FLYT993

Ok, so now we KNOW how and what these heads will do...which is extremely impressive...is it just the $$ that is making it prohibitive here in the US?? The upgrade seemed to be around $22-$23K USD, which is what Tony C. quoted for a standard "full rebuild"...or is it that these mods won't pass US emissions (especially CA)? If I ever have to rebuild my engine and I can get THIS type of performance increase for the SAME $$ as a rebuild, what fool would spend that much $$ and still have stock performance????

leosayer

I find the cost prohibitive in the UK and I've got a fairly loose wallet when it comes to my cars. You have to REALLY want a NA power upgrade in a 993 to go and do this as, for me, it would cost around 60% of the purchase price to do and from a practical perspective, that money would enable me to change my car to a GT3 that comes standard with the same power and the other all the nice suspension, brakes, seats etc already fitted.

Much as I respect the work being done and have heard lots of good things about 9m, I don't have bottomless pockets and I do keep half an eye on resale value, such upgrqades make the car a very rare and exciting product but one that may prove hard to shift at much of a premium to a standard car.

Peter R.

In racing, there are different variables that make up the equasion compared to us in the real world. WE can just bolt on a supercharger, buy a turbo, or whatever.

Racing classes often require sticking to NA's, so more drastic measures are required. It's about winning races, and how much you are prepared to pay for the privilege.

If you think the NA upgrade is expensive, wait 'till you start getting the maintenance bills.

It's all a matter of perspective.

Peter R.

Pickled Piper

I totally agree.

I've seen and heard a car in the UK with this conversion (John who posts on this thread) and would dearly love to have the conversion on my own car. However, the cost means I could look at trading my car in for a 993 TT or a GT3 for a similar outlay.

I am an Engineer myself and appreciate the Engineering integrity and quality of the product. I have no qualms about spending money on my car but the financials just don't work for me.

pp

TargaTango

It all comes down to what presses your bottons and what is "value" to you. I cannot argue with any of the posts which say they find other alternatives better value for their money. However, for one thing, the price differential is different in Hong Kong. I cannot get a 993 TT or GT3 for a 993 C2 plus 9m upgrade. Even if this were not so, a sports car to me is one which is small and light and this involves stripping a lot out of modern Porsche and a 993 TT is heavier place to start. I also like the size of the 993 narrow bodies rather than the bigger GT3s. Plus I like the charm of the 993 shape and the air-cooled engine. This preference is not based on price. I also prefer a NA engine. Value for money and making a sensible investment is not driving my car selection. If it was, in Hong Kong I would buy a 1998 Ferrari 355.

abar

Yes, again in the same boat. I guess it would be different if a top end rebuid was needed.

SwayBar

This guy here has been saying the same thing since 1999:

http://mototuneusa.com/think_fast_intake_porting.htm

In a nutshell, a high-flowing ported head on a flow-bench may not make useable power due to low port velocity throughout the RPM range. To combat that, the author Motoman will literally fill in the port to make it smaller so that subsequently, port velocity goes up, and along with it, power across the RPM range, including the top-end. This is the same stuff principle-wise that Colin is speaking about.

There is LOTS of really good engine information on that website if one is patient enough to wade through his somewhat eccentric presentation.

"Think outside the box"!

NineMeister

Can I just point out that in the UK the 9m billet cylinder heads cost less than a new bare 993RS head (with it's lovely big ports....) from Porsche, which I don't think is too bad a deal considering that they cost well over £50k to develop & then set up for manufacture?

C2MED

Colin, just out of interest, why is it that Porsche didn't think of the idea and instead went the opposite way? Was it due to production cost? But you just said the 9m head costs less than the RS head??

So what is the down side of the 9m head compared to say an RS head?

Antonov

just read the article in total 911, very impressive to say the least.

Antonov

what kind of longevity can you expect from that motor?
can you run 91 pump on 12:1 compression?

FLYT993

Indeed. Can't figure out why these heads aren't more popular here in the US? Also, wonder about it's ability to pass CA smog??

NineMeister

You have to think about the year that the original Porsche parts were designed with respect to the availability or lack of computational design techniques, but the only conclusion that I have managed to come to was that Porsche had some kind of design team change between the 964 engine and the 993 engine and the result was simply that the new team got it wrong. The same problem is also clearly seen on the 968 engine where the ports are simply huge, which may be great for turbo applications (for which the engine was originally designed) but useless for sustaining a broad torque curve in a n/a engine. This is not just my opinion either, it is also the concensus from numerous ex-Porsche engineers that I have had the opportunity to talk to after chance meetings at the Autosport shows whilst they were studying the 9m billet heads.

The cost of casting different port profiles is negligible, so there is no valid reason for Porsche casting larger ports into the 993 and 993RS heads other than simply design choice. However I must also point out that the 9m heads have a completely different area schedule (shape) in comparison to a conventional 911 port, so the performance gains we see are not just down to the port area but also the way the port controls the compression and expansion around the valve.

As for cost of the heads, my guess from a knowledge of production processes and manufacturing costs is that the RS head actually costs Porsche around 30% of the retail price (which was £825 the last time I price one up) and the remaining 70% cut is down to distribution and dealer profits.

Provided that you can afford to fit them (!) there is no downside to using 9m billet heads. They are made more accurately (completely CNC profiled including ports) from a better homogenous material and are fitted with sintered steel long life valve guides and seats that outlast the stock bronze guide by more than double. They will run with Porsche valves, springs & retainers and are a direct replacement for all production 964, 993 & 993RS engines, even the SAI port is available as an option to cover the US 993 n/a engines.

The only other design difference is the improvements to the combustion chamber which has better squish design for more efficient combustion and is also 3cc smaller than the stock head (87cc against 90cc). The benefit from this change is that if you fit the head to a stock bottom end the engine will have a slightly higher compression ratio, which is not a problem since ALL production 964/993 engines fail to make their design specification by around 0.4 to 0.5 points (most measure 10.7-10.8:1), so the 3cc reduction of the 9m head takes this up by around 0.3 of a point. What this means is that if the heads are fitted to a stock 993 engine, the compression ratio will increase from approximately 10.8:1 to 11.1:1 which is what Porsche intended it to be in the first instance, so it will be ok to run on most pump fuels (Porsche recommend 98RON in Europe, hence this was used for all our tests).

Red rooster

Colin,
Unfortunately there is no 98RON here ! or in quite a few areas of the USA .
Maybe a North America version with a little less compression ?

Geoff

C2MED

Thanks for the explaination Colin. Do you have different heads for 993 and 993RS?
If I was to just replace the stock head with the (m item, leaving the cam stock, (if that's possible) what sort of figures (cost and output) are we expecting as a rough guess? Whay I'm thinking is that I really like the idea of the 9M head but I don't fancy having the engine changed too much from stock. Not just for the power gain but also for the torque and durability of the head.