Cam Duration?

[Jerry F]

I'm in the process of buying a cam and have been on the phone with Comp and Crane. I love the sound of a radical idle so I need a cam with quite a bit of duration, around 260 - 270 degrees, The sales people are telling me how difficult the car will be to launch and drive with this type of cam. According to some of the posts, some of you are running some pretty big cams. Are you having these problems? Are you forced to keep the revs up all the time? Feedback would really be appreciated.

[niles]

Need much more info.
type engine, CI, lifter type, HP expectation, street driver?
Cam guy frequently are drag race oriented; not good for normal Cobras.
gn

[Ron61]

Jerry,

I have one cam that has a 288 duration and it works great. My other one is a 312 duration and it is to much for street crusing. Also look at what your lifts and overlaps are going to be.

Ron

[HighPlainsDrifter]

Jerry,
A cam with 260 degrees duration or more at .050 lift is a race only cam. You would need 13:1 pistons with notches cut in the top for the .700 lift valve clearances. This would be a mechanical cam and need to be adjusted every few hundred miles. Also your valve springs would need to be changed very often, guys at the drags change them every couple race weekends. Any carburator you tried to use would not see a proper vacuum signal for it to work , you need a race carb.
So if you still want to run a race cam be prepared to drive the car between 4,500 and 8,000 rpm , that's it's power band. It would have virtually no power and want to stall under 2,500 rpm.
Good Luck,
Perry.

[BB427]

A 270 cam should be fine. The street grind on todays camshafts have a very mild ramp and are very easy on valvetrain components. You should get years out of a set of valve springs and only need to run the valves once a year or so.( a silicone spring is all you need for the street) If you need to runthe valves more often you have a problem in the valvetrain. A steel flywheel will assist with low gear if you find the cam is to sloppy and hesitates from a stop. A Cobra only weighs 2500 lbs so it doesn't take much to get her going.

Brent

[HighPlainsDrifter]

CAM 101

1st off, You need to talk duration. ADVERTIZED duration means nothing, has no reference point and is different for every cam manufacturer. Therefore talk duration at .050 lift , that's the only way to compare cams. Your 270 advertised duration cam is in reality about a 220 cam at .050 lift., a mild street cam.

2nd off, go to a real engine builder as you do not know what you're doing.

[Jerry F]

Perry,
Based on my research your comments are pretty much on the mark. However, I know I've seen some of the comments on this board where guys are using cams this big. If you look at the comments that Keith Craft is making on a different thread, he's dyno-ing motors with cams this big and he's not mentioning that the motors will be impossible to drive. Also, I've looked at the specs on the 514 crate engine the cam has some big numbers and I know this motor is not a problem.

[HighPlainsDrifter]

Jerry,
You are right, people do crazy things like put 750 hp engines in their cars,good for them,just cause they have more money than brains doesn't make it right. I have trouble getting traction with a mild motor in my cobra. Professional builders such as Keith Craft are great for a serious car,roadrace, drag,etc. we won't even get into safety equipment these guys don't have on their cobra.
You can have a mean sounding engine that will still be streetable and maintenance free. A 10:1 compression motor with a comp cams 292H advertized duration cam, 244 degrees at .050 lift is a nasty combo, about as big as you should go on the street.
Perry.

[BB427]

Highplainsdrifter,
Your comment about an engine builder was aimed at who????

Brent

[scottj]

Jerry- I'm running a cam with 264I/272E @ .050, .680 lift, & 106* lobe separation.

I'm running 9.5:1 compression.

I'm also running an aluminum flywheel.

At 1000 miles valves were still no more than .003 out.

Valvesprings are good for 2000 street miles or 1000 track miles per the cam grinder.

Race carbs will not work. They are not calibrated for part throttle cruise. Race carbs are too lean at part throttle cruise for good drivability with a cam this big. In my case a carb from a good race carb builder with "street" calibration was necassary to make street driving smooth and effortless with no surging, hesitation, or bogging. It will cruise at 2200-2300 rpm and has such a smooth torque curve that you can't tell where the power comes on, it's on everywhere.

With enough cubic inches, the proper port size, and a good carb, drivability does not have to suffer at all.

Mismatch anything and you'll get the results others are describing.
Scott

[Jack21]

If some is good, than more is better.

I think this is just a young buck rite of passage that first time engine builders go through. They build this monstrosity that's totally undrivable on the street, then start wondering, "What have I done wrong?"

Then they start getting street smart about this and don't ask questions like this. They've been there, done that, and know what works for their particular car and driving style. More conservative and reliabile works better.

You don't need monster truck power to push your 2400 pound plastic car around spiritedly.

35 years ago, Shelby had two choices for Ford engines. The 289, and 427. There were no Ford 351's in 1965. The reason 427S/C's are so rare today is that they were a sales disaster in '65 & '66.

