Author Topic: 17056200 and dyno time.  (Read 147 times)

Offline 68rs/ss

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17056200 and dyno time.
« on: November 17, 2021, 07:07:04 PM »
Good Day, Just looking for suggestions on what to have to be prepared for my first dyno tune with my fresh BBC. I will be using the carb above which has been rebuilt using Cliff's kit, guidance and book suggestions. I would like to have a good variety of rods, hangers, and other tuning parts for the carb. Was wondering if the secondary hangers (using a "P" hanger) have much effect on richening up the secondary side or are changing rods a better option. Right now there are DR rods installed. I have lots of spare DR rods and was wondering if I should turn down those and by how much. I do have a small lathe.
Using #46 rods from Cliff and 79 jets. How many jet sizes can I go up or down and still use the same rods.
Fairly expensive for a day of tuning and want to be sure I have everything I might need.
Thanks Phil

Online Cliff Ruggles

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Re: 17056200 and dyno time.
« Reply #1 on: November 18, 2021, 01:53:48 AM »
All dyno tuning is done on the secondary side of the carburetor.  If you have the capabilities I'd turn down a set of rods from the DR cores with the same tip length and included angle leading to the tips.  No need to split hairs but I'd do a set with .040" tips, .045", .050", and .055".  That should be enough to get thru the dyno runs and dial things in at WOT.

Primary side tuning is done once the engine is placed in service, vacuum advance hooked up, engine fully heat soaked, etc using the APT system........Cliff

Offline 68rs/ss

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Re: 17056200 and dyno time.
« Reply #2 on: November 18, 2021, 09:06:56 AM »
Sounds good. Will attempt to turn a few sets of secondary rods.

So, guessing the hangers do not have a significant effect on the dyno other than making a smooth transition to full throttle runs.
Thanks for the input. Looking forward to some fun time at the shop. Expect to learn from this as well.
Phil

Online Cliff Ruggles

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Re: 17056200 and dyno time.
« Reply #3 on: November 19, 2021, 06:27:25 AM »
Correct.  Once you find a rod that works with one hanger machining secondary rods from the same cores with long tips on them eliminates the need to play with hangers for WOT tuning.

In contrast, IF you are using factory rods you can end up all over the "map" at WOT simply because of tip length, upper section diameter/taper, and the included angle leading to the tips. 

Over the years I've seen folks tune with various rods and swapping hangers out at the same time.  Complicated and confusing in comparison to using customer machined rods from the same cores.....IMHO.....