I have been comparing a lot of cams lately. Building a 6.0 with LS3 heads, S491, Holley Hi-Ram, Bosch 210's, etc.

Wondering what the opinions are on some of the grinds I see with like 20 or more degrees more on the exhaust. Example: 226/246 or more. Even with an LS3 head, I start wondering if it is a little excessive past a 12 deg split. Some people will say it is not about LSA or Dur, but they do somewhat define the valve event choices. Also, I am all for letting the "experts" do their job, but how much is marketing?

 

LS3 Headed Engines have made great HP with anywhere from a 6 to 2x split. Consider LG6x3 with 235-244 and GPI with 236-254. I could provide more examples to back up such.

Dyno Testing has shown that a wider split will rev higher and make slightly more power but at expense of lesser power at lower rpms. There is a trade off.

Split is more dependent on intake used and personal preference about where power and torque are made. A high ram will work best with a great split making power at higher rpm.

​I'm not into turbo builds so no expert on LSA for them.

​​​​​​As for Marketing, I would yes because most people are attracted to bigger numbers.

 

Thanks, I agree with the points you made. I think some of the marketing comes into play when sales drop on an existing cam. That is when a V2 or some other name hits the market claiming to be better. Is it really much better or just new to boost sales?

 

YES AGREE.

Small splits made power.

But then customers wanted higher rpms, so got to make cams that will rev higher but still make some power in the midrange so the big splits came.

​​​​​​Then some customers wanted more chop, so got to make cams with lower LSAs.

Customers get what they want and Businesses stay in business

​​​​​​Next...

 

The longer I've played with this stuff, the more I've realized my knowledge on cam design is pretty skimpy.

@Summitracing , Brian, what are your thoughts?

 

Cams and torque converters for me lol.

 

People have said interesting things over the years about cams.

I was talking cams a bit with a buddy who has a low 4 second twin LS combo, and he thinks they might have too much cam.

 

I have been doing some research and cams have changed along with more efficient turbos. From what I see smallish cams can make good power, but to make big power numbers you still need a sizeable cam that will allow you to turn a motor to 7500 rpm or more.

 

Hi fellas, when using the four individual valve events to determine what the engine wants; Duration, LSA and Advance become byproducts. Intake opening and Exhaust closing maximums are somewhat dictated by piston to valve clearance. An example is our biggest non-flycut cam SUM-8709R1 with its intake opening at 9 Btdc and exhaust closing at 7 Atdc.

With exhaust opening, the tradeoff is whether we want to harvest the last little bit of combustion pressure to increase low rpm torque and gas mileage like we do on the Torkinators and other truck cams (which open from 40-53 Bbdc), OR like our Automotive non-flycut stage 1/2/3/4 cams (55-59 range). Or our Big Guns (65-72 degree Bbdc range). The bigger we go on this, the more we're trading low speed torque and efficiency for the ability to evacuate the cylinder at high speed/high rpm. Any time a piston is having to push exhaust out the exhaust out the valve on the exhaust upstroke, this is a pumping loss and horsepower is being used up to do it. So blowing down early uses the residual combustion pressure to blast most of itself out before the piston even hits bdc before the exhaust upstroke.

How about some test cases:

1.) Naturally aspirated: What if a guy wants a nice rumpy idle (5 Btdc I/O) and but a stock converter in his 5th gen Camaro (45 Atdc I/C). He has a somewhat restrictive street exhaust system and doesn't care about fuel mileage (60 Bbdc E/O) and we want to carry power a bit up top even with the restrictive exhaust (5 Atdc E/C). Punching the numbers into the Summit Cam Timer results in a 230/245 113.75 + 3.75 Advance. When it comes to duration splits, we don't subscribe to the intake/exhaust flow numbers of a cylinder head by itself. We would look at the exhaust system typically used as well as listen to the other behaviors a customer wants in a cam. The key to determine each valve event separately. In other words, if a caveman said "my exhaust port don't flow good so I'm going to add exhaust duration to it"....well they are half right and but could screw things up if they add the duration to the wrong valve event. Are they going to add that number to the exhaust opening point, the exhaust closing point or split the difference? The average caveman is going to add duration without changing LSA or advance. He's helping one side but hurting the other. For this reason, the cam timer is really the best way to design a cam. Yes it spits out very unconventional LSA's and advance numbers sometimes. Folks need to get those preconceived numbers out of their heads and really look at what they are trying to achieve.

2.) A Stage 2 SUM-8706R1 T4 Turbo cam is a 226/230 113 + 4. The Stage 4 T4 Turbo cam SUM-8718R1 is 238/234 117.5 + 5. Both have very different looking lobe splits but BOTH have overlap limited to 1-2 degrees. T4 Stage 4 has an intake opening (7 Btdc), intake close (51 Abdc), Exhaust opening (60 Bbdc) and extra early -6 (Btdc) exhaust closing to hit our 1 degree overlap target. Stage 4 turns more rpm, but both cams are designed for restrictive T4 turbines and full length exhaust systems so we limit overlap to prevent harmful reversion.

3.) Next up, lets look at the larger T6/Twin turbo cams. These START at 234 degrees of duration and go as big as 251 degrees. These are heavy hitters with big budgets and capabilities. Big Stall converters starting at 4500 and up. Oversized lazy turbos bringing in boost later past typical torque peak to keep head gaskets in it. They Datalog turbine inlet pressure to ensure they are less than 2:1 and preferably in the 1:1 range if it's very efficient and the turbo is dumped to atmosphere. We allow more overlap (6 to 20 degrees) because reversion isn't as big of a detriment and close the exhaust valve up to 5 Atdc. We are also blowing down early in the 59-70 range (instead of 42-60 like the T4 cams). This is why you're seeing large splits on some turbo cams. The problem is some cam companies aren't using valve events and it shows. Our T6 cams have 116 to 117 LSA (fairly normal looking) but we ALSO grind in 5-6 advance to insure the intake closing isn't too late. Back to exhaust opening- early Blow-down can aid spool time, but like Anti-lag...it's sending super-heated gasses past the valve and we'd like to see Inconel exhaust valves at this level. Strong Pushrods too since we are pushing the exhaust valve into super high combustion pressures. SOME people can take advantage of these cams, but again...Big Cams...Big RPM...Big Converters...Big Expensive Valvetrain to handle it...and Datalogging capabilities to measure Turbine inlet pressure. These cams are the wrong choice for guys running T4's or even some of the less-than-great China T6's if everything isn't matched correctly.

Hope this helps!