Big cam + AFR heads...

 

Hmmmm, got a good flowing head, then you don't need alot of camshaft.. . .boy does that sound familar.

I'll say this and I'll leave it at this, if the I/E ratio is at around 75% based on flowing the intake with the head and the headers on the exhaust it has been my finding that a single pattern is the optimum "compromise". ( I agree with Tony on his wording, if we could have Variable Valve Timing then there would be almost no compromise). After 75% a reverse split at seat and .050 is optimum with .200" numbers varying reverse, single, or traditional. Under 75% and the trads rule the roost.

Chris

 

Big cam + Big heads = high rpm narrow powerband application. Unless this is a full blown Comp car, your just wasting your money.

 

BTW .400 lift E/I is not really that important due to the fact that there is the least amount of cylinder filling happening at this time on the intake.... a average of the curve is a better estimate but using the function of the cam lobe profile relative to the flow curve is probably better to give you a actual E/I ratio but it's not the whole story... (see below)

First to address this....

The head flow is independant of the flow with the intake attacted to the head... just because a intake chokes off the head flow to a certain point does not mean that the motor will only make the same power with a head that flows more or is a better head port....

The other end of this is what the intake manifold will do to the intake manifold pulse tuning with the motors Volumetic Efficentcy.... a increase in VE from a better suited cross sectional area and runner lenght in the intake manifold will change what the actual E/I ratio is on the motor. This is a big case in terms of the LS1, the LS intakes choke off flow in the cylinder head but they also increase the VE of the motor in the operating range so in the end the motor sees more air/fuel in the cylinder than it would if the same motor was something like a LT1 with the short small cross section intake manifold runners.

Gotta agree with Chris Straub and Ed Curtis that the lobe profiles play a big part in the way the cam acts and the E/I %

BTW I like the flow of the intake with a radius on the intake, then the intake with a manifold attached to it, then the exhaust with A PIPE and the exhaust with the header the car is running attached to it to get my working E/I ratio... just the way I have found works best for me. Others can do this different than I do, either way it's their way.

Bruce,

Don't ever compare a reverse split to a tradtional split cam with varing intake opening and closing points, it might make sense to the average guy since you have the same total duration but in reality the changing of the intake events has about a 4-5X larger effect on the shape and area of the TQ curve in a given RPM range than the change in exhaust will ever do. It sounds like the right way to go, but it's so far from the scientific method that bad/inaccurate assumptions can be made from the "results" of tests like this. The best way to do a test like this would be to have cams with the same lobe, duration and ICL for the intake side of the cam and the exhaust side of the cam would have a set duration and ECL (with most likely advance ground into the design) and then you would take duration and ECL away (to maintain the overlap) until you came to a point of lower average power numbers for the RPM band you are running in.

I've already been down this road on cams before with the intake and exhaust "splits" on another fourm, here is the basic highlight http://web.camaross.com/forums/showp...6&postcount=24

and the whole thread if you want to read it all....
http://web.camaross.com/forums/showthread.php?t=375685

Bret

 

Bret, I don't think I quite understand. Is there a chance you could touch on this a bit more? Thanks.

 

Subscribing to thread, and guessing he's referring to actual flow ratio vs. actual size ratio.

 

My heads like my X1, but they flow real well on the exhaust. I doubt I would gain with a regular split cam.

 

Hmmm guess I should start from the begining to explain this ....

There are a lot of reasons why the LS1 is a better performing stock motor compared to the LT1, and one of the biggies is the intake manifold... not for the lightweight polymer construction that doesn't conduct heat, but for the fact that is has a longer larger intake manifold runner.

Two things in intake manifold design work to help increase the VE (Vol Eff) of a motor in it's RPM range, intake manifold runner length and intake manifold cross sectional area.

Basically the longer the runner the lower the RPM it will tune for and help intake cylinder filling. The shorter the higher the RPM it will tune for.

Same goes for the cross sectional area, larger = higher, smaller = lower.

