Cam recommendation wanted

[JohnJL]

I'm hoping Mr Dougherty chimes in here, I'm a happy, about to be repeat customer...John, the 3.0 track is a handful, thanks!


Engine will be for a lightweight Targa street car built for fun revving in mind...

3.0 SC case and cylinders
10.5:1 JE pistons
34/35 Heads twin-plugged for possible future use but running MSD off the distributor on single plug for now.
SC con rods (unless someone has something lightweight and trick for sale or trade?)
Refurbished SC rockers, crank (by PR Technology in Brookvale)
ARP or Raceware rod bolts
new OEM steel coated head studs
40IDA carbs
SSIs
M&K exhaust is likely

Shooting for 8000+ rpm, just for the fun of it.

So, cam recommendations? ALso assuming I should be installing heavy-duty lightweight valve springs. Who has those?

thanks all

[Henry Schmidt]

Port size, 40 Webers and SSI are going to make 8000 rpm a struggle.

DC 60 will get you to 7000 and will be great for most driving situations.
Slightly wilder RSR sprint cams are fun but won't like the ports , Carbs and exhaust.

DR cams has springs to go with your cam choice.

[shbop]

I'm sure John can handle your spring needs, as well.

[JohnJL]

Thanks Henry. I've got a contact here with a flow bench willing to do some porting work and says he knows his way around a 911, comes with good recommendations maybe I'll try him. Do you know offhand what I need to be flowing/typical I/E ports diameters needed to get to 8000? Can it be achieved with just porting work or do valves need to be increased from 49/41.5mm intake and exhaust, respectively? ALso, I thought you did rod bolts too? Couldnt find them on your site.

Thanks Jon. I also thought John did springs but couldn't find them on his site.

Just to throw some controversy out there, I was looking over a build my shop is doing today on a mag-case 2.7RS. They were using ARP case bolts but were rather irritated to have to grind material off the cylinders in order to get the washers seat properly. Anyone else know of this issue?

thanks all!

[304065]

The factory through-bolt washers come in two versions: flat, for the early engines, and chamfered, which are intended to clear the cylinders. ARP should know this: grinding the cylinders is not the solution.

[jluetjen]

Hi John; could you please confirm your port diameters? I have you in my spreadsheet already as having 39 mm intake ports while you're now listing 34 mm intake ports. Given the amount of air that a 3.0 needs at 7000 RPM plus, you won't get there with 34 mm ports, 39 would work a lot better.

39 mm intake ports should support a DR60's peak torque engine speed of about 5100 RPM, and a peak HP engine speed of something on the order of 6500 RPM -- but if you have any sort of a venturi in the 40 mm carbs (lets say 36 mm venturi), it's going to be the ventury which will be restricting the airflow rather then the ports. With a 36 mm venturi you're going to be losing a few hundred RPM off of both of those numbers due to the air getting choked off at higher RPMs. With venturi that sized, you may also find it hard to get a good idle from the engine. If you were using either MFI or some sort of Individual Throttle Body (ITB) injection system, the 39 mm ports will be fine.

[Henry Schmidt]

DR cams is John and they do have springs.

39+ mm intake ports with 37 mm exhaust will flow enough for 8000 but 1.5 " SSI (headers) will not. We always make the intake port size larger that the manifold.

Still going to struggle with 40 Webers. Remember that Porsche never ran 40 Webers on anything larger that 2.0.

Porsche increased the diameter of case through bolts on the 3.0 case starting in 1976 with the 3.0 Carrera and 3.0 Turbo. I have never seen a need to replace these bolts.

Supertec does not make rod bolts, we use ARP with special nuts.

[tom1394racing]

I don't think the 10.5:1 CR will work with a single plug set-up and street gas.

I've always heard that 9.8:1 is the limit.

[jluetjen]

If you really want to go that route and have the 40 mm webers on-hand, it may be worth while to look at getting your 40 mm webers bored out to 46 mm, I've heard of people here having it done.

[camgrinder]

I agree with the rest. To get to 8000 rpm, you will need 46 mm carbs minimum, DC80's and bigger exhaust.

I believe the pump fuel octane is a little better in Australia than what we have here, so the DC60 cams may work with 10.5-1.

[matty74]

JohnJL,

will the 10.5:1 pistons work ok with 98 octane petrol and a single plug with an MSD? Do you know if you will get any pinging from that set up?