JAYDUBB

http://web.camaross.com/bb/Forum2/HTML/006803.html

B4Ctom1

After reading that thread for a short time I came to a couple of conclusions; 1st: everything those guys are saying is regurgitated magazine tripe, not tried, true, and tested. 2nd: the magazines say use a wide lobe sep cam because they are thinking along the lines of the average guy and increasing his cylinder pressure, but with the availability of poweradders and the lack of fear in using them, along with the fact that we have guys building exotic street setups generating obscene cylinder pressures, its time for phase two of the learning curve. 3rd: if you build a car that runs obscene boost, or nearly obscene boost and nitrous, or giant bunches of nitrous you will learn that current technology for sealing the heads (i.e. head gaskets, wire locs, stainless o-rings, ...) let alone the pistons (except TRW's) will not be able to cope with the cylinder pressures produced when a wide lobe center angle cam that has little or no overlap. Let us take a lesson from the guys running in the big engine, big power adder classes of the NMCA (or any of your other favorite similar leagues). they are building pro stock size engines and if forced to give up thier power adders would run pro stock sized cams and angles. prostocks run like circle track guys 104 to 107 degrees lobe sep. where as our power adder cohorts run like 108 to 110. With power adders no less! all power adders create ridiculous amounts of exhaust gasses (especially nitrous) and a little overlap can help vent this (and really help turbo cars spool faster) and improve scavenging as well as reduce detonation, and save you from blown head gaskets. This is not for every one, if you have a nearly stock combo, and a entry level blower, or if you run nothing but a 150 hp NOS shot or less and run a TPI intake then definitely not for you. especially because the TPI design is not for overlap cam profiles and definitely not for stock speed density ECMs. but when heavy boost is used on a TPI style manifold configuration then a trade off may be the ticket. the reason I bring this up is that this week at our shop I have changed more blown stang and blown camaro head gaskets than ever, and we run a 500 hp shot on a stang that we drive on the street and go mid nines with, it has only 347 cubes and has high compression, and we street drive it because it is so low maintainance. also we got 80 more hp on the same shot with a cam change both cams are similar but we went from 112 lobe to a 110.

JAYDUBB

Ok... do i still have a head?

j/k

I breezed through that post and figured it would make for interesting reading, considering most of those guys have already been there and done that...

Greenshamrock77

Here is something else to consider.

First off remember that EVERYTHING is a compromise. Always keep that statement in the back of your head when deciding which component to use or deciding on the next mod.

Lets take a look at what is happening inside a forced induction engine that would influence a camshaft decision. A forced induction engine does not raise cylinder pressure nearly as much as a nitrous engine does. Nitrous creates insane cylinder pressure to make it's power. A forced induction engine also increases cylinder pressure, but not nearly as much. A forced induction engine recieving ~200% VE will only net about a ~15-20% increase in cylinder pressure. Basically a nitrous engine pushes very hard for a short time. A forced induction engine pushes a little harder for a longer time.

These characteristics are important in deciding on a camshaft. With the forced induction engine, we would like to see more exhaust timing and less overlap generally. This is the part people get with no problem. More exhaust timing to vent the increased amount of exhaust created by more charge getting in, and less overlap so that less of our intake charge is wasted out the exhaust. However there is more. The wider you spread the lobe separation, the sooner you open the exhaust valve BBDC. When you increase exhaust valve timing, the sooner you open the exhaust valve BBDC. Remember in part how a forced induction engine builds it's power? It pushes down LONGER. As soon as that exhaust valve opens, the cylinder pressure that pushes the piston down dissappears. Being able to push down longer is important in a forced induction engine.

Here is where the statement I made earlier comes in. More exhaust duration breathes better, and a wide lobe separation keeps the charge in the cylinder, but both of these net an earlier exhaust valve opening... compromise, compromise, compromise.

A nitrous engine is less particular on the extra exhaust duration. It's net increase in power is due mainly to the great increase of cylinder pressure closer to TDC. Also Nitrous does not like a whole bunch of overlap either because unlike a forced induction engine, you only have "x" amount of Nos to work with. When a large overlap is introduced, some of the charge/NOS goes straight out the exhaust. This nets less actual NOS doing work, and less power.

So when comparing/deciding on cams look at when the valves open and close in relation to TDC and BDC in addition to just the duration and overlap and think about what affect that will have on your combo.

As far as forced induction blowing head gaskets is concerned VS nitrous, I have found the opposite to be true. The only way a properly clamped, not overheated head gasket will be dislodged is from to much cylinder pressure. Remember that NOS creates much higher cylinder pressures than forced induction. The most likely culprit in the blown head gaskets on the blown engines is detonation. Nos is less technical. With forced induction, you have a lot of tuning to do to prevent preignition/detonation. This step is very often overlooked/undervalued.

Nitrous is not just hard on head gaskets but bearings, rings, and pistons as well. I have seen to many NOS engines that came apart looking like a junkyard engines. The bearings are always showing copper, heads/valve seats beat up. This makes perfect sense too (high cylinder pressure, and extreme heat). I see the damn GN engines with 200K on them looking clean and the bearings looking like you just put em in! Providing the thing was taken care of. I have also seen a quite a few blown and turbocharged engines in the 500-2000BHP range apart for inspection/modification/ect. that looked pristine.

Bottom line, pick a proper cam or other component that suits YOUR needs. YOU know what you want more than anyone else. So do your homework, review the advantages/compromises, mind your budget, and make a decision that satifies YOU.

I do not measure a car's performance on what ET it does. I can't stand a lopey idle, poor fuel economy, and poor drivability. I like a car smooth and reliable like they are stock, only faster. Some people call cars with 256/268/107 cams MILD! Some think that that is a street car. "Well I can drive in on the street." Which is why I now use the term DAILY DRIVER. A car with a huge NOS shot, or 60PSI boost is no daily driver, nor could it be considered reliable, or function at in all conditions on pump gas. What about luxury items? I like to hear the stereo, and like A/C. If a car has great acceleration, handling, breaking, reliability, good economy, amenaties (sp), good stereo, is comfortable, and is clean inside/outside/underneath it has my hats off as a TRUE performance car. Not to be confused or compared to a race car (apples and oranges).

To each his own right!

...and I'm leaving alot out!!

B4Ctom1

I agree with your statement, it seems well thought out, my point would have been harder to make if I would have just cut to the chase and said you could boost a near stock geo metro 3 cylinder with 35 psi boost or a 300 hp shot of juice just by keeping cylinder pressure from getting out of control with a cam selection. Nitrous does make crazy cyl pressures, but so does silly amounts of boost (especially at low RPM).

JAYDUBB

Im hunting for my head now. Seems it got chewed off...

j/k

Fortunately, I understand everything that you said Greenshamrock (I'm a Diesel Mechanic). I put the link here because the "Cam Questions" seem to pop up quite often (not just here, but at other sites also).

dj haf

do you have any examples of good blower cams?

CRZYTRN-92Z28

Comp cam's nitrous cams are good choices given the application.

TwnTrboZ28

Comp Cams acually has a couple Turbo specific cams
Crower has supercharger specific and turbocharger specific cams also.
I am using comp's baseline turbo cam, it works really good for moderate amounts of boost (8-15 lbs.)