I just ran all 3 cams on my DynoSim Pro, all made similar power but torque on your latest installed cam is much lower dispite the roller. H-Power was in the 355-365 range. Now I just used a standard dual plane, 9.50 C.R., with small headers w/muffs. Your other major difference is the lobe C/L, which is going to effect your vacuum and carb signal. Look at your graph, air/fuel ratio (A/F Ratio) on second cam is way lean!! You need to be around 12-13 when on load, not 14.9 which is where you last run was at!! Check it out.

Take some vacuum readings and retune, may have to change power valves, etc. Read some of Lar's post on this for your carb for research.

The flow numbers I have on Sport II's are low, overall curve power increases by changing to heads with better flow for your cam ranges. If you want to go that large your going to have to look into some different heads.

Hope this helps,
Later.

 

Dennis lots of good information..thanks.
My CR should come in at 9.5 with a .040 head gasket, stock deck and dished pistons
I am concerned about wiped cam lobes if I go with a Comp/Lunati/Crane Z cam..
I just took the original cam out of my 72....lasted 34 years and 109K miles...Mark

 

GASKETDUDE

I know, the run with the 280h cam was not my best run, it was just a random run we pulled to compare the two cams. The 280h was running rich on the primarys, with some jet changes and timing changes I was able to get 324hp at the rear wheels. I know this cam is running lean on the primarys, but no amount of tuning is gonna bring this cam up to where I want it to run. I could build another motor around this cam such as, new pistons, new heads, 1 3/4 headers and a forged crank.
However, I would rather get this motor running right 330-350 hp at the rear wheels. Then build a second motor, dart block maybe.

I am also looking at another cam, but this is as big as I'll go on this motor.

Camshaft Specification Table
Part Number 12-432-8
Engine 1955-1998 Chevrolet
262ci-400ci
8cyl.
Grind Number CS XR282HR-10
Description

--------------------------------------------------------------------------------

Intake Exhaust
Valve Adjustment 0 0
Gross Valve Lift 0.51 0.52
Duration At 0.006 Tappet Lift 282 288

--------------------------------------------------------------------------------

Valve Timing At 0.006
Open Close
Intake 35 67
Exhaust 78 30

--------------------------------------------------------------------------------

These Specs Are For The Cam Installed At 106 Intake CL
Intake Exhaust
Duration At 0.05 230 236
Lobe Lift 0.34 0.347
Lobe Separation 110

--------------------------------------------------------------------------------

Recommended Valve Springs 986-16

 

You already have this:

Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 8.0 BTDC 42.0 ABDC 107 230 °
Exhaust 56.0 BBDC 2.0 ATDC 117 238 °

So going to this is actually nearly the same or worse

Duration At 0.05 230 236
Lobe Lift 0.34 0.347
Lobe Separation 110

The 110 increases valve overlap. No compression is being built while both valves are open

 

Again, unless you verified everything I highly doubt this. The CR GM lists for your motor is for a blueprinted engine. A production engine will have quite a bit less than what GM states. Often 1/2 ratio lower.

 

--------------------------------------------------------------------------------
This combination is from the AFR web site. Just imagine what a healthy dose of nitrous could do.
Displacement: 383 cu. in.
Carburetor: Holley 750 double pumper
Heads: Air Flow Research 190cc Street
Intake: Air Flow Research FloPower RPM
Camshaft: Comp Cams hydraulic roller, with 236/242° of duration @ 0.050 in. lift, and 0.520/0.540 in. lift
Headers: 1 3/4 in.
Distributor: MSD
Timing: 34°
Comp. Ratio: 9.5:1

MAX HP: 503 @ 5500
MAX Torque: 517 @ 4500

This cam is a 110 LSA. I designed my new motor similar to this but bumped the compression to 10.2 to 1 and increased the LSA to 114 to increase the dynamic compression closer to Ideal of 8.5 to 1. The cam is also designed to be installed 4 degrees advanced to lower the working RPM slightly to help streetability. The 150 shot of nitrous also likes a wider LSA.

 

Please correct me if I'm wrong, I am new to cam science, b

280h cam overlap was 60
crane cam installed is 72
xr282hr is 65
xr276 is 59

If I am wrong please advise

 

Keep in mind that comp rates advertised duration @0.006" tappet lift and crane @0.004". So the crane advertised duration is not quite as much more as it would seem.

 

Zwede touched on it. You have to compare apples and apples. I don't care about advertised duration or even .006 or .020. Just use the .050 valve event numbers and it gives a meaningful overlap.

The Crane cam has 10 degrees of .050 overlap the Comp xr282hr is 12 the xr276 is 7 degrees

the lobe center of 110 makes more overlap than 112

 

I was comparing the first cam, blue run, to the second cam, red run. In the lower a/f ratio recorded, shows the red run is to lean right off the bat. The blue run shows that over 4k the engine wants more, your just getting into the cams "curve". More carb adjust and also better flowing heads. According to my quick DynoPro calcs, you were about at max of blue (1st cams) capability. The second run (red) was no where close to what it should have done, more tuning needed. But torque of second cam is going to be less automatically.

I don't think this is the right cam for your car, though don't know your gear and tire size. With the 108-110 LSA, higher compression would be better since your bleeding off some of it with this LSA. Your cam selections so far have decreasing torque levels, not really what you want for a street car. Even though you have a stick w/tall first gear.

Sorry if this is rambling, just came in from snow clearing, got dumped on with the winter storm, still feeling a little light headed. Little more out of shape than I thought and it's gonna take a few more trips with the snowblower I'm afraid.

