stockA4

What was that old gm performance LS7 "stage 3" cam? I think the exhaust duration @ 0.050" was something really radical, okay, so I looked it up it's all the overlap for real

It's a 233°/ 276° on a 107° LSA

I bet that would sound pretty cool, " tunes well, easy to live with"

grubinski

What’s really strange about that cam is the bias on the overlap. IVO is at something llike 8,5 BTDC, and EVC is at *32 ATDC*. The exhaust valve is open waaay more than the intake at TDC. Looks like a recipe for a 3000 rpm idle.

stockA4

I can feel my mullet growing... Gutted and caged fourth gen with good coilovers or konis and 200tw 315s all the way around. Maybe the paint's not that great and some of the panels aren't even the same color. I think the rougher the bodywork the better in this instance. Anyway Drop in the Ls7 or the nastiest 6.0-6.2L you can bolt together with that cam 2" headers and flattened side pipes in front of the rear tires. Manual trans of course. 95' an older f bodies don't have to pass emissions so you could drive it on the street once you get the idle figured out.

Summitracing

Side-pipes yes. Guesses nope nope nope and nope. If we say it can work with a stock converter, what valve event would we adjust?

stockA4

Basically what summit is asking is where is putting the overlap going to cause the most reversion and idle instability?

I can say from moving around enough cams that the exhaust valve closing is the one that causes the most problems once you go past 0° @ 0.050 and on to the positive overlap area where you will be diluting the intake charge at lower speeds. It's simply the geometry of the engine valve events. Even if you open the intake really early you can close the exhaust valve earlier so there'll be less exhaust just sitting there for the cylinder to gulp back up. This is why when you back a cam off instead of advancing it, the idle becomes more unstable, advance the cam and it will sound meaner and possibly run smoother at lower speeds but it won't make as much top end power.

Atver300

iTrader: (8)

I'm guessing a 218 230 105+3

stockA4

That's a crazy If that's the correct spec did D Vizard spec that from one of his old charts? stock converter haha I ran the OG 8714 that's a 226/230 112+4 with a stock converter for a while yeah its gonna need some extra time spent on the tune to get it smooth with that much overlap but surely by maximizing the low speed cylinder pressure via such an early IVC event anything is possible? I mean the stock cam runs on the stock converter with a couple spark plugs pulled right? It might make more sense to me I guess if I think about it that way that's a lot of overlap

fwiw I'm going use this 207/232 121.3-1.2 I found with my FTI 2600 stall because that makes sense to me regardless of what camshaft you might find yourself running these days also fwiw IMO a looser and or lighter tourqe converter doesn't make the combo any easier to tune either

Woodylyf767

Off the Holdener vid?

Summitracing

Another cam test we’ve been looking forward to! Richard Holdener does what he does and puts our Summit Pro LS SUM-8711R1 Stage 4 (extra valve clearance version) against the SUM-8733R1 Big Nasty 5/4 race cam.

Two cams for two completely different missions, durations, LSA’s and Advance; but overlap (intake valve opening and exhaust closing point) is the same.

We’ve kept the specs secret on Big Nasty up until now. Check out Richard’s post and I’ll explain how we do what we did. No spoilers though!

68Formula

Ok, so other than the person who quoted the Holdner vid, my 220/232 106+4 was durn close. What did I win? :-)

Summitracing

The Big Nasty 5/4 race cam was always intended to be educational. 1.) People need to see published specs to make a good decision. Basing the cam you buy on a name like “Big Nasty 5/4 race cam” would be silly (but please buy it anyway on its other merits 2.) Lsa, Duration, and Advance are all just outputs to stick on a cam card. The valve events are what matters. 3.) Chop is overlap and isn’t directly tied to duration at all! Most of you guys know these things, but many don’t.

We designed these two cams with intake opening and exhaust closing in the same place to have adequate piston to valve. The “problem” we had is the customer’s WANT the chop of 8711, but NEED the 51 ft.lbs of torque when they mash the throttle down low. So we closed the intake valve earlier by 14 degrees to move the powerband down. Even sooner than Big Torkinator by a couple degrees, but later than 4.8 Torkinator by four. This is why it will work with a stock converter.

Note BOTH cams produced within 8 ft./lbs. peak despite DRASTICALLY different dynamic compression ratios (for people into that kinda stuff lol). We’ll take this a step further and say a given octane is going to support the cylinder pressure needed to produce 431-439 Ft./Lbs. of torque either way. Meaning static compression remains king in determining the need for higher octane. A larger duration cam isn’t a savior nor will a torque cam demand more octane (although we still recommend good gas when towing though).

As for David Vizard’s Lsa minions, would he have intended for this engine to lose 30 horsepower up high with a 105 LSA? It’s just another nail in the coffin for magic LSA for a given displacement or head flow percentage. Only by deciding each event individually do we get this kind of control and resolution.

Last note, Sum-8711R1 was on a tear wasn’t it! We wish it had been pulled to 8500 to see how stable the Pro Ls lobes are, but the junkyard sbe was puffing and not long for this world. Big Nasty went flat instead of peaking and we think this is a function of the heads and springs.

When we told him Big Nasty’s specs, Richard didn’t think the short runner was a good match. We actually tailor intake closing point earlier on our single plane cams for this very purpose. People are often stuck with short runner intakes and that’s not the best for pulling power down low. We can crutch the powerband down into a useable area and STILL make pretty good power up high.

Summitracing

Ding Ding Ding, we have ourselves a winner of the "Big Nasty 5/4 Race Cam" contest! Congratulations to @68Formula for guessing the closest cam specs for the SUM-8733R1 His guess was 220/232 106+4 and the actual specs are 218/230 105+3 providing 14* of overlap. All the CHOP

With the choice of any Pro LS cam or a Summit Racing gift card of equal value, he went with the gift card. That's a good way to spread out additional funds towards multiple parts of a project.

Thanks to everyone for joining in on the fun and participating in the contest!