I continually read on this board about not being able to run certain camshafts (ie. Skunk2 S2, Toda B's, etc) because the cam lobes are too aggressive for lower compression motors. Naturally higher compression will always yield better results as far as torque and power and drivability. My question is any reason to not run aggressive cams with a "low" compression motor (ie. 10.2 stock B16a2)? The claims sound ludicrous to me, its like saying you cannot run and exhaust without an intake because you will not reap the potential of the exhaust. Duh! Same for high compression with cams. Perhaps someone can shead some intelligence on these "high compression/aggressive cam" myths.

Oh and per Skunk2 Tech support there is absolutely no reason to not run Skunk2 S2' on a stock B16a2 with 10.2 CR. Will the make more with 11:1 CR? Duh! Yes. Even more with 12:1 CR? Yes. 13:1? Yes.

 

its all about dynamic compression
with too much duration , your dynamic compression will actually be lower

 

like dan said , with larger cams you have overlap, which is a timming event when both the intake valve and the exhaust valve are open at the same time. This will cause a loss in dynamic cr .

 

A late intake closing event (long duration) will cause the the piston to push the intake charge out of the cylinder until you reach a rpm where the intake charge will have enough momentum to over come this.

Having more static compression will help compensate for the "reversed" intake charge below the point where the cam "comes on"

Shorter rod/ratios will also help run more aggressive cams because the shorter the r/s ratio the piston will dwell at BDC longer allowing more intake charge to enter before seeing the piston move up.

 

I understand that the dynamic compression will be lower due to increased duration of the cams, but the loss in dynamic compression occurs with high static CR motor as it would with a low static CR motor, assuming the same cam change.

I am sure there is some complex fluid dynamics involved that might warrant the claims, but i have yet to see any.

 

yes , but the dyanmic compression will be higher, with pistons that yield higher static compression


compression makes power

 

search undercamming. thats why.

 

Or try it yourself, throw in some cams and see how your car feels. Once you lose 5% cranking pressure, you can tell the difference. And don't search undercamming, search overacamming. Putting in too aggressive of a cam with no compression to support it. You're better off using the stock cams on the lower (stock) compression and not LOSE power. With the longer duration and the intake valve closing later, you're bleeding off pressure in the intake port. This is due to the intake valve being partially open as it's closing during the compression stroke. The problem gets worse the more aggressive the cam is. In order to make up for this cylinder pressure loss, this is why we bump the compression. But too much of a compression for a cam is called undercamming the engine. But many times on this forum I see ppl giving advice for 12.5:1 CR, when in reality they'd be undercamming their engine. For this reason, while choosing cams, dynamic compression ratio and cranking pressure is your friend. It'll point you in the right direction.


Modified by eyeamvic at 11:16 PM 3/3/2004

 

 

The chart displays, the "advertised" durations, which for the Toda and Skunk2 is duration at 1mm of lift. The Crower and Honda data came from Crower and the measurement method is unknown. But Skunk2 cams seems like they would be a good choice for OE compression motors. Skunk2 cam profiles improve volumetric effeciency through cam lift, NOT so much duration. This would make them good candidants for OE compression motors, despite the "advice" I typically have read from H-T. The Toda cams are just the opposite. They look to improve VE by increased duration, rather than lift. The reduced lift reduces drivetrain wear and chance of valve floating, but you sacrifice that dynamic CR, as mentioned meaning high CR is needed for the Toda's, to compensate for the increased overlap reducing dynamic compression.

I realize we cannot directly compare the Todas and Skunk2's with the Crower and Honda data, but they should be fairly close.

If anyone has any additional cam profile data, pony it up and I will add it to the chart and data I have.



Modified by BryanPendleton at 8:36 PM 3/5/2004

 

Brian that is awesome

 

if i have 10:1 compression and i plan to turbo, i will be safe with my 403s? you said the dynamic compression goes down. and yes these ls 403s have some overlap, just a lil. and i plan on running strictly 7 lbs of boost.

 

Ok so what cams would you guys reccomend for H22a with Super Duper 13.5:1 pistons. It will be runing 105octane all day.

I expect Tom (Tbone) has some good advice on this also

 

There isn't a 1 cam fits all setup, you need to talk to your head porter as well as your header builder when chosing a cam for a large setup like yours OTT. The way your set flows will help dictate what cam profile will work best with your setup. You also need to decide on what the car will be used for, street , srip or both.

 

amazing info here guys!

 

great !! thx Bryan .That actually sounded very reasonable and it makes sense. Good to see someone actually taking the time to back up what they say Not often people do that here

 

 

I have relocated those cam charts to the following thread:

https://honda-tech.com/zerothread?id=794418

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BryanPendleton &raquo;</TD></TR><TR><TD CLASS="quote"> Skunk2 cam profiles improve volumetric effeciency through cam lift, NOT so much duration. This would make them good candidants for OE compression motors, despite the "advice" I typically have read from H-T. The Toda cams are just the opposite. They look to improve VE by increased duration, rather than lift. The reduced lift reduces drivetrain wear and chance of valve floating, but you sacrifice that dynamic CR, as mentioned meaning high CR is needed for the Toda's, to compensate for the increased overlap reducing dynamic compression.


Modified by BryanPendleton at 8:36 PM 3/5/2004</TD></TR></TABLE>


so if you could grind your own camshafts for lets say a high comp, low r/s ratio motor, assuming best valvtrain, would a long duration, longer than OE overlap and maximum lift ( maximum meaning... i read on some nissan forums a mathematical equation where you take into account the flow capability of your head + valve measurements, sit down calculate and figure out a lift value past which you no longer get a benefit..anyway) yeah, would this be best for an NA orientated motor?

 

damn i love h-t. The tech info here is just insane!
keep up the good work guys!

This is how "informative debates" should be, no name calling or anything.. just straight tech!!!

 

So is an 11.8:1 CR too much for S2S1's?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Blazin Si &raquo;</TD></TR><TR><TD CLASS="quote">So is an 11.8:1 CR too much for S2S1's?</TD></TR></TABLE>

11:8:1 is perfect for skunk2 stage 2.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chemicalviper &raquo;</TD></TR><TR><TD CLASS="quote">

11:8:1 is perfect for skunk2 stage 2.
</TD></TR></TABLE>

I read the whole thread and I think I understand over and undercamming an engine, but would I make more power with Stage 1's and an 11:1 CR or an 11.8:1 CR?

I was under the impression that 12+ CR is ideal for the Stage 2's.

 

one huge factor in determining compression for a cam is the cam's ABDC valve closing degree. Higher duration cams will usually have a higher ABDC valve closing degree(which means you need more compression).

yes, even with raised compression..you're still going to lose compression. But you want to retain at LEAST stock cranking pressure. perfect would be 15%-23% above stock cranking pressure, i'm told.

Theres a online calculator for all this stuff ya know..

 

What type of CR would be needed to run the Buddy Club Spec IIIs in a B16A2?
Specs: intake 304 duration, 11.59 mm lift, exhaust 294 duration, 10.71mm lift

They have a hell of a lot more duration opposed to stock and not as much lift so I assume the optimal CR for this application would be 11:1 - 11:8 (rough guess)? These Buddy Clubs seem to make the power in the midrange opposed to up top when viewing some of the dyno sheets floating around here on H-T. I can draw a conclusion, more lift is for higher revving motors and more duration is for the power punching mid range motors. Correct?

Greatly appreciated and very informative thread,
-Mike


Modified by SleepEMike at 3:53 AM 4/22/2004