best injection for race engine: MFI, Carbs, EFI
 

for starters a high compression 3.8 engine built primarily for use on the track and may see very limited time on the street if any. so my question to you is this...

A) do you go old school and run MFI on the car, just spin the pump twice as fast as it is supposed to run for a 2.0 engine or run two pumps or have it recalibrated if poss.

B) get a nice set of PMO carbs with solid fuel rails and be happy with money left over.

or get crazy...

C1) strip down a set of Zenith carbs and use them as throttle bodies for either a Motec or TEC 3 injection and ignition system.

C2) get some TWM throttle bodies, Motec or TEC 3, crank fire ignition and high output coilpacks.

if i end up with EFI i like the Motec because you can add their dash console which is very clean plus its lighter than all those guages you would run.

problem is, i dont know of any local shops with experience tuning an engine with Motec. Tec 3 would be nice because im sure I could get some base maps from Clewett here in SoCAlio

are there any other setups to consider?

my vote goes to C.

Reasons:

- MFI is expensive, hard to adapt to bigger engines, hard to adjust and wears out. There are some people (here at Pelican) that will praise it's virtues but it's hard to escape the facts that it's obsolete old system that doesn't have anything to do in modern engines.

- Carbs are hard to adjust right and almost impossible to adjust correctly trough whole RPM-range. You might get good peak power with carbs (if you are lucky) but EFI engine with same power will spank you anyway beacuse of better midrange torque.

EFI can be mapped to fit your needs and allow you to extract every last horsepower out of the engine. You don't need to limit yourself to TEC3 or Motec...there are other ECU's that can be used...Autronic, SDS and Haltech are some of them.

3.6 (and 3.8 engines, i suppose) are already dual-plugged from the start so direct-fire coilpacks with wastefire coils would be very easy to fit.

For real power, dyno-mapping is a must and is something that will cost extra money.

If I were you I would use the DTA Pro8 system with indy throttle bodies. I researched most of the systems out there and found that for what I wanted, the DTA provided, at the best price. They now have a dash readout display also.
To get a dealer contact DTA in England and they will point you to one. I didn't like my local dealer so I went across the country to find one.
Good luck

I tend to disagree with the statement in general. I have been working with Richard Parr at PMO on my Webers and I have NO flat spots between idle and 7,000 rpm. Plus, IMO, as a race engine it will live in a much more narrow rev range and thus be even easier to setup.

I'm going to have to disagree with this as well. It's a good system that works VERY well. IMHO it's less expensive than a good EFI system(3K or so same as a set of PMO's and much less than EFI) and doesn't require that much tuning BUT you're right for a 3.8 go EFI it's what gets the most HP

...you can buy SDS EFI system for $1500, injectors and coilpacks included. Yes, you need to fabricate fuel rails and tune it (well you need to tune any custom fuel-system) but i see it as much less hassle than making obsolete mechanical injection deliver almost double amount of fuel than originally intended, all regulated with a mechanical space-cam. Now that would be really interesting problem to solve for small money.

Talking about carbs, yes, seat-of-pants feeling might tell you it doesn't have flat spots (and it probably doesn't) but take it to the dyno and take a look at A/F ratio troughout the powerband and you'll see that there is no way you can adjust it to work right everywhere.

I believe Tyson S. and some other guy took their car to the dyno and there were some graphs posted, i'll try to find the posts.

Anyway...you cannot ignore the facts:

MFI, CIS, Carbs...they were all bagged by PAG (and most other manufacturers) for enviromental, efficiency, reliability and performance reasons. (So is aircooling, btw.)

I mean you can be a valve amp buff and swear that it's best sounding thing around and you had yours for 20 years and it works perfect. But then a guy comes and asks what amp to use for his 200 person gig and even an audiophile has to understand that his vintage Mcintosh gear isn't gonna cut it and that those pesky new D-class switching power amps that put out 2kW of power out of VCR-sized box are way to go.

Without joining the inevitable debate about which system is best my view is for a 3.8 go with EFI, TWM's with MoTec. Big bucks, but if you are building a 3.8 to make big power you understand what it takes.

I'd stay with MFI only if you were conforming roughly to something the factory did, e.g. 906, RS, RSR etc. Sure, you could adapt a Kugelfischer pump like the factory did in the 935, but that's a lot of engineering time and expense. If you are racing VINTAGE I'd have a different answer.

Goran,
If you can show me where to order an SDS system with manifolds, injectors and coilpacks for $1500 sign me up. The manifolds themselves are $1000

I looked at MFI for my 914-6 and decided it just wasn't worth it. I've got the SDS efi and TWM TB's and am going to get around to finishing up the install this month I hope. You can actually do the SDS for just about $1000, if you just get the fuel management system (the MFI and Carbs don't include spark management so we should compare apples with apples). However, a set of TWM TB's is going to set you back ~$2500. You can get premade fuel rails for another $100 or 150 (I forget), so that takes most of the fabrication hassle out of it. You could use an intake manifold and other hard parts form an existing Porsche FI application (3.2/3.6), but a single TB is going to affect response and power figures.


Adam

Definitly go with EFI for a 3.8 track car if you're spending that much money on the motor then put a little extra into the intake and you'll be very happy.

Re: best injection for race engine: MFI, Carbs, EFI
 

Well, that doesn't make any sense to me since the pump is timed to the engine. Of the three, carbs makes the least sense in today's technology. I can't comment on the costs of anyone's EFI, but that would seem to be the way to go.

I would have to consider class rules about induction. A 3.8 with MFI might be running against Buckler and friends. His user name says 962, so maybe it doesn't matter.

A quick walk thru the pits will reveal either Motec or DTA with TWM 3006 throttle bodies.

I vote for a Holley 4 barrel on a custom manifold. ;)

Tyson. how 'bout Hillborn mechanical alcohol FI off a 70's sprint car? Six of those hummers just pouring it in. Sucker might do wheelstands off the corners. :D

thanks a lot guys, and tyson, lets talk more about that Holley setup. haha. the only EFI systems i am familiar with are the Motec and Electromotive systems. what is this SDS and where can i find it on the web??

are there any other TB manufacturers aside from TWM that make a good product for porsche?

SDS:

http://www.sdsefi.com/

Also don't forget http://www.injectionperfection.com

Jerry Woods likes the Motec system -- partly cause of their support, and the fact that he can control spark and flow with one unit.

Check these guys out...

http://www.clewett.com/