296in 304ex 4age 16v questions - do i have the potential for time travel?

[xero]

hi folks, long time lurker recent time poster.

anyway, i have a pair of tomei 304/296 11/10.5mm lift cams for my smallport 16v. i aware of the work that needs to be done to fit them and the compression etc etc.


got my tax return and planning on doing something stupid with it, so i was looking at them last night and only just realised that the intake cam is actually 296 deg with 10.5mm lift, and the exhaust cam is 304 deg 11m lift.
so my question is this:
would 296in 10.5mm lift and 304ex with 11mm lift would be good with my 12.5:1 comp?
would there be any other issues that could be for seen?
would shit be so far out of phase that i will create a blackhole where my engine used to be?



engine specs to help:
worked/ported head
balanced crank
12:1 pistons
quad throttles
1 3/4 primaries
extractor length over 1m long (they are fucking long)
2.5" exhaust system
motor ok to rev up 10k (no way in hell im revving that high, 9500 is going to be max RPM)


TRDEE already offered some insight when we were bouncing emails around:

Cam profiling is like witchcraft. Everyone has their own secret recipe that they think works best. From my limited understanding having a bigger exhaust cam than inlet cam is good for high revving n/a engines cos you get maximum scavenging and if phased right will help draw more charge air in on the inlet stroke, but too much and you will start wasting that charge air straight out into your exhaust, you could even get exhaust gas reversion if the exhaust valves are open too long and/or your extractors aren’t tuned right. The optimum point for this is largely dependent on how many revs you’re doing and what your exhaust is tuned to.

[trdee]

disclaimer; i dont know what im talking about, so help this man oh smarty smart people of toymods!! I'd like to hear some other opinions myself

[Radar]

How do you know that your primarys have to be that big?? Also what LSA are going with? Tight or wide? What are you after peak hp or a flat tq curve? If you do opt for a tight LSA with loads of overlap have a look into anti-reverberation chambers in your exhaust.. Also might want to have a look at plenum for the ITBS to get more torque.

[NME308]

Hi there,
Sounds like you have the ingredients for a hell nasty N/A screamer!
Camshaft selection is often regarded as a black art and many people claim to have a 'secret' grind for maximum power. In reality a camshaft opens and closes the valves - which thing is quite important cos you cant fit air and fuel in when the hole isn't open...

On a twin cam engine with adjustable gears you can really dial things in with more or less overlap i.e. open either/or the intake and exhaust valves sooner or later. Those of us who insist on playing with dinosaur pushrod single cam engines have to work with the overlap ground into the cam and only get to adjust the valve events in one direction at a time.

Because of the adjustability in the twin cam design you should be able to make the camshaft pairing you have work extremely well. Exhaust having a few more degrees duration is common on engines with less than ideal exhaust port flow - I have no idea what the 4AGE is like in this regard. In theory land the bigger exhaust duration may not be perfect but the difference between perfection and 'not quite' is usually bugger all of nothing when properly tuned. Unless you are on a genuine 'max effort' build and the guy in the lane beside you is going the square root of the diameter of a fly's whisker faster than you then what you have should work brilliant is my opinion!

Your extractors sound like they are designed for low to mid range rpm work and I would not be surprised if you found shorter would work better at high rpm - once again possibly not a major issue unless this is a max effort build. Your cam pairing will promote high rpm power, as will the quad throttles. The high compression ratio will come in handy to help out the small amount of cc's in the 4A cos the cams are going to be mighty grumpy down low! Someone like yourself who has a genuine real world engine package could benefit from punching in the statistics to a program such as engine analyzer pro which will allow you to see what the effects of advancing or retarding the camshafts will be. Such software may be a little off on the extent of the predicted results but if fed real information can help point out whether a proposed change will be in the right direction. It can be equally important in telling you if you are in danger of unwanted piston to valve contact etc. Key is feeding accurate real world information in!

I hope this is all going in a lightweight track car where it can be enjoyed properly. Such an engine will not thank you for attempting to punt it around the street - not at safe and legal speeds anyhow! I'm also hoping you are going to be feeding this thing race gas or at least E85 because it is going to get some pretty big cylinder pressures going on once the rpm are up a bit. You will of course have bugger all of no cylinder pressure measured on a compression gauge cranking over on the starter...

Cheers,
Jason

[oldeskewltoy]

Find yourself a dynamic compression calculator and use it. Cams are neither witchcraft nor mysterious. Anyone who tells you that is either uneducated(about engine building) or can't be bothered to look it up and find out.

In my humble opinion... the 304 is too much cam if you are planning on keeping revs to 9500 or less, I'd find another 296, or maybe even a 288. Why do I have that opinion? HKS has valve spring specifications listed on some of their cam cards. 256 to 8000, 264 to 8300, 272 to 8800. If a well tuned 272 requires springs capable of 8800, and you have a set max rpm of 9500, then it seems that jumping 3 cam grades above will put the 304 making max power ABOVE your 9500 rpm limit.

[thechuckster]

this reminded me of this build thread - high-revving, high-comp, big cam (284 dur 10.1mm lift ) 4AGE requiring expensive valve train hardware (Supertech). From memory, he spent $2kUSD on the supertech kit but the actual spend amounts are in that build thread if you dig thru it.

[xero]

Find yourself a dynamic compression calculator and use it. Cams are neither witchcraft nor mysterious. Anyone who tells you that is either uneducated(about engine building) or can't be bothered to look it up and find out.

In my humble opinion... the 304 is too much cam if you are planning on keeping revs to 9500 or less, I'd find another 296, or maybe even a 288. Why do I have that opinion? HKS has valve spring specifications listed on some of their cam cards. 256 to 8000, 264 to 8300, 272 to 8800. If a well tuned 272 requires springs capable of 8800, and you have a set max rpm of 9500, then it seems that jumping 3 cam grades above will put the 304 making max power ABOVE your 9500 rpm limit.

the HKS guide is that based on factory compression or a high compression engine like mine?

using rough maths the dynamic compressions comes in at around 10-10.5:1.

from what we worked out with the engine builder and tuner a pair of 272's or 288's would run out of puff at about 8200-8500rpm.
as this it is for ciruit racing the more RPM would be better to have and with the 4.7s and gearset it should make power between 4000-9500rpm, which is where is going to spend most of its time on the track anyway...