Rede

iTrader: (2)

I've read serveral threads in hear about cams and what all the pretty numbers meen, but I'm pretty confuzed at what they all meen.

Is there a way to explain to me how to pick a proper cam for what a person will love v.s. the next guy's personal choise?

The car in question is a A4 2001 T/A (137,0xxkms now but we're on hollidays and should have 138,4xx on the clock when we get back home to which I'd like to add some oomph.
The lovely sound of lope-ity-lope-lope appeals to me, but I don't want to make a rash/mis-informed desission.

The car is stock except for the following:
3200 vig stall
SLP FlowPak (I should have just bought the lid and saved a few coin)
Ported and polished stock TB
3" hi-flow cats*
Hi-flow muffler*
Stock gears are 3.23s.

*I know that the cats and muffler don't meen beans HP wise, but its not stock*

65% of those km's are being spent in town.
I do plan on taking the odd summer holliday with the car, so an extra 1000 miles wouldn't be out of the question.
I also race at my local track once or twice a month from may till september.
I don't condone, nor do I seek out street racing, but I may or may not have gone over the opsted speed limit both in town and/or on the hi-way.. and I may or may not repeat this act. >_>

In the future (never in the budget, so therefore never soo enough)I would like to go with:
3.73s
Tune
LT's*
Dual exhaust*
Mayyyyybe heads...?

*If I'm not going to lose too much clearance from stock height. The town loves those speed bumps and has zounds of friggin potholes/frostheaves



Now correct me if I'm wrong, but don't charbroil my *** for waiting to double check with what I've read/understand v.s. fact, but from what I understand, LSA determins the lope of the idle...
?'s regaurding LSA:
Does this effect the hp/torque in any way?
Does 112, 114, ect. reffer to a time durration between cycles (or something like that effect)?
How much of a difference in sound is 112 v.s. 114 and how does that effect the DD comfort factor when your in rush hour traffic?

The other cluster of numbers have me baffled.
I read a thread that tried to explain their meenings and all sorts of other technical aspects. I understand the mechanics of opening valves and such a bit, but it was mostly greek to me and after reading 4 times, I was left slightly more confuzled each time I read it.


I don't want to make the mistake of picking a cam that's too large or too small for minnor gains or suffer with other side effects such as surging, ****-poor milage, ect.

The cam of choise will be installed at a local shop, but nearest dyno shop is 5+ hours away so the install might have to there to provide proper tuning, or it be okay to drive normally until I can plan a trip to get a proper tune?
I'd like to avoid added cost of upgrading valve springs, but if it can't be avoided, I guess I'll just have to deal with it...
Anyone know the max lift of the stock 241 vavle springs?


Peek dyno numbers sound impressive, but I really don't see myself hanging around the 7K mark, so a MS4 would be wild to try, but I'm pretty sure out of the question. =\ Under the curve gains across the board sound more appealing to me..
On that note, Ron from Vengance (love the tunes btw ) mentioned their VRX3 to someone in a recent thread who was looking for more go while having mild manners for the wife to drive around in (which is sorta my situation, but I don't want to pull a Taliban move in his thread).
Anyone have experience with this perticular cam without tuning, or could a simple mail order tune with provided cam specs do the trick? Any before/after dyno sheets would be a big help as well.

Sorry for the long winded post and the many questions
I hate the idea of buy parts, only to change them out later on because they no longer suit my application or didn't 'feel right' . I'd rather make the most out of my budget by choosing the right few go-fast parts by research v.s. trail and error.
Besides... I'd rather spend the summer enjoying my car than slaving away on overtime @ work to afford the next attempted combination and throw my money away yet again.

06 SS

LSA has the biggest effect on overlap of any cam characteristic. The cam will open/close the exhaust valve first (just picking a random start point in the cycle for example.) As the exhaust valve is closing, the intake valve will start to open and both valves will be slightly open at the same time. The piston is coming up and near the top of its travel. At this time, the exhaust gasses are still exiting the cylinder and that creates a slight vacuum that will help pull in fresh intake charge. Think of the two cam lobes as two hills that can move. In your mind, put one right in front of the other and have the edges just overlap with one hill on the left (exhaust) and one on the right (intake). The portions that overlap are, cleverly enough, the overlap area. The overlap area is essentially a small mishapen triange. The LSA is the distance between the center of the hills (it is in degrees, but it is taken care of in our two dimensional model). Now, if you tighten the LSA up (lower number) you move the hills closer together. As the hills get closer, the triangle gets a lot bigger and very quickly. A tightening of the LSA by 4* can add more than 40% of additional area.

