Bill Verburg

When the 2.7RS came out it used 'S' cams and low 7:31 final gearing to make a very desireable street/track package. The 993RS w/3.8 pistons seems to have a cam that is only a few degrees wilder than a regular C2. What's the consensus on other hyd. cams for a sporting 3.8 keeping in mind the higher f/d ratios currently in use?
If the hyd. cam is changed to a mech. what cams would be approprite for the same use?

I have seen the specs for the mech Webcam 20/21 anyone have experience with them in a 3.6/3.8 motronic?

Steve Weiner-Rennsport Systems

Hi Bill:

You asked a good question that does not have a simple answer,...

The quick reply to your inquiry would be that most all Motronic street-type, single-butterfly throttle intakes are unforgiving of camshafts with very much overlap or narrow lobe centers. This is why all Motronic cams that are compatible with the intake systems found on 964-993 and even 996 cars are pretty tame, when compared with the 2.7 RS cams that you mentioned.

Most of these engines must comply with Federal smog rules and either OBDI or OBDII, and that really limits how much overlap you can use.

Now then, the stock 964 cam, Carrera RS 3.8 cam, and several domestic profiles made by WebCam, Elgin, and Crane are close, but do have some subtle differences that make themselves known in certain configurations. I will tell you in practical applications that the Carrera RS cams are the most aggressive ones you can use in these 3.6 & 3.8 engines without creating major problems in drivability.

With the proper heads, chip, internal upgrades, and exhaust system, these will make good power to 7200 RPM in these larger engines and still pass smog. One will not trigger "Check Engine" lights unless there are other issues.

The only one of these camshaft profiles that feels the closest to the 2.7 RS cams is the 3.8 RS one installed into a varioram motor. If one wants that "wallop" that is part of any & all 2.7 RS clones as it comes on at 4000, you will need to ditch that Motronic and install a 6-butterfly intake with a good engine management system.

Remember, the 3.8 RSR made 350 HP but it had a special 6-butterfly intake with dual resonance chambers, aggressive cams, and it was not streetable.

Hope this helps a little,

Bill Verburg

Thanks Steve!!
That helps a lot, emissions are not a concern, flexibility and rriveability are, I want something that will run on 93-94, w/ a chipped Motronic. I looked into the RSR engines and injection, I feel that its not necessary for what I want. I have gotten some feedback re hyd. rockers and reliability(actually lack of) at DEs. Any thoughts here?

It's starting to look like the 993 RS cams are what I want w/ hydraulic rockers.

CamB

Although outside the scope of what you mention Bill, my engine builder has in his race car a 3.8 (from a 964) with GE80 cams and early MoTeC controlled EFI. It uses early (as in '70s) 50mm RSR throttle bodies but has an injector, um, "plate" under each for 944 Turbo injectors.

He gets 25 mpg on the highway and 340-350 hp on the dyno, all on 98 RON (93 I think).

Bill Verburg

CamB, that would be the RSR engines that I did look into. I actually found 2, 3.8RSR engines near by. They are not appropriate for my intended use in any way.

I guess the question has come down to,
993RS hyd. advantage maintainance disadvantage ? or
993 supersport mechanical, advantage reliability disadvatage maintainance

Steve Weiner-Rennsport Systems

[quote]Originally posted by Bill Verburg:
<strong>Thanks Steve!!
That helps a lot, emissions are not a concern, flexibility and rriveability are, I want something that will run on 93-94, w/ a chipped Motronic. I looked into the RSR engines and injection, I feel that its not necessary for what I want. I have gotten some feedback re hyd. rockers and reliability(actually lack of) at DEs. Any thoughts here?

It's starting to look like the 993 RS cams are what I want w/ hydraulic rockers.</strong><hr></blockquote>

Hi Bill:

Happy to help.

The decision about whether to use hydraulic rockers or mechanical ones, really lies with the intended usage and RPM range that the engine will be operated in. The hydraulic lifters, properly maintained, are good to 7000 RPM and thats the range of stock and RS cams.

The mechanical ones are better suited for 7000+ RPM usage as found in racing. Those engines are operated up to 8000 RPM and see continous operation at, or above 7000. In these cases, the mechanical ones are more durable, and allow the large heavy valves to follow the aggressive cams found in these types of engines.

Personally, if this was my own engine and was being optimized for DE type work, I would use RS cams with hydraulic rockers for really good overall power and minimal maintenance requirements unless you simply enjoy adjusting valves on these things,....

IMHO, its imperative to ignore Porsche's recommended oil change intervals if one is to have no issues with the hydraulic units. They are extremely intolerant to any dirt or contamination.

Bill Verburg

Thanks again Steve! what would we do w/o you?

Steve Weiner-Rennsport Systems

[quote]Originally posted by Bill Verburg:
<strong>Thanks again Steve! what would we do w/o you? </strong><hr></blockquote>

Hi Bill:

You are sure welcome,..........!

I don't how to respond to the second comment,..

AES

Any comments on the teflon lifters discussed <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=3&t=005217" target="_blank">here</a>?

Bill Verburg

Thanks just the type of stuff I need to know right now! <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />