**** 360 Piston Options ****

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krazykuda

krazykuda

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Hi gang, the boys and I are building a 360 and I just got done doing research on piston options for our engine...

The problem in picking pistons is that the manufacturers seem to pick some random compression height for the piston, and then give the "piston dome" volume as another +/- number to help confuse things a bit.

I went to the Summit Racing web site and did a piston search for 360's and came up with a few options for pistons and then calculated what compression that they would be in my engine...

the engine that I'm starting with has already been checked for compression, and I came out to 7.5:1 in my how to check compression thread here:

http://www.forabodiesonly.com/mopar/showthread.php?t=278215


Now taking that info and backing it into the specs listed for the pistons, I would end up with these options for pistons. Keep in mind that I'm looking for options to increase my compression to be between 9.0 - 9.5...


From the previous thread, my info is:

Cyl head = 69 cc
Head Gasket = 12.4 cc
Volume above piston = 34 cc
Compression height = 1.572"
Swept Volume for the cylinder = 752 cc
Area of the cylinder = 12.819 cc
 
Here are the options for Sealed Power/Speed Pro:



The Speed Pro 405P40

Comp dist = 1.576"
Piston dish = 3.140" dia x .0705" depth

The piston compression distance is slightly taller than my starting point of 1.572" from the pistons that came in it...

1.576 - 1.572 = .004"

.004" x 12.819 in**2 = .05 in**3 = .84 cc

The dish is:

Pi/4 x Bore**2 = .7854 * (3.14)**2 = .7854 * 9.860 in**2 = 7.74 in**2

7.74 in**2 x .0705" depth = .546 in**3 x (16.387 cc/in**3) = 8.9 cc

So take the 8.9 cc dish and subtract the .84 cc's from the increased height and you get 8.06 cc increase...

My original volume above the piston at 1.572" was 34 cc (measured in previous thread)

So my new volume above the piston is 34 + 8.06 = 42.1 cc

This brings my Clearance Volume to:

42.1 + 12.4 + 69 = 123.5 cc

Therefore the compression with these pistons will be:

(123.5 + 752)/123.5 = 875/123.5 = 7.09


View attachment Sealed Power 405P40 B.jpg

http://www.summitracing.com/parts/slp-w405p40/overview/make/plymouth


*****************************************************************

The next Option is the Sealed Power WH405CP40

Comp dist = 1.576"
Piston dome = + 10 cc

So for the compression dist:

1.576 - 1.572 = .004"

.004" * 12.819 in**2 = .0513 in**3 (16.387 cc/in**3) = .84 cc increase

Now add the 10 cc for the dome height:

.84 cc + 10 cc = 10.8 cc


Now adjust my old area above the piston for this:

34 cc - 10.8 cc = 23.2 cc

Now my clearance volume becomes:

69 + 12.4 + 23.2 = 104.6 cc

This will make the compression:

(104.6 + 752)/104.6 = 856.6/104.6 = 8.2


View attachment Speed Pro WH405CP40 B.jpg

http://www.summitracing.com/parts/slp-wh405cp40/overview/make/plymouth


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The last Sealed Power/Speed Pro option is the Speed Pro H116CP40:

Comp Dist = 1.660"
Piston Dome = + 5 cc

The increase in compression distance:

1.660" - 1.572" = .088"

.088" * (12.819 in**2) = 1.13 in**3 (16.387 cc/in**3) = 18.5 cc

Now we add the dome volume to the increased compression distance:

18.5 cc + 5 cc = 23.5 cc

Now adjust my volume above the piston:

34 cc - 23.5 cc = 10.5 cc

This will bring my clearance volume to:

69 + 12.4 + 10.5 = 91.9 cc

This will bring my compression to:

(91.9 + 752)/91.9 = 843.9/91.9 = 9.18


View attachment Speed Pro H116CP40 B.jpg

http://www.summitracing.com/parts/slp-h116cp40/overview/make/plymouth
 
Here are the Keith Black options:

There are basically three options for the Keith Black pistons, all of which have the compression distance = 1.675", so I will back that into my compression height:

1.675 - 1.572 = .103"

.103" (12.819 in**2) = 1.32 in**3 (16.387 cc/in**3) = 21.6 cc

This will bring my area above the piston to:

34 - 21.6 = 12.4 cc

Just for kicks, I backed it into the compression to see what the baseline compression is for the Keith Black pistons:

69 + 12.4 +12.4 = 93.8 cc

This will bring the compression to:

(93.8 + 752)/93.8 = 845.8/93.8 = 9.0

So the baseline compression for the Keith Black pistons is 9.0:1, and you can just adjust by the increase in piston dome volume for the rest of the comparisons...

