Cam Profiles...help me sound smart

[Tracy C.]

First let me just get this off my chest.... I'm as dumb as a rock on the topic of cam profiles and what all the numbers mean.

I've pulled a brand new Hyd lifter cam from my 327 that was selected by the guy who "built" my 340 hp engine a few years back. For obvious reasons I am going back to a solid cam as I completely go through this kludged rebuild.

This cam is a Norris N288H. Reportedly the N288H was 288 advertised, 230 @ .050", and .484" lift on a 108 degree LC. I am taking it to a local swap meet in Wichita this weekend with the intent of finding a new owner for it.

I need some help in terms of "offical lingo" so I can correctly describe the application it might be best suited for.

Thanks,
tc

[Duke W.]

Re: Cam Profiles...help me sound smart

High level specs that grinders advertise and guys throw around barely scratch the surface of a camshaft's true character. Then we get into velocity, accleration, and jerk, which are low level engineering details that only an engineer with a solid background in dynamics can understand.

I can tell you that for the duration, that cam has WAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAY too much overlap for a decent road engine.

I bet it's a dog down low.

Search "327 LT-1" on the TDB and from the threads here there are links to The Corvette Forum for more discussion and dyno tests.

Eighty percent peak torque at 2000 - which I consider a minimum for a high performence road engine - 90 percent at 2500 with about 290 SAE corrected RWHP at 6500 with useable power to 7000+ and the beginning of valve float about about 7200.

Find a 327 configuration with all OE components, except the conn rods, that makes better torque/power bandwidth than this, and I'll buy you a sixpack! Yeah, the LT-1 cam isn't original to a 327/340, but it is an OE part and idles just like a Duntov - 900@12" Hg.

As far as how to dispose of the POS you have, swap meets are full of bubbas that will love the specs. It will sound like a "real racer" idling across the parking lot. That's what bubba digs. He hasn't got a clue about "torque bandwidth".

Duke

[Tracy C.]

Re: Cam Profiles...help me sound smart

Thanks Duke,

I've already sourced a new LT-1 cam.

If I'm interpreting your comments correctly, would this be a good cam for a dirt track circle burner? We have a local speedway and there will likely be a few racers at the swap meet (along with plenty of bubba's)

tc

[Larry M.]

Re: Cam Profiles...help me sound smart

First let me just get this off my chest.... I'm as dumb as a rock on the topic of cam profiles and what all the numbers mean.

I've pulled a brand new Hyd lifter cam from my 327 that was selected by the guy who "built" my 340 hp engine a few years back. For obvious reasons I am going back to a solid cam as I completely go through this kludged rebuild.

This cam is a Norris N288H. Reportedly the N288H was 288 advertised, 230 @ .050", and .484" lift on a 108 degree LC. I am taking it to a local swap meet in Wichita this weekend with the intent of finding a new owner for it.

I need some help in terms of "offical lingo" so I can correctly describe the application it might be best suited for.

Thanks,
tc

Tracy:

The original Duntov cam for this motor was pretty good. Why not use it in your engine. The DRIVELINE lists a source for a correct reproduction.

The LT-1 cam also sounds like a good choice. Your decision.

Larry

[Tracy C.]

Re: Cam Profiles...help me sound smart

High level specs that grinders advertise and guys throw around barely scratch the surface of a camshaft's true character. Then we get into velocity, accleration, and jerk, which are low level engineering details that only an engineer with a solid background in dynamics can understand.....
Duke

So in the terms that I previously described for the N288H cam, how would a LT-1 or Duntov grind be defined by duration, lift and overlap?

Maybe I can learn something in the comparison.. Thier is so much inthe archives, I can't seem to zone in on any post that might have this info.

tc

[Michael G.]

Re: Cam Profiles...help me sound smart

Tracy,

I'm have the LT-1 cam in my 327/340. No regrets in using it over the original 097 cam. Nice idling sound and pulls like crazy!

[Duke W.]

Re: Cam Profiles...help me sound smart

So in the terms that I previously described for the N288H cam, how would a LT-1 or Duntov grind be defined by duration, lift and overlap?

