[Shiny]

Thanks again Jay..

[Formulas]

I cc'ed 1969 350 2bbl heads right at 80 and 1970 #11 heads at 85 and subsequent years the combustion chambers increased to the 6x4's nominal 92-94 cc so the trend was bigger chambers almost every year until a certain point

With near 9.1 compression 350P the 2800 cam acts like a mainstream GM standard 4bbl cam driving manners
Next is the 2801 with a slight loss of low end with a slight increase of top end compared to 2800
Then the 068 with a very noticeable loss of low end and a nice increase of top end power compared to 2801

2801 is the biggest I would go with a totally stock P350 car anything bigger can run just fine but would need other tweaking to get the most of it
IE more compression more gear and a torque converter, funny how you have to do the same thing with bigger engines as well when you get to a certain cam point the smaller the engine the sooner

[Shiny]

My takeaways... let me know if I miss-state, misinterpret or just don't get it:

- OP can gain a little with his 46 heads by changing cam but will be more significant in combination with a 4-bbl and dual exh

- 068 cam may be too much

- "Best" cam for a low-CR 350 (< ~8) is predicted by pastry chef's simulations to be something like:

Ultradyne hyd flat.

H11
266 @ .0045
211 @ .050
123 @ .200

112 LSA - 108 IC

0.441 valve lift with 1.5 rocker.

2800 and similar are reasonable choices

- Significant increases in hp/tq require higher CR.. different heads

- All of this applies to any 350 from 1970 to 1977... the differences in CR and power are relatively small across these designs


I found this comparison of 1971 Net and Gross HP ratings online, supposedly from Pontiac:

1971 Pontiac

350 V8
gross hp/torque 250/350
net hp/torque 180/285

400 V8
gross hp/torque 265/400
net hp/torque 205/335

400 V8
gross hp/torque 300/400
net hp/torque 255/340

455 V8
gross hp/torque 325/455
net hp/torque 260/380

[Stan Weiss]

From Ford on the difference in dyno correction factors. Almost all SuperFlow dyno sheets will use J607.

Stan

[Sirrotica]

FWIW, the 4bbl intake is much more efficient than the 2bbl is too, it alone will help efficiency, not to mention the increased flow of adding a carb with more venturi area.

In a dirt track car that required cast iron intake and exhaust, as well as a 2 bbl carb, we found that the 4bbl intake adapted to a 2 bbl always ran much better than factory issue 2 bbl intake, I'm theorizing that the larger plenum volume helps too over the much smaller 2bbl plenum. So in addition of less restriction of going to a 4 bbl carb, the intake is a much better design.

[formula kid]

If you would like to use the suggestion that H-O racing made your stock 46 heads have 2.11 intake and 1.66 exhaust valves and all 1974 heads have screw in studs. Remove the the rockers on the exhaust valves and replace with 1.65 to 1. This can be done on any 1974 Pontiac engine since all had 1.66 exhaust valves except the SD-455 still had 1.77. That will do 2 things, it will give the cam more lift and more exhaust duration with out having to change cams. That all make the 1.66 exhaust perform more like a 1.77 exhaust.

[Green Hornet]

Originally Posted by formula kid

If you would like to use the suggestion that H-O racing made your stock 46 heads have 2.11 intake and 1.66 exhaust valves and all 1974 heads have screw in studs. Remove the the rockers on the exhaust valves and replace with 1.65 to 1. This can be done on any 1974 Pontiac engine since all had 1.66 exhaust valves except the SD-455 still had 1.77. That will do 2 things, it will give the cam more lift and more exhaust duration with out having to change cams. That all make the 1.66 exhaust perform more like a 1.77 exhaust.

I forgot about HO's performance build commendations in the front of their book.......Good tip..

[Jay S]

The 46 heads that I know of all had 1.96 valves from the factory, not 2.11. I know the 46s predecessor the 4C with a 2bbl had pressed in studs. Seems like I remember not all 46 heads were screw in, for sure the 46 heads for the 350 4bbl used in the GTO were screw in studs. Sometimes you don’t know for sure until you get into the engine.

You could swap out the stock rockers for 1.65s, but honestly the 2 bbl cam grinds really do not have enough lobe lift to see much for gains from a bigger rocker ratio swap. It certainly won’t hurt, to me though Imho it is a little on the side of recreational wrenching, that little cam will only be barely .4” max lift after the rocker swap. If you got that far into the engine I would change cams.

[pastry_chef]

Originally Posted by Shiny

Is the inexpensive Desktop Dyno software worth buying to gain more understanding?

I think the cheap one hides much valuable stuff, like gas speed / pressures / mass flow. Wait until you are compelled for more.

Bang for the buck, I'd recommend reading a great deal.

This has wide topic coverage including engine cycles and valve event interactions.
https://www.amazon.com/Practical-Eng...dp/1613255241/

Absorb information from the best of the best, like George.
https://www.starracing.com/about-us

George - In Depth Cam Timing
https://www.youtube.com/watch?v=SWk4o6pYMcw

David Vizard channel is a great source.
https://www.youtube.com/user/marvingvx1/videos

I suggest reading from many sources and forums. Speed-talk.com is great, paid (Hot Pass) members can listen to the interview library - https://www.speed-talk.com/forum/viewforum.php?f=47

That will keep you busy for a bit.

[Shiny]

Thanks for taking the time to share that reading/watching list.