Cubic inch eats up duration????

Dark_5.0 · 05-30-2007, 10:35 AM

I have an engine building book that states that every 50 cubic inches eats up 8 duration.

Can anyone explain this????

tmoss · 05-31-2007, 06:19 PM

The cubic inches grow faster than the intake valve does, so a larger engine needs the added duration to keep a good cylinder fill as it takes longer than when the valve to ci ratio is smaller.

Dark_5.0 · 05-31-2007, 08:15 PM

Quote:

Originally Posted by tmoss

The cubic inches grow faster than the intake valve does, so a larger engine needs the added duration to keep a good cylinder fill as it takes longer than when the valve to ci ratio is smaller.

After reading that it seems like it should have been obvious. I couldnt figure it out for some reason though.

That is some good info to know when making a cam choice.

05-30-2007, 10:35 AM	#1
Dark_5.0 Registered Member Join Date: Apr 2001 Location: Staging lane Posts: 4,337	Cubic inch eats up duration???? I have an engine building book that states that every 50 cubic inches eats up 8 duration. Can anyone explain this???? __________________ 92' LX-Big brakes, Lots and lots of suspension, GT40X heads, Ported cobra intake, stock cam, Vortech SC trim. 00' Lightning-Stock 88'CRX-13 second ego killer

05-31-2007, 06:19 PM	#2
tmoss Registered Member Join Date: Mar 2003 Location: Saint Louis, MO Posts: 634	Re: Cubic inch eats up duration???? The cubic inches grow faster than the intake valve does, so a larger engine needs the added duration to keep a good cylinder fill as it takes longer than when the valve to ci ratio is smaller. __________________ Tom (Torque) Moss 88Gt 5spd Vert, FLowmaster Catbacks, stock cam advanced 4° @ 108.5° ICL, NMRA prepped GT40P heads 1.85/1.55 valves and 1.7 rockers, MAC P headers Jet-Hot coated, 97 Exlporer intake (ported lower), TB and injectors. 277RWHP/330RWTQ (SAE). http://www.fastlanecars.com/

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