B16B using B18Cr Block!

[hattech-v]

i think 82mm oso ok..

 

[jugbugz]

i think 82mm oso ok..

But, ctr is already 82mm

 

[jugbugz]

of course the other cars would show 150psi, they're probably in the region of 8-9 CR. Honda's usually show higher, because they run 10-11CR static CR.

195-200 isn't too shabby, but it also shows that your compression isn't that good already.. the numbers are good if it's for daily drivae use, yes, but power wise suffers a bit. It could be anything, like hattech said, either the piston seal is not so good (leakdown test will show this) or maybe your valve seats are worn.


No, assuming that the gauges are not of the cheapest variety, they read pretty much the same, assuming the compression scale is the same. psi/kpa/etc.



yes, but pistons don't wear, per se, unless it has seized. The ring does, and that's where one part of the seal comes from, the other, from the valves.

thanks for your advices on the forum, I appreciate it.

How much would you want for your SS works Block Brace?

 

[hattech-v]

But, ctr is already 82mm

ctr 81mm, oversize ctr 81.25mm

 

[jugbugz]

oh yeah, my bad, I meant 81mm. I heard 81.5mm is maximum. maybe I can just skimm the head and put flat valves?

 

[shiroitenshi]

thanks for your advices on the forum, I appreciate it.

How much would you want for your SS works Block Brace?

It's about RM4K

 

[shiroitenshi]

oh yeah, my bad, I meant 81mm. I heard 81.5mm is maximum. maybe I can just skimm the head and put flat valves?

Skimming the head introduces potential problems. For me removing material from the head isn't a good option, unless you are on a budget, or need greater compression that cannot be provided by other mods.

Flat valves + big bore + moderate piston dome (or small bore, fat piston dome) increase compression ratio greatly.

There are two ways to increase compression, make the combustion chamber smaller (by using thin gaskets, flat valves, pistons with higher dome, skimming)

Or make the swept volume bigger (increase stroke and/or increase bore), while retaining your combustion chamber volume.

I suggest you read up on octane reading and the truths and myths, I don't think 100RON is what it's cracked up to be. Then again, I don't really know much about fuels, only that if it sounds too good to be true, it probably is.

 

[jugbugz]

Skimming the head introduces potential problems. For me removing material from the head isn't a good option, unless you are on a budget, or need greater compression that cannot be provided by other mods.

Flat valves + big bore + moderate piston dome (or small bore, fat piston dome) increase compression ratio greatly.

There are two ways to increase compression, make the combustion chamber smaller (by using thin gaskets, flat valves, pistons with higher dome, skimming)

Or make the swept volume bigger (increase stroke and/or increase bore), while retaining your combustion chamber volume.

I suggest you read up on octane reading and the truths and myths, I don't think 100RON is what it's cracked up to be. Then again, I don't really know much about fuels, only that if it sounds too good to be true, it probably is.

geez, I haven't got email response so thought no one replied here...

:hmmmm: I was thinking about flat valves, but are they safe? Why arn't valves made flat in the first place?

2P 0.45mm SPOON gasket is good right? How long do these last on a B16B with Toda Spec C cams? For some reason TODA only makes gaskets for 82mm bore?

So with increasing compression, can you list out the easiest and cheapest first and expensive ones last. I don't think I need to rebuild my motor anymore, I just did another compression test with a new guage and found 230psi in all 4 cyls. lol So I think I'll just be installing Spec C cams as these gave better results on a B16. And Spec B gave better results on a B18 instead.

shiroitenshi can you please PM me how much you want for the SS works Block brace? Tell me how much you want in RM, I'll work it out in my currency. You accept credit card or paypal? Thanks!

Oh, btw, can the brace be installed without taking the engine out of the car? It isn't hard to install is it? Thanks!

 

[jugbugz]

crap! sorry I just saw the post

It's about RM4K

:lol:

Is that 4000MYR, I just need to convert it. If it is then I'll take it. Do you have everything thats included with original purchase? I mean parts and bolts ofcourse.

Also, I was told some good stuff about ARP head studs. When do I need to replace head studs? Changing gasket? block brace?

Where can I find the thread on octance readings?

 

[shiroitenshi]

Well, seems like the crank brace might be used after all, but we'll see how it goes on the B18C block that's going to be worked on at the end of this year or early next year. If you want it before then, let me know and I'll see if it's going to be used or not.

