Static compression is incidental. The earlier you make the intake valve closing, the more of that static compression is used for the dynamic compression, thereby increasing it. If you increase cam duration (and overlap) and advance the install point early enough, you can make a low comp engine turn on earlier because of this, while the increased duration (and overlap) will permit good mid-upper power as well. It will also help the engine run a bit cooler vs a retarded installed cam. Remember too that the OEM replica cams will be difficult to map if all you're used to is looking at aftermarket symmetric lobe cams. FM cs647 has 3.25* advance @.050 and 1.75* retard @.006. This results in a 71* IVC point. Melling sbc-5 has 3.25* advance @.050 and a more balanced 3.25* retard @.006, giving it a 75* IVC point. This means the Melling is a bit 'larger' and will need more static compression to achieve the same dynamic compression as the FM cam. Even though the Melling is 'larger', it is actually slightly more gentle on the valvetrain due to its decreased lifter acceleration rate (1.91 vs 1.94 for FM) If your static compression is going to be pretty low, you'd be better off with the FM cam; while the inverse is true for for higher static. Even better (if all you want is more power), cams such as the Crower level 2 cam with even earlier IVC points would increase your DCR even more, when installed at the default location. Putting an even larger cam in it with little or no exhaust emphasis, then advancing it a lot would lower the relative powerband and increase DCR, giving better performance out of lower static compression ratios. Keeping exhaust emphasis down in this scenario would permit more cam advance without making the exhaust open too early, while still permitting good exhaust evacuation.
Either way I see the cs647 out performing the comp cam in a 8 to 1 stock manifold motor with standard valves. The only difference I really see it the comp cams having a higher rpm range. Crap now I agree with Gary on something
lol, don't get your hopes up yet! That link shows a 260* duration @.006 cam with 212* duration @.050. That's 48* lobe intensity, which is way steeper than the OEM type cams. This alone will increase power. It sits at 56* IVC point (when installed at 106 CL) vs the standard setting of 71* for the FM cs647. This will *increase* dynamic over the FM cam, increasing power this way. So no, that cam would outperform the FM cam on an 8:1 engine. lol I doubt it would last even half as long though, but it would perform better power wise. :bglasses:
When you tighten the lobe intensities (less distance between .006 and .050), the cam will behave closer to the .050 specs, and if it's 212*, will have a tighter, yet more powerful powerband. Cylinder fill is increased this way and more of the static compression is utilized, even on low overlap cams in low comp engines. (vs a stock cam) If the distance is widened up between .006 and .050, more time is present for 'bleed over' gasses to pass through the partially opened valves, which increases the effect of lower durations @.050, and making the durations @.006 more influential on the cam's powerband. This is why the OEM cams act larger than they are @higher RPMs, while still retaining lower-mid RPM strengths. It's also one of the reasons why OEM cams need more compression to perform optimally (along with their later IVC points). There's many benefits to using the asymmetric lobe designs of OEM cams, but they do have their limits, and won't give the most power possible. If you sacrifice some of those benefits, you can milk more power out of an engine, but is a tradeoff.
I brought this up hoping the OP might see that it would be a better investment from my point of view to put a little bit of work into the VJ and heads rather than spending more on machine work on such a mild project. I hope it isn't viewed as arguing with you, I've done this hundreds of times. That's my point of view. Getting more into the cylinder makes more cylinder pressure, whether you do it via faster ramp rates or better breathing induction (it's the same, really). Trapped compression due to intake closing point only refers to a static engine example. A spinning engine will use the increased overlap to pull the charge in, raising cylinder pressure despite the theory of static compression 'bleed off'. It only bleeds off below where the events 'wake up' the engine. The theory of a more aggressive cam giving a narrower powerband is negated by better breathing heads. The powerband now wakes up earlier and hangs on later. Suggesting the width of powerbands is more of a theoretical comparison of the breathing/cylinder pressure curve 'when comparing cams of different specs'...that is merely a generalization. The flaw in this posts argument is that the hypothetical stock engine is both breathing limited as well as cam starved, and that there's confusion as to which theories work better based on what people read about basic engine principles in a very limited scope of application. A better port fills the cylinder more...and allows the gift of a milder cam which can close the valve earlier, a double bonus.
