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Intake biased overlap vs Exhaust biased overlap

 
Old 03-13-2019, 05:17 AM
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Default Intake biased overlap vs Exhaust biased overlap

Can someone please explain the performance difference between these two variables?
I will use my engine as an example.
For an LS 408 with LS3 heads and FAST 102mm intake.

I have two cam specifications.

242/257 113 LSA +3 (Exhaust biased overlap)
IVO 11
EVC 13
IVC 51
EVO 65
ICL 110
ECL 116

244/256 113 LSA+4 (Intake biased overlap)
IVO 13
EVC 11
IVC 51
EVO 65
ICL 109
ECL 117

What would be performances differences in terms of peak power, torque and power after peak etc?
Which one would make more mid range and top end power and hang on longer?
I have looked at cam specifications from Cam Motion, Bullet cams, Flowtech induction and the overlap is intake biased by 2 degrees.
Comp cams, Lunati, Howards Cams,and Crow Cams all have the overlap 2 degrees exhaust biased.
Very interesting to know the reasons for these decisions.
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Old 03-13-2019, 11:19 AM
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For high rpm use, you want to have your overlap centered over TDC or biased to the intake side of TDC.
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Old 03-13-2019, 12:47 PM
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Originally Posted by JakeFusion View Post
For high rpm use, you want to have your overlap centered over TDC or biased to the intake side of TDC.
So what would be the difference in rpm with the exhaust biased by two degrees vs two degrees biased the other way?

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Old 03-13-2019, 01:41 PM
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100 rpm...
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Old 03-13-2019, 01:59 PM
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Originally Posted by JakeFusion View Post
100 rpm...
So the intake biased overlap cam would hang on 100rpm later compared to the exhaust bias cam?
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Old 03-13-2019, 02:03 PM
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The first thing is to identify how Intake opening and exhaust closing events affect behavior. The earlier you open the intake, the further open the valve is when the piston starts down the cylinder atdc. The problem is you're losing idle vacuum and the idle gets progressively worse with each degree. Intake piston to valve clearance becomes more of an issue as well, so you'll see the Pro LS cams capped at about 7 BTDC in the case of Stage 4 cams to avoid issues with true flat top pistons from the factory.

With exhaust closing, we look at it in terms of this: With an open header and equal length header, the wave tuning could be used more to your advantage and exhaust valve closing can be later. Unfortunately most of these vehicles use headers that are unequal length and have full length exhaust systems. Without much ability to program the exhaust wave, the argument for late exhaust closing becomes less.

With our turbo cams, the intake events are the same as our naturally aspirated cams. We cap overlap at 2 degrees (for the most part) to reduce reversion by backing up exhaust closing in relation to how early we open the intake. Summit Pro LS cams have exhaust closing earlier in general for another reason...to reduce raw fuel (wasted energy) smell out the exhaust.

So intake or exhaust bias is really a function of what a good cam designer demanded of the individual intake opening and exhaust closing events for a given application.

Last edited by Summitracing; 03-13-2019 at 09:14 PM.
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Old 03-13-2019, 02:15 PM
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Originally Posted by Summitracing View Post
The first is to identify how Intake opening and exhaust closing events affect behavior. The earlier you open the intake, the further open the valve is when the piston starts down the cylinder atdc. The problem is you're loosing idle vacuum and the idle gets progressively worse with each degree. Intake piston to valve clearance becomes more of an issue as well, so you'll see the Pro LS cams capped at about 7 BTDC in the case of Stage 4 cams to avoid issues with true flat top pistons from the factory.

With exhaust closing, we look at it in terms of this: With an open header and equal length header, the wave tuning could be used more to your advantage and exhaust valve closing can be later. Unfortunately most of these vehicles use headers that are unequal length and have full length exhaust systems. Without much ability to program the exhaust, the argument for late exhaust closing becomes less.

