What does a motor with cams feel like?

[spetz]

Hi,
Can someone tell me what does a car with upgraded cams feel like?

The main questions:
1. Does the VTEC engagement point change?
2. Does it lose that VTEC kick?
3. Does peak power shift in the revrange?
4. If the bottom end is standard, is the goal to have peak horsepower before cutoff, or peak torque before cutoff?
5. Any other notable differences in engine behavior?

Lets assume the engine has I/H/E mods, a piggyback ECU, and lets say the engine is a B18CR.

Thanks for any help

[TODA AU]

All counts... Generally yes...

[dougie_504]

Hi,
Can someone tell me what does a car with upgraded cams feel like?

The main questions:
1. Does the VTEC engagement point change?
2. Does it lose that VTEC kick?
3. Does peak power shift in the revrange?
4. If the bottom end is standard, is the goal to have peak horsepower before cutoff, or peak torque before cutoff?
5. Any other notable differences in engine behavior?

Lets assume the engine has I/H/E mods, a piggyback ECU, and lets say the engine is a B18CR.

Thanks for any help

From my experience (pre-tuned ECU, not fully tunable yet).
1. VTEC engagement can be set to your desired RPM. Consult a good tuner IMO.
2. VTEC kick...in my example is much more aggressive (just running stage 1's). If you get VTEC killer cams then it speaks for itself, but with a lumpier VTEC lobe you should notice more power, right?
3. Yes peak power shifts, generally upwards.
4. Yeah you want to aim for peak HP IMO. AFAIK you'll pretty much always hit your peak torque before peak HP, and I'd rather have the HP than the torque.
5. Uses a little more fuel (not properly tuned). Louder. Crazy VTEC crossover (I have other mods too).

[spetz]

Dougie,
What cams do you run?

I am confused as to the hp and torque thing. Hp is always after peak torque because of how hp is calculated (nm*rpm/5252).
And I am wondering whether it's ok to get cams that make peak hp after cutoff (ie the hp will keep going up after cut off) however peak torque is before cut off obviously.
The reason I ask, is one of my daily drivers has peak torque at 1,500-4,000rpm, and peak hp from 4,500-6,000rpm, however past 5,000rpm it has no pull at all.

[dougie_504]

I run Skunk2 Pro stage 1's.

I didn't know HP and torque were related like that. Where did you get that information? I don't think that's an accurate formula but if you can convince me otherwise please do.

When you look at a Honda engine (being generally small/4 cylinder) you normally get peak torque at one RPM point (not a RPM range) and the HP will peak higher, because the engine doesn't make much torque anyway. Peak HP also comes at one point in the RPM. You might maintain this level of torque/HP output for a certain amount of time (in terms of RPM) but the peak it generally at one point.

It's fine to have cams that make power above your cutoff, but I would advise aiming for a cam shaft that will make power within the RPM range that you can USE, or alternatively increasing your cutoff.

I think the B18CR makes peak torque around 7500RPM and peak HP around 8000RPM.

What car are you talking about that has 'no pull' over 5000RPM?

[euromandeluxe]

Torque and power are related like that, as a quick google search will tell you

http://www.ebroadcast.com.au/ecars/A/Power.Torque.html

http://www.largiader.com/articles/torque.html

and one of my favourite articles on the torque/power debate that clears a lot of stuff up:

http://vettenet.org/torquehp.html

Honda engines may make relatively small amounts of torque (due to low displacement), but they make high power because of high RPM

[dougie_504]

Very interesting read, thanks!

[spetz]

Yes, an engine that revs high will always make a "lot" of horsepower. Hence why small capacity bikes always seem to make so much power compared to their engine size.
To give you an idea, a car with 100nm at 10,000rpm would make 190hp, where we know in reality a even a 1.3 liter carburetor Civic makes more torque than that.
And hence we also know that past 5252rpm the torque can start dropping off yet power can be going up, as the rpm are higher than the 5252 number it will be divided by to calculate power.

The car which has no pull past 5,000rpm but makes peak hp from 4,500-6,000 rpm is a 1.8L Audi A4 turbo (B8).
Which leads me to the question of whether when choosing cams, should cams be chosen for their peak torque rpm or peak horsepower rpm, taking into account the standard bottom end of an engine dictating not raising the cutoff

[dougie_504]

No idea about the Audi, but how does your B18CR feel past it's peak-torque point of 7500RPM?

I chose stage 1 cams because I wanted something that would be suitable for street use - smooth idle, not too noisy, but a bit of extra power. If I had to choose a part based on peak torque or peak HP I would go for the HP. IMO there is no replacement for HP

[spetz]

What engine is it you have?
And how noticeable was the improvement after cams?

[dougie_504]

JDM B16A, very healthy.

Difference was hard to gauge because I did a full head build all at once. Shafts alone...no idea what the gains would be.


Have a look here if you want:
http://www.ozhonda.com/forum/showthr...Andy-s-CRX-SiR

[trism]

Basically torque is measured rotationally, but horespower is measured linearly. Because an engine spins around the crank it is impossible to directly measure horsepower. You have to measure torque and then extrapolate the horsepower using the formula given earlier.

If I had to choose a part based on peak torque or peak HP I would go for the HP. IMO there is no replacement for HP

I disagree. Especially for tthe street, you're contradicting yourself when you chose the good street cams.

Its easier to think of it like this: torque is what gets you moving, power is what keeps you going. When you put your foot down and you get pressed back in your seat, that's torque.

Power is good when you have something light to move. Motorbikes make massive power, but no torque, likewise for Honda's. Torque is good for something heavy. a truck might only make 700hp, but it does it at 2500 rpm and makes 1500nm of torque. Even if you had a 700hp Honda motor you'd be pushing to make 500nm coz you'd be doing it at 8k rpm and it wouldn't work in a truck.

For a street car, you'd want torque over power. Most of the time you're coming from traffic lights etc, so low revs, and that's where you want the pull, and that's torque.


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