Compression ratio calculation

[62Ranchero200]

Howdy:

Ok, assuming an overbore of .030" with a dished 6.5 cc piston, a Victor head gasket @ .045" compressed thickness, cleaning up and smoothing the chambers and milling the head only enough to true the mating surface, and decking the top of the block .070" will yield a static CR of 9.1:1.

That will leave .053" deck height. That plus the .045" thickness of the head gasket will give you a deck clearance of .098". While this is way too much for ideal quench effect, it is way better than the .148" you started with.

Your probably asking why only .070" off the top of the block? Because that amount give you a CR very close to your goal. And, because I couldn't recommend removing any more material due to structural integrity and maintaining the depth of the head bolts. At this dimension you will still need to use hardened washers on each head bolt and you must verify that the head bolts are not bottoming out in its hole.

I'd sure like to hear more about the piston maker and possibilities.

Adios, David

Hi David,

I really appreciate you running those numbers for me. I like the approach you outline, and if I stick to using the large log head I'll probably use that approach.

A couple of notes:

I'm seriously considering using the aluminum head. Long story short, CI now does 2V conversions with furnace brazing, which requires that new valve guides and seats be installed after the furnace brazing, plus a three angle valve job for the best performance. That puts the cost of the 2V conversion at 2/3 of the cost of a bare aluminum head, and around half of the cost of an assembled aluminum head, depending on the options you choose for the head (most notably springs). The aluminum head has approximately 50 CC combustion chambers, which will directly enter into the CR calculations, but also I understand that detonation will be less of an issue with the aluminum head because aluminum transfers head more efficiently, and because the CI aluminum head has a more efficient combustion chamber design. I'm waiting for Mike to answer a couple of questions before I make my final decision on the head.

Second, I'm going to use ARP head studs - bottoming out the studs wouldn't be an issue like it would with bolts, right? Just a bit more stud sticking out on the nut end?

Thanks
Bob

 

[CZLN6]

Howdy Back;

Head studs are a great idea. And Mike alloy head solves a bunch of problems- all except for the big one- $$$$$$. 50 cc chambers will require some recalculation of CR. What does Mike recommend for a head gasket to deal with the different expansion rates of the alloy head and the iron block? Also does he have any recommends on how much more CR the alloy head can safely handle.

Yes, the advantages of a more efficient chamber layout is a real big plus.

It sounds like you're zeroing in on a plan. Keep it coming.

Adios, David

 

[bmbm40]

The CI head and carb may be lower than direct mount so less work if you don't have to lower the engine. A carb hat setup and remote air cleaner probably a good solution. The CI head may cost a little more but you get a lot more performance and you can sell your log head to offset some of the cost. Also a pretty good weight difference I think so less weight improves performance and handling. Plus you can't beat the way it looks.

 

[62Ranchero200]

Howdy Back;

Head studs are a great idea. And Mike alloy head solves a bunch of problems- all except for the big one- $$$$$$. 50 cc chambers will require some recalculation of CR. What does Mike recommend for a head gasket to deal with the different expansion rates of the alloy head and the iron block? Also does he have any recommends on how much more CR the alloy head can safely handle.

Yes, the advantages of a more efficient chamber layout is a real big plus.

It sounds like you're zeroing in on a plan. Keep it coming.

Adios, David

Hi David,

After receiving some information from Mike, I am definitely going to order an assembled aluminum cylinder head with single springs with dampers, and the full ARP head stud kit. There may be a couple more details to work out, but I've already told Mike that I want to order one, so the order should be finalized in the next day or two. It's a bit expensive, but I can't see building up a bulletproof 250 short block and bolting on the old log head. For about twice the price of the 2V conversion, I'll have an infinitely superior aluminum head.

Mike offers a Felpro or Corteco head gasket with the aluminum head kit, so apparently the aluminum head /iron block combination doesn't require anything exotic as far as head gasket materials.

I obviously need to recalc my CR, but I'll wait for some details from Mike on the combustion chambers. I really don't want to exceed 9.3 CR at the very most. Although I will always use 93 octane gas given the choice, I may be stuck in an unexpected situation and have to use the 87 octane, or just get a batch of lower quality gas; and the extremely hot weather and terrible traffic in Houston makes overheating a real possibility even with the best cooling system.

