Is the Comp 268H cam really that bad?

Cheaper, plus being able to rotate tires is a plus. This is a DD after all, not some old geezer (apologize if I offend any geezers) mobile that sees 1000 miles a year. Also I don't like too much of a sidewall bulge, I like them to be almost even with the wheel. I'm gonna be running 15x7 Regal T Type wheels. They look like AR Vectors, without the shank lugnuts.

 

Let's take a quick look at a typical, untouched, stock Buick 350 head.

The peak flow numbers on the intake runner show 198 CFM between .350 and .400 lift, with zero gains above .400 lift.

The peak exhaust runner flow plateau's off between .300 and .500 lift, with 124 CFM @.300, 128 CFM @.400, and 130 CFM @.500, with zero gains above .500 lift.

So between that wide margin of .300 and .500 on exhaust, the spectrum of flow only improves by 6 CFM, 4 of which is gained by .400 lift.

Camshafts with lifts above .400 lift will still give more power on a stock head, but the gains are diminished as the main improvement lies in the extra duration the additional lift affords to the lobes.

This effect planes off very quickly after lifts of around .425-.450.

Roller cams can be ground at much higher lifts and incredibly intense ramp profiles which flat tappet cams can't touch. Inside a stock iron head, you'd be gaining more from the ramp profile than you would be from the raw lift gain, though both are mutually incidental with a positive final result.

The Buick 350 stock rockers are supposed to be 1.55:1 ratio, but are closer to 1.5:1 (especially the later stamped steel rockers), which shaves off about .015" from the valve lift, so a cam that advertises ".465" lift would be closer to ".450" lift (just something to keep in mind).

This puts most mild performance camshafts using stock rockers at below .450 lifts (the TA 284-88H cam shows a straight pattern .460/.460 @1.55 which would be more like .445/.445, and this cam does not have a smooth idle...).

That out of the way, let's look at the ratio between the intake runner and exhaust runner on an untouched head.

Take 128 and divide it by 198 (both @.400 lift) to show a .6464 (.65 rounded) ratio, which is a 65% I/E ratio on an untouched head.

Knowing that a straight pattern duration (equal durations for intake and exhaust) work best between 70% and 75%, you'd need to add an additional 5% to 10% exhaust duration to help the head offset its discrepancy between its intake and exhaust flow relationship.

Realize that this is just regarding the head, and doesn't take into consideration additional exhaust restrictions that iron manifolds and/or pipes/mufflers will further introduce.

The ratio discrepancy can be decreased depending on head flow ratio and exhaust used, depending on the type of exhaust and tweaks, such as headers, merge pipes, mandrel bends, straight through mufflers, etc. etc. which will help offset or eliminate the extra exhaust emphasis needed through scavenging.

This can have the added effect of increasing cylinder fill/pressure and require a higher octane of fuel, depending on static/dynamic compression and other timing characteristics, ambient engine temperature, etc.

Getting back to the I/E ratio: if you needed between 5% and 10% exhaust duration emphasis, you'd want to add this to the number you'd be using for your intake duration.

Example: using 210* duration (as seen on the Crower level 3 Buick 350 cam) on the intake, you'd take 210 and multiply by .05 to get 10.5, which you'd then add to 210 to get 220.5.

The Crower level 3 cam has a 220 exhaust duration, so fits this nicely. The exhaust could use as much as 21 extra degrees of duration (210 x .10 = 21), depending on how restrictive other components were.

The FM cs647 (OEM replica GS cam) uses this method.

Looking at the TA 212-350 cam, we see 218* on intake duration (same as the Comp 268), but 230* on exhaust. Doing some simple math, we can see that 218 x .05 = 10.9, for a minimum of 228.9* of exhaust needed, so the TA cam gives it a bit more than minimum, which makes it more useful for engines using stock heads and exhaust manifolds.

See the pattern here?

So unless you're using near perfect ratio heads with headers, a straight pattern cam will leave power on the table inside a Buick 350 engine.

 

Lot of knowledge to swallow, but I get it. What cam would have a great lump to it, while meeting the requirements, while also not being a turd, if you know. Not really "in the loop" when it comes to buick cams, or buick stuff in general. That's why I joined the forum.

 

The TA 212-350 cam would work great with your combination and goals you have in mind.

Others here will reinforce this.

Good idle characteristics (it has a nice lope), can be used with lower compression and exhaust manifolds, has good intake vacuum for power brakes, and otherwise doesn't need anything special to perform well, although it will respond well to future upgrades, such as improved exhaust/better compression if you choose to go down that path later.

 

For a few extra dollars, have a custom grinder put these specs to a chunk of iron:

Duration @.006: 276 intake, 284 exhaust with 64* overlap (8* exhaust emphasis)
Duration @.050: 212 intake, 228 exhaust with 4* overlap (16* exhaust emphasis)
LSA 108
Lobe lift: .304 intake, .289 exhaust (.015" intake emphasis)
Valve lift: .456-.471 intake, .434-.448 exhaust
(between 1.5-1.55 rocker ratio)

I started with a 56* intensity exhaust ramp between 228 and 284 with a .289 lobe lift for an acceptable stability tolerance between 2.32 and 2.38 ramp profile, then matched the intake to this same intensity which resulted in the .304 lobe lift and a 64* intensity between 212 and 276.

