke Buick Motorsports Steel Forged crank
Carrillo 6.350 rods
Champion CNC ported Irons 46cc
The friend/board member who I bought the rotating assembly parts from, had it in a block that was decked to 9.3875, and I'm pretty sure he said it was close to zero decked, and ran Cometic HG (not sure if they were 0.57”, or 0.67”) He said he had around 9.3:1 comp with GN1's,

My problem is I have a heck of a lot of piston low in the hole with the STD 9.560 deck height. (It looks like I'm running 0.1725 in the hole.)
I was planning on running Felpro 1000's (.039)
Any idea of what CR I would run if I use it as is?
Is that much quench just asking for detonation trouble?
If I have to, can a standard 4.1 (291) block be safely decked that much?

Thanks

Don't believe a Felpro 1000 will work.

 

[Ttype6]

Standard deck height of 4.1 is 9.560
I'm going to be using
4” forged Ross pistons. Compression height on piston is 1.225"
3.625 stroke Buick Motorsports Steel Forged crank
Carrillo 6.350 rods

The pistons you are using are meant to be used with 6.50 inch rods.Did you have a machinist measure your deck height with a proper fixture or are you just assuming that that number is correct because someone told you that that is the deck height that people on this forum generally say it should be. I know of four 291 blocks in my life and they are all around 9.535" deck height. If your deck height is truly 9.560" and you use a 6.35" rod and pistons with a compression height of 1.225" your piston should be .173" in the hole. It sounds like your deck height is what you were told it is. If you use a 6.500" rod you would still be .023" down in the hole. There's no way that this combo would be at zero deck if installed in any Buick V6. you'd need a 6.50" rod or a taller comp height,somewhere around 1.390".

 

[forcefed3.8's]

Wrong compression height for the rods/ stroke. I am running 9.515 deck height, 6.3 rods, 3.625 crank, pistons .01 in the hole, and my compression height is 1.393. You have almost .2xx after a gasket quench. You should have around .040. If you have flat top pistons, you might have compression, but with that piston so far in the hole, it won't run right. Get the right pistons. A 6.5 rod and decking the block to 9.53 will get you there with those pistons. Spend the money and do it right, or it will cost twice as much later on when it breaks. You shouldn't cut a deck to 9.38, it will weaken it, and you will have major intake fit issues. Are the pistons even good for a turbo app?

 

[Sleeper]

Without the piston dish we can't calculate compression. If your pistons are that far down they are the wrong ones. Your CR will be too low

I'm trying to get some specs on the pistons. I'm thinking the same thing.

 

[Sleeper]

No way..... something is definitely wrong with that combination. Stop putting stuff together and figure out whats wrong.

The way it is it will never run decently, let alone be fast....

did you mock it up and measure the "down in the hole", or are you just calculating it?

Bob

Bob
I caught this a little late but, they were used in a different 4.1 setup that had a DH of 9.3875
I mocked it up and took a rough measurement, but did a calculation anyway and it seems pretty close to the measured.

Paul

 

[hotairgnx548]

Trying to figure some stuff out and need some help. I'm building a 4.1 stroker.
I have a stock 4.1 (291) block that I have had bored 4.005". 40 over
Standard deck height of 4.1 is 9.560
I'm going to be using
4” forged Ross pistons. Compression height on piston is 1.225"
3.625 stroke Buick Motorsports Steel Forged crank
Carrillo 6.350 rods
Champion CNC ported Irons 46cc
The friend/board member who I bought the rotating assembly parts from, had it in a block that was decked to 9.3875, and I'm pretty sure he said it was close to zero decked, and ran Cometic HG (not sure if they were 0.57”, or 0.67”) He said he had around 9.3:1 comp with GN1's,

My problem is I have a heck of a lot of piston low in the hole with the STD 9.560 deck height. (It looks like I'm running 0.1725 in the hole.)
I was planning on running Felpro 1000's (.039)
Any idea of what CR I would run if I use it as is?
Is that much quench just asking for detonation trouble?
If I have to, can a standard 4.1 (291) block be safely decked that much?

Thanks

My 291 with hypers was .103 in the hole. I used a cometic .027 THICK, 4.020 BORE DIA., 3.985 (+.020) bore, 3.40 stroke, 42c/c head, 33c/c piston dish, .103 below deck and have a 8.045 to 1 c/r. Go to Engine Compression Ratio( CR) Calculator and just type in your numbers. see ya good luck you will love it.

 

[Sleeper]

Try this;
Engine Compression Ratio (CR) Calculator

And X2 what Bison and Bob said. :wink:

Thanks for the calculator.

Ttype6
I'm assuming based on posted figures 3.8 is 9.535 and 4.1 is 9.560 the big board also said that the 3.8 reduced the DH by .025 from the 4.1 spec.
I will get my machinist to accurately measure it for me.
That is the figure I go as well. As I said it was run in a different block that was decked to 9.3875.

forcefed3.8'

It's a dished piston.
I had a lot of stuff on my plate at that time, and didn't really look into it in detail when I bought the setup from a friend/boardmember.

Ok , so what are my options now?
How much can you safely deck the 4.1?

 

[bison]

My 291 with hypers was .103 in the hole. I used a cometic .027 THICK, 4.020 BORE DIA., 3.985 (+.020) bore, 3.40 stroke, 42c/c head, 33c/c piston dish, .103 below deck and have a 8.045 to 1 c/r. Go to Engine Compression Ratio( CR) Calculator and just type in your numbers. see ya good luck you will love it.

