gomer

iTrader: (13)

I know Binks is running the grand am cam in his car, but is anyone else running a 108 or lower LSA cam in their car? Some of the Holden guys are doing it after changing to speed density, but has anyone here in the states gone that low yet?

If you have a cam with 108 or lower LSA, please list it's complete specs, what cams you've ran before and some of the major characteristics that you have observed with the lower LSA cams.
Thanks

stealth

LS1s like a lot of lsa, 114 or more. Lingenfelter uses 116/117.

gomer

iTrader: (13)

I'm assuming that when you say "like" you mean it as in driveablity and idle characteristics. I tend to think that lower LSA cams make more usable power than higher LSA cams. Idle quality isn't a concern for me.

Btw, I have never seen a Lingenfelter cam'd 346ci naturally aspirated car that was anything spectacular.... maybe it was due to that 116/117 LSA

J-Rod

I would disagree with this statement. An LS1 is an engine, just like any other. I will say it yet again, LSA is a byproduct of proper valve event selection, and should not be the criteria for designing camshafts.

gator's 99TA

iTrader: (2)

100% agreed. LSA is a variable influenced by the valve event. there is no such thing as the "same" lsa given two different lobe grinds. this is also the idea when cams are only measured at .050" lift. the rest of the area is not the same.

dazman

i had a 110 in my old camaro and it was fine... i would think that a 106 would be ok when i compare a friends 114 to my 110 just get her tuned

mike

98blackSS

eh?

stealth

Read his book, then we'll talk.

Damian

iTrader: (89)

Gomer, don't waste the driveability. Just get a cam on 112+4 to equate the 108 ICL (would be the same as 108 LSA +0). Any big cam on a 108 LSA is going to surge and idle like ****......

soundengineer

iTrader: (16)

just like mine...MTI X1 cam.... 112 +4.....= 108

and man this cam rocks...though I'm going to be taking it out to try my own mathematical experiment later this year

gomer

iTrader: (13)

I ended up ordering it on a 110 +2.. we'll see what it does in a couple of weeks, gotta do some damn flycutting next week

J-Rod

Quote:
The most important lobe in my cams is the exhaust. Specifically the exhaust VE's. Open the exhaust too early ; you lose heat energy ; velocity through the exhaust runners....you also get significant reversion of the exhaust gasses which kills power. Open the exhaust valve too late; you won't get all the gasses out of the cylinder which contaminates the intake air-charge ; drastically affects power.

The LS1 is intake limited, therefore it is RPM limited. Putting a cam in that is ment to peak at 6800rpm is just a waste of lobe. With the current intake selection (LS1/LS6) the motor can not make power that high in the RPM. So, tightening the LSA on a cam like that would boost power in the mid-top-end & keep most of the power in the usable RPM range of the motor.

I tend to approch things a little differently with these EFI intake restricted motors. Due to runner length & the current lack of cost effective shorter runner intakes, the LS1 is limited to a 4800rpm torque peak... thus 6200-6400rpm HP peak (due to the wave of the incoming intake aircharge as it bonces between the closed intake valve & open air plenum). When I do a cam for a setup like this, I go for max cylinder pressure under 6200rpm.
The area most cam companies error on is the exhaust. This causes problems with these limited intake designs. The exhaust VE's are the most important on these setups.
Simply put, on an N/A motor the intake aircharge is not assisted. (leaving wave dynamics of the aircharge out for a moment).
After the combustion stroke there is tremendous pressure in the cylinder. As soon as the exhaust valve cracks open it flows a LOT of air. It's basically boosted out of the cylinder if you want to look at it like this. Having the exhaust valve open too early not only costs heat (power) velocity through the exhaust runners, it also empties the cylinder before the intake valve is open enough to take advantage of the pressure differential. (in a limited overlap/smogable camshaft this is especially true) This causes exhaust reversion is one of the key factors in surging problems. By the airflow reversing course it is loosing a lot of it's inertia. Typically this is overcome before peak torque however. So only low-speed issues are present. At the track these motors are always above 4500rpm so this does not affect track times too much.

Stilll....there is significant power lost by allowing reversion. So it makes sense to open the exhaust valve a little later increase the overlap a bit. By adding advance into the camshaft this makes the problem even worse as now you're opening the exhaust a few more degrees earlier..... shortening the effectiveness of the intake unless you have significant overlap flow to over come this.
Simply put, advancing a cam makes it more exhaust bias relative to TDC. Retarding a cam makes it more intake bias relative to TDC.

RyanJ

J-Rod...a translation please?

gomer

iTrader: (13)

Everyone has their opinion.. my opinion is that reversion is mostly caused by an aggressive closing of the intake valve on the compression stroke, that aggressive closing causes a valve "bounce" sometimes that lets some of the intake charge to go back into or "reverse" into the intake tract.. causing reversion when the valve opens again on the bounce. Another one of my opinons is that some people are over complicating camshaft design... but you know what they say about opinions

J-Rod

All valves bounce. Go watch a spintron... Too much bounce is a function of improperly matched valvetrain. its called valve float. Unless of course you engineer float in, thats called a launcher cam, and we use them in lift limtied classes...

Reversion is a function of overlap and when in the intake and exhaust stroke you decide to open the valves.

As for simplifying things, here is the math. A 112LSA / 108ICL is in not like a 108LSA/108ICL except on intake valve opening/closing, you can see what it does to EVO...

112/108
Quick and Dirty Cam Calculator Spreadsheet
0.050
Intake Duration - ID 232
Exhaust Duration - ED 232
Lobe Center Angle - LCA (also known as LSA) 112
Intake Centerline - ICL 108


Intake Valve opens - IVO 8
Intake Valve closes - IVC 44
Exhaust Valve Opens - EVO 52
Exhaust Valve Closes - EVC 0
Exhaust Centerline - ECL 116
Overlap 8

108/108
Quick and Dirty Cam Calculator Spreadsheet
0.050
Intake Duration - ID 232
Exhaust Duration - ED 232
Lobe Center Angle - LCA (also known as LSA) 108
Intake Centerline - ICL 108


Intake Valve opens - IVO 8
Intake Valve closes - IVC 44
Exhaust Valve Opens - EVO 44
Exhaust Valve Closes - EVC 8
Exhaust Centerline - ECL 108
Overlap 16

112/112
Quick and Dirty Cam Calculator Spreadsheet
0.050
Intake Duration - ID 232
Exhaust Duration - ED 232
Lobe Center Angle - LCA (also known as LSA) 112
Intake Centerline - ICL 112


Intake Valve opens - IVO 4
Intake Valve closes - IVC 48
Exhaust Valve Opens - EVO 48
Exhaust Valve Closes - EVC 4
Exhaust Centerline - ECL 112
Overlap 8