TRW L2416F Piston Compression Height?

I don't recall that number ever being posted.

You need to measure it with a feeler gauge with the piston installed in the car, and you are measuring how far down in the hole the piston is.

With the canted reliefs in those pistons I want to say that the number was only an approximation to begin with.

They are always a problem to mill them down when the have the domes because you have to pick a common spot on the piston to measure from and that always leaves a little indecision initially.

If you just replace the dished TRW pistons with the flat top TRW you will be fine with the closed chamber heads (61cc) and pump gas. You just don't want the 47cc aftermarket aluminum heads.

You normally don't need to know exactly what the static cr is. You just need to know the vicinity it is in.

The closed chamber Cleveland head starts to show sensitivity to octane sooner then the 289 head does.

I doubt you could run over 10.5:1 actual with todays pump premium gas and don't waste your time on octane booster unless you are adding lead to the fuel. The other stuff won't work.

Doug, yes, it was posted on the 351C forum, sorry for the confusion. I am trying to do this with the motor in the car and keep the pistons that are installed. Not that many miles on them. I agree, I don't want to above 10:1, more like 9.5 or so. I may just have to take the time and pull the heads before I order. When you say "the number was only an approximation to begin with" are you referring to the dish volume? Thanks, Evan

quote:

Originally posted by Wasatch Cat:
Doug, yes, it was posted on the 351C forum, sorry for the confusion. I am trying to do this with the motor in the car and keep the pistons that are installed. Not that many miles on them. I agree, I don't want to above 10:1, more like 9.5 or so. I may just have to take the time and pull the heads before I order. When you say "the number was only an approximation to begin with" are you referring to the dish volume? Thanks, Evan

The pin height.

Obviously there is a factory dimension on it but since it isn't listed by them you need to measure it yourself and as such you have to consider it as approximate. I remember going through this myself and the engine builder said, it doesn't matter, just put them in.

I have that piston in my engine with the A3 heads. My heads were shaved by the original builder for use in a circle track race car to get them down to 59cc's.

I'm running what you want to build. Something around 9.7 to one.

My suggestion to you would be to shave a set of aluminum heads down like I did and leave the pistons alone.

I thought that the flat tops would give me too close to an 11 to one and I had just replaced an engine with the TRW popups which were nearly 12 to one.

That engine would detonate so bad on pump gas it would litterally shut itself off at 4500rpm.

Now if you ran 106 Sunoco race gas then Hell had come to supper, it was an animal. That just made no sense on the street since you couldn't drive it anywhere unless you had a tanker truck meet you with high octane racing gas.

If you run the pistons the way they are with an unshaved head you are still around 9.5 to one. I wouldn't worry too much about what exactly the static ratio is if I were you.

This is one of those go, no go situations. The engine will be responsive enough with them and the closed chamber heads.

Yes, I want to leave the pistons alone, the motor runs great. Just want to wake it up a little and replace the 40 year old valve train parts while I am in there. A new cam will probably be called for.

12:1 would be a lot of fun when you can find fuel.

Any chance you wrote down your piston to deck distance when you assembled the motor?

Sounds like I will be safe shaving the new heads down around 58-60cc. I assume I can get the machinist to cc the heads once they are done.

Thanks.

That dimension is in a locked up hard drive. Sometimes I wake up in the middle of the night and remember the numbers. I'll PM it to you if I do.

The most you can cut the iron heads is .030". Usually they get cut .020". Then you won't have to worry about cutting the manifold to fit.

There is a chart somewhere that indicates how many cc;s are reduced per .001". Your shop may have it.

I don't think you can get the iron heads under 60cc's.

If you go with the iron heads you can use a steel shim head gasket that is .020" thick instead of .037".

That saves you a lot of effort.

I personally think all of the 4v iron heads should be "cleaned up" under the valves. What this involves is pocket porting the area immediately under the valves to remove the restriction ring cast into these heads for production purposes. All the iron heads have them.

The L2416 pistons were designed to give a 351C 8.5:1 compression with quench heads. They really aren't appropriate for any other application.

I'm gonna walk through the compression ratio math, and explain why along the way.