Sure, so what?

Well, increasing this area does a couple of things. Some good, some bad. First the good; Increases peak torque, nothing will influence peak torque more than overlap in a given engine, quicker reving, and that lope you seem to crave. Increased midrange and equal or more peak power, but may be slightly lower in the powerband. The first part of the intake stroke is the most important for getting the intake charge in. The increased overlap here is huge.

The bad; lowers engine vacuum, too much overlap can drop it low enough to have problems with power brakes and other accessories. Increased emissions, much more touchy to backpressure. narrows your powerband/less flexible engine, will drop off much faster after the peak power point (which will not be in the center, but skewed towards the upper end) and be weaker at low RPM until it starts to quickly climb the steeper torque 'hill'. Imagine a third hill, it is your torque curve. It has a narrow base and a high summit. Widening that LSA will act like you took your hand and pushed down on the top of that summit. The peak will be lower (but spread out further, getting flatter) and the base will do the same, widen up, but be lower on average. The total area under that hill will be about the same, just a different shape.

The second way to increase overlap is to increase the duration of the intake and exhaust lobes. Increasing it will do two things, first it will, obviously, increase overlap, but to a much lesser degree than the LSA. Imagine the first two hills now keep them the same distance apart, but make them wider. The overlap triange is a bit larger, but not nearly the same area increase as a few degrees less LSA. This does good and bad things as well. First the good;

Moves the torque curve up in the RPM range. Slight increase in midrange (less than an LSA tightening) and a vast increase in upper end power. Also adds that choppy sound to the lope at idle (not my cup of tea, but it sounds like it might be yours).

The bad; increased emissions (not as bad as an LSA change), lower vacuum, lose of low/some mid end power (moved the power up the RPM range, so not much down low)

In a cam swap, you can change both and they are interrelated. Bottom line is you have to decide what you want for your specific usage. Myself, I prefer a strong midrange as I drive an automatic (non f-body cars) and use it 99%+ on the street vs the (maybe) once a year I might hit a track. Minimizes my 1/8th mile time (0-75 MPH), which makes me quicker on the street than someone with a huge cam because their power comes up at the top end and they have to chase me down after I pull early on them. (of course, stall speeds, gearing, traction, etc. can change that)

I like a relatively short duration, maybe 12* bigger on the intake than stock and 15* or so on the exhaust and an LSA around 4* tighter than stock. It is a happy medium for me. Not much downsides with relatively small changes like that and wakes up the midrange something fierce.

I believe an LSA wider than 110* or so for an LS1 is a band-aid for too large duration as a wider LSA will help tame some of the bad manners of big duration cams.

I am in the minority here, most everyone else will tell you to go the other way, more duration and more LSA. There is a book by David Vizard, called ~"How to build a small block Chevrolet; Camshafts and Valvetrains." I suggest you go pick it up and read it a couple of times, will teach you that, while theory is fine, there is no substitute for experimentation.

Talk to people who's cars act like you want, see if you can drive some of them, what supporting mods they have and drive it like you normally would. Then copy them. Enough cam swaps have been done that it is not hard to find most every combination available. Then you have taken the guess work out of it, you will see what you will get before the work is done.

Rede

iTrader: (2)

Thank 06 SS.

I think I understand a bit more, but I'll still have to do a more research to make sure I understand before picking one and going with it.

01Wickedwench

with the +138k on the car and motor look for a cheap decent cam. Almost any cam you get that isn't stock is going to require springs. My buddy has a FM13 like a 595. intake lift 585. exhaust, 114 LSA (lobe seperation angle) not sure of duration, 110k on motor and he has to change the double spring valve springs every 20k. I just bought a ASA cam ($370) and bought LS2 yellow (beehive) springs ($90) good to .570 lift now, in case I put 1.8 rockers on later to increase the lift. It only has 110 LSA .226/236 dur. and a .525/535 lift. Oh I only have <50k We installed the cam in 9hrs. Too make a long story short he loves the sound (wishes he had a diff LSA) and bearly pulls on me with a $700 track tune w/me untuned.