Apologies in advance for the long post, but I found this rather interesting. Rather than hijack the camshafts... semester 2... thread, I thought I'd start a new one here. Thanks to RYAN02SS for the link.

Be the Camshaft Expert from Popular Hot Rodding

After reading the article, it seems in contrast with the popular theory around here that you select the valve events to perform in the operating range you wish, thus leaving the LSA and overlap as a 'byproduct' of those events. I've noticed the trend to better street performance (higher DCR) through tighter LSA grinds, but what are your opinions on starting from LSA as stated, then arriving at the duration based on application?



346 ci (43.25 ci per cyl) with a 2.02 valve = 21.41 ci per inch of valve diameter. Based on the graph above, regardless of the operation range, 108 LSA would yield the best results.



After selecting the overlap desired, for my example here, a street performance cam, a range of 50* - 75* overlap should give the best results. Based on the formula above, I get a range as follows:
[(50/2)+108]*2 = 266 degrees, trend towards regular street cam
[(75/2)+108]*2 = 291 degrees, trend towards street/strip cam
In the middle of that range, 62.5 degrees overlap demands a duration of 278.5. To acheive this with a traditional split of 4 degrees, I'd want advertised durations of approximately 276/280.
So, what do you guys think?

 

Dave is not a dummy, and even though a lot of his testing was done on flat tappet 23° headed, carb motors it still applies. Problem is different motors like different things and LS motors do like things a little differently. One of the flaws of just sticking with advertised specs is that it will leave you all over the map, you could change the lobe series and drop down to a low of 215° @ .050"..... and for god sakes stop trying to pick a "traditional" split... the split changes with so many variables it's just crazy to think there is a set amount. There is a range but not a set number.

All in all my personal though is you will never get good camshaft knowledge reading a forum. If that is the case then why do guys with 400+ cube motors stick with the 242/248 cam when it's not to hard to destroy that cam in low to midrange TQ by 20 ft lbs and make the same peak numbers? (BTDT) There are just way to many variables that come into play that simple formulas can't find.

I would say that what vizzard puts in that article is a focus on other parts of the cam that are important to look at as well, namely overlap. Overlap, IVC, ICL, durations, lift, lobe area are ALL important. I have yet to see one thread on this forum intellgently talking about lift ever.... and nobody has a clue as to why.

I think what that article comes down to is the LSA connection to valve diameter and cubes.... I don't get that connection exactly. I've backtracked into cams I know work awesome and it fits and other times not at all. I've had motors of the same family fall on both sides of that line. So it's not an exact science but it's much closer than throwing a 112 LSA on everything.

P.S. I like your sig, from the quotes (Thanks BTW) to the TRex thread.

Bret

 

I guess my desire for a "traditional split" does deserve more explanation.

1) I figure I will be exhaust limited in an F-body, as duals the exit at the bumper are hardly cost effective, and the room for a zero-loss exhaust system seems hard to come by on this chassis. I refuse to run dumped duals ahead of the rear axle, its just to damn noisy inside the vehicle. I'll also probably run cats for sound attenuation and to keep the noxious fumes at bay.

2) At this point, I'm still pretty well sold on the consistant results acheived by AFR 205 heads on these cars, and their I/E ratio seems to still flavor a 4 degree exhaust split.

3) I think a 228/228 may give better low and mid range response, but considering the two points above, and that I'm not daily driving this setup, I would err with more exhaust duration.

As for lift, my thought is this: more lift = more dwell time at a range where the head is flowing more. I see that Vizard also supports that with a different arguement, stating that efficiency increases as 1/4 the valve diameter is approached at .500" and above, and shrouding becomes less of a concern. I'm not sure what the duration at .500" is on the LSK lobes selected, but I'm certain is has to be much, much more than the Extreme RPM lobes which peak at .534 and .539 at these advertised durations.

But I digress, as these points are more self-serving than they are on topic.

 

I have several observations:
First David Vizard has done a lot of excellent original and objective research over the years on automotive performance. I would really like to see an author/researcher of his caliber revisit subjects like cylinder head design and improvement, induction systems, computer controlled fuel injection and ignition systems. I would like to see this done with modern day pushrod designs like the LSX series and the new Chrysler Hemi engines.

Second, the late John Lingenfelter wrote an excellent book on modifying Gen I and II small block engines that emphasizes many of the recurring themes expressed in recent months on this forum about smaller being better and being realistic. My synopsis of John's book in this area is that the would be hot rodder needs to be brutally honest with himself about how the vehicle will be driven and the budget available to achieve reasonable goals.

