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Old 04-11-2021, 04:28 PM
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I read through the speed talk post’s by Vizard. A lot of good info there, but my conclusion is there is not a whole lot of info that can be moved to a d port Pontiac from his BBC info, including the 128 (??) rule, or a reverse split cams he mentions in that thread. He alluded why that is the case in his post when he was talking about head flows at the low lifts and the effect it has on the cam specs, LCA, ect. If his BBC cam tech does not allow for those changes between the platforms the cam engine combo is likely not going to run right. Especially on pump gas. I think his tech does allow for those inputs, but his basic calculators do not. One obvious input that is not correct on the 128 graph for a Pontiac is the 30 intake valve. The 30 and 45 intake valve flow different, and that 128 rule is for 45* valves.

If the engine has big exhaust flow numbers and the cam has a smaller E/I split then there is a good chance Bullet will adjusted the LCA narrower to keep the overlap where it needs to be. The biggest change is at the EVO event. That is usually what Tim at Bullet will adjust for the E/I ratio. From what I have seen, Steve C’s current cam does exactly that.

With regard to a reverse split, my suggestion on the split were more geared toward the seat timing, not really at .050” like Vizards comments on ST. We do the nearly the same thing on engines with a V series Rhoads by running more lash on the exhaust.

I think the reverse split could work in a d port 455 Pontiac, but I think it would take head work to make it work right. The 30* intakes would have to go and the bowls below the valve would need to be opened up a lot.

Better vacuum was mentioned for fuel economy. The 30* valves increase the low lift head flows a bunch, but hurt vacuum. If you were truly after economy and hp with good lift on the cam, and head flow to back it up the intakes probably need to be switched to 45* IMO. All the dyno tests I have looked at with decent heads and cam the 30* intake hurt the tq at very low rpm when compared to a 45 in the same engine. But once the 30* start working they can turn the engine into a fire breathing tq monster. Problem is though that can also create some major issues on pump gas. Especially if the cam is small.

I have probably ran some reverse splits. I can’t think of to many other than from the factory cams like IHC used on there v8. Those big reverse splits can be difficult to tune on pump gas. I know with just a slight advance the IHC V8’s have to be run on higher octane gas. We have several old IHC trucks and pickups. I have done a lot of single patterns in Pontiacs that ran great, I have a hard time picturing the reverse split working very well on a d port. By the time the cam would be big enough to manage the compression the idle would be getting a bit snarly.


Last edited by Jay S; 04-11-2021 at 04:59 PM. Reason: Edit
  #82  
Old 04-11-2021, 04:35 PM
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Regarding reverse split concept - member Andy / Torquewar
http://forums.maxperformanceinc.com/...=813621&page=3

A bit interesting and a break from what is traditionally seen.

Quote:
Cam is a custom Inverted radius hyd grind . 400 lobe 249 /233 110 LSA /107. Using Howard's hyd lifters.
This combo has 1:65s on intake and 1:5s exh. Tried 1:6s on ex for a test and lost 22 hp.

  #83  
Old 04-11-2021, 04:38 PM
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Quote:
Originally Posted by Jay S View Post
I read through the speed talk post’s by Vizard. A lot of good info there, but my conclusion is there is not a whole lot of info that can be moved to a d port Pontiac from his BBC info, including the 128 rule, or his reverse split cams. He alluded why that is the case in his post when he was talking about head flows at the low lifts and the effect it has on the cam specs, LCA, ect. If his BBC cam tech does not allow for those changes between the platforms the cam engine combo is likely not going to run right. Especially on pump gas. I think his tech does allow for those inputs, but his basic calculators do not. One obvious input that is not correct on the 128 graph for a Pontiac is the 30 intake valve. The 30 and 45 intake valve flow different, and that 128 rule is for 45* valves.

If the engine has big exhaust flow numbers and the cam has a smaller E/I split then there is a good chance Bullet will adjusted the LCA narrower to keep the overlap where it needs to be. The biggest change is at the EVO event. That is usually what Tim at Bullet will adjust for the E/I ratio. From what I have seen, Steve C’s current cam does exactly that.

With regard to a reverse split, my suggestion on the split were more geared toward the seat timing, not really at .050” like Vizards comments on ST. I do the nearly the same thing on engines with a V series Rhoads by more lash on the exhaust side.

I think the reverse split could be make to work in a d port 455 Pontiac, but I think it would take head work to make it work right. The 30* intakes would have to go and the bowls below the valve would need to be opened up a lot.

Better vacuum was mentioned for fuel economy. The 30* valves increase the low head flows a bunch, but hurt vacuum. If you were truly after economy and hp had good lift on the cam with the head flow to back it up they need to be switched to 45* IMO. All the dyno tests I have looked with decent heads and cam the 30* intake hurt the tq at very low rpm when compared to a 45 in the same engine. But once they start working they can turn the engine into a fire breathing tq monster. Problem is though that can also create some major issues on pump gas. Especially if the cam is small.

