Collector extensions/ tuning/ results- B.B. strockers day- 5

Anyone have data on header extensions / tuning/ results for strockers in 511/ 650hp and up range?
Best methods for tuning other than chassis dyno?

Thanks

Not all motors need the exact same thing on collector length, HP, weather, track altitude, traction, header size and design and many other things can and will influence that
One of the old tricks was to use a crayon and make a mark along the entire length of the collector and see where the crayon melted and cut the collector off EITHER (CRS)1 to 2 inches behind or in front of that place
The time slip will tell you for that day also what works best, it wouldn't hurt to have several different sets with 6,12 and 18 inch lengths to keep in the trailer for future testing

When I was working in the exhaust lab at Chrysler
I spent a couple of weeks testing that.. the crayon
is WAY old school and was off by a lot.. start with
the best engine tune you can get.. then start with a
collector in the 17" range then start cutting it off
in 1/2" sections.. in most BB engines it should come
in at about 16" for peak power.. you can start longer
if you want.. the reason the crayon didnt work was the
tune started way off when they started on max torque

Mike, where are you measuring from as a starting point to get 17" total length on the collector length? I have always been told to measure from where the 4 pipes end in the collector, but wasnt sure that to be correct.

At the end of the 4 tubes

Ok thanks.

PipeMax is a handy program for figuring that stuff out and it doesn't cost too much. PipeMax also gives pretty good dyno predictions and it will help you with cam selection and carb sizing and stuff like that.

Typically you'll want 1 7/8 or 2 inch tubes about 32 inches long with an 18 inch collector but it varies depending on the specific combination.

Pipe max does give alot of answers, but i'm just not sure what percent efficiency to put in the box. Usually just put 100%, but not sure thats the correct answer.

I use pipemax alot.. it has lots of good data

I use pipemax as well. To calculate volmetric effencey, if you have head flow numbers, fill in all the blanks on thwe engine specs, and then go to calculate volmetric effency and put in your flow numbers, it will then figure it for you.

Didnt know that. Thank you

Let me throw in a dyno test result on theory, the first motor I dyno tested was a stock stroke 413 M.W. pump gas motor with the stock unported 1962 M.W. heads with all new seats and stock size replacement valves, same heads, intake and carbs. as on all the production 1963 M.W. motors.
The testing was done at Pettis Performance back in the mid 1990s on their new DTS engine dyno.
We started off using a set of Hooker 1 7/8 diameter 42 inch long primary pipes A body fenderwell headers with the 3.5 inch collector dumping into a five inch dyno exhaust pipe straight into the outside air, no muffling. We made several pulls after the cam breaking in and several more different pulls testing ignition timing, valve lash and maybe some jetting, this was long before O2 wide ban sensors so we where using EGT readings and BSFC as our tuning aids.
Bob Pettis made up a new set of dyno headers while we , his Son Jason and I, where doing this testing at night after I got off from work. He made his dyno headers with 2 1/4 primary pipes 25 inch long and dumped them into a 4.0 inch collector Jason and I talked about the potential loss of HP and torque on this 426 C.I. low compression(9.4to1) pump gas street motor from these large headers, those stupid parts, that motor and headers, fool both of us It picked up the average HP and torque noticeably
Theory is one thing, real world is another thing, so test, test and test some more with a open mind and look hard at all the results

I actually tested this on my car last fall and have track results. This was the only change that i made on the car besides shock tuning and jetting changes. But i have corrected times to compare the results. I ran at the same track in the same month, but 1 year apart. Track day 1 was 10/6/16 when i was running a 13” collector extension. Track day 2 was exactly 1 year later on 10/6/17 when i made a new 18” extension the same 3-1/2” dia. The car is a 68 charger with a 505 440 based stroker. 10.4:1 comp. with edelbrock rpm heads with std port opening. Just cleaned up and polished with a good comp valve job. Comp cams solid flat cam with .640 and .620” with 262 and 264 @.050”. Victor single plane with a 2 circuit 1050 dom.

The results:
10/6/16
10.817 @128.42. Corrected time

10/6/17
10.575 @129.42 corrected time.

Granted, this is a 4 speed car and the e.t. difference cam be partially attributed to me getting more comfortable powershifting the car. I only get out about twice a year up until now.
Just wanted to add my results for you to see. It looks like the car liked the longer extensions.