Street SBC cam - ideal LSA opinions??? [Archive] - Chevelle Tech

: Street SBC cam - ideal LSA opinions???


Highway Star
May 25th, 09, 12:55 PM
I have read piles of threads and other info on this and still can't make sense of it. I got too ticked to read any further when a thread mentioned that cam companies started changing LSAs just to be able to market/sell more high-lift/big duration street cams. LSAs from 106 to 114 are readily available.

I am trying to match a cam (either single or dual pattern) to my street only 355.

Thanks!!

BillyGman
May 25th, 09, 12:57 PM
Uh ho, not again......

no offense, but you might be opening up a can of worms with this topic.

461RAT
May 25th, 09, 1:02 PM
I like a 108 myself.Great LSA for street,imo.Comes on faster than 110,but still wide enough before running out of steam.Then again,you gotta factor rear gears,compression,heads,carb,auto or manual trans,etc. into the equation.As stated from above,do a search on this.This topic has been beaten and ressurected to death.

BillyGman
May 25th, 09, 1:25 PM
Yeah, I liked the 108 LSA cam that I had on a small block engine. I had a manual trans in that car, so that might matter. I dunno.

Highway Star
May 25th, 09, 5:56 PM
I've searched and read. I hate gray areas, and that's all I seem to read. If nobody wants to play along, thats cool.

Here's more info...

TH350
rear - 2.73 currently, if I ever switch it will be no more than 3.55
heads - 601s (prolly close to 9.7:1)
pistons - 4 valve relief rebuilders
bottom end - stock, cast, 20k miles tops
intake - edelbrock 2101
carb - holley 600 VS/EC
HEI
1-5/8" primaries to 2-1/2" pipes/glasspacks/turndowns

RB69SS396Conv
May 25th, 09, 6:21 PM
There is no "one" best" LSA for any application.

There are advantages and disadvantages to EVERY facet of cam design, LSA included.

In general - and keep in mind, this is GENERAL, and not specific to any particular grind or manufacturer or combo - if you take the same cam with the same lobes, and grind several copies that are otherwise identical except with a variety of LSAs: ones with narrow LSAs will tend to idle rougher, have more low-RPM torque, reach their torque peak at a lower RPM, have higher peak torque, and power will fall off faster once that peak is passed (i.e., peak torque RPM and peak HP RPM relatively close together). Ones with a wider LSA will idle smoother, have higher idle and cruise vacuum, lower peak torque, and torque will not fall off near as fast once the peak torque RPM is exceeded (wider, flatter torque curve with lower peak values, spread out toward the top). A narrow LSA will make the car go faster IF the gear and converter keep the engine operating within that narrow band around the peaks AT ALL TIMES... i.e., a single-purpose strip car. A wide LSA will make the car go faster if the engine has to operate over a wide variety of conditions, especially RPMs; and will generally get better gas mileage on the street, especially when operated well below its peak torque RPM like 2.73 gears and a stock converter will enforce.

One is not "better" than the other; rather, it's a matter of suitability for purpose.

Gievn your combo, I would suggest a cam with low to mid 2-teens of intake duration; more exhaust than intake (with the crappy stock exh ports, you'll benefit from the lobe split), and LSA toward the higher side (110 minimum, 112 - 114 preferred). The Comp XE cams and the Voodoo cams are good examples of modern cams geared toward motors like yours, with no gear. Consider using a solid. Avoid cheap generic cams like the Edelbrock product line or the Summit cams or other clones of those same ancient designs, if you want to be competitive.

kirkwoodken
May 25th, 09, 7:06 PM
What RB69SS396Conv says: X2

eric13617
May 25th, 09, 7:27 PM
Exactly!

trmnatr
May 25th, 09, 7:43 PM
What RB69SS396Conv says: X2

Exactly!

Right !

However many drag race cars that are properly set up for drag racing can go faster with a tighter lsa.