I got 7.84:1

 

[hotairgnx548]

I got 7.84:1

My error the dome volume is 30c/c. Sorry You are sharpe Bison. See ya!

 

[Ttype6]

Thanks for the calculator.

Ttype6
I'm assuming based on posted figures 3.8 is 9.535 and 4.1 is 9.560 the big board also said that the 3.8 reduced the DH by .025 from the 4.1 spec.
I will get my machinist to accurately measure it for me.
That is the figure I go as well. As I said it was run in a different block that was decked to 9.3875
How much can you safely deck the 4.1?

I've read these numbers as well and didn't find them to be true on the four blocks I've seen. If you're saying that you installed these parts into your block and found the distance between the top of your piston and the deck surface to be .175" then your deck height must be very close to 9.560. This means that your deck height is.172" taller the you friends block. This is why your pistons are so far down in the hole. Knowing the deck height of your friends block and your block,you should never have expected this combo to work and he should never have told you it would work. It's very important that you know the volume of your piston dish. Once you find out what it is,go to the Eagle sight and install all of your numbers into there compression ratio calculator to see what your ratio is. Install 6.50 for your rod length because this is the length you'll need for those pistons. If you like the number you see,get some 6.50" rods. If you don't like the numbers you see,keep the rods you have and get some different pistons. You can use the calculator to decide what compression height and dish volume to order. Deck thickness is a precious commodity. You don't want to remove any material from the deck surface because it weakens it.

 

[bison]

I've read these numbers as well and didn't find them to be true on the four blocks I've seen. If you're saying that you installed these parts into your block and found the distance between the top of your piston and the deck surface to be .175" then your deck height must be very close to 9.560. This means that your deck height is.172" taller the you friends block. This is why your pistons are so far down in the hole. Knowing the deck height of your friends block and your block,you should never have expected this combo to work and he should never have told you it would work. It's very important that you know the volume of your piston dish. Once you find out what it is,go to the Eagle sight and install all of your numbers into there compression ratio calculator to see what your ratio is. Install 6.50 for your rod length because this is the length you'll need for those pistons. If you like the number you see,get some 6.50" rods. If you don't like the numbers you see,keep the rods you have and get some different pistons. You can use the calculator to decide what compression height and dish volume to order. Deck thickness is a precious commodity. You don't want to remove any material from the deck surface because it weakens it.

if it was me I'd be using the 6.3" rod and order a new set of CP's

 

[Sleeper]

I've read these numbers as well and didn't find them to be true on the four blocks I've seen. If you're saying that you installed these parts into your block and found the distance between the top of your piston and the deck surface to be .175" then your deck height must be very close to 9.560. This means that your deck height is.172" taller the you friends block. This is why your pistons are so far down in the hole. Knowing the deck height of your friends block and your block,you should never have expected this combo to work and he should never have told you it would work. It's very important that you know the volume of your piston dish. Once you find out what it is,go to the Eagle sight and install all of your numbers into there compression ratio calculator to see what your ratio is. Install 6.50 for your rod length because this is the length you'll need for those pistons. If you like the number you see,get some 6.50" rods. If you don't like the numbers you see,keep the rods you have and get some different pistons. You can use the calculator to decide what compression height and dish volume to order. Deck thickness is a precious commodity. You don't want to remove any material from the deck surface because it weakens it.

Thanks, for the info and help. I might be missing this, or not using it right, but I don't see where I can plug in the rod length.
My specs:

Enter Bore/Stroke Designation Type
1 = Inches 2 = Millimeters
Enter Cylinder Bore Size 4.005
Enter Piston Stroke Length 3.625
Enter Head Gasket Bore Diameter 4.020
Enter Compressed Head Gasket Thickness .039
Enter Combustion Chamber Volume In CCs 46
Enter Piston Dome Volume In CCs Negative For Dished Pistons (Use '-') -33 ? guess for now?
Enter Piston Deck Clearance Negative If ABOVE Deck (Use '-') : .1725

 

[bison]

Thanks, for the info and help. I might be missing this, or not using it right, but I don't see where I can plug in the rod length.
My specs:

Enter Bore/Stroke Designation Type
1 = Inches 2 = Millimeters
Enter Cylinder Bore Size 4.005
Enter Piston Stroke Length 3.625
Enter Head Gasket Bore Diameter 4.020
Enter Compressed Head Gasket Thickness .039
Enter Combustion Chamber Volume In CCs 46
Enter Piston Dome Volume In CCs Negative For Dished Pistons (Use '-') -33 ? guess for now?
Enter Piston Deck Clearance Negative If ABOVE Deck (Use '-') : .1725

The rod length isn't a determining factor. The swept volume and the clearance volume are what matters. If you change the rod length with the same piston, bore, stroke, head volume and head gasket bore and thickness you change the clearance volume.

 

[Ttype6]

if it was me I'd be using the 6.3" rod and order a new set of CP's

Me Too!

 

[Ttype6]

I don't see where I can plug in the rod length.

Go here,

http://www.eaglerod.com/

 

[Ttype6]

Enter Piston Deck Clearance Negative If ABOVE Deck (Use '-') : .1725

I'm not sure what calculator you're using but I see what there doing. In stead of asking for rod length they're asking for the distance between the top of the piston and the deck. The only way to do this is to buy parts and install them into the motor and then measure. This doesn't help you pick out a rod and piston combo. What do you do if it's wrong? This calculator is for determining what the compression ratio of an assembled motor is. If you want to use a compression ratio calculator to help you choose a piston and rod combo,use the link I provided.