Thoughts on this cam?

[Berserk]

Street ans strip use. All steel el camino 71. I would like at least 700hp and peak power at 6300 or lower.

[lada ok]

There ya go Mike,

But that's 79.2 bhp /lt

[swatson454]

248/254 @ .050
105 LSA
1.8/1.7 rocker arms

[wyrmrider]

Hey Mike
Grind him the one that brother Rick ground me for the 71 454 Chevelle project, this one sounds similar
He will find nothing better
Swanton
I like the rocker ratios but the durations are sort of meaningless without knowing the lash- It's duration AT THE VALVE that's important
LCA will depend on lots of things, like exhaust and smog legal, etc

[buddy rawls]

as long as you end up at the right place...

Not with formulas.
If the formula doesn't work for all engines, and you have to add or subtract from the results, based on nothing but experience with certain types of engines, it's not sound math.

If you have a formula that works well for engine "A", but when you use it on engine "B", you have to add/subtract X degrees to the results to get it to work well, it's not a very good formula.

100% agree. An engine model is not an engine model if it doesnt work across the board. Like in my case, there was alot of data gathering and establishing curve fits. There are extremes that will not fit in the primary data range, but these are pretty extreme. It needs to run the same math for 4x4 toyota 20R or a Harley, or a BBC drag motor, or Pro Stock, or Comp Eliminator, or grocery getter.

in my case, once the engine parameters are established (cross-sections, relationships to the displaced cyl volume, etc etc) it comes down to where do you want the motor run and how broad do you want the powerband (within the constraints of the engine geometry and flow parameters).


What is this 128 formula? Is this David Vizard? Or someone else. Vizard's stuff early on (at least published books/articles), utilized a constant inlet cross-section to derive his LSA relationships. So as the motor got larger, the velocity increases and increases, essentially getting more and more inlet restricted for a given rpm that really drives the need for delayed exhaust and narrowed LSA. If you keep the relationship proportional, the end effect is different. I used this graphical relationship to demonstrate the give-take between flow/rpm/port velocity. There are no numbers, because everything is completley relative to the specific engine relationships.

[CamKing]

The Comp isn't that far off from what I would recommend
Cam# R79421A-80412-110
263/270 @.050"
.421"/.412" Lobe Lift
110 LSA

[lada ok]

sorry buddy, but that chart seems to be reversed to me, I'm so used to a clockwise direction

[buddy rawls]

sorry buddy, but that chart seems to be reversed to me, I'm so used to a clockwise direction

you lost me on that, It is clockwise direction

[JoePorting]

sorry buddy, but that chart seems to be reversed to me, I'm so used to a clockwise direction

you lost me on that, It is clockwise direction

That's a counter-clockwise direction isn't it?? Or has it been too long since I looked at a cam card.

[wyrmrider]

The Comp isn't that far off from what I would recommend
Cam# R79421A-80412-110
263/270 @.050"
.421"/.412" Lobe Lift
110 LSA

Comp cams
260/268
714/714
108 lsa

Is the comp inverse radius
asymetrical
what lash and how much does that affect
comp advertized seat timing @???
what rocker ratios?

[Adger Smith]

1.8 intake /1.7 ex Used that same cam before on low static compression combos. Had one in a River Racer Jet boat hat did well. Made over 700 HP.

[buddy rawls]

sorry buddy, but that chart seems to be reversed to me, I'm so used to a clockwise direction

I thought you all were joking, but you're serious. So, ill be serious. The chart is layed out with a degree wheel orientation, so it would have a direct relationhip to degree wheels and it wouldnt cloud the intent by being opposite. That however is very far from the reason i drafted the chart. The chart goes further than a labled degree wheel by indicating the rpm, port velocity, and exh/int relationships and how those items, at a piece part level, effect the overall picture and positioning of IO/IC/EO/EC, and the resulting centerlines (as symmetrical relationships).

If it gets to a CW or a CCW question, and i suppose it can, or has, then you would also say a degree wheel is CCW. I dont see how its even a consideration, but it could be stated that way. If you superimpose the chart on degree wheel, it rotates CW on the motor, just as a degree wheel does. That how it was layed out; so someone wouldnt say its opposite from a degree wheel. CW vs CCW was not a coinsideration, however being directly overlayable on a degree wheel was an absolute consideration, for relational purposes.

The chart was not intended to derail the thread, but throw some other items into the thread as things like LSA were being discussed in the cam specs.

[randy331]

Edit: For what it's worth, "128" plus the BBC adjustments should put the OP on a 105 LSA with his current compression ratio.

248/254 @ .050
105 LSA
1.8/1.7 rocker arms:D

The OP had a 260/268 cam picked out and you said 105* LSA, then you posted a smaller cam of 248/254 and said 105* LSA.

The LSA stays the same no mater what the duration is?

Is that how 128 works? Decide LSA first, then fill in the blanks with the rest, like IVO/IVC/EVO/EVC ?

Randy

[user-612937456]

Why 105 LSA would not this bleed excessive cylinder pressure off for 10.75:1 wouldn't 107,108 or maybe pushing it a little even 109 be better for a 540 combo thst probably will not see high enough rpm to overcome the pressure bleeding on the 105 lsa grind

[Adger Smith]

Yes, Randy. 128 is what makes the Pro Stockers run so fast. Just ask Erica....;~)
Seriously, I've always wondered why builders put in a cam that limits the RPM /power curve with heads that do match the bore/stroke of the applications RPM range. For a given Head/Rpm combination you only need what you need in overlap area. I've never seen a good Comp engine with a 105 LSA, but I have seen them with way shorter duration (than the experts call for) on longer LSA's & "real good" flowing heads. It is my opinion the LSA talk/info is way over rated. All this talk and "Expert" info makes for selling magazines and How to Books.