Street cars it really depends on the engine, car and most important the DRIVER

I would go no wider than 110 and no tighter than 108 on a 218-220 @.050 in this application. A 218/218 108 would work good

BillyGman
May 25th, 09, 7:58 PM
I've searched and read. I hate gray areas, I think there will always be "gray" areas because answers that you would receive in this topic will be greatly based on opinion, preferences and perhaps to a lesser extent, even theory too. There are so many facets to cam design. So I don't believe that it can be a cut and dried case. I do have my own preference that I had made mention of in my last post, but other than that, perhaps the best thing that you can do is take a poll. the poll will be based on peoples' likes/dislikes, and their opinion. But that mostly what you should expect from a topic like this anyway. Good luck.

kirkwoodken
May 25th, 09, 8:23 PM
Interestingly, what Butch is recommending is what numerous cam grinders have offered for the SBC through the years: A cam closely related to the original Duntov. And for a hydraulic, cams close to the 327 and 350 high performance hydraulics. These are sensible street grinds, not something that NEEDS gearing in the 4's or above. A flat tappet cam with numbers like those will be peppy and not break your wallet. Also sound nice while idling.

Highway Star
May 25th, 09, 8:27 PM
Thanks!!

Right now I am sporting a "blue racer" crane grind, 284/284 advertised, 218/218 & .450"/.450" @ .050 on 110 lsa. We suspect a wiped lobe on the friggin thing, and I might be picking up a cam/lifter set. I have been told by some pretty trustworthy folks around here that this cam is WAY too big for my setup. The consensus has been towards a Comp 268 or an Isky 274. If I recall, the Isky is on a 106 lsa, and the comp is 110 or 112. That is sort of what prompted the question about lsa. The lopey idle is neat, but I'd rather have the car able to get out of its own way rather than sound tough.

The car has a 2000-2200 stall B&M converter in it, by the way.


Right now there's a set of 624 smogger heads on it, which will be switched out prolly when the cam is stuck in. I've got access to a set of 601s (mentioned above) that will bump SCR up to around 9.7:1. My cam profile will play a big role in what the DCR winds up being, and I want to make sure this is right. I know I won't really know exactly what I am working with until the heads are off and some measurements are taken. I don't know EXACTLY how far the slugs are down in the hole, and I know that I need that figure before I can get finalized on cam grind, gasket thickness, etc.

I want a torquey street engine. Revving over 5000 or 5200 is not important to me. I am shooting for 350+ torque and 300+ horses, which I think are not unreasonable numbers.

Everyone always (myself included) thinks what RB says is pure wisdom. He suggests a wider lsa, 110 or 112, but not from summit.

I have to confess, my wallet really likes the looks of the summit 1103. It is a dual pattern, 214*/224* & .442"/.465" @ .050" on 112 lsa. That fits the bill pretty well. What is wrong with it? It is pretty close in profile to the voodoo 60101. Are we getting into lobe shape and valvetrain-friendliness now? I really don't know.

yellow heap
May 25th, 09, 9:00 PM
My rule for lsa is simple(too simple?) the better the head for a given c.i.d the wider the lsa-350 somthin with stock type heads maybe a 108-killer heads maybe 110 or slightly more.
Your primary goal seems not too be allout ooommmpphh so drivability is next-a 110 or 112 would work great-wide powerband and flat torque with good idle
I would stay away from generic cams-a CC 268HE is great in mild 3fiddy's
The more modern cams do work better though the tried and tru 268 just flat out works for applications like this

travis g
May 26th, 09, 8:40 AM
Considering the gears, I would run a cam with no more than about 6* split, on a 108 to 110 lsa. You need as much low and midrange as you can get because of the gears and relatively low stall convertor. The comp cams 260AH-8 will absolutely run rings around the summit K1103 in this application...I've used both and there is no comparison under 5K rpms in an under 9.0-1 compression 350. The 1103 will pull harder on the top end, and thats about it. Either cam will ping in your setup with the small chamber 305 heads/9.7-1 compression unless you are conservative with the timing curve, but then you are giving up power/torque.
The 1103 will pull to 6K rpms with fresh stock valvesprings in a 350...the lobes are pretty gentle.
The comp 268HE will work pretty nicely with this setup too, as would the crane 272 energizer, or the Isky 264 Mega cam.