With our turbo cams, the intake events are the same as our naturally aspirated cams. We cap overlap at 2 degrees (for the most part) to reduce reversion by backing up exhaust closing in relation to how early we open the intake. Summit Pro LS cams have exhaust closing earlier in general for another reason...to reduce raw fuel (wasted energy) smell out the exhaust.

So intake or exhaust bias is really a function of what a good cam designer demanded of the individual intake opening and exhaust closing events for a given application.
Thats a good explanation.
So in other words between those two camshafts with the 2 degree difference they will drive much drive the same?
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Old 03-13-2019, 02:29 PM
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So (as expected) the smaller one has a bit smoother idle because it's opening the intake valve a little later. Intake closing is the same, so powerband is roughly the same. EVO is a wash. EVC with the smaller cam is a little later and may not be as good with a closed exhaust. So the larger of the two should run just a bit better at the expense of a little idle quality.
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Old 03-13-2019, 02:39 PM
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Originally Posted by Summitracing View Post
So (as expected) the smaller one has a bit smoother idle because it's opening the intake valve a little later. Intake closing is the same, so powerband is roughly the same. EVO is a wash. EVC with the smaller cam is a little later and may not be as good with a closed exhaust. So the larger of the two should run just a bit better at the expense of a little idle quality.
Very interesting.
What do you mean EVO is a wash?
As it's not important or is the timing too early for that size engine?
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Old 03-13-2019, 02:55 PM
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Exhaust opens at 65 btdc on both. Pretty normal for a cam of this size and would make good power higher in the rpm range.

The following depends on what you're doing with the car. Intake closing is a bit early...we'd probably change the intake valve closing to 53 degrees based on your intake manifold and cubes. By and large, these cams are pretty good already, but would lean to the 2nd one of the two.
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Old 03-13-2019, 10:46 PM
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Originally Posted by Summitracing View Post
Exhaust opens at 65 btdc on both. Pretty normal for a cam of this size and would make good power higher in the rpm range.

The following depends on what you're doing with the car. Intake closing is a bit early...we'd probably change the intake valve closing to 53 degrees based on your intake manifold and cubes. By and large, these cams are pretty good already, but would lean to the 2nd one of the two.
What difference would a 51 or 53 IVC make with my combo in terms of torque and power? Would it lose low end?
​​​​​​I also have 12:8.1 compression too.
its a street car
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Old 03-14-2019, 12:42 AM
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Originally Posted by bortous View Post
What difference would a 51 or 53 IVC make with my combo in terms of torque and power? Would it lose low end?
​​​​​​I also have 12:8.1 compression too.
its a street car
holy cow awesomeness. Yes the 51 degree point is a figure derived by the intake manifold runner length for the most part. You got more cubes, extend it a bit. Your compression ratio is extremely stout depending on your fuel, so extending the ivc a bit makes even more sense.
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Old 03-14-2019, 12:53 AM
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Originally Posted by Summitracing View Post

holy cow awesomeness. Yes the 51 degree point is a figure derived by the intake manifold runner length for the most part. You got more cubes, extend it a bit. Your compression ratio is extremely stout depending on your fuel, so extending the ivc a bit makes even more sense.
Haha.
Fuel used is e85. I would not try running pump gas with that high compression unless I was running a camshaft that was really radical.
What difference does it make from going to a 51 or 53 IVC point if you have the same cam duration?
I appreciate your responses also.

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Old 03-14-2019, 01:09 AM
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Favoring one side or the other isn't something I really take into consideration. I look at when the scavenging wave begins and ends through the peak power rpm range. This will be the result of my already determined EVO and IVC events as they take precedence over the IVO and EVC events. I set the valve events where they can take advantage of harmonics. Whether that means the overlap favors the intake or exhaust, I couldn't care less. The same applies to lobe centerlines and LSA. I sometimes don't even calculate it, because it's irrelevant information.