Realistically, today, the only car that will give you a tussle is another Cobra. Turbo Porche's, maybe, Dodge Vipers, maybe. Pro-Street '60's era Camaros', maybe. Vette's, you eat for breakfast. And you can do this with a 302 based engine, add a stroker kit and huffer and have a 10 second street machine that gets 22 MPG on trips, and behaves itself in rush-hour (or beach) traffic!

Bottom line, if there ever is one, is listen to these guys who've been there, and done that. Your engine machine shop does this every day. He knows what works on street engines, race engines, and weekend warriors. Just like your Doctor, you're paying him for what he knows.

[HighPlainsDrifter]

Hi Brent,
Didn't want to make an essay out of this. I was inferring that people that don't know the basic duration measurement won't be able to pick a proper cam, including me. Race cams trying to work on the street are not going to work without major input from an experienced engine builder and alot of maintenance. The tech line at comp cams does thousands of these combo's for the street and track and probably has the biggest database anywhere on what is going to work. They recommended the cam I have in my 460 now, it's a milder grind than I thought I should have but it is way quicker than it should be for a smogger. And that's basically the point,an individual has no chance of picking the right combo for his engine, it would be like picking the lottery #s.
Perry.

[BB427]

Highplains,
Good point, well said.


Brent

[Jack21]

I didn't want to make an essay out of this either, sorry if I rambled.

Back to the cam duration question. Crane Cams, way back when, pioneered the duration @ .050" cam lift as an industry standard for cam profile comparison. Prior to this, there was no way to compare one cam to another. "Advertized" duration of say 292 was actully a 222 @ .050" after the opening/closing ramps had been factored out.

You can still get a nasty "Rumpeta-rumpeta" idle with a 224 - 234 degree cam (@ .050") with good street performance.

[decooney]

I believe this is a pretty open question that begs for more details before anyone could effectively help to answer the question posted. The same sized cam in two different cars could produce completely different results and satisfaction...

- What size and type of engine will the cam be used in (SB, BB)?
- How heavy is the car? Total weight with fuel and driver, etc?
- Are your cylinder heads ported? e.g. blueprinting...
- What final compression will be used? Guesses don't count here...
- What final gear ratio that will be used in the differential?
- 4/5Speed manual transmission, or automatic with stall converter?
- If manual, wide ratio or close ratio transmission? 1st gear ratio? just curious...
- What diameter, size of rear tires will be used. e.g. how tall?
- How exactly will the car be driven (open country roads or in-town/traffic, race track)?
- What carb will be used and will it be jetted and set up properly?
e.g. jets, power valvles, discharge nozzles, pump cams, blueprinting...
- What sort of air filter can/will be used? Small/Large, can you get air into the motor, or will you be restricted to small air filter use? e.g. very small stellings vs. a large open, unrestricted type 14".


e.g. I'm no expert, but have done quite a bit of testing with a constant set of parameters on the same type engine platform in my Cobras. For example, I installed three different solid lifter cams in the same type engine and configuration Cobra and found interesting and varying results with each. At this point, to me it seems really hard to make a general statement about what to use without understanding more of the underlying details and use requirments first. Good Luck.

[niles]

Decooney:
the second post was "need more info"
Nothing forthcoming;
gn

[BT SNAKE]

I still ain't figured out what all this has to do with GT40 Talk ??

Hersh

[decooney]

BT,
Now that you mention it... never noticed it til now. The poster never said what type of car... If it helps, I'd like to have an ERA GT40. I guess I'll have to wish in one and and **it in the other.

[Jim Downard]

Jerry,
I've got a 393W stroker. It has Roush 200 heads in cast iron flavor, 9:1 compression, and fairly stock bottom end. Don Scott told me what cam to use in this car, and I think he was right. It's a competition cams with a lift of .544/.541 and a duration @ .050 of 246. It doesn't like being driven much below 1900-2000 rpm but it can if throttle is controlled nicely. I had the car on the chassis dyno at the spring fling this summer and with a 3.55:1 rear axle ratio I made 360 rwhp and 398 lbs. ft. of torque from 2750 to about 5000 rpm. The torque curve is as flat as a pancake and the hp is a very linear curve upward. This is a very controllable motor that STILL spins the rear tires in thrid gear when the meat of the power comes in.

Jim Downard

[FALCON]

IF YOU ARE USEING A SMALL BLOCK TWO CAMS COME TO MIND THAT WOULD BE GOOD FOR YOU 1ST HOLMAN AUTOMOTIVE'S 6250 ROUGH IDLE THAT SMOOTHS OUT AT @2500OR COMP CAMS GRIND #FS6874/6875-S108+2THIS ONE IS A CUSTOM GRIND I USED IN A 260 AND MADE 300HP ON DYNO THEESE ARE BOTH MECHANCAL CAMS AND ARE BOTH VERY STREETABLE