3.0 Motor for my RSR Clone

[tom1394racing]

I am making the final decisions in the planning of the 3.0 motor for my RSR clone and would like to get some feedback from the experts out there. The car will be used for street and track. I want to have a reliable motor that will provide reasonable low end torque and around 250 peak HP. My starting point is a '78 SC motor thast has around 80K mileage. I have read most of the threads on hot rodding the 3.0 and have a few remaining questions. I have decided not to do the 3.2 short stroke because I will probably vintage race the car and the displacement limit will be 3.0. I have also decided not to go the twin plug route at this point because of the expense and scarceness of the single head distributors, caps and rotors. I want to preserve the vintage look of the distributor and may upgrade to twin plug when the cap & rotor become more readily available.

The basic configuration that I am targetting is:
3.0 Liters/9.8:1 Compression/Single plug/PMO Carbs/Headers

My questions are:

1. I have completed the teardown have found Alusil pistons and cylinders. I believe my best options at this point are to buy new Mahle P/C's or to have my Alusil cylinders replated with Nickasil and use the JE pistons. Does anyone know the relative cost of these two options and has anyone had any experience with replated Alusil? I belive EBS can be a source for either option.

2. I am planning to use either GE 60 or GE 80 cams. I will have my CIS cams reground. Which is the better choice for me?

3. What size PMO's should I use? I am thinking 46 mm.

4. What size headers? I am thinking either 1 5/8" or 1 3/4".

5. I want to use the twin muffler configuration rather than the 2 in/2out OEM style muffler. Any recommendations that will work on the street and keep the car no louder than a Harley?

As always, your advice is extremely helpful to me. Thanks in advance.

[cstreit]

Hmmm...

250 is probably a tad on the optimistic side with that motor. I essentialy have the same one and am running about 240 I think. Never had it dyno'd though. So if you do, PLEASE post.

1. I also had Alusils and while I couldn't find my notes, I believe I budgeted about $2650 for Nikasil plating and J&E's vs. $3000 for Mahle's all the way.

2. Depends on where you want your power. Unless you also have a very optimized transmission, I'd go for the one that offers more torque and power from 4000-6500. Some of the more agressive cams don't come on to 5500 and with an SC based motor you'll find that you run out of rev's before you run out of power.

3. 46mm will work well for the motor, but you'll have less bottom end. I used 46's but think that 40's probably would have worked just as well. If you're gonna turn the motor above 7k RPM, use 46's. (this will also require uprated valve springs, retainers, and some head flow work.)

4. 1 3/4" will be better I think. 1 5/8" would work better with a more stock motor. I use 1 7/8" but only because they were free.

5. Can't help you on this one.


Finally on the distributor bit, BURN-BROS on this board is close to finalizing a twin-plug diz using a Jaguar cap. I'd look into that. MSD was also considering it. Otherwise you're stuck with the 964 modified dizzy (Rennsport) or Electromotive (which isn't very vintage looking)

[tom1394racing]

Chris

Thanks for your reply.

On the cam choice..... I will be using a somewhat optimized gearbox, recommended by Carquip, that will keep me in the upper RPM ranges (7:31 R&P, 11/35 1st, 18/33 2nd, 22/29 3rd, 25/27 4th and 27/25 5th).

I've been told that the GE 60 is will give me more low end but less peak power and the GE 80 would be the reverse. I don't want a peaky motor that has no grunt in the lower RPM ranges. Which of these is closer to the S cams that have been recommended for the 3.0L?

[cstreit]

Tom,

TO be honest, I'm not really sure. Hopefully Steve Weiner or "camgrinder" can chime in here. Personally I'm using the WebCam 120/104 cam which is good, but I think is still a little peaky even wtih my custom gearbox. I may try advancing the cams slightly to move the power band down a notch next time I take the motor out. Mine seems to be about 5k on up (the dropoff appears to be out of my rev-range) and I'd like it to be at about 4500).

I would guess the GE60 would be a better choice though, considering the overall rev-range on the 3.0L motors is lower than the early "s" spec
engines.

For a peice of good news, I've got two full seasons on essentially the same spec motor (but with racing valve springs, etc..) translating to over 35 races/100 track sessions and the motor is still going VERY strong with no signs of "tiredness".

[camgrinder]

With only 9.8-1 compression the GE 80 cams will be awful down low. It would come on the cam around 5000 or 5200 with the 46mm Pmo carbs. I would stick with the 40mm Pmo's and a GE60 style grind.
I like cams with wider lobe center when using Pmo carbs. Something like 104 , add some lift and about the same duration as the GE60.
The GE60 has 102 l/c and the GE80 has 100 l/c.

The webcam 120/104 is similar to the GE60 cam.

Also, 78 SC cams can only be made into GE60 or GE80 cams by welding. I prefer to make them on new castings.

[tom1394racing]

Thanks for the replies.

Based on the info from Chris and John, it sounds like I can go with my original Alusil cylinders replated to Nikasil with JE 9.8:1 pistons. They seem to be holding up pretty well for Chris. I would imagine that my Alusil 8.5:1 pistons are of little value to anyone.

To get better low end torque, it sounds like 40 mm PMO's with a GE 60 cam grind will be my best bet. I should plan on trading my CIS cams as cores and get newly ground cams. Any recommeded sources other than Webcam?

How about header size (1 5/8" or 1 3/4") and dual mufflers? Any recommendations?

[cstreit]

Tom,

Actually I went with the Mahle RSR setup, netting me about 10:1 with SC heads, though I haven't heard about issues with the replated cylinders.

