Help with a cam

[swilliams]

I am just wondering what the biggest differences I would notice out of the two cams.
Right now I am running the Comp but I am thinking about one of those Edelbrock top end kits the RPM 2089. I see that the two are close but I don't know enough to know any differences.
COMP Cams 249-CL12-211-2
Exhaust Valve Lift (in.)                  0.47
Intake Valve Lift (in.)                    0.470
RPM Range                                   1000-7000
Exh. Duration @ .050 in. (Deg)      224
Int. Duration @ .050 in. (Deg)       224
Exh. Duration Advertised (Deg)      270
Int. Duration Advertised (Deg)       270
-----------------------------------------------------------------------------------------------

Edelbrock Performer RPM Cam Part #: #7102
Vehicle Type: CHEVROLET 
RPM Range: 1500-6500
DURATION AS ADVERTISED INTAKE: 308°
EXHAUST:                                       318°
DURATION @ .050 INTAKE:              234°
EXHAUST:                                       244°
LIFT @ CAM (Lobe) INTAKE:             0.325"
EXHAUST:                                       0.34"
LIFT @ VALVE INTAKE:                    0.488" 
EXHAUST:                                      0.51"
 

[rich weyand]

The Comp Cams is the better cam.  Subtract the .050 durations from the advertised durations: Comp intake 46, exhaust 46; Edelbrock intake 74, exhaust 74.  The Edelbrock is not ramped very steeply, which indicates it is probably an older grind.

Think of it this way.  Horsepower is a function of flow.  The more mixture you can move through the engine, the more horsepower you can make.  One aspect of flow is the duration at .050, so longer duration means you can make more horsepower.  So longer duration at .050 gives more horsepower.

BUT *advertised* duration works against you.  The piston won't start compression until the intake valve is all the way closed, and the piston stops generating push as soon as the exhaust valve opens.  So a longer advertised duration robs torque.

With faster ramps you can make the duration at .050 longer (more horsepower) while retaining a shorter advertised duration (retain torque).  Modern cam grinds usually have faster ramps, typically 45* difference between .050 duration and advertised duration, where the older grinds have ramps that are 70 or more.

In particular, from the other thread we know you have the low-compression base crate engine, as do I.  A very late intake valve closure (that 308 degree advertised duration on the Edelbrock) delays the start of compression, so your dynamic compression ratio (from intake valve closure to top dead center) is going to be pathetic.  You don't have enough static compression to give that much intake stroke away.  A high-compression engine benefits from the later intake closure because the lower dynamic compression at low rpms will prevent detonation, and as rpms increase, the shorter times and the momentum of the mixture in the runners moves dynamic compression ratio toward static compression ratio.

The exhaust valve is also going to open earlier, which means dumping the charge earlier.  At higher rpms that won't hurt you so much, but at lower rpms it will also cost you torque.  And will reduce your gas mileage, because you aren't extracting as much energy from the charge.

So my take looking at the cam specs is that the two cams will generate about the same horsepower (similar .050 duration), but the Comp Cams unit will give much higher torque in the bottom half of the rpm range (shorter advertised duration).

As for the Edelbrock 2089 kit, that includes the Edelbrock 2209 cam.  Again, 68 degree ramps, so it's an old grind.  Not as big a problem with the 60975 heads that are also included, with 64cc chambers and maybe 9.5:1 compression, but you can do better for that kind of money.  In particular, the valves are still only .194+.155 (stock is .194+.150).  Bigger valves = more flow, other things being equal.

Look at these instead: http://www.summitracing.com/parts/drt-127121/overview/.  Add an Edelbrock 2101 manifold and the recommended lifters, and you are way money ahead, but much better off.  You keep your Comp Cam, which is a nice cam, but you get 9.5:1 compression, with 64cc chambers, plus oversize vales (.202+.160).

[rich weyand]

Sorry, had to make some edits to the above.  Changed recommended Dart heads pointer for hydraulic flat-tappet lifters.  I grabbed the one for roller cam by mistake when composing.

[swilliams]

I thank you for all the advice. I have been to about 5 or 6 different places researching the Edelbrock kits and info and nothing this good. I have also looked up about the Dart heads but had ruled them out because some of the people said that the exhaust ports don't match stock. I got a great set of Doug's headers that I don't want to lose. The Summit link shows that they will mount.

[rich weyand]

Summit is excellent on returns.  You log the return on their site, put the mailing label they send with the product on the box, and drop it at the post office.  They get a discounted rate from the post office on return postage, and then bill you the discounted postage against your refund.

