Why is the "new" thing to get bigger durrations/lifts and higher LSA's on NA motors to adjust for the high powerband?

wont this offset (and then some) the "extra power" you got from the extra lift/degrees?

How about the "driveability issue." will it tame it more than having less

someone want to help out here?



Reason i'm asking is that
THIS happened and now i'm pretty set on a blend of 236 and 230 cams-

probobly a 234/238 cam with the same lift as he 236/242.

My main issue is getting it more tame, lower RPM and as much power as humanly possibly out of an NA engine.


I'm just soooo lost with the LSA thing-
It doesn't seem logical to me to "bandaid" chop and lower your powerband with more LSA....

 

think in terms of overlap, and advancing or retarding the intake lobe in relation to the exhaust.

I would try to explain it, but I am sure somebody can do it better than i can. i know what I mean, but I don't understand it well enough to give you a good explanation.

I wouldn't be too concerned with the heads being done for that different lifts.. its not like comparing a .400 lift cam to a 650.

 

ohh yeah, i'm not TOO worried about it-

its just than my friend called me 3x to ask me my cam specs before porting I'm more pissed than anything right now. In the grand scheme of things, its probobly only .1 sec in the head difference i'm guessing. The heads really have crappy flow up top over .550 but they seem relativly strong down low from what hes gotten out of them so far (intake side) so its not the end of the world.

I just seem to be reading a lot of "230/236 with 114LSA instead of the 224/230 on 112 to push the powerband down" kind of stuff and was hoping for an "advanced" answer as to why that is a better way to go

 

Well, I would venture that the biggest reason for the recent trend towards longer LSA/LDA’s is a combination of emissions (less overlap usually = lower HC #’s) and computer controls (less overlap = better vacuum = more resolution for the ecm/pcm which allows for more precise programming).

WRT to what it does to your power band, a bigger LSA helps the bottom end with that lesser overlap, and helps the top end by closing the intake later allowing more complete cylinder filling at higher rpm’s. This does soften the midrange some.

Basically, the narrower the range is that you expect the cam to operate well in, the more you can zero in on that range with duration #’s and the stronger you can make the peak by tightening the LSA. If you require a broader range (ex, running a 4l60 with the big rpm changes at shifts), the more LSA you’ll probably need to get a suitably broad power band.

 

good info

with that said, i think a 238/246 on a 114 or so is in order

560/574 with some Xe "inspired" ramps


heres another question-
what is the big disadvantage of larger seperation angles?
granted it will push the band down some-

byt why not go with a 242/248 cam on a 116 or 117 LSA?

whats the point of dimishing returns?

 

This is what I have found. . . .

The wider lobe sep (as compared to a cam with same specs but smaller lobe sep) will have more vacuum since there is less overlap. Wider lobe seps work better with LARGE NOS systems or Superchargers for this reason. The wider lobe seperation also produces a broader powerband but less peak power. Lobe seperation as well as Intake lobe centerline has alot to do with this.

From what I have seen, a slightly larger cam with a tighter lobe sep (110) seems to "get into" the power band quicker. I would rather have a tighter lobe sep and early intake centerline with slightly larger cam specs. It seems to make the same peak power but more low end and mid range IF TUNED PROPERLY. Alot of people are running mail order tunes and a tight lobe sep. can make it "tougher" to get close. If you are getting a dyno tune there should be no problems. There again these are my opinions and I am suer that some other people can give you some more "fact based" answers.

Trey, As far as the flow #'s dropping down after .550 lift, that is not good. Even with .540 lift, you would want the flow #'s to keep climbing or level off way past that. The flow bench measures at a steady 28" of depression and it is flowing air only. When the head is on the engine it will see TOTALLY DIFFERENT conditions. The depression will ALWAYS be changing, you have valves opening and shutting, overlap, pistons coming up and down, sonic pulses, etc. I am not sure what depression it actually sees but it could be anywhere from -10" to +40". I am not sure if it is this high or less but my point is that with air AND FUEL mixed together, and all of this depression changing, the port will go turbulent at a much lower lift than a flow bench will show at 28". If you can keep it from going turbulent at .600 lift (with out destroying the low lift #'s) you will be much better off, even with a .500 lift cam.

NightTrain66

 

I believe you still don't have it all together Trey

The wider (114+) LSA does NOT move the powerband down in RPM. That can be done by changing the amount of advance/retard you run or by changing the duration.

Let's say you do go with a 238/246* .560/.574" 114LSA cam like you mentioned. Comp likes to grind 4* of advance into it's LT1 cams. With that set up on a 383, let's say you put out 525hp@6000/527tq@4500. If you were to change to 5* advance that would move the peaks to 516hp@6000/528@4500. Yet with 3* of advance that changes to 529hp@6000/526tq@4500. And finally, straight up that would be 548hp@6000/526tq@5000. I did a quick mock-up on Destop Dyno to get these numbers.

One thing to think about is the VE and how the valve timing relates to it. According to this program, up to a point, the more advance you have, the greater the VE is.

