NA, not really… just a few thoughts. A lot of people mostly worried mostly about performance end up going a little larger on intake duration and are happy because most people are running relatively crappy heads (I’ve said it before… $300 for a cam or $2K+ for porting…), because of that tendency to compensate and since a lot of people are concerned about passing emissions (or later come back and bitch that they didn’t pass and what can we do to help them) they are better off running slightly more LSA then you would recommend (no one with crappy heads that needs to pass emissions will get away with a 23x intake at .050” and a 110 LSA…).

I guess not so much nit picks so much as you just didn’t cover it…

and suddenly there is power to be found in the exhaust valve opening… Turbo cars are completely different.

FWIW, the reason that I was fairly quick to point out an SR is that there are a lot of people out there that think that they’re going to pick out and extreme lobed cam with a .050” duration over 230 and then spend the next 2 years trying to make it rev over 6500 with springs light enough to work well with a hydraulic roller cam. I for one am the KISS type that prefers to either not try that or to just run a SR, rather then go with semi exotic valvetrain parts and rev kits (on a street car)… But at this point it’s really more of a question of what you’re willing to tolerate.

 

Correct. I was trying to illustrate the same point two different ways.

Rich Krause

 

Heh, that raises a question that I’ve always wondered about but never had the opertunity to explore.

Are there any problems with a converter choice that stalls to an RPM higher then what your shift points would drop the engine down to?

 

Good points!

I really don't know much about turbo cams, by "blower" I did mean centrifugal SC as you correctly inferred.

You can increase intake flow with a longer duration intake lobe to a point. What makes this unsatisfying is the effect it has on drivability. I drove an LT1 with stock heads and a CC306 once. Eeeew! Not very pleasant. You can get a basic porting of the intake and exhaust for $6-800, spend another couple hundred on a good set of springs, and then your cam will really shine!

I agree, go SR if you want really high revs. You need to ask if you need those really high revs though. Head work can be pricey, but the $$$ needed for a high rev setup can get out of hand pretty quick. You can make a lot of hp with a set of decent heads and a well selected HR cam. But I have no problem with an SR - there's a lot of advantages to a SR for a high buck NA buildup.

Rich Krause

 

Yes, at least for a street car it would be extremely annoying to drive on the street with a converter that loose. OTOH, race automatics may have converters stalling at 6,000 or 7,000rpm.

Of course, what I find annoying might be acceptable to someone else.

Rich Krause

 

Well, the reason that I’m asking is that I’m anticipating my next street/drag ‘toy’ being an heavily boosted small block with a 700r4 behind it. I doubt that it will ever rev over 6000rpm (more likely in the 5500 range), but will probably launch hardest/make best boost off the line with a converter in the 3200-3600 range, which will be significantly higher then what you’d get in the 1-2 gear shift (3.06 to 1.63), about 2900rpm with a 5500rpm shift point. Essentially, I’d be using the converter to narrow the required powerband.

Maybe this should be a separate thread…

 

Knee jerk response, although it sounded like a ?:

Inbetween response:

I don't disagree, Cheston.

Followup response:

I wasn't picking and choosing. I was just questioning why you did!

The way I see it is, duration, overlap, and IVC point has far more impact on the cam torque characteristics than the LSA does. Why else would GM shorten the duration, IVC point, and basically leave the overlap alone for the heavier B body? According to your (and others) comment, the narrower LSA on the B body cam (111* to 117*) should have made more of an impact. In this case, a negative one. But being a variable with the lest impact, it was of little consequence. Agree?

 

Just so I understand what you stated regarding this quote:

However, compared to 238/246* 114+4LSA the torque....
the way it is written you are referring to the torque ( of the 242/248* 116+4LSA cam ) correct?
....at 2000 drops from 424 to 413. The only benefit....
again, of the 242/248* cam, correct?
...I see is the extra 2% of VE.

 

A side question- sorry if I'm hijacking the post......

I've expereinced that real tight LSA's (106-108) work GREAT on cars with open exhaust and header collectors that are of roughly the correct length to generate real exhaust scavenging.

But put the cork in the exhaust and that same cam will drop 40HP like falling off a log.

Cams with wider LSA seem to be more forgiving of street exhaust systems that have to have a muffler and can't benefit from proper length collectors, even if it's not really restrictive in the general sense of the word.

I'm guessing that if you have less overlap (due to wider LSA) that exhaust scavending becomes less of an issue simply becuase there is less overlap in which to generate exhaust scavenging.

I'm starting to be of the opinion that I see no reason to go tighter than 112* LSA on a motor that has to live with mufflers (although I have often done just the opposite many times). Keep in mind I'm a carburetor buy, so fuel injection intakes aren't my strong suit.

Yeah? No? Comments/conjecture?

 

I agree damon. when you get too much overlap with a street exhaust, the effect of the exhaust charge helping pull the intake charge in is diminished when you have pressure in the exhaust system. same reason why turbo cams generally have wide LSAs, because there is going to be a lot of pressure in the exhaust system.

 

speakin of which, hows that project coming along jordan (shoot me a pm- dont wana stop this train of a thread!)

 

The point about exhaust systems is a good one. My guidelines are in the context of a fully optimized combo. This is an illustration of the point of considering the whole combo.

Rich Krause

 

holy crap- after reading this a few times- its all starting to make sence and seem do "duh obvious"

wow, i was 100% lost and now it makes sense

 

so wait, if LSA doesn't determine how high the motor will peak (ie redline) what does? duration?

 

Durration, lift, LSA, Intake/exhuast opening & closeing points, advance, head flow all determine where you will make power.