Performance/drivability of MFI vs. Carbs for 2.0 race engine

[Henry Schmidt]

Originally posted by Plavan
Henry,
How many of your motors are running in VARA with MFI? How many of your motors are running with HSR West with MFI?

I only know of one Supertech motor that runs with VARA, and it has carbs..... Why? "Tunnel Vision" ????

We are considering an MFI engine for CP3 but that really isn't the point.
VARA and HSR won't allow them in 2.0 production class.

I walked you through the logic behind carbs VS MFI in VARA. The rules don't allow it in CP and CP 3 is a new class. Let's watch and see what happens.
If you choose to ignore the logic, that's your choice.

Cheers

[jluetjen]

MFI is also specifically excluded in SCCA's E-Production class, in spite of many other cars being allowed "Stock" type injection -- which means a common plenum CIS or EFI system.

[Plavan]

Originally posted by Henry Schmidt
Hi g force, long corners cause carburetors to starve for fuel. Hard cornering acceleration is often interrupted by a bobble.
When properly set up the MFI system doesn't make more horse power it's just more drivable.

Is this the logic you are referring to?
If you look at my previous post, you can see that with PMO's we do not get the "bobble". We have four race motors that all started on Weber's. We would get the "bobble" in the corner like you stated. Once we all upgraded to PMO's, the "bobble" went bye, bye. The cars have instant throttle response in a corner or not. No hesitation at all. Now, that maybe just be a credit to Aase Motors and their set up.
Your comments might be right when you are comparing Weber's to MFI, but does not if you compare PMO's to MFI. We know this first hand from 4 motors. PMO's are the "Newer" Webers, they are made a little differently than 30 years ago. The PMO's made all our cars more "Drivable" and more importantly more "Raceable".

[Henry Schmidt]

Originally posted by Plavan
Is this the logic you are referring to?
If you look at my previous post, you can see that with PMO's we do not get the "bobble". We have four race motors that all started on Weber's. We would get the "bobble" in the corner like you stated. Once we all upgraded to PMO's, the "bobble" went bye, bye. .............

True story, only the names were changed to protect the embarrassed.

Back in the late 70s I had a friend (Bill) that wanted to be a pro driver (IMSA). Bill was fast but pretty green. Instead of racing pro he decided to go the club racing route first.
In his first year he did pretty well. Bill finished second at SCCA regionals and was the guy to beat at POC and PCA events. In the next 2 years he finished first in class.
Now he was ready for the pros.
Bill was building engines for one of the top IMSA teams and his engines were the engines to own.
He had built many high butterfly and slide valve mfi engines but his 914/6 ran carbs because of club/ class rules.
One day, Bill had his car out at Riverside running with POC or PCA and he talked Kenny into driving his car. Kenny was the lead driver for the GTU car that Bill built engine for.
Well out goes Kenny and after one lap Kenny comes in complaining about a corning bobble in the car.
Bill was perplex. You see his car never bobbled. After all he was the guy to beat and it never bobble for him.
Apparently at higher speeds/ G-forces cars (and carburetors) perform differently. Well they jacked up the fuel pressure, raised the float level ( to an unusually high point) and Kenny went back out.
Guess what happened? Kenny ran 4 seconds a lap faster than Bill had ever run in his life.
I distinctly remember how Bill sat on his trailer, head in hand, totally demoralized.
To this day, Bill has never raced again.

This story has three morals.
First: fast times are relative to your sand box.
Second: different speeds offer completely different tuning parameters.
Third: racing is fun at any speed. You don't have to be world champ to enjoy it.

[svandamme]

speaking of g-forces...
Spitfires in the Battle of Brittain had a real hard time with the MFI 109's..why? because they couldn't handle the G's and their carbed engines would cut out completely in certain maneuvers... the ME's didn't have an issue with it though...

luckely for the Brits... the ME's couldn't carry the fuel to actually spend time dogfighting...

[KNIGHTRACE]

I think the PMO's 50's flow about the same as 3.0 RSR High butterfly injection. Hard to beat for the on a race motor and very easy to set up and service.
William Knight

[jluetjen]

Just to resurrect this old thread, I recently found this cool video on Youtube describing the 1950's MB race cars, and specifically the MFI (direct injection) technology. Interestingly, they quote MB as saying that the MFI direct injection was worth about 10% over carbs.

Enjoy!

[ficke]

Henry, Great story about "BILL" I learned alot form it and had a good laugh!!

[Porschekid962]

As far as carbs on a proffessional race car there was one that I know about. In the mid 80's at Le Mans. It was either the Bob Tulius group 44 Jaguar or the Aston Martin team but one of them ran carbs on their motors. I can double check the video I have later but I am leaning towards the Aston Martin team.

The Audi R8 uses a very high pressure fuel system with injectors that direct inject to the combustion chamber at or above 100bar. From the pictures I have seen of the R10 diesel engine they use a massive fuel rail and then direct injection with injectors at or above 100bar.

[jluetjen]

Yeah, the R8's are direct injection and I've got in a magazine somewhere the ROM pressure range that they're using. I think for the R10 they're limited to less then 100 bar (or maybe that's F1?) and they're happily running below that. I'll have to check.

[dd74]

Subscribing. Great thread!

[shbop]

..

[obrut]

its always interesting when someone breathes life into an old thread you started.

in the meantime, i did find a 69E and the race prep is almost finished. the motor is a 2.0 litre with 906 internals and running MFI (as per our rules). its a great little car. here's some pics:

http://www.early911sregistry.org/forum/showthread.php?t=13469