LSA selection

grumpyvette · Dec 9, 2010

first I want to point out the reason the I wanted you to post the results of the additional cam selection,
( it was basically to squelch the almost universal, idea that just slapping in a longer duration cam will universally boost the average and usually peak horsepower)

OK, looking at the two cams you've obviously made some improvement with the slightly tighter LSA version, so that's the obvious choice , if your maximizing the combos potential, among the listed choices
IF you can get it ground at a reasonable cost
for the potential power gains made,
but the gains are reasonably small so it may be cost prohibitive to go that route,compared to making the standard CROWER 00471 (one of my favorite sbc cams) your choice here.
Ive built several engines with that CROWER 00471 and its always produced impressive results in street/strip 383-406 combos with at least 10.0:1 cpr

Indycars · Dec 9, 2010

OK, looking at the two cams you've obviously made some improvement with the slightly tighter LSA version, so that's the obvious choice , if your maximizing the combos potential, among the listed choices IF you can get it ground at a reasonable cost for the potential power gains made,

I probably won't go that direction with the added costs. I can search for a similar off the shelf cam, then run that in DynoSim5.

According to David Vizard I should have gone with a LSA 104, but I was trying NOT to get to far the original Crower 0471. I was concerned about making changes that would make the simulation invalid. For those reading this and want to know more about David Vizard's process for picking a cam read the following,

http://www.popularhotrodding.com/tech/0 ... index.html

Thanks for all your insight, it's greatly appreciated!!!

grumpyvette · Dec 9, 2010

"Lobe Centerline Angle Determination Chart
To use this chart, first establish the number of cubes in the INDIVIDUAL cylinder, per inch of valve diameter. To get this number, divide the engine displacement by the number of cylinders, then by the intake valve diameter. Find that number on the vertical axis, then move across to the green line. At the intersection point, drop down to the base and read off the LCA required. Because big-block Chevys have angled valves, they need to have about 2 degrees less than this chart indicates."

examples

1

lets assume your building a 383 SB chevy
383/8=47.875 round that off to 48 cubic inches per cylinder
divide that by the intake valve diam, of 2.02 and we get 23.76
using the chart and plugging in the numbers we find that about a 106 LSA is about ideal

2

lets assume your building a 540 BB chevy

540/8=67.5 round that off to 68 cubic inches per cylinder
divide that by the intake valve diam, of 2.30 and we get 29.56
using the chart and plugging in the numbers we find that about a 101 LSA is about ideal

3

lets assume your building a 283 SB chevy
283/8=35.375 round that off to 35 cubic inches per cylinder
divide that by the intake valve diam, of 2.02 and we get 17.5
using the chart and plugging in the numbers we find that about a 113 LSA is about ideal

Indycars · Dec 11, 2010

I searched thru Isky, Crane, Crower, CompCams for something with a LSA of 104 and Duration of ~280 degrees, like Vizard suggests. Below is the mildest cam I could find, it's Crower 0429 solid roller with a lift of .614 / .620 inches. If your familiar with DynoSim5.....it rates lobe acceleration by using the duration from Seat-to-Seat and at 0.050 lift, then assigns a number between 1-7, the Crower 0471 was rated 2.98 and the Crower 0429 was rated at 4.46

DynoSim5 Manual states:
Use the following guidelines to evaluate Lifter Acceleration Rates :
1.00Very Low Acceleration, Mild Street, Extended Valvetrain Life
2.00 Stock Production, OEM Camshafts
3.00 Performance OEM and Aftermarket Street Performance
4.00 Drag and Oval Track Racing, Limited Street
5.00 All-Out Racing, Very High Valvetrain Acceleration
6.00 Maximum Drag Racing, Limited Valvetrain Life
7.00 Extreme And Experimental

Looks like it would be too aggressive for the street, what do you think???