Thank you,
Bob

 

[62Ranchero200]

The CI head and carb may be lower than direct mount so less work if you don't have to lower the engine. A carb hat setup and remote air cleaner probably a good solution. The CI head may cost a little more but you get a lot more performance and you can sell your log head to offset some of the cost. Also a pretty good weight difference I think so less weight improves performance and handling. Plus you can't beat the way it looks.

Hi bmbm40,

I think the intake ports were raised on the aluminum head, so the hood clearance may actually be worse than with a 2V conversion. I'm not going to worry about that just yet - I'll run without a hood if I have to. The Ranchero is not a daily driver and I don't take it out in the rain. If not able to lower the engine enough, I might have a custom hood or hood scoop made.

Thanks
Bob

 

[Gene Fiore]

I'd go with the felpro head gasket...imho the corteco's are inferior.

 

[62Ranchero200]

Howdy Back;

Head studs are a great idea. And Mike alloy head solves a bunch of problems- all except for the big one- $$$$$$. 50 cc chambers will require some recalculation of CR. What does Mike recommend for a head gasket to deal with the different expansion rates of the alloy head and the iron block? Also does he have any recommends on how much more CR the alloy head can safely handle.

Yes, the advantages of a more efficient chamber layout is a real big plus.

It sounds like you're zeroing in on a plan. Keep it coming.

Adios, David

Hi David,

Now that I have decided to go with an assembled CI aluminum head (although my order is not finalized yet), it's necessary to revisit my CR calculations:

50 CC head = CI aluminum head with ~50 CC combustion chamber
6.5 CC piston = stock type piston with 6.5 CC dish

50 CC head, 6.5 CC piston, no decking = 8.87 CR
50 CC head, 6.5 CC piston, .010 decking = 9.00 CR
50 CC head, 6.5 CC piston, .020 decking = 9.20 CR
50 CC head, 6.5 CC piston, .030 decking = 9.37 CR
50 CC head, 6.5 CC piston, .040 decking = 9.55 CR

I'm thinking that 9.55 CR is high enough to cause detonation with real world conditions, like being unable to find 93 octane gas, unknowingly using lower quality gas, or being stuck in traffic in the Houston heat. Even 9.37 CR seems too close to the edge of detonation to me. I'm thinking I'll stick with 9.20 as a CR goal.

Thank you,
Bob

 

[FalconSedanDelivery]

With a proper curve in the Dist , Id shoot for close to 10 -1 IF, you get the compression by reducing Deck , keep in mind cylinder pressure is load sensitive , in other words if you would find yourself with less than 93 octane , keep your foot out of it and its fine , with the better mixture distribution available with the alum head and it also having better chambers , I would not hesitate. to run that much

 

[CZLN6]

Howdy back:

And don't forget the extra thickness of the aftermarket head gasket when figuring CR.

I'm in agreement with FSD on going for a little more CR considering all. And in a pinch, worst case scenerio, drive it like there's a cop with a toothache behind you.

Adios, David

 

[First Fox]

FWIW, I too would lean closer towards the 10:1 number. You will have good money in this build and you might as well get as much as you can out of it and a half a point or more in compression is quite a bit to throw away. The difference in compression will cost you no more money and will give you no problems IF like was suggested before, you fix the quench issue by decking and/or selecting proper pistons.

I'm not quite sure why you feel you will have detonation issues with this combination but if you feel you will only run into problems if you get stuck with $hitty gas, you can get around that electronically. MSD makes a box that allows you to retard timing from a dial on your dashboard and in the event you get a bad tank of gas or the temp climbs too high, you just dial it back a few degrees and forget about it. A very nice convenience indeed.

 

[62Ranchero200]

FWIW, I too would lean closer towards the 10:1 number. You will have good money in this build and you might as well get as much as you can out of it and a half a point or more in compression is quite a bit to throw away. The difference in compression will cost you no more money and will give you no problems IF like was suggested before, you fix the quench issue by decking and/or selecting proper pistons.

I'm not quite sure why you feel you will have detonation issues with this combination but if you feel you will only run into problems if you get stuck with $hitty gas, you can get around that electronically. MSD makes a box that allows you to retard timing from a dial on your dashboard and in the event you get a bad tank of gas or the temp climbs too high, you just dial it back a few degrees and forget about it. A very nice convenience indeed.

