does anyone know about or have the comp cams nitrous hp cam. what makes it so special for nitrous applications. is it really worth it when my whole topend is built with edelbrock performer parts and edelbrock nitrous? whats the best thing to do? i need some feed back from you nitrous runners, what r u running?

 

I went from the Xtreme Energy 274H to the Nitrous HP 274H and slowed down 1 tenth on motor but the car made a lot more power on the bottle... so much more that it stopped hooking and still ET/MPH'd better.

 

The difference is in the lobe seperation and the exhaust pattern on the cam. If you already have a split pattern cam with say 112 lsa stay with it, if you're running a 110 or lower I'de go with the nitrous cam.

 

The simple explanation of how a nitrous cam differs from a non nitrous app cam is the exhaust opening point. ("blowdown point") A motor on nitrous needs all the help it can get to get rid of the increased exhaust volume. By opening the exhaust valve about 10deg sooner, left over cylinder pressure from the power stroke expelles the exhaust. By adding exhaust duration, widening the LSA and advancing the cam a bit more you get valve event timing that helps the motor make power when on nitrous. many of Crane cams powermax cams are ground this way already and make very good "nitrous cams" Some with just a little more cam advance dialed in from what the cam card says.
If say you have a 350ci motor that normally would make best overall torque and power with a cam ground on 108LSA (open headers). A cam with say 110 to 114 LSA that is installed slightly more advanced in the motor becomes a "nitrous cam" Especially if it has more exhaust duration than intake duration.
Esentually the intake duration and valve timing points ( opening and closing) stay the same. its the exhaust duration and timing points that are modified to assist the motor to make more power overall while on the spray. The most important factor being the exhaust valve opening point after the power stroke. ("exhaust blowdown point")
The exhaust valve is opened sooner.
Further; with a tuned header exhaust system (open headers) now because the exhaust pulse starts sooner in the header, it's returning ( reflected) negative scavegeing pressure pulse will arrive back at the combustion chamber that much sooner, so the exhaust valve can be closed sooner.
hense the earlier exhaust closing and wider LSA.
"reduced exhaust overlap"

If say you have a popular Comp XE cam now (110LSA) and you want to see if a "nitrous cam" will help your ET's, try advancing the cam you have now, some 4 to 6 deg. This will make the exhaust valve open 4 to 6deg sooner. *may* slow the car a tenth N/A but should help the car while on the spray.

* may or may not, the effect on the N/A motor will be minor.
If when re-tested on the spray, the car picks up performance by advancing your present cam, you might consider getting a cam with timing events that more favor nitrous power. "A nitrous cam"
What cam are you using now?

 

F-bird, I’m mostly agree with the sentiment, but get hung up on the fact that you go into a bit of detail and then go and oversimplify or miss the point some of those details…

And the fact is that NA (and essentially, similarly on N2O), you get most of the power transfer from the chamber to the piston early in the power stroke, and almost none at the end (relative to a supercharged engine), opening the exhaust valve earlier almost never hurts power significantly. You may loose a little MPG, you may gain a little lope at idle, but you will probably run the same time with or without the spray and usually significantly better with the spray unless you have an awesome exhaust side to start.

The justification for a longer exhaust duration is fairly simple… adding a 150hp shot of N2O to a 300hp engine is the same as increasing it’s intake breathing capability by 50%, so you’d have to increase the exhaust side by 50% to “get away with” the same cam as was optimum NA (Vizard and a few others have played with heads with things like 1.94” intake AND exhaust valves on N2O engines).

GRRR, that part was painful to read. LSA is a side effect, not a cause or a reason. If you open the exhaust valve sooner with EXACTLY the same timing on the intake side then the cam by default will have a greater LSA since the LSA is just measured from peak to peak on both the lobes. It’s not that greater LSA has some effect that it is required for an N2O cam.

Second, it makes no sense whatsoever for Crane to grind their cams with more advance then what is on the cam card. If it was done on purpose to make more power then anyone taking the time to properly degree the cam would loose power, and that would be plain stupid on crane’s part.

The rule of thumb for street strip cars is that 110 appears to make the best power. That being said, I hate rules of thumb and that turns out to be complete crap outside of a specific range. Engines making power in lower rpm ranges tend to like much tighter LSA’s and less ground advance in the cam, and engines making power in higher rpm ranges vice versa. It’s blindingly obvious that even a lot of cam manufacturers don’t seem to understand this if you look at their cams for either end of the spectrum, especially their “truck cams for heavy trucks, tight converters and relatively low gears.” For a truck cam ground for say a 4500rpm hp peak or so, LSA’s in the 106-109 range make MONSTER torque and control detonation without having to run excessively low compression. GM used to know that, look at the TBI trucks, they came with a 109 LSA cam, met emissions, didn’t ping and made good torque. But look at comp’s or crain’s grinds and you’ll see they grind their cams in that range with a 110LSA because that’s what the rest of their performance cams are ground at, and then when you look at their roller and “computer cams” you start seeing 112 and 114LSA’s which just don’t do anyone any good.

