Ok, I am just curious about this and figured the long time slant guys would have plenty of input. Here goes:
If you have good compression , ignition, head flow, fuel, etc (ie. 10:1, ported big valve head, headers, decent carb & ignition) At what point is more cam lift and/or duration not going to help? I am only speaking of a RACE engine and not street.
Just wondering if anyone has found a good cam spec for a N/A drag engine.

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-MattMan
LEANED & MEAN

If 10:1 is the limit then play with a dynamic compression ratio calculator and adjust the intake valve closing point until you get the dynamic compression ratio you want. Probably around 8 to 8.5:1 with pump premium. With the intake closing point you can then determine the intake duration. Run an exhaust duration about 6° less and a lobe separation of 108° and you'll have all the needed cam numbers. Then you pick lobes that are close and have the cam ground.

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Joshua

I can do the computations, I was just wondering what other racers have discovered (no sense re-inventing the wheel).

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-MattMan
LEANED & MEAN

250° at .050" tappet rise is about the limit at 10:1 and runs better at 11:1, but you should really know more about it than that. Knowing the static and dynamic compression ratio is rather helpful. It can keep you out of trouble. The kind of trouble you find when trying to tune your way out of a mis-matched combination. BTDT.

If I had known anything about this when I built my first "high performance" slant six I would have had much more success. It wasn't until I put big valves in the head, ported the head, whacked .100" off the block and head and got the timing curve better that I had a good running combination.

http://www.hotrod.com/events/coverage/0 ... ion-ratio/

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Joshua

I agree 250@0.050" is about max for 10:1 comp. After speaking with and gathering data from about everybody on the planet (incl Australia), here is the cam I designed for 10-10.5:1, based on Oregon Cam lobes.

OREGON CAMS lobe #34 int lobe #1628 exh

INT EXH LSA INT EXH
250 243 105 0.494" 0.48"

A bit more lift would be nice, but it won't matter much based on everyone's testing. Get 1.6 rockers if you want more lift. I ran a cam very close to this to low 14s in a 2950 lb car from 1998 - 2013. Not a great head, but good. Street driven and road raced too.

I have this cam in my 64 Dart right now (11:1 comp, pump premium gas on the street, maybe a skosh of 110 octane at the track). 13.90s on pump gas, driving in the gate after a 3300 mile roadtrip. Some wheelspin means 13.70s should be quite doable w/better traction. This is a roadtrip, road race, autoX, drag car, so you can go faster with a pure drag car.

OREGON CAMS lobe #1080 int lobe #549 exh

INT EXH LSA INT EXH
257 248 105 0.566" 0.539"

"Purrs like a kitten til the Lake pipes roar..."

If this is just a RACE car, then go for 11.5 or 12:1 and go for this second cam, or a bit bigger. 11:1 on pump premium with a big cam can be made to work just fine with sensible tuning.

Car weight expected and ET goal?? Budget limitations?

Lou

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Home of Slant6-powered fun machines

I think maybe the question was just too general. The more I ponder it, the harder it is to answer.
sigh...

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-MattMan
LEANED & MEAN

I think the main limitation is going to be the cylinder heads ability for continued flow beyond the lift of the camshaft used. If your head has peak flow around .450"-.500" lift, it will not benefit you to put a .700" lift cam in the engine. So as long as the head can provide airflow consistent at a lift matching the lift of the cam you install in it, then you should continue to see somewhat of an increase in performance, provided you don't have a conflict with other parts being mismatched for the job you are intending to do. As for duration, you may not see any gains in going bigger if the intake manifold peaks its power band before the cam peaks its power band. For instance, if you have a small runner intake like an Offy that has a peak effective RPM of maybe 5000 RPM, but you install a cam with 270°@.050" duration, you will never reach the peak RPM range of the cam because you ran out of intake to get you there, even though your lift and head flow may be in sync.

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There's no such thing as too much cam....only not enough engine!

If its a race only mill.....why only 10:1?

Lous Dart at 11:1 is still very streetable .

Its about DCR.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

It was sort of a hypothetical question. My particular engine is right at 10.62 with a Felpro gasket (11.1:1 with a steel shim gasket).
I am kind of fishing around to see what cams people are running in the N/A race engines.

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-MattMan
LEANED & MEAN

For you the 250/243° cam Lou specified would work well. Expect to spend $400+ on a torque converter that will allow it to live up to its potential.

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Joshua

..........or use a 5 speed like Lou did.

I drove his car this summer. ,,,,hard. Power on tap from idle to where you chicken out and shift. No more difficult to drive than my wifes 5 speed Honda Civic.

Keep in mind this is a car sorted by someone who really knows what they are doing....puts on the miles to make sure....has an ever evolving vision. (Thats really how its done)

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Yeah....Im the one who destroyed this rare, vintage automobile.....

I ran an old Clifford cam at 9.5:1 for years that was 300° adveritsed with .558" gross lift. I ran it N/A and sprayed. I was always very happy with it, but I would not go any bigger w/o more squeeze.

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Official Cookie and Mater Tormentor.

I ran the following Oregon Cam in my first Big Bore motor until an unfortunate incident. (broken rod) Lou helped me with the numbers and it ran sweet. Went 13.80 / 96 with my home ported head and engine builder valves. Probably a .5 second faster with a really good head and some more compression. I was at 10.7 CR

Grind # 977 Intake 251 @.050 / .513 L
Grind #1672 Exhaust 242 @ .050 / .506 L

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

That is good input, Rick. Ken, at Oregon Cams, recommended his #1271 grind which has similar specs,
Intake-248@.050 / .516 (valve lift)
Exhaust-256@.050 / .540 (valve lift)

I have his #1313 grind
Intake-238@.050 / .474 (valve lift)
Exhaust-248@.050 / .494 (valve lift)

Just wondering if I should get serious and step things up.
In for a penny, in for a pound...

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-MattMan
LEANED & MEAN

When I spoke to Mike about a cam for my car he recommended the following to me. He knew my basic car information and knew that I wanted to run 12's on motor.

Intake 256 @ .050
Exhaust 260 @ .050 plus or minus 2 degrees

.550 lift at the valves, and must figure a rocker ratio of 1.45 for stock rockers

104 degree LSA

The Oregon cam 1080 that Lou mentioned gets you pretty close to those numbers.

Rick

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6