Split Lift Cam

[Ghettogmc23]

So I bought a few new magazines today and I can't remember which one it was (I think Hot Rod) they have an article about a new cam for the sbc that runs different lifts on different cylinders.
the four inside cyl 3,4,5,6 run a different lift than the outside cyl 1,2,7,8. It was only a bit different but it gained a bit of power. They said it was more designed to even out the difference in heat and airflow.
The thing I wonder about tho is would this help an LT1? I know that we have the individual cyl fuel trims but that's more fueling than airflow. Of course they used a carb motor which is why I wonder if it would help us out. I mean it seems like a step in the right direction but at the same time seems like a band aid to a bad intake setup (not that I'm knocking a dual plane).
i guess overall I'm askin if this would help fuel injection or is it more of a carb thing to help keep things even that can't be controlled mechanically any other way?

[Injuneer]

Was it the new "dual pattern" cam from Comp Cams? If so, that cam is intended for single plane intakes, where there are significant differences in the length of the intake runners. The lobes are not different lift, they are different duration - the long runner cylinders 1,7,2,8) have more duration and a later closing, in order to flow the same volume of air tht the smaller lobe (less duration, earlier closing) flows. Exhaust lobes are also different, so you have four differnt lobe patterns on the cam.

The end product, according to comp cams is uniform A/F ratio, higher RPM capabilites, and 5-20 added HP. They claim the lobes - hydraulic lifters - are stable at over 0.600" lift and 7,500 RPM.

With a stock LT1 or LT4 intake, the runners are all the same length. Any benefit might come at very high HP/high air flow, when the plenum volume starts to become an issue, causing uneven distribution of air to individual cylinders. Or, if you were running a single plane intake, it should help, whether its a carb or fuel injected.

[Fastbird]

Fred, let me bounce this off of you. Granted the runner lengths are all the same on the LT1, but what about WHERE the air comes in to the motor? Could a case be made that an increasing duration as you move from front to back could compensate for "stolen" airflow from the rear cylinders? Think like a 230 duration on 1-4 and a 232 duration on 5-8.

[Ghettogmc23]

Yup that's the article, although I think I need to read it again cuz it sounds like I missed the main points lol. I am interested to hear bout the duration tho

[Injuneer]

The article you read could be for something different. I'm just going by a Comp Cams ad I saw in National Dragster a couple weeks ago.

In theory, the plenum volume should be sufficient to eliminate variations in pressure along the path of the inlet runners. How well it's designed would be the issue. When Second Street was tuning my setup, they were checking flow balance to the cylinders via EGT and O2, and they didn't see any problems at 500HP. They also didn't see any significant variations with the 275-shot (the original system when the engine was on an engine dyno). The ECU I run has the capability to adjust individual injector flows, but they didn't find it necessary to do that.

[Fastbird]

The article you read could be for something different. I'm just going by a Comp Cams ad I saw in National Dragster a couple weeks ago.

In theory, the plenum volume should be sufficient to eliminate variations in pressure along the path of the inlet runners. How well it's designed would be the issue. When Second Street was tuning my setup, they were checking flow balance to the cylinders via EGT and O2, and they didn't see any problems at 500HP. They also didn't see any significant variations with the 275-shot (the original system when the engine was on an engine dyno). The ECU I run has the capability to adjust individual injector flows, but they didn't find it necessary to do that.

Interesting and good to know. I would have expected some kind of noticeable variance front to back at that power level. Good stuff.

[Injuneer]

You could possibly consider that the inertia of the air, passing through the throttle body at high velocity, causes it to continue toward the back of the plenum, starving the front, or maybe compensating for the difference between front and back. Who knows? Wet nitrous systems, particularly plate systems, seem to suffer from that problem. Of course the fuel has more inertia than the air, and really doesn't want to turn corners like the air does. I avoid that issue with a dry system.

[Ghettogmc23]

avoid that issue with a dry system.

I was under the impression the LT1 pcm didn't do well with a dry system? Either way it's sounding like this is not very helpful on the LT1 intake, however do you think it may help on a dual plane or single plane conversion? From the overall sound it seems like it will only help on a high rpm motor and one that is tuning for every last hp lol so at this point I'm not even considering it, just curious.

