GT2 EVO cams on 993 Vram motor???
 

Has anyone tried these in the 993 Vram motor??

You will want to use RSR pistons which have deeper valve clearance pockets.

I will adjust piston clearance as needed. I was looking for how well the vram worked with the GT2 cams. Dynos would be great so I can evaluate the torque curve.

I can't give you dynos, but I chose between the GT2 and similar Cup cams at one point, and I ended up building (and dynoing) the Cup version. I came up with the following (rough) comparison graph between the Cup and GT2 cams on a rather simple engine sim before I built the motor:
http://forums.pelicanparts.com/uploa...1260144423.jpg
The GT2 cam has 1 degree more intake/ 4 degrees more exhaust duration, moving the torque peak up by a bit for more peak power, at the expense of low end torque.
I then built the motor with the cup cam, VRam, RS valves, headers and race gas. The following dyno was the result:
http://forums.pelicanparts.com/uploa...1260144647.jpg
Given this, I'd expect the GT2 Evo cam to look a lot like the dyno above, but with less power below about 6k and more power above it. Given that, I'd probably only choose the GT2 cam over the cup if I was prepared to raise the rev limit of the motor. In that case for a track car it may well be the ticket, but you'd likely give up some performance on the autocross or street. Hopefully someone else can give you an actual dyno.

Pete do you have the specs on both of those cams? this is what I have from Andial on the Ss and RSR cams
<pre>
93 EURO SPORT 49mm valve open 8.0 BTDC 45.0 BBDC 1.55mm
993 105 247 70 None Hydr. Lifters lobe center 112.0 ATDC 110.0 BTDC
valve close 52.0 ABDC 5.0 ATDC
AND 105 246 70 Motors earlier than 993 duration 260.0 DEG 248.0 DEG
AND 105 247 70 net value lift 0.490 inch 0.446 inch


AND 105 246 81 3.8L RSR RACING 49mm valve open 36.6 BTDC 61.7 BBDC 4.55mm
AND 105 247 81 lobe center 114.8 ATDC 108.7 BTDC
valve close 77.2 ABDC 36.6 ATDC
duration 293.7 DEG 278.3 DEG
net value lift 0.4897 inch 0.4884 inch
</pre>

Thanks bill and pete.

Do either of you guys have the specs (all of them) for the factory 993 vram cams?

I don't have full specs any more. Camgrinder would- he made mine and I got my specs from him at the time. What I do have:

SuperCup (solid lifter)
Duration at .040" I/E: 248/ 234
Duration at .050" I/E: 242/ 228
Lift I/E: .490"/ .455"
Lobe angle: 112 factory, 113 as ground for my motor in the dyno above (still required larger valve pockets for clearance w/ RS valves).

GT2
Duration at .040" I/E: 254/ 248
Duration at .050" I/E: 248/ 232 (6 degrees more intake duration, not 1 as I said above)
Lift I/E: .485"/ .470"
Lobe angle: 112

I also had a 993 motor with hydraulic lifter 3.8RS cams- the solid lifter Cup cams seemed to make 5-10 more foot lbs across the board, for what that's worth...

Ok this is where it gets more complicated. I currently have a 993 vram with turbo conversion. The motor is stock running 11.2cr (10.5-10.7 really) and 6psi of boost. Compaired to my previous 993tt (600hpx600tq) 8:0cr and 20psi this setup is much more fun to drive. The power curve and overall personality is spectacular. I am tearing the motor down friday to replace the rods and pistons (same CR). While its apart I am reluctantly considering a cam change while in there. My goal is to create the flattest torque curve possible by varying the boost with the avcr controller. I plan to up the boost slightly to 10psi.

http://forums.pelicanparts.com/uploa...1260198385.gif

The above dyno is from a 993 vram with turbo conversion 8:0cr. I love the overall power curve just would like to have mine not fall off so fast on the top end. I also suspect with my higher CR the bottom end will be stronger. If I switch to the GT2 EVO cams the later closing intake will bleed off some static compression. This should help reduce my high CR and give it back to me on the big end.


http://forums.pelicanparts.com/uploa...1260198647.gif

The above dyno is from a 3.8 turbo running GT2 evo cams. This is what I hate about high boost low CR motors. Compaired to the previous dyno torque does not follow boost evenly. I suspect this is more to do with the intake (standard) and port/valve sizes (smaller turbo heads).