So dry test-fit everything, and if it looks like it won't fit, send 'em back.  Better yet, call Dart direct and ask them about it.  The vendors know more about their products than any of us do, and I don't often run across one that doesn't have pretty good phone support, though there are a couple.  They'll know the potential pitfalls and they'll probably know whether they will bolt up to your headers.  You can also check with them that I got the right part number for your application, though I think I did.  Keywords: 64cc chambers, 180cc runners, flat-tappet hydraulic lifters, single springs.

Running that setup through Comp's dyno simulator, with the 12-211-2 cam and the Dart heads, dual-plane manifold and long-tube headers, I get something north of 400 hp at 5500 rpm.  Better yet, the torque curve comes off idle with 250 lbft at 1000 rpm, goes over 400 lbft by 2500 rpm, and stays above 400 lbft all the way to 5000 rpm.  THAT will be a handful.  Make sure you're pointed where you want to go before you punch it.  And see if you can get a quantity discount on rear tires.

[swilliams]

That sounds really good. I thought I would have to basically rebuilt the whole motor for something like this. Whats your opinion on gear drive. I like the mechanical sound. I also have a good 2 piece timing cover so when I get tired of it I can through a good double roller in.

[rich weyand]

That sounds really good. I thought I would have to basically rebuilt the whole motor for something like this. Whats your opinion on gear drive.

Nah.  The bottom end is fine, and you already have a good cam in there.  Just take care of the breathing and you'll have a performance monster.  Two cautions.  If you have an automatic transmission in it, run synthetic ATF to improve horsepower transfer and reduce heating, and bear in mind that your torque numbers are on the threshold of what that transmission will stand.  Brake-torque burnouts and the like will result in transmission failure.  Also, if you have the G80 locking differential, that is an Eaton Gov-Lock, which is plenty good for normal service.  Spin both rears while turning right -- so the primary drive wheel is on the inside of the corner -- and you will dynamite the Gov-Lock.  With that much torque, you will have the stock drivetrain at the edge of its abilities, and you can push it over the edge if your are careless.

Gear drive I know nothing about, but my suspicion is that it is unnecessary for street use with moderate lift cams.

[swilliams]

At this point the rear end is stock. I will defiantly up grade after this.

[swilliams]

Hey Rich i am getting ready to order my parts for this upgrade and i was wondering if you could you post the whole dyno simulation so i could see the results you got for the entire rpm range. Thanks for your help.

[rich weyand]

Sorry for the delay.  Just got back into town.

Here it is.  I used the actual flow numbers for the Dart heads from their catalog.

http://users.rcn.com/weyand/smalls/12-211-2%20with%20Dart%20heads.jpg

[swilliams]

Did you recomend the Dart heads because of the price as well as the flow numbers.
I ask because i have found a good deal (cheaper than the Dart heads 127121) for a set of Edelbrock performer RPM 60899.

[rich weyand]

Did you recomend the Dart heads because of the price as well as the flow numbers.
I ask because i have found a good deal (cheaper than the Dart heads 127121) for a set of Edelbrock performer RPM 60899.

I don't know anything about the Eddies.  See if they list flow numbers. 

[swilliams]

                .100           .200          .300          .400          .500          .600                                                          Edelbrock
 #60899   63/51   126/97   180/129   227/148   250/158   249/165

Dart
#127121    ??/??      139/114     190/145     218/164    222/172    218/174

There is not much difference. The only reason i am considering the Edelbrock ones is because they are on sale. If there is a reason to consider the Dart heads i would not mind they do have better overall numbers. I have gone to all kinds of sites to read about which heads to choose but the only thing worse than not knowing is the millions of opinions on the web some good some bad. I have been following this site
and its members for sometime and feel as though i can rely on the opinions here.

   

[rich weyand]

Some interesting reading for you.

http://www.carcraft.com/techarticles/ccrp_1209_eight_budget_sbc_head_shootout/
http://www.purplesagetradingpost.com/sumner/techinfo/heads1.html

[swilliams]

I have read the carcraft one before it is one of the most current ones i could find. It lists the price pre HP which i thought was neet. The other one i had not taken time to look at it. When i found it it was a much larger list and i did not want to take the time to go all through it so your link was great. One thing i find on almost all is that the AFR heads are among the best. I have set a limit on what i will spend so those are out. I was searching the site awhile ago and came across a reply you had made 290hp 350 upgrade suggestions. So do you have the dart 127121 and if so why did you choose them.