Hi FF,

As I understand it, using the 6.5 CC stock-style dished pistons and decking the block should fix the quench issue.

I know some consider them overpriced, but I _already have_ a DUI, so unless it's a significant detriment to performance, I'd like to use that - I'd really like to clean up the driver's side firewall and simplify the wiring by doing away with the coil and ignition module. I expect that the DUI can be re-curved in the same way that a DSII can be? The DUI means I will not be able to adjust timing on the fly - I'll have to have the curve and the initial advance conservative enough for any reasonable street situation.

Thanks,
Bob

 

[First Fox]

If you work with your machine shop to set the pistons at zero deck, or even slightly higher, than yes you will solve the quench problem. If you just have them deck the block a given amount to maintain a lower compression ratio that you consider to be safer, and the pistons are still too low, you will not have solved the quench issue at all. In order to minimize detonation issues, for which this engine family is notorious, this should be addressed.

Put another way: You build it with 9.0 to 1 C/R with a badly designed quench area and it will likely detonate. You will then have to pull a load of timing out of it and it will be a pig. You will then post on this board that we were wrong, the aluminum head sucks, and that I am retarded for suggesting you set up a higher static C/R.

Or you build it with 9.8 to 1 with a well designed quench area and you will have a wonderfully turbulent combustion area, and you may enjoy detonation free driving and dogs and cats all around the world will play happily together and will all live forever. This extra expense and attention to detail here is crucial.

Again, best of luck to you.

And as far as the DUI, are you sure they don't offer their own timing control? Let me check around a bit for you. A clan engine compartment is always nice, but you gotta admit that is a nice feature. 8)

 

[62Ranchero200]

If you work with your machine shop to set the pistons at zero deck, or even slightly higher, than yes you will solve the quench problem. If you just have them deck the block a given amount to maintain a lower compression ratio that you consider to be safer, and the pistons are still too low, you will not have solved the quench issue at all. In order to minimize detonation issues, for which this engine family is notorious, this should be addressed.

Put another way: You build it with 9.0 to 1 C/R with a badly designed quench area and it will likely detonate. You will then have to pull a load of timing out of it and it will be a pig. You will then post on this board that we were wrong, the aluminum head sucks, and that I am retarded for suggesting you set up a higher static C/R.

Or you build it with 9.8 to 1 with a well designed quench area and you will have a wonderfully turbulent combustion area, and you may enjoy detonation free driving and dogs and cats all around the world will play happily together and will all live forever. This extra expense and attention to detail here is crucial.

Again, best of luck to you.

And as far as the DUI, are you sure they don't offer their own timing control? Let me check around a bit for you. A clan engine compartment is always nice, but you gotta admit that is a nice feature. 8)

Hi again FF,

I think I'm going with the FelPro composite head gasket offered by Mike, so compressed gasket thickness will be about .050. Is there a figure that is generally suggested for quench height? If decked to zero deck height, I would have only .050 (the thickness of the compressed head gasket) for quench height, right?

Without custom pistons or custom piston milling (which I would prefer to avoid), I really only have two choices for piston shape, the 6.5 CC dish and the flattop pistons; and the shape and size of the CI aluminum head combustion chambers will be a known quantity, so decking is really the only variable I have. Since the CI aluminum head is much more costly than a 250 block, I would rather avoid milling the head unless it's needs milling just to true the mating surface. I view that head as a lifetime investment!

I've read that rev limiter modules are offered for the DUI, but haven't heard anything about variable timing. Since I've already spent $$$ on the DUI, I really want to use it unless someone can show that it will truly derail my performance.

Thank you,
Bob

 

[First Fox]

Yeah unfortunately for us, there are not a lot of choices in head gasket thicknesses for these engines. A smallblock Chevy may have 8 different compressed thicknesses to chooses from. We have maybe 2.

Yes you are correct, if you zero deck with a given piston, your quench distance will be the compressed thickness of the head gasket. At .050 that is pretty high. If the piston were ABOVE the deck .010 thou, you would be in better shape as that is about the minimum height suggested, and that clearance only exists to keep pistons from contacting the head from thermal expansion/ rod stretch. This is not a huge deal with a engine with a 5200 rpm redline, and I would personally run the clearance tighter. The quench height and machining should be set of course after you have your pistons and have them assembled and in the block at TDC for a mock up.