This keeps the lobe ramp profiles even on stability and wear characteristics, while still creating a more intense draw from the exhaust on the intake in a lower compression environment with the use of exhaust manifolds and a merge pipe in mind.

It will still have a good lope, 'ok' intake vacuum, but will produce more power in a low comp engine vs other cams that have later IVC points. The generous exhaust emphasis on duration, coupled with the generous intake emphasis on lift, will help an engine with a more restrictive exhaust. The powerband will start off a bit sooner (2,000-ish RPM), and still pull to 5,000 RPM no problem. I'd use tighter than stock springs (but not too tight) if it were mine. I wouldn't rev it past 5,500 RPM to be safe.

This cam would be more 'street gear' friendly, and wouldn't need any special torque converter, though a 2000 or 2500 converter would improve it.

Each custom grinder will usually have his preferences and own thoughts on this subject, but these are still good general guidelines to follow, IMO.

If any professional here disagrees with these specs or design philosophy, then take their word for it over mine, as I do not do this for a living, just for fun.

 

Gary , just so you know the 284-88 is not a straight pattern. Thou it shares the same lift duration is different and similar to the math your done. It would be a step up from the 212.

 

I was talking about the lifts, not duration.

I used that cam as an example because it is the smallest one TA has (that I know of) that has that lift pattern just to keep things simple for my example and point I was trying to make.

Did you know that the TA 284-88H is actually slightly gentler than the TA 212-350 on its exhaust ramp profile?

It's good that people keep an eye out for any mistakes I make. I'm prone to typos and other stuff and have to go back and edit.

As an example, I had listed the .304 and .289 lifts on the custom cam as a .005 intake lift emphasis, when it should have read .015. Whooptie doo I know. lol

I had to correct it though.

 

No I wasn't aware that of it's gentle ramp style. I do know advanced 4 degrees in a 430 it's way more powerful then expected. Pushing 1 hp per cube and an actual (not rated) 510 torque. But back to small buicks. Given your knowledge and math skills on cams,between head flow and dynamic compression what cams fit your profile for best hp/torque on a stock head ? And explain a bit why. We have all seen the real world combos that are proven. What I'm saying is does the math prove them also. For example I'm backing down my cam from the 310 to the level 3. I do not run headers so the advantage or the straight pattern are lost on my combo. Or are they? Oh and I do read what you say Gary. You do have a lot of information, just sometimes you could simplify alittle.

 

Thanks, Andy. I'm trying to keep things easier to read.

The custom cam I posted earlier doesn't make the most power. I wanted to put something up there that would help a restrictive exhaust and work better with lower compression.

As far as what makes good power, you're better off revving it and boosting compression (this being the foundation of the recipe), at least up to what the stock cam and pistons can do, otherwise you're just tweaking it to work with substandard components (rebuilt with poorer pistons than what came from the factory, cams with even less duration than the stock cam, etc.).

The math (and real world testing) shows that the air needs to move. Even the Crower level 3 needs a hand with this, as is shown when Steve had to retard his to improve his combination. It raised the powerband some and moves more air.

TA really hit the ball out of the park when they revised their 212-350 cam, as it puts the timing events in a very comfortable zone for air movement, even for stock heads and manifolds, with even more potential with other parts. It can still be tweaked (as could anything really), but is a good cam as is.

The same can be said for the other revised cams (the ones listed as advertised durations in the cam name, such as the TA "284-88H" cam, the "284" is the advertised intake duration, while the "88" is the last two numbers on the advertised duration for exhaust (2'88'), with the "H" representing "Hydraulic" lifters).

This nomenclature helps people identify the cam at a glance.

I think the 212 cam works better for the 350 with a 110* LSA than it does in a 455 with a 112* LSA. The big engines simply need more cam. The stock (big block) cams are larger than the 212, but broaden the power out instead of concentrating it (as do most other mild performance cams).

A more generalized performance cam would work well in a generalized environment, with leeway on what all was done to the engine so that it works well no matter what's there, but these cams do not produce the most power.

Stock cams (the older ones) do better than what people generally give them credit for, as long as the rest of the engine isn't choked off and there's good compression, but these cams aren't designed with raw power in mind, they're designed to last, while still producing decent enough power.

I noticed that cams with more intense lobe profiles make the most power, but are harder on the valve train components. I guess the trick would be to find that happy medium.

The Buick 350's piston is moving at maximum velocity at 75* ATDC (if memory serves), so orient your specs around that on the exhaust. Once exhaust is established (cam specs matched to head flow ratio and exhaust system to be used), work with the intake to get it where you want, considering camshaft balance and where you want your intake valve to open and close, affecting DCR and powerband.

The material of the head (iron or aluminum), CSA, CFM, static compression, intended ambient temperature, all play roles in determining the overall package.

