EFI Systems

[chris_seven]

There is clearly a huge amount of choice for both Throttle Bodies and Control Systems and as can be expected opinion seems strongly divided.

I have to say that I favour the appearance of the PMO systems as it looks more in keeping with an aircooled 911 and it seems easier to balance.

The Borla system also looks reasonable from this point of view.

Several people seem to favour the Jenvey System because the manifold is straight although the linkage is a PITA and I wouldn't ditch the rods and replace them with such a long cable.

Has anyone made any objective tests to compare performance with 'bent' and 'straight' manifolds as I find it hard to imagine that such a small difference would be easy to measure.

I can understand that the Jenvey system looks more intuitive but is the difference of any practical significance to outweigh the ease of hooking up the system and adding air filters ?

[Jeff Alton]

The Jenvey linkage between throttles is quite simple to adjust to balance. Replace the cable idea with a simple adjustable push rod from the standard linkage mount at rear of engine.

We built 2 almost identical motors, with the exception of induction. A 3.4 with Jenvey's and a 3.5 with PMOs. Same compression, cams and exhaust. Different ECU's, but both tuned by same tuner on the dyno. The 3.4 made more power. Obviously atmospheric conditions were likely not the same at the time of the dyno runs and really not a true apples to apples comparison at all, but interesting none the less.

[Tom_in_NH]

I'd also take a look at the TWM (now Borla) 3003 series ITB kit. They're very similar to the PMO, with the same, slightly longer path to 1,3,4,& 6. I believe their 3003 kit is inclusive of manifolds, linkage, etc.

TWM's (Borla) older, 3006 kits were a pain to balance, as the throttle shafts were not inline. This required some fairly kludgey linkages from body to body.

I wouldn't be put off by the unequal lengths of the manifold runners in the Weber-esque TWM (Borla) and PMO kits. Sure, Porsche was slaved to the Weber and Zenith port centers way back. But, they had the opportunity to make an equal-legnth setup for the MFI motors, and didn't........I believe that if they really made any difference, Porsche would have certainly gone equal-length for the MFI.

[3literpwr]

KMS offers straight runners also. Kit appears to use similar throttles to Jenvey. Complete kit with ECU, wide band lambda sensors, injectors and the like is about a grand less then the Clewett setup.

[porterdog]

Originally Posted by 3literpwr

KMS offers straight runners also. Kit appears to use similar throttles to Jenvey. Complete kit with ECU, wide band lambda sensors, injectors and the like is about a grand less then the Clewett setup.[/img]

Deets? Googling KMS ITB came up with nothing I was looking for..

[blue911rsr]

Try kronenburg auto sport I use their itbs they work nice easy to adjust

[3literpwr]

I've been trying to decide on a system myself over the last year. Have a built 3.0 waiting for fuel and spark and I can't decided on a direction (carbs vs ITB). The offset runners don't seem to
present a flow restriction, but there is no real data to compare system to system. Regardless, I do like the non-weber stuff also. Also, Porterdog. I'm in the Metro Detroit area too.

[al lkosmal]

I've spent a little time developing a nice EFI kit.
regards,
al
PS: I have also used TWM/Borla ITB kits and they work very well.

note: The early versions used cable for actuation, but now my kits use standard Weber/PMO manifolds and linkage. Just received a run of adapter plates and fuel rails from my machinist.

My Triumph Speed Triple project update

https://www.youtube.com/user/koz77911

[Tippy]

Nice, Al!!

[Flieger]

If I went EFI I'd want straight runners just because going through all that trouble and expense and still having bent runners would just drive my obsessive compulsive disorder insane.

[sp_cs]

Originally Posted by chris_seven

Jeff,



In an earlier thread I seem to remember that you commented that the Jenvey system was quite difficult to balance compared to the PMO and this has swayed my thinking.



Jenvey are about 10 miles down the road but the guys I used to know have left and now work for an ECU supplier and are developing their own ITBs but of a 40DCOE Style.



Do you have any numbers for the differences? and were the ITBs the same diameter?

Chris

Worth speaking to Neil Bainbridge at BSMotorsport. He too has an issue with the Jenvey linkage design and so has produced his own ITBs.

Think he thought the PMO ITB linkages were ok.

Shirish

[Tippy]

Originally Posted by Flieger

If I went EFI I'd want straight runners just because going through all that trouble and expense and still having bent runners would just drive my obsessive compulsive disorder insane.

Yep!!

[al lkosmal]

Tippy and Flieger..............before MFI bitz became unobtanium, i made an EFI/MFI/ITB set up that rocked.............here's a pic and video of a 3.0 I built with EFI, using MFI T'bodies (I bored them out to match the ports), mounted on aluminum turbo spacers, machined for EFI injectors and topped off with Weber stax...........straight shot in.........ran very strong.

https://www.youtube.com/watch?v=SpPM1SZL_rc&feature=youtu.be



regards,
al

[Flieger]

Originally Posted by chris_seven

.....and the poor air filter deign that normally results from the use of straight runners bugs me in exactly the same way.

