there are some cams out there that need "higher" compression to run properly in a x.xL engine.

my question is, can a higher air flow in the head along with a high flowing intake manifold and header replace the need for the higher compression?

ex. 12:1 compression 280cfm 1.8L needed to run a certain type of cam, can 11:1 compression 300cfm 1.8L work also?

 

Higher compression ( to a point) with the correct fuel will make any cam run better. B-16, NEON, D-15 etc. The air-flow (CFM) divided by displacement, will tell you where your engine will make the most BHP, you pick a cam to match it.

 

Don, could you elaborate anymore on this? thats a pretty open explanation

 

CFM/CID or CFM/Liters ?????????//
and how are either of those answers supposed to tell you where you will make the most power?? the answer is supposed to correlate with RPM?? crankshaft degrees????

280/123=2.28
280/2.0=140

 

I believe what he's saying is, the cam should be chosen based off how large the engine is, and how much air it flows. Compression being less significant to the way a cam will perform in the engine. Compression adds heat and heat = energy, it also makes the engine have better response. So this will naturally help make any cam run better.

 

In for explanation of said formula.

 

I'd like to know a little more about this, too.

 

I thought the duration of a cam with low compression (11:1) will cause the engine to actually lose compression even if it is flowing more air. Similar to a turbo spooling with a NA cam compared to a Turbo cam. The cam is opening the valves so long that the engine doesnt build enough compression.


Modified by JDM_teh_WIN!! at 9:50 AM 11/27/2006

 

Guys all he is saying is that the point at which you are getting the highest VE you will make the most power, pick a cam to match that rpm range

CFM/displacement = VE

 

gotcha. i just thought about it too deeply

 

So...

280cfm / 98.38CID (75.5x90) = 2.85VE?

That doesn't make sense.

I think what we're all looking for is what to do with this number. How does this number tell us when peak VE will occur or what our powerband will be?

 

Check your units

cubic feet per minute = cfm

you would have to know your flow vs rpm to do this....

 

When I get to the shop Iwill post the formula's that give you a place to start. Basic's are 300CFM @ 28 inches willgive a potential of 75+ BHPper cylinder. The cylinder displacement will tell you where it will make max BHP. The larger the displacement the lower the RPM.

 

Ah, sweet. Thank you, sir.

 

all hail DonF

 

 

Mr Max can you call this number its the guy from RMF 602 214 0268

 

Brad, we need some higher RPM lines for 300CFM on a B-16, atleast 14,000

 

Looking at that chart it would appear that each cylinder in my engine is capable of 48bhp@7000rpm flowing 140cfm. Is this correct? Does that formula relate to this chart at all?

 

That chart is @ 25 inches or .945 of 28 inches. It would be 38 BHP if you are talking a 1.6 litre. That would be 152 BHP MAX. with the right cams and compression for that flow number.
A 300 CFM head@ 28 corrected to 283CFM @ 25 inches in a B-16 has the potential of 305 BHP @ 14,813 RPM. Select your cams and rods carefully.
By the way the flow number is for the whole intake system, not just the head. A 300 CFM head does not do you alot of good with a D-16 throttle body That is the same reason 48mm tapered Jenvey ITB's make more BHP than 50mm TWM.s They flow better.
That same head and intake "300CFM @28" would make 305 BHP @ 10,918 RPM's on a 2.0 litre 4 cyl.

 

Oops, right point on the chart but wrong number. Thank you for pointing that out.

I'm starting to understand this a little bit better. Thank you. Time for some more research. Do you have any links that might help get me started?

 

A superflow flow bench manual is about 35-40.00 dollars. Has good info. Mostly for 2 valves per cyl. but it still works.

 

Guess its time to pay the machine shop to spend another hour or so on the flow bench good stuff

 

good stuff!!!

 

Cool. I'll pick one of those up. Thanks.