MadmanMark
May 26th, 09, 9:40 AM
You tend to learn a lot more about lsa after you go too far with the overlap and have to ditch power brakes. On my old 350 that was 10:1 with Dart 200 IEs, that point was somewhere between the Isky 264 and 270 (both are on 108 lsa). My brother had a similar setup (but with the WP heads) and switched from the XE268 to the 274 and still could use his stock booster. The CC XEs are on a 110 lsa with a 106 icl (if you line up the dots).

I crutched the Isky 270 with Rhoads lifters for a while to keep the power brakes and they seemed to work. I was concerned about them not letting the cam get to full lift, so I changed them out and added a vacuum cannister for the brakes. It would work great for 1 stop, but at a light you would start to creep forward after a while. Something had to go and it was the booster. The vacuum cannister is now my coolant overflow tank.:)

Once you get away from needing the vacuum for the brakes, you can get more aggressive with the cam and lsa. If you want to keep your stock brake setup, be real careful with your cam pick.

BillsCamino
May 26th, 09, 10:36 AM
The comp 268HE will work pretty nicely with this setup too...

Jake,
I've got one of these if interested...;)

66 BRONZE
May 26th, 09, 10:47 AM
Voodoo 262

BillyGman
May 26th, 09, 12:19 PM
Thanks!!

Right now I am sporting a "blue racer" crane grind, 284/284 advertised, 218/218 & .450"/.450" @ .050 on 110 lsa. We suspect a wiped lobe on the friggin thing, and I might be picking up a cam/lifter set. I have been told by some pretty trustworthy folks around here that this cam is WAY too big for my setup. The consensus has been towards a Comp 268 or an Isky 274. If I recall, the Isky is on a 106 lsa, and the comp is 110 or 112. That is sort of what prompted the question about lsa. The lopey idle is neat, but I'd rather have the car able to get out of its own way rather than sound tough.

The car has a 2000-2200 stall B&M converter in it, by the way.


.First of all, it's pretty easy to diagnose a camshaft lobe that's completely wiped out. Just remove the coil wire so the engine doesn't start, remove the valve covers, and have someone get behind the wheel and turn the key while you watch the rocker arms. If you see any of the rocker arms not moving up and down like the rest of them are doing, but instead is just sitting there while the engine is being turned over with the starter motor, then the corresponding camshaft lobe is completely wiped.

BTW, it's best that they don't keep the key turned to the start position for more than about 5 or 6 seconds at a time. That way, the starter won't be overheated. ;)

As far as that camshaft being too big. A cam with 218dur@.050 and a .450 lift is almost as mild (small) as you can get.

Highway Star
May 26th, 09, 10:10 PM
Well, all the rockers were rocking. I suppose that is a good sign. Perhaps all of this thread was for nothing. Wait, I found out that the baddest small block street cam is a Comp 268, with 218/218, .454/.454 on 110 lsa. The 284H crane in my sbc is 284 advertised, 218/218 with .450/.450 on 110 lsa. That is almost identical to the comp 268. I guess I found out there's really nothing wrong with it, and it is matched pretty well. It sounds like the only thing I need to address is the super low SCR/DCR I am sporting. Those numbers are around 8:1 and 7:1 respectively. Thanks for all the input fellas.

travis g
May 27th, 09, 3:50 AM
Do you still have the cam card for that cam? I am curious what that 284 duration is measured at. If it is measured at .0045" like most crane hydraulics was, then your DCR is in the toilet, and the comp 268HE would provide a pretty dramatic improvement in the low and midrange