 

Zwede I agree, until I have all the parts to check and assemble its only. for lack of better words, an educated guess. I saw your post on your CR calcuations and the variance

 

GKULL

Where are you getting the valve opening specs at .05 lift for the comp cams. I see it for the cranes, but I am either blind or looking in the wrong place.

I would like to study this futher tonight.

dennis

 

OK GKULL

I found the formula you are using to calc. overlap , but they are using the advertiised duration not the duration. at .050 lift. See below.



1) The easiest way is to add the intake opening times to the exhaust closing time. Seat to seat times (advertised duration) must be used. .050" durations or timings will not give the correct overlap. Example:
Comp Cams EX268H
Adv dur: int 268º, exh 280º
110 LSA, 106 ILC (4º advance)
Valve timing @ .006"
intake opens @ 28º BTDC
Intake closes @ 60º ABDC
Exhaust opens @ 76º BBDC
Exhaust closes @ 26º ATDC

In this example the overlap is 54º (28º+26º)

 

With programs like DD2000 you can take the .050 duration like 230/236 and 110 LSA or like Crane Cams .050 valve event numbers and plug them in and it gives you .050 valve overlap which is much more meaningful than seat to seat.

It's all in the cam lobe ramps. aggressive roller cams really lift the valve fast and set it down fast. Where a wimpy flat tappet cam lifts slow and sets it down slow with very little time at max opening. So their "Seat to Seat " duration could be exactly the same. But their .050 duration numbers and the amount of total flow is greatly different.

 

I did not copy all of the page I used above, it is below

---------------------------------------------------------------------
1) The easiest way is to add the intake opening times to the exhaust closing time. Seat to seat times (advertised duration) must be used. .050" durations or timings will not give the correct overlap.

Example:
Comp Cams EX268H
Adv dur: int 268º, exh 280º
110 LSA, 106 ILC (4º advance)
Valve timing @ .006"
intake opens @ 28º BTDC
Intake closes @ 60º ABDC
Exhaust opens @ 76º BBDC
Exhaust closes @ 26º ATDC

In this example the overlap is 54º (28º+26º)


2) If the seat to seat opening and closing times are not known, the overlap can be calculated using the advertised duration and the Lobe Separation Angle (LSA). This formula works for both single and dual pattern cams.

Add the intake and exhaust adv durations
Divide the results by 4
Subtract the LSA
Multiply the results by 2

Using the example cam above:
268+280=548
548/4=137
137-110=27
27*2=54
The overlap is 54º


Here's another example:
Comp Cams XE294H
Adv Dur: int 294º, exh 306º
110 LSA, 106 ILC (4º advance)
Valve timing @ .006"
Int opens @ 41º BTDC
Int closes @ 73º ABDC
Exh opens @ 87º BBDC
Exh closes @ 39º ATDC

Adding the int open and exh close times (41+39) the overlap is 80º

Using the formula above:
294+306=600
600/4=150
150-110=40
40*2=80
The overlap is 80º
---------------------------------------------------------------------

Using this formula, but with the .050 duration numbers my old flat tappet

280H magnum overlap is 10
the crane roller I'm using now is also 10

The problem must be in the opening point on the intake.

Dennis

 

That is what i have wondered all along. Your 280 cam was very close in it's specs to your Crane roller 230/230 110 is really close to 230/238 112. The roller cam motor should actually run better and have more manifold vacuum.

Did you have a multi keyway crank and cam gear? With your number one cylinder at TDC and your crank set to Zero on your timing cover indicator. did you match up the cam gear dot straight down at the 6 o'clock position and the crank gear dot straight up at the 12 o'clock position?

The overlap of 10 degrees at .050 for both is reasonable.

the fact that you lost power and gas mileage would lead me to believe a problem. something as simple as over adjusted valves and your never really closing them. Get a person to do a leak down test and it with give you the health of every cylinder. Additional exhaust duration has much less effect on how an engines runs compared to additional intake duration.

I had to high of compression to run my original Crane cam which is just like yours. I also used 1.65 intake and 1.6 exhaust. the motor had wonderful power and I could run it to 7500 rpm if i wanted to.

 

Did you have a multi keyway crank and cam gear? With your number one cylinder at TDC and your crank set to Zero on your timing cover indicator. did you match up the cam gear dot straight down at the 6 o'clock position and the crank gear dot straight up at the 12 o'clock position?

Gkull this is a possibility, I do have an adj. crank gear, and have thought of it. However this is the third cam I have put in this engine and untold timing sets over the years. As I have told my wife I have made one mistake in my life, maybe this was the second. I will find out tomorrow, I'm gonna pull the timing cover. If its timed straight up I'm ordering another cam.

On the overlap issue by your way at .050 lift both cams were at 10 deg. overlap. At the usual method the 280h was 60 deg and the crane was 72 .

Have to go to dinner, will post findings when I tear it down

Dennis

 

Gkull
I think this answers the cam timing question. I just pulled the front off the engine. I'm gonna pull the everything else and the cam tomorrow and order a new cam Monday. Still havn't decided on which one. but I need to be quick I'd like to have this thing up and running by next Sunday. It may be my daily driver soon

 

You have two sets of numbers for advance and retard on the crank gear, I assume you are using the outer ring, is that the correct set of numbers for yoiur setup ?

Also your camera date is a year out of whack

 

Also your camera date is a year out of whack

Motorhead, maybe that's the problem:

Yes if you notice the outer zero is lined up with the cam gear, while the inner is lined up on the crank key

dennis