You can use a calculator if you have the the compression height of the piston you want to use, (the distance between the piston crown and the wrist pin) to find out what piston will work for you. I have seen flat top replacement pistons with a lower compression distance built into them by lowering the wrist pin so it does not affect the original C/R. In other words, knowing the amount of volume in a given piston dish only means something if you know the compression height of that piston also.

A flat top piston is always better IMO for quench and if you can achieve your desired compression ratio with a flat top, that's what I would suggest. If the pistons you are looking at have a "D" shape valve relief, then that is the way to go IF you need that volume to get the compression where you need it. If they are the type that have the shallow relief around the entire piston, I would avoid them at all costs. This type of piston has next to zero quench ability and is an awful design.

Yes I agree with you as far as leaving the head alone. There is really no need to do anything with it as far as milling. You will be decking the block, and changing the pistons AND you have the option of custom pistons being made. The world is your oyster my friend.

 

[62Ranchero200]

Yeah unfortunately for us, there are not a lot of choices in head gasket thicknesses for these engines. A smallblock Chevy may have 8 different compressed thicknesses to chooses from. We have maybe 2.

Yes you are correct, if you zero deck with a given piston, your quench distance will be the compressed thickness of the head gasket. At .050 that is pretty high. If the piston were ABOVE the deck .010 thou, you would be in better shape as that is about the minimum height suggested, and that clearance only exists to keep pistons from contacting the head from thermal expansion/ rod stretch. This is not a huge deal with a engine with a 5200 rpm redline, and I would personally run the clearance tighter. The quench height and machining should be set of course after you have your pistons and have them assembled and in the block at TDC for a mock up.

You can use a calculator if you have the the compression height of the piston you want to use, (the distance between the piston crown and the wrist pin) to find out what piston will work for you. I have seen flat top replacement pistons with a lower compression distance built into them by lowering the wrist pin so it does not affect the original C/R. In other words, knowing the amount of volume in a given piston dish only means something if you know the compression height of that piston also.

A flat top piston is always better IMO for quench and if you can achieve your desired compression ratio with a flat top, that's what I would suggest. If the pistons you are looking at have a "D" shape valve relief, then that is the way to go IF you need that volume to get the compression where you need it. If they are the type that have the shallow relief around the entire piston, I would avoid them at all costs. This type of piston has next to zero quench ability and is an awful design.

Yes I agree with you as far as leaving the head alone. There is really no need to do anything with it as far as milling. You will be decking the block, and changing the pistons AND you have the option of custom pistons being made. The world is your oyster my friend.

FF,

The only pistons available "off the shelf" for the 250 are either with the full circular 6.5 CC dish in the center of the piston, or flattop. No "D" shaped dishes are available. Besides cost, another advantage to "off the shelf" pistons is that if a piston breaks (as happened to Gene Fiore recently), I can order another off the shelf piston, pay overnight shipping, and replace the errant piston in a few days. If I have custom pistons or custom milling done to the pistons, I might be facing a delay of a few weeks to many weeks before I could replace a broken one. At the end of the day, I did start the Ranchero project because I wanted to drive the Ranchero, so I'd like to keep it up and running as much as possible.

I'm starting to get some conflicting advice - David mentions that the 250 is more detonation-prone with flattop pistons, but you seem to feel that the flattop piston is a better design than the stock 6.5 CC circular dish piston.

Thank you,
Bob

 

[xctasy]

There's no conflict.

The trade off is between ideal squench and ideal compression ratio. Within any type of engine, as long as the deck register is the same, its high cold cranking compression figures that causes preignition/pinking firstly, then its mitiagated by camber design. Within a family of engines, the 250 and 200 are as differernt as you could get, and the stock 103 to 123 thou deck short fall on the 250 is a detonation creater, but if two modified 250 engines were at 9.3:1, one with a flat top, one with a dish, both with close to o 15 to 0 thou short fall, then the engine with more cold cranking compression would detonate first. The detonation level of the dish verses flat top is very small, but ledging from a 103 to 123 shortfall is much much greater.Which is why Ford engineers dropped the CR on the 250 so much.

If each engine had 180 psi cold cranking compression, dish or flat top wouldn't make much differernce. Its actually a dome piston with relief cuts which is best, but on a 250, its very hard to make it work unless you custom build a piston. So flattop or dish is a 1% er. Although on some engines, a gradual dish is the optimum, its much of a muchness on a small Fod I6.

