Late sc heads, porting vs swapping 3.2 carrera heads

[Jhogan0101]

I currently have late sc heads with the small ports.
Im trying to convert to 3.2 cylinders with 98mm pistons on my 3.0 case.
Im not sure if there is any financial/performance benefit with just buying the 3.2 heads or porting my current heads. Or just selling my 3.0 heads.
Any advice?

[Flat6pac]

The Carrera are definitely big port, same size valves. You lol need the intake spacers for the Carrera head intakes
To do the 98s the preference is with Carrera cylinders because the tapered seal surface and no need for a CE ring gasket.
The less expensive KS cylinders will open and nikisil.
Bruce

[mreid]

3.2 cylinders are also 95mm, but unlike the 3.0 95mm cylinders can be bored to 98mm and replated. I would sell the 3.0 heads and pick up a set of 3.2 heads.

[fred cook]

I used a set of race prepped Carrera heads when I built my 3.0 into a 3.3SS. So far, I have been very happy with the performance of the engine. I also used an early SC airbox to take advantage of the larger inside diameter intake runners. Even with the early airbox/intake runners, I still had to open up the intake runners about 3mm to match the heads. Some pics..............

Combustion chamber


Intake port


Exhaust port


Intake runner

[Jhogan0101]

Cool pics. What are the parts for a 3.3? Any necessary mod to the case?

[fred cook]

Originally Posted by Jhogan0101

Cool pics. What are the parts for a 3.3? Any necessary mod to the case?

Yes, these are the heads that I used on my 3.3SS engine. I also used the KN Engineering slip fit cylinders so no mods were needed for the block. The heads mated up perfectly to the LN cylinders. My pistons were rated at 10.1:1 but wound up making 10.5:1 due to some machining work done on the heads. The intake ports on the Carrera heads measured out at 42mm and the exhaust at 41mm.

[Henry Schmidt]

Conventional wisdom tells us that 41mm (stock 3.2) is to big to promote the necessary port velocity for good low end performance.
Given that and the short intake port flange on the 3.2 my preference would be to port the 3.0 heads. Depending on the build and intended use, my thoughts lean toward a 39 mm intake port.

[Jhogan0101]

Henry, i had this post in mind for my build. In hind sight would you have went with the ported sc heads?
Just another 3.2 Short Stroke

[Henry Schmidt]

Originally Posted by Jhogan0101

Henry, i had this post in mind for my build. In hind sight would you have went with the ported sc heads?
Just another 3.2 Short Stroke

First, you posed a question about financial benefit. My response was to that question. If you own 3.0 heads the cheapest way to make high quality heads is with your own heads.
Every project is built as a symbiotic assembly.
My general rule for port sizing is 80-85%. The port should be no larger than 80% of the valve size for street and 85% for race. Of course this is for NA engines and just a general rule but it has served me well.
The engine you pointed to in your link was a very special engine built without regards to cost. (mostly) If you notice it have a huge cam (very little low end potential) and 51 mm valves.
The cost to make these heads was substantial. Would I have been better served with ported 3.0 heads? perhaps but I owned both so cost or logistics in acquiring them was not an issue.

[fred cook]

Originally Posted by Henry Schmidt

Conventional wisdom tells us that 41mm (stock 3.2) is to big to promote the necessary port velocity for good low end performance.
Given that and the short intake port flange on the 3.2 my preference would be to port the 3.0 heads. Depending on the build and intended use, my thoughts lean toward a 39 mm intake port.

Henry,

First of all, let me say that I respect your knowledge and experience in all things pertaining to Porsche engines. And, it is indeed likely that the conventional wisdom would be to use the smaller (39mm) ports. However, I can speak from experience having built an engine using the Carrera heads. Perhaps it is that my engine is a 3.3SS (100mm pistons), that it is using relatively mild cams (964), cam timing or whatever, but my engine using the large port Carrera heads has plenty of low and midrange performance. In addition, it will pull quite well right up to 7000+ rpms. I have the ignition cutout set at 7500 and have gotten into it a couple of times. Perhaps the most interesting thing about this engine is that it is using CIS for the induction. Granted it is the early SC airbox with the large diameter intake pipes which are indeed the 39mm size you referred to in your post. Perhaps the slight restriction of the pipes compared to the head ports is allowing the intake velocity to remain high enough to do the job? At any rate, I am sorry that we are not close enough so that you could drive my SC. I think you might find the performance interesting! As always, thanks for your input/thoughts on this subject!