Highway Star
May 27th, 09, 8:53 AM
Do you still have the cam card for that cam? I am curious what that 284 duration is measured at. If it is measured at .0045" like most crane hydraulics was, then your DCR is in the toilet, and the comp 268HE would provide a pretty dramatic improvement in the low and midrange


Here is a cached snapshot of the crane website's card for that cam. (http://74.125.47.132/search?q=cache:XQ07XPHJpRkJ:cranecams.com/index.php%3Fshow%3DbrowseParts%26action%3DpartSpec %26partNumber%3DWG1139K%26lvl%3D2%26prt%3D5+crane+ wg1139k&cd=10&hl=en&ct=clnk&gl=us)

Yes, my DCR is definitely in the toilet, I almost want to say that the calculations I made a while back showed it below 7:1

While I have read quite a bit on factors affecting DCR, it is still not completely clear to me. I thought the actual valve events and their relationship to each other in time was the biggest contributor to dynamic cylinder pressure. Trav, do you feel like sharing what you know on this one...as in what differs between these two cams?

RB69SS396Conv
May 27th, 09, 9:11 AM
The point at which DCR is measured doesn't "affect" DCR.

Think about it this way... imagine you have a cam in your hand, just a normal street one of some sort, with some kind of clearance ramps near zero lift like they all have. If you measure the duration at .0005" of lobe lift (just barely beginning to have any lift at all), it might measure 315 from .0005" to .0005" (GM gives their specs something like this). If you measure it at .002" of lobe lift, if might have 295 of "seat" duration. If you measure it at .0045" (Crane), it might have 285 of "seat" duration. If you measure it at .006" (Comp or Lunati), it might have 270. If it was a solid with say .015" of lash at the lobe (about .0215" at the valve), it might have 260 between the lash points. If you measure it at .050" (more nearly its actual "functional" duration), it might have 220. Same cam no matter which point you choose to measure it at.

Does your choice of which one of those figures you publish, "affect" the DCR somehow?

Of course not.

But what it DOES do, is make direct comparisons between cams of different mfrs more difficult.

Back to the OP's question... the disadvantage of the Summit cams is that they are ancient designs from back in the Stone Age, with very lazy lobes and relatively short duration near max lift. Think about what you'd want your valves to do... you want them to stay closed for as long as possible when you're supposed to have compression, and then when you want flow, you want to snap them open as quickly as possible consistent with not damaging parts; you want to hold them fully open for as long as possible; then drop them back closed again, again without damaging parts or causing valve float (where the valve bounces off the seat). So you want a wide fat lobe with a rounded top and steep sides. Instead, those archaic obsolete cams have narrow pointy lobes with sloped sides, so they open the valves slowly, hold them open near max for only a very short time, and then slowly drop them back down. Great for pushing the limit of stock springs; terrible for best performance.

I would recommend a MODERN cam with more exhaust lobe than intake lobe; NOT like the old HE series. Good cams in their day for what they were made for, but obsolete now. With typical stock heads with sucky exhaust ports, the engine will benefit from the extra exh timing, to help get the spent gas out of the cylinder. The larger the engine is in relation to the heads in general, the more pronounceed the benefit is. So with a 283 or 305 or 327, the exh can be the same size as the intake; but the bigger the motor gets, the tougher it is for it to completely evacuate, and the more there is to gain from increasing the exh lobe size compared to the int lobe.

Cams in general are cheeeeep. The ratio of effect on engine operation to cost, is HUGE. There are few things that are more short-sighted than picking a cam based on price. Whatever you "saved" on an poorly chosen cam, you may lose within the first couple of miles in cash, from fuel consumption; and you will generally spend FAR more on work-arounds or other mods trying to "make up for" the inadequate cam, than the RIGHT cam would have cost in the first place. If you're at the strip, the money you DON'T win will be less than what you "saved". All in all, it's the WRONG place to "economize". Skip some chrome or other uselessness somewhere, and put your money into stuff that actually ACCOMPLISHES something.