**********************************************************

When I narrowed down the options to only pistons with positive piston dome height, I got three options...

***********************************************************

Keith Black KB373-040

Piston dome = + 2.75 cc

So we take the 93.8 cc from the first calculations above and get:

93.8 - 2.75 = 91.05 cc

This brings the compression to:

(91.05 + 752)/91.05 = 843.05/91.05 = 9.26

View attachment KB373-040 B.jpg

http://www.summitracing.com/parts/uem-kb373-040/overview/make/plymouth

*****************************************************

The next option is the Keith Black 107:

Piston dome = + 5 cc

93.8 - 5 = 88.8 cc

This brings the compression to:

(88.8 + 752)/88.8 = 840.8/88.8 = 9.47

View attachment KB107-040 B.jpg

http://www.summitracing.com/parts/uem-kb107-040/overview/make/plymouth

******************************************************

Now just for kicks, I wanted to check the Keith Black SKB232-040:

Piston Dome = + 18 cc

93.8 - 18 = 75.8 cc

This brings the compression to:

(75.8 + 752)/75.8 = 827.8/75.8 = 10.9

View attachment SKB232-040 B.jpg

http://www.summitracing.com/parts/uem-skb232-040/overview/make/plymouth
 
Those are the affordable options for a 360 engine with stock heads and using the fel pro .055" head gasket that comes in all the engine teardown gasket kits....

The Speed Pro 405P40 = 7.09

The Sealed Power WH405CP40 = 8.2

The Speed Pro H116CP40 = 9.2

The Keith Black KB373-040 = 9.26

The Keith Black KB107-040 = 9.47

The Keith Black SKB232-040 = 10.9

*Note: I used the .040" over pistons for the calculations as that is what my engine is bored at. The similar pistons in stock or less overbore will be slightly different, but close enough to use these numbers as a ball park if you are choosing pistons for your 360 build....


Have a good day!!! :D
 
How sure are you on that gasket info? Unless the gasket changed, Felpro stock replacement (blue permatorque) gaskets are .045 or so compressed thickness. Victor Reinz are thicker, in the .055 range. Those have not changed since the 80s and 90s respectively when they each came out.

My standby is the KB-107. Lightest of the bunch (I always internally balance the engines I build), plenty strong unless the user plans for big nitrous, and very stable with the tight piston to wall. However - if your engine is already run at +.040 then I would use the Speed Pro H116CP because the KB needs a tight piston to wall and is best on a fresh bore/hone job. The Speed Pro doesn't.
 
moper said:
How sure are you on that gasket info? Unless the gasket changed, Felpro stock replacement (blue permatorque) gaskets are .045 or so compressed thickness. Victor Reinz are thicker, in the .055 range. Those have not changed since the 80s and 90s respectively when they each came out.

My standby is the KB-107. Lightest of the bunch (I always internally balance the engines I build), plenty strong unless the user plans for big nitrous, and very stable with the tight piston to wall. However - if your engine is already run at +.040 then I would use the Speed Pro H116CP because the KB needs a tight piston to wall and is best on a fresh bore/hone job. The Speed Pro doesn't.
Click to expand...


I measured a compressed one myself with calipers and did the calculations for my How to check compression thread, and it came out to 12.4 cc.

They do not sell the fel pro .039" thick gasket in the teardown kits, you can only buy them as singles for $40 each... You can get a complete gasket kit for less than those two gaskets cost.... :banghead:
 
Felpro 8553pt head gaskets are real inconsistent, any where from .045 to.057,I always use the 1008's.
Great job Karl
 
The old stand by KB 107's get my vote, and yes the FP8553's I have seen were at least .050 or more. I normally use the 1008, but am going to try the Mr Gasket 1121g .028 thin gasket to gain a few points compression.
 
