Stock VW/Porsche injector figures Do add up

[theKbStockpiler]

If I use the info from this page on the 914 1.8 injectors http://users.erols.com/srweiss/tableifc.htm and use a injector calculator that includes a turbo option, I would be short about 6lbs an hour for 200hp.

From what I read in forums the porshe 914 injector ; which is close to the stock injected beetle injector, it's way too small.

Is it because the factory ECU used a low duty cycle or what else could it be?

Thanks for your expertise!

[Clonebug]

When you figure injector size you need to calculate at 80% Duty Cycle. That is what most sites say is max rating for a N/S or turbo setup to give enough safety factor and overhead.

For 200 hp you would need four 32# injectors at 80% Duty Cycle. Those same injectors will support 230 hp at 100% DC.

I used 32 lb./hr. injectors for my 1679 and was hitting 103% DC with them.
I now use 45 lb./hr. injectors on the same engine and will see 73-76% DC at 22-24 lbs. boost.

You would be better off picking an injector that will support a higher max hp than you think you might ever need to save yourself from having to buy them twice.

[theKbStockpiler]

From the chart I posted and the online calculators they are rated at 180hp at %80 duty cycle.



From this PelicanParts forum;
http://forums.pelicanparts.com/porsche- ... wners.html
The builder feels that they are way undersized but I have to assume this is because of the stock system with a low duty cycle.

[Clonebug]

You can use any injector you desire if you have a way to log a run so you can see what kind of DC you are getting. I saw mine at 95% and more a few times when I revved it out farther than I usually do. I found the larger ones for a really great price so it was a no brainer to change them out during my winter upgrade.
I'm good to about 360 hp now.

[andy198712]

also the DC is only as accurate as the figures you put in so just make sure you have everything correct and your math will be golden

[theKbStockpiler]

I got it figured out. It's because only one bank of injectors can be pulsed at a time with the D-jet.
They had to be too big for a modern systems standards. I have been reading all of the articles I can because I wan't to modify a D-jet and It just hit me.

[MarioVelotta]

Just because it is bank fire would not change the injector size requirements.

[theKbStockpiler]

Just because it is bank fire would not change the injector size requirements.

So how is that physically possible if you don't mind explaining?

[MarioVelotta]

In bank fire applications the injector is opened twice during an engine cycle instead of once like with sequential. The same amount of fuel is delivered, just not at an optimized time.

[theKbStockpiler]

Where can I find this explained in a D-jet system? I have not seen it stated as of yet.

[panel]

I don't think Mario is saying it's D-Jet specific.......that's just the characteristics of injectors re duty cycle. What mods are you doing to the D-Jet ?

https://oldtimer.tips/en/d-jetronic/52-overview

[theKbStockpiler]

I was reading the PelicanParts forum thread on using a D-jet with a turbo and I don't think the author understood some of the fundamentals of a D-jet.
I want to at least use a 914 D-jet system as a starter FI system for a 1904 type I and then try to make a PowerBox and use it with a turbo.

I'm going to flood my head with as much of the D-jet system as is possible and then try to come up with a few ideas like:

1-Keeping it all analog but substituting the MAP with a different circuit that will enrich it on boost.
2-Substituting one sensor and grafting in a MicroController to enrich on boost ,and add a O2 sensor to keep it within a specified A/R at all times.

[Clonebug]

Sounds like a great way to get a big headache.

There is sooo much out there that will ease the frustration of a FI turbo setup. Working on them gets old after a while.
It really is fun to just drive them.

[theKbStockpiler]

The plan is to remove/disable the turbo and just drive on the stock D-jet so I'll only be experimenting with it on a part time basis. I really should install a cutout before the turbo. I'm sure I won't get it right the first time.

I have been a computer/electronics hobbyist for years and I really don't like complicated garbage that you don't fully understand and are held for ransome by a corporation that makes it that way. In the event I get tired of it I'll try a blowthrough SU system.

[panel]

I have been a computer/electronics hobbyist for years

....and you're not running Megasquirt yet ?