Octane readings, just google.

ARP head studs have two purposes. They are not 'bolts' like the normal type R because they are there to facilitate head removal.

Reason A:
If you keep removing the head, the threads on the block (or bottom end) may wear out, so ARP used the stud type to prevent this, because the studs don't need to be removed from the block, ensuring that the threads on the block aren't weakened by constant removal and retorquing.

Reason B:
Another is for extra strength, because high compression engines make more pressure during combustion, it's more stressful on the stock bolts, and when they stretch over time, there goes your head gasket sealing. ARP 'claims' their bolts resists stretch better, so there's the strength argument. So the strength part can be said to be marketing speak.

But for most intents and purposes, it's usually reason A, so if you have a car that you want to work on slowly and steadily (means you remove the head many times as you upgrade each part slowly/high maintainance race engines), then ARP bolts are the way to go. if not, just buy the normal R bolts, and when they wear out, but another. ARP bolts is like near quadruple the price of normal bolts in Malaysia, so it's up to the buyer to decide what he needs or not.

 

[jugbugz]

Well, seems like the crank brace might be used after all, but we'll see how it goes on the B18C block that's going to be worked on at the end of this year or early next year. If you want it before then, let me know and I'll see if it's going to be used or not.

Octane readings, just google.

ARP head studs have two purposes. They are not 'bolts' like the normal type R because they are there to facilitate head removal.

Reason A:
If you keep removing the head, the threads on the block (or bottom end) may wear out, so ARP used the stud type to prevent this, because the studs don't need to be removed from the block, ensuring that the threads on the block aren't weakened by constant removal and retorquing.

Reason B:
Another is for extra strength, because high compression engines make more pressure during combustion, it's more stressful on the stock bolts, and when they stretch over time, there goes your head gasket sealing. ARP 'claims' their bolts resists stretch better, so there's the strength argument. So the strength part can be said to be marketing speak.

But for most intents and purposes, it's usually reason A, so if you have a car that you want to work on slowly and steadily (means you remove the head many times as you upgrade each part slowly/high maintainance race engines), then ARP bolts are the way to go. if not, just buy the normal R bolts, and when they wear out, but another. ARP bolts is like near quadruple the price of normal bolts in Malaysia, so it's up to the buyer to decide what he needs or not.

Thanks for the info. So would it be recommended to change the head bolts when I install the new gasket?

If your willing to let the block brace go, I'll take it ASAP. Can you install the brace without removing the engine?

 

[shiroitenshi]

Thanks for the info. So would it be recommended to change the head bolts when I install the new gasket?

If your willing to let the block brace go, I'll take it ASAP. Can you install the brace without removing the engine?

Actually it's supposed to be done with the engine out. because I don't know any mechanic that torque crank cap bolts from underneath the car :P

Oh, and about the compression numbers, improper ring gapping also gives you lower compression even with new rings, so make sure the guy that re-rings your piston can enlighten you on why ring gap is important (i.e. it means he knows why it needs to be gapped, and means that he will actually do it before plonking them in)

You can run tight ring gaps for better compression, but too tight and you will seize the engine when it goes above the normal operating temp (driven hard)

The guy that does the piston rings should know what kind of gaps to use. Most aftermarket piston makers have suggested numbers, so you can use them as reference, though it's more of a guideline that hard numbers you should follow to the letter.

 

[evoX2]

how much is the normal R bolt??

 

[jugbugz]

Actually it's supposed to be done with the engine out. because I don't know any mechanic that torque crank cap bolts from underneath the car :P

Oh, and about the compression numbers, improper ring gapping also gives you lower compression even with new rings, so make sure the guy that re-rings your piston can enlighten you on why ring gap is important (i.e. it means he knows why it needs to be gapped, and means that he will actually do it before plonking them in)

You can run tight ring gaps for better compression, but too tight and you will seize the engine when it goes above the normal operating temp (driven hard)

The guy that does the piston rings should know what kind of gaps to use. Most aftermarket piston makers have suggested numbers, so you can use them as reference, though it's more of a guideline that hard numbers you should follow to the letter.

oh, the I guess the block and head needs to be separated... hmm, timewise it's expensive and long to fit the brace isn't it? I was hoping it could be installed quick. As for piston rings, I choose not to do it as my compression numbers were 230psi all four this time. My other mechanics guage was stuffed or he didn't do it properly.

