What does the intake and headers do in relation to each other?

What affect will a change on one have on the other?

What is the optimal configuration for an LS1 heads / cam car?

 

Bigger intake allows for better intake airflow and longtube headers allow easy access for the exhaust gas to push through...smooth flow

LS6 intake and Longtubes headers is a good setup on a heads and cam car.. <img src="graemlins/fluffy.gif" border="0" alt="[Fluffy]" />

[ November 14, 2001: Message edited by: BIGBOS ]</p>

 

does everyone agree with what he said?

 

yup, he stated the basics, you can get really in depth with things like that, if you want some more info just ask away.

 

what modifications can I make to my existing Grot headers to take FULL advantage of the LS6 intake ... what would cutting off the collector and extending the tube length gain me.

What if I had an intake that I could extend or shorten the runner lentgh ... would I want to shorten or extend them to match my headers?

 

[quote]Originally posted by BIGBOS:
<strong>Bigger intake allows for better intake airflow and longtube headers allow easy access for the exhaust gas to push through...smooth flow

LS6 intake and Longtubes headers is a good setup on a heads and cam car.. <img src="graemlins/fluffy.gif" border="0" alt="[Fluffy]" />

[ November 14, 2001: Message edited by: BIGBOS ]</strong><hr></blockquote>

does bigger intake mean longer runners or shorter runners or increased cross sectional area ... I understand that a bigger hole flows more air but there is more to an intake then that. Headers are almost the same way ...

 

I think if you extended them to match the headers it would work perfectly...but I really wouldn't mess with it too much unless you needed to..

How long and how far do your headers extend down?

 

maybe longer runners and a bigger plenum mean more hp and tq a.k.a. LS6 intake compared to the ls1 intake

Eric

[ November 14, 2001: Message edited by: wizkid ]</p>

 

Yea the LS6 intake is the best you can get for pretty heavily modded cars right now..

 

[quote]Originally posted by java:
<strong>what would cutting off the collector and extending the tube length gain me.</strong><hr></blockquote>
In order to REALLY get the right collector length, you will need about 2 days of dyno time. Serious. Start long and start cutting and runnin.
Simple way to do it is to put a length of collector on and paintin it with some cheap paint. Make a pass with car. Where the paint stops burnin off, cut it there.

Tim

 

Food for thought about headers...

There is another, more complex reason why 5" pipes on a normal sized naturally aspirated engine won't work. It isn't that the engine needs more backpressure, it's that static pressure is only half the equation. The equation for the "equivalent" pressure at the exhaust port is P-pv^2, the static pressure minus the exhaust density times the square of the exhaust velocity at the port. A 5" pipe may see a slight reduction in static pressure but will kill off the velocity making it harder to push the exhaust out. Some tuned header systems can make the exhaust velocity high enough that the engine effectively has a lower amount of backpressure than the atmospheric
pressure! This is known as exhaust scavenging and is what separates good headers from bad ones.

 

I'm with Java on this one...seems like there would be a few tricks that haven't been used yet to free up a little more power out of each...

Like if the can the length of the exhaust and intake be matched so that they "tune" together? Each enhancing what the other does?

Would a Tri-Y long tube work for the LS1? I know no one makes one of these, but I know someone with the needed skills that been thinking about rigging up a custom set of Tri-Y style headers for his LS1 while work is slow.

Would wrapping headers to keep the heat in help them flow better? Or do coatings already take care of that?

 

[quote]Originally posted by TA_2001:
<strong>Food for thought about headers...
The equation for the "equivalent" pressure at the exhaust port is P-pv^2, the static pressure minus the exhaust density times the square of the exhaust velocity at the port. <hr></blockquote></strong>

I guess I am curious as to how you derived this equation - bernoulli tells us that static + dynamic pressure = total pressure (constant for a system) - so if you had your 5" pipe going to a 3" pipe the total pressure would remain the same, just the values of static and dynamic pressure would change (this is roughly analgous to KE and PE with respect to mechanical energy systems).


[quote]
A 5" pipe may see a slight reduction in static pressure but will kill off the velocity making it harder to push the exhaust out.<hr></blockquote>

Static pressure would depend on cross-sectional area as would velocity - both on the square of radius - so it again seems to me you are really just trading out one for the other (assuming your equation is correct)?


[quote][b]Some tuned header systems can make the exhaust velocity high enough that the engine effectively has a lower amount of backpressure than the atmosphericpressure! This is known as exhaust scavenging and is what separates good headers from bad ones.[/QB]<hr></blockquote>

Exhaust scavenging is setting up the length of the primaries/collector based on the wavelength of a pressure wave for a given rpm - and using the properties of these waves to create pockets of low pressure which provide a greater differential for other exhaust gasses to flow out.
Off the top of my head I don't know how well this would work with the LS1 firing order - just with a cursory glance it seems like there might be problems - has anyone ever actually set down and worked this out on paper?


