Try a 107 lsa. if you like rough idle, 5" vac, happiest idling at 1,000-1,200. & healthy sound....:TU:
Have to disagree Nick. LS and or overlap IS what changes the power band. Like Marts example at 107 theres so much overlap it won't run below 1000 RPM. Because theres not enough velocity to overcome the reversion. I'll bet it revs like crazy. Most stock OE cams are in the 117 to 115 range and won't rev past 5000 RPM. Full on drag only cars run as little as 104 to 106 because they need the RPM and don't care about anything under 4000 RPM.
You can grind a cam on a 108 l/s angle that idles well and one on a 112 that sounds like a pro stocker. L/s isnt the reason why . As for tighter lobe center cams revving higher......hmmmmm
Here is some of what Nick is referring to Th Buick 350 2 barrel stock cam had a 102 LSA and you could idle at 500 rpm and count the smooth interval exhaust pulses A 110 LSA will produce more low end torque than a 112 LSA providing the overlap is less than zero. And I could go down the list of statements and show each to be true or false depending on the other cam parameters and engine intake and exhaust systems. And that's the point. It is not a simple matter. You look at what you need to fit your application and juggle ALL the parameters so the total performance falls within your guidelines. Buick 350: It seems evident that the idle is smooth (and possibly decent fuel mileage) with valve overlaps less than zero. Inversely, Low end performance begins to be affected once valve overlap goes beyond zero, is very noticeable near 10 degrees and becomes "light switch" off to on as you approach 20 degrees. Overlap is a result of both intake and exhaust duration and LSA. If the intake and exhaust durations are short then you can have a tight LSA and still have very little overlap with a smooth idle and good low end torque. The most significant parameter that affects cylinder fill or torque is the intake valve closing point. Early closing relates to low end power while later closing relates to high end power. So for a given duration a tighter LSA closes the intake valve sooner which actually does not help high end power. However if there is a properly tuned header, the extra overlap may help the scavenging pulse start the intake charge into the cylinder earlier which mimics a longer duration intake duration. So here again, Yes and No depending. If the exhaust system creates more back pressure than scavenging as in stock, then a wide LSA which reduces overlap and delays the intake closing may produce better higher rpm power. The example of the Thumper Cam on a 107 LSA, the overlap is 20 degrees so there is no power below 2500 rpm and the intake valve closes relatively soon killing upper end power. You end up with a short power band with a good mid range and that's it. It does what it is supposed to which is to produce the old Hot Rod sound while still maintaining a strong midrange. Once the intake and exhaust durations get very long, you may want to spread the LSA to limit the overlap for a specific need or class rule. Example: I had Robert custom order a Buick 455 cam with a 118 degree LSA because the rules in Zurich dictate that the engine must idle near stock. Anyway you get the picture without going any further. There are no really good generalizations. Even in this post words like "relates to" and "may" are used because there is always a special case. Paul
Umm, sort of... (Responding to Underdog350) (The 2 posts above were dropped while I let this one hang awhile) Different applications need different things, obviously. Bigger engines revving higher tend to go wider (112-114* or more) in situations where there is little demand below peak torque, and still have plenty of overlap due to huge duration. Generally speaking the wider LC helps hang on longer past peak hp as opposed to the tighter lobe seps. shut off sooner. HP is usually very close at peak between the two, if talking only a few degrees changed (until tipped off too far one direction). Wide Lobe seps. tend to have a smoother idle and a lower, longer torque curve. This is well known and used as a strategy in CT racing where heads are limited and gears are not. The loss in torque from the wider lobe seps. is made up for with gear and the ability to hang on longer is an advantage when the tighter lobe sep. engine runs out of steam earlier. You don't have to believe me, custom cam grinders (such as Jones Cam) will say the same. Also generally speaking tighter lobe seps. and more overlap tends to turn on like a switch, going from a rough idle to a