[94Blackbird]

I was under the impression the LT1 pcm didn't do well with a dry system? Either way it's sounding like this is not very helpful on the LT1 intake, however do you think it may help on a dual plane or single plane conversion? From the overall sound it seems like it will only help on a high rpm motor and one that is tuning for every last hp lol so at this point I'm not even considering it, just curious.

the reason why you would see a benefit from this on a single plane or any other unequal runner manifold is because of the varying runner lengths providing slightly different velocities in the airflow (i.e some runners being faster flowing than other runners). Hence the split durations, some cylinders in that type of application don't need the door held open as long to get their optimum fill. This is also why this type of cam would not show a significant, if any improvement, on an LT1 style manifold, because we have equal length runners feeding from a common tunnel ram style manifold (even though the TB is on the front of the manifold instead of the top). Of course there are variances in both the intake and exhaust side, but not enough to warrant something like a dual pattern camshaft.

[Puck]

Interesting idea, but like stated this is all intake dependent.


You could possibly consider that the inertia of the air, passing through the throttle body at high velocity, causes it to continue toward the back of the plenum, starving the front, or maybe compensating for the difference between front and back. Who knows? Wet nitrous systems, particularly plate systems, seem to suffer from that problem. Of course the fuel has more inertia than the air, and really doesn't want to turn corners like the air does. I avoid that issue with a dry system.

I have heard of this being an issue and see it pop up every once in a while while discussing big wet shots on the stock style intake. Not sure who it was anymore but I want to say one person compensated by adjusting fuel delivery in the front two cylinders while on the nitrous tune to help. This was a long time ago, one of those can't put the face to the name things so I'm shady on the details.

If you showed no issues with individual cylinder EGT monitoring with a 275 shot though it makes me wonder if its as big of an issue as some have claimed.

[joelster]

For those guys that read the article, notice the power differences between the standard camshaft and this magical "split" camshaft. The magical camshaft had more duration and more lift but only made a few more hp. (I'm going off of the top of my head here). I was laughing when I read the results. It wan't an apples-to-apples comparison for duration/lift numbers. I really don't believe that there is nearly enough of a mismatch between the runners to necessitate 4-5 more degrees of duration among the outer cylinders.

It sounds like a marketing pitch.

[94Blackbird]

For those guys that read the article, notice the power differences between the standard camshaft and this magical "split" camshaft. The magical camshaft had more duration and more lift but only made a few more hp. (I'm going off of the top of my head here). I was laughing when I read the results. It wan't an apples-to-apples comparison for duration/lift numbers. I really don't believe that there is nearly enough of a mismatch between the runners to necessitate 4-5 more degrees of duration among the outer cylinders.

It sounds like a marketing pitch.

It's actually something that is very common in NASCAR due to being restricted on what manifold they are allowed to use, and they use a 4 pattern camshaft to equalize the airflow between the cylinders.

[joelster]

It's actually something that is very common in NASCAR due to being restricted on what manifold they are allowed to use, and they use a 4 pattern camshaft to equalize the airflow between the cylinders.

I'm sure the NASCAR pieces are 100x more high tech than just arbitrarily giving the outer cylinders a few more degrees of duration.

[94Blackbird]

I'm sure the NASCAR pieces are 100x more high tech than just arbitrarily giving the outer cylinders a few more degrees of duration.

of course, but it's just like the difference between a normal shelf grind and one that is custom ground for a specific application.

[joelster]

of course, but it's just like the difference between a normal shelf grind and one that is custom ground for a specific application.

I have run single plane intakes on sbc's since 1992. I know of hundreds of engines that run them throughout the years. When you make a jetting change, all of the plugs change. I have never in my life heard of a single plane equipped car that had the outer cylinders running leaner or richer than the inner cylinders. The difference is miniscule enough that you just can't see it unless you have some really good test equipment. It's MINISCULE enough for a NASCAR team to experiment with it to find out if it indeed makes more power, which i'm sure in their cases it does. But I don't believe for 1 second that they (NASCAR teams) just arbitrarily have the outer cylinders getting more duration/lift. I believe that it is possible that they might even have a camshaft with 8 different intake durations and 8 different exhaust durations to fine tune it until it's perfect. You can't just assume that because a runner is longer that it requires more duration to be able to fill the cylinder as effectively as a slightly shorter runner. Firing order, intake pulses, airflow through the tb/carb, temperature differences in the intake tract, etc, etc, all can have an effect. 2 or 3 years ago they came out with Thumpr camshafts, now it's this.