For the OP's situation, the Comp XE or Voodoo series, or similar MODERN offerings from other top-line cam gmfrs such as Crower or Isky or Crane or from the better custom grinders, are the better choice. Just because something "worked good" in the 60s or 70s, doesn't mean that it's still the best there is. We've learned a thing or 2, as a species, in the last 40 years (about how long those Summit cams have been around) about how to make engines run better; as well as, the circumstances around cams have changed (like the fuel for example), and drivers' expectations have changed. Time to move on.

UDHarold
May 27th, 09, 12:17 PM
With current rear gear, Lunati VooDoo 60101, maximum.
256/262 at seat, 213/219 at .050, .454"/.468" gross valve lift, 112 LSA.


UDHarold

SWHEATON
May 27th, 09, 4:56 PM
Well your currently running 273 gear with a possible future change to 355 gear which is a substantial change in ratio when choosing the best LSA let alone cam/duration in general .

So you really need to 1st figure out where your going to be staying gear wise the longest weather it be with 273 gear or will you relistically be changing in the very near future for sure to 355 gear before choosing a cam, LSA,duration, etc.

I would suggest fairly different cam for a 273 vs 355 gear ratio,you should not choose a cam for a possbile 355 gear swap in future that maybe never happens for what ever the reason and then expect the best cam choice for 355 gear & your intended use to perf just as well or even almost as well with 273 gear ,it will not and will be somewhat of a mismatch of cam to gear wise .

Other then over carbing a motor somewhat over caming a motor for 273 gear with a best cam choice for a 355 gear ratio is generally the wrong thing to do IMHO "unless your 100% sure " your installing 355's in the very near future.

If you cant say your going to with certanty install the 355's in the very near future you should error on the conservative side for cam choice/LSA/Duration etc for the not very perf freindly 273 gear your currently running.

BTW,thats why the cam guru/Harold suggested a perfect cam for your current 273 gear ratio & not the best cam choice for the 355 gear that may or may not ever be installed.

Scott

RATtyCamino
May 27th, 09, 6:06 PM
I would recommend a MODERN cam with more exhaust lobe than intake lobe; NOT like the old HE series. Good cams in their day for what they were made for, but obsolete now.

For the OP's situation, the Comp XE or Voodoo series, or similar MODERN offerings from other top-line cam gmfrs such as Crower or Isky or Crane or from the better custom grinders, are the better choice. .

Right on target IMO. And like UDharold posted above....something like the voodoo 256 is what I'd go with.

To the previous point; 15 years ago I had almost the exact same combo as yours. Back then I went with the comp 268 and was very happy.... even when I went from 2.56's to 3.23's. All the further mods to the engine/chassis combo just made it better. If faced with the same situation now I'd be running a Voodoo or XE.

In 15 years the industry has come a long way. Take advantage of the millions of dollars in Engineering and manufacturing advances in a modern cam design.

Bill

zwede
May 27th, 09, 6:12 PM
I have to confess, my wallet really likes the looks of the summit 1103. It is a dual pattern, 214*/224* & .442"/.465" @ .050" on 112 lsa. That fits the bill pretty well. What is wrong with it? It is pretty close in profile to the voodoo 60101. Are we getting into lobe shape and valvetrain-friendliness now? I really don't know.

Nothing wrong with the Summit 1103. I put that cam into a 350 almost 20 years ago and it worked great. Newer designs make a little more power, but the 1103 is a good cam.

pdq67
May 27th, 09, 8:51 PM
Please stop right here.

"With current rear gear, Lunati VooDoo 60101, maximum.
256/262 at seat, 213/219 at .050, .454"/.468" gross valve lift, 112 LSA.

UDHarold "

The MAN has spoken....

And I'd think hard about backing it off a 1/2 a cam smaller IF one is made.........

pdq67