big jump in torque...assuming not being over-cammed.... which brings us to mileage... Comparing the 2 different lobe sep. engines in the same vehicle would show the one with more torque delivering better mileage, at the same rpms and power output. (Whichever one that is...having a mismatched cam to begin with would possibly show the opposite!) Having more part throttle torque forces you to use a lesser throttle opening or accelerate from increased output. The lesser throttle opening further helps atomization/vaporization. I would gather that one would see a better BSFC if dyno'ed, but people tend not to dyno test part throttle, esp. A to B. Who would want to pay for this? Engineering books intended for educating the OEM engineer also state that increased torque (at same rpm) delivers better mileage. The books show dyno curves demonstrating this, along with math for the student to prove it. OEM's tend to use wider lobe seps. for a few reasons. One is that the computer is happier with better idle vacuum. Another is that wider lobe seps. tend to leave less hydrocarbons for the cat. converter to deal with, although different strategies have been used over the years. [Thanks P Muller for the well complimented info!] [Edited for clarity]
Would be shocked if a stock Buick cam had a 102 LSA. I'll bet it more like 115. Will check tomorrow. You guys are using lobe separation and lobe centerline terms as if they are the same. They are not. Every cam makers catalog lists cams with a tighter/smaller lobe separation as having higher RPM ranges. Meaning a cam with 106 has a higher RPM limit than one with a 112. All else being the same.
Some of the catalogs are using the descriptions to sell cams, ie. marketing hype. You can take those descriptions with a grain of salt. The rpm ranges can be generalized and often based on demographics. The rpm ranges seen would obviously vary greatly depending on many factors, such as the CSA and flow characteristics of the heads and size of the cylinders. You are correct! I edited my post for better clarity...sorry, lack of sleep I'm not the originator of the info I posted, that's how I learned it and have seen it in the real world. Another example is the Comp 4x4 intended cams have tighter lobe seps. and act as PMuller also describes, rough idle and on like a switch. They pretty much "run into a wall" after peak hp.
Lobe seperation is.ground into a cam core and is therefore not adjustable. As for cams out of a catalog....well you get what u pay for Again not directed to any sp ecific person Expand your horizons and quit treating these engines special. Good things will follow
OK... to be more exact When the cam only has 172/182 duration, ICL 106, ECL 105 for a 105.5 LSA there is very little overlap even though the LSA is tight. Anyway the point is, just because a cam has a tight LSA doesn't mean there is a lot of overlap. The GS350 cams had more duration and a wider LSA (as you pointed out). That's not what I'm seeing for the SBB or the BBB. Looking at the TA catalog, as you go down the list of cams, a jump to a tighter LSA for the same duration specs (or close to it) shows an increase in the low end rpm of the listed power band without an increase in the upper end rpm. Shorter power band. The cases where the upper end increased is when the intake valve .050 closing point is later or the exhaust valve opened sooner or both. When you read through the many posts here involving different cams actually being driven on the street and the engines being dyno tested, for the same or similar intake and exhaust durations the theme is the same. The tight LSA with a lot of overlap produce an abrupt transition coming into the power band with an almost equally abrupt fall off. The wider LSA cams are smoother coming into power and produce a wider power band. Just to be clear, in this last paragraph we're talking about cams that have over zero .050" overlap. Paul
Nick, would be interested in the cam you refer to for your street car. As far as not being anything like cams being made now. Could you start a new thread to discuss your theories with the group?
No big mystery really. The factory heads stink. The intakes choices stink. And regardless what some people seem to think, these things won't make peak power past 6500 and that's probably a 500-1000 rpm higher estimateon most combos. In my opinion I would tighten up the lobe centers and work on my intake valve closing point to build as much cylinder pressure and make as much power up to 5800 rpm or so. Then gear the car to be shifted at 62 - 6400 and that's that.