Third, as someone who is older than most of the forum members at 57, I'm seeing the maturation of a number of participants in this forum regarding what they really want out of a vehicle. Just like a high-strung race horse, a car that is set up to produce 700 plus horsepower isn't very useful for transportation. Most folks really can't afford a track only vehicle with a trailer and tow vehicle plus a true daily driver and make the mortgage payment on the house.

Now, I've gone a bit afield from the thread topic of cam selection based on duration category versus intended use and the character of a cam selected by lobe separation guidelines. I apologize for this diversion . . . but it's a small apology, because I don't think that these comments are very off-topic considering hammertime's signature line quotes and SStrokerAce's comments about the quotes.

Steve

 

Ok how about this to make some guys think.... when you start running a restrive exhaust either due to the header/manifold design, cats or just the plumbing why do you think the motor wants more time to hold the exhaust valve open, and when would that be happening? Intuitively we all think it WANTS more but that's not always the case.... sometimes it depends on how much intake duration is there and the RPM range you are working in.

I agree with Steve on his point of tamer cams, and more drivable setups. There has been way too much emphisis on selling products in terms of rwhp numbers and cam design. Higher the peaks the better, or the lower the ET times the better in race prepped cars. That scene plays out to the 20 year old guys who can live with a street car that drives like that, older guys want something tamer and easier to drive with LOTS of TQ. Doing that might take less or more exhaust duration split that normal, depends on the RPM range, application and intake duration.

Bret

 

You need to base your cam on head flow,DRC/SCR,valve diameter and exhaust design/backpressure and where you want peak hp to be

Get your head flow or head flow thru the intake mainfold for optimum resaults

Select a lift 20-25% above peak head flow and get the quickest opening ramp on the intake but aggressive opening ramps,high valve pressure and lift shortens the valvetrain life

 

how having cats on the car isnt so bad on the stock cam, but how restrictive and limiting are the cats on a car with a larger cam? what would you look for in a cam if you have catted long tubes and say a side exit exhaust which is free flowing? im sure you'll see gains from any cam but im just wondering what i should be looking for in a cam longer exhaust duration? higher LSA's no overlap? just wondering

 

not to answer a question with a question but, is it safe to say a motor like that, any motor, would want a smaller cam that still takes advantage of what flow/velocity there is? basically using both flow and velocity as equally as possible.

further more, could you actually use the restrictive exhaust to your advatange, abeit limited?

 

I think it's funny that 2.02 valve 346 would like a 109 lsa cam best and HELLO TREX...

 

Vizard will still best be remembered as the guy who proved that Flowmaster mufflers suck. The rest of his research is just an added bonus to the community.

 

Huh??

 

No real way to use resticitive exhaust to your advantage unless you have the overlap all screwed up or were working on better emissions.

Any motor reguardless of the exhaust situation wants a set duration for a RPM level. Saying that's the only thing you are changing is exhaust and cam. The different exhausts will like different things if they are radically different, like stock manifolds or shortie headers or LT's, then cats or no-cats.

Restrictive exhausts depending on their RPM range can really hate overlap, so you have to watch out for that.

Bret

 

The LSA stuff is nonsense. Dave's chart would have Pro Stock running 104 LSA!

I would say it's more like the opposite of that chart in reality.

 

With 30 degree intake valve seats, right?

Remember his "30 degree technology" deal he was so proud of?

Smart guy, but sometimes way off in left field.

 

It would be nice if all engine parameters were this linear!

That formula puts me at a 107 lobe center. Not very friendly for a
street, or street/strip motor under 6500 RPM.

I'd have to drop some duration, and rocker ratio to reduce overlap.

To restore the required valve lift and "A.U.T.C." on a flat tappet cam
would need some tricky lobe ramps and profiles (better suited for a roller
I'm sure).

Does the article mention if this guideline is specific to a certain motor/generation?

 

His book and that article focus on SBC, but he does cover the beehive springs which tend more towards the LSx engine series.

 

Guys remember Dave had to take his dick out first before he stepped on it. There has been a lot of times that he didn't!

The low lift flow and 30° seats were not winners but some of his stuff is.

Bret

 

I think that little graphic and the cam advice with it,
may not really comprehend the aggressive lobe profiles
that the LS1 crowd likes to use. This aspect lets you
have more effective duration at less real overlap, ja?

 

Vizard spec'd a cam for PopRod's "Budget Sledgehammer" a few issues ago. It was a stock 350 short block (reused the pistons!) with Vortec-copy heads, a single plane and a carb. HR cam was on a 108° LCA and made fine torque and power from fairly low revs to low 6's. True, it was a 224° @ .050, but it worked well and wasn't the 112°-116° LCA stuff I see offered a lot.

I guess that says there is more than one way to skin a feline...or design a cam. Results count. Here's the results:

http://www.popularhotrodding.com/tec...der_heads.html

 

Bret - hehehe....................................touche!