Camshaft 101

[Jet City]

Timinator and I started a discussion about cams on another thread, I thought it was interesting enough to continue, and wanted to attract other opinions. Here is what we started with (sorry for the long intro)...
Timinator:
Over 230 deg at .050 is fine for low(8.0 to 1)compression motors,the low compression only really affects the bottom end torque, somthing that jets don't need. A tight lobe separation angle works better in a low compression deal too. Comp Cams tight lobe center jetboat grinds work awesome! Have used a lot of them in stock 330 HP Big Block Chevys. Comp Cams will grind them on an Olds blaank for you,we order custom stuff from them all the time.Also for an Olds, find an old O4-B dual plane Edelbrock intake, works better than the Torker if you can find one.Also if anyone wants to debate compression V.S. duration at .050 step up and convince me that I'm wrong, I'll listen.
JCR:
I have run both the Comp 268H and the 280H in my 8.0:1 CR 460 jetboat, the 268H resulted in 400 more rpm's and nearly 5 mph (GPS), it starts better and revs out quicker, the 280H was very lazy. No other changes on the engine took place (other than carb jetting of coarse). basically, the 268H builds more cylinder pressure in a low CR engine. I have also read that if you don't have sufficient static compression for a large cam, you will not effectively burn the A/F mix (due to the low-mid rpm compression bleed off of a larger cam in an engine that cannot afford the loss) causing the raw fuel to glaze the cylinder walls, my 8.0:1 engine has 145-150 PSI compression and 180+ PSI is needed for a 230 @ .050 cam to run at optimum, jetboat or not.
Timinator:
78 SLEEK... The biggest problem we see here with cam changers is that almost nobody knows how or takes the time to check the degreeing. Also the timing requirements change,sometimes jetting, and carb cfm or manafold design too.If the impeller is too tight (AA),the motor can never see the rpm range that the new cam will make its power gains at. If the new combination is not THOROUGHLY worked with, oftentimes a more powerful combination is given up on before its true potential is realized. We have run MANY Comp Cams 280 and 292s in jet boats and ALL have run faster with the proper setup changes. Don't give up! Ask more questions! Pay someone if you have to! THERE ARE NO HARD AND FAST RULES REGARDING DURATION AND COMPRESSION, CIRCUMSTANCES ALTER CASES! As far as Edelbrock goes, the reason the Performer fits with an HEI, is because THE RUNNERS ARE WAY SMALLER! So is the plenum(gosh I LOVE using capital letters!), That affects cylinder filling and rpm range of operation. Would you believe that you can run 276deg @.050 with 9.5 compression an AA impeller and go way fast too? (the smart guys will recognize this as bait and know not to get into that discussion)
JCR:
Timinator, if you see no "hard and fast rules between duration and compression", what guidelines do you use for selecting a camshaft. Certainly there must be more to your cam selection process than just picking a super big cam and tuning until it works. There is certainly a point of deminishing returns in regard to duration. If you want to continue this mabe we should start a new thread, no need to hi-jack Dgie's thread. I'd love to hear what others have to say on this too.

[flat broke]

JCR,
In defense of Timinator, did you ask around about where the 280 should be degreed in at? At the very least, I would think that you would want to advance the valve timing a little to move the peak HP down the RPM scale a bit. If you just lined up the dots and slapped her together, you may have left a lot on the table in terms of performance.
After doing a couple of cams, I can say that I always start the degreeing process with the dots lined up to see where I fall and each time the cam has been retared by 1-2 degrees. That is not to say that it will always be that way, but if I would have just lined up the dots and went on my way, I would have moved the peak HP even higher up the RPM band than it already was. I ended up installing the cam at 105 on a 108 LC for 3 degrees advance. That was based on the advice of the cam manufacturer.
This is one area where desktop dyno may be of assistance. Even though the HP numbers that it spits out may be off, the curve should be close in shape to the real deal. By changing the valve timing, you can see where that moves the peak HP and effectively slide the curve back and forth accross the RPM band to suit the needs of your application.
Chris

[dgie]

dont bail on me too fast, I came up with 2 cams for my motor that were suggested at realoldspower.com. Go back to the thread and check them out and tell me what yall think.

[Jet City]

Dgie, I'm not bailin' on ya', just thought this cam selection thing was taking over your thread. I didn't post this as a means of settling a disagreement between Tim and myself. I really wanted to see different viewpoints about the subject (the relationship between duration and CR, etc.).
As for the degree deal (FB), I did phase (degree) the 280H that I discussed earlier, it was installed straight-up on a 110 lsa that ended up being less than 110.5 degrees installed. In all fairness, I did not try advancing it. Instead, I shelved the 280H until I can install my small chamber heads and increase the CR.

