Engine capacity increase, wilder cam?

[spetz]

Just wondering...

If for example there is a B16A VTEC, and the heads are mated to a B20 block and still revs to 8000+ rpm
But the B20 now has quad throttle intake, ported heads, larger valves etc
Would the cams still need to be upgraded? Or would the B20 with B16A cams but all the other work still generate enough power/torque at the 8000rpm mark?

[Slow96GSR]

You tell me. In order to accurately tell you would need a dyno. I would think, I know, but ya, more aggressive cams could create more power. But you would of course have to tune the motor and do tests. Just taking a guess!! Also what is "enough power/torque at the 8000rpm mark"? To me there is never enough.

[ZeForce]

This article might be worth a read.....

http://www.theoldone.com/archive/too...ro_on_cams.htm

[Mr_will]

i think what you are getting at is, would the stock b16a cams be restrictive, with respect to the fact that theyre designed to deal with 1.6 capacity.

i do not claim to be any sort of authority on the subject, but my feeling would be the stock cams ARE restrictive, because since the capacity is increased, you would need more lift/duration to fill a larger combustion chamber.

b18cr cams might be worth a try?

[pornstar]

The best answer is to use some maths to calculate what your engine in theory will ingest in terms of air and then calculate what your cams and intake combination will in effect provide

[spetz]

I realise the cams would be restrictive considering the larger engine capacity

But, also considering larger valves, so 1mm lift now brings more air in/out
And ported heads etc

And when I say by enough power, I mean power will be peaking around 8000rpm instead of declining to that rpm range

[pornstar]

spetz, theres more to it than just that the engine is larger so it will ingest more air, therefore more lift on cams etc.

Some considerations that you might want to look at that I certainly look at plus more are:

velocity of air at given rpm range, throttle body opening size, intake runner length, turbulence in the air stream, the theoretical VE (of swept volume), the amount of reversion in the exhaust side, the port shape, compression ratio, BSAC, heat/cooling affect on the air flow, the mass of air flow in regards to the tunability of the ecu, harmonic resonance, etc etc, the list continues

for example,
At a given rpm say 5000, the mass of air flow may be that the engine will ingest say x units of air. however, at 6,000 it might not be as simple as 1k rpms more so include about 1k rpms worth of air more, simply because the amount of time that the piston spends at tdc dwell (and accelerates down at a much faster speed) will not be equal as to what it would ingest at delta 2,000-3,000, therefore you have much less time to feed the air into the engine.

Some ways of adding the air in faster might be to give your cam more lift and more duration, but what does that do the lower lobe or lower rpm? another might be to advance/retard the cam timing, but that changes the window of powerband, so does this affect the higher rpm or the lower rpm adversely, ie where do you want the power?

hope i didnt rant on too much, and im abit drunk from sunday afternoon drinks, but i hope that gives you some insight to the considerations you might want to look at.

[TODA AU]

Just wondering...

If for example there is a B16A VTEC, and the heads are mated to a B20 block and still revs to 8000+ rpm
But the B20 now has quad throttle intake, ported heads, larger valves etc
Would the cams still need to be upgraded? Or would the B20 with B16A cams but all the other work still generate enough power/torque at the 8000rpm mark?

With a highly modified B20 with DOHC Vtec head...
It seems a bit of a waste not to get the best from it.

As a general rule of thumb,
If the air flow of the engine remains the same (head etc)
A larger bottom end will tolerate a larger cam & give the same power charateristic of a smaller engine.
Should the cam remain smaller, the larger engine will peak sooner, running out of puff before it reaches it's potential.

[tinkerbell]

my experience shows that a lot can be gained by upgrading the stock B16A cams on a B20VTEC...

even ITR cams are too small IMO, especially with porting and ITB's...

as you will have noticed with your B20, you could move the VTEC point down to under 5000rpm as it pulls harder earlier due to the combination of extra capacity and lower bore/stroke ratio...

[honest muz]

i think what you are getting at is, would the stock b16a cams be restrictive, with respect to the fact that theyre designed to deal with 1.6 capacity.

i do not claim to be any sort of authority on the subject, but my feeling would be the stock cams ARE restrictive, because since the capacity is increased, you would need more lift/duration to fill a larger combustion chamber.

b18cr cams might be worth a try?

Mr_Will,
It's not as simple as just increase duration and height.
Think about bore and stroke of each engine. Are they comparable? Is one a stroked version of the other? Think about what gas flow characteristics are getting the best scavenging. Need x-ray specs here. You should checkout the following site that says better scavenging can be had from smaller ports. How does that fit with higher lift/duration?
http://www.mototuneusa.com/break_in_secrets.htm

[tinkerbell]

Mr_Will,
It's not as simple as just increase duration and height.
Think about bore and stroke of each engine. Are they comparable? Is one a stroked version of the other? Think about what gas flow characteristics are getting the best scavenging. Need x-ray specs here. You should checkout the following site that says better scavenging can be had from smaller ports. How does that fit with higher lift/duration?
http://www.mototuneusa.com/break_in_secrets.htm

hey muz, that site you quote, is that about Honda's?



does that look like a honda port to you?

What are some of the other common myths about engines ??

Here are some popular engine tuning concepts in which the truth is
quite the opposite of what is commonly thought:

- Bigger Ports

- Polishing The Ports

- Ignition Advancers

- Flatslide Carburetors

- Fuel Injection Tuning

- Cam Timing

- Jetting

and then to come up with the astounding comment:

Smaller Intake Ports Gain 7 % More Power !!
Never Before Seen in Magazines

i really dont even need to tell you how useless posting that link in this forum, in response to the original question was, do I?

[BlitZ]

increase capacity means more air is needed to fill cyclinder.. so cams with higher lift and duration would work well even if std compression is used..


Tink is a perfect example.