Cam for ported GT40 heads
03-10-2010, 08:05 AM
#27
5th Gear Member
Join Date: Jan 2006
Location: Puerto Rico
Posts: 3,926
.....total valve lift has nothing to do with PtV clearance, like Adder said, you need to check for PtV regardless if it cleared in another similar setup..... things are not exactly the same between engines. Real life example.... X-303 cam with 1.72 rockers = .583" lift in stock '87 block/pistons and '66 289 HO heads...... running for 16+ years.... PtV clearance?.... >.095" on both valves. Will it clear with E7/GT40 heads?.... you need to check in your setup however, that would be a waste of time and $$.BTW.... the "limit cam lift to head peak CFM results from a flow bench"........ is simply wrong.
03-10-2010, 08:39 AM
#28
4th Gear Member
Join Date: Jul 2008
Location: alabama
Posts: 1,812
Most cams are advertised with the lift using 1.6 ratio rockers, to get lift with a 1.7 divide the list lift by 1.6 then multiply by 1.7 and get lift with the 1.7.
example: .544/1.6= .340 x 1.7= .578
During overlap where the ptv issue is supposed to happen the vlv is at a % of its full lift, that is why the total lift dosent matter! (that is an iffy statement) becasue max lift make the % of lift during overlap greater!
most of the time a stock piston will allow up to a .530 lift cam to clear with no problems! the biggest issue is duration!
example: .544/1.6= .340 x 1.7= .578
During overlap where the ptv issue is supposed to happen the vlv is at a % of its full lift, that is why the total lift dosent matter! (that is an iffy statement) becasue max lift make the % of lift during overlap greater!
most of the time a stock piston will allow up to a .530 lift cam to clear with no problems! the biggest issue is duration!
03-10-2010, 04:05 PM
#30
Thread Starter
Join Date: Mar 2010
Location: Michigan
Posts: 18
I completely understand the CHECK PTV- I guess the point I'm trying to make is this. The stock lower end 5.0L is pretty common, the stock GT40 heads are pretty common, and these OTS cams are pretty common. Surely someone has put these three things together, and there is someone out there that has done the research and discovered what cam(s)will work and what won't work with stock style setups. Some have learned the easy way, and some the hard way I'm sure.
But- thank you to all who have given their advice and opinions, espsecially those who have done this before and know their ****
But- thank you to all who have given their advice and opinions, espsecially those who have done this before and know their ****