But thats good advice again. I'll keep it in mind or come back here for reference. Right now, I can only see the headgasket being the easiest mod to increase compression. I'm still not to certain with flat valves... If I want to change pistons then I might as well stroke it to 1.8 and get forged rods and pistons. Spec C is going to be overkill with my CR. But then it still makes power. :D

 

[shiroitenshi]

oh, the I guess the block and head needs to be separated... hmm, timewise it's expensive and long to fit the brace isn't it? I was hoping it could be installed quick. As for piston rings, I choose not to do it as my compression numbers were 230psi all four this time. My other mechanics guage was stuffed or he didn't do it properly.

But thats good advice again. I'll keep it in mind or come back here for reference. Right now, I can only see the headgasket being the easiest mod to increase compression. I'm still not to certain with flat valves... If I want to change pistons then I might as well stroke it to 1.8 and get forged rods and pistons. Spec C is going to be overkill with my CR. But then it still makes power. :D

Yeah, the headgasket is the easiest means of increasing compression, but you need to 'remove' the head to do it.

usually you can do a few things at one go when you remove the head.

A) new v/s retainer set
B) new LMAs (or hydraulic tappets to some) (if they're already leaking)
C) valve grind / new valves + grind.
D) port work

Spec C (part number ends with -00C)is 255@1mm on intake/exhaust. about 10 degs or so increase from CTR cams. (advertised, I don't know, see spec sheet of the cams) The primary and secondary are higher than CTRs though, so expect to remap your ECU/retune piggyback/whatever.

the Spec C2 (part number ends with -02C) is 260@1mm (advertised is 300)

As with all toda cams, the spec mirror each other for intake and exhaust.

I'm assuming you're going to use the C2, since the Spec C (-02C) is the ones that's more 'available' ATM.

With the lack of compression, your tuner can play retard the intake and/or exhaust and see how the torque curve goes (Hopefully he remembers to adj. the distributor because the retarding the intake cams retards ignition as well)

Retarding the intake cams should help compensate for the lack of higher compression, but you only have a very small leeway before the valves and piston clearance become an issue (there's a reason why there's the minimum clearance of 0.035" - 0.060" depending on rods used, to compensate for crank and wrist pin bearing wear, and how high a peak RPM you're shooting for) Not checking clearance results in many dead engines, so naturally you need to trust your mechanic on this, and that everything works out well and there isn't a date between your piston and valves when you are at 9K rpm. Valve float is also an issue, then again, with c2 cams you can't use the stock valve springs.

There's also worry about the aggresive lobes on the cams, which means that you shouldn't use a stock timing belt if you want longevity.

Well, don't forget to post your results when you are done.

As to the bolts, I think I was pretty clear.. it's up to you.. stock R bolts hold up pretty well, and the only reason you want to use studs is to maintain the block's thread from wearing out.

Measure your bolts with new ones, if they're a bit longer, it's time to replace the bolt before they snap when being torqued.

EvoX2,
The stock R bolts are not expensive, but price wise.. I think in the region of 200-ish, not sure though.

 

[10KRPM]

Yeah, the headgasket is the easiest means of increasing compression, but you need to 'remove' the head to do it.

usually you can do a few things at one go when you remove the head.

A) new v/s retainer set
B) new LMAs (or hydraulic tappets to some) (if they're already leaking)
C) valve grind / new valves + grind.
D) port work

Spec C (part number ends with -00C)is 255@1mm on intake/exhaust. about 10 degs or so increase from CTR cams. (advertised, I don't know, see spec sheet of the cams) The primary and secondary are higher than CTRs though, so expect to remap your ECU/retune piggyback/whatever.

the Spec C2 (part number ends with -02C) is 260@1mm (advertised is 300)

As with all toda cams, the spec mirror each other for intake and exhaust.

I'm assuming you're going to use the C2, since the Spec C (-02C) is the ones that's more 'available' ATM.