All these cams have the same overlap (14*@.050), but the points where valves close change greatly.

What are you wanting from your engine? What powerband do you want it to shine in? What transmission is going behind it? Lopey idle or smooth?

By the way, I put in the 242/248* 116+4LSA, but with the same lift (that will probably go up with the bigger duration) and I don't think you would like the results. For the peaks, HP is 524@5500 and TQ is 523@4500. However, compared to 238/246* 114+4LSA the torque at 2000 drops from 424 to 413. The only benefit I see is the extra 2% of VE.

Of course my thoughts are probably not totally correct. So if any of the cam gurus read this, please correct any of my statements.

 

Be warned, that I don’t know anyone (at this point about 10 people will crawl out of the woodwork to argue with this, but you get my point) that has gone with the larger XE lobes that didn’t have some valvetrain problems. The lobes work but need a lot of valve spring/light valvetrain to keep the lifter in contact with the lobe. I’ve known more then a few people that ended up going with a ‘normal’ lobe on the bigger exhaust lobe for just that reason, but if you’re running good springs and a light valvetrain you’ll be OK, or if you run a rev kit.

It won’t push the powerband down. You can think it as it will take that HP and torque curve on the dyno graph and push the peak down, but make both the low end and the top end better, you get a broader, but flatter powerband that’s centered in roughly the same area.

What you’re asking about is pretty much what OEM’s (GM since the TPI engines) and even Indy/formula one builders have been doing recently. They’re willing to give up some of the peak to get a broader useful powerband, and an engine that feels smoother/easier to drive (flat torque curve).

Where is the point of diminishing returns? Well, we’re probably somewhat past that. If everything was optimized for an NA application you probably would get best results in an SBC with about a 110*LSA (assuming that your engine management isn’t an issue). At that point you’d get the crispest throttle response and nice fat midrange. There are cams ground with LSA’s in the 106-108 range for specific classes, but you’d probably never want them in a street car, they wouldn’t idle and only work in a very narrow RPM band.

What I would choose would really depend on the application. For most street setups (daily drivers or almost daily drivers, cars that see much more street time then track time), I like cams with 114lsa’s, the only ‘issue’ that I’ve got with them is that with moderate durations they can really sound tame (with good tuning you can pass off a 218/230/114 as a stock cam in a 350, and a 224/230/114 in a 383). I like 112lsa’s in my definition of street cars (they see say 5K miles a year (I use my ‘tow vehicle’ as a daily driver), and probably 150 or more dragstrip passes). I think that for the most part, 112lsa’s feel more “fun” they feel more aggressive for what they are, and I’d consider a 110 for a much more serious street/strip/race car, especially if I was trying to get away with a smaller displacement/duration and a lot of compression.

To be honest, I don’t see much point in going above 114 an NA application (boosted on the other hand, I’ve seen LSA’s as big as 123* that worked GREAT). To be completely honest, I don’t really see the point in going with a hydraulic roller as big as what you’re considering at all. Above about 224/230 (with XE lobes) they just become an unnecessary hassle that could easily be avoided with a solid roller, which could be made significantly bigger, make more power, idle better and work with a much lesser valvetrain.

HTH

 

The better the heads the less cam you need. Even a small duration Solid Roller (say a 230/240) with a excellent LT1 or good LT4 port job is going to be too much cam for a 355.

Good head guys need a lift range to work in, then you need the flow specs and port size to get the cam.

I agree, flow that drops off at higher lift is not good, flow that levels off is not bad.

More LSA will flatten out the curve and likes advance more than less LSA on a street car. The low rpm driveability is improved on a higher LSA.

Bret

 

yea, but often it comes down to you can make the power with what amounts to fairly lame heads (say, don't touch whatever you've got now) with a larger cam for about $300, or you can get the much happier combination with a smaller cam for $1-2000 (if you’re lucky) and run the same #’s at the track…

FWIW, I'd rather err on the side of too small a cam if the car is going to see any street time, but really you should be choosing a cam based on the rest of your combination anyway, so I'd wait to see the flow #'s that your head porter gets.

BTW, Bret, did you get my email?

 

just as a point of refrance-
i have a 383, not a 355.

Also, i think the broad powerband would be more desirable since this is going into a motor backed by a 4L60E and 3.73 gears.

The car sees only a few weeks a year of street time and maybe 50 runs a year.

Springs are ok i guess, the comp 103080 (or something like that), pro mag rockers, stainless valves. Valvetain isn't weak or heavy, bt its not light or incredible either.

 

"The low rpm driveability is improved on a higher LSA."

Bret, how would you explain the heavier B-body oem LT1 cam using a LSA of 111*? This is obviously less than the oem cam LSA used on the F-body.

 

That's simple, we only got 191/196@.050 duration

 

BTW I had a 95 Z28 cam checked and it was 117LSA

 

just to have more facts here
the B-body cam got 111LSA with I think a 106.5 ICA.