opinions on setting rev limiter!

[KEVTI]

Hi guys, basically i have a jdm b18cr and just got my p30 chipped ecu. Now i know that my engine has uprated valve springs so i was wondering do you think it is safe to set the rev limiter at 10,000rpm ? Also using crome, is there a way that you can choose for the limiter to work e.g. Ful cut or ignition cut ? I know you can on hondata but wasnt sure if crome has that function.

Thanks

 

[Kozy]

No. The engine does GAF what head spec you have, the limiting factor is the stroke. A B18 at 10k will be putting insane loads on the rods and pins and you could risk piston to head contact.

It would be unwise to set it much above 9k, unless you've got some seriously lightweight pistons and stronger rods.

 

[KEVTI]

No. The engine does GAF what head spec you have, the limiting factor is the stroke. A B18 at 10k will be putting insane loads on the rods and pins and you could risk piston to head contact.

It would be unwise to set it much above 9k, unless you've got some seriously lightweight pistons and stronger rods.

hi kozy, what you mean by the engine does gaf ? I have a stock b18c at the moment.

 

[Kozy]

GAF - Give A Fook.

At 9000rpm, the piston speeds in a B18 are higher than those in an F1 engine at 18000rpm. The pistons are likely to be a fair whack heavier too.

How lucky do you feel going higher?

The engine won't make any power there anyway.

 

[KEVTI]

GAF - Give A Fook.

At 9000rpm, the piston speeds in a B18 are higher than those in an F1 engine at 18000rpm. The pistons are likely to be a fair whack heavier too.

How lucky do you feel going higher?

The engine won't make any power there anyway.

wow, thats an interesting bit of information. How is it that the piston speeds are faster then ? I like the idea of a high revving engine, maby i will just wait until i build the engine before i raise it.

 

[Kozy]

Stroke. Every rev, the piston needs to travel 87.2mm down the bore, then 87.2mm back up it.

In an F1 engine, it only needs to go about 40mm in each direction, so for each rev, it's going under half the distance, so it can spin twice as fast and the speed of the piston will still be lower.

Why does it matter?

When you go from the max piston speed on the up stroke, to 0 at TDC, then back to max speed on the down stroke, you have an acceleration. Imagine going from 110mph to 0 then back to 110mph in the opposite direction in the space of 44mm.

It's about 5200G in a B18 at 9000rpm. Add a mass to that acceleration and you have a force. B18 pistons are 305g, so at 5200G that's 1600kgf load on the rods and wrist pin at TDC.

That's an absolute **** load. At 10k, it would be knocking on 2000kgf.

An F1 piston weighs about 200g. The acceleration is about 9000G, which gives 1800kgf.

Puts it into perspective a little I find...

 

[_JT]

If you really love to rev, get a B16b - don't know how much less the stroke on that is though. You can stretch the revlimit a bit to play with the margins, say 400rpm or so. To rev 10k rpm you have to spend insane amounts of money; K20 is probably cheaper and for sure it's a lot faster.

GAF - Give A Fook.

Stroke. Every rev, the piston needs to travel 87.2mm down the bore, then 87.2mm back up it.

In an F1 engine, it only needs to go about 40mm in each direction, so for each rev, it's going under half the distance, so it can spin twice as fast and the speed of the piston will still be lower.

Why does it matter?

When you go from the max piston speed on the up stroke, to 0 at TDC, then back to max speed on the down stroke, you have an acceleration. Imagine going from 110mph to 0 then back to 110mph in the opposite direction in the space of 44mm.

It's about 5200G in a B18 at 9000rpm. Add a mass to that acceleration and you have a force. B18 pistons are 305g, so at 5200G that's 1600kgf load on the rods and wrist pin at TDC.

That's an absolute **** load. At 10k, it would be knocking on 2000kgf.

An F1 piston weighs about 200g. The acceleration is about 9000G, which gives 1800kgf.

Puts it into perspective a little I find...

God I love your math and scientific approach! I can't give you more rep First I have to spend it on others Did that yesterday though...

 

[KEVTI]

Stroke. Every rev, the piston needs to travel 87.2mm down the bore, then 87.2mm back up it.

In an F1 engine, it only needs to go about 40mm in each direction, so for each rev, it's going under half the distance, so it can spin twice as fast and the speed of the piston will still be lower.

Why does it matter?

When you go from the max piston speed on the up stroke, to 0 at TDC, then back to max speed on the down stroke, you have an acceleration. Imagine going from 110mph to 0 then back to 110mph in the opposite direction in the space of 44mm.

It's about 5200G in a B18 at 9000rpm. Add a mass to that acceleration and you have a force. B18 pistons are 305g, so at 5200G that's 1600kgf load on the rods and wrist pin at TDC.

That's an absolute **** load. At 10k, it would be knocking on 2000kgf.

An F1 piston weighs about 200g. The acceleration is about 9000G, which gives 1800kgf.

Puts it into perspective a little I find...

lol thanks for narrowing that down for me. I will keep it at 9 for now, 9 is pretty high anyway.

Why would i go from my b18c to a b16b ? I know it may rev better but would be such a down grade.

 

[Kozy]

If you really love to rev, get a B16b - don't know how much less the stroke on that is though. You can stretch the revlimit a bit to play with the margins, say 400rpm or so.

B16B is 77.4mm, she's good to spin a full 1000rpm over a B18C with ease. In fact as standard, the B16B is relatively unstressed. Most sources will suggest 25m/s is the safe limit, a B18C at stock 8400rpm rev limit is 24.3m/s and a B16B at 8600rpm is only 22m/s.