With the lack of compression, your tuner can play retard the intake and/or exhaust and see how the torque curve goes (Hopefully he remembers to adj. the distributor because the retarding the intake cams retards ignition as well)

Retarding the intake cams should help compensate for the lack of higher compression, but you only have a very small leeway before the valves and piston clearance become an issue (there's a reason why there's the minimum clearance of 0.035" - 0.060" depending on rods used, to compensate for crank and wrist pin bearing wear, and how high a peak RPM you're shooting for) Not checking clearance results in many dead engines, so naturally you need to trust your mechanic on this, and that everything works out well and there isn't a date between your piston and valves when you are at 9K rpm. Valve float is also an issue, then again, with c2 cams you can't use the stock valve springs.

There's also worry about the aggresive lobes on the cams, which means that you shouldn't use a stock timing belt if you want longevity.

Well, don't forget to post your results when you are done.

As to the bolts, I think I was pretty clear.. it's up to you.. stock R bolts hold up pretty well, and the only reason you want to use studs is to maintain the block's thread from wearing out.

Measure your bolts with new ones, if they're a bit longer, it's time to replace the bolt before they snap when being torqued.

EvoX2,
The stock R bolts are not expensive, but price wise.. I think in the region of 200-ish, not sure though.

good write up shiroi U need to opt for the thinnest headgasket possible to bump the compression up :P

 

[jugbugz]

Yeah, the headgasket is the easiest means of increasing compression, but you need to 'remove' the head to do it.

usually you can do a few things at one go when you remove the head.

A) new v/s retainer set
B) new LMAs (or hydraulic tappets to some) (if they're already leaking)
C) valve grind / new valves + grind.
D) port work

Spec C (part number ends with -00C)is 255@1mm on intake/exhaust. about 10 degs or so from CTR cams. (advertised, I don't know, see spec sheet of the cams)

the Spec C2 (part number ends with -02C) is 260@1mm (advertised is 300)

As with all toda cams, the spec mirror each other for intake and exhaust.

I'm assuming you're going to use the C2, since the Spec C (-02C) is the ones that's more 'available' ATM.

With the lack of compression, your tuner can play retard the intake and/or exhaust and see how the torque curve goes (Hopefully he remembers to adj. the distributor because the retarding the intake cams retards ignition as well)

Retarding the intake cams should help compensate for the lack of higher compression, but you only have a very small leeway before the valves and piston clearance become an issue (there's a reason why there's the minimum clearance of 0.035" - 0.060" depending on rods used, to compensate for crank and wrist pin bearing wear, and how high a peak RPM you're shooting for) Not checking clearance results in many dead engines, so naturally you need to trust your mechanic on this, and that everything works out well and there isn't a date between your piston and valves when you are at 9K rpm. Valve float is also an issue, then again, with c2 cams you can't use the stock valve springs.

There's also worry about the aggresive lobes on the cams, which means that you shouldn't use a stock timing belt if you want longevity.

Well, don't forget to post your results when you are done.

Very cool advice...:nice:

yes the Spec C cams are pretty aggressive on the valve springs, I will be using Toda Valve springs, retainers and timing belt. The cams are of local in Japan. the part number is;

14111-B16-00C 250 (11.0) / 295 (12.5) / 250 (11.0) IN
14121-B16-00C 250 (11.0) / 295 (12.5) / 250 (11.0) EX

It's basically a stock B16B +;
Spec C
Toda v/s
aftermarket v/s retainers
Toda timing belt
Toda cam gear

I don't know if I really need to use toda oil pump. It pumps more oil through. I will only be using it on the street, so I don't think I need it. It's pretty expensive.

I think I'll just limit my redline to 9100rpm without the block brace.

B) new LMAs (or hydraulic tappets to some) (if they're already leaking)what does LMA stand for? So I can order them
C) valve grind / new valves + grind.why does the valves need to be grinded?
D) port workis there a specific way to port polish with the B16B head or is it standard way?

You seem to be very experienced with hondas, It'd be cool if you were building and tuning my car. hehe the tuners in Perth for honda are none. They're not experienced with hondas. Only skylines, V8s and turbo cars etc. I don't like the local workmanship here. They are all terrible! Only person I can trust is my BMW mechanic, he is my mechanic for my honda. bmws and hondas are similar but different and technology wise is similar.

 

[shiroitenshi]

Very cool advice...:nice:

yes the Spec C cams are pretty aggressive on the valve springs, I will be using Toda Valve springs, retainers and timing belt. The cams are of local in Japan. the part number is;

14111-B16-00C 250 (11.0) / 295 (12.5) / 250 (11.0) IN
14121-B16-00C 250 (11.0) / 295 (12.5) / 250 (11.0) EX

It's basically a stock B16B +;
Spec C
Toda v/s
aftermarket v/s retainers
Toda timing belt
Toda cam gear

I don't know if I really need to use toda oil pump. It pumps more oil through. I will only be using it on the street, so I don't think I need it. It's pretty expensive.

