I think it is directed more at Gen 1 engines with so-so cylinder heads and primarily carb'ed applications....and at that I feel the Vizard info is a guideline at best. There are too many factors and variables that play into the picture to say A + B always equals C (weight of car, application, trans and gear choice, idle quality, etc. etc.....all the typical stuff that applies).

In our Gen III applications, different manifold design to promote more TQ (longer runners) doesnt need as tight an LSA (to crutch and enhance midrange TQ) and in fact benefits from a wider LSA to carry that TQ (and the added upstairs power numbers that always brings). No need for tha additional overlap for better carb signal in the Gen III engine....and better airflow traits and combustion chamber design in general warrant wider LSA's (the low lift flow is better so you dont need as much overlap to generate the same amount of intake charge pull from the high speed exhaust gases exiting during the overlap period).

I have never been a huge fan of wide LSA's but I must say the Gen III engines just seem to love them. All of my combinations have made great power from the bottom of the curve till redline and most of them have been built around a 113 or a 114 LSA camshaft.....unheard of numbers in the older Gen engines (you would kill the midrange TQ with that wide a stick).

Gen III stuff kicks butt....except a Gen I/II engine built with our new Eliminator heads of course (shameless plug I know....LOL)

 

Not true at all..

Tight LSAs bring hp and torque curves closer together and will generate more power and torque sooner. If the right lobes are chosen can even run to 7500 without falling on its face or EGRing (ie reversion.)

 

So if this is the case....why arent the LSx community using them ? why are wider LSA's more prevalent ?

 

Because LSx motors, and heads dont NEED tight LSA cams. Plus all the driveability bullshit that goes along with running high overlap cams with EFI.
That being said, there are guys out there running high 240s/250s on a 108/110 in LSx motors. They're just not the norm.

 

What driveability BS ??


Exactly what problems do you encounter when tuning big cams with efi ?

 

I run a 239/251, 106 LSA in my 346/LS6 - stock bottom end except for valve notches. It's a GM LSx cam for road racing.

No surge hot or cold. Self tuned. Low end torque sucks < 2500 rpm.

But, nice broad tq curve from 3000 -7000 rpm (350-400 lb-ft. rwtq).

fwiw.

 

I'm sure you can lugg thru a school zone, in second gear, at 25 mph, and 1200 rpms, right?

 

I think so. Not sure....so I'll try it.

 

what is with this presumption that Overlap has anything to do with Mid ragne power ? It doesn't. It's all about focusing the power curve through helmholtz tunning. If you get the correct runner lengths on the input and output side the right cam timming IVC IVO EVO EVC and the correct cube's and you find the FQ, tunning in a bit of overlap can "Ehance Power In a Very Narrow RPM Band" not make it.Typically what I find is that very efficiently headed Engines, high Revving 4cylinders dohc 4v engines come to mind Do Not need or benefit from lots of overlap.

Usually Overlap is a very vain attempt to procude more power through a limited and highly restricted induction system. go to far with it on a system that has a fairly low restriction level and you'll start killig power.

And thats All I have to say about that.

 

Thank you!

 

Mamma Always said Life was like a box of chocolates.

 

Depends on who you ask....And it depends on application. I have a 110 cam in my car straight up. I know of a few others about to get one similar. They tend to get peakier per say but do start to make power sooner and dependant on other things do carry it out as well.

 

You shouldnt have any to be honest. Overlap=torque. Tightening up LSA's moves the hp and torque graphs closer together and therefore are more friendly. If things are setup right and are effiecient together a tight LSA cam will still pull 7200-7500 in hydraulic applications and not run out of steam like some tend to think they do. The 236/242 110 cam in my car will go 7200+ no issues but the stock A4 wont. So we put the rev limiter at 6800. Its actually flat and not climbing hard but its not nose diving either. RPM=HP with this cam.

 

This guy hit the nail on the head. Read the part about better carb signal with tight LSA. Now go take the blue pill.

D.J.

 

too much overlap will hurt intake vacuum...so how would that improve a carb signal ???

With modern EFI....you can map it, and you dont even need to see a intake manifold signal. Just use TPS vs RPM.

 

Vacuum is a good thing.

 

Interesting nut on overlpa discussion here. 244 244 on a 116 is the same amount of overlap as a 28 218 on a 110. Well it might not really be the same but you get the jist of what I am saying here. LSA is a stupid number. Overlap degrees is useful.

I would say overlap additively from what I have seen shortens the power band. the more you ad the shorter it gets. Its all bout focusing the powerband with overlap. If you have a 15 speed transmission and a slipper clutch you could creat the most insane 500rpm powerband possiable and the car would be fast.

 

Except for the fact that overlap lowers vacum and therby lowering carb signaling.

 

this would be why so many Carberated engines run like dogshit.

 

No, that is usually operator error. Nobody really knows how to work on them anymore, b/c everything has went to some form of injection over the last 19 yrs.