Also keep in mind that just because the degrees of overlap may favor one side doesn't mean the total overlap area favors that side.
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Old 03-14-2019, 01:41 AM
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Originally Posted by Polyalphaolefin View Post
Favoring one side or the other isn't something I really take into consideration. I look at when the scavenging wave begins and ends through the peak power rpm range. This will be the result of my already determined EVO and IVC events as they take precedence over the IVO and EVC events. I set the valve events where they can take advantage of harmonics. Whether that means the overlap favors the intake or exhaust, I couldn't care less. The same applies to lobe centerlines and LSA. I sometimes don't even calculate it, because it's irrelevant information.

Also keep in mind that just because the degrees of overlap may favor one side doesn't mean the total overlap area favors that side.
No worries,
Can you please give me a detailed example on how you would choose a camshaft for my engine?
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Old 03-14-2019, 04:50 AM
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Originally Posted by bortous
What difference would a 51 or 53 IVC make with my combo in terms of torque and power? Would it lose low end?
​​​​​​I also have 12:8.1 compression too.
its a street car
What follows is oversimplified, but I hope helpful.

IVC is the single biggest influence on the cam that determines at what rpm you will make peak power. Leaving out intake harmonics for a second, delaying your IVC from 51 to 53 will move your peak hp 200-500 rpm higher.

The factory style plastic intakes with factory runner length typically will try to force peak torque to 4800-5000 and peak hp to 6300-6500. You can use the cam to cheat this, and that will typically result in the double hump torque curves you see on many larger cam builds. You can google and find exceptions, but that is the general pattern.

Moving to a shorter runner shifts the torque curve to the right. People will typically say you lost torque down low and gained hp up top. I just look at it as the whole torque curve moved to the right. Makes the same torque just at higher rpm, and rpm is power. There is a displacement effect also. In general I find larger engines will gain low end torque even with smaller runners. Simple way to explain, breath through a straw, cut the straw in half and breathe through the same straw. It is easier to breath.

Example, my old 346, on the fast peak hp was at 6500 rpm and tq curve had three humps. Switched to msd. No other changes, torque curve smoothed out, because the cam and intake were no longer fighting, hp peaked at 6850 rpm. Same torque, but hp was 10 higher. Also the shorter runners carried better past peak. On my 428, going from stock ls7 intake to sniper raised the entire torque curve. Similar results all over the place going from even the fast102 to the msd on the ls7's. Whole torque curve goes up.

In general, I tend to see in hybrid street/strip builds, 346 likes 44-45 degree IVC, 376 likes 46-47 degrees, 427 likes 52 degrees. 408 I usually like to use 49-50, but I will generally move later with compression, because you can. The 51 degree IVC in your OP is a good match with your displacement and compression. Likely will want to peak at 7000 rpm.

EVO I do based on compression. Higher compression can open earlier, lower compression later. I would actually tend to open around 60 degrees on a 408, but with your compression, 65 makes sense.

Power past peak is where overlap comes in. Increased overlap will carry better but drive worse. Increase overlap will also have the effect of making your LSA get tighter if you keep the same IVC and EVO. The cam spec will look radically different. Without knowing your goals 24 degrees looks like a relatively strip oriented cam. You could get away with 32 degrees and really rev or you could drop to 12 and have nice street manners. If I am stuck between two cams and a car is a driver I will generally err to the reduced overlap. You gotta be honest about how you want it to behave. Brutally honest.

Now to your OP. I prefer to not bias overlap. IMO the two cams you posted the differences would be subtle at best. On a 24 degree overlap, it is either 13/11 or 11/13. Splitting hairs. That is basically balanced. If you have 6 degrees overlap and go 4/2 that is biased. On street cams I will generally intake bias IF at all. I prefer centered. Strip only I may slightly exhaust bias, but that is head dependent. Your heads I would leave centered.

Since you mentioned power past peak, I will assume more track oriented. Keep 51,65 but stretch overlap to 28 degrees, puts it at 245/259. 108.5 ICL, 115.5 ECL, 112 LSA. 245/259-112+3.5. ,685/.670 on the lift. Since you are running corn, when you tune it in, spark timing likely 28-30 at peak power/WOT.
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Old 03-14-2019, 06:24 AM
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Originally Posted by Darth_V8r View Post
What follows is oversimplified, but I hope helpful.

