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Reverse Split Cams

Old 02-26-2021, 09:19 AM
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Default Reverse Split Cams

I'm just curious why we don't hear about more reverse split cams with today superior flowing exhaust. I read somewhere years ago a 75 % I/E ratio is the magic number for single patern or even reverse split in some cases. 80/85% + - reverse split was proven to make more power almost every time. (More intake duration than exhaust). The deg can vary depending on efficiency. Let's just use NA builds for example to keep it simple. Forced induction etc with excessive heat to exhaust doesn't apply. Restricted exhaust of any kind will demand or need addition duration/time which makes complete sense. Just as poor exhaust ports will. Wet exhaust would even play a part. Several factors...

Just kind of an interesting topic that I at least don't hear of or read about often. Look at all the old school shelf grinds out there that worked well with GM heads however had 10-14 deg split. You run across a cam with say 260/255-670/670??? Or even much greater like 270/255??? Custom grinds yes but you won't get many who actually tell you that or spec a cam out like such. Anyway something to ponder on. Once again I get every build and make up are different however there are a ton of 454-540 extremely similar builds that this would apply.

This is nothing new just not discussed much. I really respect the individuals who not just talk about it but proof it. After talking to many cam grinders I had only one who spec'd out with more intake duration than exhaust (reverse split). All others were a 4 to 8 deg split and they all got the same exact info on build specs and application.



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Old 02-26-2021, 01:52 PM
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The only cams I know of with a larger intake were used in turbo applications, and I believe even they moved away from it. I tried a 4 degree spit with Big Duke heads and lost RPM over the 8 degree split. Didn't gain anything, anywhere.
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Old 02-26-2021, 05:29 PM
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Usually adding more exhaust duration helps make power past peak, while lowering actual peak # just a tad. This (making decent power past peak vs dropping quickly) is important for many vehicles and many types of racing.
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Old 02-26-2021, 06:13 PM
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Originally Posted by GPM View Post
The only cams I know of with a larger intake were used in turbo applications, and I believe even they moved away from it. I tried a 4 degree spit with Big Duke heads and lost RPM over the 8 degree split. Didn't gain anything, anywhere.
One of my friends had a well known ford guru grind him a custom turbo cam 10-15 years ago. It had less duration on the exhaust. It was a dud. He swapped the cam out for one that he picked. Engine picked up a lot of power. I can't remember how much off the top of my head, but a decent gain.

The thought years ago on turbos was less ex duration to spool the turbo. Didn't work well for him.
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Old 02-26-2021, 07:13 PM
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I just did a google search on the subject. Is a bit interesting! Turns out Chris Straub was one who did quite a bit of testing. I'm certainly not trying to convince anyone just find it interesting. Btw Its the Internet so reader beware.

https://www.chevelles.com/threads/af...mp-gas.596529/

Last edited by getrdunn; 02-26-2021 at 07:21 PM. Reason: Added link
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Old 02-26-2021, 10:33 PM
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I don't think many had good luck with Straub's cams in marine engines. What does Jim suggest you run?
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Old 02-26-2021, 11:37 PM
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Jim-The comp HUC lobes. Never really discussed split just duration which pretty much dictates max lift. I rarely take the time to call and talk to any tech let alone a custom cam designer or cam company but surprisingly how similar they all came in with specs with one exception which brought me to start the thread. Guy uses both comp and ultradyne lobe profiles (No newbie and not Straub) Not much outside the norm lately so thought I'd throw it out there.

I've never had any direct dealings with CS however do believe he's pretty knowledgeable and contributes a lot to the HP community in general.
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Old 02-27-2021, 08:55 AM
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Pick something and try it
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Old 02-27-2021, 09:32 AM
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If you have the time, call Billy Carrol, AKA Billy Boats. The guy knows his stuff and all his cams come from Ultradyne. If I remember right, he bought Ritchie Zuls shop and Ritchie still helps out. When I bought my cams from him for my 572's, they were $15 less per cam than an off the shelf Crane cam. If you need/want his number, I can send it to you.
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Old 02-27-2021, 10:45 PM
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Originally Posted by endeavour32 View Post
If you have the time, call Billy Carrol, AKA Billy Boats. The guy knows his stuff and all his cams come from Ultradyne. If I remember right, he bought Ritchie Zuls shop and Ritchie still helps out. When I bought my cams from him for my 572's, they were $15 less per cam than an off the shelf Crane cam. If you need/want his number, I can send it to you.
Bullet Cams ?
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