First some accurate statistics:

351C nominal deck height = 9.215"
351C nominal connecting rod length = 5.78"
351C nominal piston compression height = 1.65"
351C nominal deck clearance = 0.035"

Nominal combustion chamber volume:
1970 D0AE heads = 63cc
1971 D1AE heads = 66cc
1971 D1ZE heads = 75cc
1972 D2ZE heads = 75cc
1973 D3ZE heads = 78cc
1974 D3ZE heads = 78cc
_____________________________

The formula for static compression ratio is: (Vs + Vc ) ÷ Vc = static compression ratio

Everything is converted to cubic centimeters to perform the calculations (0.061 cubic inches = 1cc)
____________________________

Vs = volume of the swept area, i.e. the bore x stroke of one cylinder

351 cubic inches = 43.875 cubic inches per cylinder = 719cc per cylinder
357 cubic inches (0.030" oversize) = 44.625 cubic inches per cylinder = 732cc per cylinder
____________________________

Vc = volume of the clearances above the top piston ring at top dead center

-----------------------------------------------------
+ combustion chamber volume
-----------------------------------------------------
Clearance Volumes (use both):

+ volume of head gasket (1cc per 0.005" of compressed thickness)
+ deck clearance (1cc per 0.005")

(Note: with a flat top piston I like to keep the sum of these clearances,
which I call the "total clearance", in the range of 0.045" to 0.080";
i.e. 9cc to 16cc. This insures good resistance to detonation)
-----------------------------------------------------
Piston Top Volume (use one):

- volume of domed piston top
+ valve notch volume of flat top piston (normally 3cc-4cc)
+ volume of dished piston top
-----------------------------------------------------
+ clearance between the piston and the cylinder wall (0.2cc or less)
___________________________________________



To calculate the Vc of your Pantera's motor

+ 66cc combustion chamber volume (D1AE/1971 cylinder head = 66cc nominal)
+ 8cc volume of head gasket (0.040" compressed thickness normally)
+ 15cc deck clearance (9.215 - 1.75 - 5.78 - 1.61 = 0.075" nominal)
+ 8.5cc volume of dished piston top
+ 0.2cc cylinder wall clearance

Vc = 98cc total (rounded to the nearest 1 cc)

the compression ratio is therefore

(732 + 98) ÷ 98 = 8.47:1 compression ratio

The variables would include whether or not the block has been decked, whether or not the heads have been milled and the actual volume of the head gasket used. For what its worth, the Cleveland is compatible with 91 octane US/Canadian pump gas (equivalent to 95 octane anywhere else in the world) set at 10.0:1 compression equipped with all but the mildest or hottest of camshafts. Quench heads or open chamber heads, makes no difference. That is in fact a conservative recommendation, it is in no way pushing the limits of detonation if the "total clearance" dimension is less than 0.080". If the alloy heads you are purchasing have high swirl combustion chambers, they should be able to tolerate a half point more than that (10.5:1). Of course, too much compression is even less of a concern at high altitudes.

However, notice that the sum of the head gasket thickness and deck clearance is 0.115". That's too big of a gap between the head and the piston top, which takes the Cleveland combustion chamber out of the range of having excellent resistance to detonation and is headed into the range where it is less resistant to detonation. This much clearance is OK if the comprssion ratio is 8.5:1, BUT it would not be a good choice to leave this clearance this large AND raise the compression ratio to 10.0:1.

If it were me, since you're removing the heads anyway, I would pull the motor to make replacing the heads easier, and replace the pistons with a set of Speed Pro L2379F forged flat tops while the heads are off.

That change alone makes the compression ratio 9.5:1

New Vc of your Pantera's motor

+ 66cc combustion chamber volume (D1AE/1971 cylinder head = 66cc nominal)
+ 8cc volume of head gasket (0.040" compressed thickness normally)
+ 7.6cc deck clearance (9.215 - 1.75 - 5.78 - 1.647 = 0.038" nominal)
+ 4cc valve notch volume of flat top piston
+ 0.2cc cylinder wall clearance

VC = 86cc (rounded to the nearest 1 cc)

(732 + 86) ÷ 86 = 9.5:1

IF you replace the dished pistons with flat tops then ordering the new heads with 66cc chambers will give the motor 9.5:1 compression if that's what you want. Or 61cc chambers would give the motor 10.0:1 compression. Or 57cc chambers would give the motor 10.5:1 compression. The "total clearance" (sum of the head gasket thickness and deck clearance) would be 0.078" which insures good detonation resistance; and all the dimensions are back to being factory/normal, nothing has to be machined or milled to an extreme or wonky amount to achieve a healthy normal compression ratio in the range of 9.5:1 to 10.5:1.

Also FYI, Ford's recommended maximum amount to mill from Cleveland heads is 0.060". Every 0.006" milled from a quench chamber head reduces chamber volume by 1cc. Milling a 1971 D1AE head the maximum amount would reduce the chamber volume by 10cc, i.e. nominal 56cc combustion chambers. Its not uncommon to mill open chamber heads quite a bit, but its usually not necessary for street motors with quench chamber heads (if they have the proper pistons installed ).