What I am looking to do is keep the torque curve shape of the first dyno but keep it going longer up in the RPM's. I feel that the GT2 evo cam is better suited for a boosted motor than the factory 993 cam. The million dollar question is will it idle etc well with the vram?

I converted the factory hydralic rockers to solid without changing cams. I was amazed at the power difference. Solids are really the way to go in any real performance application. Yes the maintenance does suck but it really comes down to how commited you are.

Looks like a fun motor...

Will it idle "well"? I doubt that... My Cup cam idled at 1200 and that was with wider lobe centers. With normal lobe centers I believe it has 2 mm lift at overlap; the GT2 has 2.5 mm, so it will be that much worse...

I believe that if you boosted the dyno of my motor above you'd move peak power to a slightly higher RPM- not sure if that 200 rpm or how much. This is due to increase the increased compression you'd see from the boost.

I also suspect, however, that going to cup cams might increase the effective compression ratio enough to push you over the detonation limit and force you into running lower boost. Widening the lobe centers would counter that, though perhaps not enough to let you run 10 psi is my guess (what gas are you running, by the way?). The GT2 with wider lobe centers would improve idle, decrease effective compression and give you plenty at the top. I suspect you'd spool the turbo slower, unfortunately, but I don't think there is a good way around that while still being able to hit your 10 psi target...

I'd also consider dropping the C/R half a point or so and use the cup cams- might get the best of both worlds...

Interesting- I wouldn't have expected that. I was under the impression solid lifters simply let you use more aggressive ramp-rates in the cam profiles. Thus I wouldn't have expected more power with the same profile, but it's quite possible I'm mistaken...

I have seen the GT2 evo cams installed in street cars. The idle is unique but not bad. This was on 3.3 carerra motors with single throttle body. Would my vram be better or worse than those cars?


I always run 103 oct fuel. The corrected compression on my last car was 15.37. This one would be 15.00 at 12 PSI (using the cup cam specs).

I will scan some other engine dynos today from a 3.3ltr GT2 EVO cams. At 1 bar the car hits 400tq at 3,000 rpms.

I did not expect it either. I suspect when the hydralic lifter crashes into the ramp it compresses some. This is the only explanation I have. The difference was pretty dramatic. No other changes were made at the time.

Good question- do you mean 3.2 carrera, or 3.3L more likely the 3.3 Turbo Carrera with CIS? I seem to remember the mass flow sensor of the the VRam is particularly sensitive to reversion at idle (ie it reads the same air more than once as it moves back and forth due to the overlap) compared to the 3.2 carrera's barn door sensor. No real idea how it compares to a CIS 3.3 Turbo at idle.

If you're running 103 I'm sure you can get away with quite a bit- 10 psi sounds much more sane in that case...

It was a 930 slope nose with EFI pressure sensing conversion. So its the MAf sensor that causes the problems? Can it be calibrated around the reversion? I will have to check with Todd at Protomotive.

Here is the link for the compression calculator. http://www.wallaceracing.com/dynamic-cr.php

Yea, I think MAP sensing will be almost immune to reversion- much easier to get a good idle. I wouldn't expect that with MAF.

If it was easy everyone would do it...

What's your car weigh, by the way...

I sent Todd at Protomotive an e-mail. Let's see what he thinks. I know I can do a MAP conversion on mine as well. That would also solve my desire to run H2O injection.


3126lbs.

FYI neither of those dynos are mine. I live in the bay area so I would be happy to take you for a ride. I am about 450hp-475hp in the current configuration.

Nice- where do you get 103 around here? I just know the two pumps on the peninsula with 100.

I'd be curious to see how your car runs, both by itself and compared to my '69 (which I just got back on the road).

No cats or O2's installed. When tuning the car I run 100 oct unleaded because of the wideband. After I get the tune sorted I remove the wideband and run 116/91 mixed to 103. I buy it at infinion by filling 5 gallon jugs. The motor comes out friday for new pistons and rods. I will take you for a ride after that. I expect 550hp out of my setup.

Nice- that will be a wild ride. Should also be pretty even if we run I'd think, though the delivery will be very different. Do you track or autocross it, or get out to any of the local events? If so I'll likely see you around.