I think I'll just limit my redline to 9100rpm without the block brace.

B) new LMAs (or hydraulic tappets to some) (if they're already leaking)what does LMA stand for? So I can order them
C) valve grind / new valves + grind.why does the valves need to be grinded?
D) port workis there a specific way to port polish with the B16B head or is it standard way?

You seem to be very experienced with hondas, It'd be cool if you were building and tuning my car. hehe the tuners in Perth for honda are none. They're not experienced with hondas. Only skylines, V8s and turbo cars etc. I don't like the local workmanship here. They are all terrible! Only person I can trust is my BMW mechanic, he is my mechanic for my honda. bmws and hondas are similar but different and technology wise is similar.

LMA= Lost motion assembly.. it's what keeps the rocker arm from rattling.

I am building and tuning a car.. mine, but I'm doing it on available spare budget (a.k.a. petty cash), so it's slow process, and I still do learn as I go along, so naturally my thinking changes as it goes. I'm really in it for the tech, so things like bodykits and other stuffs are not really something I'd think about.

The toda oil pump does not pump more oil. You can check the toda catalogue, and not in any way it claims pump more oil. It's made from better materials so TODA claims it lasts longer, but I seriously don't think that something that looks and is sized exactly like the stock oil pump can pump more oil. The trick for oil pressure is the bypass spring, and that's what people use.

Valve grind doesn't actually mean grinding the valves in local Malaysian-speak. It means grinding the valves and valve seat together to ensure a good seal.

Since you have very good compression, it's not a necessity, though with the head out, sometimes you have to think 'why not?'. Then again, compression is not dependent on valve seal alone, so perhaps your valves are still in very good condition (I'd leave that to your mechanic to check, maybe he may think that there's too much deposits, and the valve and seats should be ground?)

Port work... well, this is a bit difficult. No one can really do it without a flowbench, because it's supposed to be an exact science of getting the four ports to flow exactly the same. Different head porters have different methods, and they all get results. I'd only trust hard numbers though, so if a port work doesn't include flow numbers, why bother? But good port flow can be ruined by poor exhaust/intake choices, so that's the hard part that I can't really put a finger on yet.

Based on your part numbers, those are Spec C, not C2, as is apparent by the part num.
Those numbers are advertised durations, in the order of : Primary lobe (pre-vtec) : Mid lobe (vtec) : secondary lobe (pre-vtec)

Look at the Toda C cam sheets and you will see that the number I mentioned are Spec C's middle lobe (HI as TODA calls it) numbers at 1mm valve lift.

Can you help me out and note the numbers in the cam papers?

I'm looking for the Cam Top Centre number and the Degrees of the Spec C cams. They are in a box below the diagram of the cam phase.

The opening and closing numbers I can obtain from those two numbers so I don't need those.

Please post here when you can. I'm seemingly at loss at how to find Toda C cam sheets as no shops in Malaysia has it at the moment.

Oh, and I forget, you're supposed to lock the middle lobe in place in order to measure clearance, your mech should be able to figure out how.

 

[jugbugz]

LMA= Lost motion assembly.. it's what keeps the rocker arm from rattling.

I am building and tuning a car.. mine, but I'm doing it on available spare budget (a.k.a. petty cash), so it's slow process, and I still do learn as I go along, so naturally my thinking changes as it goes. I'm really in it for the tech, so things like bodykits and other stuffs are not really something I'd think about.

The toda oil pump does not pump more oil. You can check the toda catalogue, and not in any way it claims pump more oil. It's made from better materials so TODA claims it lasts longer, but I seriously don't think that something that looks and is sized exactly like the stock oil pump can pump more oil. The trick for oil pressure is the bypass spring, and that's what people use.

Valve grind doesn't actually mean grinding the valves in local Malaysian-speak. It means grinding the valves and valve seat together to ensure a good seal.

Since you have very good compression, it's not a necessity, though with the head out, sometimes you have to think 'why not?'. Then again, compression is not dependent on valve seal alone, so perhaps your valves are still in very good condition (I'd leave that to your mechanic to check, maybe he may think that there's too much deposits, and the valve and seats should be ground?)

