ok, im building up a every high performance 383. I've selected pretty much everything but the cam. I'll either do

Comp Magnum 305 w/ .525" lift intake and exhaust

or

Comp Xtreme 294 w/ .519" intake and .523" exhaust

both are flat tapped, which i want for sure, does anyone know the the biggest diff. between the magnum's and xtreme cams?

 

Distortion, first off you said that this is going to be a high pow 383 and you have all the parts picked out but the cam, for anyone to properly help you pick your cam you need to tell them what the car is for, what the other mods are, goals, etc.

But cam selection generally speaking isnt technically advanced, and should be posted in a normal tech forum. I will move this to Classic Tech since it looks like that is what you are working with from your other posts...

Thanks bud.

 

Consider this: the Magnum series has been out for 15+ years, the Xtremes came out a few years ago. Considering Comp Cams reputation for constant research and developement, you would think they learned something after the Magnums came out and probably used what they learned on the Xtremes.

 

Engine specs.

350 bored .30 over 400 crank = 383 cu
Micro Ground Cast crank
Forged Arias Racing Pistons
moly rods
Trick Flow Big Port 215 cc heads
Edelbrock Air Gap RPM manifold
Holley 760 cfm double pumper

Target HP >470

 

Go SOLID!

I had the XE284, and swapped to the Comp 294s solid....WOW HUGE difference....and all on a daily driver. So I would do either the 282s or 294s if your compression is high enough for the 294s......

 

This is how it works. If you have good flowing heads on intake and exhaust, then its best to go with a single pattern cam. If you have a anywhere in the 71 percent range or more on intake to exhaust ratio, (divide the 2) then I would go with the comp 305H. If you are going to squezze the motor alot and want to run better with bottle, the the spilt duration one is the way to go. Me, I like to run as hard as I can on motor and use juice as a add on to give me the extra little power.

Michael

 

Here is the combo we had in our 383 motor in our 67 Camaro.

350 Block
GM pink rods
Keith Black Hypereutectic flat top pistons
GM Cast Iron Bow Tie Heads, Angle plug, 2.02/1.60 valves, Lazer Cams springs, 65cc combustion chambers
Total compression 11:1
Lazer hydraulic cam P/N 2900116, Duration Adv. 290/295, Duration @.050 240/245, Lift .519/.502, 108 lobe separtion, 104* intake centerline
Special bleed rate lifters
1.6:1 Roller rockers
Team G single plane manifold
Holley 800 double pumper
Coan 5500 stall
Powerglide Transmission
4.88 rear gears with spool

Car ran 11.10s constantly even when a valve went bad. The car hit the finish line at 6900 rpms and the cam held up for six years of racing.

 

holy **** 4.88 gear ratio, do you even have tires left?

 

You got to remember that the PG only has a first gear ratio of 1.82 or 1.76 depending on which one you have in the car. A lot different than running with a TH400 or a 700R4. But to answer your question, NO We would go through a set of tires in less than a year. We were getting inconsistant 60' times because the motor had soo much torque off the line. We have since switched to 4.56 gears.

 

Much more aggressive than the magnums.

 

They started making the extreme line of cams because of the low flowing numbers on the exhaust side of the stock heads. Think about it, if the exhaust side is weak, lets make a cam that holds the exhaust valve open longer to help it. These cams are made for lower compression motors, something like 9.5 and lower. I have called before and this is how they explained it to me. After hearing it, it realy makes alot of since. I even saw a 2 test dyno in hot rod magazine I think it was. They did a test on 2 simliar cams with a GOOD set of flowing heads. Ratio in the 71 percent range and higher and the single pattern won by the whole rpm range with as much as 15 to 20 horse increse on topend. Speaks for it self really.

Michael

 

I ran the 305 magnum in my 1980 camaro the combo was:

small journal 283, .030 over ( 292 total ci )
all forged, 11:1 TRW domed pistons
Dart Sportsman II heads, home ported
Comp 305 Magnum w/ 1.5:1 on intake and 1.6:1 on exhaust
2.02"/ 1.60" stainless valves
1 3/4" super comp headers, 3" flowmasters
Victor Jr. intake, port matched, Barry Grant 750 double pumper
HEI distributor w/ MSD 6-AL
Holley electric fuel pump
TH350 w/ 3500 stall
8.5" 10 Bolt, summit 4.56 gears with a mini spool
weight removal
125 NOS powershot kit (not adjustable)

Best et ever w/ 305 mag cam was 11.57 ( I think I could've gotten more with a 4000 stall and 4.88's small motor = !torque)

The car sounded so bada$$ with they way that cam idled, and ran really strong at WOT, BUT at anything under 3500 rpm it was a dog and no fun to drive, between 3500 and 7700 it was insane. I lived with it only because I only drove it to and from the street races ( and very carefully I might add- spool + slicks on street is crazy dangerous if there is even a little water )

Eventually I couldn't put up with it anymore, the 305 in such a small motor was VERY tempermental, and switched to a solid 294 magnum and was much happier with it. Got back some (not a whole lot, but some) driveability and actually ran 11.44.

With all the extra cubes you'll have the 305 should be tamer but I still think I'd go with the Xtreme solid.

Good luck!

 

I have NEVER used a roller cam in a street motor. OK, not quite true- I've built a few late model 87-up SBC's that had roller in them already, so we kept using it. But it's not my thing, really and for good reason.

Race motor? Extracting the last few percent from a motor? Fine, roller's the way to go.

But bang for the buck? Solid lifter flat tappet. All day long, every day, 365 days a year.

Putting that aside, I agree with Old School- if you've got a good exhaust port you want to go with a single-pattern cam. If they don't flow so good, go dual pattern. I like to peg it at 75% E/I flow ratio as the break point, but don't go by just raw head flow numbers- remember that your exhaust system (with mufflers) plays a part in the actual exhaust flow.

Here's the E/I flow ratio of some common heads out of the box:

L-31 "Vortec" heads: 69%
World Products Sportsman II: 70%
Edlebrock Performer: 75%
AFR 190: 78%
Dart Iron Eagle 200cc: 78%
Trick Flow Twisted Wedge G2: 83% (!!!)

This is NOT to say they flow the same!!! It's just the RATIO of their intake to exhaust flow. The AFR 190 will outflow the Dart Iron Eagle, but the numbers are higher/lower on both the intake and exhaust sides such that they maintain the same RATIO between them.