IVC is the single biggest influence on the cam that determines at what rpm you will make peak power. Leaving out intake harmonics for a second, delaying your IVC from 51 to 53 will move your peak hp 200-500 rpm higher.

The factory style plastic intakes with factory runner length typically will try to force peak torque to 4800-5000 and peak hp to 6300-6500. You can use the cam to cheat this, and that will typically result in the double hump torque curves you see on many larger cam builds. You can google and find exceptions, but that is the general pattern.

Moving to a shorter runner shifts the torque curve to the right. People will typically say you lost torque down low and gained hp up top. I just look at it as the whole torque curve moved to the right. Makes the same torque just at higher rpm, and rpm is power. There is a displacement effect also. In general I find larger engines will gain low end torque even with smaller runners. Simple way to explain, breath through a straw, cut the straw in half and breathe through the same straw. It is easier to breath.

Example, my old 346, on the fast peak hp was at 6500 rpm and tq curve had three humps. Switched to msd. No other changes, torque curve smoothed out, because the cam and intake were no longer fighting, hp peaked at 6850 rpm. Same torque, but hp was 10 higher. Also the shorter runners carried better past peak. On my 428, going from stock ls7 intake to sniper raised the entire torque curve. Similar results all over the place going from even the fast102 to the msd on the ls7's. Whole torque curve goes up.

In general, I tend to see in hybrid street/strip builds, 346 likes 44-45 degree IVC, 376 likes 46-47 degrees, 427 likes 52 degrees. 408 I usually like to use 49-50, but I will generally move later with compression, because you can. The 51 degree IVC in your OP is a good match with your displacement and compression. Likely will want to peak at 7000 rpm.

EVO I do based on compression. Higher compression can open earlier, lower compression later. I would actually tend to open around 60 degrees on a 408, but with your compression, 65 makes sense.

Power past peak is where overlap comes in. Increased overlap will carry better but drive worse. Increase overlap will also have the effect of making your LSA get tighter if you keep the same IVC and EVO. The cam spec will look radically different. Without knowing your goals 24 degrees looks like a relatively strip oriented cam. You could get away with 32 degrees and really rev or you could drop to 12 and have nice street manners. If I am stuck between two cams and a car is a driver I will generally err to the reduced overlap. You gotta be honest about how you want it to behave. Brutally honest.

Now to your OP. I prefer to not bias overlap. IMO the two cams you posted the differences would be subtle at best. On a 24 degree overlap, it is either 13/11 or 11/13. Splitting hairs. That is basically balanced. If you have 6 degrees overlap and go 4/2 that is biased. On street cams I will generally intake bias IF at all. I prefer centered. Strip only I may slightly exhaust bias, but that is head dependent. Your heads I would leave centered.

Since you mentioned power past peak, I will assume more track oriented. Keep 51,65 but stretch overlap to 28 degrees, puts it at 245/259. 108.5 ICL, 115.5 ECL, 112 LSA. 245/259-112+3.5. ,685/.670 on the lift. Since you are running corn, when you tune it in, spark timing likely 28-30 at peak power/WOT.
What a response!
Thanks
You are way more knowledgeable than me with all this.
Lets see if I am understanding this correctly.
Going from a 50 to a 51 IVC point will shift peak hp up by about 100-200rpm higher? (Averaging the difference between 51 and 53 IVC points)
Current camshaft peaks at 6300 rpm and then drops off. Torque also drops off quite quickly after 5500rpm.
My shift points are at 6200rpm currently and want them to shift at 6600rpm+.
Looks like based on your explanation, I will gain another 500-700rpm in the top end.
Current camshaft has 12 degrees of overlap and drives almost like stock because I have a good tuner. My tuner has stated even with 23 degrees of overlap it won't drive much different after he is done tuning it.
I have been thinking about the change of intake but the MSD isn't available for the LS3 head.
The FAST flows enough for my combination I think as it is a street car.
The other cam recommendation you gave me would also work really well from what I understand and looking at the valve events, but the overlap being 5 degrees more would probably make it almost not driveable on the street.
In regards to the overlap bias discussion, everyone has their preference for sure.
Patrick G either has it centred or intake bias. There is no right or wrong answer.
My tuner prefers cams that have overlap exhaust biased for the LS3 heads.
When I get this cam fitted and say, I really don't like how it drives I have come up with another spec which may suit..
What do you think?
234/249 117 LSA+3
It has the same IVC and EVO as larger cam but less overlap. It obviously won't set the dyno on fire, but should carry a lot better than current cam while driving a bit smoother too.



