Redoing 400, need help
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Joined: Dec 2002
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From: chicago burbs
108* LSA is hardly a race cam by itself, a 108* will run much 'sportier' than a 114*
LSA plays a big role in how much valve overlap a grind will have, narrow LSA = more overlap... wide LSA = less overlap
in general, more overlap = lower dynamic compression... less overlap = higher dynamic compression
dynamic compression relates to actual cylinder pressures and how much octane an engine needs to not ping or run in detonation, and how much ignition advance the engine will tolerate
LSA plays a big role in how much valve overlap a grind will have, narrow LSA = more overlap... wide LSA = less overlap
in general, more overlap = lower dynamic compression... less overlap = higher dynamic compression
dynamic compression relates to actual cylinder pressures and how much octane an engine needs to not ping or run in detonation, and how much ignition advance the engine will tolerate
Senior User
Joined: Sep 2007
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Thanks GClark, I wasnt going to go into the science behind it but what you said is pretty much spot on. Its been my experience and in talking to others that for whatever reason canted valve motors tend to like the wider LSA, even on performance builds. My guess is that it has something to do with valve train geometry and the airflow path in and out of the cylinder. But I cannot say for sure on that.
Postmaster
Joined: Dec 2008
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From: Southern Oregon Coast
I believe the cam the OP is referring to is the Summit SUM-5201.
Summit recommends using Comp Cams 972-16 valve springs with this cam.
I was thinking of running this cam myself so, I asked them for the spring recommendation...
Summit recommends using Comp Cams 972-16 valve springs with this cam.
I was thinking of running this cam myself so, I asked them for the spring recommendation...
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Posting Guru
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From: Norton, MA
To Furyus1, the engine has been done for about a month now (and although my transmission destroyed itself almost as soon as I first hit the gas), and the .509/.509 lift cam worked great, had to mess with the timing some, but when I got it right the thing rips. And unless they've added them, I ended up calling summit too, and asking which valve springs to use, and they recommended those to me, but said they no longer carried them. I ended up getting some just slightly more aggressive ones from JEGS, and the whole setup works great. The JEGS part number for the springs to match that .509 is 249-972-16. The retainers and locks for me were also tricky, because my exhaust valves were 4 groove. Is this how all 400 heads were made?
AleX
AleX
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From: Southern Oregon Coast
The Jegs 249-972-16 is the Comp Cams 972-16 spring...
The exhaust valves on my 400 are single-groove, but they are not original...
Autozone sells 4-groove valves for the 400...
I've found valves in both single-groove and 4-groove varieties that interchange between the 351C/351M/400... I've found that, to make sure to get single-groove, look for valves for '78-'79 351M/400...
I've ordered a set of single-groove Cleveland valves from Tim Meyer for the set of 2V heads I plan on putting on my 400...
The exhaust valves on my 400 are single-groove, but they are not original...
Autozone sells 4-groove valves for the 400...
I've found valves in both single-groove and 4-groove varieties that interchange between the 351C/351M/400... I've found that, to make sure to get single-groove, look for valves for '78-'79 351M/400...
I've ordered a set of single-groove Cleveland valves from Tim Meyer for the set of 2V heads I plan on putting on my 400...
Last edited by Furyus1; Feb 17, 2010 at 04:42 PM. Reason: Added info...
