I've seen 383 LT1 cars with stock ported heads that couldn't possibly flow past .600 lift yet the sollid roller cams they install in the cars have lift higher than .600 with a lot of duration. Is it beneficial to run higher lift than what your heads flow because with the long duration the cam is at least above the max flow of the heads longer thus producing more power?

Alos, I know that the more duration a cam has the higher rpm the cam is designed for but does the lsa (valve overlap) affect this also?

 

Basing cam specs, especially max lift on head flow rather than valve motion is a bad idea and really a expensive proposition like lift limited classes. The standard trend in high end racing is to run as much lobe lift as possible to control the valve the best... long story on the how but trust me on this.

The big deal with the heads is if they level off that they don't go turbulent or drop off at higher lifts. Then it doesn't matter if the cam is getting the valve to lower than this drop in flow or higher than it, the port ain't gonna make the power it should if that was a smooth non turbulent port... FWIW lots of LS1 stuff has this issue, especially if you have a lot of depression pulling on the port.

That's a novel idea.... overlap having something to do with effecting the TQ curve. LSA is a byproduct of getting everything else right, and IMHO overlap is a much more important thing to look at.

Justin, plain and simple I think you are asking the right kind of questions here.

Bret

 

That's what ya call overcaming ya know "some is ok but more is a lot better syndrome".
It is beneficial to lift the valve past max flow to take the curtain area out of the flow path,but ya go by a formula as to valve size.It ain't always right either.
The main thing to remember is ya don't go to .800 lift on a .600 max flow head. Now if ya enter duration into the pict......= another book.

 

I still might go to .800 lift on that .600 max flow head. All depends what the bench tells ya.

Bret

 

I was speaking in terms of a street engine with not a max port job and small numbers. Most flow sheets I have seen on not so good castings will read .500-220 .550-232 .600-236 .650-2? those show the heads are done at .550 and I wouldn't go over .650 lift with the proper duration.That's shy of the formula but I like my valve guides to much.
I wouldn't go that high on any street engine except mine but it's a race engine in street clothes. It's a bunch.

 

Another LSA question I have is how narrow of an lsa is too narrow for a blower application?

 

Dude,

IMHO street motors have lift limitations based on spring life and selection MORE than on the cylinder head ports.

Vortech,

Go get the new Engine Masters magazine... they really strike on something in a article about supercharging a small block..... IMHO they found the emperical evidence to make the right blower cams but they didn't come to that conculsion. This would be a great story for someone like Rich to read since he has a idea what I am talking about and what works.

You can have more overlap than you and the majority think on a blower cam, problem is you can't handle the idle and drivability if you go too far.

Bret

 

Ya left out guides.

Yea I read the article.The hyd roller didn't do bad,But didn't appear the best.

 

The Key thing left and is ultimately the make or break of any combo is Tuning ..

Need to have the ability or resources to finish the job completely,when factoring what works best...What may be the best choice in cam selection and "should" work best...may not be at all, if tuning capability is not there...

I think tuning gets lost in the hysteria of cam, heads or what ever combo is being worked with...


so before asking what cam is best....find the best tuner available to you and ask them thier opinion...They either have tuned something similiar or not...

There is several threads on here that can make a head porter look bad or cam grinder...And its tuning, thats ultimately most likely the culprit....

 

Nah... just have to know how to read the results of that test... I've been there done that on those cams. They had the answer in front of them they just didn't know it.

I agree Joe, tuning is a vital part to getting a combo to work... asking a tuner what he can work with does put limiations on the combo since most tuners I know don't realize what the duration and LSA numbers really mean and what they actually give you so they have preconcieved notions. Been there done that.... OTOH I have found real HP in understanding theory and testing it out.... I would say that 95% of the time what should work does when it is excuted properly.

Bret

 

Brett ,need to know some better Tuners then...LOL I think your reading into what I wrote more than need be... after all said and done either you have the resources to finish the job or not... Some tuners I really wouldnt call tuners and other Tuners understand cams ,how they work and the affects they have on a efi engine...Hell most in what I call "the circle" know every aspect of the engine to the point of duplicating , the combo they are tuning.. but at the same token its not discussed outside, the tuner and his client...yes you can tune a engine blind ,done it several times and I can look at how the car idles what timing it likes, what map readings I get in the fuel map and almost tell what a cam is without being told the specs...

Like I said, thier is active threads at this very moment ...Where as the combo may or may not be optimal but tuning and or improper build has hendered the results to the point of disgust... hence why I said IF you cant tune or not experienced in tuning...seek someone that can and see what the limitations of the TUNER is...I can tell someone all day long what should work well,,but if the guy cant tune the thing what good is that info or me sending him a cam that will probably wash the rings out the motor ...

 

I was going up north to have Brian Herter of PCMforless do the tunning. I've been talking to him about various aspects of what he's done. I'm confident he can get the car tuned right. Anyway thanks for the answers, I'll go get the magazine. I like reading anyting I can about how components work. I love to learn and expand my knowledge. Can you guys reccomend a good source (book, etc.) that I can get and read about cams, cam & heads combos and building an engine to work together nicely?

 

Brian is very good at what he does...I'd still ask him what the limitations of the factory PCM is..I cant really give any input on that since I dove right into engine management years ago... As far as expanding your learning or atleast the basis, believe it or not most major cam company's explain it well in layman's terms in there catalogues usually the back .Which you can get for free or minimal price..Though its only discusses cam basics it doesnt get much involved with the rest of the engine as in intake( resonance,runner length etc.),heads , exaust and so on which will affect how efficient or optimal A vs. B would be...Your application being a forced one, I'd look at scavengeing first ...since heads, intake though do have a bearing is not as important compared to say a naturally aspirated arrangement...

 

As mentioned above by others there are a lot of factors. Another thing to remember is that many times once the intake is bolted to the heads the "stall point" (so to speak) in the flow is masked and the higher lift can be utilized.
Steve...

 

Last time I checked my parents spelled my name with one T, not two, it's not like I don't spell it correctly at the bottom of every post I make. I don't spell your last name Ovary. Hell it has a O and a V in it that must be close. ;-)

It's not people I have worked with but what I hear some of them say, and even with good motors out there that they tuned they still don't get it..... IMHO tuning a motor is really just understanding the feedback you are given from the scanners and the dyno and doing the right adjustments to give the motor what it wants... in reality if you have a scanner and a dyno, all you need is time and/or experience to dial the motor in. Getting the right physical parts in place to me takes a ton more talent.

In reality most of us don't get motors completely, it's the degree of what we get is how good or bad you are. There are things I don't grasp 100%, but then again I know other things extremely well.

As for a book, not really anything out there on valvetrain that I would say is the bible, just tid bits here and there. Figuring out what cams work takes lots of back to back experiments. Blower cams are interesting.... I just mentioned the EM article because I was suprised with what they came up with in the tests. A centrifigal blower cams specs have more to do with the boost curve than about anything else IMHO.... just another case of give the motor what it wants not what you want to give it.

Bret