-G

George,

Thanks for all the great information. Others have pointed out that if I am replacing the the heads and cam, I would be way ahead in time and hassle to just pull the motor and trans. This would also give me an opportunity to inspect and replace any questionable items and make the exact measurements you indicated regarding compression ratio. Also good advice about milling too much off the heads and losing the benefit of a modern combustion chamber when there is too much space below the head.

I am hoping the my number for the compression height of the 2416s is wrong and I do not have that much space above the piston. If I have to replace the pistons, can I install them with new rings without doing any work on the cylinders? The motor has about 8000 miles on since it was bored and the 2416s were installed?

Thanks again, Evan

quote:

Originally posted by Wasatch Cat:
George,

Thanks for all the great information. Others have pointed out that if I am replacing the the heads and cam, I would be way ahead in time and hassle to just pull the motor and trans. This would also give me an opportunity to inspect and replace any questionable items and make the exact measurements you indicated regarding compression ratio. Also good advice about milling too much off the heads and losing the benefit of a modern combustion chamber when there is too much space below the head.

I am hoping the my number for the compression height of the 2416s is wrong and I do not have that much space above the piston. If I have to replace the pistons, can I install them with new rings without doing any work on the cylinders? The motor has about 8000 miles on since it was bored and the 2416s were installed?

Thanks again, Evan

Just change the pistons? Racers in the 60s at the track did it all of the time.
Really depends on what the cylinder walls look like now.
Mark Donahue once made a remark that he had found that a race engine made more power if the rings and pistons were just "friendly" with the bore (he meant a little loose) and the heads were fresh and tight.
Most engine builders will say no you can't, you need to run the cylinder hone through it, but the fact is that you can sometimes.

Since this motor has only 8000 miles on it since a rebuild, I would re-use the rings too.

Just make sure they go back into the same bore they came out of.

(assuming both pistons use the same ring package)

while the motor is out of the car its a good time to replace the pilot bushing and the throw-out bearing unless they are only 8000 miles old. while the pan is off its a good time to make sure the rod nuts are not the factory parts, but have been replaced with good quality ARP stuff (factory rod bolts are OK, its the nuts that fail). The crank damper should be replaced if the motor is still equipped with the 40 year old factory part.

-G

All items on my growing list.

Will take a close look at the cylinder walls before I install new pistons. Good suggestion on re-using the rings that are already broken in. I really think that will work.

Thanks, Evan

quote:

Just make sure they go back into the same bore they came out of.

I assume clocking of the rings will also be important or will they naturally move to the position they broke in at???

The rings constantly rotate in the cylinder.

quote:

The rings constantly rotate in the cylinder.

So how come when you install rings the instructions say they must be installed with the gaps in certain locations? I always wondered about that as I figured they must rotate as well unless there was a pin that kept them in a certain location like on some motorcycle pistons...

Indexing the ring gaps at 120 degrees assumes that the rings all rotate at the same rate so you index them at the start and none of the gaps can ever align to allow blow-by.
This is not true- some rings rotate faster, some in the opposite direction to the others and a few do not rotate at all. We all do this but it likely makes zero difference since in a properly built engine running at its design temp, the ring gaps are minimal and end-gap blow-by is insignificant. Very large gaps, or too tight end- gaps will cause big problems but you can't go wrong following the ring mfgrs specs.

quote:

Originally posted by Bosswrench:
you can't go wrong following the ring mfgrs specs.

The only thing that I have found is that the TRW chrome moly rings are supplied with big gaps. .018 to .020".
Most engines require .012 to .014, so in order to get that you need to use the .035 over on a .030 piston and file the gaps to spec.

If you are going to reuse the existing rings, index the gaps (mark the positions) in relation to the pistons, they should be marked up or topside, and wash them first in clean keroscene and then brush cleaner.

The bores also. There can be no debris at all, and don't get cut on the top of the bore. IF the guy who bored it out didn't chamfer the top edge then you can get cut to shreds on the edge.

quote:

Originally posted by ZR1 Pantera:

... unless there was a pin that kept them in a certain location like on some motorcycle pistons...

Two stroke motors have a pin to keep the ring from rotating, and to align the ring's end gap at a specific spot on the cylinder wall ... a spot where there are no ports!

You can imagine what would happen if the ends of a ring were to align with a port in the cylinder wall ...

-G