Bonus of this is, what you lose in torque with the smaller capacity you can potentially make up with more revs, so the power potential of a B16B is theoretically no different to a B18C despite being smaller.

 

[tama666]

B16B is 77.4mm, she's good to spin a full 1000rpm over a B18C with ease. In fact as standard, the B16B is relatively unstressed. Most sources will suggest 25m/s is the safe limit, a B18C at stock 8400rpm rev limit is 24.3m/s and a B16B at 8600rpm is only 22m/s.

Bonus of this is, what you lose in torque with the smaller capacity you can potentially make up with more revs, so the power potential of a B16B is theoretically no different to a B18C despite being smaller.

theoretically

I do agree with Kozy on higher revs with the b16 over the b18. The torque for me is more important over the little use higher revs would give me, this is not about me. However, I think you need to think about what you would be using more over just wanting a higher reving. engine.

 

[Kozy]

theoretically

Well, I've seen a 250bhp B16 (Buddyclub) and I've never seen a B18 putting out any more than that, they all seem to plateau around 245bhp.

Maybe over that side of the pond where you guys have smaller horses perhaps...

 

[tama666]

Well, I've seen a 250bhp B16 (Buddyclub) and I've never seen a B18 putting out any more than that, they all seem to plateau around 245bhp.

Maybe over that side of the pond where you guys have smaller horses perhaps...

good one!

sorry about using the word "you" in my above post, I was referring to the OP.

 

[ijwhiteman]

Stroke. Every rev, the piston needs to travel 87.2mm down the bore, then 87.2mm back up it.

In an F1 engine, it only needs to go about 40mm in each direction, so for each rev, it's going under half the distance, so it can spin twice as fast and the speed of the piston will still be lower.

Why does it matter?

When you go from the max piston speed on the up stroke, to 0 at TDC, then back to max speed on the down stroke, you have an acceleration. Imagine going from 110mph to 0 then back to 110mph in the opposite direction in the space of 44mm.

It's about 5200G in a B18 at 9000rpm. Add a mass to that acceleration and you have a force. B18 pistons are 305g, so at 5200G that's 1600kgf load on the rods and wrist pin at TDC.

That's an absolute **** load. At 10k, it would be knocking on 2000kgf.

An F1 piston weighs about 200g. The acceleration is about 9000G, which gives 1800kgf.

Puts it into perspective a little I find...

B16B is 77.4mm, she's good to spin a full 1000rpm over a B18C with ease. In fact as standard, the B16B is relatively unstressed. Most sources will suggest 25m/s is the safe limit, a B18C at stock 8400rpm rev limit is 24.3m/s and a B16B at 8600rpm is only 22m/s.

Bonus of this is, what you lose in torque with the smaller capacity you can potentially make up with more revs, so the power potential of a B16B is theoretically no different to a B18C despite being smaller.

You BLOW my mind!

 

[King Sir]

my opinion no higher than 9000 and only do that if ur racin someone car will be fine but its rare that theres power beyond 9000

 

[kammy11]

Kozy your machine! Best of it is I genuinely believe you can just rattle off these facts and figures off the top of your head. Too guy

 

[KEVTI]

theoretically

I do agree with Kozy on higher revs with the b16 over the b18. The torque for me is more important over the little use higher revs would give me, this is not about me. However, I think you need to think about what you would be using more over just wanting a higher reving. engine.

yes deffo, i would much prefere my extra bit of torque than a little more revs. There is no replacement for displacement on an n/a setup. Thats my opinion and im sure its fairly accurate.

 

[_JT]

B16B is 77.4mm, she's good to spin a full 1000rpm over a B18C with ease. In fact as standard, the B16B is relatively unstressed. Most sources will suggest 25m/s is the safe limit, a B18C at stock 8400rpm rev limit is 24.3m/s and a B16B at 8600rpm is only 22m/s.

Bonus of this is, what you lose in torque with the smaller capacity you can potentially make up with more revs, so the power potential of a B16B is theoretically no different to a B18C despite being smaller.

Awesome information!

Why would i go from my b18c to a b16b ? I know it may rev better but would be such a down grade.

There are people who choose a B16b over a B18c for the revs. I wouldn't though, it was only a suggestion if you want to rev really high

 

[Kozy]

yes deffo, i would much prefere my extra bit of torque than a little more revs. There is no replacement for displacement on an n/a setup. Thats my opinion and im sure its fairly accurate.

Yes most people will do, generally it's nicer/easier to drive.

The thing to remember though is that when you want to go fast, it is torque at the wheels which matters, not torque at the engine. You can take your B16B with 10000rpm and gear it down with a shorter FD so that it produces the same wheel torque curve as a B18C. The performance will be nigh on identical, the only difference is the B16B will be making more noise!

If you want to have a look at how engine torque and gearing combine to make the wheel torque (aka 'thrust curve') check out my free web app here:

Black Art Racing - Thrust Curve Calculator

Default settings are roughly right for the EK9 but with an H22. No idea why I did that. Hit refresh to bring up the charts and have a play around with gearing and torque curves.

 

[rd55 dun]

^ Very good and educational read!

Kozy…you have a wealth of knowledge!

 

[KEVTI]

Awesome information!



There are people who choose a B16b over a B18c for the revs. I wouldn't though, it was only a suggestion if you want to rev really high

ye thats fair enough mate, surely it would be even better to have a b18c with a lower fd then you have even more torque. Someone i know had a b18c4 and used to rev it to 10k every time, i guess he was just lucky that it didnt go pop! Do you think it is worth changing the vtec crossover or keep it the same ?