Nu stiu unde sa pun asta asa ca las la latitudinea ta yula unde sa muti postul
Un tip a pus o intebare simpla iar raspunsul a fost cum nu am mai vazut de mult pe un forum auto "
KEVTI;666505 Wrote: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;666508 Wrote: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;666512 Wrote:hi kozy, what you mean by the engine does gaf ? I have a stock b18c at the moment.
Kozy;666515 Wrote: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? :nerv:
The engine won't make any power there anyway.
KEVTI;666518 Wrote: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;666521 Wrote: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 shit 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;666535 Wrote: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.
:lol:
God I love your math and scientific approach! I can't give you more repFirst I have to spend it on others
Did that yesterday though...
KEVTI;666539 Wrote: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;666542 Wrote: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;666564 Wrote: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;666624 Wrote: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...
KEVTI;666689 Wrote: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;666693 Wrote: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;666704 Wrote: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. :nice:
