2,8L MFI Advice
 

Hello,

We are currently planning a 2,8L MFI engine for my 2050lbs 911.

It will see 80% fast road and 20% DE use and should have a very nice torque curve suitable for the intended use and peak around 250-255HP at 6,6-6,8k RPM.

Current specs are:

-7R cases bored & shuffle pinned
-70,4 x 92mm
-slightly lightened & fully balanced crank
-Carrillo rods
-replated Nikasil cylinders (at Mahle factory)
-JE pistons 92mm, 10,5:1
-ported heads
-forged rockers
-bored MFI throttles with K&N air-filters
-twin plug ignition, restored 2x3-point Bosch CDIs
-MFI pump recalibrated by Koller & Schwemmer
-RSR flywheel
-RSR type exhaust

It would be nice if you guys could give me your opinion on the following as an appreciated 'second set of eyes':

1. What port sizes would you recommend? We are currently aiming at 40mm intake and 38mm exhaust ports.

2. What diameter would you bore the throttle bodies/ stacks? We are currently aiming at 40mm at the port, 42mm butterflies and 46mm at the top of the stacks with 46mm PMO funnels.

3. What cam would you suggest? We are currently planning a DC60 MFI cam.

Many thanks,
Chris

Hi Chris,

Based on what you have listed, I would choose a DC40 or a DC43 cam with 38mm intake ports. Other than that, looks like a nice build!

I'm with Aaron on the cam choice. I have a DC60 with 106mm lobe centers on my EFI, ITB, 3.3SS. I like the cam but don't think I'd go with it on a 3.0 not to mention a 2.8 unless you plan very high RPMs.

I went with 48mm butterflies and 40mm ports. It has worked well on my engine. I don't know should my butterflies have been smaller or my ports larger, or should yours be different. I wouldn't (but what do I know) go bigger at the ports. Maybe a touch bigger butterflies.

I overlooked this, sorry!

Depending on the condition of the throttle bores you can run 38mm all the way thru. Ideally I would run a 40mm throttle plate and then reduce down to 38mm to match the intake port.
Stacks would be 40 at the bottom and 46 on the top.

Thank you, Aaron.

So you would think 40mm intake ports are on the large side for the specification mentioned above and recommend to do them 38mm?

38mm would be perfect for a Mod S cam and your expected hp requirements. Plus you will get great midrange with this combo.

The build you are doing is a good one, enjoy!

Chris,

Good advice above.

Do some searching on Mahle cylinders and JE pistons.
There has been discussion as to the differential rate-of-expansion between these pistons and these cylinders.
I understand that this difference requires larger piston-to-cylinder clearance than the Mahle P&Cs.
Apparently the ‘Nickies’ cylinders are better matched to JE pistons allowing tighter clearance.
I can’t speak 1st-hand as I have always used Mahle cylinders and matched Mahle pistons.

Starting with street 911 heads (not RSR) and the proper JE pistons will let you have the CR at your desired 10.5:1.
Using the original 92 mm Mahle RSR pistons with street heads, it is a struggle to get the CR down to 10.5:1.

What is your access to high octane fuel?


Use the original forged steel RSR 6-bolt flywheel as cool wall decoration.
(I have one.)
While you won’t have a problem with the rpm limit below 6800, these flywheels were noted for the bolts braking or coming loose due to high-rpm resonance.
These issues occurred above 8000 rpm but I’m always cautious.
A modified cast steel flywheel can be almost as lightweight and not exhibit this resonance problem (… and it is less cost).


I trust the 7R case has the ‘oil bypass’ provision (either original or mod).

What oil pump are you using?

What distributor and 12-plug cap are you using?
What provision to fire both CDI simultaneously?

What throttle bodies are you starting with?
When K&S recalibrated the pump, what specs did they use?


You are going to have a lot of fun.
This is about the same power-to-weight ratio as my street 914-6, 2.8S MFI.
Wonderful at embarrassing 5-liter Ferraris. :D

Best,
Grady

Many thanks, Grady & Aaron.

I have heard about different expansion rates of the Mahle cylinders compared to the 2618 alloy of the JEs. There are a lot of engines on the street here in Germany with this combo and it is perhaps not such a big problem short to mid-term. But a full Mahle combo might be better...

We will of course use the street 911 heads (not RSR) and aim at 10,5:1 with twin-plug ignition. We have 105 octane premium fuel available here at German gas stations so that shouldn't be a problem.

The 7R cases will have the oil bypass provision.

We plan to use the 964 oil pump.

The twin-plug distributor is a newly developed solution with a proprietary designed and injection molded cap & rotor from Germany.

We start with 70E throttles and mag stacks and bore them as mentioned below.

Koller recalibrated the pump to 2,8RSR specs.

Grady, what intake diameters (ports/ butterflies etc.) and cams are you running on your 2,8MFI?

Kind regards
Chris

Chris,

Or maybe a matched set of Nickies and JE…
I see the issue as matching expansion rates.

Many of the builders I know are hesitant to use normal ‘close’ tolerance piston-to-cylinder with Mahle cylinders and JE pistons.
The wider tolerance allows for more piston ‘rock’ in the bore, resulting in shorter life
Another is piston design (contour) determines the clearances.