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Old 03-14-2019, 07:37 AM
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Originally Posted by bortous View Post
Going from a 50 to a 51 IVC point will shift peak hp up by about 100-200rpm higher? (Averaging the difference between 51 and 53 IVC points)
Current camshaft peaks at 6300 rpm and then drops off. Torque also drops off quite quickly after 5500rpm.
My shift points are at 6200rpm currently and want them to shift at 6600rpm+.
Looks like based on your explanation, I will gain another 500-700rpm in the top end.
As long as you change your intake to match. If you are peaking at 6300, your intake has stock length runners. Depending on your driving habits, this is fine. If you want to raise peak power 500-700 rpm, you should also switch to fast mid length runners. you can order the runners, split the plenum open, replace the runners, and reseal the plenum. Far cheaper than buying a whole new intake. If you keep the existing intake, you'll peak at 6300-6500, hold peak power until about 6800, and then it will start to fall more gradually. But peak will be in the 6300-6500 range. The intake harmonics will keep it there. If you overlay the curves, you'll see the gap between the two cams gets greater as RPM increases.
Current camshaft has 12 degrees of overlap and drives almost like stock because I have a good tuner. My tuner has stated even with 23 degrees of overlap it won't drive much different after he is done tuning it.
It will drive different. Most likely you'll have to deal with bucking a couple hundred RPM higher than you are now. For a good reference, I run 18 degrees overlap and daily drive on the 428. but 428 is bigger, so it can tolerate more cam. I make peak power at 7000 RPM, and it carries past 7800. I don't know about 8000+, because I let up on the dyno, but it was falling gently, not crashing. However, if I was going to go max effort, I would likely go to 32 degrees overlap. Overlap is power, especially past peak power.
I have been thinking about the change of intake but the MSD isn't available for the LS3 head.
The FAST flows enough for my combination I think as it is a street car.
The other cam recommendation you gave me would also work really well from what I understand and looking at the valve events, but the overlap being 5 degrees more would probably make it almost not driveable on the street.
See above comment on fast mid length runner option. The fast does flow enough for your engine, but the runner length will likely fight the cam. If you do go to one of the cams in your OP, it would benefit from shorter runners.
In regards to the overlap bias discussion, everyone has their preference for sure.
Patrick G either has it centred or intake bias. There is no right or wrong answer.
My tuner prefers cams that have overlap exhaust biased for the LS3 heads.
There are benefits and compromises made no matter which way you go. All power comes with a price. The real reason I like it centered is that it tends to be the best blend between midrange grunt and top end power under the most conditions. To each their own. There are merits for exhaust bias and intake bias, but it depends on what you are willing to trade. Centered generally has the least amount of sacrifice. And both cams in your OP are fundamentally centered.
When I get this cam fitted and say, I really don't like how it drives I have come up with another spec which may suit..
What do you think?
234/249 117 LSA+3
It has the same IVC and EVO as larger cam but less overlap. It obviously won't set the dyno on fire, but should carry a lot better than current cam while driving a bit smoother too.
It actually would not carry as well due to reduced overlap. It will rev and drive nicely for sure. With your compression you may not lose much torque at all with it. So if your goal is a smoother overall ride that revs good, it is a good cam spec. If your goal is to carry power past peak, then this cam would hurt more than it helps. If you're truly more concerned about higher RPM power, let's consider 18 degrees overlap, which is where my 428 is and it revs to 7700. Same IVC, EVO. 238/253-115+3. That will drive good and rev as high as you're willing to take it. Depending on intake selection, would peak in the 6500-6800 range. Actually knowing more about your intentions now, I'd say that is damn near where you will want to be.

