Dan87IROC-Z

Just please explain what the LSA affects the power band.

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission with 2.77:1 Rear End

Current Mods: Edelbrock TES 1 5/8" Headers, Hooker Aerochamber Cat-Back System, Performance Resource Chip with 160* Thermostat, Accel Ignition Components, K&N Filters, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET : 14.3 @ 97mph
(corrected for elevation)

Scott C

Picture 2 cams with identical duration and lift. Cam #1 has a 115 LSA and cam #2 has a 112 LSA. Cam #2 will have more midrange power than cam #1 strictly due to the LSA. Many stock cams are in the 114-116 range to achieve a balance of economy and performance.

Most aftermarket cams are in the 110-112 range to lean towards the performance side, while still retaining drivability. I'd stick close to 112.

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'92 RS, ZZ4 10:1 350, Edelbrock 6085 heads, Crane 208/214 467/482 cam, GM 1.6 true roller rockers, Holley Projection TBI intake, Holley 670 TBI, SLP/Jet-Hot 1-5/8" headers, Catco 3" cat, Flowmaster 3" catback, Hughes 2500 stall converter, stock 700R4, Auburn Pro posi w/3.42, 17x9" SS rims w/BFG tires, Medium Quasar Blue w/white SS stripes, 48,000 miles....

MRZ28HO

Plus the less over lap (wider LSA) the smoother the idle, conversly, the more over lap (narrower LSA) the lumpier the idle.

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George P. Lara
1994 Z28 LT1 T56
1984 Z28 High Output
Member: SCCA, SCFB, SC3GFB

Jim85IROC

iTrader: (2)

BUT, if you plan on forced induction, a wider LSA will help retain cyllinder pressures longer.

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The IROC Homepage
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View the restoration of an 85 IROC</A>
"I didn't know a bored out Ford could go so slow" -Shenandoah

AlkyIROC

There are actually 5 specifications you need to know when picking a cam. Advertised or total duration, duration at .050 lift, valve lift, LSA and valve overlap.

Cams with identical lift and duration can behave totally different if the LSA and overlap are different. Typical drag race performance cams have a short LSA of 106-110. This moves the torque curve higher in the powerband but also narrows that power band. Prostock cars have valve lifts of over .800 but also have a LSA of 114-116. The wider LSA lets the engine idle smoother.

Back to the identical cams. Lets say they both had 240 duration @ .050 and .500 lift. Both would be good cams for a street car. If one had 114 LSA, it would idle smooth and be good for computers. If the other had 106 LSA, it would have that distinctive lop at idle and totally confuse a computer.

That's why cam manufactures have hundreds of different cam grinds available. Someone asks me if I have a 3/4 race cam in my car. I say "what's that?" 1960's termenology doesn't work in todays market.

As another example, I use some software to determine what works best for my race car. I plugged in every compcams and cranecams big block cam available to see what would work best with my car combination. The majority of the cams had 110 LSA which made my combination require a higher stall converter than what I already have (3800). As of yesterday I finally found a cam that works perfectly. Its the LS6 grind and is ground with 114 LSA.


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Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas
LS6 Big Block buildup now in progress

Best results before the engine blew up
Best ET on a time slip: 11.857
Best corrected ET: 11.163
Best MPH on a time slip: 117.87
Best corrected MPH: 126.10
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!

Member of the Calgary Drag Racing Association

Vader

Stephen,

Very good points on cam profile selection. I'll give you a hint - even back in the '60s we didn't identify cams by "3/4 race" or "full race". You could always spot a wanna-be as soon as you heard that one being thrown around.

Cam profiling has always been done by the lift, duration, and overlap specs. Separation (which helps determine the overlap) is a more important specification lately, and rightly so with the more sophisticated fuel and control systems' sensitivity to valve event timing. I'm glad you have a good understanding of the importance of lobe design and grind centers.

Now if we could just break everyone of the "motor" habit. My car has eleven motors (headlights, blower, antenna, windows, hatch pull-down, wipers, tape player, fuel pump, and the all-important starter) but only one engine. I'd hate to have to drive a car without an engine.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

fun Pain

vader i couldn't of said it better. but the tape deck part is a little of. Do they still make tapes....hehe

MIKES 88GTA

Could yall explainthe3/4 race cam to me?
Where did that come from anyway,my dad bought a 67 Z-28 new with some dealer mods on it, he said it came with 4.11 gears a 4spd muncie,high rise intake,3/4 race cam?),
and afew other things that didn't come standard equipment.Any idea what it was?
He bought it in california new but cant remember the dealer.
I've seen the 3/4 cam advertised in a Summit before, is it an old school thing or what?

AlkyIROC

It's just bad terminology. 3/4 race cam is right up there with "cheater slicks" and "stall converter".

Another bad one I hear all the time is "gas pedel" If the engine is diesel or propane or any other fuel then it's not a gas pedel. More correctly it's an accellerator pedel. Want to totally confuse a parts salesman. Go buy an air filter and ask for a backfire flame arrester.

[This message has been edited by Stephen 87 IROC (edited September 27, 2000).]

Jim85IROC

iTrader: (2)

I think I've told everybody the story in the past about the ******* that started telling me all about his 500hp small block in his malibu. He had a 3/4 race cam. I told him that I chose a 7/8 race cam just for the extra top end

I told my father about it and he jumped all over me. he said that back in his day they didn't know all about cam specs and they just referred to a specific camshaft style (i'm guessing a fairly radical cam to most of today's standards) as a 3/4 race cam. I dunno. Still sounds totally stupid to me.

------------------
The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
"I didn't know a bored out Ford could go so slow" -Shenandoah