Port work... well, this is a bit difficult. No one can really do it without a flowbench, because it's supposed to be an exact science of getting the four ports to flow exactly the same. Different head porters have different methods, and they all get results. I'd only trust hard numbers though, so if a port work doesn't include flow numbers, why bother? But good port flow can be ruined by poor exhaust/intake choices, so that's the hard part that I can't really put a finger on yet.

Based on your part numbers, those are Spec C, not C2, as is apparent by the part num.
Those numbers are advertised durations, in the order of : Primary lobe (pre-vtec) : Mid lobe (vtec) : secondary lobe (pre-vtec)

Look at the Toda C cam sheets and you will see that the number I mentioned are Spec C's middle lobe (HI as TODA calls it) numbers at 1mm valve lift.

Can you help me out and note the numbers in the cam papers?

I'm looking for the Cam Top Centre number and the Degrees of the Spec C cams. They are in a box below the diagram of the cam phase.

The opening and closing numbers I can obtain from those two numbers so I don't need those.

Please post here when you can. I'm seemingly at loss at how to find Toda C cam sheets as no shops in Malaysia has it at the moment.

Oh, and I forget, you're supposed to lock the middle lobe in place in order to measure clearance, your mech should be able to figure out how.

oh i see, lost motion assembly LMA.

How did you find out about todas oil pump? Toda said this is the most important part of the engine and refered it as the heart of the engine. Geez, for 22000yen also. So does someone make the bypass springs that you can buy?

I'll keep that valve grind in mind, I always thought port and polish wouldn't be easy and the lack of honda builders and tuners puts me off from doing any of that. Unless theres an instruction on how to do PP on a b16b head then most likely I won't bother. My intake is J's Racing CF with heat shield and 5zigen 4-2-1 with 2.5in collector and custom 2.25in plumbing with 3 extra large resonators(hotdogs) to make it sounds extremely deep. None of that high pitched weak sounding stuff. I'll post a video once I get a chance to video it. I have to install a high flow cat on next service with J's Racing headers replacement. Some people say 2.5in is better, but I think it's way to big and loose a lot of torque and velocity in low and mid range. I've studied that 2.0in pipings are best for 1.6L engines. But I think for a high output engine 2.25in is best. What do you think?

As for the toda cam specs, I'll definitely post it up for you when I get the package and put a pic up. I'm also bringing in Spec A to try out first and see how much difference between stock, A and C.

 

[shiroitenshi]

oh i see, lost motion assembly LMA.

How did you find out about todas oil pump? Toda said this is the most important part of the engine and refered it as the heart of the engine. Geez, for 22000yen also. So does someone make the bypass springs that you can buy?

I'll keep that valve grind in mind, I always thought port and polish wouldn't be easy and the lack of honda builders and tuners puts me off from doing any of that. Unless theres an instruction on how to do PP on a b16b head then most likely I won't bother. My intake is J's Racing CF with heat shield and 5zigen 4-2-1 with 2.5in collector and custom 2.25in plumbing with 3 extra large resonators(hotdogs) to make it sounds extremely deep. None of that high pitched weak sounding stuff. I'll post a video once I get a chance to video it. I have to install a high flow cat on next service with J's Racing headers replacement. Some people say 2.5in is better, but I think it's way to big and loose a lot of torque and velocity in low and mid range. I've studied that 2.0in pipings are best for 1.6L engines. But I think for a high output engine 2.25in is best. What do you think?

As for the toda cam specs, I'll definitely post it up for you when I get the package and put a pic up. I'm also bringing in Spec A to try out first and see how much difference between stock, A and C.

yep. 2.25 usually gets good results for most 1.6 applications. Some people have gotten good results with a 2.5, but I haven't really seen that with any B16's I've encountered.

Cat will always kill power (even if they're high flow), so don't expect to beat some dyno results of cat-less B16s.

3 resonators eh? heh.. even with one I'm having clearance issues going over speed bumps, I dunno how you manage with 3 (O_o)

As for the toda oil pump, just say that I've seen it, and it looks exactly the same as a stock unit.

Bypass springs, that one usually engine builders know where to get. The spring stiffness regulates the pressure, so they usually have played around enough to know what stiffness works best.