2.4T MFI pump onto high comp/big valve 2.7

obrut · 11-10-2003, 06:39 PM

Greetings from down under

I have just finished a new 2.7 litre race motor for my track/rally car. Basic specs as follows:

10.5:1 comp
drilled for twin plug (but presently awaiting dual dist)
2.7RS spec ports/valves (i think)
GE80 cams

I have bought a mfi setup with 36 to 38 mm stacks (which I understand is 2.7RS spec)

The pump is # 0408 126 015 - ie 911TE 2.4 litres 72/73.

My mechanic's initial impression is that the pump is not flowing enough fuel for the motor as it pulls well to 4000 rpm then "runs out of puff"

I though that all of the pumps had similar maximum flow characteristics and that differences in the space cams really only effected mid range throttle response.

1. Is my understanding right?

2. Should I send the pump off for rebuilding into a 2.7RS or 2.8RSR spec?

3. Can a space cam be easily installed without sending the pump off for rebuilding (which was recently done by PO)?

Thanks in advance - Ryan

Wayne 962 · Wayne 962's Garage

I would get a portable air/fuel mixture machine (we're going to be carrying a really cool one shortly) that will be able to tell you if you're running out of fuel, instead of guessing.

That is really one of the only ways to tell. Or, put it on a dyno, where they can measure that stuff while you're running through the paces...

-Wayne

Tyson Schmidt · 11-10-2003, 09:49 PM

You can change the space cam yourself. You need a pair of snap-ring pliers to remove the centrifugal governor springs, and you can grind a socket down so it has two prongs to engage in the special nut that holds on the governor. Once that's out of the way, you can remove the space-cam.

Your T pump is capable of delivering enough fuel, but the contour of the T space cam may not allow enough movement of the main rack to allow it to deliver enough fuel. You may run out of adjustment on the main rack.

The follower that moves 3-dimensionally on the space cam is moved up or down as the space-cam is twisted about 90 degrees right to left by throttle position, and fore-aft by rpm. The more the cam is contoured downward, the more the follower will drop, making the main rack move further rich.

The T space cam has a flatter arc than an E or an S/RS. So while the main rack is capable of delivering enough fuel, the T cam may be preventing it from ever moving to a rich enough position. There just may not be enough adjustment to compensate for the flatter curve of the T space-cam.

You could possibly recontour the T space-cam to give it more of a dropping arc, but that may be out of your skill range. Kinda risky. If you can get an RS space-cam, it is very possible to change it yourself. If you get into trouble, I can send you pictures of a disassembled rack to help you get it back together correctly.

obrut · 11-10-2003, 09:58 PM

Tyson - many thanks (again) pls send pictures. If not electronic then my fax is (intl code) 612 9261 5486 attn: ryan

Cheers - Ryan

ps: if you ever get down here beers are on me!

Wayne 962 · Wayne 962's Garage

Sorry - didn't see that you were using a 'T' pump - I thought you were using an 'S' pump. Yup, that T pump *will not* work well with your setup, you need that more agressive space cam. See if Pacific Fuel Injection has one for sale for you, and change it out yourself. That will probably fix all your woes...

-Wayne

obrut · 11-12-2003, 04:59 PM

Thanks guys - I have access to a 2.7RS pump so I will try that and, if the engine likes it, pop a new space cam in.

ps: Put my old carbies on, rough tune - made 228hp on the dyno. This thing will be a rocket when the MFI is fitted/tuned and the lower plugs hooked up!

obrut · 11-12-2003, 06:29 PM

PPS: two last questions

1 - will swapping out the space cam affect the calibration of the MFI pump?

2 - who has the best price on space cams?

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by obrut
PPS: two last questions

1 - will swapping out the space cam affect the calibration of the MFI pump?

2 - who has the best price on space cams?

1- Hmm, I don't know enough about the internal rebuilding of these pumps to answer this question.

2- Hah, who has any at all? It's not exactly a corner-drugstore item...

-Wayne

Fishcop · Fishcop's Garage

Ryan, if you can get your hands on your friend's RS space cam, maybe a good machinist can reproduce it for you?

BK911 · BK911's Garage

I was working on a 69E that died at 4k rpm's. I just knew it was a timing issue. Wrong! It ended up being the electric fuel pump. It wasn't flowing enough fuel to the MFI pump. MFI and carbs use different electric fuel pumps, I can't remember which flows more.

jluetjen · jluetjen's Garage

Keep in mind that MFI fuel pumps pressurize the line going to the MFI Injection pump, and there is a return line that vents excess fuel back to the fuel tank. So MFI pumps are always moving fuel in excess of what the injection pump need at WOT.

Carb pumps on the other hand just pump the fuel on a one-way trip to the carbs. As a result I figure the MFI pumps have to pump more fuel.

At least that's my logic...

obrut · 11-13-2003, 02:45 PM

Wayne - supertec quoted me US$375 for a cam, which sounds like a deal.

John 1 - hadn't thought of that, but feels kinda risky

John 2 - we had the correct 45psi pump and return fuel line all hooked up, but i might throw a pressure gauge into the engine bay to make sure

BK911 · BK911's Garage

You don't need a pressure gauge. Disconnect the suppply line going to the fuel filter and insert into a bottle. Turn the key and measure the flow rate.