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Site Admin |
Joined: Thu Feb 03, 2005 1:04 pm Posts: 185
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Hi Jack, The orignial Jets were/are designed to have a short parallel section. When they get drilled out beyond their original value the parallel section becomes the whole length of the jet which makes the jet more restrictive so you only get 90 - 95% of total flow.
The newer jets are desinged the same way but to allow an even greater overall flow capability they have an even shorter parallel section which has caused them to very slightly 'over flow'.
The problem isn't really that they flow more than they're supposed to (eg @ 200 bhp they might actually flow 206 bhp @ 950 psi - so not a big difference). The problem is the difference between the two. For example an old 400 jet might flow 186 bhp where a new 400 jet might flow 206 bhp. That's a 20 bhp difference which may cause a problem for a highly tuned system.
Bascially, if your changing from older style jets to the new larger style (This only applies to jets over 300 BTW) then be aware that you might need to up your fueling a little because your old jets were slightly 'under flowing'.
_________________ Regards,
Ant
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