Cam options for a modified 2.4E engine?

[dtw]

Well guys, I guess I won't know for sure until I can lay a ruler on it this Saturday. I don't think it is an ROW engine, I looked the motor up when I bought it. It's also got MFI. Guess if worse comes to worse and the machine shop was wrong, I'll be asking you (Tyson) for more info on opening up the ports! What did you use to grind material?

[Tim Walsh]

I am doing nearly the same thing with my 2.4T. I'm planning on running relived 2.2T pistons with late E cams. The flycut heads should bump the CR up to about 9.5. Is there anything wrong with this setup?

The only difference is that dtw will be running the crane cams while I'll have E cams.

[blau911]

Well Guys,
I have been thinking about it more. The 2.4E engine will need to come out of my 67 911 once I finish rebuilding my 2.0S engine next month. When it does, I plan to replace the engine shroud and fan housing and modify the air deflectors between the inner cylinders. When I do, I will pull apart the top end and deal with the cams and heads. It seems based on comments made here that the best thing to do would be to have the machine shop close my intake ports to either 35mm or 36mm and drop in a set of stock S cams. Since the engine will be out and the shroud will be off, I figure it's an extra day's labor and a few hundred extra $$$ for the machine work. Just a PITA. Live and learn.

As regards the machine work, I am assuming that my machine shop who opened the intakes up to 39mm will be able to close the intake ports up again, right? Worst case, I have an extra set of 2.4 heads that I can use. However, I have alot of money already tied up in the current heads I am using in the form of new valve guides, valves and a flow package. I would like to think that it won't be pissed out the window.

By the DTW, I don't mean to be rude, but you should have started your own message thread. This thread keeps bouncing back and forth between my issues and yours which makes it difficult to follow. Your port issues are certainly as important as mine. They just belong on a separate thread.

[dtw]

Blau
How does a shop close up the ports? Do they sleeve them or something? I think I might have a set of core heads buried in the garage if you need to start from scratch.

I thought the mesh/contrast of our issues was good, which is why I posted here. But yep, I hijacked. Sorry.

[blau911]

DTW,
Not sure if they can, but I am guessing that they could simply refill the holes and then bore them back out. Since the machine shop I used overdid it in the first place, I will challenge them with the problem.

[jluetjen]

The heads that you have should be a nice set of 2.7+/- Race heads and good for at least 270 HP with the proper cams, intakes, CR, capacity, etc. They could be worth quite a bit to the right people. Why not sell them and try to pick up a set of T heads to have bored out to your spec? It would most likely net out to less money then having your existing heads welded to fill them in and then re-ported.

Unfortunately the port shape is not as simple as a straight cylinder with a curved right angle. Actually stock heads open up at a constant rate from the manifold face before they make the turn.

[blau911]

Interesting thought John. As regards the head openings, you state that Porsche head ports open up at a constant rate from the manifold. I recall reading elsewhere that the stock 911 head port sizes all start out at either 30mm or 32mm and larger ports only vary in the first inch of the opening.
As for selling my heads, unless someone is willing to offer me in the neighborhood of 1,300 for my heads and 39mm intake mainifolds (which are practically new), I expect that I will be better off sending my own heads back to the machine shop to re-do.

[Tyson Schmidt]

Originally posted by dtw
Well guys, I guess I won't know for sure until I can lay a ruler on it this Saturday. I don't think it is an ROW engine, I looked the motor up when I bought it. It's also got MFI. Guess if worse comes to worse and the machine shop was wrong, I'll be asking you (Tyson) for more info on opening up the ports! What did you use to grind material?

I used a sandpaper wheel that wraps around a little expanding rubber piece. It chucks into a drill or die-grinder. The sandpaper wraps around the rubber tool like you would wrap something around your finger. Except it is a a seemless piece that slips over the end of the rubber expanding tool, and the tool expands to hold it.

O.K. that actually confused me too. It'll make sense when you see it. I think I bought it at an auto parts store, so it should be easy to find.

[jluetjen]

Blau 911,
I've checked a set of '73.5 2.4TK heads and some 2.2S heads and the ports never share the same dimensions, at least not until the valve pocket directly behind the valve.

I suspect that the heads may share the same external casting, but have been manufactured with different inserts for the ports. From what I've seen it doesn't look like they started with the same measurements.

As far as selling your heads, you might want to consider posting them on Ebay with a $1300 starting price. I suspect that you'd get more then that. Just make sure that all of the BBS's (Pelican, Rennlist, etc) know that a new set of race heads is for sale so that you get the right buyers bidding on them. I honestly don't believe that it will be cheaper to go through the hassle of welding and re-porting the heads and manifolds to match compared to refurbing and porting a set of stock heads and manifolds.

The only people that I've heard about welding ports have been the Super Touring folks who were/are required to start with stock heads. They basically filled all the ports (and more) on the stock heads and then CNC'd them to be perfect heads for racing. This was one of their tricks for getting 300 HP at 8000 RPM out of a 2.0 liter engine.

[Mr Beau]

Blau,

Any idea on your compression ratio? If the only change is the flycut heads, maybe you're at 8.5:1 vs the stock 8.0:1. This isn't helping your low speed situation.

With that said, even with the big cams, you should be able to do the following at little cost:
1) Recurve the distributor so that you run more initial advance with the same total. With the wild cams and low CR, I'd say 15 or even 20 degrees initial would be tolerable on premium. Throttle response will be noticable improved. Cheap and something you could probably do yourself.
2) Use smaller chokes. The choke sizes in a Weber greatly affect low-speed torque. By going smaller, you'll increase the signal strength which means you'll need smaller mains to compensate. Relatively easy if you have a buddy with spare jets etc and know your way around the carbs.
3) Adjust cam timing. You can advance the intake cam and reduce the amount of overlap by moving the exhaust cam, but you're probably pretty limited in how much this will help, and if you go far enough, you could even run into clearance issues.

I'd try #1 first, and you may be pleasantly surprised.

[jluetjen]

Hi Matt;
I agree that your first 2 points are good suggestions to prop up the performance at lower revs. As far as your third idea though...

3) Adjust cam timing. You can advance the intake cam and reduce the amount of overlap by moving the exhaust cam, but you're probably pretty limited in how much this will help, and if you go far enough, you could even run into clearance issues.

This might be hard to do without getting new cams ground since a 911 is a SOHC design with both the intake and exhaust lobes on the same shaft. I assume that you mean getting new camshafts made up which may not be a bad idea considering the costs of a new set of heads.

[Mr Beau]

Uh, yeah you're right about that one... I was going through my magazine "collection" in anticipation of moving, and with all the modern vehicles out there, I had twin-cams on the brain.

I'd be really interested in how more timing helps matters with how little work it would be. On other vehicles I've worked on, it's made a huge difference, especially after going from a mild cam and carb to wilder cam with individual runner carbs.

Witness the 5 deg ATDC specified on the early cars (with vacumm retard). No reason for this other than emissions.