Some more food for thought:

* I have seen dynos fall hard past peak for many reasons. Not always the cam. Sometimes it's valve springs, pushrods, overall valvetrain stability. Sometimes it is the cam. Sometimes it is the intake choice. I would order a set of 11/32 summit pushrods no matter what you do. I'm assuming you're running the BTR dual plats. If not, it's a good all around spring to put on there to control your valves and reasonably priced.
* If you are peaking at 6300, your shift points should already be 6600 or even higher. Power past peak is good power. Many people subscribe to the "It peaked so it stopped making power" school of thought. If your torque is 450 at 4400 rpm in second and 350 in first at 6600, you are still FASTER in FIRST due to gear multiplication. 4000 lbs at the tires vs 3400 lbs. In fact, torque has to fall off to 300 to break even on the upshift in that scenario.
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Old 03-14-2019, 09:00 AM
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Originally Posted by Darth_V8r View Post
As long as you change your intake to match. If you are peaking at 6300, your intake has stock length runners. Depending on your driving habits, this is fine. If you want to raise peak power 500-700 rpm, you should also switch to fast mid length runners. you can order the runners, split the plenum open, replace the runners, and reseal the plenum. Far cheaper than buying a whole new intake. If you keep the existing intake, you'll peak at 6300-6500, hold peak power until about 6800, and then it will start to fall more gradually. But peak will be in the 6300-6500 range. The intake harmonics will keep it there. If you overlay the curves, you'll see the gap between the two cams gets greater as RPM increases.

It will drive different. Most likely you'll have to deal with bucking a couple hundred RPM higher than you are now. For a good reference, I run 18 degrees overlap and daily drive on the 428. but 428 is bigger, so it can tolerate more cam. I make peak power at 7000 RPM, and it carries past 7800. I don't know about 8000+, because I let up on the dyno, but it was falling gently, not crashing. However, if I was going to go max effort, I would likely go to 32 degrees overlap. Overlap is power, especially past peak power.

See above comment on fast mid length runner option. The fast does flow enough for your engine, but the runner length will likely fight the cam. If you do go to one of the cams in your OP, it would benefit from shorter runners.

There are benefits and compromises made no matter which way you go. All power comes with a price. The real reason I like it centered is that it tends to be the best blend between midrange grunt and top end power under the most conditions. To each their own. There are merits for exhaust bias and intake bias, but it depends on what you are willing to trade. Centered generally has the least amount of sacrifice. And both cams in your OP are fundamentally centered.

It actually would not carry as well due to reduced overlap. It will rev and drive nicely for sure. With your compression you may not lose much torque at all with it. So if your goal is a smoother overall ride that revs good, it is a good cam spec. If your goal is to carry power past peak, then this cam would hurt more than it helps. If you're truly more concerned about higher RPM power, let's consider 18 degrees overlap, which is where my 428 is and it revs to 7700. Same IVC, EVO. 238/253-115+3. That will drive good and rev as high as you're willing to take it. Depending on intake selection, would peak in the 6500-6800 range. Actually knowing more about your intentions now, I'd say that is damn near where you will want to be.

Some more food for thought:

* I have seen dynos fall hard past peak for many reasons. Not always the cam. Sometimes it's valve springs, pushrods, overall valvetrain stability. Sometimes it is the cam. Sometimes it is the intake choice. I would order a set of 11/32 summit pushrods no matter what you do. I'm assuming you're running the BTR dual plats. If not, it's a good all around spring to put on there to control your valves and reasonably priced.
* If you are peaking at 6300, your shift points should already be 6600 or even higher. Power past peak is good power. Many people subscribe to the "It peaked so it stopped making power" school of thought. If your torque is 450 at 4400 rpm in second and 350 in first at 6600, you are still FASTER in FIRST due to gear multiplication. 4000 lbs at the tires vs 3400 lbs. In fact, torque has to fall off to 300 to break even on the upshift in that scenario.

