Big Jim Slade

As I read through the threads on this forum I am amazed at the knowledge that I find, and the experience or actual trials to back it up. I am familiar with cam specs, but I have a question. A TSP 228R is spec'd at 228/228 595/598 at either a 112LSA or 114 LSA. The Torquer V2 is 232/234 595/595 113LSA or 114 LSA. While if I what I have understood is the lower the LSA is a rougher idle and better lower RPM power, what does the larger duration provide? To go one step farther the V3 is 231/234 634/598. What does the substantially larger intake lift provide, when compared to the exhaust lift, and what is the benefit? Sorry to be so ignorant, but I just had to ask.

Sigforty

Duration tells you how long the valves will be open. The lift is how far the valve opens. Both increased duration and lift will get more air/fuel into the cylinder and exhaust out. The issue with big duration is typically the increase in overlap, which is when both valves are open at the same time. Overlap is good to have at high rpms, but hurts at idle. This is why cams with bigger duration chop more as well. You have a process where exhaust is going back into the intake (reversion). There are a lot more complex issues going on as well, but I will save you from them.

radar502

http://www.hotrod.com/how-to/engine/...-pontiac-tech/ This is older but some good info on cams well the comp cam but good info just the same kinda what is what and how it works or not..

racebum

and also why variable valve timing or better known as vtec was invented. you can run some absolutely silly cam combos on hondas since they have this ability. with a fixed cam there are always trade offs. a lot of overlap as stated above makes the idle choppy and the car a lot less fun to drive in traffic, BUT, they go like mad. with the long gears so many corvettes have more overlap and a boost to that midrange usually make them faster. cars with short gears often do best with high rpm screamers.

there is a reason the 228deg@.50 on 112-114 with .600 lift is so popular. they fit within the rpm limits of the stock block, work on stock 243 heads or ported and drive pretty decent

LSOHOLIC

well.........its fairly straight forward, once shown. But its quite the rabbit hole. Hard to talk cams without talking the entire induction system. Because the cam is just giving the induction system what it wants and was designed to do at specific rpms.

The cam has 5 basic "events"
IVO (intake valve open)
IVC (intake valve close)
EVO (exhaust valve open)
ECV (exhaust valve close)
overlap (IVO + EVC) "overlap is when both valves are open at the same time"

LSA (lobe separation angle) is just a by product of where the events end up in relation to each other. It really does not mean a thing, its only used to give a relation to the events.


The durations can be misleading at times....example.

228/228 113+1 has a 46* IVC <---this cams has more intake potential
235/247 110+4 has a 44* IVC

IVC is "intake valve close" point ABDC "after bottom dead center. Typically the "later" (bigger number) the IVC number the more rpm the cylinder wants. Meaning the VE (volumetric efficiency) moves up percentage wise as well as power moving up (in the rpm band).

If you really want to become familiar with cams....get use to breaking down the events....then comparing the events, that is the only way to know what your looking at....period.




Then we could get into how each of the events effects VE, which in turn makes power.

There is no "black art" to this, just lots of trial and error and data collection.


.

LSOHOLIC

We can compare the three cams you brought up.

TSP V3 is 231/234 634/598 112+2
IVO 5.5*
IVC 45.5*
EVO 51*
EVC 3*
overlap 8.5*

TSP V2 is 232/234 595/595 113+2
IVO 5*
IVC 47*
EVO 56.5*
EVC 6.5*
overlap 11.5*

TSP 228R 228/228 595/598 at either a 112+2
IVO 4*
IVC 44*
EVO 48*
EVC 0*
overlap 4*

Each event has a "perfect" timed event (x5) for the induction system at a specific rpm.
The trick is getting all the parts to work together (head runner length, head runner shape, intake runner length, intake runner shape, mean cross section area of intake and head runner, valve size, valve angle, chamber shape, cam events)...etc...etc...its a life long rabbit hole.



EDIT.....if you want to dig a little deeper, I'll try to answer any question. Just didn't want to keep rambling if you've already lost interest......lol.


.

racebum

the most usable answer for most people would probably be the ls6 intake manifold, 1/3-4" long tube headers and 243 heads, stock or ported for 15%+ flow or there abouts along with a 5700-6000rpm peak power point and shifts at 6500-6600

that's simply where a lot of hot street builds fall.

thoughts?

Sigforty

Lol, it is a serious rabbit hole. A few years back I got into some issues with exhaust pulse. Intake and exhaust pulses play a big issue as well. Just have to design everything around the engine.

Paul 75 L82

Great thread, one of the best past times a guy can have is talking about cams. We've come a long way in my lifetime, started off with a Duntov 30-30 in 1968. WOW!

LSOHOLIC

I'm sorry man, but you lost me......

What does this have to do with understanding cam numbers ??

.

LSOHOLIC

Yes.....I do like r&d .....in my next life I would love to be a Bischoff or Morgan protégé !!


.

racebum

if you don't get it

i can't help you

sorry

try re reading perhaps?

LSOHOLIC

Lmao.....you ask for my thoughts....lol.

My thoughts are....if its to burdensome for you to ask the question in a more direct sense instead of a statement structure, then nah...ain't got nothing for ya.

Carry on.....


.

Big Jim Slade

Thanks for the replies. The rabbit hole isn't boring its actually very interesting. I haven't lost interest just been traveling, work, and had some time to review my thread. I understand more now than I did and that may be dangerous, but the jury is still out. Thanks guys.

dagon138

FYI, there are engine simulators out there that can tell you how cam X compared to cam Y will look as far as power curves, hp etc.
This is assuming you give it accurate data regarding supporting mods, flow data.

PRE-Z06

I'm going to say there'd be less than 8hp/300rpm peak difference in between the largest and smallest cam, your thoughts as to how each would differ or which would be best for the OPs setup?

Personally I'd rule out the v3 if heads aren't ported or it's a dd because of the lift, then decide between the other two based on where he wants powerband...though really need to know his combo as there may be a better option.

To me IVC is most critical and what I look at first for powerband, then overlap comes into play to help decide on driveability needs of owner.

I'd say peak should be around 6300 and redline of 6800 on average based on an ls6 intakes runners.

RIKKITIK

If you're really interested and don't mind reading, (ugh.....homework )
http://www.hotrod.com/how-to/engine/...mshaft-basics/

http://www.crankshaftcoalition.com/w..._Dimitri_Elgin

http://www.elgincams.com/campaper.html