Ragtop 99

iTrader: (7)

Parameters:

* 02 FBody stock manifolds with SS exhaust or assume a basic catback.

* Medium fast cam lobes such as the Comp XE lobe with ~ .550 lift on small duration cam lobes for the intake, and maybe an XE-R on the exhaust.

Looking at some of the cam results I've seen on the board, it seems that cams with -11 to -13 overlap at .05 seem to be common. I know that some have tried 0 overlap cams with very disappointing results. But what happens inbetween? Say -8 or even -6. I come up with what seem like should be some strong torquey daily driver cams in the -8 or -9 overlap range (e.g 212/222 113, 210/222 112). I've thought about using an XE-R on the exhaust lobe to get a fast lift to reduce overlap at .006 and help out since the XER will open fast on the blowdown.

So the question is at what overlap does power really start to drop off?

Patrick G

iTrader: (14)

Joel, I've seen people run up to 0 overlap with log manifolds and get OK results, but once past -5, it's a steep slope to disaster...reversion city. -10 to about -5 (@ .050") seems to be the ideal area to be for maximum performance with manifolds. Interestingly, that's also about the limit I like to recommend for people wanting cams with stock-like idle and good low-end torque.

I like to decide where I want my motor to make peak power first. 6000 rpm peak, I'll choose a 40 degree IVC. For a 6300 peak, I'll choose more like 45 degree IVC (ABDC at .050"). Next, I decide on the overlap I'm willing to accept. Let's just use -10 for this exercise. Then final item is EVO. I'll choose an earlier opening like 52-53 degrees if it's possibly going to run nitrous and no later than 50 degrees (BBDC at .050") since we still need a fairly early opening for the manifolds. Plug the numbers into your spreadsheet and Walah, you have your cam. This is basically how Thunder Racing came up with the CheaTR cam. The CheaTR is VERY insensitve to back pressure, making it ideal for running pretty much any exhaust out there.

Ragtop 99

iTrader: (7)

Patrick:

The cheater makes great power, especially on the top end. It is an impressive cam for a stock manifold drag racer as it transforms the power in the 5500 - 6500 rpm in to a car that rivals non-emission compliant cars. The fact that the Cheater spins so high is the early exhaust opening and long duration.

The way I'm looking at it, almost any aftermarket cam makes good power from 3500 - 5500. I'm focused on making better power off the line, from 2000 - 3500 since that is where the car is most of the time driving in an urban environment. I'm willing to give up some of the gain over 5500 and shift at 6000. To that end I've been looking at the stock cams and the valve timing is very conservative.

The stock 02 cam has an IVC of ~34 and the 99 cam is around 38 (IIRC). The Z06 which spins higher is around 42. EVO on all 3 cams is 40 - 44. That Katech 204/218 112 produced a nice graph and closely matched the 02 cam. What I plan to do is keep my valve timing close to stock but increase the duration and overlap. Faster ramps on the exhaust should allow better exhaust flow during blow down without having to open the exhaust much sooner than stock. Here I'm willing to trade HP at 6000 rpm for more torque at 2000 rpm by keeping the valve closed a few degrees longer.

Knowing that I'm safe in the -8 or -9 range will allow the use of one of the above cams which I think would be a good match with 3.73s. If I go to 4.10s, the Cheater or a 214/228 115 would be a good choice as I would not need as much low end and would want a 6300+ shift point.

Patrick G

iTrader: (14)

I really like the CheaTR/Old Man 215 .600 lift lobe. I'd recommend using that if you can. I'd also recommend an XE-R exhaust lobe for really good idle and better low end torque. A 38 IVC is probably what you're looking for. That said, here's something you might like: 215/224 .600/.581 114LSA, 110ICL

CheaTR 2 0.006 0.050 0.200
Intake Duration - ID 265 215 141 OMC .600 lift lobe
Exhaust Duration - ED 273 224 146 3722 XE-R lobe
Lobe Center Angle - LSA 114 114 114
Intake Centerline - ICL 110 110 110

Intake Valve opens - IVO 22.5 -2.5 -39.5 BTDC
Intake Valve closes - IVC 62.5 37.5 0.5 ABDC
Exhaust Valve Opens - EVO 74.5 50 11 BBDC
Exhaust Valve Closes - EVC 18.5 -6 -45 ATDC
Exhaust Centerline - ECL 118 118 118
Overlap 41 -8.5 -84.5 degrees

nuzee

iTrader: (2)

IIRC, the 206/212 XE Compcam that I use has a -15 overlap at 0.50". It does not idle cleanly. I'm running it retarded 2 degrees with 1.85 rocker arms and stock manifolds/cats. I never dyno'd it, but I feel I'm close to that Katech Torquer cam. Without much weight reduction it'll get low-112 mph traps. With a some weight reduction, I hit 113 mph.