Chris

 

Uh yeah, im with ChrisB on this one <img src="images/icons/grin.gif" border="0">
Stock grots and LS6 intake will work fine, thats the setup I have right now <img src="images/icons/cool.gif" border="0">

 

About the tuning effect of these columns of gas that pass through each primary tube and dump into the collector during and after their respective cylinder's exhaust stroke...

I can see where whatever low pressure area caused by a column of gas passing just in front of another column of gas entering the collector could be lessened by a slower velocity. However, if these events ARE NOT timed at least close to this fashion there would be no low pressure area anyway.

I do not believe (aside from a tuning effect as descibed above or some similiar phenomenom) that slower velocity due to a larger cross section can mean increased back pressure.

 

Oh yeah, Chris, I think due to the firing pattern of the LS1 you would need primaries from each side of the engine going to collectors on the opposite side for a true tuned header setup. This is why the SLPs are not.

 

java,

For the best results you want your intake and exhaust tuned together (obviously). There are two main factors to consider... how much flow is needed, and what rpm is the system going to be designed for. Of course, factors such as cams and ECMs help narrow down the rpm range and give a good guide for how much flow will be needed.

For the rpm tuning, runner length is the key dimension. In general, a shorter runner is better suited for high rpms, and the longer the runner the lower the rpm range it is tuned for. Why? Resonance. Inside the intake and the exhaust manifolds (headers) there are sonic waves traveling back and forth. At a certain freqeuncy, that corresponds to a certain rpm, the sonic waves will resonante with the motor and give a big "push" the the charge in the manifolds. It's the principle of the "sonic boom" that makes an expansion chamber on a two stroke work.

The size of the runners (diameter) is based upon the requirement of flow. You want to keep flow high, but not so high that friction losses in the pipes become a negative factor. Furthermore, you don't want the runner too large because you will lose velocity and run into problems of actually increasing packpressure as TA_2001 mentioned.

On the header, it works by using the above mentioned resonance to create the scavenging effect ChrisB mentions. A "good" header will try to space the pulses coming through the collector evenly to try to take advantage of resonance AND pressure differences. When 1 exhaust pulse (the actual exhast gases) passes through the collector, it leaves a negavtive vacuum behind it that helps to pull the next charge into the collector. A correctly tuned header will have 4 pulses, at 90* each, per side, per cycle of the motor.

Look at this from a standpoint of products on the market today. The LS1 works great on a stock motor and receives very little, if any, gain from a LS6 manifold. This is because the manifolds are close to the same shape - same runner length but slightly larger diamerter runners. Only a modified car will see the benefits of losing the LS1's restricitve manifold. Now, look at the Spyder. It's runners are very short (high rpm resonance) and thus kill low end torque. Why? A main reason is that it doesn't have the sonic pulsing to help it along. This principle can also be seen on rock crawler jeeps with tiny two barrels and long 25" intake runners. They have no top end hp, but they have gobs of torque off idle up to about 2500 rpms.

To answer the question why the exhaust header runners are so much longer than the intake runner... it's because of heat. The header is of course, much hotter than the intake air, and thus the sound wanves travel much faster (hotter air = faster sound). Therfore, to obtain the same resonant frequency at a given rpm, the runner must be longer (about 2 1/2 times...).

Many people don't realize the power of sonic pulsing in an intake/exhaust system. Ideally they should work together and be tuned for the same rpm range. If you have ever ridden a two stroke powered motorcycle or quad and felt its "powerband" then you would see sonics in action.

Hope this clears some of it up for you

John

 

thanks for the explanation guys ... what affect does the headers have on evacuating the cylinders as well as pulling fuel/air into the cylinders. Does the intake have any affect on this?

I would imagine that the header and intake configuration have a lot to do with this (not withstanding the timing events).

 

Also another point - if you build your engine as a complete combination you can compensate for the low rpm hp/torque loss with short runner manifolds (like the spyder).

They will kill your VE in the lower rpm range (why you make less power - less cylinder fill) - but this will also allow you to kick up your compression.

This increase in compression will help you at the lower rpm's where you have lost some hp/torque, and at the higher rpm's where your VE is now better you are naturally more tolerant of higher rpm.

Chris

 

Interesting question when somebody ponders a "new" approach to "old" technology.Guess you had to ask the mass public their opinions <img src="images/icons/confused.gif" border="0">

This is why true racers dont give away all their aquired experience. <img src="images/icons/wink.gif" border="0">

Intake-exhaust relationship and their opposing lenths\diameters are affected by MANY variables...but than again I'am just that "shop out there" and anybody can make an LS1 run,right?

Allan