Using desktop dynos that use cfm and valve size only to estimate are limiting to one's understanding and application of induction principles. Because of the assumptions made in the programs, they do give the impression of the cam controlling things more than the induction. There's definitely more education and resources out there.
It all matters, although consumer marketed programs ignore things and assume others. There's VE increases from both the intake and exhaust side, so it's tough to disregard 10% each way and consider things valid. (Wave reflection intake side, scavenge exh.) One point illustrated nicely is Bob's example of the Minimum Cross Sectional Area in his fantastic flowing heads being 2.0" inches. If the valve is 1.920" (guess) and the port's throat is 90%, then the area is 2.345 sq in, much bigger than the MCSA. Port limiting velocities would be reached sooner with the 2.0 area...even without considering that the corners could be somewhat dis-included. (The reason that round and oval ports are more 'efficient' than square, that area is relatively dead, hence..oval-ish in the way the engine really sees things). Peak torque would be at a lower rpm due to this, with the rest of the curve shaped around these limitations. If one was to use the basic programs to estimate changes you would need to cheat the valve size to get peak torque at a realistic rpm. Flow bench #'s can give relevant data, but the velocities and CSA are what you are after... with the CFM's used for different metrics than for peak power rpms. Engines such as some LS or aftermarket heads MAY have the valve seat throat as the MCSA, rather than somewhere up the line. Obviously this situation would be sensitive to increases in port area slowing down velocities and affecting the powerband. Tough to do that in a nailhead. Much of the gain seen for larger valves when the throat already exceeds the rest of the port is from low lift flow gain, (curtain area). The port is far from tapped out at that point. Duration becomes more forgiving as well. Max port an Olds or Pontiac 455, put in a 270+ @ .050" cam with the appropriate supporting goodies and your musclecar is square in the 10 second (potential) range. Neither of which are 7500 rpm screamers. (Compression goes up to match the duration, but the rpm range doesn't due to the port area being similar. It narrows the powerband in those cases, not raises it. Peak torque is similar but the bottom drops out below that...make sense?)
had the car out again, pulling to 6000 rpms with no problem. if i was smart i would put the 323 gears i have down in the basement and call it a day, oh no that would be to easy. would never have thought it would pull past 5500 at the most. no headers and 2.25 exhaust too. been thinking about or over thinking lol. longer rods yes are helping top end, Tom's rockers must be helping top end too, with the extra rocker ratio giving the cam more lift and duration making the cam bigger and hurting the bottom end a little too, which in turns lowers cranking compression and bottom end torque too. thinking a smaller cam will get me where i want to be for the mild built i was trying for in the first place. for a more performance built 342 gears and headers with a 2.5 exhaust would do wonders. old cam 111 LSA on a 108 centerline 224*-230* @.050.. new cam will be on 110 LSA and 106 centerline. 218-224 @.050. toying with 218-230 but thinking its got so much top now won't need the big spread and will have a little better bottom end and idle too. losing 400-500 rpm top end would not bother me a bit. please tell me if am missing something here ? well besides brains for changing cams on good running motor.
Damn that engine runs good! Toms rockers will add a lot of lift and increase duration at higher lifts (0.200"-up), but won't increase duration seat-seat, so dynamic compression and low end torque should not be reduced! You have a 218-230 can already, right? According to Dyno 2003, stepping up from a 218-224 to a 224-230 barely reduces the low end but helps the top end a lot. When you jump to a 224-236, you do lose a decent amount of low end.... and gain more top end. With a 3000 hi-stall converter, you won't notice the low-end loss too much. Here's a graph of the 3: Green is torque, red is hp. Head flow are 'stock' numbers from Mike Kamm. The 'ramp rate' I mentioned is just a scale from 1 to 6, with 2= oem, 6= max . What did Comp say when you asked them to grind so much extra exhaust duration into it?
Walt, my old 425 had the 218-230 hyd. now gs Bob has that motor. that ran 12.89 at track, and on dyno of 403 hp and 501 tq. the top guy at comp cams did that one. had to push the fact about small exhaust valve and intake to exhaust flow ratio to him. he came back with that on 110 lsa and 108 centerline on the fast ramp xfi lobe on intake and extreme energy exhaust lobe. he said about putting less lift on the exhaust side. 521 intake and 490 exhaust. it was all done at 5200-5400 rpms because it was a fast ramp and hyd . now on my 401 that were a talking about it has a solid lifter cam 224-230 on 111 lsa. i want to go to a 218-224 or the most 218-230 on a 110 lsa.
