Porsche Enthusiasts Club Forum

Mittelmotor sent me this curve this afternoon. The stock dizzy only runs to 1.0bar boost. My dizzy is their 'race' dizzy with new boost sensor up to 2.0bar. This map should be the one and used tonight



and this is the dashboard before I shut it down after the hoon. The vacuum/boost gauge only shows half of the true boost as it max's out at 1.0 bar rather than actual 2.0 bar

looks like a nice bit of kit!!

be good to see results once you have this setup properly and running higher boost

I'd love to know what power your engine is making at 1bar with optimised timing and fuel.
What does it feel like now at 1bar Steve? Any better on pick-up off-boost?

There is a marked difference between 0.7 bar which we know was 210bhp at 4900rpm on a tight 1200mile engine and now 0.9-1.0 bar and revving up to 5500rpm. Because I drive a diesel on a daily basis I can't always bring myself to rev to 6000rpm, it feels so cruel. The rev limit on the dizzy has been programmed to 7200rpm by Mittelmotor!!

I will try and get it on the rollers pre Christmas and do a few power runs. Mittelmotor suggested I would be bumping into fuelling issues from 1.0 to 1.2 bar at the 250bhp threshold. The butt dyno suggests I may be in the 230-240bhp area already.

Tonight I am debating whether to drive it to Kings Lynn tomorrow without cabin heater and on lightly gritted roads. I did say I wouldn't drive it on salt! But I just want to drive it lots at the minute.

can you explain the purpose this distributor and how It works without going into mega detail. I am not familiar with tuning cars still running distributors, especially when coupled with boost.

whats the next stage once you run into fuelling issues?

and do you still need to tune the engine using the adjustable WUR?

im sure I saw some pics of you modifying your inlet manifold for front face tb, where can I find them, just out of interest!

cheers
nick

This dizzy allows you to reprogramme the advance/retard curve relative to vacuum/boost. A slightly more elaborate recurve of a pendulum weighted dizzy, but with electronic accuracy. Only thing it doesn't do is retard to inlet temps or knock as per standalone ecu.


USB access


Inside


Next stage of fuelling is a visit to Jon Mitchells where he claims a box of tricks? an adjustable WUR and possibly firing a 5th injector at key times may help. I need to re read this thread again as he did mention this a few times. Beyond this then there's the GTS upgrade of a 928 fuel distributor. 8 feeds into 4 injectors. This is Mittelmotors GTS spec car. I could use the fuel system as per below. Note the same dizzy. This car runs 340bhp


The modified intake system is all my fabricators work with my lead of photos of other cars and GTS'. He did a really good job. Plenum is tapered. All is smoothed and flowed inside


I need to tidy up the swirl pot and coolant pipework now it all works!! Plus that ugly elbow on the wastegate control line

An email from Mittelmotor this morning responding to my observations in driving last night gives them the concern I am running out of fuel at 1.0bar.

Despite turning up the boost controller I didn't get far beyond 1.0bar
The car ran well, AFR on boost/WOT was 10.5-11.0 so didn't appear to be leaning off at the top end
I did suffer one large misfire on 1.0+bar boost/WOT at circa 4500rpm which they believe is fuel related due to reaching my cars limits
The curve loaded on the dizzy should be good for more fuel and boost if I modify further
I also guess the current CGT spec turbo could be reaching its limits as well.

Time to hold back on pushing it further until more analysis is done. It is currently 'quick enough' under 1.0 bar.

Hmmm this doesn't ring true with me. I don't think you've reached the fuel distributors limits. I worry about the stock WUR above 0.8bar. Maybe Jon has ideas about this and maybe all the fuelling needs is fine tuning.
The Carrera GT turbo compressor will definitely be flat out at 1bar+. This is probably pushing inlet air temps up a bit, even with the intercooler. If that is the case then a turbo change is the only answer to get more boost efficiently.

I agree not to push further. It's just not worth destroying all your excellent hard work, especially as it feels quick as it is

I see a Jon Mitchell electronic control pressure regulator box of tricks on your horizon.

It would be nice to be able to see what the pressure is inside the car as you drive on boost.

I could be entirely wrong about all this. CIS ain't my strong point!

Mittelmotor uses a Mercedes fuel metering head/ mass air flow meter. I don't know from what type. Maybe you can ask them ?

This is also an interesting fuel distributor set-up:

So been on the rollers this morning and the scores are

224 bhp at the wheels / 256 bhp est. flywheel @ 5000rpm
256 ft lbs at the wheels / 284 ft lbs est flywheel @ 4000rpm

This!

Correct

Jon, we need to discuss booking it in for some fuelling upgrades in the New Year, please.

I'm going to try a new exhaust system in the New Year with an open wastegate. May not like the noise, but its worth a try.

924turbo2... That's an interesting "intake-a-cooler" too!

Where did that picture come from?

Steve, good dyno results, did you get a chart with an AFR plot on it? I would be interested in seeing what that is doing.

I believe that the '928' fuel metering head was also used, and probably used a great deal more, on Mercedes V8 engines.