[BURN-BROS]

Originally Posted by fred cook

Henry,

First of all, let me say that I respect your knowledge and experience in all things pertaining to Porsche engines. And, it is indeed likely that the conventional wisdom would be to use the smaller (39mm) ports. However, I can speak from experience having built an engine using the Carrera heads. Perhaps it is that my engine is a 3.3SS (100mm pistons), that it is using relatively mild cams (964), cam timing or whatever, but my engine using the large port Carrera heads has plenty of low and midrange performance. In addition, it will pull quite well right up to 7000+ rpms. I have the ignition cutout set at 7500 and have gotten into it a couple of times. Perhaps the most interesting thing about this engine is that it is using CIS for the induction. Granted it is the early SC airbox with the large diameter intake pipes which are indeed the 39mm size you referred to in your post. Perhaps the slight restriction of the pipes compared to the head ports is allowing the intake velocity to remain high enough to do the job? At any rate, I am sorry that we are not close enough so that you could drive my SC. I think you might find the performance interesting! As always, thanks for your input/thoughts on this subject!

Hi Fred, It's all about lobe center. The wide lobe center generates good vacuum to help with too large a port. As soon as you put in a cam that would be appropriate for Carburetors your ports would be way too big.

A 3.2SS with a mod S cam will pull all the way to 7500 with a 38mm port.

[Henry Schmidt]

Specs for each engine varies. We were able to produce great dyno readings (independent 3rd party) using very small ports.

Written a few years back.

SUPERTEC VENTI-PORT

--Supertec Venti Port is a new development in Porsche 2 valve porting which allows the customer to change the porting depending on the engine application. The small insert 36mm is great for low end torque (rally and high performance street use) and the larger insert is appropriate for tarmac and road circuits.
Our most resent example of the Venti Port in use in xxxxxx xxxx 3.0 rally car that uses the 36mm insert to produce 310 hp @ 7260 and 242 f/lb of torque. The end result was a flat torque curve from 3500-5800. This was accomplished using a DC 80 cam. This cam is generally considered too aggressive for vintage rally. The Venti-Port made the difference.
xxxxxx just finished the Mallorca Rally in forth place. This was his first rally with a new car.
Many head specialists told me that my idea wouldn't work and yet on the flow bench we could produce flow specs better than an RSR head all the way to 7000rpm. (once again 3rd party testing.)







We even used this system to repair an overly ported set of 3.6 heads for use on our 4.0 engine.

[KTL]

Weber 46 chokes/venturis counterbored into the intake port? Wow. Impressive on several levels!

I think Jeff Spicoli said it best when he said

https://youtu.be/hReFx1kjuIE?t=1m9s

AWESOME! TOTALLY AWESOME!! Pretty creative thinking for an "old dog."

[fred cook]

Originally Posted by BURN-BROS

Hi Fred, It's all about lobe center. The wide lobe center generates good vacuum to help with too large a port. As soon as you put in a cam that would be appropriate for Carburetors your ports would be way too big.

A 3.2SS with a mod S cam will pull all the way to 7500 with a 38mm port.

There are so many variables in engine design/configuration that it would seem to be impossible to say "this is best" or "that is the only way to go", etc. In the case of my 3.3SS engine, the end results were probably due to a mixture of engine savy, good parts, and luck! I won't try to estimate the percentages of each! The good folks at Supertec have done so many interesting things with Porsche engines that it numbs the brain! Other engine builders have also contributed much to this forum for those of us that will only build one or two Porsche engines in a lifetime. Thanks to all!

[mreid]

I'll have a set of 78 3.0 large port heads available soon if you're interested. Just need to remove them from the engine.