[mattgouras]

Just playing around with a copy of desktop dyno. Thought I would start by plugging in specs for the 1969 428 that Pontiac rated at 360 horsepower. (066 cam, 46 heads, log manifolds, roughly 10-1 compression)
Desktop dyno says that is worth 244 horsepower at 3500 rpm. Torque is 431 at 2000 rpm.
Got the head and cam profiles from: http://ronspontiacpage.com/indexes/index.html
So did Pontiac overrate these motors by more than 100 horsepower, or am I missing something with DD?

[63Banshee]

Can you post a screen capture of the DD output?

[mattgouras]

I'll try

[mattgouras]

Screen capture:

[RAIV55]

Out of curiousity I plugged your numbers into Engine Jr. and came up with 299@4050 and tq 440@3100

[Pete D]

What are the flow numbers you are using for the heads?

[Will]

Consider that in the '60s most engines were rated with no engine driven accessories, possibly not even the water pump being turned, and with headers and open exhaust. Also, the standard temp and pressure the dyno was corrected for were different.

Still, using the flow numbers I recall (which may be inaccurate) for stock small valve heads (190/150 cfm @ .500"/28") and an intake port volume of 150cc this is what I came up with replicating '60s dyno testing conditons:

[mattgouras]

Thanks, Will. That's interesting.
The 324 horsepower that you got is closer to the 360 Pontiac claimed. But the engine they put in the car, which of course has to turn accesories and push exhaust through log manifolds, comes out roughly 100 horsepower less than they claimed! That's quite a bit less, needless to say.

[mattgouras]

Pete D,
I got the facotry cam profiles and 46 small-valve head profiles from that Web site I put in the above post.
I think he has 'em flowing 181 on the intake side and 125 on the exhaust side. I have no idea if that is really correct, though.
But it appears to dovetail with results from here:
http://www.wallaceracing.com/ultimateflow.htm

[Tempest68]

I think my numbers are underrated based on factory 455 h.o. numbers, but i dont know if it considers accessories robbing power on the sim.

[Tempest68]

of course, Im not sure too sure on factory build specs (parts, etc), so i guess i cant compare too much.

[Jack Gifford]

Matt- Something's not right with your input. How about cam specs- only 200/210 degrees duration @ .050"? When entering head-flow data, did you enter the correct pressure differential (12"/25"/28"/whatever)?

I just noticed- cam specs are really messed up- almost -18 degrees of overlap (that's NEGATIVE overlap!). That's like an old stationary engine from around 1910 intended to make best torque at under 1,000 RPM.

[mattgouras]

Thanks Pontiac Jack. Appears the source files I imported for the Pontiac cam numbers are not correct. I'll input the numbers from scratch and see what I get.

[formulabird428]

i don't know the accurate specs of the 066 cam, but I did a simulation (DD 2003) of a 428, 10.25 compression, #46 heads (202/150), stock exhaust, dual plane, 800cfm.

315hp @ 3500rpm, 451 ft-lb @ 2500rpm with comp cams #51-206-4.

281 hp @3500rpm, 458 ft-lb @2000rpm with comp cams #51-229-3.

I came across these specs, (either 066 or 067 cam?):

273/282 advertised, 197/206 @ .050", 112 separation, 107 icl, .407/.407 lift. With that camshaft...desktop dyno claims...

271 hp @ 3500rpm, 448 ft-lb @ 2000rpm.

[mattgouras]

271, eh? Did Pontiac really overate these motors by that much?

[mchell]

all the manufacturer's overrated everything before the 1972 net HP ratings........what would you have purchased, a lowly 250HP(real HP) Pontiac or a Mighty 425HP(inflated) Hemi????

[leecorrell]

Just making conversation here, because I have no real first hand knowledge of this stuff, but... Several of the Pontiac history books that I have say that Pontiac very frequently under-rated their engines hp output especially in the late 60's because of GM's limits on hp to weight ratios.

[Jack Gifford]

Originally Posted by mattgouras

... Did Pontiac really overate these motors by that much?

Hey, we're only talking numbers from a simulator here- no reason to rush to such a conclusion. Don't get me wrong- I use Dyno2000 a lot- but it's not a physical dynamometer.

[Will]

Originally Posted by leecorrell

Just making conversation here, because I have no real first hand knowledge of this stuff, but... Several of the Pontiac history books that I have say that Pontiac very frequently under-rated their engines hp output especially in the late 60's because of GM's limits on hp to weight ratios.

Yes, on the high performance engines. A small-valve headed 428 intended for use in a land yacht would not have been under-rated like that, though may have been over-rated for marketing purposes.

[uneasyrider]

HOLD THE PHONE!! I watched "American Muscle Car" and a stock Hemi is 800 and somthing horsepower! LOL! And JC is coming to my house for dinner.

Originally Posted by mchell

all the manufacturer's overrated everything before the 1972 net HP ratings........what would you have purchased, a lowly 250HP(real HP) Pontiac or a Mighty 425HP(inflated) Hemi????