What you guys think about this type valve seals? I've heard some engine builders leave that small spring off because they think it wont let enough oil to go for guides. Im also thinking my cam and piston choice, 10.2:1 is too much static for crower 3 right? Another piston option gives me 9.4:1, but that is bit low...?
steve mentioned the crower level 3 is good to around 9.7 and shifts around 5800. 10.2 may be abit to high for pump gas. you could polish your chambers to lower comp with the 10.2 comp setup. or run the 9.4 . might even be able to advance cam with the 9.4
If you think you're on the edge with compression/octane tolerance you have to consider elevation in your region, as well as things like sharp edges around the chamber , plug heat range/type, and one of the biggest...air intake and coolant temps. The vehicle itself may have more bearing on octane tolerance than the engine's specs sometimes. You're not going to remove enough cc's by polishing to lower compression, and you might be giving up valuable surface roughness. Sharp edges and end gas dead space is far more important. Another biggie is exhaust valve seat width. You can lower the valve temp by a hundred degrees or more with a wider seat. Going from 10.2 to 9.4 isn't going to lose enough torque through the curve to break the deal if you suspect 10.2 is too high. 2-3% loss maybe? Zero loss if you are having combustion problems @ 10.2... You'll give up more mid range by compromising on header selection or tuning. I think unless ALL temps and weather are carefully controlled, I'd err to slightly lower compression and enjoy your ride. A couple hundred higher flash with a good converter will hide any "softness".
Hold on now, this guy is from Finland so he may have higher octane fuel available to him, if so I say if you have 96 octane(or higher?) readily available to go ahead and run it with the level 3 with the 10.2:1 compression. Boy oh boy if you have the higher octane available to you that 2-3% which I think would be closer to 3-4% would register at the seat of the pants on the butt dyno even if it was only 2-3%. Most of that higher compression would be most helpful on the lower end so by all means if you have the octane there in Finland go for the 10.2:1 compression run the high test and enjoy! GL Derek
I think 98 octane there is equivalent to our 91. I could be mistaken. Or off by a bit. My comments weren't based on doing any specific calculations, which should be more extensive than the engine's static and dynamic compression calcs. Simply pointing out that a very slight reduction would not be a noticeable loss IF it was on edge to begin with. Why risk running into detonation when you can't easily hear the first 9 degrees out of 10 on the scale of severity? I don't know this guy's tuning or detection skills. Or if he'll put in an iridium spark plug or something that can actually promote detonation under some circumstances. All it takes is some heated intake air from a faulty factory air cleaner diaphragm and it could be game over. Out of dozens of very high compression engines with tame cam specs I've had only one really bite me in the ass. I was unaware that a different brand of plug cross referenced to several heat ranges to the brand I was used to running. It failed from pre-ignition, the silent engine killer. No signs of detonation. Only got a couple heavy throttle romps for a few seconds each before severe damage was noted. Oops. I can think of a lot of ways to make up a 3-4% perceived power loss on a mild engine like that.
Well, my point was if he has the 10.2:1 pistons already and if there is the higher octane fuel where he is then why buy different pistons that would probably be very expensive to import to where he is. o No: Perhaps thicker head gaskets with a larger bore might solve the problem seeing how the sbb 350 doesn't utilize quench anyway? http://www.buyracingparts.com/ has sbb 350 performance head gaskets that are .050" thick with a 3.905" bore diameter that would bring the compression down at least that .5:1 to get her to 9.7:1 for the level 3 instead of buying more pistons and rebalancing again? GL Here is link to the gaskets; http://www.buyracingparts.com/gaskets/buick-350-severe-duty-head-gaskets.html Derek
Awesome! More options or solutions are always good. Nowhere did I suggest he buy pistons. You wouldn't necessarily rebalance the engine anyways. You could easily mill a few cc's out of the pistons or chamber without affecting balance or dealing with shipping. I agree with the notion of utilizing higher grade fuel. I don't think it is though. Again, bigger factors than static or dynamic compression are touched on. If it's being stated that 9.7 is a reasonable high limit, then it stands to reason that 9.4 would not be too low.
