Rebuilding 2.4 MFI Engine

[72TE_KIWI]

My thinking to date is that if going to the expense of overhauling throttle bodies, stacks, MFI pump, P&C's .. might as well put an 'S' cam and build a small spigot 2.7RS replica specs, to make a more driveable road car. By all accounts the 2.7 is a great road / track engine. Chatting with Gus at Pacific Fuel Injection, he was quite clear that the cam needed to match the 3D spacecam .. and the costs don't seem to vary depending on choice of space-cam.

By using thin-walll 89mm 9.5:1 Nickies P&C's, the 3R case does not need to be bored to accept 97mm 90mm cylinders and only results in 59cc less volume (2.629 vs 2.688) & this should not be large enough to affect MFI tuning.

So what am I missing? Other than the 2.35 becoming a non-original 2.63, what's the downside?

Interested in your opinions ..

[9er]

My thinking to date is that if going to the expense of overhauling throttle bodies, stacks, MFI pump, P&C's .. might as well put an 'S' cam

So what am I missing? .

One cam for a start.
Sorry couldn't resist.

[9er]

There are only a few expert Porsche engine builders in Australia.
Although many others could build you a good one.
To get the sort of bespoke build that you are thinking of I would suggest you talk to one of the experts.
For me Mark Poole (RSR Sports)and his engine builder Dave.

[e72phil]

Phil Hearn (ex Auto Coupe) and Spencer Harrison have also built many early 911 engines and know what they are doing for sure.

[72TE_KIWI]

Thanks for the comments guys .. I can't be the only one going through the the machinations of design options .. anyone used the the 92mm small spigot thin wall cylinders??

[9er]

I'm not smart enough to have machinations but I did get confused by all the opinions that I read on internet based forums.
So I worked out the characteristics that I wanted from my engine rebuild and went to an engine builder with that.
Between he and I we decided to use a crankshaft with a longer stroke, have some cams ground to a particular profile, and were also able to bore out my old cylinders to suit the new JP pistons.
Along the way they were also able to advise me of weak points in the standard engine such as rod bolts and the factory valve springs and retainers which I chose to upgrade along with oil supply, boat tailing etc.

[Merv]

I did something similar, after deciding to stay with my stock 2.0L capacity. Nickies', JE pistons, rods, crank and cams testing and profiling and several case enhancements with an SC pump and a bearing on the IMS. Phil Summich did the work with Don Munro's guys. I would always seek expert advice as these motors are not simple and one you vary from stock, other things can be affected.

[Cairns888]

What Chris said.

[72TE_KIWI]

With a view to retaining the 3R mag case, and seeing downsides on boring spigots to 97mm, options are limited. As I am intending retaining MFI, cam choices are limited to those with suitable matching space-cam. I think engine cc is less of a concern since the main rack in the MFI pump should be able to be adjusted to scale up or down to suit.

89mm cylinders in 92mm bores will only leave 1.5mm sleeve iwall thickness nserted into the cylinder .. can good longevity be anticipated or would the lower portion of the cylinder go out of round sooner? LN Engineering seem to think it's OK bit anyone have any real world experience?

[reedminor]

I don't think cc's is as important as other things now.

20 years ago you would have found the biggest set of pistons and cylinders and gone with that.

Now there are so many cams available / better ignition etc.

JR

[epilot]

I think engine cc is less of a concern since the main rack in the MFI pump should be able to be adjusted to scale up or down to suit.

the adjustment and thus fueling capability of the MFI pump is not infinite, it is well worth sticking with a known combination of MFI cam, engine cam and cc. if you end up with the MFI pump unable to fuel
your modified set up it is time consuming to get it right ($$$$...) and most of the pump expertise is OS

[reedminor]

or you carefully pack your mfi away .... and put some carbs on the engine.

jr

[72TE_KIWI]

So far nobody mentioned 89mm Nickies as having very thin walls .. 89mm pistons in a 92mm case spigot must leave very little cylinder wall thickness into the spigot. Anyone know of these actually in service?? Also I assume heads would need to be ported to 36mm to provide good top end as per RS2.7.