2.4 engine rebuild w/modifications

[QROtarga]

Hi all, hope you are doing well these ever complicating days!

About 15 years ago I purchased a 1972 911T Targa, in good running condition. The engine had clearly been opened before and was not assembled too cleanly, with a lot of silicon pouring out everywhere. As I had a good 1970 E-type engine, I installed that and put away the original engine, to open it sometimes and see what should be done to it, and in the mean time I collected parts to do some mild performance increase (2.2 pistons to increase the compression ratio and a corresponding camshaft). This happened this year and when we revised the different parts we were surprised that some previous owner already modified the engine, by installing RS pistons and cylinders, and machining the block accordingly. Which made my collection pretty useless, I guess.

So my questions to the experts (as such a combination is not even mentioned in the engine bible) are: after machining the block to the 2.7l diameter, is there any simple way back to use 2.4l components? Would it make sense to use the E-type cam for the RS setup (as it was, the engine used the T-cams)? Do we need to install a RS type distributor (or 1-2-3-ignition programmable one)? The last would be a simple thing to do after installing the engine and testing it. To get the best out of the RS components, what should be done to the heads?

What I´m looking for is not the ultimate power increase, but some nice power increase combined with driveability (I do not participate in racing more that old-timer rallies), combined with avoiding throwing a lot of money out of the window. If using the 2.4l option, I will have to purchase 2.4l cylinders, if using the 2.7l option I will have to purchase piston rings and the other parts you may recommend.

Thanks and be well!

[OCG911T]

Hello,

There are a lot of options, but to simplify matters you essentially have a 2.7RS short block and currently the T camshaft and presumably 2.4 liter 32/32 heads. If it were me, and your piston and cylinders are still in spec, I would install ARP rod bolts, get some S cams and open your cylinder head ports to 36/36 and essentially have a 2.7RS engine. If you want higher compression you can order custom pistons in any compression ratio, but keep it below the 10.0:1 CR unless you want to twin plug. Like you mentioned before, you can either have your current distributor recurved or go with an electronic 123Distributor and have full control when tuning. What are you using for fuel delivery? If you have the MFI system it will need to be setup for the new cam. If you have carbs they will need to be adjusted too. You mentioned you like the E cam, which I would imagine could also be used and just keep your ports at their stock 32/32. I would say it really comes down to choosing your camshaft!

Whatever you decide I would suggest you use ARP rod bolts and make sure you have the oil bypass modification and case savers done so you don’t pull any head studs from that magnesium case.

Good luck and Happy Holidays!

[OCG911T]

Forgot to mention the hydraulic chain tensioner update.

[CASair]

I have a new in the box set of Mahle 2.4 Pistons and Cylinders if you decide to go that route.

[targa72e]

Keep it a 2.7 if the P&C in in spec. No replacement for displacement. As mentioned above if not already done open up the ports and then its all ablout the Cams you pick. You can use E, S mod solex (DC30) or Mod S (DC40) cams. A friend of mine built a 2.7 with RS pistons and Mod S cams. I had this installed in my 914-6 for a while as I rebuilt my motor. This was a great combination. He has since sold the engine, specs and dyno in link below.

911 Engine for sale

Previously this engine had E cams and while fun it was not as fun as with the Mod S cams. FYI the curve for distributor in most of the 2.4 and 2.7 are the same.

john

[QROtarga]

Thanks for the suggestions! To update, the cams are indeed DC30, and yes, up to the moment I have Weber carburettors. The pistons and cylinders are in good shape. As the block has been machined by previous owner to 90 mm, I guess it makes not much sense to install the smaller cylinders, or does this not matter at all? Saludos from Mexico!

[OCG911T]

If that is the case I wouldn’t do anything to it other than rebuild and use what you have and can! The DC30 is the Mod Solex cam, basically somewhere between an E and an S, which for what you seem to be looking for in your engine is probably the best you will find!

[Henry Schmidt]

Although the RS pistons advertise 8.5:1 they are really closer to 8:1.
Crazy low. My suggestion would be to reuse the cylinders (if in spec), order a set of new 9.5:1 pistons (using stock Goetze ring pack), port the heads to 36 if they are stock "T"and run the Mod Solex or Mod "S"
Your engine would also benefit from larger throttle bodies. If the throttle shaft bushings are still tight, you can enlarge the port size with even taking them apart.
This is something you can do later so put that on the "maņana" list.

[Richey]

Follow Henry's suggestion , you will not be disappointed , and you won't be spending a lot of money . I built a similar engine , nice !

[911pcars]

Twin plugs usually not necessary unless compression ratios are not greater than 9.5:1, especially with higher lift/duration cams that lower the effective compression pressure.

Sherwood

[Walt Fricke]

Henry - my race 2.7 has Mahle nominal 10.3 CR pistons I bought from Andial many moons ago for my twin plugged motor. When I Whistled the motor the actual CR was only in the high 9s, probably because I didn't measure things and adjust when I assembled the motor. I thought they were RS pistons, but maybe they were RSR?

Elgin 315s and 46s gave 220 RWHP. Very tractable motor.

[gled49]

Mahle made a 90mm RS high compression piston @ about 9.5, for a while, I’m using a set in a RS spec engine, mine was at 9.3.