As long as you change your intake to match. If you are peaking at 6300, your intake has stock length runners. Depending on your driving habits, this is fine. If you want to raise peak power 500-700 rpm, you should also switch to fast mid length runners. you can order the runners, split the plenum open, replace the runners, and reseal the plenum. Far cheaper than buying a whole new intake. If you keep the existing intake, you'll peak at 6300-6500, hold peak power until about 6800, and then it will start to fall more gradually. But peak will be in the 6300-6500 range. The intake harmonics will keep it there. If you overlay the curves, you'll see the gap between the two cams gets greater as RPM increases.

Will those mid length runners make the engine lose low and mid range torque?
I have seen tests in an LS3 where the use the long, mid and short runners in the FAST manifold.
The results showed that the low mid and top end torque was lower with the mid length and shorter runners.
Only peak hp was higher and the rpm was 500rpm higher where it made the extra peak hp compared to the long runners.
From what you have said I think the FAST 102mm will be ok for my combination.
As long as the peak holds close to 7000rpm I am happy.

It will drive different. Most likely you'll have to deal with bucking a couple hundred RPM higher than you are now. For a good reference, I run 18 degrees overlap and daily drive on the 428. but 428 is bigger, so it can tolerate more cam. I make peak power at 7000 RPM, and it carries past 7800. I don't know about 8000+, because I let up on the dyno, but it was falling gently, not crashing. However, if I was going to go max effort, I would likely go to 32 degrees overlap. Overlap is power, especially past peak power.

I expect a little more bucking for sure but now it is almost non existent.
Pat G told me a while that for my combination 20 degrees of overlap is about the limit where you want to go because once you go past this, your power gains become small and your driveability becomes way worse.
On a 428 I would guess he would say 25 degrees would be about the limit.
I was specified a camshaft from someone recently 250/263 111 LSA +3.
No thanks. 35 degrees of overlap is just overkill for me.....

It actually would not carry as well due to reduced overlap. It will rev and drive nicely for sure. With your compression you may not lose much torque at all with it. So if your goal is a smoother overall ride that revs good, it is a good cam spec. If your goal is to carry power past peak, then this cam would hurt more than it helps. If you're truly more concerned about higher RPM power, let's consider 18 degrees overlap, which is where my 428 is and it revs to 7700. Same IVC, EVO. 238/253-115+3. That will drive good and rev as high as you're willing to take it. Depending on intake selection, would peak in the 6500-6800 range. Actually knowing more about your intentions now, I'd say that is damn near where you will want to be.

If I was to fit something slightly less radical compared to the 242/257 113 +3 cam that is a great camspec for sure. I will save that. only 15.5 degrees of overlap and will definitely work better than my current camshaft.

* I have seen dynos fall hard past peak for many reasons. Not always the cam. Sometimes it's valve springs, pushrods, overall valvetrain stability. Sometimes it is the cam. Sometimes it is the intake choice. I would order a set of 11/32 summit pushrods no matter what you do. I'm assuming you're running the BTR dual plats. If not, it's a good all around spring to put on there to control your valves and reasonably priced.
* If you are peaking at 6300, your shift points should already be 6600 or even higher. Power past peak is good power. Many people subscribe to the "It peaked so it stopped making power" school of thought. If your torque is 450 at 4400 rpm in second and 350 in first at 6600, you are still FASTER in FIRST due to gear multiplication. 4000 lbs at the tires vs 3400 lbs. In fact, torque has to fall off to 300 to break even on the upshift in that scenario.


The peak power begins to drop off at 6300 on my dyno sheet.