grumpyvette · Dec 11, 2010

Much of this thread has been spent discussing minor cam tuning and selection changes that will gain or cost you 5-10hp, and while its good to know, a great deal of the cams "DRIVE-ABILITY" is related to the, the engines displacement,compression ratio, and drive train factors like transmission,gearing, rear gear ratio,tire height,and car weight, since you intention is sticking that cam into a light car, with decent gearing and what Im guessing is a 2800RPM or higher stall speed converter that looks like the best choice yet!, notice that the tight 104 LSA retains a good deal of the low rpm torque curve that the wider LSA in the previous lunati cam with only a bit more duration lost......now theres little doubt the cam will have an aggressive lopey idle but I doubt that it will noticeably effect drive-ability once you reach about 3000rpm, you've got a great deal more leeway in a light car with a stiff rear gear, than if you had put the same engine in a 3500lb car
I'd also suggest getting the cam ground as a 4/7 swap version as that's a change thats also worth an additional 5-7 hp

So which cam would you pick when looking at the graph above and the specs below???

Engine Specs:
- Block: Dart SHP
- Size: 401 cu in
- Bore: 4.125â€
- Stroke: 3.750â€
- Rod Length: 6.0â€
- Heads: Brodix IK200, 70 cc Chamber
- Rockers: Full Roller - Steel
- Carb: 750 CFM
- Comp Ratio: 10~10.5 to 1
- Manifold: Dual Plane
- Exhaust: 1 5/8" Primaries, 3 1/2" Collector
- Max RPM: 6200
- Scat Forged Rotating Assembly with Mahle Flat Top Pistons

Car Specs:
- Weight: 1800 lbs
- Rear Gear: 3.7 to 1
- Tire Dia: 28 inches
- Trans: TH350 with high stall converter
- Application: High Performance Street

Indycars · Dec 11, 2010

grumpyvette said:
Much of this thread has been spent discussing minor cam tuning and selection changes that will gain or cost you 5-10hp, and while its good to know, a great deal of the cams "DRIVE-ABILITY" is related to the, the engines displacement,compression ratio, and drive train factors like transmission,gearing, rear gear ratio,tire height,and car weight, since you intention is sticking that cam into a light car, with decent gearing and what Im guessing is a 2800RPM or higher stall speed converter that looks like the best choice yet!, notice that the tight 104 LSA retains a good deal of the low rpm torque curve that the wider LSA in the previous lunati cam with only a bit more duration lost......now theres little doubt the cam will have an aggressive lopey idle but I doubt that it will noticeably effect drive-ability once you reach about 3000rpm, you've got a great deal more leeway in a light car with a stiff rear gear, than if you had put the same engine in a 3500lb car
I'd also suggest getting the cam ground as a 4/7 swap version as that's a change thats also worth an additional 5-7 hp

The cost just went up, the assembled Brodix IK200 head don't come with the valve springs required. Even the Wild Thing IK210 only goes up to .600 lift and cost another $700 from Summit.

It was interesting that NO WHERE from 1000 to 7000 RPM did the Crower 0429 ever have less torque! I don't think I can go with the extra cost when it's going to be in the $700 range.

In your experience, is it always more expensive to buy the bare heads and individual components, compared to the assembled heads??? Is it worth my time to run down the cost of the separate components.???

grumpyvette · Dec 11, 2010

grumpyvette · Dec 11, 2010

notice that although the intake duration timing changes over a 236-248 duration range for both the mild 00471, and the 00429 crower cams both the 236 and 248 duration cams have the same valve close point (.050 timing) and those cams produce similar low speed torque while the lunati cam with the wider LSA AND increased DURATION has only 243 duration with its later intake close point,it traps less cylinder volume so, thats one reason it tends to produce less low rpm torque

crower 00471 236/240 duration, intake valve closes at 44 ABDC

lunati 60113 243/252 duration, intake valve closes at 47.5 ABDC

CROWER 00429 248/250 duration, intake valve closes at 44 ABDC

Indycars · Jan 12, 2011

I was reading this thread again when I noticed the wrong terminology
on the Chart by David Vizard. I hope I have this right!!!

So I edited the chart labels to agree with our discussion about the differences in LCA and LSA. Grumpy, I thought
you should have a chart that does NOT add to the confusion. Feel free to use it !!!

grumpyvette · Jan 12, 2011

looks GREAT!
and having that change, to the correct terminology, it makes more sense!

LSA selection

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