Re-check your WH405CP CR; the top is a dish, not a dome, so the dish volume should be added, not subtracted. The CR should be only fractionally different from the 405CP, if at all. The W stands for 'individual' (not a set)and the H stand for hypereutectic, and the C stand for coated skirt, but they are the same pistons. Both should work out to around 7.6:1 SCR, not 7.0:1, with 69 cc combustion chambers and .051" head gaskets (the number I used for standard Felpro's).

http://www.fme-cat.com/digipubZ/sealed-power-vintage/#?page=402

I hope you will forgive me for saying so, but one problem with the above calcs is that you are modifying from your original CR number of 7.5 based in the assumption that the old pistons were flat topped. Is that known to be the case? (I am assuming they are not...) Plus you are starting from a number derived from a static compression measurement. That compression measurement is limited in accuracy and in its translation to SCR. It is more accurate to work with straight computations.
 
nm9stheham said:
Re-check your WH405CP CR; the top is a dish, not a dome, so the dish volume should be added, not subtracted. The CR should be only fractionally different from the 405CP, if at all. The W stands for 'individual' (not a set)and the H stand for hypereutectic, and the C stand for coated skirt, but they are the same pistons. Both should work out to around 7.6:1 SCR, not 7.0:1, with 69 cc combustion chambers and .051" head gaskets (the number I used for standard Felpro's).

http://www.fme-cat.com/digipubZ/sealed-power-vintage/#?page=402

I hope you will forgive me for saying so, but one problem with the above calcs is that you are modifying from your original CR number of 7.5 based in the assumption that the old pistons were flat topped. Is that known to be the case? (I am assuming they are not...) Plus you are starting from a number derived from a static compression measurement. That compression measurement is limited in accuracy and in its translation to SCR. It is more accurate to work with straight computations.
Click to expand...


I used the data provided in the postings for deck height and piston dome volume. A positive dome is sticking up and taking away volume, a negative dome is a relief and adding more.

The way that I interpret the listings is that they specify the piston deck height, and then you adjust for the dome...


My old pistons were flat top with a dish that I measured the volume above the piston myself to be 34 cc, then backed it into my compression calculations to target a flat top piston. Unfortunately, they don't give the piston specs that way and you have to cross reference the compression height with the dome volume to see how it will affect the new engine....


I'm trying to make an educated guess with the information that is provided to get my engine in the ball park where it needs to be...


I just measured a 340 recently that was supposed to have 10.5 compression pistons that came out to 8.11.... You need to take the stack ups for block deck height and cylinder head volume into account, which is what my process does...
 
summit is messing with U, the w405cp under notes: recessed head .070" deep, and U are adding 10cc for a "dome" just cuz they say +10cc when U should be subtracting 10cc for a dish. what was the compression height on those 340 pistons, probably the 1.73 from the 1972-3 8.5:1
 
moper said:
How sure are you on that gasket info? Unless the gasket changed, Felpro stock replacement (blue permatorque) gaskets are .045 or so compressed thickness. Victor Reinz are thicker, in the .055 range. Those have not changed since the 80s and 90s respectively when they each came out.

My standby is the KB-107. Lightest of the bunch (I always internally balance the engines I build), plenty strong unless the user plans for big nitrous, and very stable with the tight piston to wall. However - if your engine is already run at +.040 then I would use the Speed Pro H116CP because the KB needs a tight piston to wall and is best on a fresh bore/hone job. The Speed Pro doesn't.
Click to expand...
Don't suppose you want to calculate useing a 3.79" stroke and trw L2405f .030 (cheap forged pistons)? What's gonna be my CR with 70 cc cc heads.?
 
Run the pistons at zero deck height, 74cc heads, head gasket with a 4.125" bore size, 0.039" compressed thickness. Pistons have 5cc valve reliefs and the compression ratio is 9.56:1. This set up gives you a 0.039" quench distance. I don't know for a fact but I've read that the KB pistons are more brittle than the speed pro pistons and the speed pros have a friction coating on the piston skirts.
 
I just realized I agreed with something that was posted SEVEN years ago.


But given a choice, for an engine that's gonna be run hard, I'll always put forged pistons in it. Can't remember that far back that I built a cast (or hyper)piston engine.


No wait, that's not true. I used cast pistons.... in my 1933 straight eight.
 
gtsdude said:
The old stand by KB 107's get my vote, and yes the FP8553's I have seen were at least .050 or more. I normally use the 1008, but am going to try the Mr Gasket 1121g .028 thin gasket to gain a few points compression.
Click to expand...
Good choice that .028" gasket. I think perfect for usewith a closed chamber 65-68 cc aluminum head. ..and yes, that's what I got.
 
.028" bout as perfect as you can get for quench. That's what "tuneing for performance " says in one of my old motorcycle SA design books....don't laugh, those engines get rung up all the way to 11,000 rpm.
 
And I might add, with pump gas and high compression,but they had the squish also built in the combustion chamber. I am thinking, a savy engine builder could easily design his own squish if he had small closed Chamber aluminum heads, allowing the increase CC's for the cut, all= rev / run like a motorcycle on pump gas and high compression ...if you get the cam right.
 
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