The 111 LSA hurts bottom end and midrange. The smoother idle from wide LSA is to some degree due to the delayed opening starving the cylinder. With durations that small I'd tighten LSA quite a bit more. I've run similar with a 106 LSA installed at 101 but with good long tube headers (228, 236 @ 050) It wakes up immediately. It will won't idle too terrible, but wake up sharply...then run out of steam earlier than the 111. The idea behind the extra overlap (which isn't that much with these tiny cams) is to initiate the pull on the intake tract and begin filling the cylinder earlier in the cycle. Your top end pull is because the heads supply it. The rockers certainly help, but if you are pulling 225-250 cfm then the intake port is capable of more than 500 hp. Your cam and cubes combination aren't intended for that, therefore it hangs on longer than you expect. Longer rods might be contributing a percent or two up top, but more past peak hp as things drop off. Those were always an advantage when porting wasn't allowed and already restricted with an over-cam strategy ,your induction is no longer restricted, nor overcammed.
Hi Walt, that graph looks very familiar. Nailheads seem to run out of power at around 4700 with stock heads even with cams and bigger carbs and parts. Joes bigger engine has been a very good test mule for us. We have tested two cams and 4 head configurations with them. After joe ran 12.38 I called the guy that goes by cam King on speed talk and talked to him for a few min. About the cam he was using and he seemed to think there was more in the cam, somthing was holding us back on top end. I am guessing it is just lack of air. Joe your new 401 will like that new cam you are looking at. It will give more tq and that's what your looking for. it's kinda hard to make more hp if your only peaking between 4600 and 4900 in my opinion
f85 i would go to 109 lsa that is whats in the 446 ci now, but no lower, want a smooth idle as possible.. Bob i will get to the track sometime with the 446 mini stroke to test your latest heads before the end of this season.
A non-nailhead but similar proportioned short block example of how a port can change the behavior of a cam; I toned down a near 700hp pump gas deal to make more pleasant for the owner to deal with. After engineering, machining, flowing everything and tuning it, I decided to change only the heads due to the wild nature being a bit more than what I wanted to give the owner. Having an very unstable 1400rpm neutral idle and poor vacuum isn't any surprise with 270+ @ .050 , .650" lift, 105 LSA in @101*, a 328 cfm port, a SP intake that flowed more than that and a 1000 CFM carb with appx. 400 cubes. Getting to a 950 rpm stable idle with a few more inches of vacuum was more impressive, being that the port was only a few cc smaller and flowed 10 CFM less. The main difference in the port was the smaller CSA and measured velocity in certain areas of the port. Keep in mind that the same short block would reach the critical velocities and power peaks earlier (lower rpm), it would tap out the port sooner. The combustion patterns definitely looked different, even though they had exactly the same chamber. The larger port required a hotter plug to not die. There was absolutely no comparison in throttle response on a stand. I didn't dyno the toned down version from it's original 687hp (I've duplicated this one) , but being that it exceeded expectations by a mile already I thought the end justified the means. It wouldn't have been worth the cost to see it lose appx. 20 hp or see the peaks come down as expected.
just ordered a new cam be here in a week. solid lifter- 218-224 on 109 LSA with 105 centerline. smaller cam will go better with my compression too.
Nice! I might use that one on my 4 speed car.... want lots of low end power. Extreme Energy lobe or the XFI fast ramp lobes? Will a fast ramp lobe work okay with 1.9 ratio roller rockers, or will that make valve action TOO fast? It's odd that Comp doesn't list other Nailhead cams in their catalog other than the Thumper series, but you can buy the Magnum and Extreme Energy cams thru Summit on ebay.
it is a solid lifter Extreme Energy lobe. with the shorter push rod it comes out to about 1.67 ratio. i wouldn't do 1.9 ratio on a fast ramp maybe 1.75 on intake and 1.65-1.70 on the exhaust.
