desktop dyno and pontiac v8s some thing wrong here....

[YeLLowBoaT]

I was sending desktop dyno to a member on ***boat.... so I desided to for a gigle to see what kind of power my motor would not make.... not sureprising a 421 was not on there so I used its sister 389( basicly .030 smaller in bore, pontiac just over bored the 389 to get a 421 it was a cost saving thing they used the same casting.).... well the funny thing is with my set up it says I will only make 231 hp so I deside to run the factory specs and see what I get.... I got a whapping 239hp now the funny thing is that from the factory they came with 390 for a 2 barrel and 410 for a 4... now I know pontiac probly bsin those #s but off by more then 100 hp I think not.....I wonder if it has to do with the fact that desktop dyno does not compute D port heads any ways just something I thought was funny. Only with the hotz-totz heads could I get it to break into the 300 mark. Just something funny I found.

[LakesOnly]

I not sureprising a 421 was not on there so I used its sister 389 (basically .030 smaller in bore, pontiac just over bored the 389 to get a 421 it was a cost saving thing they used the same casting.)..
No, not just .030" overbore but also .250" more stroke...
Pontiac
Engine.....Bore.........Stroke
389........4.0625".........3.75
400........4.12.............3.75
421........4.09375........4.00
428........4.12.............4.00
455........4.15.............4.21
Pontiac's can make some serious power...parts are scarce and expensive.
LO

[YeLLowBoaT]

I knwo about the longer strok I am just saying it was kind of funny that it could be that far off. and yes parts are way up there in price. as far has hard to find... in 65 they made 16 bonnviles with 421 4 bolt mains and a 4 barrel carb.... I got "lucky" to find one in a boat.....

[Norseman]

Could it be the difference between Gross and Net HP numbers?????

[GofastRacer]

A little FYI here. Desktop Dyno is pretty damn accurate(especially the latest version)but you have to remember it don't know anything other than the information you feed it. The list of heads are general off the shelf stuff, to get accurate readings you need to feed it actual flow numbers of your heads. The program has a "what if" feature which is cool because you can change numbers and it will give you results, so you need to be very specific on what it asks or you will not get accurate readings and that goes for all specs it asks for!.. I did a friend's motor once for the fun of it that he had dynoed and I came within 1hp and 2lbs of torque difference from the dyno sheet!..

[Sleek-Jet]

A little FYI here. Desktop Dyno is pretty damn accurate(especially the latest version)but you have to remember it don't know anything other than the information you feed it. The list of heads are general off the shelf stuff, to get accurate readings you need to feed it actual flow numbers of your heads. The program has a "what if" feature which is cool because you can change numbers and it will give you results, so you need to be very specific on what it asks or you will not get accurate readings and that goes for all specs it asks for!.. I did a friend's motor once for the fun of it that he had dynoed and I came within 1hp and 2lbs of torque difference from the dyno sheet!..
Agreed.
I've found that the head flow files are the most important in getting an accurate simulation. Try to find someone that's flowed a set of heads like you've got on your engine, or better yet, have the ones you've got flowbenched.

[rrrr]

Ah, memories. My dad bought a '65 4D Bonneville, we flew from Albuquerque to the factory in Arlington, TX to pick it up.
Thing was a monster, 428 ci and weighed about eight tons. :D
We had a shop and house in Eastern AZ, took a lot of trips between there and Albuquerque on Route 66. It was a two lane blacktop back then. I remember seeing the speedo many times waaaaay past 120 MPH. :messedup:
Showing what an old phucker I am... :sleeping: :sleeping:<----------rrrr

[Jet City]

Seems to work for me, I used flow numbers from as cast Edelbrock RPM B/RB Mopar heads, 11:1 CR, 245/255 @ .050 cam, 850 carb on dual plane and got 481hp @ 6000 and 498ft lbs @ 4500.
I agree with the others above, the program is only as accurate as the information you enter, if your not already, building accurate head air-flow files will really help, the canned cyclinder head data is crap.