rev limit????

**Non Vtec** · 26-02-2006 06:14 AM

I dont see why something with big power N/A isnt streetable.. its not just the top end that has the gains..
my K20A has heaps of midrange and bottom end power, plus I wouldnt say it has a slim power band and I dont think it has a vtec change over point from low to high cam either really, the motor changes tone but its not really visible in the tuning.. we had an issue with cam placement in this graph and have fixed it since but I didnt worry about getting another graph, peak power is at around 10,000rpm but I'm not revving the motor that high..

the only thing stopping this motor from being street driven is the car its in and the radiator size.. as for bottom end driveablity I drive the car on the road when I have to take it to the dyno, I drive the car down the return roads etc at the drags, 50kmh in town isnt a problem at all, just need to learn how to drive it slowly thats all, given 3rd gear on roadies it will spin at 50kmh under full throttle.

**Non Vtec** · 26-02-2006 06:21 AM

Originally Posted by VTi_b0i

i wana see the dyno graph too lol and pics! an EF civic with a 150kw atw would be a rocket!

We have a couple of EF civic road cars running B18C's 160wkw they run 12.6 and 12.7 street trim on semi slicks.. over here..
they have B16B pistons or better which makes about 12.5-13:1 compression, big cams (crane stage 2's and rocket motorsport stage 3's) one has a Hondata S300, the other a Link plus ecu, ported heads, stock valve size though. and good headers etc..

**VTi_b0i** · 26-02-2006 11:23 AM

fark man thats fast :P i wish my car could do 13s

lol

**ewendc2r** · 27-02-2006 06:01 PM

What fuel (OR) are they running or has ignition timing been retarded to compensate for high compression?

**ProECU** · 27-02-2006 06:09 PM

"retarded" timing... you refer to it as a bad thing ????

**Non Vtec** · 28-02-2006 06:04 AM

they run pump gas, the timing is set so the car doesnt detonate, retarded timing isnt a bad thing as ProECCU will tell you. It not a big job to tune a motor with over 13:1 compression for pump, you wont see the real benefits of going to the high compressionas much though

**ewendc2r** · 28-02-2006 09:44 AM

Well, its done mainly as Non Vtec says, to compensate for high compression / low octane fuel. It certainly isn't an ideal solution. The same result could possibly been achieved with lower compression, more advanced timing etc (at least a more efficient burn).

I guess it all depends on what you guys consider streetable -- I am sure Croydon's GTR COULD be driven on the street (if legal) but hardly a streetable setup. Just as any car could be driven on the street, but suddenly a lot of other factors come into play that I would consider taking away from the easy ability to drive the vehicle around suburban streets.

**ProECU** · 28-02-2006 11:23 AM

Originally Posted by ewendc2r

Well, its done mainly as Non Vtec says, to compensate for high compression / low octane fuel. It certainly isn't an ideal solution. The same result could possibly been achieved with lower compression, more advanced timing etc (at least a more efficient burn).

Mate,
where are you getting this from? Are you making it up or what?

Can you explain how ignition timing actually works for the masses to understand your twisted logic?

**ewendc2r** · 28-02-2006 09:10 PM

Sorry I'm not a genious in that field (not being a smartass and if you can explain why I'd love to learn more in depth) -- I always thought that if you are pinging an easy solution is the retard the ignition timing (very very generalised) until the pinging/detonation/pre-ignition stops at the cost of power OR using a higher Octane fuel on the tune (and when its run). Is that not right?

The more advanced the timing, the more time the flame has to burn through the mixture of air & fuel before the cylinder reaches maximum compression at TDC. Of course, if this is too advanced, then the mixture will try and push the piston down before it reaches TDC (causing pinging). This can then be combatted with scavenging cam profiles that actually have an overlap for high rpm efficiency (to pull / suck mixture through the cylinder to ensure maximum saturation and usually suitable for NA cars I think).

I have also heard though at high rpm's due to increased engine temperature and resultant burn speeds that ignition timing can be further retarded to allow for a better burn without detonation. This would normally apply to high revving, high compression drag engines.

I am on the right track here?

EDIT: Did a bit of research:

EXAMPLE (Don't worry about the Figures etc - Just look at the maths).

Cylinder pressure of 1000 PSI at TDC, (FIG. 1), can drop to 500 PSI with less than 3/8" of piston travel, (FIG. 2). If you can manage to get 1000 PSI in the same engine after the 3/8" travel, (FIG. 3), the pistons will have to travel an additional 3/4" to lower the cylinder pressure to 500 PSI, (FIG. 4). Work is defined as a force times distance. An average pressure, (750 PSI X 12-1/2 sq. in.), times distance in feet, (3/8" divided by 12), equals 293 foot pounds of work. Our second example, because it has twice the chamber volume above the piston location, must move twice as far to lower the cylinder pressure by 1/2. Since all the other numbers, by our own definition are the same, the force multiplied by a distance twice that of the first example will equal twice the work done, 586 foot pounds of work. There is no free lunch in horsepower equations because to get 1000 PSI above the piston in the second example takes twice as much fuel and energy as the 1000 PSI in the first example. What this offsetting of the peak pressure does is allow us to use the extra fuel mix available to a nitrous engine without breaking and melting things. The system that allows us to postpone maximum cylinder pressure is ignition timing retard. To a lessor extent short rod ratios, lower compression ratios, high RPM, aluminum heads, a tight quench, a rich fuel mixture, a small carburetor and hotter cams tend to delay maximum cylinder pressure.

Understand that, in our quest to delay cylinder pressure's peak time, more is not necessarily better. Instead, consider that the ideal cylinder pressure would be just short of detonation pressure and this pressure would be maintained from top dead center, and as long as possible after TDC. If timing is really late, you won't build enough cylinder pressure to start the car, let alone drive it. The 1000 PSI pressure in the example is not the maximum allowable combustion pressure but, rather, a comfortable pressure for illustration of the work principle.

Furthermore (non-quote and from my understanding) I would imagine that because the burn process is delayed, the heat generated from retarding the ignition to compensate for the higher cylinder pressures would be greater (not a good thing obviously) -- Am I right?