Brett

How does a lobe separation aide in making power with an engine with forced induction? What would be the difference between 112 and 114 degrees of lobe separation? This is one of the shady spots I have about cam knowledge.
I returned my whole LT4 Hot cam kit and decided to go with what is turning out to be an all-Crane valvetrain. What I need to do now is pick a cam. For me it is a toss-up between the Comp Cams 305-8 and 306-8 for the LT1. Here are the specs...

220/230 .544/.544 114 #305 with 1.6rr's
230/244 .510/.540 112 #306 with 1.5rr's
or .544/.577 with 1.6rr's but I think I'd stick to 1.5's with the 306 cam.

Anyway, the car is geared with 3.73s, has 1 3/4" headers, will be getting a 2400tc, and the heads are being cleaned up and worked on a bit, and of course I will be using a D-1sc next year. The displacement will either be 350 or 355 depending on if I can find a new block or only used ones.

The car will be daily-driven. Gas milage is not a concern. We have emissions in this state and I think think the 305 'might' clear it but not sure about the 306. The two conflicting ideas I have are power vs. drivability. Where I live isn't like any large city and the driving is usually pretty easy, but I don't want the car to surge or be too extreme for the street. I like a car that is a little hairy to drive but most of the power will be coming from positive manifold pressure

I dunno, what are your thoughts on these cams? Anyone ever use one, or something with a similar grind?



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1991 RS LT1
every imaginable bolt-on, and an all-forged 355 on the way with an ATI following in '01

2000 C5 Coupe
black/black 6-spd, optional polished rims, 'mostly' stock....

"So what DOES the back of a Mustang look like?"

Vader

Brett,

Selecting a cam profile is like picking a spouse - everyone can offer suggestions, but you're the one who has to live with the choice. In essence, no one can pick one for you. You should do a little research and determine what is best for your setup and how you intend to use the vehicle.

I have a 305-8 installed in my '94 LT1, and I like the difference over the stock cam. I'm using 1.5:1 rockers until Comp can get the Pro Magnums produced in a self-aligning configuration (they were supposed to be available last spring). I'm running normally aspirated, and I know I need to get a higher stall torque converter and probably do soem PCM reprogramming to take full advantage of the cam/valve/port changes. I'll probably have to get a larger TB, too. These are the kind of things you find after the fact, and just some reasons why no one can make the decision for you. I've spoken with two of the tech people at Comp about cam selection, and in my opinion they tend to be a little conservative for street cam recommendations. Other peoplpe will tend to be too agressive or radical, and you need to weight the advantaqes and disadvantages of any selection.

As far as the LSA and resultant overlap, depending upon the intended RPM range, you might want a larger LSA (less overlap) with a charger, since scavenging is not a problem at street RPMs. If you're building for 6,500 RPM operation, the sky's the limit.

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Later,
Vader
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"Make Me Bad"
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Brett

Good point about the cam selection. I suppose I am already pre-disposed towards the 305-8 since it is so close to the Hot cam that I chose originally eccept for minor duration and lift changes. I found a site that has a sound clip of the 306-8 and as much as it sounds awesome I think it will be a little too much for my car. My whole goal is to build as much of a sleeper car as possible. Except for the 255/50zr16s everything on the outside and interior looks 100% bone stock. I even had the muffler tips done like the stock turn-down style to avoid attention. Granted, with the 305-8 it will have a bit of a lope to it but hopefully that will be the only givaway. There are enough people out there who wouldn't know any better if I told them it was just the exhaust or maybe just a 305 with a 350 cam I'll see what I can get away with.

As for rockers...Crane makes a Gold Race 1.6 self-aligning for centerbolt heads 88-present right now. Only trouble is they're pricy at almost 300 per set. But that's what I believe I will end up using for the motor. Supposedly Crane was outsourced to make the 1.6rrs for the LT4 and the kit I had bought and returned. Those rockers looked to be really well-designed. They'd certainly be a great alternative to plunking 300 dollars down for the Crane pieces.