After gettign a target cold cranking copmpression figure low enough to reduce the effective comopression ratio enough to equal the stock engine, the second best way to reduce knock is to run forged pistons. There's 100 degrees F of less combustion temperature under load right there.

As for being able to get cast pistons quickly verses a forged piston, the arguament is a moot one. Over the last 10 years on this forum, six people too many have had broken cast piston skirts, and based on that, I'd use forged every time. Got plenty of photos here over the years to say I'd not use a stock Ford piston ever. Just throwin good money after bad.

The other option is CP factory pistons for the Coyote or Modular V8. I doubt Does10's has had any problem after he got rid of the low rent cast pistons in his Turbo 250.

 

[CZLN6]

Howdy All:

The 250 engine in 8:1 CR stock form, in the type of vehicles it came in, with the gearing behind it and an automatic trans- plus on-the-rich-side tuning from the factory, very low duration cam timing for very high cylinder pressures, produced a hot, carboned up chamber that seldom saw four grand. In all most all cases the engine was lugging in anything other than low. It was built for torque, Period!!!! This is how it got a rep for knocking under hard use. BUT, the small 3.68" bore, the small dish piston and the wedge combustion chamber were all there to resist pre-ignition. Once carbon built up in the chambers it quickly becomes a source for glow plugs and/or hot spots causing pre-ignition. I have yet to tune or disect a virgin 250 that wasn't heavily carboned up. The 250 was in heavy Granada, Zypher, Mavericks and Comets. All most all heavy four doors and mostly all automatic trans. All had 3:1 rear gearing or higher- 2.79:1 was the standard later. The other standard was an ever lower octane gas standard and cheap oil. GIven this scenerio, what engine wouldn't be prone to knock. The pluses of small bore, dished piston and a wedge shaped combustion chamber could not overcome the minuses.

Yes, the dreadful deck clearance of over .100" kill any positive from a quench effect, but it is still not a knock prone as the open chamber design.

But, in Bill case none of the above will occur. Yes, the deck height will be less than ideal. But, he will have lower cylinder pressure due to a longer duration cam, a much better combustion chamber, small dish pistons, a good exhaust and ignition system, proper gearing and an optimize tune. Given this assumption I doubt that he'll ever hear a ping- even at 9.5:1 on a hot day with 91 octane gas.

The 250 engine is an enigma. Just 50 cubes away and yet- no easy solutions to become the ideal in every way. only compromises, and they're not bad.

Stick to your plan Bill. You'll do all right.

Adios, David

 

[62Ranchero200]

There's no conflict.

The trade off is between ideal squench and ideal compression ratio. Within any type of engine, as long as the deck register is the same, its high cold cranking compression figures that causes preignition/pinking firstly, then its mitiagated by camber design. Within a family of engines, the 250 and 200 are as differernt as you could get, and the stock 103 to 123 thou deck short fall on the 250 is a detonation creater, but if two modified 250 engines were at 9.3:1, one with a flat top, one with a dish, both with close to o 15 to 0 thou short fall, then the engine with more cold cranking compression would detonate first. The detonation level of the dish verses flat top is very small, but ledging from a 103 to 123 shortfall is much much greater.Which is why Ford engineers dropped the CR on the 250 so much.

If each engine had 180 psi cold cranking compression, dish or flat top wouldn't make much differernce. Its actually a dome piston with relief cuts which is best, but on a 250, its very hard to make it work unless you custom build a piston. So flattop or dish is a 1% er. Although on some engines, a gradual dish is the optimum, its much of a muchness on a small Fod I6.

After gettign a target cold cranking copmpression figure low enough to reduce the effective comopression ratio enough to equal the stock engine, the second best way to reduce knock is to run forged pistons. There's 100 degrees F of less combustion temperature under load right there.

As for being able to get cast pistons quickly verses a forged piston, the arguament is a moot one. Over the last 10 years on this forum, six people too many have had broken cast piston skirts, and based on that, I'd use forged every time. Got plenty of photos here over the years to say I'd not use a stock Ford piston ever. Just throwin good money after bad.

The other option is CP factory pistons for the Coyote or Modular V8. I doubt Does10's has had any problem after he got rid of the low rent cast pistons in his Turbo 250.

Hi Xctasy,

Your first remarks were a bit over my head, so I'm going to have to digest them for a while.

