ez2cdave

Guys,

I have a question . . .

Typically, the Torque Band or Peak HP moves about 500 RPM +/-, for each 10 degrees change in Duration in a motor of a given displacement.

QUESTION: How much do the "effective" Cam Specs vary as displacement changes and what specific "adjustments" are required to put the cam back "on-spec" for any given displacement ?

EXAMPLE: A cam for a 350 motor is used in a 427 stroker motor . . .

Obviously, the cam will be a lot "milder" in the larger motor. The object is to be able to "readjust" the Lift, Duration, Lobe Separation, Valve Timing Events, & Overlap to "square up" the Dyno Sheet to produce the same performance curve in the 427 as it would in the 350, but with the numbers "bumped up" on the sheet due to the higher torque produced by the larger cubic inch displacement motor.

THOUGHT & IDEAS ???

This way, specs for custom camshafts could easily be determined by folks without having to deal with "salesmen" at companies or making the wrong choice of cams for their vehicles !

Dav

ez2cdave

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Patrick G

iTrader: (14)

Lots of cam companies use 8-10 degrees of duration increase for every 50 ci increase in displacement. So if you have a cam optimized for a 346, a 427 is going to want a cam that is 13-16 degrees bigger. This is generally speaking of course. Head flow and airspeed demands will be different in a bigger motor. The heads will need to keep up with the displacement increases. Intake manifold runner length and CSA will skew the numbers too.

ez2cdave

************************************************** *******
Hello, Patrick,

I am trying to get a handle on cam specs for the following motor combination (below). . . 1995 Pontiac Firebird Formula

Originally, I was considering a LINGENFELTER GT-11 but don't think it is aggressive enough in a 427 motor . . . The goal is a minimum 500 RWHP and 500 RWTQ in a smooth idling, mild-mannered daily-driver, at least until the "hammer" is dropped !

( Goal is a BROAD, FLAT Torque Curve with 6000 - 6500 RPM max. / 4L85E transmission (rear gears & converter are TBD ). . . 600 ft/lb +/- flywheel torque / 600 HP +/- @ flywheel . . . SMOOTH to VERY MILD IDLE with less than 40 kpa MAP @ idle of 950 RPM or less )

Basic Engine Components:

LS7 block (4.125" bore) ... CNC LS3 cylinder heads w/68-70cc chambers (2.165 hollow-stem intake valves / 1.59" sodium-filled LS9 exhaust valves )... Callies Dragonslayer 4340 forged crank (4.000" stroke) ... Callies 4340 H-Beam rods (6.125") . . . MAHLE coated pistons (11:1 CR) ... Comp Cams Ultra Pro Magnum Roller Rockers (1.8:1 ratio - Chrome Moly) ... etc, etc, etc.

Head Flow Numbers: (CFM)

LIFT INT EXH
----------------------------
.200 153 118
.300 225 180
.400 280 201
.500 324 217
.600 350 230
.650 355 236

Dave

cam

iTrader: (9)

Im a pretty simple minded fellow so I'd go at this quite simply as a guesstimater as there are a lot of different factors that would have to play to make this comparo sound but this should be fairly close.

Seeing as lift and duration is individual per cyl you need a multiplier per CID to get a cam with the same behaviors on a larger displacement engine. I'd take the cam that you like ( Cam1 ) for the small displacement engine ( engine1 ) and calculate out the volume for each cyl that the Cam1 engine has. Then I'd calculate out the cyl volume of the new engine and cross multiply Cam1/engine1cyldisplacement against x/engine2cyldisplacement to find your multiplier ( x ) then multiply x to the events of Cam1 and it would probably be close to the same behaviors and power per cubic inch ratio as Cam1 is with engine1 providing the heads/intake/exhaust are all the same.

If they are not this gets a hella lot more complicated. I'd have to compare the flow numbers of the heads from engine1 to engine2 in a similar fashion to above method. But again I'd cross reference to factor out the difference and multiply that as a percentage to Cam2. Apply to intake differences, exhaust, etc etc as I said complicated

I know thats a bit jumbled but something close to that should suffice. If I lost you then forget it and get a cam spec'd

In fact why dont you just click this link from PatrickG's sig right here

here.


Good luck

ringram

David Vizard recons the square root of the difference in cubes.
(ie) 100 cubes more = 10* more duration.
Seemed about right to be when going from 346 to 440

cam

iTrader: (9)

HA! Even simpler and easier! You'd end up with about the same percentage either way but thats a MUCH faster way of calculating.

ez2cdave

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