D_Amlee

Not an expert here, but that doesn't stop me from posting, does it? With forced air induction systems, it is generally thought to be better to have less valve event overlap than with NA applications. Short LSAs and long durations make for a large overlap when both the intake and exhaust valve are open, and for NA engines this can improve scavenging at high rpms. Put the same cam on a forced air system, and the overlap may allow too much of the intake charge to keep going straight out the open exhaust valve due to the fact that the pressurized intake fills the cylinder so much faster.

Box of Rocks

Brett,
The 306 is a "nitrous/blower" grind, with the wider LSA it will bleed off less of the charge. It will also tend to make your car stronger at high RPM, say, in the 5,000 - 6,500 range.
The 305 will pull harder in the midrange, say, 2,500 - 4,500 RPM. The 306 will have a stout, rumpity idle. Nice.
I'm running a N/A 327 with Comp's 230/236 Extreme Energy grind, cut on a 110 LSA. Rumpity = just right.

If you are definitely going with the artificial respiration (blower), I'd recommend the 306. Also, take a peek at Comp's new series of 113* LSA cams built expressly for nitrous cars. They look a lot like the 306, and would work great with a blower.

Lastly, remember this: "There is no such thing as too much cam, just not enough motor."

Good luck, sounds like you're building another honkin' SBC.

BOR
"Hey, I'm just here for the weather."

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oldvette

Vader

Brett,

A little inside on the Crane Gold Race rockers:

Yes, GM did have Crane supply the rockers for the LT4 engine. However, being afraid of the weakness of the design, Chevorlet specified a heavier rocker with a thicker extrusion in the pivot area. They knew the basic Crane design had some "flex" in that area and wanted no part of that for their engines. The LT4 rockers are differentiated from the off-the-shelf Cranes by the Bow Tie stamped in the valve end and their increased mass.

I understand they might seem a bit expensive at $300.00, but I was willing to pay $375.00 for the forged steel Comp rockers because they are both lighter and stronger than either the LT4s or Crane standard Gold Race rockers. They also allow more clearance at the sides for the cover tubes and are "friendly" toward stud girdles. I think I'll still wait for the forged steel ones...

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Later,
Vader
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"Make Me Bad"
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Brett

Interesting, I hadn't heard of the forged rockers from Comp. When did they say they'd be available?

Scott C

Guys,

I have those GM 1.6 roller rockers from the LT4. I chose them simply because SDPC was out of the Crane Gold rockers when they assembled my engine. The GM rockers are very impressive. They are of excellent construction and the attention to detail with the Chevy bowtie and the 1.6 stamped on each one. They are supposed to be a bit quieter too. My engine hasn't been fired yet, so I can't comment on the performance. I am counting on them to help improve my relatively mild cam choice.

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'92 RS, ZZ4 10:1 350, Edelbrock 6085 heads, Crane 208/214 467/482 cam, GM 1.6 true roller rockers, Holley Projection TBI intake, Holley 670 TBI, SLP/Jet-Hot 1-5/8" headers, Catco 3" cat, Flowmaster 3" catback, Hughes 2500 stall converter, stock 700R4, Auburn Pro posi w/3.42, 17x9" SS rims w/BFG tires, Medium Quasar Blue w/white SS stripes, 48,000 miles....

RB83L69

I have the Comp stainless rollers in my 400, part # 1102. They appear to be superior to aluminum in every way. They are not self-aligning; but all you have to do is use guide plates to overcome that limitation. You'll have to go with screw-in studs with any of the cam configurations you list anyway.

The cam discussion is fairly complete, but I'd like to add one more thing: with any type of forced induction, all that the "forcing" accomplishes is to jam more stuff into the cylinder from the intake side. As a result, you really don't need to push the envelope of driveability by increasing intake duration. However, there still remains the problem of getting the used-up stuff back out through the exhaust side. Over there you can use all the help you can get, from lift or duration or both.

I would suggest getting Comp to grind you a custom; the 305 intake lobe, and the 306 exhaust lobe, on 114° centers. I would strongly recommend using 1.6 roller rockers and good strong valve springs (Comp 987 would be my choice). This will give you a cam that will be plenty manageable while you're NA, but will be ready for the blower.

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"So many Mustangs, so little time..."