I have probably ran some reverse splits. I can’t think of to many other than from the factory cams like IHC used on there v8. Those big reverse splits can be difficult to tune on pump gas. I know with just a slight advance the IHC V8’s have to be run on higher octane gas. We have several old IHC trucks and pickups. I have done a lot of single patterns in Pontiacs that ran great, I have a hard time picturing the reverse split working very well on a d port. By the time the cam would be big enough to manage the compression the idle would be getting a bit snarly.
Jay,
Do you have a link to which thread on Speed Talk about David and 128 you are talking about?

While David may have said it when talking with me, I just don't remember him talking about reverse split cams. We did talk about single pattern cam.

David has said that BBC 's should use 132.

Stan

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  #84  
Old 04-11-2021, 04:46 PM
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Quote:
Originally Posted by Stan Weiss View Post
Jay,
Do you have a link to which thread on Speed Talk about David and 128 you are talking about?

While David may have said it when talking with me, I just don't remember him talking about reverse split cams. We did talk about single pattern cam.

David has said that BBC 's should use 132.

Stan
Oops. Yes. I was thinking it was 128. The 4 degree reverse split was on the page Steve linked in one of Vizards posts.


Last edited by Jay S; 04-11-2021 at 04:58 PM. Reason: Edit
  #85  
Old 04-11-2021, 06:26 PM
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Originally Posted by Jay S View Post
Oops. Yes. I was thinking it was 128. The 4 degree reverse split was on the page Steve linked in one of Vizards posts.
Page 10 quote. Sorry Stan I miss read it as a reverse split. It was a single pattern 4 degrees bigger.
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Last edited by Jay S; 04-11-2021 at 06:31 PM. Reason: Add
  #86  
Old 04-11-2021, 08:10 PM
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I had 4 cams in my RAIV 400 when running NMCA. the 288/296 UD on a 108, the UD 304/312 on a 112(first retarded 4 degrees for more V-P then advanced like Harold said to do-ran the same to the 0.01sec), UD SFT 288/292 on a 110 and finally a Comp reverse split 292/288(? I'll look at the card) HFT on a 110. The reverse split ran the best. The 304/312 on a 112 lost little open headers to mufflers the 288/296 on the 108 picked up around 0.2 uncorked. Not dyno comparison but a lot of track runs and a consistent car some taking class record or wins in the Top Stock NMCA class.

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Old 04-11-2021, 09:22 PM
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Originally Posted by Steve C. View Post
Lee Atkinson's 455
Ultradyne, 231/239 intake / exhaust @ .050"; advertized duration 288/296 intake/ exhaust; .526" lift intake / .550" lift exhaust; 108 LSA

https://pontiacstreetperformance.com...uild45500.html

.
Lee is the one who ran the dyno sims for me. And he did need the intake closing info, and head flow etc. Funny that after multiple testing, the cam he came up with for a low CR/pump gas cam for towing is the same cam, same lobes apparently but on a much wider LSA with a little less lift. For around 8.0:1 CR, the torque was the best, vacuum was the best. Even those just simulations, there should be some value as far as comparison, especially when the simulation runs close to what real life has shown. He ran at least 15 different sims, maybe more, making adjustments in LSA, advance, difference between 1.5 and 1.65 rockers on each one. Some had a little higher peak torque/HP, but this one had about the highest torque at low rpm, and held it a little longer

Lee said his program was not necessarily 100% accurate (of course), but all the cams he has actually real life dyno tested came in close to projections, within a narrow range.

I thought the original post was specifically asking about towing, low CR and lower octane fuel. So any cam that peaked out above around 5500 rpm wasn't in consideration.

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Old 04-11-2021, 09:35 PM
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And everyone's goals are different. And low CR like 7.7: and 9.5: will change which cam is 'best' as will heads, rocker ratio, lifter choice, spring choice. There isn't enough time to test all the variables that might make one cam perform better, and even your transmission and rear axle ratio and weight of vehicle may make the 'best' dyno cam a dog. Anyone with that much money to test all the possibilities has better ways to spend it. That
's why I like Cliff's general rules of thumb.

  #89  
Old 04-11-2021, 09:47 PM
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Quote:
Originally Posted by Skip Fix View Post
I had 4 cams in my RAIV 400 when running NMCA. the 288/296 UD on a 108, the UD 304/312 on a 112(first retarded 4 degrees for more V-P then advanced like Harold said to do-ran the same to the 0.01sec), UD SFT 288/292 on a 110 and finally a Comp reverse split 292/288(? I'll look at the card) HFT on a 110. The reverse split ran the best. The 304/312 on a 112 lost little open headers to mufflers the 288/296 on the 108 picked up around 0.2 uncorked. Not dyno comparison but a lot of track runs and a consistent car some taking class record or wins in the Top Stock NMCA class.
Skip did you use race gas on that engine. Happen to notice if it changed the engine octane needs, change cylinder pressure?

Rocky Rotella flowed a friends RA 4 stock 614s. After seeing that it is not hard to imagine a reverse split working on some engines. Almost had a 90 % E/I ratio on a couple ports. Here is one of the end cylinders. The exhaust was even flowed without a pipe. This is port number 1, the second column up is .550 lift. Was pretty eye opening.