The Comp cam 268 (this number represents the duration @.006 on both intake and exhaust) actually doesn't do too bad even in the Buick 350, if the exhaust flow ratio was improved on the head and headers are used. It produced good torque in that Hotrod article even with stock heads, more torque than any dual pattern cam of that caliber, but the powerband could have been improved (it ran out of breath at 4600 RPM). By doing this, you would trade a few ft. lbs. for many more horsepower (math and real world testing supports this) in the Buick 350.

Consider also that the Comp 268 uses incredibly intense ramp profiles, which I wouldn't feel comfortable using myself on a flat tappet. This makes it look better (power wise) than it would if it were ground on a gentler profile, with the split pattern cams outperforming it even more this way.

Once the aluminum heads become available, the cams will be more straightforward, I think.

We'll see straight pattern cams being used more often, and with better results.

Tweaks will probably still be useful (dual pattern), but won't need to be as offset as with iron heads.

May see more intake intensive tweaks.

There's a lot to it. Heck, I'm still learning stuff myself. I'm sure there's professionals out there who chuckle at all this, having figured it out long ago.

I could keep typing, but this post is already pretty long.

Apologies for the novel. lol

 

To answer your question in a more direct way, don't use the Crower level 3 if you enjoy the idea of a larger cam.

Take the specs on the 310 and offset them.

Take the intake duration and lower it, while increasing the exhaust duration an equal amount, then do the same for the lifts, only in the opposite direction.

Less intake duration, more exhaust duration.

More intake lift, less exhaust lift.

Keep the LSA the same.

The cam will behave similarly as it does with straight pattern lobes, but works better with a more restrictive exhaust.

Get others to clarify this, don't just take my word for it, because I can still be wrong. I'm just relaying the patterns in changes I've witnessed for myself.

The idea here is to get the intake and exhaust to work more hand in hand with the flow you have to work with. If you increase the head flow ratio to over 70%, keep the straight pattern and use headers.

Or you could still offset it, but just by a smidge (a few degrees) and keep lifts symmetric (straight pattern on lift).

Some changes are just splitting hairs though, so keep that in mind also.

I'm going to stop posting for a little while to let others chime in with their thoughts, as I do not wish to hog up or bloat the thread with nothing but gary posts. lol

 

Appologize if it seems like I'm just picking stuff and random like a kid in the cereal isle and asking about it, but what about this cam from TA? It says it's for 8.5 (my compression should be at least 9.1:1, or around that with 340p pistons, as said before) to 10:1 compression, and is for people who want a lump with low compression. Would this be good? I'd still be using the stock rocker setup for the time being. http://www.taperformance.com/proddetail.asp?prod=TA_C110-350 or if one of the previous (or custom, anyone know any good cam grinders who know what they're doing)?

 

The largest component for me at least, is sound. I'm not after that extra 10 hp or that extra .3 seconds in the 1/4. Sure, I want performance, but I don't want an engine that wheezes out before at 4600rpm. So, should I choose one of the above cams that have been mentioned, and go with one that mostly matches the parameters while also having high (compared to the 268 anyway) duration to give it the lope? I will try my hand at porting my heads on my own, if only just to clean up and smooth some bits, and I would hog out my manifolds and port match the exhaust sides of the heads and the manifold faces themselves.

 

So basically, don't just go with the biggest longest duration cam I can find? Got it. So much knowledge in this thread. :O

 

I found a compression calculator, and put in the specs for my engine to the best of my ability.
Are these parameters right? It's from the UEM piston website. I put in the parameters to the best of my ability, the only thing I'm not sure on is the CC of the dish on the 340p pistons and how far in the hole my pistons were. Seems a little high to me, but I'm not a math person.

 

Yeah, I understand how it works. Thanks for the link. Does anyone happen to know the dish of the 340p pistons? it/s 3.050x.085.

 

OK, so when you are referring to an engine that 'wheezes out' a bit early with a cam having a healthy amount of overlap vs. a similar cam having slightly less overlap what's happening is that it's finding the weak spot in your induction earlier, by a few hundred rpm. The latter cam doesn't so much 'make' hp as much as it simply hangs on a tad bit longer, showing a few more hp from peak hp and after, at the typical expense of a weaker midrange.
The heavier overlap cam with more aggressive lobes 'usually' wakes up stronger and remains that way until the very end.
When you start to improve the heads with some porting, the same thing happens. It still remains stronger all the way through, but on a bigger scale before it runs into that wall.
These aren't wild enough cams that you would be worried about pulling too much out the exhaust, rather...the extra overlap is pulling on the intake tract helping jumpstart things.
Buicks have a high swirl port. Anything you do to help pull more in reaps benefits.
As far as that rowdy sound...porting usually smooths out some of the lope and helps the aggressive cams wake up sooner anyways.

 

It's about 10.3 cc on the 340 piston. The factory Pistons seem to sit about.058 down hole in the 68-75 engines using a 1.835 compression height, 76-80 and v6 engines use a 1.805 compression height and 24.5 cc dish. . But don't assume a rebuild is correct, partscan be machined off , crank , rods, Pistons. Might not be correct. Things happen. Measure. And higher compression will make the sound you want.