Of course new cores (as camgrinder mentioned) are the best, but I had my SC cams hard-welded by WebCam and so far, so good.

Muffler-wise, is this a street car, or race?

[tom1394racing]

Chris

Are you running 10:1 with single plug? No detonation problems? Race gas only?

I am also guessing that the difference in price between trading my Alusil P&C's as cores and buying new Mahles vs replating my Alusil's and using the JE pistons may not be that great and I may just go ahead and get new Mahles P&C's.

[cstreit]

Tom,

I'm running twin plug. As much as I run the car, I realized that converting to twin plug would save me $ in teh long run because I could run street gas. Paid for itself in 2 years. Could also run single plug with race gas. Sure I lost a few ponies with only 10:1 but I was shooting for longevity over HP and took that money I saved on race gas to pay for better gear ratio's that had a much more dramatic impact.

I think my $2650 was a "retail" price sourced through anotehr shop, so your price will most likely be significantly cheaper if you source directly.

[blue72s]

with an SC based motor you'll find that you run out of rev's before you run out of power.

Why?

[cstreit]

Blue,

Well I suppose I should have qualified that... A GE-80 cam and some others will support power well into the 8000+ RPM range. Getting a 3.0L motor to turn those sort of revs reliably for long periods without extensive and expensive modifications is difficult. I think there is plenty of power and cam selection down low to not need to turn these motors to 8000...

I use a WebCam 120/104 which shows continuiing power increase well past my self-imposed 7300 RPM redline... I donn't see any indication of dropoff meaning I run out of reasonable rev's before I start losing power.

[blue72s]

cstreit,

What if one use early S cams?

Incidentaly, do you know if original S cams # 901.105.183.01 (left) and 901.105.168.00 (right) will fit in an SC engine?


Is the SC conrod the same length as the 2.7 rod?

[cstreit]

Blue,

I think the GE-60 and Webcam 120/104 are similar to the "S" cam, but I'm not sure what the differences are physically with the bearings, but I believe that the cam sproket mounts on the earlier cams are the 46mm nut/spring washer style while the SC's use the bolt and chamfered washer.

The conrods are different. (unsure about "length" but not swappable without work.)

[camgrinder]

An original Porsche S cam is milder than the GE60 or GE 80 cam.
The S cams will not fit the SC camshaft carriers, wrong bearing diameter.


Tom, I sent you a PM.

[blue72s]

Thanks.

What does PMO stand for?

With 3.0RSR set-up for mainly street use and occasional track days, is the SC cylinder head (49/41.5, 34/35) OK? or what about '76 Turbo heads 49/41.5, 32/36? Can these be ported out if necessary?
Did Porsche ever supply sodium filled valves for these heads?

Are the heads and cam carriers interchangeable? Sorry I don't know much about later cars.

[Walko]

Tom,

If you are building a 3.0RSR replica motor and you would like to keep it looking vintage I would recommend you don't use PMO but go the MFI route.

It will alleviate the lag that some carburetted cars have and will provide more power.

I built a short stroke 3.2 with MFI and 2.7RS cams and it made just a tad under 300HP Flywheel.

Whilst the 3.0 will make less I believe that you should easily get your 250Hp .


My two cents worth.

Michael

[cstreit]

Michael,

300 HP? TO what to you attribute the extra 50 HP to? (other than displacement I mean)

[Walko]

Well
I can tell you what was in my motor.
JE pistons 98mm 10.5.1 comp
2.7RS cams
bored out MFI manifolds and intakes (Eurometrix)
Ti valves and retainers
Stock rods
bottom end was cleaned up for air flow
heads massaged
3/4" headers
care taken putting it together.

My view when building any porsche motor is to look at what the factory was doing in the period and try and use the bits that they carried over.

If you look from the 906 onwards they used MFI as opposed to carbs.

There is a guy that lives near me who has the same setup as I had except he had 3.4 capacity, RSR cams and a Kuglefischer injection pump. The motor was making in excess of 350hp. It was a pretty peaky motor to drive. I also understand the motor would rev to 8500RPM.

In my opinion the older motors can make a lot more power now than when they were being raced in the period. this comes down to our ability to access the modern technology in components. IE light weight pistons / rods / barrels ///

I am currently building a 2.3 litre ST replica and hope to acheive a power in the range of 230- 250hp flywheel.

We shall see waht eventuates.

Regards


Michael
82 911
71 911
69 911

[Wayne 962]

PMO stands for "Porsche Mail Order" - the name of the company before Porsche forced Richard Parr to change it.

Some answers:

1- I don't think Mahle makes a kit like you've mentioned so I think a replate and/or used cylinders and JE's would be your only choice. JE's are what I have in my 3.0L

2- GE60/80 cams - pretty aggressive, but should work okay. I don't think you can "regrind" the SC cams into these - they will require rewelding of the lobes, which is not really a big deal. Profiles close to the 'S' cams work well in these engines.

3- 46mm = bad decision. Too much carburetor for that engine. Go with 40mm carbs, and 34 venturis for the street or 36 for extended RPM driving on the track.

4- Headers / either one should be fine - smaller for street / low RPM driving, larger for track...

5- Not sure what you mean by "twin-muffler" - I recommend a standard sport muffler, like I have on my RS...

-Wayne

[jluetjen]

Walko, you keep mentioning a 2.7RS cam. If my memory is correct that is just the standard early S camshaft. I don't think that there was a special cam for the RS. The RSR on the other hand...