I think when you say cold cranking compression, you're referring to dynamic compression, and to the fact that a cam with more duration and overlap will reduce the dynamic compression. So I could run a 10:1 static compression ratio, but a considerably larger than stock cam (more duration and overlap), such as say one of the Clay Smith 274 cams, and the dynamic compression would not be so high as to cause knocking, even though the static compression is rather high for a street engine running on pump gas.

Now you've told me something that I haven't even heard a hint of before ... that "forged pistons reduce knock, and have about a 100 degree less combustion temperature under load." Can you explain why that is so? If so, a set of forged pistons might aid in controlling knock, and of course increase durability as you mention.

Thank you,
Bob

 

[bubba22349]

From CZLN6 above post

Quench happens best in a head with a "wedge" shaped combustion chamber, and it happens best when the "deck clearance" is in the .030" to .040" range. Any more and the quench effect is diminished. Any less and the risk of parts occupying the same space at the same time is risky.

I also agree with SD, David, and others that the best combo is going be short block is set up right with .030 to .035 deck clearance. Been kicking some ideas around for my 77 250 combo, as good as my near stock 250 runs now (it's in a 77 Maverick) I think there is lots more performance left in it. Rather than decking the block .070 or .100 am thinking of using a longer rod with a custom piston height and or offset grinding the crank. Like maybe a Ford 300 length rod and about a 1.300 pin height piston if can find the time this winter might try a mockup to see what it looks like. I see no problem with pistons .010 or or maybe even .015 out the top of the block using a .050 head gasket.

 

[First Fox]

FF,

The only pistons available "off the shelf" for the 250 are either with the full circular 6.5 CC dish in the center of the piston, or flattop. No "D" shaped dishes are available. Besides cost, another advantage to "off the shelf" pistons is that if a piston breaks (as happened to Gene Fiore recently), I can order another off the shelf piston, pay overnight shipping, and replace the errant piston in a few days. If I have custom pistons or custom milling done to the pistons, I might be facing a delay of a few weeks to many weeks before I could replace a broken one. At the end of the day, I did start the Ranchero project because I wanted to drive the Ranchero, so I'd like to keep it up and running as much as possible.

I'm starting to get some conflicting advice - David mentions that the 250 is more detonation-prone with flattop pistons, but you seem to feel that the flattop piston is a better design than the stock 6.5 CC circular dish piston.

Thank you,
Bob

If those are the only two choices Bob, and you decide to go with an off the shelf piston, then the only logical choice is to use the flat top. I would personally go the off the shelf route. I am a fan of making power with the induction and cylinder heads and using the most cost effective parts in the bottom and.

The power is made upstairs. Forged cranks, pistons, rods, and main caps with a half dozen bolts in them don't add a bit of power, and if a bread and butter bottom end will hold together and make power, use it and spend the money somewhere else. I always figured if I dropped a valve in a 200 dollar short block and destroyed it, I could replace it with another 200 dollar short block, bolt my good head(s) on it and wouldn't lose much sleep.

If you feel you need custom pistons get 'em. I was good friends with a racer that ran an alcohol funny car, and amongst other things he had to use custom pistons. He would order sets of 10 instead of 8 just in case. Always had a spare or two on the shelf.

Forged pistons do run cooler but require more clearance and can be a bit noisy when cold. They themselves are also going to be more expensive than having another fully prepped bread and butter short block on the shelf in the event of catastrophe.


The deal with forged pistons and detonation is this: Detonation destroys cast pistons pretty quickly. It destroys forged pistons also, it just takes a little longer. Detonation needs to be avoided, you just cant rely on forged pistons to be your safeguard against that type of abuse. If you add forged pistons and continue detonating the engine, then the head gasket will give. If you then shore up the head gasket with a copper gasket and o-rings and still enjoy the detonation, you will start knocking out main bearings, if you then reinforce the main bearings you will learn what it is like to break a crankshaft etc. Something will always give because nothing can stand the destructive forces of continued detonation.


Also Bubba raises a good point. If in order to get a decent quench height you find you have to cut too much from the deck, you can look for other ways to move the piston UP the bore to achieve it instead of cutting the block down. As he said, longer rods, taller pistons, or you can also offset grind the crank. That would give you the benefit of a few more cubic inches to put in your signature. 8)