cbracerx

I've got an opportunity to exchange $$$ for 3.8 RSR (964 Vintage) Pistons and Cylinders. I am rebuilding my '90 964 engine for primary street use with the occasional track event - for now. Later in the life of the car it will become a dedicated track car. So my thoughts are to use 3.8RS Cams now, to pass emissions and then get the 3.8RSR cams going once the need to satify the Gov't passes. I ma using a Varioram intake and Euro DME, so getting the tuning done ala Steve Wong should not be too tough.

Another option on the table is increasing the intake valve size a bit while the engine is apart.

Any thoughts? Somebody done this with the stock 964 heads rods yet?

Steve Weiner-Rennsport Systems

Chris:

Might I offer some suggestions & comments?

1) I would not use RSR cams unless you install a 6-throttle intake system otherwise you will be quite unhappy with how the car drives; Varioram or not. Those have too much duration for any single throttle intake system. Use either RS or 3.8 RS Cup cams (2 deg narrower lobe centers).

2) To take full advantage of the displacement increase and a camshaft change, install the RS (51.5mm) intake valves and open the intake ports to suit (or use 993 heads).

3) Don't overlook upgrading valve springs & retainers; the OEM stuff doesn't cut it.

4) Don't use stock rods in this application. Install either Pauter or Carrillo rods for insurance.

Hope this helps,

cbracerx

Thanks Steve. I appreciate all the feedback! I've already checked with you on the intake valve upgrade and your shop would get this work

The other option I have is to install RSR 3.8 heads also. I'm comparing the $$$ for that vs reworking the heads that I have.

And if I did the dedicated track car later I would probably do the TWM/Motec thing if my credit card could handle it...

agentpennypacker

Chris - let me know how this works out for you, and what your final cost is!

Geoffrey

The RSR cylinders will require boring the engine case to 109mm since they are not slip fit cylinders like the 3.8RS street engine. The 3.8RSR heads are different than the street cars with different stud spacing for the intake manifold. The Varioram will not bolt on. Additionally, they have 45mm port sizes which in my opinion is too large for even a racing engine. I have found the varioram intake does not work well with camshafts with narrow lobe centers so you'll need to be cautious with camshaft selection when using that intake manifold. If you use an aftermarket cam, be aware that the RSR pistons don't have very large valve pockets, so pay attention to the cam specs to ensure you don't purchase a cam that is too large.

If you go to an individual throttle body setup, you may check with Steve W. who offers a nice set. I have some similar to his on my racing engine. The TWM 3006 are not nearly as nice and don't work as well and I've seen screws from them go through engines.

I'd leave the heads with 41mm intake ports, but have them cleaned up with a good port design. I'd also consider installing larger intake valves, either 50 or 51.5mm valves depending on what your goals are. FWIW, my racing heads from Ninemeister were specified for 50mm intake valves.

JasonAndreas

Take advantage of your location (Pennsylvania) and have Cyntex perform the ECU tuning on a dyno.

cbracerx

Thanks Geoffrey, that was just what I needed to know! Sounds like the RSR heads are certainly not for me (I knew the ports were quite large for a mostly street engine - 54mm titanium intake valves and 43mm titanium exhaust valves. 45.5mm intake ports, 38.50mm exhaust ports). I'm suprised that the pistons have small valve pockets, I guess this is to keep the compression nice and high

Steve suggested using 993 heads instead of reworking the 964 heads, and I am seriously considering that. Is there any difference in the 95 heads vs. the 96-98 heads?

Thanks again guys!

cbracerx

Jason,

Right now the Cytex Euro 993 v-ram performance chip baseline has a flaw that randomly lowers the rev limit to 5K RPM, requiring a recycle of power to the DME. Until they resolve that, I'll have to look elsewhere.

Geoffrey

The RSR heads you specified are the Sprint configured RSR heads which are considered 30 hour heads. The 54mm intake valves are very close to the exhaust valves and the heads crack between them. The normal RSR heads have a 51.5mm intake valve and both heads have a 43.5mm exhaust valve. RSR technology is old and I believe the port size to be way too large and unnecessary. There is a difference between the 95 non varioram heads and the 96-98 varioram heads. The latter have a 1mm larger intake valve at 50mm compared to the 95 heads which have a 49mm intake valve. The 993 heads have a 43mm port where the 964 heads have a 41mm port.

I would not go out of my way to find a set of 993 heads, and I think the 964 heads with the 41mm ports after porting flow better than the 993 due to the higher velocity. If you find a 964 or 95 993 head, you can easily install a 50mm intake valve if your machinist has a Serdi style valve cutter machine without replacing the seat. If you are going with new guides anyway, I'd install the 8mm stem 993 size valves and valve guides which improve flow due to their smaller size.

The RSR pistons with the street 964 or 993 heads will produce a compression ratio of less than 11:1 due to the chamber size of the 993. I'd want to be in the 11.5-11.7:1 compression ratio, even on 93 octane street fuel. Bottom line is that the RSR pistons aren't all that great, but in 102 is all that is available from Mahle at this point in time. I did speak with them recently and they did fix the deaxised wrist pin issue (at least this spring they will have new ones) and if you beg hard enough, they will make you a custom set out of the RSR blanks.

The pistons pictured above are not the standard RSR pistons. They are unique and I've never seen them before. Without measuring them, they look like standard RSR domes at 11.5:1 with RSR heads, but the skirt is completely different. I'm rather interested in what those are from.

cbracerx

Thanks again Geoffrey, your comments are invaluable. The RSR pistons pictured are the "rare full competition version" and would cost me about $600 more than the standard RSR pistons (which would be used and not from new production). It sounds like in my application these are just not worth the effort. I really appreciate all your insight. No need to go _down_ on CR compared to the stock 3.6 pistons, even with the extra 200cc of displacement. As long as I do not have valve clearance issues with the RS cams, that seems to make the most $ and cents.

Geoffrey

The 3.6l street engine has 10.5-10.7:1 compression from the factory, not 11.3:1 as advertised.

cbracerx

Oh boy, now you got me interested in the pistons again... What is the issue with the wrist pin location all about?

Larry Herman

Chris, is that you?

cbracerx

Hi Larry - yes, this is me . Haven't seen you since Timmins party! What happened to the GT3?

Larry Herman

After renting the cup car last fall for the Summit Point club race, I really started jonesing to get back into racing again. And a lot of the people that I knew were still there! Long story short, I was only using the GT3 on the track anyway, it was too expensive to crash, and much too expensive to let it sit in the garage, so it went to a new home in Las Vegas, and the RSA in my avatar is on the way, just as soon as the motor gets rebuilt. Plus I had money left over to buy a 24' featherlite enclosed trailer. So I'm back racing this season. Hope to see you somewhere.