Now how is happens is more complicated but to put it simply, you have the air in the cylinder moving in waves (basic principal of dynomation software and any good engine software) at certain RPM and length/cross sections the waves work much better than others. This basically creates a faux "boost" in the runner (5-7psi at some points, but not the whole time the intake valve is open) which helps increase cylinder filling....

Hence this is why I say the LS1 changes the E/I% dynamically. Even though that intake (LS6) will limit flow to around 285-290cfm it still helps the cylinder filling, not around peak lift but as the intake valve closes (this is usually where the faux boost happens).... (start off topic rant here) in the LS1 this is a good thing since most LS1 heads stock and ported have problems with extremely high velocity over the short side and the upper lifts of the flow curve are usually crutched by this extra high velocity... from what the guys who do SS heads say nobody has cured this in stock or aftermarket heads, without slowing the whole port down (notice it has been done by some very good head porters)... long story. It goes to show in the HP per CFM that these motors make as well, we are inching closer but the be all end all of heads is not out yet and most likely the market can't take the price. (end rant)

Basically take out of this that the restrictive LS intake design sucks at flowing air thru it but it does add TQ thru the RPM band that street cars are run thru that it more than makes up for it's restrictive intake flow with intake pulse tuning in the right RPM band.

Bret

 

That's not a fad...

It's the way things "need" to be if common sense takes priority over ***** envy...

Ed

 

Bret, if this VE increase is taking place on the back of the intake lobe lobe or when the valve is shutting... what dictates how much exhaust lobe your going to throw back at the setup despite the given I/E ratio?

I was viewing a post where you quoted the percentage of flow area during a lift curve. Low, and high lift seemed to be the ticket in that test. Now, where does the most flow occur during the exhaust event? If a setup needed an increase in exhaust lobe because of this VE pick up, where would you add it?

Thanks for your info. Good stuff.

 

That's a awesome statement!

 

Well this is where computers, calculations and experience come in. I'm more of a "single pattern" type of guy, if that says anything, and cams with more exhaust duration than intake I like as well. That doesn't say that just because my .050 numbers are the same or larger on the exhaust that the rest of the specs will be as well.... lobe area, shorter seat timing etc... all have their place on the smaller, lighter exhaust valve. (aggressive lobes on the exhaust can help street manners AND can be done since there is less mass to control there)

Glad you pay attention.

Where would your guess be for the most exhaust flow? Probably at the opening when the pressure in the cylinder is highest.

As for adding exhaust duration... I want to keep the opening as late as possible but I also don't want too much overlap (which is closing) on some street motors... in a performance application with enough RPM to do so I would add it to the overlap or closing side of the cam. The more comprimises or the less midrange TQ I can use the more I will keep the same ECL and add the duration to both sides. I'm like Tony Stewart though, I can never have enough midrange TQ if I can get the forward bite I want.

Bret

 

This is a great technical discussion and probably the most popular thread I’ve ever started… I think I’ve picked up on a couple of things, but since a lot of its still over my head, can you experts comment on a couple of observations I have assuming the following set up:

• AFR 205 heads, straight out of the box
• Cam 230/227 .591/.571 112 lsa, I believe it has X-ER lobes (still talking about the MTI X1 cam)
• Long tube headers, off road y pipe, Borla muffer
• Lid, FTRA & Ported TB
• Moser 12 bolt with 4.10s
• MN6
  

This set up should provide good top end power (440+ rwhp through the 12 bolt w 4.10s) without having to rev past 6,600 rpms, while sacrificing a little peak torque for moving it slightly lower in the power band than if it was a single pattern or traditional split cam of similar duration and the same type of lobes. Idle quality should be a bit better than a traditional split cam of similar specs, but the same traditional split cam might built slightly more horsepower, and do it at higher rpms.

My car is a daily driver and occassional track car. My goals are decent midrange torque but sacrificing a little for more high end hp. I’d like to keep peak power lower in the rpms and make peak power a little before 6,500 rpms so I can shift at 6,600.

 

Cam 230/227 .591/.571 112 lsa, I believe it has X-ER lobes (still talking about the MTI X1 cam)