Indy cars and similar high rpm engines are the other end of the scale… after making their cam to do what they need it to do you end up seeing 116-118LSAs.

The fact is that real world, it would be much easier if people just forgot that there was such a thing as LSA and just ground cams depending on the open and close events that you need to do what you’re trying to do.

“ground more advanced…” Well… most cam manufacturer’s stick to a generic “ground 4* advanced for all their cams. At that point if you go strictly by that, then no, no nitrous cam is ground more advanced, but if you look at it from the perspective of you’re opening the exhaust lobe sooner, so the lobe’s peak (if it was symmetrical) would be sooner and so on… well yea, it is ground more advance, but like LSA, it’s a side effect of a standard, not because it is some magic number.

What N2O cam closes the exhaust valve earlier??? Typically if you go by say comp’s line they’ll take a 218/224/112 cam and make it a N2O cam with 218/230/114… the exhaust valve is closing later… I suppose if you want to compare their strictly flat tappet carb stuff, but then in most cases they go from 110 to 113 and typically have the exhaust valve closing +/- 1* of where it was on the NA cam. That’s still not significantly sooner if at all.

That’s opening a whole other can of worms. Whether or not the car could benefit from an N2O cam depends on the exhaust setup and how much spray you’re running. If you advance your current cam and run faster then usually you’re spotting a combination mismatch. Either your cam is overall too big and making power at too high an rpm range, or you have too little gear or converter for the chassis.

 

"The rule of thumb for street strip cars is that 110 appears to make the best power."
Thats not true. It just sells the most cams.
Comp sells em on 110 cause thats what people think is best.
Actually each application is different.
Tight LSA Generally makes more torque, but mostly only with tuned , open headers. Closed and/or less than optimum exhaust tuning always needs something different.
The cam with the best power LSA usually has too rough an idle for most street driving. Usually you're better off and happier overall with a little less than maxed out overlap.
on a street driven car.

You have it wrong. Wide LSA idles smoother, has better throttle response and generally drives nicer.

More overlap (tight LSA) increases midrange and upper rpm cylinder filling/power ( header scavegding) tight LSA with a good bit of advance maximizes the average torque output at WOT but can and usually costs emissions and part throttle effiecintcy. (overfueling) Thats why the motor doesn't ping at low rpm ( exhaust dilution) EGR effect.
A race motor is easy to cam for. What ever cam timing events make the most power for that combination is the right cam. Designing the best cam fo a street driven motor is a whole different ball game.

Crane designs their street cams with ground in advance that works pretty good overall. Its not ideal or optimized or carved in stone. You can move it around quite a bit to good effect. Try it. Especialy with nitrous.

"Either your cam is overall too big and making power at too high an rpm range, or you have too little gear or converter for the chassis."

Or, you're moving the exhaust timing events to a more optimum nos friendly spot that lets more exhaust out while on the spray. Ya can't burn it twice.
Some things are just.....simple.

 

Well, since you’ve just about misquoted, or missed the point of everything that you commented on in my post, I’m going to clarify:

Way to go… let’s put the next sentence back in after what you quoted:
“That being said, I hate rules of thumb and that turns out to be complete crap outside of a specific range.”

Add in most of the rest of that paragraph and the rest of your comments are pretty much pointless. Possibly with the exception of your “Thats not true. It just sells the most cams,” as far as 110 being a standard. To that I say open any book dealing with chevy valvetrain/valve timing and you’ll see some similar comment, my first line there is pretty much straight out of Vizard’s SBC cam book.

Um, I NEVER said anything about idle and driveablility.

Yes, a wider LSA does idle smoother and is easier to tune for driveablility, it also has a stronger top end like I DID say. See comments about indy cars and other high end race engines

Midrange, yes, and that’s what I said, upper, no… like I’ve said multiple times now, a wider LSA will make more power up top.

Exhaust dilution/egr effect shouldn’t be an issue at any part of the usable rpm range (with modern FI systems that’s not always true anymore… look at the vettes built in the last bunch of years). Detonation is a question of cylinder pressure, which is greatest at the torque peak which is determined by valve events, tempered by a bunch of “detonation control” factors that do not have much to do with valve timing.

It’s always a question of “just” making the most usable power in the intended power band, it just gets difficult with a street engine because people either don’t understand that or have unrealistic expectations.

Yea, you keep saying that, but what does it mean? I haven’t seen anything besides the typical ~4* that almost everyone uses.