Is 10:1 static, and 8:1 dynamic too low for an alum head setup?

Inverse dome pistons, -16cc
55 cc chambers, alum tfs heads
.044" quench
5.850" rods (stroker pistons)
3.48" stroke
Pistons down .005" in hole
CAM with 66* ABDC

The current setup I'm running (cc-306), is as above except the cam is 73* ABDC, which puts the DCR at 7.4:1, which makes the car kinda lazy I think. If the motor was 11:1 and I wanted to rev to 6800 it would be a great cam. But the motor is 10:1, and I'd like to shift around 6k max.

I'm considering going back to a XR276HR-12 cam.

-- Joe

 

I think your planned setup is a pretty good idea.
What's the stall speed on the convertor? If you're not running the car hot, lugging it with too low of a stall speed, (and a heavy car), then you *could* go higher on the CR. With injection you can get away with more DCR.
I think you already know the answer don't you? It'll be better than your current setup, as far as low end, but far from standing on the razors edge, leaving a bit on the table. You've got a lot working for you there, FI, good quench, etc. Going to a fast ramp cam will build the most cylinder pressure and give you the best low end torque. The xe276HR-12 should work pretty good.

 

I was just about to send you a PM, to see if you'd comment on the thread.

I think I do know the anwer, and i've been thinking about this for a while. I'm just questioning if there IS a better cam. I've learned a lot building motors over the years, but I'm least happy with this current combo - and I think it's the CC306 cam. Like you said, I have everything else together for me. The best bottom end I can afford, pistons, machine work, alum heads, etc. But I think the cam choice was wrong.

I'm also seeing huge discrepencies with the DCR calculators. The one I downloaded reports like 6.9 dcr, where as this one:
http://kb-silvolite.com/calc.php?action=comp says 8:1..

The converter is a 2800 stall raptor 5x. Now, 2800 stall is a little misleading. The converter is rated for a 750hp motor, so the stall is probably closer to 2400. Infact, if I did a brake test in the parking lot i'd think the thing would catch even lower.

-- Joe

 

I like that kb-silv DCR calc, but rather than ABDC @.050 +15* I just use the ABDC as listed (not @ .050). I use that as my gospel.

This is in your vette? What's it weigh?

haha, I didn't know the specs offhand for the CC306, so I looked it up
http://www.f-body.com/forum/printthread.php?t=9063
Looks like you're not the only one in that position.

I think that CC306 is more meant for a stock type of head which really *needs* the wide exhaust spread. For your aftermarket heads the exhaust ports aren't so bad to need a really wide split, heck I think a straight pattern might even work well for your needs. I'm not wise to the many roller cam choices available, so i'll skip suggesting anything.
You really get a wide powerband with the roller setup, so what I would normally think is too small in a flat tappet, would actually do well for you in a roller. I think the xr276HR is a good choice, but maybe look at any straight pattern rollers in the 23x @.050 range. And/or see what comp says of course.

 

About 3050 lbs w/out a driver..

Yeah. It's really not the right cam for my combo. Be great if it was a track only car, shifting gears at 6500+.

Guess I'll keep searching. I ran the slp-51010 cam for years and loved it. Then I sold it. wish I kept it. its similar to the 276, but a little more duration I think.

Thanks!

-- Joe

 

i'd think you'd like the 503 cam or the 276. its an extreme energy grind which has faster ramps than the CC computer controlled cams such as the 305 and 306 cam. look at the advertised duration and the actual duration at .050". the bigger the difference in advertised duration and duration at .050, the lazier/slower the ramp rates.

The XFI series is VERY nice for modern cylinder heads and fuel injection. very fast ramps and 113 lsa for smooth idle, but they still make power. too bad they dont have a 22x duration cam like the CC503/276hr. they have a 218/224 and a 230/236. the larger cam will be like the CC306 and wants to rev over 6000rpms easy. the 218 might push peak power to 6000rpms but i was thinkin more of a 5500-5700 area. See if comp cams could grind a custom 224/230 on the XFI lobes. that be a HOT setup for 6000-6200rpm shift points

 

Hi Anesthes,

You can download a good DCR calculation at my site, it is Excel Sheet that you can adjust if you want.
http://www.donostia.demon.nl/index_files/Engine01.htm
Check at the bottom right of the page.

I hope this help.
Regards,
Cobra289

 

Where do you fill in the cam specs?

-- Joe

 

Hi,
I work with the "Advertised Intake Closing timing (Angle) in degrees ABDC"
and is located at the bottom left of the sheet.
The yellow field is marked with 60.5 degrees.

Regards,
Cobra289

 

Heh, Didn't see it

7.9:1 it says for DCR.. i wish that number was closer to 8.4...

-- Joe

 

How do you feel about the 280?

It has 5 degrees less overlap than the 276, is a single pattern cam, but do you think its got lazy ramps?

Part Number 08-430-8
Engine -Present Chevrolet
305ci-350ci
8cyl.
Grind Number CS 280H-R10
Description
Intake Exhaust
Valve Adjustment 0 0
Gross Valve Lift 0.525 0.525
Duration At 0.006 Tappet Lift 280 280
Valve Timing At 0.006
Open Close
Intake 34 66
Exhaust 74 26
These Specs Are For The Cam Installed At 106 Intake CL
Intake Exhaust
Duration At 0.05 224 224
Lobe Lift 0.35 0.35
Lobe Separation 110
Recommended Valve Springs 982-16

 

looks like the ramps would be alittle lazier than the 276. the magnum cams are a less aggressive design than the extreme energy.

The difference between the two powerwise probly aint much. but the 280 is on a 110 lsa which will have a rougher idle. the 276 is on a 110 lsa as well but the 503 is the computer controlled version on a 112 lsa and i think that will be abit better for the tuning.

the 503 cam is definately a tried and true setup

 

Couple of things. You can get the Comp Cam XFI series with a 224 degree lobe on the intake. They list it in the cam lobe section. You would have to special order it from Comp Cams. Then go 230 degress on the exhaust lobe.

I'm running a DCR of 8.5:1 with my aluminum heads and 91 octane gasoline with no problems. Quench is .035". With your pistons .005" in the hole and the GM .028" gasket that would put your quench at .033". With tight fitting pistons I think you could get away with it. I have seen where people are running even tighter quench.

 

It's funny how desktop dyno simulates cams. Makes you wonder which one is closest. Here is an example, of the same cam. Specs are plugged in .006" (advertised) and .050" . Look how different it graphs them!

This is the 503 cam.

 

thats why i dont necessarily take what those simulators give you as a good estimate of what your motor will make.

 

I have DynoSym and it says to use the .006" numbers for the best accuracy.

 

Thats what desktop dyno says too. I think the biggest problem is, you don't have enough cam specs to really simulate the cam. As Sonix was saying about the lazy ramp rates.

It's interesting though. When you use the .006 vs the .050" it moves your powerband up by like 500rpm, yet on .050" it shows greater torque. Weird.

-- Joe