I don’t recall the OP talking about towing? But some of the towing parameters like dependability and outstanding fuel economy apply?
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  #90  
Old 04-12-2021, 08:04 AM
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"Gasp! 106 LSA for a Pontiac.
How could that be.. LMAO."

Comments like that only show that you are completely BIAS when it comes to this topic....IMHO

Couple of months ago I get a call for carb rebuild/tuning parts from a guy building a big block Chevy 454 for his truck. He says that he is raising the compression slightly and installing a 106LSA cam with the ICL down around 100 or 102 (can't remember exactly at the moment). It was also a tiny cam, around 260 advertised something seat timing.

I asked him "why"? He asks me if I have followed the DV threads and magazine articles etc about how LSA doesn't matter and how they are making 8 zillion HP running really tight LSA cams in BBC builds, etc, etc, etc. I tell him that I haven't went that direction and don't recommend it for what he is doing. He replies that it's just a "truck" engine and he wants TONS of low end power and could care less what it does past 4000rpm's.

Well guess what, it didn't work for chit. Not only does that engine NOT make nearly the power he was expecting, it pings on the highest octane pump gas he can find even with all the timing pulled out of it to a point where it doesn't want to idle or run well anyplace.

It's not a Pontiac engine but folks quickly forget that ALL of these engines are simply 8 pistons moving up and down in 8 holes so the fundamentals really don't change with them. When you use "small" cams in them and tight LSA, you can and will very quickly run into issues with making too much cylinder pressure for pump gas.

Once you get up to about 240 @ .050" and have over about 284 @ .006" seat timing it really doesn't matter what you pick for LSA. If you want a "menacing" idle pull the lobes together. If you want high vacuum production, smooth idle and a broader/flatter power curve push the lobes away from each other some. Either way it will make great power and effectively push 4000 lbs of vehicle into the 11's without much effort. You just have to decide at that point if you want to burn everyone's eyes who stands behind the car while it's idling at the Dairy Queen car cruise and if you wife will ride in it because it stinks her hair up when you stop a traffic lights!.....LOL.....

PS: if anyone is wanting a few flat cams for dyno testing I have some very lightly used ones in the back room I'll donate to the project. One is Comp 292H, may also have a XE274 back there as well.........

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  #91  
Old 04-12-2021, 09:31 AM
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Jay yes race gas for sure had to be mixed in on the 455. ON the 400 when we did dyno it no audible detonation but race gas picked up some HP on it I want to think 5-8hp.

I know John Schloe on his RAIV stocker and John Angeles on his RAIV SS car both run single patterns.

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  #92  
Old 04-12-2021, 07:05 PM
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He ran at least 15 different sims, maybe more, making adjustments in LSA, advance, difference between 1.5 and 1.65 rockers on each one.
Simulation wise usually I run 6561 different valve event combinations (9 x 9 x 9 x 9) Plus / minus 16 degrees adv duration span on intake, same for exhaust. The program displays the top 10 results. Among the 10 best normally see minor deviations in duration and centerlines.
Then I will correlate timing events to real world cam lobe scans and see if the trends continue to line up. An eye opener sometimes is how much different real cams are from the curve the computer estimates using lift, adv duration and .050 specs.

For this image the real cam is the dark.. the lighter curve the computer guessing.

My only bias is in favor of science. Lobe separation is a man-made concept. As it relates to an engines pressures and gas flows a given LSA cam has nothing in common with another of the same LSA, unless the cam is fully identical. Even valvetrain deflection will impact what events / LSA an engine favors.



Last edited by pastry_chef; 04-12-2021 at 08:01 PM.
  #93  
Old 04-13-2021, 04:38 PM
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It is nice to see how simulations can be very close to real world results.

I should have said that Lee ran simulations of about 4-5 stock cams from various manufacturers and several different sets of lobes from Bullet/Ultradyne's master lists, in maybe 8-10 various combinations , for about 15 different cams to compare.

I eliminated a lot of them based on the rpm range they operated best in, or actually let Lee do it, and he gave me maybe the top 8 or so.

I narrowed those down to maybe 5-6 by max peak torque average torque, broad torque curve compared to rpm and by looking at overlap based on some reading about overlap and octane/detonation tendencies as I wanted to be able to use 86 octane safely. Lee went through those with the adjustments to lift, duration, adv, LSA to maximize those, Of course, he couldn't adjust the off the shelf cams, with those you are stuck with the parameters they set other than rocker ratio

My final two choices came down to the H5/H15 combo vs H15/H8, and I think the peak with the H5/H15 peaked a little lower in the rpm range, with slightly higher peak just off idle, and higher vacuum. I had also looked at overlap and went through some math after reading how overlap affects octane requirements and detonation resistance. Some of the off the shelf cams were more likely to detonate based on that.

Some of Cliff's least favorites ended up on the discard pile, but it is all subjective to what you want to accomplish. With just a different gear ratio, you can change the cruise rpm by a lot, same with overdrive

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