Which heads (port sizes) are appropriate in a 2.4E with 2.2S p/c's and 40mm Webers?
 

Hi guys

The title says it all.....I am about to start my build, but which heads are most appropriate for the application:
- 2.4E heads with 32 mm intake and exhaust ports or
- 2.7S heads with 35 mm intake and exhaust ports
I have both types of heads available, so please help me choose.

Thanks....and greetings from Denmark SmileWavy

Mikael

Hi,

What cams will you be using?

And what is your RPM budget? That is how high can you afford to rev it?

I will use E-cams.

Too much compression to worry much about port size.
Fuel quality and twin plugging are the first questions.
Why so much compression with such a lame cam?

I'd be using the E heads to maintain good port velocity & torque.

Remember, you will have a lot of compression using your 2.2S pistons so 98 RON fuel is mandatory with single ignition.

I am actually doing something very similar. 2.2E pistons and cams into a 2.7R 2.4 case with 2.7 crankshaft and rods. Only issue seems to be the wrist pin size from the 2.7 is different size than the 2.2E piston. I was also very concerned about the S pistons driving tooo high compression. I think the 2.2E iin a 2.4 is supposed to give 9.5-9.6 compression ratio. I will be watching.
thanks
Marlin

All the wrist pins from 2.0 to 3.0 are 22mm. If you have an issue it should only be a few thousandths.

I am not sure I understand the question :confused:
The engine will be a 2.4E (but with a little more compression), so I guess it will rev like a normal 2.4E.

98 and 99 Octane fuel is no problem here in Scandinavia.

I just want to build a strong 2.4E engine and higher compression seems to be a way forward. I have read lots of threads here on pelican and it seems to be a common mod to use 2.2S or 2.2E pistons in an 2.4E.

However the questions about port sizes haven't been debated enough for me to be able to conclude 100% on which heads to use. So tips and recommendations are highly appreciated :)

It's a streetcar, so the E cam should be appropriate for my type of driving ;)

Which type of heads will You be using?
Will You run Webers too? :)

Compression ratios have been debated a lot here on pelican and You are probably right about the 9.5.

Piston-to-head clearance has also been debated, but neither your (E-pistons) or my (S-pistons) with E-cams should not be a problem.

I can't speak intelligently about "what you've read" but I can tell you that 2.2 "S" pistons on a 2.4/2.7 (70.4mm ) crank will create a calculated compression of 10.4:1. Even with 98 octane fuel you are gambling (almost guaranteed) with detonation. Add to that a dynamic compression .5 :1 higher than the "S" cam using the "E" cam and you have little chance of success.

There were people back in the day building high performance "S" style engines by putting 2.2 "E" pistons on a 2.4 crank. That was a compromise for people who wouldn't/couldn't budget a proper engine configuration. The "E" pistons were available and the higher compression 2.4 racing pistons were expensive. The "E" piston produced a calculated 9.6:1 compression (seemingly desirable) but using the cast "E" piston in an "S" engine (high performance) was not optimum.

Using the E-heads (with 32/32 mm ports) were my first instinct, but there are many different opinions on this subject....I guess it will be a compromise between low end torque and high RPM power.

Thanks for the advice. I really appreciate all the help I can get....especially since I haven't begun the build yet (no time has been wasted yet).

10.4 compression + the add on due to dynamic compression does sound scary. Other people have however succeeded in using 2.2S p/c's with E-cams (and 2.2/2.4 heads with 32/32 ports). Please see the links below.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/219558-911-2-2-2-4-e-s-pistons.html

http://forums.pelicanparts.com/porsche-911-technical-forum/326214-2-2-s-pistons-e-cams.html

I have also read somewhere (can't find the thread though) that the combustion chamber on 2.2-2.7 heads are in the range of 68cc, but that the 2.7 heads are a little bit larger. I guess that speaks for using the 2.7S heads in order to reduce compression - or is the difference insignificant?

How about using a thicker cylinder head gasket? That should decrease compression a bit...or am I wrong?

I am looking forward to hearing from You all......this is really interesting, inspiring and instructive :)

I believe Henry was stating that dynamic CR is 0.5 points higher with low overlap E cams than with S cams and that don't mean that it adds to static CR. Dynamic CR is lower than static.

I would try this combination and if there is detonation in spite of quite good quality 98 octane gas that is readily available in Scandinavia, you can always swap S cams in. On high CR 2.4, S cams are not as wild as on 2.0/2.2 engines.

Or, you can always twin-plug the heads just in case and go twin-plug anytime later without takingapart the engine.

906 cam on 2.7 with JE 9,5 cr pistons single plug
 

is the 906 cam on a 2,7 with JE 9.5 cr pistons a good combination vs an S cam

The Cylinder Base Gasket is primarily used for setting the deck height but can be used to adjust CR. Our host sells them in two sizes, .25mm and .5mm but thicker ones can be found...or made.

JMHO, but that's a poor choice (even for a race engine). There are far better options now for good performance.

At 9.5:1, you really don't want to give up any low & mid-range torque so I would use a Mod-S or Solex cam for street use & stock gearing. Makes a fun ride. :) :)

Would you still use the stock ports with the Solex cam and 9.5:1 CR on a street motor?

Steve is absolutely correct about the 906 cam. I would go so far as to say that the 906 is a poor choice for any modern build.

One of the best motors I ever built for my 914-6 was a Solex cam 2.7 RS spec engine.
9.5:1 will only make it better.