Here is a list of my build:

CNC LS3 heads with 12:8.1 compression (runs on e85)
FAST 102mm intake manifold (long runners)
236/244 .626 .626 114LSA +2 camshaft (Will be fitting a 242/257 .660 .655 113 LSA+3 camshaft soon)
3200rpm stall converter
3:91 rear gears
Yella Terra Pro street adjustable rockers in 1:8.1 ratio with 10mm bolts (Camshaft lift figures for new cam are with the higher roller rocker ratio)
PAC 1209X Valve spring kit
New intake and exhaust valves in stainless steel from Manley (Race Series line)
Mezeire electric water pump
Heads have to be machined to fit the larger rocker bolts and also the valve seats will need machining too.
Already has chrome moly pushrods

It's a very stout build
Thoughts?
Tell me yours too
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Old 03-14-2019, 09:02 AM
  #20  
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Originally Posted by Darth_V8r View Post
As long as you change your intake to match. If you are peaking at 6300, your intake has stock length runners. Depending on your driving habits, this is fine. If you want to raise peak power 500-700 rpm, you should also switch to fast mid length runners. you can order the runners, split the plenum open, replace the runners, and reseal the plenum. Far cheaper than buying a whole new intake. If you keep the existing intake, you'll peak at 6300-6500, hold peak power until about 6800, and then it will start to fall more gradually. But peak will be in the 6300-6500 range. The intake harmonics will keep it there. If you overlay the curves, you'll see the gap between the two cams gets greater as RPM increases.

It will drive different. Most likely you'll have to deal with bucking a couple hundred RPM higher than you are now. For a good reference, I run 18 degrees overlap and daily drive on the 428. but 428 is bigger, so it can tolerate more cam. I make peak power at 7000 RPM, and it carries past 7800. I don't know about 8000+, because I let up on the dyno, but it was falling gently, not crashing. However, if I was going to go max effort, I would likely go to 32 degrees overlap. Overlap is power, especially past peak power.

See above comment on fast mid length runner option. The fast does flow enough for your engine, but the runner length will likely fight the cam. If you do go to one of the cams in your OP, it would benefit from shorter runners.

There are benefits and compromises made no matter which way you go. All power comes with a price. The real reason I like it centered is that it tends to be the best blend between midrange grunt and top end power under the most conditions. To each their own. There are merits for exhaust bias and intake bias, but it depends on what you are willing to trade. Centered generally has the least amount of sacrifice. And both cams in your OP are fundamentally centered.

It actually would not carry as well due to reduced overlap. It will rev and drive nicely for sure. With your compression you may not lose much torque at all with it. So if your goal is a smoother overall ride that revs good, it is a good cam spec. If your goal is to carry power past peak, then this cam would hurt more than it helps. If you're truly more concerned about higher RPM power, let's consider 18 degrees overlap, which is where my 428 is and it revs to 7700. Same IVC, EVO. 238/253-115+3. That will drive good and rev as high as you're willing to take it. Depending on intake selection, would peak in the 6500-6800 range. Actually knowing more about your intentions now, I'd say that is damn near where you will want to be.

Some more food for thought:

* I have seen dynos fall hard past peak for many reasons. Not always the cam. Sometimes it's valve springs, pushrods, overall valvetrain stability. Sometimes it is the cam. Sometimes it is the intake choice. I would order a set of 11/32 summit pushrods no matter what you do. I'm assuming you're running the BTR dual plats. If not, it's a good all around spring to put on there to control your valves and reasonably priced.
* If you are peaking at 6300, your shift points should already be 6600 or even higher. Power past peak is good power. Many people subscribe to the "It peaked so it stopped making power" school of thought. If your torque is 450 at 4400 rpm in second and 350 in first at 6600, you are still FASTER in FIRST due to gear multiplication. 4000 lbs at the tires vs 3400 lbs. In fact, torque has to fall off to 300 to break even on the upshift in that scenario.



Here is my dyno sheet. Thoughts?
bortous is offline  

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