what i have read the extra exhaust ratio will hurt more than helps. on the intake i read you will see very little gain going above 1.70. just what i read no facts to back it up. another reason on Toms rockers when you use a long push rod to get more ratio like 1.9 there is a lot of side load on the valve guides. even at 1.6 ratio there is a lot of weird angles going on with the short nailhead rockers. what i read and just my opinion no real facts. oh yea f85 i went with the 109 LSA now your on the hook, LOL
I was pushing for tighter than 109 for that small of a duration to cube ratio, so it's still on you I definitely support an easy by comparison exhaust profile, that's pretty well proven. The rocker ratio doesn't show large effects until midway and later in the cam lift cycle, so I don't believe you are going to overcam the induction. There isn't enough spring here or rpm to think we are dealing with a potential mechanical disaster from a stability or wear standpoint. At .200" lift the difference at numeric value (not measured) is [only] .060" or so, not that this is accurate due to rockers having a variable ratio through their arc of travel. It seems to me that it would benefit from more degrees of rotation with the valve near max lift. I don't believe you are at a VE% high enough with everything in the balance to see any harm. I also respect the idea of some safety margin because you already have a really good working combo.
Perhaps a better statement on my part would be, just because you slap better flowing heads on something doesn't mean a big cam will suddenly act tame. That was my interpretation of your earlier statement. Joe wants to keep idle quality in mind so this is important to consider. Again, it is not an end all be all for determining the exact horsepower power and torque curves, or the exact horsepower and torque values at a given RPM. There are way to many dynamic variables at hand. But based on my experience, it is pretty good at predicting an overall trend. Do you think an average individual has the resources to dyno their particular combo with mulitple intake, head, cam, and exhaust combos? The answer is no. Hell, if I gave you all of the input parameters, could you provide a more accurate prediction for values and curves? Maybe, based on a lot of estimates from empirical formulas and a lot of time.
@.050 the old cam had 5* overlap. the new cam comes out to 3* overlap. so its safe to say idle should be as smooth as old cam ? and maybe even a 1/2 lb more vac.
Yes. As stated... you can do it from the induction system and work outwards from there. Info been available for decades, but the average fellow didn't have things as easy as today for sure. Peaks obviously easier than curves. Need more than cfm #'s to do things, engines are velocity air pumps. I never needed to math out an accurate dyno estimation to meet goals. Working with the flow bench and swelling the torque curve according to a computer sim as a time saver to tribal experience is effective enough to keep profitable without redesigning the entire engine on paper and the time involved. I was making a distinction between fast flowing heads and heads achieving CFM #'s due to a larger slower port. My intent was to encourage the goals of the OP and attempt to do so with info that tends to go against the grain of information that floats the net, no offense intended. IME, the engine's behavior always changes for the better under this premise (velocity based improvements). I'm sharing this info here because it is rarely discussed through normal media and most enthusiasts don't have things like flow benches or do very many top end swaps or get involved with making aftermarket heads and such. The aftermarket promotes what they need to in order to sell their wares, and downplay or ignore what doesn't help that goal. I'm kind of being the bad guy here and pointing out the virtues that lie within the factory pieces instead of pushing the aftermarket. Sadly, this premise goes largely overlooked because of a couple things. Porting, flowbench, and induction work is really expensive. The other is that such work is almost universally done to justify full throttle performance goals. You would be hard pressed to find any part throttle or lower powerband test data or even protocols. So, not only is it ignored but there isn't an easy way to quantify data. I happened to pay more attention to the behaviors due to the extensive mileage testing I've done. As far as programs, there are good ones such as Pipemax available these days, that uses more measured data rather than parameters such as 'stock manifolds with mufflers' or 'max flow dual plane intake'. Not practical for the hobby consumer. The easy to use programs are good for seeing where the curves swell from changes. Head #'s and a couple of formulas are more accurate predictors of power potential if you aren't relying on guessing the right parameters to use. I'm not knocking any programs, just saying that they lead to people thinking things such as the cams having more influence over peak #'s when it's really the heads, due to the way they work.
If a person was concentrating on low and mid lift cfm and letting the higher lift numbers fall where they will my opinion is you would want a fast ramp to get thing really moving for the little amount of air that your going to get. And for reasons already stated a solid lifter is the way to go on a nailhead. If a person was looking for performance and not just a nice cruiser. Guess we need more poeple with some track testing, including myself