[94Blackbird]

It's not an assumption, it's a proven fact that the various length runners on a single plane flow differently. Maybe not enough for the average person to notice, but they do. A short straight runner is not going to have the same port velocity and fluid flow dynamics as a longer, curved runner, period. The biggest benefit I can honestly see to a split pattern cam isn't necessarily hp increase, but more similar to the purpose of a 4-7 cam swap. By going to a split pattern cam, the more sluggish longer, curved runners could achieve closer parity with the shorter straight runners, equalizing combustion pressures and keeping combustion temps at a more equal level and helping the engine run smoother, thereby reducing harmonics and making the engine more reliable.

You may see a marketing pitch, but the technology is proven. Is it necessarily for the average enthusiast and his hopped up street car, probably not.

[joelster]

It's not an assumption, it's a proven fact that the various length runners on a single plane flow differently. Maybe not enough for the average person to notice, but they do. A short straight runner is not going to have the same port velocity and fluid flow dynamics as a longer, curved runner, period.
You can't compare what a flowbench sees to what an actual running engine sees. A flowbench is a STATIC measurement. An engine that is running is DYNAMIC with all sorts of variables thrown into the mix.

The biggest benefit I can honestly see to a split pattern cam isn't necessarily hp increase, but more similar to the purpose of a 4-7 cam swap. By going to a split pattern cam, the more sluggish longer, curved runners could achieve closer parity with the shorter straight runners, equalizing combustion pressures and keeping combustion temps at a more equal level and helping the engine run smoother, thereby reducing harmonics and making the engine more reliable.
The 4-7 swap has the benefit of making the bearing loads on the mains more even. I run a 4-7 swapped camshaft. Nobody knows exactly why the loads even out. But GM tested over 20 different firing orders with the LS engine. The LS firing order has the best bearing load spread, the 4/7 swap is second.


You may see a marketing pitch, but the technology is proven. Is it necessarily for the average enthusiast and his hopped up street car, probably not.

Again, who says it's proven and in what application? It's being targeted to the average street/strip enthusiast crowd. It may only be beneficial on engines that approach the 2.2 hp/cube level running n/a and that can also scream to 8500rpm. Hardly what COMP is marketing the cams too.

I don't believe that you read the article. If you did, go re-read the spec on both cams, and then go look at the power differences. The new "split" cam only made a few hp more, but it had more duration and more lift.

[Injuneer]

I was under the impression the LT1 pcm didn't do well with a dry system?.

I don't run an LT1 PCM. I run a MoTeC M48Pro engine management system, that is capable of running multiple programs. I have a base tune for normally aspirated, an overlay program for 1st stage (switches programs when the system is armed) and 2nd stage nitrous (over-writes the single stage program when the button on the shifter is pushed). Manages the 78#/HR low impedance injectors, operating at 58psi, with 410 LPH pump capacity. Runs speed-density, open loop, no knock sensor. I do still use the stock LT1 PCM for the speedo, and the idle air control.

[BIG CAT]

roundy round guys have been doing it for a long time. its no advantage for a factory ltx intake. our runner are equal length unlike a typical single plane. they speed a lot of time optimizing those setup to get the best ave hp and trq numbers they can. remember they don't operate in a narrow rpm band like we do. they may come out of a corner at say 4500 and by the the time they get to the next corner they could be turning upwards of 8 or 9k rpm. so as you can see the number below peak hp and trq would be very important to making a car perform.

[Injuneer]

I have heard of this being an issue and see it pop up every once in a while while discussing big wet shots on the stock style intake. Not sure who it was anymore but I want to say one person compensated by adjusting fuel delivery in the front two cylinders while on the nitrous tune to help. This was a long time ago, one of those can't put the face to the name things so I'm shady on the details.

If you showed no issues with individual cylinder EGT monitoring with a 275 shot though it makes me wonder if its as big of an issue as some have claimed.

I have no issues, because I run a dry system, with nitrous introduced in the outlet of a ram air box.

19445

[Ghettogmc23]

I have no issues, because I run a dry system, with nitrous introduced in the outlet of a ram air box.

19445

Not only did i enjoy reading what your setup is, but i also enjoyed the pic. That setup is awesome!

I can see why circle track uses it too. The local machine shop builds motors for the guys running the little sprint cars on the dirt track n i remember he told me they spend thousands just to get that little extra that most wouldnt bother with because the rules keep everything so close.

It seems like this is an idea that is more for those running high competition race-only setups. Definitely not for anybody just looking to have some fun lol.