Take 5 cams. Same intake and exhaust duration, same DCR, same valve lift, different LSA's

Cam 1 226/234 112+1 6* of overlap
Cam 2 226/234 113+2 4* of overlap
Cam 3 226/234 114+3 2* of overlap
Cam 4 226/234 115+4 0* of overlap
Cam 5 226/234 116+5 -2* of overlap

In a SBE LS3, I calculate the DCR to be about 8.1:1 in all of them. Intake valve closing in the same place. Pretty sure the last one will run smoother than the first. How would the power curves differ though?

 

Less lobe separation angle = more torque and low end, overall lifts the torque peak.

More lobe separation angle = less torque, possibly equal high rpm power, less chop at idle.

Of these I would pick the 113.

 

Here's a real world example of a 2 degree change in LSA and its effect on cams with the same specs other than LSA.

MTI T1 112 vs B1 114

LS1Tech - cam-guide see post #2 section C

While doing my research on the T1 I cam across this dyno in which if I recall Tony (Nineball) stated that the blue graph was a T1 (112 lsa) and the other 2 where a B1 (114) lsa. 112 vs. 114



MTI T1 (blue) 221/221 112 vs MTI B1 (other colors) 221/221 114

 

#4 looks super familiar... :-)

 

I'd add that the higher LSA should spread the peak broader. It will not *peak* as high, but it will have a wider peak.

 

Hell, I thought the narrower LSA would have the broader torque peak with the wider LSA maybe peaking a little higher on the horsepower curve.

Similar to Black Bird's post, I would like to have seen two bigger same duration camshafts tested with maybe 4 degrees difference in LSA and same intake valve closing. In that scenario and the one in the first post, nothing changes with intake timing and all the changes are on the exhaust side.

And yeah, I have about 35K miles experience with cam 4 and quite a few miles with a 114+2 using same specs only less lift (Pat G cam).

 

In the performance engine world, cam overlap has a different name. It's called horsepower.

 

I’m going to put this on a t-shirt. This post wins the internet today.

 

Yeah, but I *still* don’t want to have to drive around the resulting bad behavior in a daily/road trip car.

 

Yup. By not having any overlap, I know I'm giving up a little HP. I'll take that trade-off.

 

I like the StarBucks/TacoBell/Burger King test...pull up to the drive thru window: if you can see the barista wiggle nose, gasp for air and quickly shut the window due to gas fumes...you probably have too much overlap for a daily driver...wink...Extra points if someone complains, says get a hybrid or EV, passes out or falls out the drive through window...

Never had issues with ^^^ when my T/A had ~0 overlap cam, now with ~13 degrees overlap ^^^ that happens pretty often.

Alternative test, crank car and if your "woke" grand kids immediately start whining about noise and smell...probably too much overlap for a daily driver...wink.

In the typical LS1/5.7 liter ~4 degrees of overlap will drive nice very near stock with good tuning but it will smell more than ~ -2 degrees overlap. Bigger displacement & compression can take a more overlap and still drive nice.

 

Totally get it. I was simply agreeing with the statement. Overlap is an attribute of a camshaft that’s completely combination specific. So many factors in the build will cause overlap to either stand out, or blend in with the build. And of course it’s application specific. For instance I was talking with my machinist recently who works with Joe Gibbs, and we were discussing overlap. He sent me specs of a very recent Cup camshaft that has over 60 degrees of overlap, but the engine is designed to run at 8500. I wish I could tell you guys durations and lifts vs valve sizes…TOTALLY goes against what you see in builds here on Tech. Under caution if you watch NASCAR…which I can’t anymore…the cup cars at about 4500 and light throttle are bucking like crazy. 358 cubic inches and short intake runners will cause overlap to “stand out” more so than an engine with more cubic inches and longer intake runners. Also a well designed exhaust will help here. Reversion can go either direction. If the exhaust is NOT optimized the reversion will tend to utilize the the intake tract, which is where longer runners will calm the effect to an extent. Don’t get me wrong, it still there, just not as evident. Air will be “drawn” toward the vacuum, which is evident in the intake AND the exhaust (again, in a well optimized exhaust system). A well optimized exhaust system will scavenge and “pull” the air charge. Cubic inches will calm the effect as well. What most neglect to see with reversion is that air has weight. It’s because of the weight of the air that it’s so hard to overcome at low rpm. An efficient intake runner that promotes velocity will help immensely…keeping in mind that the intake runner starts at the plenum btw. A high speed air charge will help combat reversion at low rpm, which is why Tony’s heads work so well on the street. They utilize really fast air speed in the port. There are also porting tricks that can be done to combat reversion such as making the intake manifold higher than the intake port….at the point where the two meet…in order to make the air charge under reversion (going BACKWARDS up the intake runner momentarily) get kicked up into the incoming air charge…coming DOWN the port….and help calm the “muddiness”.
My 434 has 33 degrees of overlap, and because of the cubic inches, the air speed in the ports (MMS heads) and really good ARH headers, the bucking is very minimal, and only exists in first gear with very light to zero throttle and zero load. And even there, it’s nowhere near as bad as other vehicles I’ve been in with far less overlap, that buck worse. All being manual trannys, to keep this apples vs apples. Of course tuning can have a huge effect on this also and often does.

