IMO it doesn't matter about displacement either. Just because you build a huge engine, does that necessarily mean it won't be used for high RPM racing? Similarly, if you build a smaller engine, does that automatically mean it gets a small cam because it's going to be driven on the street? It's about application and RPM range. Granted larger engines can generally tolerate a larger cam than a smaller one with the same goals in mind, but that doesn't dictate which cam gets picked over another.
True,but that´s not the point I was trying to make.A smaller engine generally needs more rpm and more compression to make the same power as a larger engine.BMEP and effective compression ratio is basically what I am talking about and that is a cam and displacement issue ( not entirely but a large portion).A smaller engine needs more cylinder pressure to make the same or more power than a larger displacement engine.How much a head flows is of course useful as that will also determine how much rpm the port will support and how much air will flow at a certain valve size and lift.Even if both engines have the same amount of cylinder pressure i.e. 180 psi,the larger engine will make more power because it has more air volume to compress allowing for a more powerful combustion than the smaller engine.Also at which rpm each engine will achieve that cylinder pressure is dependant on the cam.Generally the larger engine will achieve that pressure at less rpm.
A radical cam in a small displacement engine will work of course in an NA or forced induction application,it just moves the efficiency range and torque further up and you generally have more peak horsepower and a smaller range of useful power.If the cam is to small (in any application) you´ll make torque earlier and peak sooner anfd generally make less power also.That´s nothing new,everyone knows that.So the cam will dictate how much cylinder pressure you make.A radical cam will more than likely give you more cylinder pressure,but much later.The smaller the engine the evident that becomes.If the cam is "too big" you won´t achieve the desired cylinder pressure and therefore less power among other problems that will follow.
I've just read through this whole thread. Interesting. Can I make some observations...
The vast majority of the engine recipes on here appear too be;
Close to or above 2000cc
Max rpm above 6500rpm
Connected with drag racing
Wally's 1200cc is an interesting exception to this, but even still it's listed as a "competition" engine.
With all that said, I found it really hard to know what to make of comments re Engle TCS cams in my specific application;
TCS10 cam,
CB hideaway header,
Factory 1585cc (factory pistons and barrels),
stock motor aside of balanced bottom end,
Microsquirt EFI,
Water/air intercooler,
I've not chosen a turbo for it yet. The plan is a torquey street motor for skidpan events and autocross rather than a huge top end. As you might imagine, in my case I wondered whether the discussion was working across purposes for my aim. Am I right?
It'll be fine Pete, but you guys are too much focussed on cam choice. Its a TURBO engine! Turbo choice is wayyyy more important then cam choice.
Spool moment and turbo choking moment is what its all about. When a turbo spools, you forget you ever thought about 'coming on cam'.
I have been running a W-100 cam on my turbo with a stock crank and it will continue pulling hard up to and past my self impose rev limit of 5200 rpms.
So much so now with the WRX turbo that it will hit 5400-5500 before I can shift in first and second gears.
Stripped66 wrote:The point wasn't to argue air temps with the current world record holder, but to dispel the claim that the K03 is wrapped up at 150 HP. It's not.
That's because the additional intake pressure causes a cam to breathe farther into its range than it normally would at atmospheric pressures, it helps me to remember that we're not just pressurizing the intake- we're adding more pressure than it usually sees.
miniman82 wrote:That's because the additional intake pressure causes a cam to breathe farther into its range than it normally would at atmospheric pressures, it helps me to remember that we're not just pressurizing the intake- we're adding more pressure than it usually sees.
OTOH, the backpressure on the exhaust side makes that the pressure DIFFERENTIAL between intake and exhaust is not that much.
If you look at it that way, its easily explainable why a N/A cam works so well... I think we both agree on that
T4T: 2,4ltr Type 4 Turbo engine, 10.58 1/4 mi www.apfelbeck.nl "Mine isn't turbo'd to make a slow engine fast, but to make a fast engine insane" - Chip Birks
True, but I'd say most people who try to go turbo are simply happy getting any boost at all, never mind the scientific reason behind why it works. lol I just can't figure out why someone would grind a cam that's short on exhaust duration, and call it a turbo cam. Turbos are powered by exhaust, so why choke it off? Makes no sense.
miniman82 wrote:True, but I'd say most people who try to go turbo are simply happy getting any boost at all, never mind the scientific reason behind why it works. lol I just can't figure out why someone would grind a cam that's short on exhaust duration, and call it a turbo cam. Turbos are powered by exhaust, so why choke it off? Makes no sense.
I agree on that. Supposedly by reducing duration on exhaust, the overlap is reduced which helps build cylinderpressure earlier, which helps spool. So the theory. In reality, it's a compromise for reducing intake charge flowing into the header during overlap. With efi that can be controlled better.
70dragbug wrote:..., the overlap is reduced which helps build cylinderpressure earlier, which helps spool. So the theory.
Call me stubborn, but I don't support that theory and have evidence on my own motor of it. For the far larger part, the exhaust (mass)flow gives spool, not more or less cylinderpressure (due to a different cam). Thats why a larger duration cam doesn't give a later spool. A larger duration cam just gives less torque down low when there is no boost yet. Has (virtually) nothing to due with the forming of boost.
I see and read a constant misplacement of these two parameters. Please lets keep those two seperate .
T4T: 2,4ltr Type 4 Turbo engine, 10.58 1/4 mi www.apfelbeck.nl "Mine isn't turbo'd to make a slow engine fast, but to make a fast engine insane" - Chip Birks
True Wally,I agree totally, which is why I agreed that a shorter duration on the exhaust makes no sense. The theory I mentioned is what Engle says regarding their TCS series cams. I am convinced that you will achieve the same hp at a lower boost level than before because your new heads are much more efficient and flow a lot better. You changed your cam also,so an actual 1:1 comparison can't be made really, but you will see it anyway. You said changing the turbo makes a bigger difference than changing the cam. You've proven that also,however I remember when you added the Pauter rockers to your 2 Liter and gained 40hp at the same boost and rpm. So making the engine more efficient compliments the turbo greatly. The more power you make,the higher your cylinder pressure will be. Turbo efficiency, housing size etc. will make the power and also how fast it spools,but don't forget the NA side of the engine that gets you to that starting point.
70dragbug wrote:I am convinced that you will achieve the same hp at a lower boost level than before because your new heads are much more efficient and flow a lot better. You changed your cam also,so an actual 1:1 comparison can't be made really,...
My reference on a 1:1 comparison came from last motor where I only changed the cam from a 163 Web to a EMW cam with 260 duration @ 0.50 lift. I think it even spooled faster... Reason to open the engine back then was because it had 3 bend rods... I changed them for Pauter rods and later sold the engine alltogether...
The new engine will be a while (especially as it will be N/A first) and due to the heads a even wilder cam (!) a whole different animal.
You said changing the turbo makes a bigger difference than changing the cam. You've proven that also,however I remember when you added the Pauter rockers to your 2 Liter and gained 40hp at the same boost and rpm. So making the engine more efficient compliments the turbo greatly. The more power you make,the higher your cylinder pressure will be. Turbo efficiency, housing size etc. will make the power and also how fast it spools,but don't forget the NA side of the engine that gets you to that starting point.
Exactly!
Love you too mate!
T4T: 2,4ltr Type 4 Turbo engine, 10.58 1/4 mi www.apfelbeck.nl "Mine isn't turbo'd to make a slow engine fast, but to make a fast engine insane" - Chip Birks