Maybe I can learn something in the comparison.. Thier is so much inthe archives, I can't seem to zone in on any post that might have this info.

tc

First rule is you can't directly compare a hydraulic to a mechanical lifter cam unless you have detailed lobe data and know the heights of the clearance ramps.

On a hydraulic cam the first .050" of lobe lift fully translates into lift at the valve, but with a mechanical lifter cam the first 10 to 20 thou of lobe lift is clearance ramp and the valve doesn't move.

Being as how I have the detailed lobe lift data for the LT-1 cam, I know the clearance ramp heights and can tell you that the .050" lifter rise duration - net of the clearance ramps is 231/239, which is what you use to compare to hydraulic cams. The LSA is 116 deg, and the inlet POML is 110 ATC, so the exhaust POML is 122 BTC. For the same inlet duration as your mongrel aftermarket cam, it has a lot less overlap, which is why it has useable low end torque.

The only way I was able to improve on the LT-1 cam - with massaged heads - was to shorten the exhaust lobe and reduce the overlap. I came up with a design that used the 30-30 lobe on the inlet side and the Duntov lobe on the exhaust side with a very wide LSA, but Crane couldn't grind it because there was not enough material on the blank to grind long durations with that much LSA, so I abandoned the design, which was probably not that much lost because the simulation programs only predicted a modest increase in low end torque for the same top end power.

The LT-1 cam is tough to beat for a broad torque bandwidth high performance 7000-rev road engine.

Searching as I previously described is pretty easy if you really want to know the deal.

I can't turn everyone into and engine system engineer, but I've published thousands of words on the subject - on the Web and in The Corvette Restorer - in an attempt to explain it all, but some may have to take it on faith if they can't absorb it all. Or they can go to bubba he engine builder, and take whatever he makes for everyone else.

It sounds to me like that's what you got with your 327/340 rebuild.

Duke

[Michael H.]

Re: Cam Profiles...help me sound smart

The LT-1 cam is tough to beat for a broad torque bandwidth high performance 7000-rev road engine.
Duke

It won't sound like a correct 097 340 HP cam though. It won't reproduce that unique "Corvette sound".

Doesn't anyone make an exact copy of the 63 097 cam?

[Larry M.]

Re: Cam Profiles...help me sound smart

It won't sound like a correct 097 340 HP cam though. It won't reproduce that unique "Corvette sound".

Doesn't anyone make an exact copy of the 63 097 cam?

Mike:

There is at least one source.........possibly more. Ad for one source is shown in the latest DRIVELINE on page 96.

Larry

[Duke W.]

Re: Cam Profiles...help me sound smart

It won't sound like a correct 097 340 HP cam though. It won't reproduce that unique "Corvette sound".

Doesn't anyone make an exact copy of the 63 097 cam?

They both have about the same effective overlap and pull the same idle vacuum at the same idle speed. How can you tell the difference?

Duke

[Duke W.]

Re: Cam Profiles...help me sound smart

Thanks Duke,

I've already sourced a new LT-1 cam.

If I'm interpreting your comments correctly, would this be a good cam for a dirt track circle burner? We have a local speedway and there will likely be a few racers at the swap meet (along with plenty of bubba's)

tc

Yes, the moderate duration (for a race cam) and high overlap would yield a pretty good torque curve for a short track car with headers and open exhaust and an intended rev range of 4500-7000 in a short to medium stroke configuration, but if they rev higher or are running a long stroke configuration another ten degrees duration would be better, and I think most racers prefer mechanical lifter cams because they can rev higher before valve false motion sets in. And if the rules allow, a solid roller would be better.

It's really a bubba cam, and he'll love it for his '72 high-jacker Nova. I'll sound like an L-88 at idle, have no low end torque and not particularly impressive top end power through any reasonable street exhaust system.

Duke

[Duke W.]

Re: Cam Profiles...help me sound smart

It won't sound like a correct 097 340 HP cam though. It won't reproduce that unique "Corvette sound".

Doesn't anyone make an exact copy of the 63 097 cam?

AFAIK you can still buy a Federal Mogul/Speed Pro CS113R from NAPA, which is ground to the 3736097 print.

