"Most" Cam for 3.8 with Varioram

CBRacerX · CBRacerX's Garage

Greetings All,

Now that I have broken in my 3.8 with the stock Varioram induction, I find that I can qualify for an emissions except status in PA (less than 5K miles a year driven). So my modest DR "DC-20" cams could be swapped for, well, just about anything that would work with my configuration:

964 Crank
964 R&R Rods (stock length)
Mahle RSR Pistons and Barrels (102mm)
Stock 964 Heads, DR Springs
993 HE with "Happy Crab" Dual Exhaust
European 993 Varioram Induction (1998)

This is a street driven car, and I want to retain the Varioram. Chip changes (this is Euro Electronics with a socketed chip) are fine, even injectors if it came to that. But no budget for individual throttle bodies or other esoterica.

So am I looking at the RS cam as the most likely upgrade? Or do I have more _interesting_ options?

Thanks folks,

petevb · 05-07-2007, 09:37 PM

What's the max RPM are you building the motor for, where do you want the power, and how do you like your idle?

I'm very happy with my 3.8 supercup cams (solid lifter) in my 3.6 VRam with big valves. I built it for the widest possible power band, so despite the fact that the motor spins to 7300 I didn't put in something with more top end... Clearly there are wilder options- the GT2 seems the next step up, and they keep going from there. As you know you can't get anything too interesting without ITBs, though...

CBRacerX · CBRacerX's Garage

RPM Range is "fun street", with very infrequent track use. Stock 964 crank with R&R Rods and ARP Bolts, very lightweight pistons and wrist pins. Solid rockers with DR springs (stage 1). So 7K should be no problem I guess.

3.8 Supercup sounds good to me! Are stock valves going to work wth these?

petevb · 05-08-2007, 07:26 AM

Well I'd be interested to hear what everyone else has to say, but I'd think the supercup cams would be very good for what you're talking about...

This is roughly my motor, depending on the whp to crank hp conversion you use. On pump gas I loose around 6-8 across the board. If you used cup cams on pump gas, I'd make the educated guess that you'd be a little above this in torque on the low end, especially at around 4k, due to your extra displacement, and then below it slightly from 6k RPM up due to my bigger valves. That would make a great high torque street motor. I'd guess that with GT2 cams your dyno would look very much like this one- a little less low end and a little more top end compared to the Cup cams. So take your pick...

One of the guys with some experience and/ or a good engine sim program could really tell you what's up, and I'd be interested to hear myself...

Steve@Rennsport · 05-08-2007, 09:53 AM

Hi Chris:

Supercup cams work very well for some of these applications but be aware that these cams feaure 112 deg LC's that these single-throttle intakes do not like,..

(RS cams have 114 LC's)

Above 1200 RPM they run very well but are reluctant to idle below 1K.

FWIW,.. I have several sets of new Webcam Supercup billets if that helps you.

petevb · 05-08-2007, 10:04 AM

Good point on the lobe centers. I forgot to mention I had camgrinder cut these supercup cams with a 113 degree lobe center for me to split the difference. Good compromise, I think.

BTW, I have 3.8 RS hydraulic lifter cams in the other motor- idle is better, but they don't have the area under the curve. Didn't think that was what you were looking for when you mentioned a wild cam...

CBRacerX · CBRacerX's Garage

Thanks for all the input guys. I am looking for a still street friendly cam that lets me take advantage of the motor's size and piston reliefs, but does not require changing the hardware of the intake.

Steve@Rennsport · 05-08-2007, 10:14 AM

If you use the Varioram, I'd stick with the RS ones,...

petevb · 05-08-2007, 10:36 AM

Maybe I'm mistaken, but he's already running DC-20 cams with a 113 degree lobe center and a fraction more .040" duration compared to the supercup cam. So the 113 degree supercup cams would only add more lift, and I wouldn't think they'd make the idle worse?

I'd have thought that the RS cams would be a small step backwards in terms of power compared to the DC-20s...

How do you like the idle now?

Bill Verburg · Bill Verburg's Garage

I agree, the DC20 aka superC2 is about it, they are comparable to the GT2 cams.

though it would be nice to hear from somone w/ DC21 which has considerably more lift.

I use the hydraulic RS and even they want an idle just under 1k

CBRacerX · CBRacerX's Garage

Quote:

Originally posted by petevb
Maybe I'm mistaken, but he's already running DC-20 cams with a 113 degree lobe center and a fraction more .040" duration compared to the supercup cam. So the 113 degree supercup cams would only add more lift, and I wouldn't think they'd make the idle worse?

I'd have thought that the RS cams would be a small step backwards in terms of power compared to the DC-20s...

How do you like the idle now?

I think the idle is fine, but high. The stock Euro V-ram programming is idling at ~900 when cold, but when warmed up I am getting more like 1100 - which is mildly annoying.

petevb · 05-08-2007, 01:36 PM

So the list of cams more aggressive than your DC20s but that will still work with the VRam is short. Some of them, in what I think is mildest to wildest.

Before selecting my 113 degree supercups I was advised that the GT2s would need about a 200 rpm higher idle, and would make +8 to 10 hp at 7500 rpm compared to the Supercups, but would be lower below 6k. We only looked at 113 degree lobe center versions of both the supercup and GT2, as I understand going to 112 makes the idle significantly worse.

The DC22 cams are also used with the VRam, though these are more for racing- most of the gain from the GT2 or DC22 would probably come in above your operating RPM...

I'd talk to Camgrinder- maybe the DC21 on a 113 degree lobe would be pretty good. I modeled my motor beforehand, and it came out exactly as expected, so if you know what you want you can probably get it...

