Port sizing - 2.4 + twin plug

cameron.arnott · 12-01-2007, 06:59 PM

Hi guys

I am currently running a 2.4 engine - 70mm crank, 2.2 S pistons, S heads & cams with carbs.

Thinking about going twin plug and using my old 2.2 T heads and wondering if there are any benefits in going any larger than the standard 36/36 for the S porting?

Also is it worth polishing the ports while they are at it or is this only for full race applications?

Lastly any thoughts on facing the heads for a slight compression bump? Or is this likely to cause valve clearance problems?

The car is revved to the 7300 redline only.

Use is a little street, track and tarmac rally.

Thanks for your help

wmunchovie · 12-01-2007, 07:55 PM

I'm currently working a set of 3.3 heads; I'm also obviously polishing them.
Will it make it faster? Mabe just a bit, I think at least the carbon will have a tougher time sticking to a smooth surface.

munchovie.

eapcpa · 12-03-2007, 07:10 AM

It is my understanding that the valve size and cam combination you are running is the limiting factor, not the size of the ports at 36/35. You might consider smoothing the ports especially around the valve guide boss that protrudes into the ports. In addition on the intake ports you should pay careful attention to blend all seams to eliminate any obstructing edges. For example, on my motor there were slight mismatches from the throttle bodies to the head and from the MFI stacks to the throttle bodies. I don't know how much this helps but it can't hurt. Smooth flow through the ports into the engine has to flow better. The question is was it restrictive enough to limit flow. I feel better knowing I spent the time to smooth things up. You need to be careful on the exhaust side as you need to consider the header tubes size. I am running SSI exchangers and the tubes are 35mm inside diameter. I am glad I checked before I opened the heads to 36 because at 35mm I did have to open up the SSI tubes slightly to blend the edge from the port to the header tube.

jluetjen · jluetjen's Garage

The standard 2.2S heads are the same as the 2.7RS used to generate 210 HP. With the smaller cylinder capacity, you could most likely even get the HP a little higher then 210 HP, but the engine would be spinning pretty fast.

As a rule of thumb, if you're not putting out 210 HP yet, you'll most likely be OK with the 36 mm intakes and I wouldn't spend a lot of time thinking about the heads. If you change the cams to something with more lift, then you'll most likely need to ask the same question again with the potential for a different answer.

cameron.arnott · 12-04-2007, 01:06 AM

Thanks Guys

Any thoughts on shaving a whisker off the heads?

Is this a check clearance 1st and shave later situation or is there a safe margin that can always be observed? I.e. as per the Sports Purposes Manual from 1970 that says .5mm

Thanks for your thoughts and assistance

Cam

jluetjen · jluetjen's Garage

You might get the same affect without cutting metal by eliminating the copper washer (or using a thinner washer) under the cylinder when you are building your engine. What you might want to do is check your deck height when you're taking the engine apart, so that you'll know what you have to start with. If you're going to have the case line bored, you're going to lose a little deck height (and gain CR) at the same time.

If it were me, I'd try to save cutting the heads until last, because once you've done that, you can never put the metal back. Changing Cu washers is cheap.

cameron.arnott · 12-04-2007, 10:43 PM

Thanks John