Carpokes Porsche Forum

When I started down this road of modding my 951 I was sold a kit where in addition to the MaxxECU Race they also provided 630CC Siemens Deka injectors.

Two tuners told me they're crap. Something to do with a lack of information available that would help them fine tune them to my motor.

Doing a bit of digging last night I found some saying they can contribute to bad idle which, after my tune, seems to be an issue.

What would the group recommend as an alternative?

My tuner only did a custom chip tune for me since I don't have a MAF setup or standalone. He did use these injectors and I haven't had a problem with them.

I’m not a tuner, but I play one on the boards haha So of course take this with a hand full of salt.

That doesn’t make sense to me. As you know, I just started down the same journey as you with my MaxxECU. Not knowing didley squat, I figured out that you can infinitely tune your injectors. I figured out how to adjust my dead time, which improved my AFR from 12.5 to mid 14’s. I know I have a TON more to learn and I’m sure I can improve my idle even further, but not knowing anything about my injectors, I got far enough that I’m happy with my idle and cruising. (Note, I’ve yet to go into boost. Playing it really safe).

Edit: I’m using Siemens Deka 80 lb

I used injector dynamics injectors for a long time and liked them. They are made for tuned car basically, so all needed tuning info should be available. As with all injectors, however, you'll find those who swear by them, and those who swear at them....

Can't really comment on the injectors you have, although I'm not sure I'd shell out big bucks for new injectors without doing more to see if yours are really the issue. What issues are you having? Do those problems go away if you re-install your stock injectors for example?

I second Injector Dynamics, the amount of effort they put into correctly measuring the dead time and characterization data makes a big difference to how your car runs, especially with a modern ECU that can use it.

Great podcast from HPA on this subject
https://podcasts.apple.com/au/podcast/0 ... 0587424032

Tom wrote: Sat Jul 12, 2025 11:51 am I used injector dynamics injectors for a long time and liked them. They are made for tuned car basically, so all needed tuning info should be available. As with all injectors, however, you'll find those who swear by them, and those who swear at them....

Can't really comment on the injectors you have, although I'm not sure I'd shell out big bucks for new injectors without doing more to see if yours are really the issue. What issues are you having? Do those problems go away if you re-install your stock injectors for example?

I believe that's what the issue was for the guys I was talking to. The tuner info isn't available for the Dekas I believe is what they or one of them said.

Third vote here for Injector Dynamics.

If you need good data, the net is a good place to start.
https://www.msextra.com/forums/viewtopic.php?t=36303
A good tuner would know that finding the right settings for injectors can take some trial and error. It's rare to drop in a new set of injectors and plug in the fuel scalar and deadtime numbers and have it run perfect from the start.

Jotronic wrote: Sat Jul 12, 2025 8:28 pm
I believe that's what the issue was for the guys I was talking to. The tuner info isn't available for the Dekas I believe is what they or one of them said.

Interesting. I have Siemens-Deka 830cc injectors on my 951, was able to find dead time curve via a quick Google search. Idles perfectly (VEMS engine management, engine stock internally), even passes the tailpipe emissions portion of the CA smog test at idle, less than 2.0ms open time. My setup is batch-fired, though. It could be that sequential injection is more sensitive to precise dead-time settings, if that is what you are attempting.

I have always heard good things about Injector Dynamics, including from the HP Academy folks.

A good tip for buying Siemens-Deka or Bosch or other brands is to only buy from a known fuel injector specialist like Five-O Motorsports, RC Fuel Injection, etc, and NOT eBay or Amazon. There are a lot of counterfeit parts out there, and the good retailers guarantee genuine parts and sell matched/balanced sets. It's possible that your tuners worked on cars with fake parts.

Siemens and Bosch are probably very similar as they're all under the BSH umbrella corp.

Also to bear in mind, some injs don't like E85. So if you're going to be using any of that it would be worth looking into. We went through a phase of running 2 sets of injs and having to get them cleaned after each track day.