Tony's the man, I'm just the peanut gallery. lol It would be wise to listen to him. I know I have. :TU:
You may be right but I did not see any gain when I ran this cam straight up in my 77 engine . It only had an extended rpm range. Increase in power after 2800. Otherwise it made the foggiest improvement to the 77 engine. I end end up with a 72 engine for it after my brother flipped my 72 hardtop. Sold that weak dog to a guy with a 79 regal . Put a 2200 convertor on it . He liked it better then his v6. But still the biggest slug and could barely turn a 275-60 tire. Yet my 72 engine with 2400 convertor would turn it no problem. Big difference in power. Both had duals. From experience the 268 was useless compared to the stock 72 cam.
The 77 came with a cam similar to the Melling sbc-11 cam, which had a 50* closing vs the 60* a straight up installed 260 cam would give. You lost DCR, but the improved timing events helped to balance it out (this proves Tony's point to some degree), while extending the powerband some. A 72 used a cam closer to the GS replica cams offered by FM and Melling, and had slightly better compression, so power would definitely be better with this. This also proves Tony's point again to some degree, since compression is still low, but the camshaft size is increased. Put in a cam even larger, without too much exhaust emphasis, advance it even further, and watch that low comp engine wake up. It fattens the power with increased cylinder fill without too much exhaust bleed off. Where people seem to get the doggy effect down low on large cams is when they don't advance them, but will still get decent power up higher as long as the engine can breathe. Of course, increasing compression will always be better than not increasing it...but sometimes this isn't an option, or at least will be more expensive after it's all together and you find out the compression is lower than you wanted. At least the pump gas will be good to go! I know it's not the exact same thing, but has anyone here ever took a low comp engine that ran fine off regular and advanced the ignition timing and put in premium? The difference is like day and night. My Buick 350's loved advanced timing and it really woke them up. Just another opinion from the peanut gallery.
Didn't I just say I have 10 years on this trans with nitrous banging it right out of the hole using MT DR's each and every time. Probably have about 100 nitrous full throttle runs on it right out of the hole. I would think you would have it "built" before you would just go to the junkyard and throw in this trans. If it is a stock 350 then Nothing is going to happen.
I had this in my car in 1983 in a bone stock 71 engine stock stall. 256 gears./ It took till 3000 to get going and ran to 5500 easily. It would do 100mph in 2nd gear. You would need at least a 2000 stall convertor and 355 gears to work well with this cam. Some head porting would help too and a little more compression would not hurt either. But you don't have too if you do not want to. Mine ran fine with out the other stuff done. In the end I ran 373 gears with 28"tall tires 275-60-15's NO stall in trans just stock and I ran a best of 14.89 96mph. No head work No more compression than the 8.5 that the book said for a 71 engine. It wiped most peoples butts on the street back then. I would get the TA 212 cam instead of the 268h, cam
FYI that Comp cams intense ramp will hammer your exhaust valve seat to nothing in short order. Do not use this cam with out having hardened seats installed. Also, its I who love the Crower cams, not Gary so much. Hes the stock replacement guy. Now back to your regularly scheduled Gary/Derek/Tony/Alex debate. Thats a joke guys.
Like this really helps? I suppose your posts and experiences transcends all the other ones here? I'm actually attempting to go past the nit picking and personal opinions and just stick to the tech...without personal gain. I suppose even participating in this lumps me into the rest of the show? There actually is useful information in this.
Here's a custom cam I came up with some time back, trying to get one that had similar behavior as the TA 212-350, but was more low-comp/stock engine friendly.
I guess I need to insult people more to really fit in Let's get drunk and beat each other up, then go back into the bar...toothless but happy :laugh: Can't say that I don't put myself in that position, lol.
Just a bunch of toothless buddies. lol You were just standing there so you got hit anyways. You just can't stand there at a bar fight and not expect to be hit. Now lets have a shot, of Crown. lol How about this, No one wants to venture out into the solid lifter cam arena That will make it rev past 6 grand with the new intake, how about the TA112s .480"-228'/ .540- 240' 112 or maybe for a more adventurous person that wants to put some race into that 350 how about the TA21S .528"-248'/ .528"-254' 110 you'll have to take your cutter out and fly cut the pistons while they are still in the engine for this one. I have notched pistons in mine, 20 years ago come on boys man up and get some real 350s going. Maybe I will put that sucker in mine when I change the intake. But it has to be a roller don't you thinK? I forgot, I want to stay with that boring E-Or oh bother stock cam.
It's just as funny when people are amazed by the 'new tech' of ls engines with wide powerbands, drive-ability, etc.... Must be the fancy kom-pooTor. Nope...it's all about the top end.
