Old 04-30-2015, 07:19 AM
My Feedback: (6)
av8tor1977's Avatar
Join Date: May 2003
Location: Tucson, AZ
Posts: 7,213
My Gallery
My Models
My Feedback

In this case, 180 does not refer to the exhaust duration. It refers to the distance between TDC and BDC; 180 degrees. Exhaust port timing is measured in degrees ATDC for the opening, and ABDC for the closing. Using the 180 in the formula I gave, results in obtaining the total exhaust duration.

(Copy and paste of post): A special note here because I know people will ask. Here’s how you find that exhaust duration:

180 – 106 = 74 degrees. 74 (from ATDC to BDC) + 74 (ABDC) = 148 total degrees the exhaust port is open. If it is easier for you, just count the total open degrees on the degree wheel.

Another copy and paste explaining exhaust total durations and effect: What I generally recommend is 150 to 155 degrees on the exhaust and 130 to 140 degrees on the intake for operation from around 7000 to 8000 rpms or a bit above.

For operation at 9000 and slightly above, 160 to 165 on the exhaust and about 150 on the intake seems to work well. Much more duration than 165 degrees on the exhaust is getting into tuned pipe area/timing.

One really should be quite familiar with engines in general and be handy with metal working and modification/fabrication skills before attempting a hop up project such as this. It is an advanced skill, and as mentioned, a mistake could be costly and frustrating .


Last edited by av8tor1977; 04-30-2015 at 07:23 AM.
av8tor1977 is offline