But it's really not that good a cam for a later small block road engine. It was designed as a "racing cam" for the short stroke small port/valve 265s and 283s, but it has too much overlap for the duration for best road friendly torque bandwidth. It would work better on early small blocks if the LSA was widened to 114 degrees with a 110 ATC inlet POML in which case it would be a mechanical lifter equivalent of the L-79 cam, albeit with less lift, and that's an issue on later larger valve heads. Crane has the Duntov lobe masters and they can grind them at any indexing you specify.

Larger valves need more lift to achieve best flow/power on the engine, and the durations should be appropriate for the E/I flow ratio.

The later big port heads have lower E/I than the early small port heads, so they need more exhaust than inlet duration, but that changes with massaged heads. The E/I goes up, so equal durations on both sides or even a shorter exhaust event is best.

The 30-30 cam was a step in the right direction, but it went too far because it killed too much low end torque.

Chevrolet finally got it right with the LT-1 cam that was the result of a decade of analysis and experimentation on head flow, valve train dynamics and an understanding of the kind of torque bandwidth a road-going high performance engine needs to be flexible and responsive from off-idle to peak revs.

Duke

[Tracy C.]

Re: Cam Profiles...help me sound smart

...

It's really a bubba cam, and he'll love it for his '72 high-jacker Nova. I'll sound like an L-88 at idle, have no low end torque and not particularly impressive top end power through any reasonable street exhaust system.

Duke

Go Bubba Go... I'm also taking some new K-Motion K-700 gorilla valve springs, Harlan Sharpe roller rockers, new comp cam hyd. lifters, a new set of Comp Cam 7.90" .080 wall hardened push rods and a set of mismatched reconditioned OEM rods out of this same "build".

I shutter to think where I would be downstream without the good advise I've picked up around here. The $1400 I spent with the goon who build my motor years ago was the worst money I've spent on this restoration yet.

Thanks for your help....And for others reading this thread, tell Bubba his new 327 performance parts will be waiting for him at the Sunflower Swap Meet at the Kansas Coliseum this weekend.

http://www.wichitaas.com/swapmeet/swapmeetdocs/swap2010.pdf

[Duke W.]

Re: Cam Profiles...help me sound smart

Whether restoring a mild 300 HP engine or a SHP/FI engine, I've never advocated using anything but OE or OE equivalent parts, with one major exception - the connecting rods, particularly the early small block versions up to the '66-'67 time frame, which have been blowing up engines for over 50 years.

The OE parts I recommend might not be OE for your specific year because later designs were often better, but no one will ever know through Flight judging or even a PV.

The trouble with bubba the engine builder is that he's got a monkey see, monkey do attitude. He sees all the trick parts on drag racing engines that only need to last for a weekend and only need to make power above 4000 revs with absolutely no regard for fuel consumption. He thinks they're the hot setup for his customers who mainly cruise the drive-ins in their automatic transmission high-jacker Novas with 3000-stall speed converters, most of whom share his bubba brain.

Some bubbas have lab dynos, but they never start the pulls below 3000 revs and always use headers and open exhaust. If that's the way your engine is configured and you never get below 3000 revs and don't care if your small block can't even break 10 MPG, then the results are worth looking at. If not, the results are worthless.

As I've said before, these decades old engines are exceptionally well engineered, especially when you consider that they didn't have anything like the set of engineering analysis tools I have on my home PC, and they had severe production cost constraints. It was all intuitive engineering - some of it very clever - and testing, but, in time, any design shows a weakest link, and the demand for low production cost left a good deal of top end power and revs on the table.

A proper configuration of OE parts and some judicious undetectable modifications such as head massaging and achieving the highest compression ratio that modern pump premiums support for a given configuration will maintain these engines' normal driving behavior, fuel economy, and durability with a much stonger top end and another 500-1500 useable revs up top.

And all at a reasonable cost because OE replacement parts are widely available and inexpensive - a lot less expensive than hotrod parts!

Duke

[Robert S.]

Re: Cam Profiles...help me sound smart

I would also recommend the LT-1 cam. Low end torque is where a lightly driven street machine lives. Also, the Harlan Sharpe roller rockers will fit under the stock valve covers. The reduce heat and friction. The OEM parts are very reliable, but these are free.