DW SD · 05-08-2007, 01:55 PM

As a point of reference, I have the 993 SuperSport Web Cams and torque peak is 275 ft lbs (rear wheel) at 4600 rpm. The HP peak is 6100 rpm @ 274 RWHP. No varioram - I have the '95 intake setup.
I think this cam is too small for what you are considering.

My idle quality is best from 950 rpm and up.

Doug

petevb · 05-08-2007, 02:08 PM

Also a 3.8? '95 valves? That's crazy torque...

DW SD · 05-08-2007, 02:19 PM

Pete,
3.6, '95 993 heads. Here's the text data file. Dyno was a dyno-dynamics, Australian made. Maybe it is generous?

Graph File
:2VKY842.025
Description: 71 911 3.6
03/08/2006 A:0.996 X:1.100
Speed Ign. RPM Power Torque Temp Air/Fuel VacBoost
MPH RPM HP FtLb OF Gasoline (Atmos)
50 2629 108.2 216 72.5 13.1 -0.1 inHg
52 2731 115.8 223 72.5 13.1 -0.1 inHg
54 2843 120.9 223 72.5 13.1 -0.1 inHg
56 2952 125.4 223 72.5 13.1 -0.1 inHg
58 3061 133.8 230 72.5 13.1 -0.1 inHg
60 3173 137.5 228 72.5 13.1 -0.1 inHg
62 3281 142.1 227 72.5 13.1 -0.1 inHg
64 3389 145.6 226 72.5 13.1 -0.1 inHg
66 3499 149.0 224 72.5 13.0 -0.1 inHg
68 3603 156.8 229 72.5 13.1 -0.1 inHg
70 3718 167.8 237 72.5 13.0 -0.1 inHg
72 3832 175.0 240 72.5 13.0 -0.1 inHg
74 3944 184.9 246 72.5 13.1 -0.1 inHg
76 4059 189.9 246 72.6 13.0 -0.1 inHg
78 4161 201.2 254 72.5 13.0 -0.1 inHg
80 4275 209.6 258 72.5 13.0 -0.1 inHg
82 4391 221.5 265 72.5 13.0 -0.1 inHg
84 4501 232.6 271 72.5 13.0 -0.1 inHg
86 4609 240.7 274 72.5 12.9 -0.1 inHg
88 4720 243.4 271 72.5 12.9 -0.1 inHg
90 4830 249.3 271 72.5 12.8 -0.1 inHg
92 4935 254.0 270 72.5 12.8 -0.1 inHg
94 5052 257.0 267 72.5 12.9 -0.1 inHg
96 5159 263.1 268 72.5 12.9 -0.1 inHg
98 5261 267.4 267 72.5 12.9 -0.1 inHg
100 5367 267.7 262 72.5 12.9 -0.1 inHg
102 5475 267.6 257 72.6 12.8 -0.1 inHg
104 5568 260.6 246 72.6 12.8 -0.1 inHg
106 5672 266.8 247 72.6 12.8 -0.1 inHg
108 5776 266.0 242 72.6 12.8 -0.1 inHg
110 5879 272.8 244 72.5 12.8 -0.1 inHg
112 5981 271.6 239 72.6 12.8 -0.1 inHg
114 6094 270.4 233 72.5 12.7 -0.1 inHg
116 6189 266.9 227 72.5 12.6 -0.1 inHg

petevb · 05-08-2007, 02:54 PM

Well something isn't normal, one way or the other...

Above is your dyno.

Above is my 3.6 with RS cams.

And one of Jack's old dynos...

And another VRam.

And TonyGs first 3.6 configuration...

Notice the trend? The all have more HP than torque, and that's what i'd expect. I'd guess that either you have something like really small headers that are helping you at low RPM and hurting up top (or cam timing?), or you've got a problem right around 6k. Notice how your dyno gets bumpy up there? I could be off, but it looks pretty suspect to me... What's the rest of your engine spec, and how does it feel?

DW SD · 05-08-2007, 03:12 PM

Interesting analysis, though it looks to me like all of the dyno results are somewhat bumpy? Could be an issue with the flapper valve opening. The motor was freshly rebuilt at that point with only a few hundred miles.

Seems to pull strong, but the chassis only weighs 2200 lbs. It is a bit more refined, now, since Steve Wong did another chip, following the above dyno results. We monitored timing, at the time, to make sure that the timing was not being retarded by the computer (via the knock sensor).

It is an odd combination:
964 crank, pistons and cylinders, 993 heads, 964 cam towers, 993 supersport cams (webcam), '95 993 plastic intake and engine management + Steve Wong chip (after above dyno results), 993 factory Heat Exchangers, M&K dual outlet RSR style muffler.

petevb · 05-08-2007, 03:35 PM

Yea, could be that I'm imaging the bumps being something they are not...

All of the above cars except Jack's have larger valves than yours, and that helps a little up top, but not too much, and the '95 intake, etc should all flow well. When is the flapper supposed to change over?

Well it's not too far off, and perhaps you've already fixed any issue with your new chip or service. I was just shocked when I saw more torque than HP- in the tuned 3.6s I'm always used to seeing at least 20 more hp than tq. If you dyno again and it's the same I'd check back and perhaps go looking for a flow restriction (clogged cats, etc) or other problem starting right around 5250. With 275 tq I'd just expect more like 295 or 300 hp.

petevb · 05-08-2007, 03:58 PM

OK, searching results in:

"993 (and I believe late 964 w/ plastic intakes but I can't find the documentation for the 964s) open from 0 - 3500 and from 5520 - 6640"

From Bill Verburg. When we changed to the cup cam we had to move the changeover point for the VRam by a few hundred RPM, and I'd bet it's similar for the '95 intake, but I think you're right- that flat spot starting at 5300 or so looks very much like a broken flapper. My friend had one on his 928, and it was hole compared to other similar dynos just like that...