2.7RS - cam choice

Jim Richards · 07-27-2004, 03:32 AM

Phoenix's RS spec post and cam choices (E vs. Solex) got me thinking...

This fall/winter my 2.4E MFI will grow up to be a 2.7RS MFI engine. For the most part, I had intended to keep to the basic 2.7RS specs; however, I've been contemplating different cam choices. I drive the car on the street and on tracks that favor both torque (Summit Point, Mid-Ohio) and horsepower (Watkins Glen, VIR). I have a pair of T MFI cams that I'd like to have reground for whatever cam profile I choose. Based on my intended use, what are your recommendations?

Thanks for your advice.

69911e · 07-27-2004, 06:48 AM

I just built a 2.7E motor (only 150miles on it).
2.7 RS pistons
7R case
"E" cams
36mm ports
"S" stacks and throttle bodies
2.4 E MFI pump
boat-tailed
updated oil pump/bypass

The pump has not been used for many years and needs to be driven more.
Engine is strong from 2K to 6.5K (I have not taken higher until it has more miles), but does not have the extra kick at 5K the RS spec motor probably has. Maybe the MFI needs more tuning.
I will post the torque curve as soon as I get the MFI dialed in. I will not have accurate dyno numbers, but will have a correct curve; I will be using the RoadDyno.
The best part of the motor is it's total cost less than $1300 due to years of scrounging around for cheap parts.

Jim Richards · 07-27-2004, 02:04 PM

Thanks Ed. I guess I'll probably will just go with tried and true S cams.

jpnovak · 07-27-2004, 02:10 PM

Jim, As Dino gets farther away from that beautiful car and more like a track beast, the S cam would be a better choice. If you look at torque curves for a 2.4S vs E there is little difference down low. The S cams will be slightly more mild on the larger 2.7.

S cams
S cams
S cams

If you say it enough times it will become a reality.

Maybe you should just build up a new case and keep your E stock.

Jim Richards · 07-27-2004, 02:19 PM

Hahaha! Thanks Jamie, but Dino is still quite good looking.

I agree with your suggestion to build up another case. I'm keeping my eyes open for a good 2.4 core to build on. Hopefully I'll be able to tuck my 2.4E away in the basement.

S cams
S cams
S cams

Thanks again!

Eagledriver · 07-27-2004, 07:49 PM

Jim,

I just switched my 2.7 MFI engine from Solex to "s" cams. I gained 20 peak hp (according to my G-Tech). I don't really notice a difference on the lower end. I suspect the Solex pulls harder below 4k but can't tell from the seat of the pants. The motor really screams from 5-7k now.

-Andy

camgrinder · 07-27-2004, 10:00 PM

With the MFI T cams as cores, you would have to hard weld. You might as go with the MOD-S profile. It has more torque and a wider powerband than the original MFI S profile.

Jim Richards · 07-28-2004, 03:47 AM

Andy, that's just the kind of feedback I was hoping for. Thanks!

John, what you're suggesting is very interesting. Any compromises for my intended use - street, most DE's at tracks favoring torque, but a couple of DE's at HP tracks? Any recommended engine modifications away from standard 2.7RS specs that I should consider (e.g., intake/exhaust port size, compression ratio, etc.)?

Eagledriver · 07-28-2004, 01:41 PM

Be careful if you get away from original Porsche profiles. I looked at doing the mod S and my machine shop recommended only doing this if I went with stiffer valve springs. If you use the standard "S" profile you will be safe to 7300 RPM with stock valve train (if set up to 911s/rs spring heights).

-Andy

camgrinder · 07-28-2004, 09:59 PM

Jim,
Andy is right about the valve springs. The Mod-S is a more aggressive camshaft than an early S profile. Other than the valve
spring issue there really is no down side to replacing an S cam with the Mod-S camshafts.
Set the compression ratio at 9.5-1 and the engine will be happy.

skinnerd · skinnerd's Garage

I also had solex cams (by mistake) in my 2.7 MFI engine. When it came apart for a rebuild, we noticed the solex cams and changed them out for S cams. The difference was quite noticable. You want the S cams I am telling you. Above 4000, they blow the solex's away.

Jim Richards · 07-29-2004, 03:23 AM

Quote:

Originally posted by camgrinder
Jim,
Andy is right about the valve springs. The Mod-S is a more aggressive camshaft than an early S profile. Other than the valve
spring issue there really is no down side to replacing an S cam with the Mod-S camshafts.
Set the compression ratio at 9.5-1 and the engine will be happy.

Thanks John. Will it be happy at the stock 2.7RS compression ratio (8.5:1)?

Quote:

Originally posted by skinnerd
I also had solex cams (by mistake) in my 2.7 MFI engine. When it came apart for a rebuild, we noticed the solex cams and changed them out for S cams. The difference was quite noticable. You want the S cams I am telling you. Above 4000, they blow the solex's away.

Thanks Doug. I'll definately shy away from anything less aggressive than the S cams.

camgrinder · 07-29-2004, 02:50 PM

Jim
I believe most mod-s cams are put in engines with 8.5-1 CR.
I like 9.5-1 which will make more torque in the mid range (3000 to 5000) rpms.

jgparker · jgparker's Garage

Jim,

I know I'm late to this question, but I've had E, Solex and S-cam engines, and I love the personality my S-cam the best. Great peak power at high RMP, but idles and drives fine for the street. It would probably get annoying as a daily driver though.

Good luck,

JP

Jim Richards · 07-30-2004, 12:08 PM

Quote:

Originally posted by jgparker
Jim,

I know I'm late to this question, but I've had E, Solex and S-cam engines, and I love the personality my S-cam the best. Great peak power at high RMP, but idles and drives fine for the street. It would probably get annoying as a daily driver though.

Good luck,

JP

JP, I'm not commuting with with this car so that won't pose a problem. It looks like it's either going to be S-cams or Mod-S-cams. I guess I'll need to decide whether or not I want to spring for stiffer valve springs. I might want to think about a little overrev insurance.

BTW JP. I lived in Merritt Island and Satellite Beach for more than a dozen years. How's the weather down there?

KobaltBlau · 07-30-2004, 02:16 PM

Mod-S with upgrade valve springs and 9.5-1... mwuhahaha!

RoninLB · 08-08-2004, 05:38 PM

Your choice can be changed out at another time. That said go for the meanest cam you can live with and worry about de-tuning later. There won't be any wondering "if I only had the hotter cam?"

Jim Richards · 08-09-2004, 05:14 AM

Good point Ron. Can't see second guessing myself on this issue.