[malcolm]

Timinator, instead of reinventing the wheel, why not use the experience of 75+ years of engine builders and put some more compression in the motor. No matter what you do to an 8:1 motor, the one with 9 or 10:1 will have more power with the same cam. Without the extra compression, the fire will not burn all the extra fuel you're gonna throw at it, advance and retard all you want. We may have to agree to disagree on this, I know how hard headed we gear heads can be. argue

[Hal]

Cam info
More cam info
Dynamic compression ratio
[ September 18, 2003, 08:51 PM: Message edited by: Hal ]

[TIMINATOR]

JCR: LSA is Lobe Separation Angle,NOT intake lobe center line.Comp Cams wants the 280 installed at 106 deg.(point of max lift)after TDC, that makes your installation 4.5 degrees RETARDED from Comps instructions. That moves the peak horsepower up about 250-350 RPM, and lowers the EFFECTIVE Compression and efficiency throught the range. Most American V-8s prefer that the cam is installed at 4 deg advanced from split overlap. TIMMINATOR

[TIMINATOR]

Malcolm:I am not reinventing the wheel,but I have been racing for 35 yrs. and have owned a Race Engine Machineshop for the last 20 or so,(I'm 51). Come on down to Phoenix and I'll give you a ride in my 21 Eliminator Daytona,SPECS: AA impeller & Don's preinducer turned by a 572 BBChevy at 5800 RPM, running on 87 octane REGULAR GAS at 9.5 compression and ONE DOMINATOR 1050 carb! The cam? a Comp Cams 312CR-10 SOLID ROLLER with 278/282 deg at .050 and .714/.680 lift!!! YES THATS 9.5 to 1 compression and 87 octane REGULAR GAS!!! IT HAS RUN A BEST OF 95.9 MPH in our 110 degree summer heat! (speed verified by Magellan GPS and my STALKER RADAR GUN!) I'm trying to get it to run 100 MPH on regular gas WITH NO POWER ADDERS! Sometimes I do things to prove a point,this boat is proof,it also gets us a LOT of business! The locals know the boat! The fire is not out and no offense taken or intended. TIMMINATOR argue argue argue

[Jet City]

TIMINATOR:
JCR: LSA is Lobe Separation Angle,NOT intake lobe center line.Comp Cams wants the 280 installed at 106 deg.(point of max lift)after TDC, that makes your installation 4.5 degrees RETARDED from Comps instructions. That moves the peak horsepower up about 250-350 RPM, and lowers the EFFECTIVE Compression and efficiency throught the range. Most American V-8s prefer that the cam is installed at 4 deg advanced from split overlap. TIMMINATOR If I didn't understand what "intake center line" was, how the hell would I use a degree wheel? But you are right, I did say LSA instead of "installed at XXX* CL", etc. I did look at my cam card (280H), your right (again) it would have been installed just shy of 106.5, not 110.5 (I forgot the 280H has 4 degrees of advance installed straight up), it was 2 years ago and all I could remember was that it came in less than .5 degree (retarded).

[Jet City]

TIMINATOR:
Malcolm:I am not reinventing the wheel,but I have been racing for 35 yrs. and have owned a Race Engine Machineshop for the last 20 or so,(I'm 51). Come on down to Phoenix and I'll give you a ride in my 21 Eliminator Daytona,SPECS: AA impeller & Don's preinducer turned by a 572 BBChevy at 5800 RPM, running on 87 octane REGULAR GAS at 9.5 compression and ONE DOMINATOR 1050 carb! The cam? a Comp Cams 312CR-10 SOLID ROLLER with 278/282 deg at .050 and .714/.680 lift!!! YES THATS 9.5 to 1 compression and 87 octane REGULAR GAS!!! IT HAS RUN A BEST OF 95.9 MPH in our 110 degree summer heat! (speed verified by Magellan GPS and my STALKER RADAR GUN!) I'm trying to get it to run 100 MPH on regular gas WITH NO POWER ADDERS! Sometimes I do things to prove a point,this boat is proof,it also gets us a LOT of business! The locals know the boat! The fire is not out and no offense taken or intended. TIMMINATOR argue argue argue Timinator, just when I was loosing interest in this thread... OK, that would be about 745 HP out of a 572 engine on cat pee regular? Very impressive indeed, I know of a few similar cube engines that make similar power, but they are on the ragged edge using super unleaded (smaller cams with less blead-off I imagine). I would be interested to here more details about this combination, that is if its not cripto top secret. I see that cam also uses a 110 LSA, is it also installed on a 106 CL? Also, what led you to choose this particular cam? What head, piston and deck height is being used, etc.