 

​​​​​​That was really well said. You should make that specific post a sticky in the cam section.

 

Just a thought, but with those cam specs, you are a stone's throw away from Spinmonster cam specs(230/234 114) Just from my experience, most 22x cams either do not make any more power than a smaller 215-219 cam and/or have less driveability like what you are trying to avoid. For most of what I build, either customer wants stock driveability or wants big power, not much in between. Spin has been on here lately, you should DM him. His cam works, it's proven and has tons of reference points. The 224-227 have a lot of reference points too, but very few have stood out and outshined something else slighty smaller/bigger. Just some thoughts on what I have seen. For reference, I am taking my own advice and going from a 215 cam to a 230-238 cam. Not even looking at the 22x somethings at all.

 

Agree 💯%, Che70velle's post should be added to the cam stick. That's an outstanding post with great information.

Side track questions on reversion...

Out of the typical off the shelf LS1 fbody exhaust's are there key ingredients to optimize a combination of long tube headers sizes, Y pipe, true dual, etc to run to reduce reversion?

Would a 1 3/4 to 1 7/8 stepped long tube header generally better than a 1 3/4 or 1 7/8?

Y pipe vs X pipe make any difference?

Mufflex's big dual 3 inch Y pipe into a 4 inch merge offers advantages vs the typical 3 inch Y to 3 inch merge. I think the dual 3 inch Mufflex Y to 4 inch Flowmaster merge seems to better torque than the typical 3 inch Y to 3 inch merge.

Thanks

 

I agree on the exhaust all the way. I am reminded of a 383 SBC I built a customer a long time ago. Had nice longtubes/sidepipes in a C3 Vette. Did Brodix RR200's w/ a Comp off the shelf 220/220 110lsa HYD roller. The exhaust/exhaust port/int-exh ratios all worked out. The straight pattern Cam worked well. 485hp w/ shitty Fitech injection on pump. Had an easy 40hp more in minor changes. Have to cam the whole combo, not just the "motor" .

​​​​As far as your question as to what exhaust has less reversion, it's an individual chassis problem. If it were my F body, I would do 1 7/8 to the 4in single, mostly for packaging. The Y pipe is critical to making it work. Stepped headers are better, but not sure if the gains are from reversion migration or the extra exhaust velocity gained. Kinda same effect vise/versa. A exhaust pressure gauge and multiple checking points would help find out if there is a specific weak point. That being said, true duals and a x pipe will be better, but I still believe a properly done single exhaust will trump them all.

 

Good question Wade. All the testing you’ll find by anyone that I’m aware of, is testing for power, without any thoughts given on exhaust reversion. The key to fighting intake reversion is having the exhaust scavenge. By scavenge I’m talking about having the exhaust actually “sucking” or being able to pull on the cylinder. This boils down to collector design, and how the banks react…or effect…to each other. The banks have to meet each other at an exact spot….which rules out a true dual setup. This meeting place is 100% dictated by exhaust gas velocity and temp, which is dependent on the combination in front of it. So there’s no specific answer to what diameter primary, or primary length, or collector diameter, or collector design, or Y vs. X, or muffler design, etc.
To find this answer would require a ton of testing, both on an engine dyno and chassis dyno.
What’s known as a general rule that will apply to any combination to aid in exhaust scavenging and fighting exhaust reversion is having your exhaust port diameter slightly smaller than your primary tube diameter, in an effort to make the exhaust gas under reversion, go turbulent when being pulled back into the exhaust port. Ironically this exact topic was brought up this past week….I think it was this week. I’m not even sure what today is lolz….Another constant here is a 180 degree design, which is intended to help adjacent firing cylinders pull on cylinders that are about to fire. But again, diameters, lengths and merge locations are totally dependent on the engine combination and intended operating range, even with a 180 degree system. It’s an interesting topic for sure. I will say this without going into specifics about the Cup camshaft I mentioned above. The exhaust duration is a good bit LESS than the intake duration because their exhaust systems are so efficient. And they are currently running a smaller exhaust valve than what you’d likely imagine. Makes you scratch your head. Scavenge is key.

 

Is that a restrictor plate cam or unrestricted?

 

I'm feeling over exhausted, lol.

 

This is starting to look like one very sticky-worthy thread. SO much info here!