Rebuild 2.4...Questions/confirmation

[Mike R]

I have purchased a 73 T 2.4 7r with Carbs. Will be primarily street driven. Pulled engine because it was leaking oil. Pulled the engine brought all parts to machine shop. Here is the story...Crank good, Heads need new intake and exhaust valves, Cams good, Pistons shot, Cylinders will need to be bored, Oil pump marginal, rods good. Case good. I would like to go forward and rebuild this and kick it up a bit but have some questions. I was thinking new pistons 85mm with a CR of high 8, bore the Cast iron cylinders to match, and an early cam (solex, early E?).
Questions are:
1. Solex or early E cams. What years would I look for.
2. While the heads are being redone, I did not intend on increasing the size of the ports. Will this be a problem with what I have outlined above.
3. Is there anything else I need to be aware of (specific to this setup).
This is my first rebuild of a Porsche engine and know much of this is covered on various posts but just want to make sure.
Thanks,

[Tim Walsh]

hmm.. sounds very similar to my project. i started with a 2.4t ended up with a hot rod 2.4e+. I went with mfi but webers will make things easier.

pistons: a set of je's will cost about $900 and wil acomadate any cam profile you want, come in 85mm and can have the compression tailored exactly. I'm running @10:1 even if my race shop swears 10.2 is just fine.

cams: early E or solex will be great but don't discount aftermarket cams. I have a friend running crane 288 grind which is something like a solex with more lift. Mod-S might be interesting as well.

Ports: if you go any hotter you'll probably need larger ports if you have the 29mm ones like I had. I found a set of heads with 32mm ports and i'm running early e cams which are borderline. if i had more $$ to play with I would have them taken out to 34 (or 36 for s cams)

[dtw]

1. Early E = Solex. You probably won't find old Solex cams anywhere but early E I believe is '67-'69.
2. You likely have 29mm intake ports; many (including myself) will argue these ports are too restrictive for hot cams. Consider 32-34 mm depending cam selection. John Luetjen prepared a great Excel worksheet for determining ideal port sizes and gas speeds, email me if you'd like a copy.
3. Yes. Oiling system upgrades, induction and exhaust tweaking, more. Get the Anderson and Dempsey books and read 'em, also hunt around in the archives of this forum for tons of good info.

-Why high 8? No reason not to go high 9 on your compression while retaining single plugs. The race/machine shop I use actually swears by 10.5:1 in 84-85mm street engines with single plugs, in fact. I'm at 9.8:1 myself on my hotrod 2.4, it is a sweet motor.

[jluetjen]

BTW, Given my engine's 9.9:1 performance on 93 octane (since 94 just went away this year), I'd hesitate suggesting that people go that high without twin plugging. My car starting pinging pretty bad with Sunoco 93, worse in fact then it has in the past on Texico 93. Right now I'm running a tank of Texico 93 with 1 gallon of Toluene which seems to work. I'm planning on doing the following as a result to try to clarify the choices.

1) Confirm the performance of 1 gal of Tuloene for a tank of gas. Intial results are that it seems to work.

2) Confirm the ignition timing that I have on the car.

3) Fill up the next tank full with straight 93 octane. Retard the ignition timing until it doesn't ping. Make note of any changes to the tuning (for example the idle speed).

4) Put the car on a dyno (hopefully as part of a Boston Area Dyno day) and try running both configurations. First half a tank 93 octane and retarded ignition timing. Then top off the tank with a mixture of 4 gallons of gas and 1 of Toluene and reset the ignition timing to what I have now and re-run it on the dyno.

[Mike R]

Thanks for the great posts. Quick question - How high a CR can you go on 93 octane with single plugging without problems? 9.0, 9.5?

[Tim Walsh]

John,
I'm not sure if your car is representative of what kind of compression a 2.2 or higher engine can run. The combustion chamber was redesigned in 1970 because of pinging problems on the 2.0's. I'd still say if you're running more than 9.5 or so you're running the risk of pinging (I'll give an update later on mine when it's all sorted out)

This is all explained in wayne's book BTW

[jluetjen]

Good point Tim -- my S-pistoned 2.0 has about the least optimal combustion chamber shape of the 911 family. Although if I can get my '69 to run at 9.9:1 without pinging, you should be able to do it on a 2.2 or later with some margin.

[Wayne 962]

Yes, good point Tim. General consensus is that anything less than 10:1 can be made to run on the crappy 91 octane fuel we have here in CA by simply playing with the timing...

-Wayne

[camgrinder]

The compression ratio should be matched to the camshaft duration. The later you close the intake valve the greater the compression ratio can be. With an E cam 9-1 is ok.
I have been grinding a "mod-solex" grind using the solex cam profile on 102 lobe centers. Its a right in between a solex and our "mod-S" grind.
9.5-1 would be fine with the Mod-Solex grind.