Caveman

It's probably 96 or 97 RON. I think that's what our premium fuel is rated at. Pretty impressive numbers!

Cheers,

David

sidned

I always use Shell Optimax which i think is rated at 98 octane. You can even get 99 octane at Tesco, but I'm not sure of the quality of their fuel.

Caveman

My mistake; it's 97 or 98 RON. I know Shell Optimax is the higher one. The Tesco 99 RON fuel is rare! I'm always a bit sceptical of supermarket fuel but it probably all comes out of the same tanker anyway...

Cheers,

David

GrantG

Is the compression increased with the new heads? Otherwise, octane requirements should be same as stock, no?

'95 993

Shell optimax - 98 RON, afaik the compression is pretty much as standard?

Maybe colin or robin can chip in on the CR?

John

Red rooster

John,

Thanks for that. I guessed it must be more than just heads .
How lumpy is the idle with these cams ?
You mention 100 cell cats. Does this mean a "crossover " exhaust system with seperate cats ?
Just trying to get a view of the conversion !
Sounds like you are having fun !!

All the best

Geoff

graham_mitchell

For those who aren't aware, UK petrol is given a RON rating whereas the US figures are not RON but (RON+MON/2), even though the figures are mistakenly represented as 'RON', so the same petrol will have a higher rating in the UK than the US.

Geoffrey

The 9M heads have a slightly smaller combustion chamber compared to the 993 head. I have a set here in the US (see my flow testing thread on the 964 board). I'll be up and running shortly, also on 93 octane US fuel.

There are many factors that go into fuel requirements including camshaft profile, VE%, dynamic compression ratio, and ignition timing to name a few.

'95 993

Red rooster,

yes seperate cats, with a 100 cell cat from each header to its own exhaust can, no cross over between the exhaust cans.

Idle is not lumpy at all, I have the LWF stalling issue but will do the ISV mod to fix this after the final remap.

Interestingy on the Dyno right before me was a GT3 Mk1 my BHP and torque matched his up to my red line, he went on from my 6800 rpm red line which was how he made extra power and torque but this would explain why I suprised a few GT3's at the track day :-)

Fun - its fantastic, interestingly before there was a real kick mid range when it came on cam / hit the resonnance frequnecy of the inlet manifold, now it is just seemless wave of power and torque right up to the red line which just gets stronger and stronger the higher you rev it, wish I had a 8,000 + red line!

John

viperbob

Very nice. Most folks don't know what these do. To folks that do not, they actually give the body a slight nose down attitiude in relation to the rear suspension cage.

GrantG

What would it take to nudge the redline higher without compromising reliability? Solid lifters, Ti Conrods?

NineMeister

OK, here's the full spec of John's engine:

1. 9m/4T billet cylinder heads
* high velocity intake port
* optimised combustion chamber for stock piston, reduced volume by 3cc, closer squish clearance to sides of piston
* 9m race valve spring/ti retainer set
2. 9m sport (hydraulic) cams
* similar cam to our 964 Motec +1 cam
3. Split flow 100 cell cats
* any silencer will work with these cats. In development on Robin's 993VR conversion we tried stock, Techart and Cargraphic silencers and they all made the same power on the day.
4. Live remap.
John's car had a live remap in its previous guise with the sport cams and standard heads, but we ran out of time to do this before the track day. However we did manage to get the car on the rollers for a power test and to check the mixture throughout the rev range, where we found that it was running towards lean 3-5000rpm, ok 5-6000 and rich 6-7000. We definiitely expect to see more power from it after more tinkering.

The build was actually finished earlier in the week, but on testing the power was found to be down from expected. This was eventually traced to the 88,000 mile hydraulic followers, so rather than risk future problems we replaced the lot, hence why the car was only completed the day before the event.

As John mentioned, a selection of cars tested on the day were:

3.2 Carrera remapped = 242bhp
stock 993NVR engine in early race car on headers, 9m remap = 312bhp
stock 964RS = 275bhp
2 x 964RS with cat bypass & full remap = 305/309bhp
3 x 996GT3 mk1 = 364/375/390bhp (last one had exhaust mods)

Johns 993NVR (Non Vario Ram) = 352bhp with 317bhp at the tyre
I'll post a copy of the dyno curves as soon as we have finished the fine tuning.

Earlier in the day I also ran up my 993RS with 9m 3.82 engine where it made over 415bhp (there is a large post on this engine elsewhere on the 993 forum)

You can also see more information on the heads on the new joint 9m/4Tech website:
http://www.4tech-9m.com/

NineMeister

This is an interesting question, and one which we will be able to fully address fairly soon.

The limiting factors are the stock pistons and rods, the pistons are relatively heavy and the rod bolts/rods are weak, the rods flexing above 7000rpm.

A secondary factor is that to benefit fully from high rpm you need to use camshafts with slightly more duration & overlap, but this is not possible with the stock piston because it has insufficient valve clearance. Suffice to say that there will be new 9m/4T sport pistons and connecting rods available by mid 2006.
The rods will be available in a range of lenghts and pin diameters to suit the stock 964 & 993 cranks, our new 80mm "4 litre" stroker crank, all 23mm standard pistons up to the super chort 9m 103 race piston that uses a 22mm pin.
The sport pistons will be made as a direct replacement for the factory 100 & 102 pistons to use standard rings, the features including CNC machined intruder (crown) optimised to the cylinder head, increased pin boss bracing and of course will be a lot lighter than standard.
With the sport pistons & rods we will be looking to run the bottom end safe to beyond 7500rpm, whereas with the stroker crank, race pistons & rods we are aiming for at least 8500rpm.

Robin 993 c2

John
Good thread. here is a photo of you and I at the track just about to worry some GT3s. no doubt.
It was good fun, the performance of the cars was great. It was my first track day, don't think it will be my last.
I now have 4,800 miles on my conversion and it is looking good. The car is with Colin now having the tappets replaced as a precaution (104,000 miles). I plan to rack up miles on my car, so i should find any problems quickly.
It was great to meet you at Oulton, and I am pleased to say that all of the people at the track were very friendly and helpful, giving me good advice that allowed me to bring the car back in one piece.
350 HP NA 993 is the way to go.

Robin

wayne325

Is there anyone in the US doing mods such as this ?
That's pretty impressive - just shy of 100 bhp/litre out of an air-cooled engine.

Are you guys worried about heat ? I guess it's OK as long as ambient is low such as it is
(compared to a Texas summer) in the UK and there is an oil cooler rejecting heat like
crazy up front ???

Going to the UK next week for the first time since I was a wee lad... ;-)

W.