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.

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.

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.

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.

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/

I don't think many had good luck with Straub's cams in marine engines. What does Jim suggest you run?

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.

Pick something and try it

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 ?

Already have. My purpose of the thread was to discuss the reverse split. Good, bad, indifferent.

From my limited experience, 5 different cams, 3 different motors, it didn't work as well as a larger split toward the exhaust. Maybe yours will be different, good luck.

just remember,their dyno sessions are already suspect.
as others have said,reverse cams w/ most heads don't work well.
way back in 1987,did a single turbo 355,cam 244,244,,made 700hp,people kept telling me it wouldn't work,,surprise.most turbo cams I do are intake,intake + 4.

Ok sounds like it just plain ol sucks regardless!

a long time ago,cslob had a motor at scogg and dickey,,I called and talked to them,said,cam made some power,tuning it was a pita,,pulled out the cam and put in a proper normal split cam and made a whole lot more power.think around then is when cfm and I became friends.:D

Yup, after the 6th or 7th tuning disaster I dug up lobe specs and got .006” thru .200”s and wallah. I have most of those cams somewhere in my computer.
Helped a few bigger engine builders and carb pro’s figure out what their engine tuning disasters where from.

Bad news: lots of oeople and builders lost lots of time and money.

Good news, found out what wacko cam spec’s did to motors.

I did a little research on over weekend and ya kinda real hit and miss. Mostly miss but hey gotta give some credit for trying especially back in the day. Kind of what I gather works in the select few. Not exclusive to just the BBC family. It just threw me back a little when I got the recommendation of. I didn't really agree with any but what do I know. 😖

I was told by my motor guy, who is also a boat enthusiast, that a single pattern cam does really well if the peak RPM is moderate as in a not crazy marine application. With the real benefit being a bump in low and middle RPM output.

Single pattern was my first 383 build in high school. That was even with the old camel back double hump closed chamber heads. 292 magnum cam. 435 hp at the time in a 73 Z28 was rockin.

Ha yes. I don't know why I typed Ultradyne

SB don’t miss much. 😂. You can pretty much spot out a Harold B lobe from one company to another. He was a legend!!!

Did you compare it to anything else ?

Because probably Ultradyne lobes. :)
Bullet bought the Ultradyne lobes when it folded.

So.....You can get Ultradyne lobes, just have to buy from Bullet.

Don’t worry, you didn’t have a brain fart. :)

Getrdun, if you ever want a talk from a serious scholar of retarded cam lobe pickings, I’d be happy to condense 10yrs of them into a shorter phone call. PM me sometime with # and availability and we’ll see if we can trade sone knowledge, hardships, and s chuckle.