Its like you are "on the cam" as soon as you touch the throttle. I'm adding headers soon and expect to see a decent gain, but won't hold my breath.

RevGTO

iTrader: (12)

I've been studying this concept for a long time for my automatic application, and thus a 6000 rpm shiftpoint. The CheaTR is too top-end biased for that, plus I don't want that aggressive of an intake lobe beating up on the valve springs. I'm thinking a 214/224 XE on a 114+2 would work well and give good spring life with 918's - pretty close to what Ragtop is looking at.

Patrick G

iTrader: (14)

The OMC lobe that Thunder uses is not hard on valve springs. That's a myth. Lots of people getting lots of miles out of that lobe. Just need to set the springs up properly (ie shimming the springs to within .050" of coil bind). For a 6000 shift point, you want a 5800 power peak, which means you want a 38 degree IVC. On the 214/224 cam, you'd need the ICL to be 111 to close at 38 degrees.

white2001s10

iTrader: (4)

hijacking in progress...

nevermind

RevGTO

iTrader: (12)

Thanks, Patrick. For an automatic, what do you think would be the best way to get there, 112+1, or 114+3?

Patrick G

iTrader: (14)

Depends on how much overlap you're willing to accept. Both cams have the same IVC, but the 112LSA cam has -5 degrees of overlap at .050" vs. -9 degrees on the 114LSA cam. -9 is going to be better with manifolds.

Ragtop 99

iTrader: (7)

Patrick, I know you like a little more bias to the high end, but I did 3 cams that should have lots of low end punch. Like Nuzee said, I want to feel I'm on the cam by 2000 rpm, if not sooner. The first one almost matches the 02 F-body cam, the third one closely matches the 99 F-body cam, and the second one is in between. They have -8 or -9 overlap
intake/exhaust LSA ICL IVC EVO
208 / 220 111 111 35 41
210 / 222 112 112 37 43
212 / 222 113 112 38 45

At the moment I somewhat partial to the second choice, I think the first cam may run out of breath a bit too early although it would be very fun to drive. It looks like it would be similar Nuzees with a little earlier exhaust opening.

I'm not ready to do this yet (unless a cam lands in my lap ) but I will call Thunder to talk about their lobes. I've wondered if the same lobe profile used in their 224 cam could be made available in other sizes. That lobe is fast off the ramp which work well. I'll inquire about the OMC lobe too. Maybe Geoff will be interested in experimenting some more.

PREDATOR-Z

This is what I have on the way:
Comp XE lobes
(6100 rpm shiftpoints, estimate 5800/5850 peak))

0.050
210/224, .556/.568 115+1
IVO>-9
IVC>39
EVO>48
EVC>-4
ECL>116
Overlap>-13

~8.5 DCR with 11.0:1

Stage 1 243 LS2 heads, stock manifolds, 400cfm cats, x pipe, Magnaflow catback, Haltech air intake, ported TB.
03 C5

Target, Stealth ~400rwhp/380+ trq (give or take a few)

Geoff

iTrader: (3)

I am using that lobe (214/.600) as the intake lobe of the cam in my truck. I have 35,000 miles on the same set of springs and I daily drive this thing. No problem here with beating up the valvesprings.

JS

iTrader: (4)

Where do u suppose this cam would peak?
214-222 559-566 115+4

I'm running it threw shorties and stock cats...
FWIW it idles like stock and makes great power threw the whole rpm band

Ragtop 99

iTrader: (7)

JS
that cam has early IVC and EVO. I'd guess that it would peak at 5800 but the early EVO would help it carry to a 6200 shift, maybe 6300.

JS

iTrader: (4)

Thanx,u made me very happy
Thats exactly what I wanted to hear....

yellergto

PatrickG, how stealthy would the cam you recommend, 215/224 114+4 be with a stock exhaust?

Patrick G

iTrader: (14)

The overlap of this cam is only slightly more than the CheaTR, which means it will be pretty stealthy with a raised idle speed (850-900rpm). At 800 rpm or lower, it would have a beat to it. At 700 rpm, it would have a noticable lope (if that's what you like).

orangeapeel

iTrader: (18)

how about my cam?

PREDATOR-Z

Patrick,
If you remember in my previous thread you were pushing 42 IVC, with the reason that I will be missing 10 rwhp if i didn't use that.
Yet here, you recommend a 38 IVC.
What is your philosophy behind this? Is it because you are choosing XE-R over XE lobes?
I'm just trying to understand your logic.