I am not sure you can describe the runners on a tall-ish inlet manifold as bent and I do have a set of 911R Inlet Manifolds we are just about to use for making new patterns. I think angled in a similar manner to high butterfly stacks would be more appropriate.

The reason for my first post was to try to eliminate subjective arguments by finding some numbers which I realise is difficult.

I believe that MFI Throttle bodies are available again but they are quite a small diameter and I am not sure how much impact this would have but the idea is appealing.

Who needs filters- they just cover up the trumpets anyway.

[jpnovak]

I like Al developed a system based on MFI. In my case it was adapters to put EFI injectors in the MFI ports. This works well on early engines where you just use the entire MFI TB/stack/linkage setup. It is still cost effective compared to some aftermarket ITB setups.

It is not hard to add the MFI ports to 2.7, 3.0 and 3.2 heads as part of regular machine work but as the engine gets bigger and the rpm range increases the Inside diameter and flow restrictions become a real issue.

Back to your original question, I have tried cable setups and this always presents problems. The co-linear shaft design like the Borla 3003 series is much easier to keep working in sync. I have not seen any real numbers saying that the offset runner on 1,3,4,and 6 really make much of a difference. Generally the comparisons are before and after with EFI ITB conversions having a tuning efficiency advantage, so it is incredibly difficult to say how much the runner configuration contributes.

I have installed a few of the Borla 3003 setups and I have set myself. The weber style linkage is super easy to setup. I have synced a multi-bar linkage system like the Jenvey style and it take significantly more time but is not necessarily difficult as long as you are methodical.

I think if you had a lateral throttle shaft arrangement (like MFI) then a similar linkage would be best. This would require a high mounted bracket to connect the cross-bar across the banks. I have seen this done once but can not find the picture.

[Flieger]

Who was the one who was thinking about electrically actuating the rack on an MFI pump to take advantage of the high pressures while allowing for much easier tuning than via spacecam and flyweight adjustments?

[Flieger]

Originally Posted by chris_seven

Max,

Do you have any idea of the position control resolution you would need for this to work.

The response rate and hence the acceleration needed to start and stop the rack would be useful to know.

The PID controller needed would be quite involved but it is an interesting idea and if it were really smart it may even be possible to make it adaptive.

To be honest I never did any calculations to see if that was feasible. I'm not sure what the rack travel is from cutoff to full throttle (I realize there is more flow available than on a stock space cam, usable for RSR or other applications).

I think if there was a problem one might be able to put an actuator on the thermostat port for example and just use it as a fuel trim device with input from an O2 sensor, leaving the flyweights and mechanical throttle connection to handle the alfa-N control and giving quick response. Or perhaps the acuator inline to the throttle linkage such that you effectively change the length of the throttle linkage.

The other way around position resolution is to use a linkage system to give a favorable motion ratio between the actuator and the rack.

Now that I've mentioned it, I think a system that plugged into the thermostat and acted as a fuel trim device would be very cool. I've got a flat spot that might be the S cams but I'm not sure. My pump is 019 spec but the rest of the motor is a bit different from RS spec (heads are T part numbers, throttle bodies were bored to S when refurbished). I also don't have heat exchangers so I've got the thermostat set to the fully warm position permanently.

What would be nice would be an O2 sensor and a MAP or MAF sensor but that is difficult with 6 throttles so maybe just a TPS and rpm signal would be enough to fix the flat spot if it needs to be leaned or richened before it comes on cam.

[Jeff Alton]

Originally Posted by chris_seven

Jeff,

In an earlier thread I seem to remember that you commented that the Jenvey system was quite difficult to balance compared to the PMO and this has swayed my thinking.

Jenvey are about 10 miles down the road but the guys I used to know have left and now work for an ECU supplier and are developing their own ITBs but of a 40DCOE Style.

Do you have any numbers for the differences? and were the ITBs the same diameter?

Chris,

True, but after spending more time with both systems, adjusting the jenveys became quite easy. It is a bit more finicky but not bothersome.

The Jenveys were 48mm with custom tapered manifolds. The PMO's were 50's and untouched and used as delivered.

IIRC the 3.4 made 285whp and the 3.5 made around 270whp. Both had similar shaped torque curves and I can't recall the outright numbers. But again, not a true apples to apples as we had different ECU's and different atmospheric conditions.

We currently have a 84 M491 in the shop on PMO's. They certainly get the nod for period correct looks.

What ECU firm did the employees migrate too?

Cheers

[Jeff Alton]

On another note,

We have a set of odd throttles on a 2.8 we are building. I will post some pics and would love someone to identify them for us...

Cheers

[SexOnTheBeach]

Best setup out there is the Rothsport (uses Jenveys) bar none.