For discussion's sake...When tuning an engine, which is better for power under the curve? What's best for peak hp numbers? I'm trying to get a better understanding, and I know there are numerous tuners on board the ITR forum, like sgT, CHEETAH, etc. Is it generally better to have a smoother crossover? I know there are a lot of questions, but I'm trying to get a better understanding about the tuning of these engines.

 

It depends on your mods and tuning.

 

Smooth curve is what you want. As smooth as possible.

When you see a power 'spike' at VTEC engagement, think of all the power that could be made by moving the vtec xover to a more 'correct' spot and adjusting the fuel. You could gain all that area under the curve that was lost with the violent spike.

VTEC engagement isn't best at one spot, it depends on your setup: some cams like a higher xover, some don't.

Edit: Took out unnecessary ? mark.


[Modified by Chris N, 4:44 PM 1/30/2003]

 

For discussions sake - you need to specify which cams (at least) you are talking about.

 

From what I have seen with Stock cams and light mods a lower VTEC xover (approx 5200 rpm) is best for the curve to reduce the dip.

 

Also depends on the cars intended purpose. The ideal curve would vary depending on what sort of situation the motor will be running in....drag, low-speed autox, circuit, etc.
I think a smooth delivery throughout the power band, especially at crossover, would make the car a lot more driveable, manegable, and easier on the tires than a wild crossover.

 

I can't honestly see the reson to have a different crossover for any application. Seems like one would want the curve with the best area under the curve and quickest power delivery.

Am I missing a situation you had in mind?

 

Just in general. For different set ups, not just mine. I'm trying to be general as to get numerous responses for different set ups.

But for ***** and giggles, how about these cams, all on a B16A.

Toda B
Jun 3
Skunk2 stage 1
R

 

That's the point of changing it if you have to.

I've got mine set at 5 grand and it still spikes at the crossover. I could probably go lower and get 2-5 extra lb/ft over a couple hundred rpm but driving around with it that low is annoying. I don't shift till just before 5000 under normal driving, and having VTEC cross over on every shift would drive me crazy.

 

Eh? I dont understand...did i imply that one should change the crossover point?

 

Chris N...you said that generally with stock cams VTEC should be lowered to smooth it out. Now I have heard that the mugen program for the B16 was designed for stock cams. This program raises the point from 5500 to 5700. First, does anyone know if this was for stock cams; and second, does this increase peak hp by raising the crossover?

 

I don't see how it would. All it should effect is the area between the stock x-over and where you set it to.

 

you set the crossover point to where the cams make the most power.
more or less this usually means the lowest point at which the vtec cam can make power.
if its making power, that means its making MORE power than the non vtec cam.

So the answer is, as low as possible(within reason).
You do run into other restraints, such as you cant go much below 3500 due to
lack of oil pressure.

 

how bout for a drag setup? you would want to keep it in VTEC the entire time, so I would imagine you would want more power up top and the Xover wouldnt matter as much, and, possibly it would be good to have a nice strong VTEC Xover?? just throwing stuff out

 

more power is more power
does it really matter what you are doing with it?
i dono about some of you, but i would want the most power out of all parts
of the powerband.

 

You stated . . .

Seems to me you implied that the crossover point varies per application. I was saying that it woudl tend to reason the most power delivery due to cross over would be specific to a motor regardless of application. If a car makes the most power at 5000 rpm crossover then why woudl one set it to 5200 or 4800 to drag race or change it again to road race? power is power.

Cam gears to affect where the power is and the tq curve is one thing but the Xover is just a dip and moving it smooths the curve and increases area under the curve. Seems this would be a set point per motor (varying per motor and mods)

 

exactly what I was saying

 

I agree with Steve too. It doesn't matter what application.

 

i dont wanna argue, im just guessing. but i still think drag setups would be different!!! a smooth crossover doesnt matter...you would want to have as much power in vtec as possible. it wouldnt matter if you had a smooth xover or not.

 

you're right, it wont matter. but if you are drag racing you wont even HAVE vtec
in the first place.

 

For drag racing it doesnt. For autocross and/or road racing it is rather important to have a smooth power curve.

 

You are just guessing.

Steve KNOWS.

Many other people on this board also know, and are not guessing.

Try it. Go to the drag strip untuned. Get a dyno graph of your untuned engine.

Then go buy Hondata or something along those lines, not just a VAFC. First of all, your dyno chart will look much better after tuning for a 'smooth' curve, and secondly, your car with be faster at the track, drag strip, highway, autox, EVERYWHERE.

Edit: I forgot. If you are above VTEC at the strip the whole time, it won't matter, But... tuning for a smooth curve would give you more power up top as well as low/mid. you would want to tune for that power, wouldn't you? That makes the smooth crossover issue kind of a moot point, IMO.


[Modified by Chris N, 5:21 PM 1/30/2003]


[Modified by Chris N, 5:22 PM 1/30/2003]

 

not sure if thats a reference to drag race cars other than honda or not. anyway, i guess i should say you would want as much power as possible on the vtec lobe.

 

its all honda.
if you are drag racing, you would have no reason for vtec since you have no
need for streetablility. just need upper rpm power of the vtec lobe.
so reduce weight and remove the other lobes and hardware.

 

I launch at 4000 rpms with street tires so crossover in 1st gear matters to me. the smoother the better. (my xover is 5200)