to twin plug or not, a 3.2
 

help, I'm trying to decide if I buy a set of redone heads that have been ported, new valve guides, seals, with stock Porsche valve and springs, that have also been modified for 12mm twin plugs
would they be a suitable replacement for the stock 3.2 heads that need valve guides and have started to allow the motor to consumme a bit too much mobil-1. The owner states they really flow well up high. would this mean all my beloved 3.2 torque
would be lost. the price is cheaper than waht i could send mine off and have redone, so you can see my paradox.I wouldn,t be useing the second plug hole just putting a 12mm plug in it to seal it and running the rest of the stock configuration.

thanlks

Someone just emailed this week about this. This is my opinion and not a very educated one but this is what I told him:

"I would be very cautious about any porting work on a 3.2. Was
it done by someone who really knew what they were doing?
How many of their 911 heads have raced Daytona? The 3.2 head
is a really great head right out of the box. More flow does not equal more horsepower (but it sells to people who don't know any better). The gains available to a 3.2 head are much smaller than previous 911 heads. Conversely, it is easy to make LESS horsepower by "porting a polishing" if you don't know what you are doing. I have links to more info on heads if you are a geek/motorhead like me."

-Chris

Chris,
Thanks for your reply, thats what I tought too, its just that for the
price I don,t think I could get my head done to stock configuration.
The seller SAYS he ports heads for a living and did these on a
Super flow 600 flow bench, also he notes that he exceeded the flow caracteristics of a set of 930 heads done by "DAVE JARVIS"
who ever he is. Anyone know who "DAVE JARVIS" is? Thanks
for your reply and Merry Christmas.

Keith Epperly

Heads cost about $400 to have done by Anchor Atlantic or EBS if you reuse your valves.
Dave Jarvis is a very respected engine tuner in the Porsche world. Lots of people can probably make a port that flows more on the flow bench especially up high. More flow does not translate into more usable horsepower. If you enlarge the port and get 20 more horsepower at 7000rpm (past redline) and loose 20hp at 3-5000rpm are you ahead? If this stuff interests you check out this PowerNews article
-Chris

I would suggest that because the heads were machined for dual plugs - the porting would be more aggressive than one would want in an otherwise stock 3.2 no matter who did the work. Had they just been smoothed/cleaned up - like for a "stock" class, they might be interesting, although the "stock" heads that I have seen look mighty good already. I have also heard that the intake manifold is the weakest link in the Carrera intake system.

Perhaps one way to tell if the ports were attacked too aggressively is to look at the valve guides in the ports. In the interests of better high rpm "flow", the valve guide is often abbreviated (cut off or reduced in height) as it intrudes into the port. This increases airflow, but as there is less valve stem support, so there is increased valve guide wear - all and well for track engines that favor more power over 100,000 mile longevity.

How about measuring the current port dimensions and comparing with your stock heads? However, porting isn't necessarily all about enlarging the I.D.

If the rest of your engine is stock, increased power potential beyond 7000 rpm (at the expense of useable low-speed torque) is of no consequence since the factory bottom end rev limit safely ends at 7000. If you were to upgrade the con rod fasteners, cams and pistons, then you could take advantage of the increased airflow.

Sherwood Lee
http://members.rennlist.org/911pcars

What is the price that he is charging? Might be a good deal to snatch up and dump on eBay...

-Wayne

Wayne,
they are currently asking $1350.00 and the add is posted
in the pelican classified.

Keith

Chris, according to the article, with the 34 mm intake ports on my '82 SC ('78 thru 80 had 39 mm) I have the best heads!
It's true that smaller intake ports keep intake velocity higher than large ports. High velocity is better at low RPM and yields better low-end torque. It's not that simple, though. There's the interaction of compression ratio and cam overlap to consider and that article doesn't address that. It made for interesting reading, however.

Paul,
I wouldn't necessarily draw the conclusion that the "small" port SC heads are better. They might very well be better but from what little I know it seems that there are no simple answers when it comes to heads. I think we agree on that.
I find this stuff pretty interesting so indulge me if I ramble a bit.
Here is the article that got me thinking about this stuff originally:Motorcyclist June 1996: Cylinder Head Tech
If you read the PowerNews DIY intake porting (The 2007 Superbike ! (Porting Part 3 )) article he explains how find the "dead" area of the intake port using modeling clay and a flowbench. To get to all the PowerNews articles I recommend that you sign up but here is a direct link to the index: PowerNew index
To sign up for PowerNews, got to Mototune's website.
-Chris

Chris, was that $400.00 each or $400.00 for six ?

keith

$400 for all six. The last set I had done was $722 including new valves and shipping.
-Chris

Well, I was making a little joke there.
What's interesting is, in looking at the latest edition of "Porsche 911 Story", the cutaway drawing of the dreaded water pumper 996 engine had an intake post of the same configuration as the ideal one described in "Power News".
Interesting indeed!