WOW, I’m jealous. (How many €/l?)


Tell us more.

Generally MFI likes matched engine cams, pump ‘space cam’ and matched engine intake and exhaust breathing.

It looks like most of what you are proposing IS a 2.8RSR.

I can tell you 1st-hand that, while a lot of fun, it isn’t easy or particularly ‘comfortable’ to drive an RSR engine on the street.

Around ’73, we bought several new type 911/72 engines from Porsche and used them in street 911s.


http://forums.pelicanparts.com/uploa...1298308493.jpg

Here is from a prior thread with one of these engines an a friend’s 911:

There is little and poor power below about 4500 rpm and ‘real’ performance doesn’t start until about 6000 rpm.
The engine likes 7000 to 8300 rpm.
The cams and light weight clutch/flywheel make starting from a stop difficult, even with a ‘street’ disc.

That said, when you can keep the revs above about 6000, this is a stellar performer.

This one is a stock ‘73 type 911/50 2.4S with 92 mm RSR Mahle P&Cs. The only other mods are the oil bypass and getting the CR down from above 12:1. On the engine dyno, I adjusted the pump to run properly. It has all the running characteristics of a 911S only ‘milder’. The low rpm performance is far better than original and it get better gas mileage.

You cannot tell it isn’t a stock 2.4S except for the injury to your neck.
Thankfully a 914-6 has a passenger headrest. :D

Best,
Grady

The JE issue as been address quite a while ago. We have run as little as .0007 p/c clearance without issues.


The pump would have been the last thing to do. At this point, the best thing to do is to install and see where the mixture is and readjust as necessary.


Grady has stock 36mm ports which work very well with his cam choice. The newer cam profiles benefit from a larger port.

The resonance issue with the 2.7 crankshaft starts around 7500 rpm and progressively becomes worse as rpms increase. Flywheels and crank breakage occur above 8000rpm. BUT crank breakage from resonance induced fatigue has occurred in race engines that do not exceed 7500rpm. It is rare, but our parts are no longer new so be aware.

The realistic engine build that I see would be;

38mm ports
twinplug
10.5/1
DC40 or DC43
2.7RS injection pump tuned for increased displacement and compression.

Any year throttle body would work for this configuration as throttle plate size is doable on all of them.

http://img825.imageshack.us/img825/1485/l1000249.jpg


This is my new 2,8L MFI LS.

We will have a second run on the MAHA next week - during the first run it showed 269HP at around 6,8k RPM and a nice usable torque curve from 1,8k RPM with a peak of 221 ft-lbs. What really amazes us is the torque characteristics and the very good drivability on low RPMs, especially with the cam profile we used.

It features a lightened & knife-edged 70,4 crank, streamlined and shuffle-pinned 7R cases, RSR flywheel with Sachs Sport alloy pp, 92mm JE pistons 10,5:1 with custom coated Nikasil cylinders (at Mahle factory), Carrillos, 964 oil pump, DC60 cams on 105 lobe center, 41/41mm ports, bored throttle bodies with 43mm butterflies, bored mag stacks with 43mm bottom/ 48mm top with 48mm funnels, 010 MFI Bosch pump reworked by Koller & Schwemmer with custom space cam, custom made twin-plug distributor with reworked 3-pin Bosch CDIs etc.

Many thanks to Oliver from boxer-motoren.de who actually built the engine, Grady, Aaron and John Dougherty for your advice!

Cheers,
Christian

WOW, that is a thing of beauty right there. I have a few question if you don't mind.. Where did you get the mfi fuel lines? What kind of fan pulley is that and where did you get those ignition wire straps?

The fuel lines are bulk stock high - temperature/ pressure plastic hydraulic lines with proper fittings. They were provided by Oliver but you can get these in your local hydraulic equipment store for sure.

I use a 930.106.101.0R 226mm fan & housing on this engine and the stock pulley.

The ignition wire straps are available from many suppliers - I know that Mike Bruns of jbracing.com also has these.

Cheers,
Christian

Great, thanks!

Christian,

VERY NICE!

Best,
Grady

Hello G ,

I'm curious , would an over the counter complete RSR 2.8 motor have a normal type unit number stamped on the case ? Like 683 x x x x .

Do you remember how any of these were stamped .....if they were.

We had a successful second run yesterday and Valentin Schneider of TS Motorsport (see his own Gruppe H car here: YouTube - ‪St. Agatha 2009 V.Schneider TS-Motorsport‬‏) did his magic again on the rolling road. :)

We finally came out at around 282 HP @7,0k RPM and 220 ft-lbs @4,1k RPM.

The space cam Koller configured is very near 2.8RSR specs and it is nice to see that it does not lean out at the top end as we initially feared. What impresses us again and again is how well the DC60s perform down-low. I have a stock 915/03 mag RS gearbox in the car and the ratios fit perfect.

Cheers,
Christian

Fantastic! :D

Do you have any dyno graphs you can post, wondering what kind of numbers you have elsewhere in the rpm range (Please)? Looks fantastic. . . sounds very fun!

Awesome! And hefty dyno results too. May we see some photos of the 911 you are running this?